Journal of Electromyography and Kinesiology - Articles in Press

Detection of surface electromyography recording time interval without muscle fatigue effect for biceps brachii muscle during maximum voluntary contraction - Corrected Proof

Abdullah Ruhi Soylu, Pinar Arpinar-Avsar — 2010-03-08

Abstract: The effects of fatigue on maximum voluntary contraction (MVC) parameters were examined by using force and surface electromyography (sEMG) signals of the biceps brachii muscles (BBM) of 12 subjects. The purpose of the study was to find the sEMG time interval of the MVC recordings which is not affected by the muscle fatigue. At least 10s of force and sEMG signals of BBM were recorded simultaneously during MVC. The subjects reached the maximum force level within 2s by slightly increasing the force, and then contracted the BBM maximally. The time index of each sEMG and force signal were labeled with respect to the time index of the maximum force (i.e. after the time normalization, each sEMG or force signal’s 0s time index corresponds to maximum force point). Then, the first 8s of sEMG and force signals were divided into 0.5s intervals. Mean force, median frequency (MF) and integrated EMG (iEMG) values were calculated for each interval. Amplitude normalization was performed by dividing the force signals to their mean values of 0s time intervals (i.e. −0.25 to 0.25s). A similar amplitude normalization procedure was repeated for the iEMG and MF signals. Statistical analysis (Friedman test with Dunn’s post hoc test) was performed on the time and amplitude normalized signals (MF, iEMG). Although the ANOVA results did not give statistically significant information about the onset of the muscle fatigue, linear regression (mean force vs. time) showed a decreasing slope (Pearson-r=0.9462, p<0.0001) starting from the 0s time interval. Thus, it might be assumed that the muscle fatigue starts after the 0s time interval as the muscles cannot attain their peak force levels. This implies that the most reliable interval for MVC calculation which is not affected by the muscle fatigue is from the onset of the EMG activity to the peak force time. Mean, SD, and range of this interval (excluding 2s gradual increase time) for 12 subjects were 2353, 1258ms and 536–4186ms, respectively. Exceeding this interval introduces estimation errors in the maximum amplitude calculations of MVC–sEMG studies for BBM. It was shown that, simultaneous recording of force and sEMG signals was required to calculate the maximum amplitude of the MVC–sEMG more accurately.

Muscle fibre conduction velocity and cardiorespiratory response during incremental cycling exercise in young and older individuals with different training status - Corrected Proof

M. Lenti, G. De Vito, P. Sbriccoli, A. Scotto di Palumbo, M. Sacchetti — 2010-03-04

Abstract: We investigated the effect of ageing and training on muscle fibre conduction velocity (MFCV) and cardiorespiratory response during incremental cycling exercise. Eight young (YT; 24±5 yrs) and eight older (OT; 64±3 yrs) cyclists, together with eight young (YU; 27±4 yrs) and eight older (OU; 63±2 yrs) untrained individuals underwent to an incremental maximal test on a cycle ergometer. Ventilatory threshold (VT), respiratory compensation point (RCP) and maximal oxygen uptake (VO2max) were identified and MFCV recorded from the vastus lateralis muscle using surface electromyography with linear arrays electrodes.In YT MFCV increased with the exercise intensity, reaching a peak of 4.99±1.02 [m/s] at VT. Thereafter, and up to VO2max, MFCV declined. In YU MFCV showed a similar trend although the peak [4.55±0.53m/s] was observed, at 75% of VO2max an intensity higher than VT (66% of VO2max). In both YT and YU MFCV did not decline until RPC, which occurred at 78% VO2max in YU and at 92% VO2max (P<0.01) in YT. Differently from young individuals, MFCV in older subjects did not increase with exercise intensity. Moreover, maximal MFCV in OU was significantly lower [3.53±0.40m/s;] than that of YT (P<0.005) and YU (P<0.05).The present study shows that, especially in young individuals, MFCV reflects cardiorespiratory response during incremental dynamic cyclic exercise and hence can be used to investigate motor unit recruitment strategies.

Effect of the contraction of medial rotators of the tibia on the electromyographic activity of vastus medialis and vastus lateralis - Corrected Proof

Andreia Sousa, Rui Macedo — 2010-03-02

Abstract: Purpose: This study attempted to assess if the resisted contraction of medial rotators of the tibia increases the ratio between the activity of vastus medialis (VM) and vastus lateralis (VL) during maximal isometric contractions (MIC) of the quadriceps femoral (QF) muscle at 90° of knee flexion.Methods: About 24 female subjects participated in this study, performing four series MIC of the QF. In the first series subjects performed only MIC of the QF muscle, whereas in the other three there was MIC of the QF with resisted contraction of medial rotators of the tibia, with the tibia positioned in medial, neutral and lateral rotation. During each contraction, VM and VL electromyographic signal (EMGs) and QF force were collected, being the EMGs root mean square (RMS) used to access the activity level of these muscles.Results: The use of the General Linear Model (GLM) test showed that for α=0.05 there was a significant increase in the VM:VL ratio when the resisted contraction of medial rotators of the tibia was performed with the tibia in medial (p=<0.0001), neutral (p=<0.0001) and lateral rotation (p=0.001). The same test showed that during MIC of the QF associated to resisted contraction of medial rotators of the tibia there were no significant differences in the VM:VL ratio between the three tibial rotation positions adopted (p=0.866 [medial–neutral]; p=0.106 [medial–lateral]; p=0.068 [neutral–lateral]).Conclusions: The resisted contraction of medial rotators of the tibia increases the VM:VL ratio during MIC of the QF and the tibial rotation position does not influence the VM:VL ratio during MIC associated to resisted contraction of medial rotators of the tibia.

Follow-up of ankle stiffness and electromechanical delay in immobilized children: Three cases studies - Corrected Proof

2010-03-02

Abstract: Clinical manual tests refer to increased ankle stiffness in children immobilized due to hip osteochondritis. The aim of the present study was to investigate musculo-articular stiffness via different techniques in immobilized children to confirm or not and quantify these observations.Ankle stiffness was quantified monthly during the long immobilization period in three diseased children and compared to healthy age-matched children. Sinusoidal perturbations were used to evaluate musculo-articular (MA) stiffness of the ankle plantar-flexors. The stiffness index (SIMA-EMG) was the slope of the linear relationship between angular stiffness and plantar-flexion torque normalized with electromyographic activity of the triceps surae (TS). The stiffness of the ankle plantar-flexors was also indirectly evaluated using the TS electromechanical delay (EMD).SIMA-EMG was greater for diseased children, and this higher stiffness was confirmed by the higher EMD values found in these immobilized children. Furthermore, both parameters indicated that ankle stiffness continues to increase through immobilization period.This study gives a quantitative evaluation of ankle stiffness changes through the immobilization period imposed to children treated for hip osteochondritis. The use of EMD measurement to indirectly evaluate these stiffness changes is also validated. This study shed for the first time some light into the patterns of muscle modifications following immobilization in children.

Summation of motor unit forces in rat medial gastrocnemius muscle - Corrected Proof

H. Drzymała-Celichowska, P. Krutki, J. Celichowski — 2010-02-25

Abstract: The summation of contractile forces of motor units (MUs) was analyzed by comparing the recorded force during parallel stimulation of two and four individual MUs or four groups of MUs to the algebraic sum of their individual forces. Contractions of functionally-isolated single MUs of the medial gastrocnemius muscle were evoked by electrical stimulation of thin filaments of the split L5 or L4 ventral roots of spinal nerves. Additionally, contractions of large groups of MUs were evoked by stimuli delivered to four parts of the divided L5 ventral root. Single twitches, 40Hz unfused tetani, and 150Hz fused maximum tetani were recorded. In these experimental situations the summation was more effective for unfused tetani than for twitches or maximum tetani. The results obtained for pairs of MUs were highly variable (more- or less-than-linear summation), but coactivation of more units led to progressively weaker effects of summation, which were usually less-than-linear in comparison to the algebraic sums of the individual forces. The variability of the results highlights the importance of the structure of the muscle and the architecture of its MUs. Moreover, the simultaneous activity of fast and slow MUs was considerably more effective than that of two fast units.

A noninvasive, log-transform method for fiber type discrimination using mechanomyography - Corrected Proof

2010-02-22

Abstract: This study examined the log-transformed mechanomyographic (MMGRMS) and electromyographic (EMGRMS) amplitude vs. force relationships for aerobically-trained (AT), resistance-trained (RT), and sedentary (SED) individuals. Subjects performed isometric ramp contractions from 5% to 90% maximal voluntary contraction. Muscle biopsies were collected and thigh skinfolds, MMG and EMG were recorded from the vastus lateralis muscle. Linear regression models were fit to the log-transformed EMGRMS and MMGRMS vs. force relationships. The slope (b coefficient) and the antilog of the y-intercept (a coefficient) were calculated. The AT group had the highest percentage of type I fiber area, the RT group had the highest percentage of type IIa fiber area, and the SED group had the highest percentage of type IIx fiber area. The a coefficients were higher for the AT group than the RT and SED groups in both the MMGRMS and EMGRMS vs. force relationships, whereas the b coefficients were lower for the AT group than the RT and SED groups only in the MMGRMS vs. force relationship. The group differences among the a coefficients may have reflected subcutaneous fat acting as a filter thereby reducing EMGRMS and MMGRMS. The lower b coefficients for the AT group in the MMGRMS patterns may have reflected fiber area-related differences in motor unit activation strategies.

The role of anticipatory postural adjustments in compensatory control of posture: 2. Biomechanical analysis - Corrected Proof

Marcio J. Santos, Neeta Kanekar, Alexander S. Aruin — 2010-02-16

Abstract: The central nervous system (CNS) utilizes anticipatory (APAs) and compensatory (CPAs) postural adjustments to maintain equilibrium while standing. It is known that these postural adjustments involve displacements of the center of mass (COM) and center of pressure (COP). The purpose of the study was to investigate the relationship between APAs and CPAs from a kinetic and kinematic perspective. Eight subjects were exposed to external predictable and unpredictable perturbations induced at the shoulder level while standing. Kinematic and kinetic data were recorded and analyzed during the time duration typical for anticipatory and compensatory postural adjustments. When the perturbations were unpredictable, the COM and COP displacements were larger compared to predictable conditions with APAs. Thus, the peak of COM displacement, after the pendulum impact, in the posterior direction reached 28±9.6mm in the unpredictable conditions with no APAs whereas it was 1.6 times smaller, reaching 17±5.5mm during predictable perturbations. Similarly, after the impact, the peak of COP displacement in the posterior direction was 60±14mm for unpredictable conditions and 28±3.6mm for predictable conditions. Finally, the times of the peak COM and COP displacements were similar in the predictable and unpredictable conditions. This outcome provides additional knowledge about how body balance is controlled in presence and in absence of information about the forthcoming perturbation. Moreover, it suggests that control of posture could be enhanced by better utilization of APAs and such an approach could be considered as a valuable modality in the rehabilitation of individuals with balance impairment.

Neuromuscular activation of vastus intermedius muscle during fatiguing exercise - Corrected Proof

Kohei Watanabe, Hiroshi Akima — 2010-02-04

Abstract: The purpose of this study was to investigate neuromuscular activation of the vastus intermedius (VI) muscle during fatiguing contraction. Seven healthy men performed sustained isometric knee extension exercise at 50% of maximal voluntary contraction until exhaustion. During the fatiguing task, surface electromyograms (EMGs) were recorded from four muscle components of the quadriceps femoris muscle group: VI; vastus lateralis (VL); vastus medialis (VM); and rectus femoris (RF) muscles. For the VI muscle, our recently developed technique was used. Root mean square (RMS) and median frequency (MF) of the surface EMG signal were calculated and these variables were then normalized by the value at the beginning of the task. Normalized RMS of the VI muscle resembled those of the other three muscles at all given times. At 95% of exhaustion time, normalized MF of the VI muscle was significantly higher than that of the VL muscle (p<0.05). These results suggested that neuromuscular activation is not consistent between the VI and VL muscles at the exhaustion for isometric submaximal contraction and this could reflect the dissimilar intramuscular metabolism between these muscles.

Effects of ageing on motor unit activation patterns and reflex sensitivity in dynamic movements - Corrected Proof

J. Kallio, J. Avela, T. Moritani, M. Kanervo, H. Selänne, P. Komi, V. Linnamo — 2010-02-01

Abstract: Both contraction type and ageing may cause changes in H-reflex excitability. H reflex is partly affected by presynaptic inhibition that may also be an important factor in the control of MU activation. The purpose of the study was to examine age related changes in H-reflex excitability and motor unit activation patterns in dynamic and in isometric contractions. Ten younger (YOUNG) and 13 elderly (OLD) males performed isometric (ISO), concentric (CON) and eccentric (ECC) plantarflexions with submaximal activation levels (20% and 40% of maximal soleus surface EMG). Intramuscular EMG data was analyzed utilizing an intramuscular spike amplitude frequency histogram method. Average H/M ratio was always lowest in ECC (n.s.). Mean spike amplitude increased with activation level (P<.05), whereas no significant differences were found between contraction types. Both H-reflex excitability, which may be due to an increase in presynaptic inhibition, and mean spike frequency were higher in YOUNG compared to OLD. In OLD the mean spike frequency was significantly smaller in CON compared to ISO. Lack of difference in mean spike amplitude and frequency across contraction types in YOUNG would imply a similar activation strategy, whereas the lower frequency in dynamic contractions in OLD could be related to synergist muscle behavior.

The effects of accelerometer placement on mechanomyographic amplitude and mean power frequency during cycle ergometry - Corrected Proof

2010-02-01

Abstract: The purposes of this study were threefold: (1) to compare the power output related patterns of absolute and normalized MMG amplitude and MPF responses for proximal and distal accelerometer placements on the vastus lateralis (VL) muscle during incremental cycle ergometry; (2) to examine the influence of accelerometer placements on mean absolute MMG amplitude and MPF values; and (3) to determine the effects of normalization on mean MMG amplitude and MPF values from proximal and distal accelerometer placements. Fifteen adults (10 men and 5 women; mean±SD age=23.9±3.1years) performed incremental cycle ergometry tests to exhaustion. Two accelerometers were placed proximal and distal on the VL muscle. Paired t-tests indicated that absolute MMG amplitude values for the proximal accelerometer were greater (p<0.05) than the distal accelerometer at all power outputs. The normalized MMG amplitude also had greater values for the proximal accelerometer at all power outputs, except 50W. There were no differences, however, between proximal and distal accelerometers for absolute MMG MPF, except at 75W, and normalization eliminated this difference. Twenty-seven percent of the subjects exhibited different power output related patterns of responses between accelerometer placements for MMG amplitude and 47% exhibited different patterns for MPF. These findings indicated that normalization did not eliminate the influence of accelerometer placement on MMG amplitude and highlighted the importance of standardizing accelerometer placements to compare MMG values during cycle ergometry.

Head and shoulder posture affect scapular mechanics and muscle activity in overhead tasks - Corrected Proof

2010-01-25

Abstract: Forward head and rounded shoulder posture (FHRSP) is theorized to contribute to alterations in scapular kinematics and muscle activity leading to the development of shoulder pain. However, reported differences in scapular kinematics and muscle activity in those with forward head and rounded shoulder posture are confounded by the presence of shoulder pain. Therefore, the purpose of this study was to compare scapular kinematics and muscle activity in individuals free from shoulder pain, with and without FHRSP. Eighty volunteers were classified as having FHRSP or ideal posture. Scapular kinematics were collected concurrently with muscle activity from the upper and lower trapezius as well as the serratus anterior muscles during a loaded flexion and overhead reaching task using an electromagnetic tracking system and surface electromyography. Separate mixed model analyses of variance were used to compare three-dimensional scapular kinematics and muscle activity during the ascending phases of both tasks. Individuals with FHRSP displayed significantly greater scapular internal rotation with less serratus anterior activity, during both tasks as well as greater scapular upward rotation, anterior tilting during the flexion task when compared with the ideal posture group. These results provide support for the clinical hypothesis that FHRSP impacts shoulder mechanics independent of shoulder pain.

The effect of increased physical load during an active straight leg raise in pain free subjects - Corrected Proof

Darren John Beales, Peter Bruce O’Sullivan, N. Kathryn Briffa — 2010-01-20

Abstract: Purpose: It has been proposed that pelvic girdle pain (PGP) subjects adopt a high load motor control strategy during the low load task of the active straight leg raise (ASLR). This study investigated this premise by observing the motor control patterns adopted by pain free subjects during a loaded ASLR (ASLR+PL).Method: Trunk muscle activation, intra-abdominal pressure, intra-thoracic pressure, pelvic floor motion, downward pressure of the non-lifted leg and respiratory rate were compared between resting supine, ASLR and ASLR+PL. Additionally, side-to-side comparisons were performed for ASLR+PL.Results: Incremental increases in muscle activation were observed from resting supine to ASLR to ASLR+PL. During the ASLR+PL there was a simultaneous increase in intra-abdominal pressure with a decrease in intra-thoracic pressure, while respiratory fluctuation of these variables were maintained. The ASLR+PL also resulted in increased pelvic floor descent and greater downward pressure of the non-lifted leg. Trunk muscle activation was comparable between sides during ASLR+PL in all muscles except lower obliquus internus abdominis, which was more active on the leg lift side.Conclusion: Pain free subjects respond to an ASLR+PL by a general increase in anterior trunk muscle activation, but preserve the pattern of greater activation on the side of the leg lift observed during an unloaded ASLR. This contrasts to findings in PGP subjects who, despite having a high load strategy for performing an ASLR on the symptomatic side of the body, display equal bilateral activation of the anterior abdominal wall during the ASLR. This differentiates PGP subjects from pain free subjects, supporting the notion that PGP subjects have aberrant motor control patterns during an ASLR.

The peroneus reaction time during sudden inversion test: Systematic review - Corrected Proof

2010-01-18

Abstract: The purpose of the study was to determine whether peroneal reaction time is influenced by ankle’s impairment in subjects with ankle injury assessed by surface electromyography. The studies were identified by electronic research by two independent reviewers at the following databases: MEDLINE (1966–2009), EMBASE (1980–2009), LILACS (1982–2009), CINAHL (1982–2009) and, SPORTDiscus (1975–2009). Studies were divided into following groups: I – subjects with injury (paired by the opposite limb); II – subjects with or without injury (paired by limbs from different subjects) and III – subjects with or without injury (other situations). Studies that used the sudden ankle inversion test were selected. As result, 25 articles were included. The comparison of the reaction time paired by the opposite limb, showed a statistically significant difference in favor of the injured ankles (standardized mean difference – SMD=0.40; IC 95% [0.01;0.79], P=0.05). The comparison paired by limbs from different subjects presented a statistically significant difference, in favor of the injured ankles (SMD=3.49; IC 95% [1.26;5.71], P=0.002). The effect size measured was 0.54 and 1.61, respectively. The greater reaction time delay showed in the subjects with ankle injury compared to that of asymptomatic subjects should be taken into consideration.

The impact of damaging exercise on electromechanical delay in biceps brachii - Corrected Proof

Glyn Howatson — 2010-01-11

Abstract: Electromechanical delay (EMD) can be a useful tool in providing information on muscle function changes following a number of exercise interventions. The purpose of this investigation was to examine the effect of damaging exercise on EMD. Twelve volunteers completed 45 maximal lengthening contractions of the elbow flexors. Indices of muscle damage (maximum voluntary isometric torque and isokinetic torque (60s−1 and 210s−1), creatine kinase (CK), muscle soreness (DOMS)) were recorded pre-exercise, 48h and 96h post-exercise; electromyography was recorded from the belly of biceps brachii and EMD was determined during each contraction condition. Significant time effects were observed for all damage indices (P<0.05). Whilst muscle function was close to full recovery at 96h, both CK and DOMS were significantly (P<0.001) elevated above baseline. EMD was significantly greater at 96h for all contraction conditions (P⩽0.017), but not at 48h. Damaging exercise induces alterations in EMD beyond the apparent recovery of maximal voluntary contractions, which is likely to be a reflection of the changes in post-synaptic events. These data have applications for the use of EMD as a tool for exercise prescription and monitoring recovery following strenuous damaging exercise.

Disturbed motor control of rhythmic movement at 2 h and delayed after maximal eccentric actions - Corrected Proof

Reijo Bottas, Kari Miettunen, Paavo V. Komi, Vesa Linnamo — 2010-01-11

Abstract: The aim of this study was to examine the influence of exercise-induced muscle damage on elbow rhythmic movement (RM) performance and neural activity pattern and to investigate whether this influence is joint angle specific. Ten males performed an exercise of 50 maximal eccentric elbow flexions in isokinetic machine with duty cycle of 1:15. Maximal dynamic and isometric force tests (90°, 110° and 130° elbow angle) and both active and passive stretch reflex tests of elbow flexors were applied to the elbow joint. The intentional RM was performed in the horizontal plane at elbow angles; 60–120° (SA-RM), 80–140° (MA-RM) and 100–160° (LA-RM). All measurements together with the determination of muscle soreness, swelling, passive stiffness, serum creatine kinase were conducted before, immediately and 2h as well as 2days, 4days, 6days and 8days post-exercise. Repeated maximal eccentric actions modified the RM trajectory symmetry acutely (SA-RM) and delayed (SA/MA/LA-RM) until the entire follow up of 8days. Acutely lowered MA-RM peak velocity together with reduced activity of biceps brachii (BB) at every RM range, reflected a poorer acceleration and deceleration capacity of elbow flexors. A large acute drop of BB EMG burst amplitude together with parallel decrease in BB active stretch reflex amplitude, especially 2h post-exercise, suggested an inhibitory effect originating most likely from groups III/IV mechano-nociceptors.

Postural reactions following forward platform perturbation in young, middle-age, and old adults - Corrected Proof

Paulo B. de Freitas, Christopher A. Knight, José A. Barela — 2010-01-08

Abstract: The aim of the study was to examine how individuals of different ages react to forward balance perturbations. Thirty-six volunteers, divided into four groups [young (YA), middle-age (MA40 and MA50), and old (OA) adults], stood on a platform that was either kept stationary, moved backward, or moved forward. EMG onset, EMG time-to-peak, iEMG, and agonist–antagonist co-activation, as well as cumulative angular excursion, maximum center of mass (CM) backward displacement, and CM time-to-reversal were assessed after forward translations. Postural synergies were assessed using principal component analysis (PCA). The results showed that OA activated their muscles later than YA [TA=25ms, RF=17ms] and OA and MA50 reached the peak of activation later than YA [MA50:TA=23ms, RF=32ms, OA:TA=28ms, RF=21ms]. Moreover, OA kept a higher level of activation longer than all younger groups. No differences among groups were observed in co-activation, kinematic, and PCA variables. We conclude that changes in temporal EMG patterns can be seen in the fifth decade. However, such changes have no effect on the CM horizontal displacement and CM time-to-reversal after perturbation, which cannot be justified by the use of different postural synergies, suggesting that temporal aspects of muscle activation could play a minor role in controlling excessive CM displacements after perturbations.

Repetitive eccentric muscle contractions increase torque unsteadiness in the human triceps brachii - Corrected Proof

Andrew J. Meszaros, Masaki Iguchi, Shuo-Hsiu Chang, Richard K. Shields — 2010-01-08

Abstract: Torque steadiness and low-frequency fatigue (LFF) were examined in the human triceps brachii after concentric or eccentric fatigue protocols. Healthy young males (n=17) performed either concentric or eccentric elbow extensor contractions until the eccentric maximal voluntary torque decreased to 75% of pre-fatigue for both (concentric and eccentric) protocols. The number of concentric contractions was greater than the number of eccentric contractions needed to induce the same 25% decrease in eccentric MVC torque (52.2±2.9 vs. 41.5±2.1 for the concentric and eccentric protocols, respectively, p<.01). The extent of peripheral fatigue was ∼12% greater after the concentric compared to the eccentric protocol (twitch amplitude), whereas LFF (increase in double pulse torque/single pulse torque), was similar across protocols. Steadiness, or the ability for a subject to hold a submaximal isometric contraction, was ∼20 % more impaired during the Ecc protocol (p=.052). Similarly, the EMG activity required to hold the torque steady was nearly 20% greater after the eccentric compared to concentric protocol. These findings support that task dependent eccentric contractions preferentially alter CNS control during a precision based steadiness task.

Investigation of motor unit recruitment during stimulated contractions of tibialis anterior muscle - Corrected Proof

L. Mesin, E. Merlo, R. Merletti, C. Orizio — 2009-12-31

Abstract: This work investigated motor unit (MU) recruitment during transcutaneous electrical stimulation (TES) of the tibialis anterior (TA) muscle, using experimental and simulated data. Surface electromyogram (EMG) and torque were measured during electrically-elicited contractions at different current intensities, on eight healthy subjects.EMG detected during stimulation (M-wave) was simulated selecting the elicited MUs on the basis of: (a) the simulated current density distribution in the territory of each MU and (b) the excitation threshold characteristic of the MU. Exerted force was simulated by adding the contribution of each of the elicited MUs. The effects of different fat layer thickness (between 2 and 8mm), different distributions of excitation thresholds (random excitation threshold, higher threshold for larger MUs or smaller MUs), and different MU distributions within the muscle (random distribution, larger MU deeper in the muscle, smaller MU deeper) on EMG variables and torque were tested.Increase of the current intensity led to a first rapid increase of experimental M-wave amplitude, followed by a plateau. Further increases of the stimulation current determined an increase of the exerted force, without relevant changes of the M-wave. Similar results were obtained in simulations.Rate of change of conduction velocity (CV) and leading coefficient of the second order polynomial interpolating the force vs. stimulation level curve were estimated as a function of increasing current amplitudes. Experimental data showed an increase of estimated CV with increasing levels of the stimulation current (for all subjects) and a positive leading coefficient of force vs. stimulation current curve (for five of eight subjects). Simulations matched the experimental results only when larger MUs were preferably located deeper in the TA muscle (in line with a histochemical study). Marginal effect of MU excitation thresholds was observed, suggesting that MUs closer to the stimulation electrode are recruited first during TES regardless of their excitability.

Quadriceps EMG frequency content following isometric lumbar extension exercise - Corrected Proof

Joseph M. Hart, Christopher D. Ingersoll — 2009-12-30

Abstract: A relationship exists between muscles of the lumbar spine and those of the lower extremity where the quadriceps become more inhibited after lumbar paraspinal. The purpose of this experiment was to compare surface electromyography (sEMG) total frequency content after lumbar paraspinal fatiguing exercise. Scope: 50 subjects performed fatiguing lumbar extension exercise indexed by downward shifts in median frequency calculated from lumbar paraspinal sEMG signal. Before and after each exercise set we recorded maximal, isometric knee extension torque and quadriceps central activation ratio (QI) using the superimposed burst technique while recording vastus lateralis sEMG. We calculated total frequency content of the sEMG signal (fEMGTOTAL) as the area of the quadriceps sEMG frequency spectrum. Quadriceps fEMGTOTAL decreased from baseline following the first and second exercise sets. There was no significant change in quadriceps sEMG median frequency among baseline and post-exercise measures. The change in fEMGTOTAL was correlated with the change in QI following the first (r=−0.41, P=0.003) and second (r=−0.32, P=0.02) exercise sets. Conclusion: Quadriceps fEMGTOTAL decreased following fatiguing lumbar extension exercise, in the absence of a significant change in quadriceps median frequency.

Neuromuscular and psychological influences on range of motion recovery in anterior cruciate ligament reconstruction patients - Corrected Proof

Kathryn Hemsley, Michael Sitler, Ray Moyer, Carol Oatis — 2009-12-25

Abstract: To identify distinguishing characteristics for knee surgery patients who experience a protracted recovery process, we sought to determine if there is an association between the neuromuscular stretch reflex and psychological factors of pain perception and anxiety on the range of motion (ROM) recovery rate of post-operative anterior cruciate ligament reconstruction (ACLR) rehabilitation patients. The ACLR participants were categorized into a slow recovery group (SRG: >6weeks to recover 0–125° knee flexion [n=10]) and a normal recovery group (NRG: <6weeks to recovery 0–125° knee flexion [n=12]). Control participants (n=22) were age, gender and activity-level matched to the surgical participants. Neuromuscular testing consisted of sagittal plane video kinematics of the Wartenberg Pendulum Test for determining lower limb stiffness indices and electromyography-monitored patellar tendon tap reflex responses. Psychological and health status assessments consisted of the State–Trait Anxiety Inventory and SF-36™ Health Survey. Data revealed that neuromuscular reflex profiles, lower limb stiffness indices, pain, anxiety and SF-36™ indices of function were not significantly different between the two surgical groups (SRG and NRG). The surgical groups exhibited significantly greater pain (2.67±2.27 SRG, 1.49±1.15 NRG) than the control group (p⩽.05). SF-36™ indices were significantly lower for the surgical groups for total score (546.55±94.70 SRG, 577.57±125.58 NRG), function 69.00±20.24 SRG, 67.08±19.12 NRG), role physical (53.75±22.85 SRG, 53.12±23.15 NRG), social (76.24±25.31 SRG, 65.62±27.24 NRG), and emotional (82.49±19.81 SRG, 81.38±23.02 NRG) subscales (p⩽.05). These results suggest that neuromuscular reflex responses, visual analogue scale (VAS) pain, and anxiety are not distinguishing factors for ROM recovery rate between the SRG and NRG. Decreased SF-36™ indices, including pain as it influences function, though clinically relevant factors, were not statistically associated with post-operative ROM recovery rate.

Effects of two neuromuscular fatigue protocols on landing performance - Corrected Proof

C. Roger James, Barry W. Scheuermann, Michael P. Smith — 2009-12-14

Abstract: The purpose of the study was to investigate the effects of two fatigue protocols on landing performance. A repeated measures design was used to examine the effects of fatigue and fatigue protocol on neuromuscular and biomechanical performance variables. Ten volunteers performed non-fatigued and fatigued landings on two days using different fatigue protocols. Repeated maximum isometric squats were used to induce fatigue on day one. Sub-maximum cycling was used to induce fatigue on day two. Isometric squat maximum voluntary contraction (MVC) was measured before and after fatigued landings on each day. During the landings, ground reaction force (GRF), knee kinematics, and electromyographic (EMG) data were recorded. Isometric MVC, GRF peaks, loading rates, impulse, knee flexion at contact, range of motion, max angular velocity, and EMG root mean square (RMS) values were compared pre- and post-fatiguing exercise and between fatigue protocols using repeated ANOVA. Fatigue decreased MVC strength (p⩽0.05), GRF second peak, and initial impulse (p⩽0.01), but increased quadriceps medium latency stretch reflex EMG activity (p⩽0.012). Knee flexion at contact was 5.2° greater (p⩽0.05) during fatigued landings following the squat exercise compared to cycling. Several variables exhibited non-significant but large effect sizes when comparing the effects of fatigue and fatigue protocol. In conclusion, fatigue alters landing performance and different fatigue protocols result in different performance changes.

Position accuracy and electromyographic responses during head reposition in young adults with chronic neck pain - Corrected Proof

Chih-Hsiu Cheng, Jaw-Lin Wang, Jiu-Jenq Lin, Shwu-Fen Wang, Kwan-Hwa Lin — 2009-12-11

Abstract: The head reposition test is traditionally used to examine the proprioceptive sensitivity of the neck. The aim of this study was to investigate the position accuracy and corresponding cervical electromyographic (EMG) responses of the neck pain subjects during sagittal head-to-neutral tasks. Twelve young subjects with chronic neck pain and twelve young healthy subjects were recruited. The position accuracy was measured by the constant error, variable error, and root mean square error of joint angles during head-to-neutral tasks in flexion and extension directions. Surface EMG of neck flexors and extensors were analyzed by the voluntary response index, including the similarity index (SI) and electromyographic magnitude (MAG) of muscle groups. The normalized average integration of EMG activity (NAIEMG) of individual muscle was also calculated. The results showed: (1) significantly larger constant error and root mean square error but similar variable error in patients compared with controls, (2) smaller SI but similar MAG in patients compared with controls, (3) greater synergistic/antagonistic NAIEMG in patients than controls. The findings suggested that young adults with chronic neck pain exhibit proprioceptive dysfunction and altered EMG pattern during voluntary sagittal neck motions. This study provides guidelines which could lead to the development of therapeutic exercise programs.

Test–retest reliability of the soleus H-reflex is affected by joint positions and muscle force levels - Corrected Proof

2009-12-11

Abstract: The purpose of this study was to determine the test–retest reliability of the soleus (SOL) H-reflex during rest and isometric contractions at 10%, 30%, and 50% of the maximal voluntary force (MVC) at the ankle joint angles of neutral (0°), plantarflexion (20°), and dorsiflexion (−20°) respectively, in a sitting position. Ten healthy participants, with mean age of 24.9±5.0 (SD) years, height 168.3±8.8cm, weight 62.7±12.3kg, were tested for the SOL H-reflex (Hmax) on two separate occasions within 7days. The intraclass correlation coefficient (ICC) for the test–retest of the SOL H-reflex during rest was found to be high at ankle joint angle of neutral (ICC=0.92) and plantarflexion (0.96), and moderate at dorsiflexion (0.75). Inconsistent ICC values (range from 0.62 to 0.97) were found during the submaximal voluntary contractions at the three ankle joint positions. High ICCs were also found in Hmax/Mmax ratio at neutral (0.86), plantarflexion (0.96), and dorsiflexion (0.84) positions. It was concluded that the test–retest reliability of the SOL H-reflex was affected by the intensity of voluntary contraction and ankle joint position. The H-reflex demonstrated a higher reliability at the neutral and plantarflexion positions than that at the dorsiflexion position during rest, and a higher reliability at 10% MVC than that at 30% and 50% MVC.

Classification of multi muscle activation patterns of osteoarthritis patients during level walking - Corrected Proof

Vinzenz von Tscharner, Victor Valderrabano — 2009-12-11

Abstract: The study compares the timing and frequency changes of surface EMGs recorded from osteoarthritis patients with previous traumatic ankle injury and normal subjects during level walking. EMG intensity (power) was obtained by a wavelet analysis. There were intensity values for each frequency characterized by the wavelets for every time point. The intensities were compounded into Multi Muscle Patterns (MMP) simultaneously showing the time and spectral aspects of the lower leg muscle activity.The aim of the study was to test the hypothesis that the differences between the group of the MMPs from the affected leg (AFL) and the not affected leg (NAL) allow detecting whether a newly measured MMP results from an AFL or NAL. This hypothesis was tested by a spherical classification procedure yielding the correctly classified MMPs thus indicating the significance of the differences between the MMPs of the AFL and NAL. The hypothesis was supported (not falsified) by the results. Thus there were common features of muscle activity in the AFL of most osteoarthritis patients that allowed detecting whether the MMP of a new patient was of the kind seen in most other osteoarthritis patients. The spectral, timing and intensity factors in the MMP that allowed this classification were visualized in the mean MMPs of the patients and the control group. The comparison revealed where on average the relative timing and spectral differences of the muscle activation of osteoarthritis patients and control subjects occurred.

Women with stress urinary incontinence demonstrate motor control differences during coughing - Corrected Proof

Stéphanie J. Madill, Marie-Andrée Harvey, Linda McLean — 2009-12-07

Abstract: Introduction: This study compared the patterns of pelvic floor muscle (PFM) activity during coughing between women with stress urinary incontinence (SUI) and continent women, using surface electromyography (EMG) and posterior vaginal wall (PVW) pressure.Methods: Twenty-four women participated: eight continent, eight with mild SUI and eight with severe SUI. Volunteers performed three maximum coughs in supine and standing. Maximum PFM EMG and PVW pressure amplitudes and the timing of the EMG peak relative to the PVW pressure peak were determined. Ensemble average PVW pressure versus EMG curves were created.Results: There were no significant differences among the groups in the maximum EMG or PVW pressure amplitudes. The EMG and PVW pressure peaked simultaneously in both positions in the continent group. In the mild SUI group, the EMG and PVW pressure peaked simultaneously in supine, but the EMG peaked before the PVW pressure in standing. In the severe SUI group, the EMG peaked before the PVW pressure in both positions. The shapes of the PVW pressure versus EMG curves were similar among the groups and positions, however the SUI groups displayed higher EMG-intercepts than the continent women. Conclusion: These findings suggest that urine leakage during coughing in women with SUI may be related to delays in force generation rather than PFM weakness.

Training a multivariable myoelectric mapping function to estimate fatigue - Corrected Proof

Daniel R. Rogers, Dawn T. MacIsaac — 2009-12-04

Abstract: The mapping index (MI) is a fatigue assessment index that uses multiple time-domain myoelectric features to train an artificial neural network (ANN) to track the progression of fatigue. This work showed that mapping functions trained using data from independent subjects and contraction conditions to yield a generalized mapping index (GMI) can assess fatigue as well as functions trained with subject and contraction-specific data to yield MI. Surface myoelectric signals were collected from nine healthy participants during isometric, cyclic and random fatiguing contractions. Two datasets were collected: one for tuning the functions and the other for testing. The performance of fatigue indices was evaluated using a newly proposed piece-wise linear signal to noise ratio. ANN based indices were compared to normalized spectral moments (NSM) and mean frequency (MF). GMI performed as well as MI and outperformed NSM and MF demonstrating that subject and contraction-specific baseline data is not needed in order to train a mapping function which can effectively assess fatigue.

On the suitability of using surface electrode placements to estimate muscle activity of the rotator cuff as recorded by intramuscular electrodes - Corrected Proof

Danielle L. Waite, Rebecca L. Brookham, Clark R. Dickerson — 2009-11-23

Abstract: Background: Electromyography (EMG) is commonly used to assess muscle activity. Although previous studies have had moderate success in predicting individual intramuscular muscle activity from surface electrodes, extensive data does not exist for the rotator cuff. This study aimed to determine how reliably surface electrodes represent rotator cuff activity during 20 maximal exertions.Methods: Five channels of EMG were recorded on the following rotator cuff muscles: supraspinatus and infraspinatus intramuscular and surface recordings, and teres minor intramuscular recordings. An additional 3 surface electrodes were placed over the upper and middle trapezius and posterior deltoid. Subjects performed ramped maximal voluntary contractions (MVCs) for each muscle, followed by 20 isometric maximal exertions. Linear least squares best fit regressions (unconstrained and constrained with zero-intercept) were used to compare: intramuscular and surface supraspinatus and infraspinatus signals, respectively, and intramuscular teres minor and surface infraspinatus signals.Findings: Relationships existed between wire and surface electrode measurements for all rotator cuff muscles: supraspinatus (r2=0.73); teres minor (r2=0.61); infraspinatus (r2=0.40), however prediction equations indicated large overestimations and offsets.Interpretation: When appropriate multiplicative coefficients are considered, surface supraspinatus and infraspinatus electrodes may be used to estimate intramuscular supraspinatus and teres minor activations, respectively, in maximal exertions similar to those tested. However, until these relationships are better defined in other postures, intensities and exertion types, the use of surface electrodes to estimate indwelling rotator cuff activity is cautioned against.

Application of a new method in the study of pelvic floor muscle passive properties in continent women - Corrected Proof

2009-11-09

Abstract: The aim of this study was to present a new methodology for evaluating the pelvic floor muscle (PFM) passive properties. The properties were assessed in 13 continent women using an intra-vaginal dynamometric speculum and EMG (to ensure the subjects were relaxed) in four different conditions: (1) forces recorded at minimal aperture (initial passive resistance); (2) passive resistance at maximal aperture; (3) forces and passive elastic stiffness (PES) evaluated during five lengthening and shortening cycles; and (4) percentage loss of resistance after 1min of sustained stretch. The PFMs and surrounding tissues were stretched, at constant speed, by increasing the vaginal antero-posterior diameter; different apertures were considered. Hysteresis was also calculated. The procedure was deemed acceptable by all participants. The median passive forces recorded ranged from 0.54N (interquartile range 1.52) for minimal aperture to 8.45N (interquartile range 7.10) for maximal aperture while the corresponding median PES values were 0.17N/mm (interquartile range 0.28) and 0.67N/mm (interquartile range 0.60). Median hysteresis was 17.24N∗mm (interquartile range 35.60) and the median percentage of force losses was 11.17% (interquartile range 13.33). This original approach to evaluating the PFM passive properties is very promising for providing better insight into the patho-physiology of stress urinary incontinence and pinpointing conservative treatment mechanisms.

The effects of unsupervised movement training with visual feedback on upper limb kinematic in persons with shoulder impingement syndrome - Corrected Proof

Jean-Sébastien Roy, Hélène Moffet, Bradford J. McFadyen — 2009-11-09

Abstract: Persons with shoulder impingement syndrome (SIS) present impairments that can be improved following supervised movement training with feedback; however, retention is low. The purpose of this study was to evaluate if kinematic changes observed following supervised training can be maintained using unsupervised training with visual feedback. Thirty-three subjects with SIS participated in two visits, one day apart. Kinematic patterns of the upper limb were evaluated once during the first visit, immediately after supervised training; they were evaluated twice during the second visit, before and immediately after unsupervised training. Kinematic patterns were characterized by total excursion and final position during reaching. Unsupervised training consisted of reaching movements performed in front of a mirror. The day after supervised training, subjects with SIS used significantly larger trunk rotation and finished reaching with the trunk more rotated as compared to immediately after supervised training. Following unsupervised training, kinematics of the trunk was back to the level observed immediately after supervised training. Subjects who presented the largest kinematic deficits also significantly improved their shoulder and clavicular movements. Unsupervised training appears to be a good complement to supervised training in order to normalize the kinematic impairments of persons with SIS as compared to healthy subjects.

Impaired action potential conduction at high force levels after eccentric exercise - Corrected Proof

Harri Piitulainen, Reijo Bottas, Paavo Komi, Vesa Linnamo, Janne Avela — 2009-11-02

Abstract: High-density surface electromyography was used to examine whether gross sarcolemmal function is impaired in m. biceps brachii after intensive eccentric elbow flexor exercise, when measured at wide range of isometric contraction levels.Root mean square (RMS), mean power frequency (MNF) and mean muscle fibre conduction velocity (CV) were calculated before and up to four days post-exercise.Maximal isometric voluntary (MVC) force decreased by 21.3±5.6% two hours after exercise, and by 12.6±11.1% two days post-exercise. CV and MNF decreased both during MVC (CV from 4.1±0.3m/s to 3.8±0.4m/s and MNF from 92.6±10Hz to 85.2±11Hz) and during electrically evoked maximal M-wave (CV from 4.1±0.3m/s to 3.0±0.5m/s and MNF from 97.1±27.2Hz to 78.0±24.4Hz) two hours post-exercise. Furthermore, at submaximal isometric force levels, CV and MNF decreased only at higher contraction levels (40%, 50% and 75% of MVC) two hour post-exercise.It can be concluded that intensive exercise can temporarily impair gross sarcolemmal function. In addition, since this only occurred at high force levels, based on Henneman’s size principle, it seems that higher threshold motor units were predominantly affected.

On the feasibility of obtaining multiple muscular maximal voluntary excitation levels from test exertions: A shoulder example - Corrected Proof

Jaclyn N. Chopp, Steven L. Fischer, Clark R. Dickerson — 2009-11-02

Abstract: Currently, contrasting views exist regarding which body and arm postures are most effective for eliciting maximal voluntary exertions in the shoulder muscles. Informed exertion standardization may improve comparisons between subjects and muscle groups for normalized electromyography values. Additionally, identifying exertions that can produce equivalent maximal electrical activity values can reduce experimental setup time and reduce the likelihood of fatigue development. This research study examined twelve posture and force direction defined test exertions to identify those that elicited maximal electrical activity from the deltoid (anterior and middle fibres) and pectoralis major (clavicular and sternal heads). Further, the question of whether a single test exertion could obtain maximal electrical activity from multiple muscle fascicles was explored. Maximal activation was demonstrated for the deltoid during several exertions that incorporated an upward force exertion and the pectoralis major for multiple exertions that included an inward force direction. Finally, two test exertions produced maximal electrical activity from both muscles of interest. This research supports the notion that a range of exertions can elicit maximal electrical activity from a muscle, rather than one specific exertion. This suggests that researchers may be able to leverage a smaller set of test exertions to evaluate multiple muscles simultaneously without loss of data quality, and thereby decrease overall experimental data collection time while maintaining high fidelity data.

Unilateral lower limb muscle fatigue induces bilateral effects on undisturbed stance and muscle EMG activities - Corrected Proof

L.L. Berger, S.C. Regueme, N. Forestier — 2009-10-30

Abstract: The study investigated the effects of an unilateral ankle muscle fatigue onto independent postural control parameters including the trajectories of the estimated resultant CoP (CoPres) and his components: the centre of gravity (CG) and CoP–CG trajectories.Nine healthy men realized series of 10 toe-lift immediately followed by 10 knee flexions until exhaustion with one (Ex) leg. Maximal isometric voluntary contractions, postural sway measures of each leg, and muscular activities of the ankle muscles were recorded before and immediately after the fatiguing exercise.As expected, the latter induced a decrease in maximal voluntary peak force associated with a greater variability of the relative contribution of each leg on the CoPres, enhanced all postural parameters of the non-exercised leg. A significant decreased of the tibialis anterior EMG activity for the Ex leg and an increased one for the NoEx leg. Finally, following unilateral fatigue, the body sway destabilisation seemed to occur only along the medio-lateral (ML) axis.The enhanced and greater variability of the variance along ML axis might be explained by the recourse at the loading–unloading strategy choice and suggests a central attempt to compensate for pain sensation.

Uncovering patterns of forearm muscle activity using multi-channel mechanomyography - Corrected Proof

Natasha Alves, Tom Chau — 2009-10-26

Abstract: A coordinated activation of distal forearm muscles allows the hand and fingers to be shaped during movement and grasp. However, little is known about how the muscle activation patterns are reflected in multi-channel mechanomyogram (MMG) signals. The purpose of this study is to determine if multi-site MMG signals exhibit distinctive patterns of forearm muscle activity. MMG signals were recorded from forearm muscle sites of nine able-bodied participants during hand movement. By using 14 features selected by a genetic algorithm and classified by a linear discriminant analysis classifier (LDA), we show that MMG patterns are specific and consistent enough to identify 7±1 hand movements with an accuracy of 90±4%. MMG-based movement recognition required a minimum of three recording sites. Further, by classifying five classes of contraction patterns with 98±3% accuracy from MMG signals recorded from the residual limb of an amputee participant, we demonstrate that MMG shows pattern-specificity even in the absence of typical musculature. Multi-site monitoring of the RMS of MMG signals is suggested as a method of estimating the relative contributions of muscles to motor tasks. The patterns in MMG facilitate our understanding of the mechanical activity of muscles during movement.

Passive knee movement-induced modulation of the soleus H-reflex and alteration in the fascicle length of the medial gastrocnemius muscle in humans - Corrected Proof

2009-10-26

Abstract: In humans, an inhibitory via Ia afferent pathway from the medial gastrocnemius (MG) to the soleus (SOL) motoneuron pool has been suggested. Herein, we examined the relation between MG fascicle length changes and the SOL H-reflex modulation during passive knee movement. Twelve subjects performed static and passive (5° s−1) knee movement tasks with the ankle immobilized using an isokinetic dynamometer in sitting posture. The maximal H- and M-waves were measured at four target angles (20°, 40°, 60°, and 80° flexion from full knee extension). The MG fascicles length and velocity were measured using a B-mode ultrasonic apparatus. Results demonstrated that the SOL Hmax/Mmax; i.e., ratio of the maximal H- to M-waves, was attenuated with increasing MG fascicle length in static tasks. The SOL Hmax/Mmax at 20° was significantly attenuated compared with 60° and 80° with increasing MG fascicle length and lengthening velocity in passive knee extension. However, no significant differences in the SOL Hmax/Mmax were found across the target angles in the passive knee flexion task. In conclusion, as muscle spindles increase their discharge with lengthening fascicle velocity, but keep silent when fascicles shorten, our data suggest that lengthening the MG facilitates an inhibitory Ia pathway from MG to SOL, and modulates SOL motoneuron activity during movements.

Delayed abdominal muscle onsets and self-report measures of pain and disability in chronic low back pain - Corrected Proof

Paul Marshall, Bernadette Murphy — 2009-10-23

Abstract: Objective: The objective of this study was the measure the onset time of the transverse abdominis (TA) muscle during rapid unilateral shoulder movements in individuals with chronic low back pain (LBP), and to evaluate the relationship between latency times and self-report measures of pain and disability.Design: Descriptive cross-sectional study.Setting: University laboratory.Participants: Eighty individuals with chronic LBP of a non-specific origin (males n=44, females n=36).Main outcome measures: Responses of the right and left surface TA/internal obliques were measured using surface electromyography (EMG) during rapid unilateral shoulder flexion, abduction, and extension. Pain intensity was measured using a visual analog scale (VAS), and disability with the Oswestry disability index (ODI).Results: Seventy-five percent of individuals were identified as lacking feedforward activation. A significant side×direction main effect was identified, with the ipsilateral latency more delayed in flexion and abduction (F(2316)=58.2, p<0.001). Individuals without feedforward activation had lower ODI scores (23.2±6.9% vs 31.0±9.2%, mean difference 7.8%, 95% CI 3.9 to 11.6%, p<0.001). Regression analysis found that 17% of the variance in VAS scores for the entire sample (n=80) were explained by the latency times measured. This relationship was stronger when the sample was separated into individuals who did (n=20), and did not (n=60) have feedforward activation.Conclusion: Deep abdominal muscle onsets during rapid limb movement were significantly associated with self-rated pain scores. Seventy-five percent of individuals with chronic non-specific LBP exhibited delayed activation. No evidence has been provided in this study to support, or refute the use of specific localized deep abdominal contractions for exercise rehabilitation programs.

Estimation of handgrip force using frequency-band technique during fatiguing muscle contraction - Corrected Proof

2009-10-19

Abstract: In this paper, we propose a force estimation model to compute the handgrip force from SEMG signal during fatiguing muscle contraction tasks. The appropriate frequency range was analyzed using various combinations of a wavelet scale, and the highest accuracy was achieved at a range from 242 to 365Hz. After that, eight healthy individuals performed a series of static (70%, 50%, 30%, and 20% MVC) and dynamic (0–50% MVC) muscle contraction tasks to evaluate the performance of this technique in comparison with that of former method using the Root Mean Square of the SEMG signal. Both methods had comparable results at the beginning of the experiments, before the onset of muscle fatigue. However, differences were clearly observed as the degree of muscle fatigue began to increase toward the endurance time. Under this condition, the estimated handgrip force using the proposed method improved from 17% to 134% for static contraction tasks and 40% for dynamic contraction tasks. This study overcomes the limitation of the former method during fatiguing muscle contraction tasks and, therefore, unlocks the potential of utilizing the SEMG signal as an indirect force estimation method for various applications.

Physiotherapy vs. capsular shift and physiotherapy in multidirectional shoulder joint instability - Corrected Proof

Rita M. Kiss, Árpád Illyés, Jenő Kiss — 2009-10-15

Abstract: Purpose: The aim of the study was to compare the kinematic parameters and the on–off pattern of the muscles of patients with multidirectional instability (MDI) treated by physiotherapy or by capsular shift and postoperative physiotherapy before and after treatment during elevation in the scapular plane.Scope: The study was carried out on 32 patients with MDI of the shoulder treated with physiotherapy, 19 patients with MDI of the shoulder treated by capsular shift and postoperative physiotherapy, and 25 healthy subjects. The motion of skeletal elements was modeled by the range of humeral elevation, scapulothoracic angle and glenohumeral angle, scapulothoracic (ST) and glenohumeral (GH) rhythms, and relative displacement between the rotation centers of the humerus and scapula. The muscle pattern was modeled by the on–off pattern of muscles around the shoulder, which summarizes the activity duration of the investigated muscles.Results: The different ST and GH rhythms and the increased relative displacement between the rotation centers of the scapula and the humerus were observed in MDI patients. The physiotherapy strengthened the rotator cuff, biceps brachii, triceps brachii, deltoid muscles, and increase the neuromuscular control of the shoulder joints. Capsular shift and physiotherapy enabled bilinear ST and GH rhythms and the normal relative displacement between the rotation centers of the scapula and humerus to be restored. After surgery and physiotherapy, the duration of muscular activity was almost normal.Conclusion: The significant alteration in shoulder kinematics observed in MDI patients cannot be restored by physiotherapy only. After the capsular shift and postoperative physiotherapy angulation at 60° of ST and GH rhythms, the relative displacement between the rotation centers of the scapula and humerus and the duration of muscular activity were restored.

Shoulder and elbow muscle activity during fully supported trajectory tracking in people who have had a stroke - Corrected Proof

A.M. Hughes, C.T. Freeman, J.H. Burridge, P.H. Chappell, P.L. Lewin, E. Rogers — 2009-10-07

Abstract: An inability to perform tasks involving reaching is a common problem for stroke patients. This paper provides an insight into mechanisms associated with recovery of upper limb function by examining how stroke participants’ upper limb muscle activation patterns differ from those of neurologically intact participants, and how they change in response to an intervention.In this study, five chronic stroke participants undertook nine tracking tasks in which trajectory (orientation and length), speed and resistance to movement were varied. During these tasks, EMG signals were recorded from triceps, biceps, anterior deltoid, upper, middle and lower trapezius and pectoralis major. Data collection was performed in sessions both before, and after, an intervention in which participants performed a similar range of tracking tasks with the addition of responsive electrical stimulation applied to their triceps muscle. The intervention consisted of eighteen one hour treatment sessions, with two participants attending an additional seven sessions. During all sessions, each participant’s arm was supported by a hinged arm-holder which constrained their hand to move in a two dimensional plane.Analysis of the pre intervention EMG data showed that timing and amplitude of peak EMG activity for all stroke participants differed from neurologically intact participants. Analysis of post intervention EMG data revealed that statistically significant changes in these quantities had occurred towards those of neurologically intact participants.

Rapid torque development in older female fallers and nonfallers: A comparison across lower-extremity muscles - Corrected Proof

Dain P. LaRoche, Kim A. Cremin, Brittnee Greenleaf, Ronald V. Croce — 2009-09-27

Abstract: The objective of this study was to compare reaction time, joint torque, rate of torque development, and magnitude of neuromuscular activation of lower-extremity muscles in elderly female fallers and nonfallers. Participants included 11, elderly, female fallers (71.3±5.4years) and twelve nonfallers (71.3±6.2years) who completed a fall risk questionnaire. Then, maximal, voluntary, isometric contractions of the knee and ankle muscles were performed in reaction to a visual cue to determine joint torque, rate of torque development, reaction time, and nervous activation of agonists and antagonists. Results indicated that significantly more fallers reported “dizziness upon rising”, “use of balance altering medications”, “stress or depression”, “not enough sleep”, “arthritis in lower body”, “chronic pain in lower body”, and “tiring easily while walking” (all P<0.05). Normalized dorsiflexion and plantarflexion strength scores (summation of peak torque, rate of torque development and impulse) were lower in fallers than in nonfallers (P<0.05). When summed across lower-extremity muscle groups, fallers demonstrated 19% lower peak torque and 29% longer motor time (P<0.05). In conclusion, comprehensive fall risk screening and prevention programs should address both neuromuscular and non-muscular factors, and, weakness of the ankle dorsiflexors and plantarflexors should be further studied as potential contributors to falls in older adults.

Auditory evoked blink reflex and posterior auricular muscle response: Observations in patients with HFS and PFS - Corrected Proof

Meral E. Kızıltan, Ayşegül Gündüz, Rahşan Şahin — 2009-09-22

Abstract: Our goal was to investigate the characteristics of the auditory brainstem reflexes in patients with hemifacial spasm (HFS) and postparalytic facial syndrome (PFS).The spasm activities and responses by supraorbital and auditory stimuli were recorded from the orbicularis oculi, the posterior auricular and the mentalis muscles in 27 HFS and 21 PFS patients. The results were compared with those of 20 controls.Blink reflex (BR) was obtained by supraorbital stimulation in normal controls and on both sides of HFS and PFS patients whereas sound evoked bilateral auditory blink reflex (ABR) in 96.3%, 90.5% and 100%, respectively. Both BR and ABR showed synkinetic spread on symptomatic sides in all patients. The posterior auricular muscle response (PAMR) was observed bilaterally in 59.3%, 42.9% and 75.0% of groups, respectively. However, there was no synkinetic spread of PAMR.Since PAMR does not show synkinetic spread even in the presence of synkinetic spread of ABR and BR, we may suggest that a distal origin may be responsible of the synkinetic spread, or PAM is probably governed by a smaller nucleus in the brainstem. Thus it may be speculated that its excitability is insufficient to stimulate the ABR nucleus, whereas the reverse process is possible.

Methodological aspects of SEMG recordings for force estimation – A tutorial and review - Corrected Proof

Didier Staudenmann, Karin Roeleveld, Dick F. Stegeman, Jaap H. van Dieën — 2009-09-16

Abstract: Insight into the magnitude of muscle forces is important in biomechanics research, for example because muscle forces are the main determinants of joint loading. Unfortunately muscle forces cannot be calculated directly and can only be measured using invasive procedures. Therefore, estimates of muscle force based on surface EMG measurements are frequently used. This review discusses the problems associated with surface EMG in muscle force estimation and the solutions that novel methodological developments provide to this problem. First, some basic aspects of muscle activity and EMG are reviewed and related to EMG amplitude estimation. The main methodological issues in EMG amplitude estimation are precision and representativeness. Lack of precision arises directly from the stochastic nature of the EMG signal as the summation of a series of randomly occurring polyphasic motor unit potentials and the resulting random constructive and destructive (phase cancellation) superimpositions. Representativeness is an issue due the structural and functional heterogeneity of muscles. Novel methods, i.e. multi-channel monopolar EMG and high-pass filtering or whitening of conventional bipolar EMG allow substantially less variable estimates of the EMG amplitude and yield better estimates of muscle force by (1) reducing effects of phase cancellation, and (2) adequate representation of the heterogeneous activity of motor units within a muscle. With such methods, highly accurate predictions of force, even of the minute force fluctuations that occur during an isometric and isotonic contraction have been achieved. For dynamic contractions, EMG-based force estimates are confounded by the effects of muscle length and contraction velocity on force producing capacity. These contractions require EMG amplitude estimates to be combined with modeling of muscle contraction dynamics to achieve valid force predictions.

Reliability and interpretation of single leg stance and maximum voluntary isometric contraction methods of electromyography normalization - Corrected Proof

Marc F. Norcross, J. Troy Blackburn, Benjamin M. Goerger — 2009-09-11

Abstract: Normalization of electromyographic (EMG) amplitudes is necessary in the study of human motion. However, there is a lack of agreement on the most reliable and appropriate normalization method. This study evaluated the reliability of single leg stance (SLS) and maximal voluntary isometric contraction (MVIC) normalization methods and the relationship between these measures for the gluteus maximus (GMax), gluteus medius (GMed), rectus femoris (RF), vastus lateralis (VL), hip adductor group (ADD), and biceps femoris (BF). Surface EMG was recorded in 20 subjects during three 5s trials of SLS and MVIC. SLS and MVIC methods both demonstrated good-to-excellent reliability in all muscles (ICCs>0.80). Intrasubject coefficients of variation were lower for the MVIC method (9–36%) than for the SLS method (20–59%). EMG amplitudes during MVIC and SLS were significantly correlated for all muscles (Pearson r’s=0.604–0.905, p<0.005) except GMax (r=0.250, p=0.288). Use of SLS normalization for the RF, VL, and BF is not recommended due to a lack of measurement precision. However, this method is justified in the GMax, GMed, and ADD and may provide a better representation of coordinated muscle function during a functional task.

Reciprocal influences on performances of a postural–suprapostural task by manipulating the level of task-load - Corrected Proof

Cheng-Ya Huang, Rong-Ju Cherng, Ing-Shiou Hwang — 2009-08-28

Abstract: The objective of this study was to investigate the reciprocal influences of stance pattern (bilateral stance vs. unilateral stance) and thumb-index precision grip task (static target vs. dynamic target) on postural–suprapostural tasks by manipulating task-load. Fifteen healthy volunteers participated in four postural–suprapostural tasks, including static force-matching in bilateral/unilateral stance (BS_static; US_static), dynamic force-matching in bilateral/unilateral stance (BS_dynamic; US_dynamic), and two control tasks in bilateral and unilateral stances without a finger task. The normalized force error (NFE), reaction time (RT) of the finger tasks, and normalized change in center of pressure sway (ΔNCoP) were measured. For suprapostural task performance, a significant interaction effect between postural and suprapostural tasks on NFE of the finger tasks was noted (static: BS US), but RT was not different among the four tasks. For postural task performance, negative ΔNCoP during unilateral stance indicated a spontaneous reduction in postural sway due to added force-matching. In contrast, addition of force-matching tended to increase postural sway during bilateral stance, but postural fluctuations decreased as task-load of suprapostural task increased (BS_dynamic

Analysis of the peak-to-peak ratio of extracellular potentials in the proximity of excitable fibres - Corrected Proof

Javier Rodriguez, Armando Malanda, Luis Gila, Ignacio Rodriguez, Javier Navallas — 2009-08-26

Abstract: In a previous work we studied the ratio between the amplitudes of the second and first phases (which we call PPR, after peak-to-peak ratio) of the single fibre action potential (SFAP) for a collection of fibrillation potentials (FPs) extracted from two pathological muscles. These FPs showed a wider PPR range than the Dimitrov–Dimitrova (D–D) convolutional model could provide. We proposed a modification of the D–D intracellular action potential (IAP) in order to obtain a range of PPRs comparable to that observed in our FPs. This paper extends that study to a large number of SFAPs extracted from the tibialis anterior muscle of normal subjects. The estimation of the average PPR range of non-diseased muscles in non-fatigued conditions is important since it can be used as a reference to establish a comparison with PPR ranges from muscles suffering some disorder or from fibres that are fatigued. Other aspects of the PPR, as its sensitivity with volume conductor parameters or to what extent changes in the SFAP PPR reflects changes in IAP spatial profile are also examined. We found that the PPR of experimental SFAPs ranges from 0.3 to 2.5 in all subjects and that all PPR histograms contain a well-defined single peak around the PPR value 1.0.

Application of the segment weight dynamic movement method to the normalization of gait EMG amplitude - Corrected Proof

Y. Nishijima, T. Kato, M. Yoshizawa, M. Miyashita, H. Iida — 2009-08-25

Abstract: This study aims at determining the applicability of a segment weight dynamic movement (SWDM) method as an alternative for normalizing gait EMGs in comparison with the conventional isometric maximal voluntary contraction (MVC) method. The SWDM method employs reference exercises, each being a dynamic, repetitive movement of a joint under the load of the segment weight (i.e., the total weight of all segments distal to the joint). EMG amplitudes of 28 healthy male subjects walking at 120steps/min were normalized by the two methods. CV and VR were used to assess the inter-individual variability of both the normalized gait EMG for 8 muscles. The CV and VR values attained with the two methods were close to each other, as well as to those obtained by other researchers using the isometric MVC method. These results suggest that the SWDM method has a comparable level of applicability to gait EMG normalization as the isometric MVC method.

A wavelet-based adaptive filter for removing ECG interference in EMGdi signals - Corrected Proof

Choujun Zhan, Lam Fat Yeung, Zhi Yang — 2009-08-19

Abstract: Diaphragmatic electromyogram (EMGdi) signals convey important information on respiratory diseases. In this paper, an adaptive filter for removing the electrocardiographic (ECG) interference in EMGdi signals based on wavelet theory is proposed. Power spectrum analysis was performed to evaluate the proposed method. Simulation results show that the power spectral density (PSD) of the extracted EMGdi signal from an ECG corrupted signal is within 1.92% average error relative to the original EMGdi signal. Testing on clinical EMGdi data confirm that this method is also efficient in removing ECG artifacts from the corrupted clinical EMGdi signal.

Adaptations of upper trapezius muscle activity during sustained contractions in women with fibromyalgia - Corrected Proof

2009-08-17

Abstract: The study compared the distribution of electromyographic (EMG) signal amplitude in the upper trapezius muscle in 10 women with fibromyalgia and in 10 healthy women before and after experimentally-induced muscle pain. Surface EMG signals were recorded over the right upper trapezius muscle with a 10×5 grid of electrodes during 90° shoulder abduction sustained for 60s. The control subjects repeated the abduction task following injections of isotonic and hypertonic (painful) saline into the upper trapezius muscle. The EMG amplitude was computed for each electrode pair and provided a topographical map of the distribution of muscle activity. The pain level rated by the patients at the beginning of the sustained contraction was 5.9±1.5. The peak pain intensity for the control group following the injection of hypertonic saline was 6.0±1.6. During the sustained contractions, the EMG amplitude increased relatively more in the cranial than caudal region of the upper trapezius muscle for the control subjects (shift in the distribution of EMG amplitude: 2.3±1.3mm; P<0.01). The patient group showed lower average EMG amplitude than the controls during the contraction (P<0.05) and did not show different changes in EMG amplitude between different regions of the upper trapezius. A similar behavior was observed for the control group following injection of hypertonic saline. The results indicate that muscle pain prevents the adaptation of upper trapezius activity during sustained contractions as observed in non-painful conditions, which may induce overuse of similar muscle compartments with fatigue.

Time-related changes of motor unit properties in the rat medial gastrocnemius muscle after spinal cord injury. I. Effects of total spinal cord transection - Corrected Proof

2009-08-13

Abstract: The contractile properties of motor units (MUs) were electrophysiologically investigated in the medial gastrocnemius (MG) muscle in 17 Wistar three-month-old female rats: 14, 30, 90 and 180days after the total transection of the thoracic spinal cord and compared to those in intact (control) rats. A sag phenomenon, regularly observed in unfused tetani of fast units in intact animals at 40Hz stimulation, almost completely disappeared in spinal rats. Therefore, the MUs of intact and spinal rats were classified as fast or slow types basing on 20Hz tetanus index, the value of which was lower or equal 2.0 for fast and higher than 2.0 for slow MUs. The MUs composition of MG muscle changed with time after the spinal cord transection: an increasing proportion of fast fatigable (FF) units starting one month after injury and a disappearance of slow (S) units within the three months were observed. In all MUs investigated the twitch contraction and half-relaxation time were significantly prolonged after injury (p<0.01, Mann–Whitney U-test). Moreover, a decrease of the fatigue index for fast resistant (FR) and slow MUs was observed in subsequent groups of spinal rats. No significant changes were found between twitch forces in all MU types of spinal animals (p>0.05). However, due to a decrease of the maximal tetanic force, a significant rise of the twitch-to-tetanus ratio of all MUs in spinal rats was detected (p<0.01). The considerable reduction of ability to potentiate the force was noticed for fast, especially FF type MUs. In conclusion, the spinal cord transection leads to changes in the proportion of the three MU types in rat MG muscle. The majority of changes in MUs’ contractile properties were developed progressively with time after the spinal cord injury. However, the most intensive alterations of twitch-time parameters were observed in rats one month after the transection.

Time-related changes of motor unit properties in the rat medial gastrocnemius muscle after the spinal cord injury. II. Effects of a spinal cord hemisection - Corrected Proof

2009-08-13

Abstract: The contractile properties of motor units (MUs) were investigated in the medial gastrocnemius (MG) muscle in rats after the spinal cord hemisection at a low thoracic level. Hemisected animals were divided into 4 groups: 14, 30, 90 and 180days after injury. Intact rats formed a control group. The mass of the MG muscle did not change significantly after spinal cord hemisection, hind limb locomotor pattern was almost unchanged starting from two weeks after injury, but contractile properties of MUs were however altered. Contraction time (CT) and half-relaxation time (HRT) of MUs were prolonged in all investigated groups of hemisected rats. The twitch-to-tetanus ratio (Tw/Tet) of fast MUs after the spinal cord hemisection increased. For slow MUs Tw/Tet values did not change in the early stage after the injury, but significantly decreased in rats 90 and 180days after hemisection. As a result of hemisection the fatigue resistance especially of slow and fast resistant MU types was reduced, as well as fatigue index (Fat I) calculated for the whole examined population of MUs decreased progressively with the time. After spinal cord hemisection a reduced number of fast MUs presented the sag at frequencies 30 and 40Hz, however more of them revealed sag in 20Hz tetanus in comparison to control group. Due to considerable changes in twitch contraction time and disappearance of sag effect in unfused tetani of some MUs in hemisected animals, the classification of MUs in all groups of rats was based on the 20Hz tetanus index (20Hz Tet I) but not on the standard criteria usually applied for MUs classification. MU type differentiations demonstrated some clear changes in MG muscle composition in hemisected animals consisting of an increase in the proportion of slow MUs (likely due to an increased participation of the studied muscle in tonic antigravity activity) together with an increase in the percentage of fast fatigable MUs.

Three-dimensional spine kinematics during multidirectional, target-directed trunk movement in sitting - Corrected Proof

Richard A. Preuss, Milos R. Popovic — 2009-08-12

Abstract: The current study provides a quantitative assessment of three-dimensional spine motion during target-directed trunk movements in sitting. Subjects sat on an elevated surface, without foot support, and targets were placed in five directions, at three subject-specific distances (based on trunk height). Subjects were asked to lean toward the target, touch it with their head, and return to upright sitting. A retro-reflective motion analysis system was used to measure spine motion, using three kinematic trunk models (1, 3 and 7 segments). Significant differences were noted in the total trunk motion measured between the models, as well as between target distances and directions. In the most segmented model, inter-segmental trunk motion was also found to differ between trunk levels, with complex interaction effects involving target distance and direction. These findings suggest that inter-segmental spine motion is complex, task dependent, and often unevenly distributed between spine levels, with motion patterns differing between subjects, even in the absence of pathology. Use of a multi-segmental model provides the most interpretable findings, allowing for differentiation of individual motion patterns of the spine. Such an approach may be beneficial to the understanding of movement-related spine pathologies.