Journal of Electromyography and Kinesiology - Articles in Press

Effect of cervical spine position on upper limb myoelectric activity during pre-manipulative stretch for Mills manipulation: A new model, relations to peripheral nerve biomechanics and specificity of Mills manipulation - Corrected Proof

2012-01-27

Abstract: Objectives: (A) Describe a new method of investigation of the possible muscular effects of the commonly practiced Mills manipulation for lateral elbow pain (epicondylalgia), (B) ascertain if myoelectric activity is influenced during the pre-manipulative stretch for Mills manipulation, (C) establish whether muscle responses are influenced by ipsilateral lateral flexion of the cervical spine which reduces mechanical tension in the peripheral nerves of the upper limb.Sample: Eight asymptomatic subjects were tested bilaterally (N=16).Methods: Myoelectric measurements – EMG signals were recorded with a 16 channel pocket EMG patient unit and processed off-line. Measurement of joint positions-three CCD adjustable cameras sensitive to 10mm reflective passive markers applied at specific locations on the subjects’ bodies were used to reconstruct and verify accuracy of body movements and were correlated with EMG recordings.Results: Compared with the standard (anatomical) position of the cervical spine in which Mills manipulation is typically performed, cervical spine ipsilateral lateral flexion produced significantly reduced activity in muscles that restrain the manipulation movement (elbow extension), namely biceps brachii (P=0.018) and brachioradialis (P=0.000). The affected muscles may therefore produce protective effects during the manipulation.Conclusions: Changes in myoelectric activity were in a pattern that suggests that muscle and neural mechanisms may be an integral part of the Mills manipulation. Cervical spine ipsilateral lateral flexion may be used to reduce mechanical stresses in the peripheral nerves and extraneous muscle activity, making Mills’ manipulation potentially safer and more specific.

EMG–force modeling using parallel cascade identification - Corrected Proof

2012-01-27

Abstract: Measuring force production in muscles is important for many applications such as gait analysis, medical rehabilitation, and human–machine interaction. Substantial research has focused on finding signal processing and modeling techniques which give accurate estimates of muscle force from the surface-recorded electromyogram (EMG). The proposed methods often do not capture both the nonlinearities and dynamic components of the EMG–force relation. In this study, parallel cascade identification (PCI) is used as a dynamic estimation tool to map surface EMG recordings from upper-arm muscles to the induced force at the wrist. PCI mapping involves generating a parallel connection of a series of linear dynamic and nonlinear static blocks. The PCI model parameters were initialized to obtain the best force prediction. A comparison between PCI and a previously published Hill-based orthogonalization scheme, that captures physiological behaviour of the muscles, has shown 44% improvement in force prediction by PCI (averaged over all subjects in relative-mean-square sense). The improved performance is attributed to the structural capability of PCI to capture nonlinear dynamic effects in the generated force.

The effects of electromechanical wrist robot assistive system with neuromuscular electrical stimulation for stroke rehabilitation - Corrected Proof

X.L. Hu, K.Y. Tong, R. Li, J.J. Xue, S.K. Ho, P. Chen — 2012-01-25

Abstract: An electromyography (EMG)-driven electromechanical robot system integrated with neuromuscular electrical stimulation (NMES) was developed for wrist training after stroke. The performance of the system in assisting wrist flexion/extension tracking was evaluated on five chronic stroke subjects, when the system provided five different schemes with or without NMES and robot assistance. The tracking performances were measured by range of motion (ROM) of the wrist and root mean squared error (RMSE). The performance is better when both NMES and robot assisted in the tracking than those with either NMES or robot only (P<0.05). The muscle co-contractions in the upper limb measured by EMG were reduced when NMES provided assistance (P<0.05). All subjects also attended a 20-session wrist training for evaluating the training effects (3–5times/week). The results showed improvements on the voluntary motor functions in the hand, wrist and elbow functions after the training, as indicated by the clinical scores of Fugl-Meyer Assessment, Action Research Arm Test, Wolf Motor Function Test; and also showed reduced spasticity in the wrist and the elbow as measured by the Modified Ashworth Score of each subject. After the training, the co-contractions were reduced between the flexor carpi radialis and extensor carpi radialis, and between the biceps brachii and triceps brachii. Assistance from the robot helped improve the movement accuracy; and the NMES helped increase the muscle activation for the wrist joint and suppress the excessive muscular activities from the elbow joint. The NMES–robot assisted wrist training could improve the hand, wrist, and elbow functions.

Comparison of occupational exposure methods relevant to musculoskeletal disorders: Worker–workstation interaction in an office environment - Corrected Proof

2012-01-24

Abstract: Work related musculoskeletal disorders have been associated with office work yet exposure quantification is challenging and not measured consistently. Our objective was to examine associations within and across exposure measurements guided by a conceptual model of three measurement locations: external to the body, at the interface, and internal to the body.Forty-one office workers (71% female), mean age 41years (SD=9.6), mean height 168cm (SD=10.3), and mean weight 74kg (SD=19), were recruited from a large urban newspaper. Four methods of quantifying mechanical exposure were used linked to locations: equipment dimensions (external), relative fit and postures (interface), and EMG (internal). We explored: (1) a within-location analysis of relationships among methods; and (2) a cross-location analysis of relationships among methods.Exposure method comparisons showed mostly weak correlations among equipment variables, moderate correlations among posture variables, and strong or moderate correlations among EMG variables. For the majority of pair-wise comparisons between exposure measures across locations, the correlations were weak or moderate. Comparisons of relative fit revealed some differences in dimensions, postures, and EMG measures.Few strong associations between various exposure measures were found, although worker-reported relative fit holds promise. Future work might link exposure methods (specific measures) with locations for particular purposes.

High density electromyography data of normally limbed and transradial amputee subjects for multifunction prosthetic control - Corrected Proof

Heather Daley, Kevin Englehart, Levi Hargrove, Usha Kuruganti — 2012-01-24

Abstract: Pattern recognition based control of powered upper limb myoelectric prostheses offers a means of extracting more information from the available muscles than conventional methods. By identifying repeatable patterns of muscle activity across multiple muscle sites rather than relying on independent EMG signals it is possible to provide more natural, reliable control of myoelectric prostheses. The purposes of this study were to (1) determine if participants can perform distinctive muscle activation patterns associated with multiple wrist and hand movements reliably and (2) to show that high density EMG can be applied individually to determine the electrode location of a clinically acceptable number of electrodes (maximally eight) to classify multiple wrist and hand movements reliably in transradial amputees. Eight normally limbed subjects (five female, three male) and four transradial amputee subjects (two traumatic and congenital) subjects participated in this study, which examined the classification accuracies of a pattern recognition control system. It was found that tasks could be classified with high accuracy (85–98%) with normally limbed subjects (10–13 tasks) and with amputees (4–6) tasks. In healthy subjects, reducing the number of electrodes to eight did not affect accuracy significantly when those electrodes were optimally placed, but did reduce accuracy significantly when those electrodes were distributed evenly. In the amputee subjects, reducing the number of electrodes up to 4 did not affect classification accuracy or the number of tasks with high accuracy, independent of whether those remaining electrodes were evenly distributed or optimally placed. The findings in healthy subjects suggest that high density EMG testing is a useful tool to identify optimal electrode sites for pattern recognition control, but its use in amputees still has to be proven. Instead of just identifying the electrode sites where EMG activity is strong, clinicians will be able to choose the electrode sites that provide the most important information for classification.

Relationship between muscle coordination and forehand drive velocity in tennis - Corrected Proof

2012-01-16

Abstract: This study aimed at investigating the relationship between trunk and upper limb muscle coordination and stroke velocity during tennis forehand drive. The electromyographic (EMG) activity of ten trunk and dominant upper limb muscles was recorded in 21 male tennis players while performing five series of ten crosscourt forehand drives. The forehand drive velocity ranged from 60% to 100% of individual maximal velocity. The onset, offset and activation level were calculated for each muscle and each player. The analysis of muscle activation order showed no modification in the recruitment pattern regardless of the velocity. However, the increased velocity resulted in earlier activation of the erector spinae, latissimus dorsi and triceps brachii muscles, as well as later deactivation of the erector spinae, biceps brachii and flexor carpi radialis muscles. Finally, a higher level of activation was observed with the velocity increase in the external oblique, latissimus dorsi, middle deltoid, biceps brachii and triceps brachii. These results might bring new knowledge for strength and tennis coaches to improve resistance training protocols in a performance and prophylactic perspective.

Effects of transcutaneous electrical nervous stimulation on electromyographic and kinesiographic activity of patients with temporomandibular disorders: A placebo-controlled study - Corrected Proof

Annalisa Monaco, Fabrizio Sgolastra, Irma Ciarrocchi, Ruggero Cattaneo — 2012-01-16

Abstract: The purpose of this study was to assess the effect of a single 60min TENS application on sEMG and kinesiographic activity in TMD patients in remission, and to assess the sEMG and kinesiographic effect of TENS in placebo and untreated groups. Sixty female subjects, selected according to the inclusion/exclusion criteria, suffering from unilateral TMD in remission were assigned to one of the following group: Group TENS, that received a single session of 60min of TENS; Group Placebo that received a single session of 60min of sham TENS; Group Control, that received no treatment. Pre- and post-treatment differences in sEMG of TA, MM, SCM, and DA and interocclusal distance values within groups were tested using the Wilcoxon test. Differences in sEMG and kinesiographic data, among the three groups, were assessed by Kruskal–Wallis test. Significant differences were only observed in the TENS group, for masticatory muscles of both sides; one-way analysis of variance revealed that sEMG values of masticatory muscles of both sides in the TENS group were significantly reduced, in comparison with placebo and control groups. Kinesiographic results showed that the vertical component of the interocclusal distance was significantly increased after TENS only in the TENS group. TENS could be effective to reduce the sEMG activity of masticatory muscles and to improve the interocclusal distance of TMD patients in remission; the placebo effect seems not present in the TENS application.

Neuromuscular fatigue during dynamic maximal strength and hypertrophic resistance loadings - Corrected Proof

Simon Walker, Lisa Davis, Janne Avela, Keijo Häkkinen — 2012-01-16

Abstract: The purpose of this study was to compare the acute neuromuscular fatigue during dynamic maximal strength and hypertrophic loadings, known to cause different adaptations underlying strength gain during training. Thirteen healthy, untrained males performed two leg press loadings, one week apart, consisting of 15 sets of 1 repetition maximum (MAX) and 5 sets of 10 repetition maximums (HYP). Concentric load and muscle activity, electromyography (EMG) amplitude and median frequency, was assessed throughout each set. Additionally, maximal bilateral isometric force and muscle activity was assessed pre-, mid-, and up to 30min post-loading. Concentric load during MAX was decreased after set 10 (P<0.05), while the load was maintained throughout HYP. Both loadings caused large reductions in maximal isometric force (MAX=−30±6.4% vs. HYP=−48±9.7%, P<0.001). The decreased concentric and isometric strength during MAX loading was accompanied by reduced EMG amplitude (P<0.05). Conversely, hypertrophic loading caused decreased median frequency only during isometric contractions (P<0.01). During concentric contractions, EMG amplitude increased and median frequency decreased in HYP (P<0.01). Our results indicate reduced neural drive during MAX loading and more complex changes in muscle activity during HYP loading.

Flexion relaxation of erector spinae response to spinal shrinkage - Corrected Proof

Xinhai Shan, Yanbing Zhang, Tailai Zhang, Zhentao Chen, Yugang Wei — 2012-01-16

Abstract: The purpose of the study was to investigate the effect of spinal shrinkage on the characteristic of flexion relaxation phenomenon in erector spinae muscle. Twelve male university students volunteered for this study. The spinal shrinkage was created with a load of 20% body weight on shoulder in 10min. Each performed three trials of lumbar flexion–extension with the cycle of 5s flexion and 5s extension in standing before and after shrinkage. Surface electromyography from right erector spinae muscle as well as trunk flexion performance was recorded synchronously in video camera. A one-way ANOVA with repeated measures was used to evaluate the effect of shrinkage. The results showed that there was a significant (p<0.001) stature change with mean magnitude of shrinkage 5.9mm. The erector spinae was active through a significantly larger angle during flexion and began activity significantly earlier during extension after shrinkage. It was concluded that shrinkage caused by prolonged compressive loading will elicit the change of flexion relaxation characteristic, which may be closely related to low back disorder.

Symmetry and reproducibility of the components of dynamic stability in young adults at different walking velocities on the treadmill - Corrected Proof

Florian Süptitz, Kiros Karamanidis, María Moreno Catalá, Gert-Peter Brüggemann — 2012-01-13

Abstract: In the literature, analysis of dynamic gait stability using the extrapolated center of mass concept is often an objective that assumes reproducible and symmetrical data. Here, we examined the validity of this assumption by analyzing subjects walking at different velocities. Eleven healthy young subjects walked on a treadmill at six different velocities (1.0–2.0m·s−1). Dynamic stability at touchdown of the left and right foot (10 gait trials for each body side) was investigated by using the margin of stability, determined as the difference between base of support and extrapolated center of mass. Dynamic stability parameters showed no significant differences (P>0.05) between gait trials, with a root mean square difference in margin of stability of less than 1.62cm. Correlation coefficients between trials were above 0.70 for all parameters, demonstrating that two gait trials are sufficient to obtain reproducible data. In more than 90% of the cases, the absolute symmetry index was below 8% with no relevant functional differences between body sides. We concluded that analyzing two gait trials for one body side is sufficient to determine representative characteristics of the components of dynamic stability in healthy young adults while walking on the treadmill at a wide range of velocities.

Chewing pattern and muscular activation in open bite patients - Corrected Proof

2012-01-11

Abstract: Different studies have indicated, in open bite patients, that masticatory muscles tend to generate a small maximum bite force and to show a reduced cross-sectional area with a lower EMG activity. The aim of this study was to evaluate the kinematics parameters of the chewing cycles and the activation of masseters and anterior temporalis muscles of patients with anterior dental open bite malocclusion. There have been no previous reports evaluating both kinematic values and EMG activity of patients with anterior open bite during chewing. Fifty-two young patients (23 boys and 29 girls; mean age±SD 11.5±1.2 and 10.2±1.6years, respectively) with anterior open bite malocclusion and 21 subjects with normal occlusion were selected for the study. Kinematics parameters and surface electromyography (EMG) were simultaneously recorded during chewing a hard bolus with a kinesiograph K7-I Myotronics-Usa. The results showed a statistically significant difference between the open bite patients and the control group for a narrower chewing pattern, a shorter total and closing duration of the chewing pattern, a lower peak of both the anterior temporalis and the masseter of the bolus side.In this study, it has been observed that open bite patients, lacking the inputs from the anterior guidance, that are considered important information for establishing the motor scheme of the chewing pattern, show narrower chewing pattern, shorter lasting chewing cycles and lower muscular activation with respect to the control group.

Variable stimulation patterns in younger and older thenar muscle - Corrected Proof

Barbara M. Doucet, Lisa Griffin — 2012-01-06

Abstract: Neuromuscular electrical stimulation (NMES) is typically used with older adults receiving rehabilitation therapies, but little is known about the stimulation patterns that maximize force output and minimize fatigue in this population. The purpose of this study was to apply variable patterns of stimulation to the thenar muscles of the hand in younger and older adults to determine if force production and neuromuscular fatigue effects were similar. Three submaximal stimulation patterns were administered: A 20Hz constant frequency pattern, a pattern that increased from 20 to 40Hz, and a pattern that incorporated two closely spaced (5ms) doublet pulses. The doublet stimulation produced significantly higher average forces and force–time integrals (FTIs) than the constant frequency and increasing frequency patterns in both age groups. Additionally, older adults showed less fatigue than the younger group during isometric contractions performed after the fatiguing stimulation patterns. These results suggest that variable pulse NMES patterns enhance force production in the hand in both younger and older individuals better than constant frequency patterns, which are typically used in clinical applications. Also, greater fatigue resistance to electrical stimulation protocols may exist in the older population; this is critical information for the design and application of NMES rehabilitation regimens used with older adults.

Effects of loading on maximum vertical jumps: Selective effects of weight and inertia - Corrected Proof

2011-12-30

Abstract: A novel loading method was applied to explore selective effects of externally added weight (W), weight and inertia (W+I), and inertia (I) on maximum counter-movement jumps (CMJ) performed with arm swing. Externally applied extended rubber bands and/or loaded vest added W, W+I, and I corresponding to 10–40% of subjects’ body mass. As expected, an increase in magnitude of all types of load was associated with an increase in ground reaction forces (GRF), as well as with a decrease in both the jumping performance and power output. However, of more importance could be that discernible differences among the effects of W, W+I, and I were recorded despite a relatively narrow loading range. In particular, an increase in W was associated with the minimal changes in movement kinematic pattern and smallest reduction of jumping performance, while also allowing for the highest power output. Conversely, W+I was associated with the highest ground reaction forces. Finally, the lowest maxima of GRF and power were associated with I. Although further research is apparently needed, the obtained finding could be of potential importance not only for understanding fundamental properties of the neuromuscular system, but also for optimization of loading in standard athletic training and rehabilitation procedures.

Electromyographic indices, orofacial myofunctional status and temporomandibular disorders severity: A correlation study - Corrected Proof

2011-12-29

Abstract: This study examined whether there is an association between surface electromyography (EMG) of masticatory muscles, orofacial myofunction status and temporomandibular disorder (TMD) severity scores.Forty-two women with TMD (mean 30years, SD 8) and 18 healthy women (mean 26years, SD 6) were examined. According to the Research Diagnostic Criteria for TMD (RDC/TMD), all patients had myogenous disorders plus disk displacements with reduction. Surface EMG of masseter and temporal muscles was performed during maximum teeth clenching either on cotton rolls or in intercuspal position. Standardized EMG indices were obtained. Validated protocols were used to determine the perception severity of TMD and to assess orofacial myofunctional status.TMD patients showed more asymmetry between right and left muscle pairs, and more unbalanced contractile activities of contralateral masseter and temporal muscles (p<0.05, t-test), worse orofacial myofunction status and higher TMD severity scores (p<0.05, Mann–Whitney test) than healthy subjects. Spearman coefficient revealed significant correlations between EMG indices, orofacial myofunctional status and TMD severity (p<0.05).In conclusion, these methods will provide useful information for TMD diagnosis and future therapeutic planning.

Basis for spinal manipulative therapy: A physical therapist perspective - Corrected Proof

Joel E. Bialosky, Corey B. Simon, Mark D. Bishop, Steven Z. George — 2011-12-26

Abstract: Physical therapists internationally provide spinal manipulative therapy (SMT) to patients with musculoskeletal pain complaints. SMT has been a part of physical therapist practice since the profession’s beginning. Early physical therapist clinical decision making for SMT was influenced by the approaches of osteopathic and orthopedic physicians at the time. Currently a segmental clinical decision making approach and a responder clinical decision making approach are two of the more common models through which physical therapist clinical use of SMT is directed. The focus of segmental clinical decision making is upon identifying a dysfunctional vertebral segment with the application of SMT to restore mobility and/or alleviate pain. The responder clinical decision making approach attempts to categorize individuals based on a pattern of signs and symptoms suggesting a likely positive response to SMT. The present manuscript provides an overview of common physical therapist clinical decision making approaches to SMT and presents areas requiring further study in order to optimize patient response.

The development of rhythm regularity, neuromuscular strategies, and movement smoothness during repetitive reaching in typically developing children - Corrected Proof

Robyn Traynor, Victoria Galea, Michael R. Pierrynowski — 2011-12-26

Abstract: Introduction: This study examined the development of paced coordinated reaching characterized by the successful entrainment of the movement to an external pacer, synchronous muscle activations and movement smoothness.Methods: Thirty children, 5–10years of age, and ten adults were instructed to repeatedly reach for and move an object from a lower shelf to an upper shelf in time to a metronome. Surface electromyography data were recorded. Amplitude and cross-correlations were calculated on three muscle pairs crossing the shoulder and elbow. A motion capture system captured the space curve accelerations of hand, forearm and upper arm segments to quantify movement smoothness.Results: The 5–6year old children showed the greatest amount of temporal variability, followed by 7–10year olds and then the adults. Correlations between muscle pairs stabilizing the shoulder girdle were higher in each group as compared to the other two muscle pairs but the correlations for all pairs were consistently higher for adults. Movement smoothness for children 9–10years of age was closer to an adult-like pattern with respect to control of the upper arm, but the hand segment had the greatest variability across groups.Conclusions: The increased temporal variability and decreased movement smoothness of the hand and forearm segments suggest that control of more distal musculature may be more difficult in children. The neuromuscular strategies adopted by adults were more optimal than those adopted by children as reflected by smoother and more consistent reaching.

Spinal reflex properties in the long term after stroke - Corrected Proof

2011-12-23

Abstract: In the long term after stroke, secondary functional deterioration may be observed while patients also get older. Possible underlying mechanisms are largely unknown. We aimed to assess neuromuscular degeneration represented by alterations in peripheral reflex loop characteristics as a function of follow-up time after stroke, controlled for age.Twenty-one stroke survivors within a small age range (62–67years) but large variance in follow-up time after stroke (1–15years) and both five age matched (59–62years) and young subjects (28–36years) participated. Short and long latency reflexes evoked by ramp and hold stretches were identified from EMG traces of the m. flexor carpi radialis.Short latency reflex onset time was not enhanced (mean difference 1.6ms compared to age matched controls) and did not relate to follow-up time after stroke (p=0.81). Young controls showed significantly lower reflex delay times (mean difference 7.2ms with respect to older subjects, p=0.009).No evidence was found for peripheral neuromuscular deterioration as a function of follow up time after stroke. Functional deterioration as a result of ageing of stroke patients that may interact with post stroke follow-up time is of further interest.

Non-uniform muscle adaptations to eccentric exercise and the implications for training and sport - Corrected Proof

Nosratollah Hedayatpour, Deborah Falla — 2011-12-22

Abstract: Due to the variations in morphological and architectural characteristics of fibers within a skeletal muscle, regions of a muscle may be differently affected by eccentric exercise. Although eccentric exercise may be beneficial for increasing muscle mass and can be beneficial for the treatment of tendinopathies, the non-uniform effect of eccentric exercise results in regional muscle damage and as a consequence, non-uniform changes in muscle activation. This regional muscle weakness can contribute to muscle strength imbalances and may potentially alter the load distribution on joint structures, increasing the risk of injury.In this brief review, the non-uniform effects of eccentric exercise are reviewed and their implications for training and sport are considered.

Alterations in evertor/invertor muscle activation and center of pressure trajectory in participants with functional ankle instability - Corrected Proof

J. Ty Hopkins, Mark Coglianese, Philip Glasgow, Shane Reese, Matthew K. Seeley — 2011-12-19

Abstract: Participants with ankle instability demonstrate more foot inversion during the stance phase of gait than able-bodied subjects. Invertor excitation, coupled with evertor inhibition may contribute to this potentially injurious position. The purpose of this experiment was to examine evertor/invertor muscle activation and foot COP trajectory during walking in participants with functional ankle instability (FI). Twelve subjects were identified with FI and matched to healthy controls. Tibialis anterior (TA) and peroneus longus (PL) electromyography (EMG), as well as COP, were recorded during walking. Functional analyses were used to detect differences between FI and control subjects with respect to normalized EMG and COP trajectory during walking. Relative to matched controls, COP trajectory was more laterally deviated in the FI group from 20% to 90% of the stance phase. TA activation was greater in the FI group from 15% to 30% and 45% to 70% of stance. PL activation was greater in the FI group at initial heel contact and toe off and trended lower from 20% to 40% of stance in the FI group. Altered motor strategies appear to contribute to COP deviations in FI participants and may increase the susceptibility to repeated ankle inversion injury.

Comment on “Can muscle coordination be precisely studied by surface electromyography?” - Corrected Proof

Laura A. Frey Law, Keith G. Avin — 2011-12-12

We read with interest the recent paper by , which addresses several current issues surrounding the usefulness of surface electromyography (EMG) to characterize muscle coordination under dynamic conditions. We commend the author on providing a thoughtful and provoking paper on the application and use of surface EMG. We would like to further discuss two specific issues related to this paper. First, the author brought to light an important topic that is not commonly addressed in the dynamic literature: electromechanical delay. This often neglected phenomenon may be particularly relevant for those studies quantifying angle-specific muscle coactivation during isokinetic contractions (). Typically, EMG activity is assessed in a direct time-linked manner to specific joint angles, without considering the consequences of electromechanical delay across multiple angular velocities. Although, not explicitly described by Hug, we were interested in estimating the potential error due to the range of electromechanical delays reported by Hug (41 to 77ms) across a range of contraction velocities. To accomplish this we calculated the range of angle offsets (i.e. the angular contraction velocity multiplied by the electromechanical delay) indicating how “distant” the measured EMG signal might be from the resulting force it produces in degrees (see ). Thus, to extend Hug’s discussion, the angle offset between the measured EMG signal and its corresponding joint angle at which force is produced could be as small as 2.4° or as great as 24°. Additionally, the relationship between contraction velocity and electromechanical delay is not clear; nor if the delay is constant throughout the range of motion. We therefore suggest the use of angle-specific reporting of EMG activity be avoided when being compared across varying contraction speeds if possible or at a minimum consider the potential error resulting from electromechanical delays.

Evaluation of electromyography normalisation methods for the back squat - Corrected Proof

Thomas G. Balshaw, Angus M. Hunter — 2011-12-12

Abstract: The aim of the study was to evaluate maximal isometric (dynamometer based {MVC-NORM} and isometric squat {MIS-NORM}) and sub-maximal EMG normalisation methods (60%-NORM, 70%-NORM, 80%-NORM) for dynamic back squat exercise (DSQ-EX). The absolute reliability (limits of agreement {LOA}, coefficient of variation {CV%}), relative reliability (intra-class correlation coefficient {ICC}) and sensitivity of each method was assessed. Ten resistance-trained males attended four sessions. Session one assessed maximum back squat strength (three repetition maximum {3RM}). In the remaining three sessions Vastus lateralis (VL) and Bicep femoris (BF) EMG were measured whilst participants completed normalisation tasks and DSQ-EX sets at 65%, 75%, 85% and 95% of 3RM. MIS-NORM produced lower intra-participant CV% compared to MVC-NORM. 80%-NORM produced lower intra-participant CV% than other sub-maximal methods for VL and BF during eccentric and concentric phases. 80%-NORM also produced narrower 95% LOA results than all other normalisation methods. The MIS-NORM method displayed higher ICC values for both muscles during eccentric and concentric phases. The 60%-NORM and 70%-NORM methods were the most sensitive for VL and BF during eccentric and concentric phases. Only normalisation methods for the concentric action of the VL enhanced sensitivity compared to unnormalised EMG. Overall, dynamic normalisation methods demonstrated better absolute reliability and sensitivity for reporting VL and BF EMG within the current study compared to maximal isometric methods.

Targeted gripping reduces shoulder muscle activity and variability - Corrected Proof

Joanne N. Hodder, Peter J. Keir — 2011-12-12

Abstract: The purpose of this study was to determine if the effect of visually targeted gripping on shoulder muscle activity was maintained with repeated exposures. Eleven healthy males had eight shoulder muscles monitored via surface electromyography while maintaining shoulder elevation at 90° in the scapular plane with and without a 30% grip force. Three non-gripping trials were followed by 15 gripping trials and another 3 non-gripping control trials. Gripping significantly decreased the activity of the anterior deltoid, trapezius, and latissimus dorsi over the exposure of 15 trials. Gripping also reduced variability in all muscles’ activity. The changes in shoulder muscle activity are likely in response to forces being transferred through multi-articular muscles spanning from the forearm to the shoulder. Targeted gripping during shoulder elevation resulted in small but significant decreases in muscle activity and reduced variability which supports previous evidence for increased risk of upper extremity disorders in occupational settings.

Neuromuscular manifestations of viscoelastic tissue degradation following high and low risk repetitive lumbar flexion - Corrected Proof

M. Solomonow — 2011-12-08

Abstract: Cumulative lumbar disorder is common in individuals engaged in long term performance of repetitive and static occupational/sports activities with the spine. The triggering source and of the disorder, the tissues involved in the failure and the biomechanical, neuromuscular, and biological processes active in the initiation and development of the disorder are not known. The hypothesis is forwarded that static and repetitive (cyclic) lumbar flexion-extension and the associated repeated stretch of the various viscoelastic tissues (ligaments, fascia, facet capsule, discs, etc.) causes micro-damage in their collagen fibers followed by an acute inflammation, triggering pain and reflexive muscle spasms/hyper-excitability. Continued exposure to activities, over time, converts the acute inflammation into a chronic one, viscoelastic tissues remodeling/degeneration, modified motor control strategy and permanent disability. Changes in lumbar stability are expected during the development of the disorder.A series of experimental data from in-vivo feline is reviewed and integrated with supporting evidence from the literature to gain a valuable insight into the multi-factorial development of the disorder. Prolonged cyclic lumbar flexion-extension at high loads, high velocities, many repetitions and short in between rest periods induced transient creep/laxity in the spine, muscle spasms and reduced stability followed, several hours later, by an acute inflammation/tissue degradation, muscular hyper-excitability and increased stability. The major findings assert that viscoelastic tissues sub-failure damage is the source and inflammation is the process which governs the mechanical and neuromuscular characteristic symptoms of the disorder. A comprehensive model of the disorder is presented. The experimental data validates the hypothesis as well as provide insights into the development of potential treatment and prevention of the disorder.

Task-dependent spatial distribution of neural activation pattern in human rectus femoris muscle - Corrected Proof

Kohei Watanabe, Motoki Kouzaki, Toshio Moritani — 2011-12-07

Abstract: Compartmentalization of skeletal muscle by multiple motor nerve branches, named as neuromuscular compartment (NMC), has been demonstrated in animals as well as humans. While different functional roles among individual NMCs were reported in the animal studies, no studies have clarified the region-specific functional role within a muscle related with NMCs arrangement in human skeletal muscle. It was reported that the rectus femoris (RF) muscle is innervated by two nerve branches attached at proximal and distal parts of the muscle. The purpose of the present study is to clarify the possible region-specific functional role in the human RF muscle. Multi-channel surface electromyography (SEMG) were recorded from the RF muscle by using 128 electrodes during two different submaximal isometric contractions that the muscle contributes, i.e. isometric knee extension and hip flexion, at 20%, 40%, 60% and 80% of maximal voluntary contraction (MVC). Results indicated that the central locus activation for the amplitude map of SEMG during hip flexion located at more proximal region compared with that during knee extension. Significant higher normalized root mean square (RMS) values were observed at the proximal region during the hip flexion in comparison to those at middle and distal regions at 60% and 80% of MVC (p<0.05). In while, significant higher normalized RMS values were demonstrated at the distal region comparing with that at the proximal region at 80% of MVC (p<0.05). The results of the present study suggest possible region-specific functional role in the human RF muscle.

Individual muscle contributions to knee joint impedance following a sudden perturbation: An in vivo inverted pendulum model - Corrected Proof

Joel A. Cort, Jim R. Potvin — 2011-12-05

Abstract: Previous research has suggested that muscle forces, generated by reflexes, contribute to joint stability prior to the more coordinated voluntary muscle forces. The purpose of the current study was to quantify the behaviour of the leg muscles, through the calculation of individual muscle contributions to joint rotational impedance (MJRI), with a specific interest in the neuromuscular contribution in the period following shortly after a sudden knee extension perturbation. The knee was selected as an in vivo system to represent an inverted pendulum model. Kinematic and sEMG data were collected while subjects were in a prone position and exposed to sudden knee extension perturbations. A biomechanical model was used to estimate muscle forces and moments about the knee and these data were then used to calculate instantaneous MJRI. Data indicated that pre-voluntary muscle forces do contribute significantly to MJRI following a sudden knee extension perturbation as there was a 40% increase in total MJRI in the flexion/extension and valgus/varus axes immediately following the perturbation, suggesting their importance in stabilizing the joint immediately after a disturbance. Additionally, knowledge of perturbation timing was shown to increase anticipatory MJRI levels, pre-perturbation (p<0.05), indicating that it is advantageous for the neuromuscular system to prepare for a sudden disturbance. In conclusion, the data show that the neuromuscular feedback system significantly contributes to MJRI and it is believed that this behaviour enhances joint impedance following a sudden knee extension perturbation.

Posture and hand load alter muscular response to sudden elbow perturbations - Corrected Proof

Michael W.R. Holmes, Peter J. Keir — 2011-12-05

Abstract: Joint stiffness and stability are reliant on coordinated muscle activity which may differ depending on initial posture and loading during sudden perturbations. This study investigated the effects of arm posture and hand load on muscle activity during perturbations of the arm. Fifteen male participants experienced perturbations to the wrist causing elbow extension using a combination of three body postures (standing, supine, sitting) and three hand load conditions (no, solid, and fluid loads), with known and unknown timing. Surface EMG was collected from eight muscles of the right upper extremity. The response to sudden loading was examined using muscle activities pre (baseline) and post (reflex) perturbation. During the baseline period, known perturbation timing resulted in greater muscular activity than for unknown timing, while the opposite was found for the reflex period. During the reflex period with fluid load, biceps brachii and brachioradialis demonstrated increased activity of 2.4% and 4.0% of maximum respectively, from supine to standing. During the reflex period, the fluid load resulted in forearm co-contraction 23% and 47% greater than the solid and no load conditions. Body orientation and hand loading influenced muscular response to elbow perturbations. Muscle co-contraction at the elbow during known timing suggests a contribution to elbow joint stability that may reduce injury risk caused by sudden elbow loading.

Effect of the upper limbs muscles activity on the mechanical energy gain in pole vaulting - Corrected Proof

Julien Frère, Beat Göpfert, Jean Slawinski, Claire Tourny-chollet — 2011-12-02

Abstract: The shoulder muscles are highly solicited in pole vaulting and may afford energy gain. The objective of this study was to determine the bilateral muscle activity of the upper-limbs to explain the actions performed by the vaulter to bend the pole and store elastic energy. Seven experienced athletes performed 5–10 vaults which were recorded using two video cameras (50Hz). The mechanical energy of the centre of gravity (CG) was computed, while surface electromyographic (EMG) profiles were recorded from 5 muscles bilateral: deltoideus, infraspinatus, biceps brachii, triceps, and latissimus dorsi muscles. The level of intensity from EMG profile was retained in four sub phases between take-off (TO1) and complete pole straightening (PS). The athletes had a mean mechanical energy gain of 22% throughout the pole vault, while the intensities of deltoideus, biceps brachii, and latissimus dorsi muscles were sub phases-dependent (p<0.05). Stabilizing the glenohumeral joint (increase of deltoideus and biceps brachii activity) and applying a pole bending torque (increase of latissimus dorsi activity) required specific muscle activation. The gain in mechanical energy of the vaulter could be linked to an increase in muscle activation, especially from latissimus dorsi muscles.

Catchlike property in human adductor pollicis muscle - Corrected Proof

Rafael Fortuna, Marco Aurélio Vaz, Walter Herzog — 2011-10-28

Abstract: The “catchlike” property is defined as the dramatic force increase in skeletal muscles when a single pulse is added at the onset of a sub-tetanic low-frequency stimulation train. This property has been observed in single motor units, whole animal and human muscles. It is an inherent property of muscle fibres and is not related to an increase in motor unit recruitment. Despite an abundance of observations, its origin remains unclear. The aim of this study was to induce the catchlike property in human adductor pollicis and identify its possible origin. Thumb adduction forces were measured using ulnar nerve electrical stimulation at 10Hz for reference trains (RTs) with one extra pulse 8ms after the first stimulation pulse for the experimental trains (ETs). Tests were performed at two muscle length and three stimulation levels and muscle stiffness and potentiation were quantified for all test conditions. The ETs showed higher forces and greater rates of force increase than the RTs. In addition, force increase was more pronounced at short compared to long muscle length, but no differences were found in force increase for the three stimulation levels. Furthermore, potentiation and stiffness were similar across all experimental conditions. Together, these results suggest that the increase in force associated with the catchlike property is neither caused by an increased proportion of attached cross-bridges nor potentiation of the muscle, but appears to be muscle length dependent and present in both slow and fast motor units.

The effects of motion artifact on mechanomyography: A comparative study of microphones and accelerometers - Corrected Proof

A.O. Posatskiy, T. Chau — 2011-10-24

Abstract: Mechanomyography (MMG) is an important kinesiological tool and potential communication pathway for individuals with disabilities. However, MMG is highly susceptible to contamination by motion artifact due to limb movement. A better understanding of the nature of this contamination and its effects on different sensing methods is required to inform robust MMG sensor design. Therefore, in this study, we recorded MMG from the extensor carpi ulnaris of six able-bodied participants using three different co-located condenser microphone and accelerometer pairings. Contractions at 30% MVC were recorded with and without a shaker-induced single-frequency forearm motion artifact delivered via a custom test rig. Using a signal-to-signal-plus-noise-ratio and the adaptive Neyman curve-based statistic, we found that microphone-derived MMG spectra were significantly less influenced by motion artifact than corresponding accelerometer-derived spectra (p⩽0.05). However, non-vanishing motion artifact harmonics were present in both spectra, suggesting that simple bandpass filtering may not remove artifact influences permeating into typical MMG bands of interest. Our results suggest that condenser microphones are preferred for MMG recordings when the mitigation of motion artifact effects is important.

The effects of circumferential pressure on the soleus muscle F-wave in healthy subjects - Corrected Proof

James Agostinucci — 2011-10-14

Abstract: Circumferential pressure (CP) was shown to decrease muscle activity in subjects without neuromuscular disorders and in individuals with spinal cord injury and cerebrovascular accidents. The mechanism for this decrease is unknown although it is hypothesized to be spinal in origin. The purpose of this study was to investigate the effect CP has on the soleus F-wave. Results will help determine the mechanism CP uses to effect motoneuron reflex excitability. Thirty-seven healthy volunteers participated. A 16cm air-splint was placed around the calf and during the pressure phase of the experiment it was inflated to 40–45mm Hg. F-waves were evoked by supra maximally stimulating (20%>Mmax) the tibial nerve with a 0.1ms pulse at 0.2Hz using a bipolar surface electrode on the skin of the popliteal fossa. Fifty F-waves were recorded before (baseline), during, and 3) after CP was applied. F-waves were then identified and mean latency, persistence, and mean F/Mmax amplitude ratios were measured and calculated. Friedman Repeated Measures on Ranks tests were conducted on each of the three parameters (p⩽0.05). No statistically significant difference was found for any of the F-wave parameters evaluated. These results were contrary to previous CP studies that observed a significant decrease in muscle activity. Possible reasons for this discrepancy are discussed.

Activity of upper limb muscles during human walking - Corrected Proof

Johann P. Kuhtz-Buschbeck, Bo Jing — 2011-09-26

Abstract: The EMG activity of upper limb muscles during human gait has rarely been studied previously. It was examined in 20 normal volunteers in four conditions: walking on a treadmill (1) with unrestrained natural arm swing (Normal), (2) while volitionally holding the arms still (Held), (3) with the arms immobilized (Bound), and (4) with the arms swinging in phase with the ipsilateral legs, i.e. opposite-to-normal phasing (Anti-Normal). Normal arm swing involved weak rhythmical lengthening and shortening contractions of arm and shoulder muscles. Phasic muscle activity was needed to keep the unrestricted arms still during walking (Held), indicating a passive component of arm swing. An active component, possibly programmed centrally, existed as well, because some EMG signals persisted when the arms were immobilized during walking (Bound). Anti-Normal gait involved stronger EMG activity than Normal walking and was uneconomical. The present results indicate that normal arm swing has both passive and active components.

WITHDRAWN: Quantification of trunk muscle activation in subjects post-stroke using surface electromyography - Corrected Proof

Paul S. Sung, Dongchul C. Lee — 2008-11-27

This article has been withdrawn at the request of the editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.