Journal of Electromyography and Kinesiology - Articles in Press

Peak and average rectified EMG measures: Which method of data reduction should be used for assessing core training exercises? - Corrected Proof

A.E. Hibbs, K.G. Thompson, D.N. French, D. Hodgson, I.R. Spears — 2010-07-26

Abstract: Core strengthening and stability exercises are fundamental for any conditioning training program. Although surface electromyography (sEMG) is used to quantify muscle activity there is a lack of research using this method to investigate the core musculature and core stability. Two types of data reduction are commonly used for sEMG; peak and average rectified EMG methods. Peak EMG has been infrequently reported in the literature with regard to the assessment of core training while even fewer studies have incorporated average rectified EMG data (ARV). The aim of the study was to establish the repeatability of peak and average rectified EMG data during core training exercises and their interrelationship. Ten male highly trained athletes (inter-subject repeatability group; age, 18±1.2years; height, 176.5±3.2cm; body mass, 71±4.5kg) and one female highly trained athlete (intra-subject repeatability group; age; 27years old; height; 180cm; weight; 53kg) performed five maximal voluntary isometric contractions (MVIC) and five core exercises, chosen to represent a range of movement and muscle recruitment patterns. Peak EMG and ARV EMG were calculated for eight core muscles (rectus abdominis, RA; external oblique, EO; internal oblique, IO; multifidis, MF; latissimus dorsi, LD; longissimus, LG; gluteus maximus, GM; rectus femoris, RF) using sEMG. Average coefficient of variation (CV%) for peak EMG across all the exercises and muscles was 45%. This is in comparison to 35% for the ARV method, which was found to be a significant difference (P<0.05), therefore implying that the ARV method is the more reliable measure for these types of exercise. Analysis of the inter-subject and intra-subject CV% values suggest that these exercises and muscles are sufficiently repeatable using sEMG. Five muscles were highly correlated (R>0.70; RA, EO, MF, GM, LG) between peak and ARV EMG suggesting, that for these core muscles, the two methods provide a similar evaluation of muscle activity. However, for other muscles (IO, RF, LD) the relationship was found to range from poor to moderate (R=0.10–0.70). The relationship between peak and ARV EMG was also affected by exercise type. Dynamic low and high-threshold exercises and asymmetrical low-threshold exercises had a moderate correlation between the variables (R=0.74–0.81), while the static exercise showed a poor correlation (R=0.46). It can be concluded that there are similarities between the two EMG variables, however due to the effect of type of exercise and muscle on the EMG data, both methods should be included in any future EMG study on the core musculature and core stability exercises.

Effect of the degree of hip arthritis on equilibrium ability after sudden changes in direction - Corrected Proof

Rita M. Kiss — 2010-07-26

Abstract: This research addressed the effect of hip osteoarthritis severity on equilibrium ability after sudden changes in direction among 20 healthy elderly people, 20 with moderate hip osteoarthritis (mOA), and 20 with severe hip osteoarthritis (sOA). The Lehr’s damping ratio calculated from testing while standing on both limbs (; ; () did not differ significantly from results of testing while standing on the dominant limb in healthy subjects () and on the unaffected limb in patients with varying degrees of osteoarthritis (). Results from testing during standing on the non-dominant limb in healthy subjects () and on the affected limb in patients with osteoarthritis (, ) differed significantly from the results of the other two scenarios, indicating that the healthy side is dominant. In cases of sOA, equilibrium ability decreased with standing on both limbs or on the healthy limb compared to the control group and to the patients with mOA. Furthermore, an increased degree of hip osteoarthritis significantly decreased equilibrium ability on the affected side after sudden changes in direction, based on a comparison of the affected side in patients with sOA to the affected side in patients with mOA. Deterioration of equilibrium ability may indicate an increased risk of falling.

Piper rhythm in the activation of the gastrocnemius medialis during running - Corrected Proof

Lisa M. Stirling, Vinzenz von Tscharner, Patrick Kugler, Benno M. Nigg — 2010-07-23

Abstract: The presence of temporal rhythmicity in electromyographic (EMG) signals at frequencies of 35–60Hz was initially noted by . This modulation and synchronization of motor unit activity is generally accepted to represent a centrally generated coding of motor commands. The purpose of this study was to resolve and quantify the Piper rhythm in the gastrocnemius medialis (GM) muscle during running. EMG was recorded from the GM of 14 female runners during 1-h treadmill runs. The average wavelet transform was computed for EMG from series of steps taken at 2min intervals throughout the run. The total intensity across three wavelets (center frequencies: 170, 218 and 271Hz) was computed and a histogram indicating the incidence peaks in this signal was generated for each subject. In order to rule out effects of the analysis process, the process was repeated using simulated EMG data. Autocorrelations of the histograms were used to extract the frequency of the peaks resulting in rhythmicity at 25–55Hz. The ability to measure superimposed rhythmicity in EMG signals during dynamic tasks allows investigation of the role of aspects of central drive during movement. In particular, the changes in central control during dynamic activities can be examined with this approach.

A study of forearm muscle activity and wrist kinematics in symptomatic office workers performing mouse-clicking tasks with different precision and speed demands - Corrected Proof

Grace P.Y. Szeto, Joseph K.M. Lin — 2010-07-21

Abstract: The present study examined various biomechanical parameters in symptomatic and asymptomatic computer users during mouse-clicking tasks with different speed and precision demands. Surface electromyography (EMG) of right wrist flexors and extensors were compared between individuals with computer-related wrist/hand symptoms (n=9) and pain-free controls (n=8). Each subject performed four mouse tasks with high and low precision, constant and fastest speed of 5min each. Results showed that Case subjects recorded significantly lower EMG amplitudes during maximum voluntary contractions in three out of four forearm muscles (p=0.001–0.019). Normalised median amplitudes of extensor carpi radialis and flexor carpi ulnaris showed significant differences between groups in the speed conditions (p=0.01, 0.04, respectively). Case subjects reported significant discomforts in the wrist/hand region in all tasks, while recorded significantly longer response time and fewer mouse clicks compared to controls. Results suggested that forearm muscles in symptomatic individuals were inhibited in their maximal activation as well as during functional tasks, and this may imply altered motor control mechanisms in forearm muscles contributing to work-related musculoskeletal disorders.

Strict actions of the human wrist extensors: A study with an electrical neuromuscular stimulation method - Corrected Proof

2010-07-20

Abstract: Motion and force produced by electrical neuromuscular stimulation (ENS) to each of the extensor carpi radialis longus (ECRL) and brevis (ECRB), and extensor carpi ulnaris (ECU) with the prone (P), semiprone (SP), and supine forearm (S) were studied in ten normal human subjects. Abduction (AB), extension (E), adduction (AD), and flexion (F) directions were represented by, respectively, 0°, 90°, 180°, and 270°. ENS to ECRL, ECRB, and ECU produced motion in direction of, respectively, 60° (mean), 87°, and 205° with P, 66°, 83°, and 166° with SP, and 47°, 66°, and 116° with S to maximal range. Direction/strength (Nm) of force by ENS to ECRL, ECRB, and ECU were, respectively, 54°/1.75, 74°/1.78, and 184°/1.49 with P, 34°/1.65, 63°/1.66, and 152°/1.43 with SP, and 32°/1.66, 70°/1.49, and 147°/1.25 with S. ENS to ECRL exhibited force of 15–20% of maximal E (15–20%Max-E) and 19–29%Max-AB, that to ECRB 24–32%Max-E, and that to ECU 17–30%Max-AD. The force study results suggest that ECRL is an abductor and extensor and ECRB is an extensor rather than an abductor. ECU should be an adductor rather than an extensor with SP and S and an adductor with P. The data must contribute to reconstruct motor functions of paralyzed hands.

Wavelet based correlation and coherence analysis reveals frequency dependent motor unit conduction velocity of the abductor pollicis brevis muscle - Corrected Proof

Vinzenz von Tscharner, Marina Barandun — 2010-07-15

Abstract: The purpose of this study was to investigate the motorunit conduction velocity (CV) as a function of frequency. A wavelet based correlation and coherence analysis was introduced to measure CV as a function of frequency. Based on the most simple assumption that the power spectra of the motor unit action potential is shifted to higher frequencies with increasing CV, we hypothesized that there would be a monotonic or linear trend of increasing CV with frequency. This trend was only confirmed at higher frequencies. At lower frequencies the trend was often reversed leading to a decrease in CV with increasing frequency. Thus the CV was high at low frequencies, went through a minimum at about 170Hz and increased at higher frequencies, as expected. The observed CV at low frequencies could not be fully explained by assuming non-propagating signals or variable groups of motor units. We concluded that spectra and CV contain partly independent information about the muscles and that the wavelet based method provides the tools to measure them both simultaneously.

Biofeedback effectiveness to reduce upper limb muscle activity during computer work is muscle specific and time pressure dependent - Corrected Proof

2010-07-12

Abstract: Continuous electromyographic (EMG) activity level is considered a risk factor in developing muscle disorders. EMG biofeedback is known to be useful in reducing EMG activity in working muscles during computer work. The purpose was to test the following hypotheses: (1) unilateral biofeedback from trapezius (TRA) can reduce bilateral TRA activity but not extensor digitorum communis (EDC) activity; (2) biofeedback from EDC can reduce activity in EDC but not in TRA; (3) biofeedback is more effective in no time constraint than in the time constraint working condition. Eleven healthy women performed computer work during two different working conditions (time constraint/no time constraint) while receiving biofeedback. Biofeedback was given from right TRA or EDC through two modes (visual/auditory) by the use of EMG or mechanomyography as biofeedback source. During control sessions (no biofeedback), EMG activity was (mean±SD): 2.4±1.1, 2.5±2.1, and 9.1±3.1%max-EMGrms for right and left TRA and EDC, respectively. During biofeedback from TRA, activity was reduced in right TRA (1.7±1.6%max-EMGrms) and left TRA (1.2±2.0%max-EMGrms) compared to control. During biofeedback from EDC, activity in EDC was reduced (8.3±3.3%max-EMGrms) compared with control. During time constraint, activity was reduced in right TRA (1.9±1.3%max-EMGrms), left TRA (1.5±1.5%max-EMGrms), and EDC (8.4±3.2%max-EMGrms), during biofeedback compared to control. Conclusion: biofeedback reduced muscle activity in TRA by ∼30–50% and in EDC by ∼10% when given from the homologous or bilateral muscle but not from the remote muscle, and was significant in the time constraint condition; while feedback source and presentation mode showed only minor differences in the effect on reducing homologous muscle activity. This implies that biofeedback should be given from the most affected muscle in the occupational setting for targeting relief and prevention of muscle pain most effectively.

Kinematic analyses of trunk stability in one leg standing for individuals with recurrent low back pain - Corrected Proof

Yong Woon Ham, Dong Myung Kim, Ju Yeoul Baek, Dongchul C. Lee, Paul S. Sung — 2010-07-09

Abstract: This prospective study examined normalized stability differences based on dominance side and visual feedback. Subjects with low back pain (LBP) (n=26; 9 men, 17 women) and without LBP (n=28; 11 men, 17 women) participated in this study. All subjects were asked to maintain single leg standing balance with the contralateral hip flexed 90° for 25s. The outcome measures included normalized holding duration and stability. The combined rotation (Rxyz) was also calculated to compare the upper and lower thorax and lumbar axes relative to the core spine axis. The holding duration was significantly different between groups (T=−2.21, p=0.03). The subjects without recurrent LBP (control group) demonstrated longer hold duration times (24.60±4.2s) than the subjects with recurrent LBP (21.2±7.1s). For the normalized hold duration, there was a significant difference between groups based on visual input (F=7.13, p=0.009). There was also a significant difference in standing stability based on visual input (F=93.93, p=0.0001) and trunk area (F=101.51, p=0.0001). In addition, the normalized stability was significantly different based on dominance and visual input (F=11.28, p=0.002). Therefore, trunk stability could prompt an uncoordinated bracing effect with poor proprioception from injury to passive structures or due to interference of pain during central processing of information in subjects with recurrent LBP.

The effect of cadence on timing of muscle activation and mechanical output in cycling: On the activation dynamics hypothesis - Corrected Proof

David McGhie, Gertjan Ettema — 2010-07-01

Abstract: The purpose of this study was to examine the activation dynamics hypothesis, which states that, in cycling, the pattern between muscle activity and crank position shifts in regard to its angle in the crank cycle with increasing cadence to maintain invariant positioning of the mechanical output. We measured surface EMG of six muscles, and by means of force measurements at the crank and inverse dynamics calculated hip, knee, and ankle joint dynamics during cycling at five cadences (60–100rpm) at 75% of maximal power in trained cyclists. The joint dynamics (net muscle moment and power) showed a consistent positive phase shift with increasing cadence. The phase shift in muscle activation patterns was highly variable amongst subjects and was, on average, close to zero. Our results are in contradiction with the activation dynamics hypothesis.

Distribution of motor unit potential velocities in the biceps brachii muscle of sprinters and endurance athletes during prolonged dynamic exercises at low force levels - Corrected Proof

2010-07-01

Abstract: In surface electromyography (sEMG), the distribution of motor unit potential (MUP) velocities has been shown to reflect the proportion of faster and slower propagating MUPs. This study investigated whether the distribution of MUP velocities could distinguish between sprinters (n=11) and endurance athletes (n=12) in not-specifically trained muscle (biceps brachii) during prolonged dynamic exercises at low forces. sEMG was acquired during 4min’ exercises: unloaded, 5%, 10% and 20% of maximal voluntary contraction (MVC). The features extracted from the sEMG were: the mean muscle conduction velocity – estimated using the inter-peak latency and cross-correlation methods, the within-subject skewness (expressing the proportions of faster and slower propagating MUPs) and the within-subject standard deviation of MUP velocities (SD-mup). Sprinters showed a greater proportion of faster propagating MUPs than endurance athletes. During fatigue, the SD-mup of sprinters broadened progressively, whereas that of endurance athletes did not. The findings suggest that sprinters conveyed a greater proportion of faster motor units than endurance athletes and that motor unit behavior during fatigue differed between groups. Thus, the distribution of MUP velocities enables distinction between a muscle of sprinters and endurance athletes during prolonged dynamic exercises at low forces.

Distribution of motor unit potential velocities in the biceps brachii muscle of sprinters and endurance athletes during short static contractions at low force levels - Corrected Proof

2010-07-01

Abstract: In surface electromyography (sEMG), the distribution of motor unit potential (MUP) velocities has been shown to reflect the proportion of faster and slower propagating MUPs. This study investigated whether the distribution of MUP velocities could distinguish between sprinters and endurance athletes in not-specifically trained muscle (biceps brachii). sEMG results were acquired from 15 sprinters and 18 endurance athletes during short static contractions (3.8s) at three force levels: unloaded, 10% and 20% of maximum voluntary contraction. The features extracted from the sEMG were: the mean muscle conduction velocity (CV) – estimated using the inter-peak latency and the cross-correlation methods, the within-subject skewness of MUP velocities (expressing the relative proportions of faster and slower propagating MUPs), and the within-subject standard deviation of MUP velocities. Sprinters had a higher CV than endurance athletes using both methods. Sprinters also demonstrated a greater proportion of fast propagating MUPs, as indicated by the skewness. Thus, the distribution of MUP velocities was able to demonstrate physiological differences between sprinters and endurance athletes during short contractions at low forces. The findings can be extrapolated to the motor unit level. Since the investigated muscle was not involved in specific training, the differences seem to reflect inherited properties.

Effects of postural and visual stressors on myofascial trigger point development and motor unit rotation during computer work - Corrected Proof

Jeffrey A. Hoyle, William S. Marras, James E. Sheedy, Dennis E. Hart — 2010-06-28

Abstract: Musculoskeletal complaint rates are high among those performing low-level static exertions (LLSEs), such as computer users. However, our understanding of the causal mechanisms is lacking. It was hypothesized that myofascial trigger point (MTrP) development might be one causal mechanism to help explain these complaints and that static postural and visual demands may be contributing factors. Therefore, the purpose of this experiment was to examine MTrP development and the behavior of multiple parts of the trapezius muscle under postural and mental stress (represented by visual stress) conditions during computer work. Twelve subjects (six male and six female) were monitored for MTrP development via expert opinion, subject self-report, and cyclic changes in EMG median frequency across fourteen spatial locations. Results showed that MTrPs developed after one hour of continuous typing, despite the stress condition. Interestingly, both the high postural and high visual stress conditions resulted in significantly fewer median frequency cycles (3.76 and 5.35 cycles, respectively), compared to the baseline low stress condition (6.26 cycles). Lastly, the MTrP location as well as locations more medial to the spine showed significantly fewer cycles than other locations. Findings suggest that MTrPs may be one causal pathway for pain during LLSEs and both postural and visual demands may play a role in muscle activation patterns, perhaps attributing to MTrP development and resultant discomfort.

sEMG wavelet-based indices predicts muscle power loss during dynamic contractions - Corrected Proof

2010-06-25

Abstract: The purpose of this study was to investigate the sensitivity of new surface electromyography (sEMG) indices based on the discrete wavelet transform to estimate acute exercise-induced changes on muscle power output during a dynamic fatiguing protocol. Fifteen trained subjects performed five sets consisting of 10 leg press, with 2min rest between sets. sEMG was recorded from vastus medialis (VM) muscle. Several surface electromyographic parameters were computed. These were: mean rectified voltage (MRV), median spectral frequency (Fmed), Dimitrov spectral index of muscle fatigue (FInsm5), as well as five other parameters obtained from the stationary wavelet transform (SWT) as ratios between different scales. The new wavelet indices showed better accuracy to map changes in muscle power output during the fatiguing protocol. Moreover, the new wavelet indices as a single parameter predictor accounted for 46.6% of the performance variance of changes in muscle power and the log-FInsm5 and MRV as a two-factor combination predictor accounted for 49.8%. On the other hand, the new wavelet indices proposed, showed the highest robustness in presence of additive white Gaussian noise for different signal to noise ratios (SNRs). The sEMG wavelet indices proposed may be a useful tool to map changes in muscle power output during dynamic high-loading fatiguing task.

Effects of the pelvic compression belt on gluteus medius, quadratus lumborum, and lumbar multifidus activities during side-lying hip abduction - Corrected Proof

Kyung-Mi Park, Suhn-Yeop Kim, Duck-Won Oh — 2010-06-21

Abstract: The aims of this study were to assess the effect of the pelvic compression belt on the electromyographic (EMG) activities of gluteus medius (GM), quadratus lumborum (QL), and lumbar multifidus (LM) during side-lying hip abduction. Thirty-one volunteers (15 men and 16 women) with no history of pathology volunteered for this study. Subjects were instructed to perform hip abduction in side-lying position with and without applying the pelvic compression belt. The pelvic compression belt was adjusted just below the anterior superior iliac spines with the stabilizing pressure using elastic compression bands. Surface EMG data were collected from the GM, QL, and LM of the dominant limb. Significantly decreased EMG activity in the QL (without the pelvic compression belt, 60.19±23.66% maximal voluntary isometric contraction [MVIC]; with the pelvic compression belt, 51.44±23.00% MVIC) and significantly increased EMG activity in the GM (without the pelvic compression belt, 26.71±12.88% MVIC; with the pelvic compression belt, 35.02±18.28% MVIC) and in the LM (without the pelvic compression belt, 30.28±14.60% MVIC; with the pelvic compression belt, 37.47±18.94% MVIC) were found when the pelvic compression belt was applied (p<0.05). However, there were no significant differences of the EMG activity between male and female subjects. The findings suggest that the pelvic compression belt may be helpful to prevent unwanted substitution movement during side-lying hip abduction, through increasing the GM and LM and decreasing the QL.

Characterization of postural control deficit in whiplash patients by means of linear and nonlinear analyses – A pilot study - Corrected Proof

Pascal Madeleine, Mogens Nielsen, Lars Arendt-Nielsen — 2010-06-17

Abstract: The ability to maintain balance is diminished in patients suffering from a whiplash injury. The aim of this study was to characterize the variability of postural control in patients with chronic whiplash injury. For this purpose, we analyzed static postural recordings from 11 whiplash patients and sex- and age-matched asymptomatic healthy volunteers. Static postural recordings were performed randomly with eyes open, eyes closed, and eyes open and speaking (dual task). Spatial–temporal changes of the center of pressure displacement were analyzed to assess the amplitude and structure of postural variability by computing, respectively, the standard deviation/coefficient of variation and sample entropy/fractal dimension of the time series. The amplitude of variability of the center of pressure was larger among whiplash patients compared with controls (P<0.001) while fractal dimension was lower (P<0.001). The sample entropy increased during both eyes closed and a simple dual task compared with eyes open (P<0.05). The analysis of postural control dynamics revealed increased amplitude of postural variability and decreased signal dimensionality related to the deficit in postural stability found in whiplash patients. Linear and nonlinear analyses can thus be helpful for the quantification of postural control in normal and pathological conditions.

Effect of bilateral versus unilateral exertion tests on maximum voluntary activity and within-participant reproducibility in the shoulder - Corrected Proof

Steven L. Fischer, Tej-Jaskirat Grewal, Richard Wells, Clark R. Dickerson — 2010-06-14

Abstract: Normalized surface EMG requires known muscle activity from a well defined reference contraction, often a maximum voluntary isometric exertion (MVIE). One factor that may impact the activity obtained during a MVIE is the use of a bilateral or unilateral version of the test. The objective of this work was to investigate how performing MVIE tests unilaterally or bilaterally affects maximum voluntary electrical activity (MVE) for selected shoulder muscles. Further, we examined if within-participant reproducibility could be improved with the use of bilateral or unilateral MVIE tests.Sixteen participants completed five repetitions of a palm press, empty can, and external rotation MVIE tests both bilaterally and unilaterally. Muscle activity was recorded from seven muscles acting at the glenohumeral joint during the performance of each test. Repeated measures ANOVAs were used to determine within-participant differences on muscle specific MVEs and hand force measures between the two versions of the test. Gender was compared as a between participants factor. Within-participant reproducibility in muscle activity between bilateral and unilateral MVIEs was compared using coefficients of variation.Performing a bilateral empty can MVIE test elicited significantly higher MVEs for the upper trapezius (14%) and supraspinatus muscles (15%) than a unilateral test in this study population. MVEs during the palm press and external rotation were not affected by performing the tests bilaterally or unilaterally. Reliability was similar between unilateral and bilateral exertions across MVIE tests. Hence, we recommend that the empty can MVIE test be performed bilaterally, while either bilateral or unilateral configurations are equivalent during the palm press and external rotation MVIE tests.

Postural control and thigh muscle activity in men with knee osteoarthritis - Corrected Proof

2010-06-11

Abstract: The aim of this study was to examine the standing balance and the function of vastus medialis (VM) and biceps femoris (BF) muscles with surface electromyography (EMG). Fifty-four subjects with uni- or bilateral knee osteoarthritis (OA) (aged 50–69years) and 53 age-matched randomly selected clinically and radiologically healthy men participated in this study. Postural control was assessed on a force platform with a bipedal stance with eyes open (EO) and closed (EC) and a monopedal stance with EO. The balance parameters, mean sway velocity, velocity along AP and ML axes, elliptical area, standard deviation of center of pressure, average radial displacement, mean frequency and frequency domain balance parameters and different power spectral density frequency bands were determined. Root mean square (RMS) for EMG amplitude, mean EMG frequency (fEMG,mean) and median EMG frequency (fEMG,med) of motor unit activity were calculated from the normalized EMG data. During bipedal stance with EC and EO, there were no significant differences in balance parameters between groups, but during bipedal stance with EO, the RMS in VM was about 56% higher (p<0.05) in subjects with knee OA than in the control subjects and the values of fEMG,mean and fEMG,med were about 48% higher (p<0.05) in control subjects than subjects with knee OA. It is concluded that subjects with knee OA do not have any standing balance deficit, but they do exhibit increased muscle activity in VM muscle compared to control subjects.

Comparison and reproducibility of sEMG during manual muscle testing on land and in water - Corrected Proof

W. Matthew Silvers, Dennis G. Dolny — 2010-06-07

Abstract: The objectives of this study were to: (1) compare the sEMG recordings from maximal voluntary contractions (MVC), and (2) examine the reproducibility of sEMG recordings from MVCs for selected lower extremity muscles derived from manual muscle testing (MMT) on dry land, and in water prior to and following aquatic treadmill running. Twelve healthy recreational male runners participated. The selected muscles were: M. quadriceps–vastus medialis (VM) and rectus femoris (RF), M. biceps femoris (BF), M. tibialis anterior (TA) and the M. gastrocnemius caput mediale (GAS) of the right leg. The MVC testing conditions were: dry land, underwater prior to (Water 1) and following an aquatic exercise trial (Water 2). For each muscle, a one-way analysis of variance with repeated measures was used to compare MVC scores between testing conditions, and the intra-class correlation coefficient (ICC) and typical error (CV%) were calculated to determine the reproducibility and precision of MVC scores, respectively, between conditions. For all muscles, no significant differences were observed between land and water MVC scores (p=0.88–0.97), and high reliability (ICC=0.96–0.98) and precision (CV%=7.4–12.6%) were observed between MVC conditions. Under MMT conditions it appears that comparable MVC sEMG values were achieved on land and in water and the integrity of the EMG recordings were maintained during water immersion. Future studies using sEMG waterproofing procedures should conduct MVC testing in water for data normalization and perform post-exercise verification of sEMG signal integrity.

EMG in rotation–flexion of the torso - Corrected Proof

Shrawan Kumar — 2010-06-04

Abstract: The objective of this study was to determine the magnitude and phasic relationship of the torso muscles in rotation–flexion of varying degree of asymmetries of the trunk. Nineteen normal young subjects (7 males and 12 females) were stabilized on a posture stabilizing platform and instructed to assume a flexed and right rotated posture. A combination 20°, 40° and 60° of rotation and 20°, 40° and 60° of flexion resulted in nine postures. These postures were assumed in a random order. The subjects were asked to exert their maximal voluntary isometric contraction (MVC) in the plane of rotation of the posture assumed for a period of 5s. The surface EMG from the external and internal obliques, rectus abdominis, latissimus dorsi and erector spinae at the 10th thoracic and 3rd lumbar vertebral levels was recorded. The abdominal muscles had the least response at 40° of flexion, the dorsal muscles had the highest magnitude.With increasing right rotation, the left external oblique continued to decrease its activity. The ANOVA revealed that rotation and muscles had a significant main effect on normalized peak EMG (p<0.02) in both genders. There was a significant interaction between rotation and flexion in both genders (p<0.02) and rotation and muscle in females. The erector spinae activity was highest at 40° flexion, due to greater mechanical disadvantage and having not reached the state of flexion–relaxation. The abdominal muscle activity declined with increasing asymmetry, due to the decreasing initial muscle length. The EMG activity was significantly affected by rotation than flexion (p<0.02).

Isometric torque–angle relationships of the elbow flexors and extensors in the transverse plane - Corrected Proof

Ilona J. Pinter, Maarten F. Bobbert, A.J. “Knoek” van Soest, Jeroen B.J. Smeets — 2010-05-31

Abstract: Maximal voluntary isometric torque–angle relationships of elbow extensors and flexors in the transverse plane (humerus elevation angle of 90°) were measured at two different horizontal adduction angles of the humerus compared to thorax: 20° and 45°. For both elbow flexors and extensors, the torque–angle relationship was insensitive to this 25° horizontal adduction of the humerus. The peak in torque–angle relationship of elbow extensors was found at 55° (0° is full extension). This is closer to full elbow extension than reported by researchers who investigated this relationship in the sagittal plane. Using actual elbow angles during contraction, as we did in this study, instead of angles set by the dynamometer, as others have done, can partly explain this difference.We also measured electromyographic activity of the biceps and triceps muscles with pairs of surface electrodes and found that electromyographic activity level of the agonistic muscles was correlated to measured net torque (elbow flexion torque: Pearson’s r=0.21 and extension torque: Pearson’s r=0.53). We conclude that the isometric torque–angle relationship of the elbow extensors found in this study provides a good representation of the force–length relationship and the moment arm–angle relationship of the elbow extensors, but angle dependency of neural input gives an overestimation of the steepness.

Trunk and hip muscle activity in early walkers with and without cerebral palsy – A frequency analysis - Corrected Proof

2010-05-17

Abstract: Poor control of postural muscles is a primary impairment in cerebral palsy (CP), yet core trunk and hip muscle activity has not been thoroughly investigated. Frequency analysis of electromyographic (EMG) signals provides insight about the intensity and pattern of muscle activation, correlates with functional measures in CP, and is sensitive to change after intervention. The objective of this study was to investigate differences in trunk and hip muscle activation frequency in children with CP compared to children with similar amounts of walking experience and typical development (TD). EMG data from 31 children (15 with CP, 16 with TD) were recorded from 16 trunk and hip muscles bilaterally. A time–frequency pattern was generated using the continuous wavelet transform and instantaneous mean frequency (IMNF) was calculated at each interval of the gait cycle. Functional principal component analysis (PCA) revealed that IMNF was significantly higher in the CP group throughout the gait cycle for all muscles. Additionally, stride-to-stride variability was higher in the CP group. This evidence demonstrated altered patterns of trunk and hip muscle activation in CP, including increased rates of motor unit firing, increased number of recruited motor units, and/or decreased synchrony of motor units. These altered muscle activation patterns likely contribute to muscle fatigue and decreased biomechanical efficiency in children with CP.

Isometric back muscle endurance: An EMG study on the criterion validity of the Ito test - Corrected Proof

Roland Müller, Kurt Strässle, Brigitte Wirth — 2010-05-14

Abstract: The validity of the Sorensen test as a measure for back muscle endurance is controversial due to a possible impact of hip extensor muscles. The aim of this study was to investigate the criterion validity of an alternative test (Ito test) compared to the Sorensen test. Both procedures were performed by 29 healthy subjects (11 women) for 5s and until exhaustion (randomized order). EMG activity was measured from 3 lumbar back and 3 hip extensor muscles. Muscular involvement in test positions was calculated as percentage of maximal voluntary contraction (MVC). Muscle fatigue was determined by the normalized regression coefficient of the median frequencies of the EMG power spectrum (NMFslope). Prediction of holding time by NMFslope values was investigated using regression analysis. In the test positions, the hamstring muscles were activated to a higher MVC percentage in the Sorensen than in the Ito test, while the iliocostalis muscle was less activated. Similarly, the iliocostalis (p=0.006) and the multifidi muscles (p=0.03) significantly contributed to predict holding time in the Ito test, whereas the multifidi muscles (p=0.001) and the semitendinosus muscle (p=0.046) did so in the Sorensen test. The results of this study indicate that the Ito test might present a valuable alternative for testing back muscle endurance in LBP patients.

The effect of elbow angle and external moment on load sharing of elbow muscles - Corrected Proof

M. Praagman, E.K.J. Chadwick, F.C.T. van der Helm, H.E.J. Veeger — 2010-05-10

Abstract: To study elbow muscle load sharing we investigated the effect of external flexion–extension (FE) and pronation–supination (PS) moments and elbow angle on muscle activation and oxygen consumption ().Two data sets were obtained. First, (n=6) electromyography (EMG) of elbow flexors (long and short heads of biceps brachii, brachioradialis, brachialis) and extensors (long and short heads of triceps brachii and anconeus) was recorded in all combinations of FE and PS moments at three force levels and four elbow angles (50°, 70°, 90° and 110°). Second, (n=4) EMG and of three muscles (both heads of biceps and lateral head of triceps) were measured simultaneously during a subset of the above conditions.Joint angle and therefore both moment arm and muscle length influenced both EMG amplitude and the load sharing between muscles. The principles behind load sharing, however, were difficult to quantify, since it was impossible to distinguish between all individual aspects that affect muscle activity. We found a linear relationship between EMG and , while joint angle had no major effect. Although in general subjects showed comparable muscle activation patterns, there were also considerable inter-individual differences, which might be explained by the use of different optimisation strategies or differences in morphology.

The peak-to-peak ratio of single-fibre potentials is little influenced by changes in the electrode positions close to the muscle fibre - Corrected Proof

Javier Rodríguez, Javier Navallas, Luis Gila, Ignacio Rodríguez, Armando Malanda — 2010-05-07

Abstract: In a series of previous works we studied the ratio between the amplitudes of the second and first phases (the peak-to-peak ratio) of single fibre action potential (SFAPs) using the Dimitrov–Dimitrova SFAP convolutional model as a reference. From experimental potentials extracted from both healthy and diseased muscles, we determined typical peak-to-peak ratio (PPR) values and ranges for both normal and pathological conditions. In addition, we investigated the changes observed in the PPR of consecutive potentials recorded at different fibre-to-electrode distances. However, our results were not conclusive due to insufficient data. The objective of the present work was to obtain a more concrete description of the relation between PPR and radial distance. To this end, we recorded 135 sets of consecutive SFAPs from the m. tibialis anterior of four normal subjects. The needle was intentionally moved whilst recording each SFAP set. We found that PPR was largely independent of small changes in electrode position when the electrode was close to the fibre and sufficiently far from the neuromuscular and/or fibre–tendon junctions. In the discussion, we provide evidence that this result is in agreement with the generation of extracellular potentials considering the spatial extension of the intracellular action potential (IAP) along the fibre.

Amplitude cancellations in surface EMG signals - Corrected Proof

Vinzenz von Tscharner — 2010-05-06

Amplitude cancellation is a seemingly well known phenomenon. In a review about the extraction of neural strategies from surface EMG wrote “The extensive use of such indexes in basic and clinical studies underscores the lack of appreciation for the significance of signal cancellation.” And later on “The limitations of these techniques are often not appreciated, which sometimes leads to erroneous interpretation of the results and conflicting reports in the literature.” A detailed model computation was presented by the group headed by Roger M. Enoka . These model calculations are usually based on a random discharge rate assuming a stochastic nature of the surface EMG. The model calculations have revealed valuable insight into the properties of EMG signals. However, as mentioned at conferences and in personal talks the aspect of the power of the EMG signal has not been considered. The authors missed commenting or proposing an alternative measure, one that is not primarily subject to cancellation effects. Looking back into well-known methods of signal processing is usually suppressed by referees. However, the purpose of this letter is to remember some basic theoretical aspects of power computation of the EMG which shows the well known additive property of energy, power and variance. A very simple model, superimposing a randomly occurring mimicked fixed motor unite action potential (MUAP) reveals the following properties:

A standardization method to compare isotonic vs. isokinetic eccentric exercises - Corrected Proof

Gaël Guilhem, Arnaud Guével, Christophe Cornu — 2010-05-03

Abstract: The present study aimed to standardize isotonic (IT) and isokinetic (IK) eccentric exercises by equalizing the amount of work and the angular velocity at two intensity levels, to be able to compare specific effects of these exercise modes on the neuromuscular system. Fourteen subjects participated in three test sessions consisting of two IT and two IK sets on a customized isokinetic dynamometer. IT sets were comprised of 8 eccentric contractions of the knee extensors at 120% of the maximal repetition (1RM) in the first two sessions, and 100% in the third session. IK sets were performed at the same mean angular IT velocity and stopped when the amount of work performed corresponded to the IT set. External work, angular velocity and Root Mean Square (RMS) of electromyographic activity of three superficial muscles of the quadriceps femoris were calculated. Results showed concordance of work and angular velocity for each test session. Both modes involved the same number of repetitions at 120% and fewer repetitions in IK mode at 100% of 1RM. Work and RMS values remained steady in all sets. This study allowed the standardization of isotonic and isokinetic eccentric exercises, a first step before determining their specific effects on neuromuscular function.

The effect of summation of contraction on acceleration signals in human skeletal muscle - Corrected Proof

Yoichi Ohta, Norihiro Shima, Kyonosuke Yabe — 2010-04-30

Abstract: The purpose of this study was to determine the effects of summation of contraction on acceleration signals in human skeletal muscle. The torque parameters of dorsiflexion and acceleration signals in the tibialis anterior muscle were measured during evoked isometric contractions. In an examination of two-pulse trains with different inter-pulse intervals, the torque and accelerometer responses to inter-pulse intervals of 10–100ms were recorded. In an investigation of the effects of different numbers of stimuli, the torque and accelerometer responses to 1–8 pulses with a constant inter-pulse interval of 10ms were recorded. The present study found that there was a difference in acceleration amplitude between the single-pulse and two-pulse trains with an inter-pulse interval of 10ms but not two-pulse trains with an inter-pulse interval of 20ms or more. In the investigation of different numbers of stimuli, we found a similar MMG amplitude across 2–8 pulses. Moreover, we observed that the maximal time to the peak acceleration signal was ∼27ms. In a comparison of torque parameters with acceleration signals, the present study clearly shows that acceleration amplitude is poorly correlated to changes in force parameters when the inter-pulse interval or the number of stimuli are increased. These results suggest that the absence of associated changes in acceleration peak is due to the long interval for the subsequent pulses relative to the time at which acceleration peak is achieved (∼27ms). These findings will provide useful information concerning the method for assessing summation of contraction with an accelerometer.

Neural control of leg stiffness during hopping in boys and men - Corrected Proof

J.L. Oliver, P.M. Smith — 2010-04-21

Abstract: The purpose of the study was to investigate whether boys and men utilise different control strategies whilst hopping. Eleven boys (11–12yr old) and ten men completed hopping at 1.5Hz, 3.0Hz and at their preferred frequency. A footswitch measured contact and flight times, from which leg stiffness was calculated. Simultaneously, surface electromyograms (EMGs) of selected lower limb muscles were recorded and quantified for each 30ms period during the first 120ms post-ground contact. At 1.5Hz there were no differences between the groups in relative stiffness or muscle activity. At 3.0Hz men had significantly shorter contact times (P=0.013), longer flight times (P=0.002), greater relative stiffness (P=0.01) and significantly greater soleus (P=0.012) and vastus lateralis (P<0.001) activity during the initial 30ms post-ground contact. At the preferred frequency men hopped significantly faster than the boys (P=0.007), with greater leg stiffness (P<0.01) and with more extensor activity in most time periods. Boys and men demonstrated similar control strategies when hopping at a slow frequency, but when hopping frequency increased men were able to better increase feedforward and reflex muscle activity to hop with greater relative stiffness.

Quantitative biomechanical workplace exposure measures: Distribution centers - Corrected Proof

2010-04-20

Abstract: Physical work exposure characteristics assessed in most previous epidemiologic studies have been described mostly in gross categorical terms (e.g. heavy work, lifting and forceful movements, etc.) and have resulted in relatively moderate associations with low back pain risk. We hypothesized that it was necessary to characterize work demands in a much more quantitative fashion so that the precise biomechanically meaningful measures of exposure were available for risk analysis. In this study, we used sophisticated instrumentation to continuously document 390 physical exposures during lifting (in four types of distribution centers) throughout work. This study profiles these exposures and shows how these exposures vary as a function of the type of distribution center and compares the exposures to (previously documented) manufacturing exposures. Static load and load moment measures were found to greatly under-represent true (dynamic) load and load moment exposures to workers. Lift durations averaged 11–12% of the cycle time in distribution environments. This study indicates that distribution workers are commonly exposed to greater extreme loads and move much more rapidly than manufacturing employees. The information provided here can serve as a basis for low back pain risk assessments.

Influence of bite force on jaw muscle activity ratios in subject-controlled unilateral isometric biting - Corrected Proof

Lei Chen, Peter Alfred Pröschel, Thomas Riccardo Morneburg — 2010-04-20

Abstract: Ratios of muscle activities in unilateral isometric biting are assumed to provide information on strategies of muscle activation independently from bite force. If valid, this assumption would facilitate experiments as it would justify subject-control instead of transducer-based force control in biting studies. As force independence of ratios is controversial, we tested whether activity ratios are associated with bite force and whether this could affect findings based on subject-controlled force. In 52 subjects, bite force and bilateral masseter and temporalis electromyograms were recorded during unilateral biting on a transducer with varying force levels and with uniform subject-controlled force. Working/balancing and temporalis/masseter ratios of activity peaks were related to bite force peaks. Activity ratios were significantly but weakly correlated with the bite force. The subject-controlled force varied within ±25% around the prescribed force in 95% of all bites. This scatter could cause a variation of group mean activity ratios of at most ±6% because of the weak correlation between bite force and ratios. As this small variation is negligible in most cases, subject-control of bite force can be considered an appropriate method to obtain group means of relative muscle activation in particular when force control with transducers is not feasible.

Short term bed-rest reduces conduction velocity of individual motor units in leg muscles - Corrected Proof

Corrado Cescon, Marco Gazzoni — 2010-04-20

Abstract: Space permanence simulations such as prolonged bed-rest can mimic some of the physiological modifications in the human body and provide study conditions that are more accessible than during space flight. A short term bed-rest experiment was organized to simulate the effects of weightlessness for studying the adaptation to this condition. Eight healthy young volunteers were studied before and immediately after the 14day periods of strict bed-rest.Surface EMG signals were detected with linear electrode arrays from vastus medialis, vastus lateralis and tibialis anterior muscle during isometric voluntary contractions at 20% MVC. Motor unit action potentials (MUAPs) of individual motor units were extracted from the interference EMG signals with a partial decomposition algorithm and averaged.MUAP templates generated by the same motor unit could be retrieved before and after bed-rest period. Muscle fiber conduction velocity (CV) was estimated from each averaged MUAP template and from the global EMG signal. Both global and single MU conduction velocity was observed to decrease by about 10% after the bed-rest period (p<0.05). Amplitude and power spectral parameters did not significantly change after the bed-rest period.It is concluded that a short term bed-rest reduces the CV of individual motor units without a significant effect on muscle force or on other electrophysiological parameters.

Analysis of various conditions in order to measure electromyography of isometric contractions in water and on air - Corrected Proof

2010-04-12

Abstract: The aim of this study was to verify if there are differences in the amplitude of signals from surface electromyography (EMG) during maximal and submaximal voluntary isometric contraction (MVC and 50% MVC, respectively) under different conditions, in our case, water and air, with and without extra protection (water-resistant tape) on the electrode. The isometric force and muscle activation of the MVC and 50% MVC of the biceps brachial muscle of nine healthy trained men were measured simultaneously, performed in water and on air, with and without protection of the EMG electrode. The multivariate analysis of variance with a post hoc Tukey test was applied to detect significant differences between the levels of muscular force. For the amplitude values of the EMG signal, the Wilcoxon signed rank test was applied to compare all experimental conditions in order to detect a significance of p<0.05. The values of isometric force were not significantly different among conditions (MVC and 50% MVC). The results showed a significant difference among conditions in the water without extra protection compared to the conditions on air with and without extra protection and in water with extra protection. Reduced EMG amplitude was seen in water without extra protection from 37.04% to 55.81% regarding the other conditions. However, no significant difference was seen among conditions in water with extra protection in relation the conditions on air (with and without extra protection). This study suggest that it is necessary to use a water-resistant tape as an extra protection on the electrode when using EMG underwater, to avoid having a significant decrease in the EMG amplitude underwater and not to suffer interference from the water. There was no significant difference among the recordings of EMG with and without the use of protection on air; therefore, the protection does not influence the recording of EMG amplitude and isometric force on air.

Approach run increases preactivation and eccentric phases muscle activity during drop jumps from different drop heights - Corrected Proof

Mianfang Ruan, Li Li — 2010-03-29

Abstract: The purpose of this study was to investigate the effects of a horizontal approach run and drop height on the activation of lower extremity muscles during drop jumps. Ten participants performed drop jumps from drop heights of 15, 30, 45 and 60cm with zero (standing), one, two, and three approach run steps. The EMG activities of the Gluteus Maximus (GM), Rectus Femoris (RF), Biceps Femoris (BF), Vastus Lateralis (VL), Tibialis Anterior (TA), Gastrocnemius (GA) and Soleus (SO) were recorded, full-wave rectified, and averaged (aEMG) during the preactivation (50ms before touchdown), downward, and push-off phases. Increasing drop height did not enhance the muscle activation level of any examined muscles except GA. During the preactivation phase, the aEMG of all muscles except TA increased with the number of approach run steps. The aEMG of RF, BF, VL, and SO also increased with the number of approach run steps during the downward phase, while no aEMG changes were observed during the push-off phase. These results suggest that a horizontal approach run preceding the drop jump is an effective strategy for increasing the muscle preactivation level, which contributes to a higher level of muscle activity during the eccentric contraction phase and could potentially contribute to the reported higher power output during the concentric contraction phase.

Location and sequence of muscle onset in deep abdominal muscles measured by different modes of ultrasound imaging - Corrected Proof

Christian Westad, Paul J. Mork, Ottar Vasseljen — 2010-03-26

Abstract: Various modes of ultrasound (US) imaging have been introduced as an alternative to electromyography for determining muscle onset. The purpose of this study was to compare the agreement between US motion-mode (USm-mode) and US strain rate (USSR) derived from tissue velocity imaging in determining latency time, location and sequence of muscle onset in abdominal muscles using the same data set (contractions). Twenty-four subjects performed four rapid arm flexions in response to a light signal while US recordings were made from the abdominal muscles on the contralateral side. The examined muscles were transversus abdominis (TrA), superficial and deep obliquus internus abdominis (OIdeep and OIsup), and obliquus externus abdominis (OE). The results showed that the two methods detected the first muscle onset on average within 0.1ms (95% CI; ±1.4ms) of each other. USSR detected the second muscle onset on average 27ms after USm-mode. While USSR and USm-mode can be used interchangeably to detect the first muscle onset, the location of both first onset and subsequent muscle onsets can be reliably detected by USSR only. Furthermore, this study indicates that OI may be functionally subdivided into a superficial and deep region, with onset in OIdeep occurring on average 53ms before OIsup. First onset was detected more frequently in OI than in TrA (65% versus 25% of detected onsets, 10% were equal).

Effects of a noncircular chainring system on muscle activation during cycling - Corrected Proof

2010-03-11

Abstract: Previous studies evaluated cycling with noncircular chainrings and suggested that changes in muscle activation would occur in response to altered pedaling mechanics throughout the crank arm revolution. However, no previous study addressed this question. The aim of this study was to compare the magnitude of muscular activity between a conventional and a noncircular crank system during an incremental maximal cycling test. Seven mountain-bike trained cyclists completed two incremental maximal tests, separated by 48h, one for each crank system. Each test started with a workload of 100W and was increased by 30W every minute until exhaustion. Power output, pedaling cadence and heart rate were monitored and compared between the crank systems using paired t-tests. Surface EMG was recorded from the right rectus femoris, vastus medialis, biceps femoris and gastrocnemius medialis. EMG was compared using a general linear model considering as factors the crank system and workload with post hoc analysis at α=0.05. RMS presented effect of workload, but no effect of crank system was found for the muscles analyzed. The present results do not support effects of the noncircular crank system on variables of performance and muscle activation during incremental cycling in trained mountain bike cyclists.

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.

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.

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.

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.

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.

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.