Journal of Electromyography and Kinesiology - Articles in Press

The effect of perspiration on the sEMG amplitude and power spectrum - Corrected Proof

Mohammad Abdoli-Eramaki, Caroline Damecour, John Christenson, Joan Stevenson — 2012-05-21

Abstract: Sweat accumulation underneath surface EMG (sEMG) electrodes is a common problem in workplace studies which compromises electrode adherence to the skin as well as signal fidelity. In this study, the effect of sweat accumulation on signal amplitude and mean frequency (MF) was examined to determine if the sEMG signal becomes altered through the sweat layer and whether this effect can be avoided by interrupting the pool of sweat using a thin strip of medical adhesive between the electrode snaps. Nine males performed a maximum, isometric contraction of their right quadriceps as sEMG was collected. Skin conditions under the electrode were dry and wet in incremental layers of 0.02mm of artificial sweat. The results demonstrated that sweat accumulation under sEMG electrodes dampens the amplitude of the EMG signal in a predictable way (r=.88 and .97 for double and single snap electrodes, respectively) with almost 2% and 3% deterioration for every 0.02mm of sweat depending on the type of electrode used. The medical adhesive proved to be highly effective at preventing amplitude deterioration indicating that signal shunting can be prevented. MF was not influenced by sweat accumulation even under the extreme wet condition.

Novel formulation of a double threshold algorithm for the estimation of muscle activation intervals designed for variable SNR environments - Corrected Proof

G. Severini, S. Conforto, M. Schmid, T. D’Alessio — 2012-05-21

Abstract: The aim of this work is the development of an improved formulation of the double threshold algorithm for sEMG onset–offset detection presented by Bonato and co-workers. The original formulation, which keeps the threshold fixed, suffers from performance degradation whenever the SNR changes during the analysis. The novel approach is designed to be adaptive to SNR changes in either burst or inter-burst zones of sEMG signals recorded in static and dynamic conditions. The detection parameters (i.e. detection and false alarm probabilities) are updated on the basis of an on-line estimation of the SNR. The proposed formulation has been assessed on both simulated and real sEMG data. For constant SNR the performance of the original formulation is confirmed (for SNR>8dB, bias and standard deviation less than 10 and 15ms, respectively; detection percentage higher than 95%), while the novel implementation performs better with time-varying SNR (for SNR varying in the range 10–25dB the standard approach detection percentage decreases at 50%). Detection on signals recorded during isometric contractions at different force levels confirms the performance on simulated signals (StD=134ms; FP=22%, and StD=42ms; FP=2%, respectively for standard and novel implementation calculated as average on five experimental trials). The pseudo real-time detection allowed by this formulation can be profitably exploited by biofeedback applications based on myoelectric information.

Spring–mass behavior and electromyographic activity evolution during a cycle-run test to exhaustion in triathletes - Corrected Proof

Y. Le Meur, S. Dorel, G. Rabita, T. Bernard, J. Brisswalter, C. Hausswirth — 2012-05-21

Abstract: Purpose: To evaluate spring–mass (SM) behavior and associated electromyographic (EMG) activity during a run to exhaustion following a cycle exercise in trained triathletes.Methods: Ten triathletes completed four tests: a cycling test to determine ; a running test to determine the lactate threshold (LT); a 5min control run at LT (C-Run) followed after a total recovery period by a cycle-to-run session to exhaustion [30min of cycling at ∼80% followed by a run until exhaustion at LT (T-Run)]. SM behavior and EMG signals in nine lower limb muscles were recorded throughout the running sessions.Results: Immediately after cycling, leg stiffness was 12.1% higher than its C-Run value and a concomitant increase of EMG activity of knee extensors was observed during pre-contact. Throughout T-Run, leg stiffness decreased by 7.3%, while knee extensors and ankle flexors activities decreased during pre-contact and braking phases. No significant variations in SM parameters and no significant increase of muscle activity were reported between C-Run and the end of T-Run.Conclusion: SM behavior during the cycle-run test was consistent with EMG activity changes. Cessation of exercise was not associated with significant alterations of stiffness values and EMG activity.

Altered preparatory pelvic control during the sit-to-stance-to-sit movement in people with non-specific low back pain - Corrected Proof

Kurt Claeys, Wim Dankaerts, Lotte Janssens, Simon Brumagne — 2012-05-18

Abstract: People with non-specific low back pain (LBP) show hampered performance of dynamic tasks such as sit-to-stance-to-sit movement. However, the underlying mechanisms remain obscure. Therefore, the aim of this study was to assess if proprioceptive impairments influence the performance of the sit-to-stance-to-sit movement.First, the proprioceptive steering of 20 healthy subjects and 106 persons with mild LBP was identified during standing using muscle vibration. Second, five sit-to-stance-to-sit repetitions on a stable support and on foam were performed as fast as possible. Total duration, phase duration, center of pressure (COP) displacement, pelvic and thoracic kinematics were analyzed.People with LBP used less lumbar proprioceptive afference for postural control compared to healthy people (P<0.0001) and needed more time to perform the five repetitions in both postural conditions (P<0.05). These time differences were determined in the stance and sit phases (transition phases), but not in the focal movement phases. Moreover, later onsets of anterior pelvic rotation initiation were recorded to start both movement sequences (P<0.05) and to move from sit-to-stance on foam (P<0.05).Decreased use of lumbar proprioceptive afference in people with LBP seemed to have a negative influence on the sit-to-stance-to-sit performance and more specifically on the transition phases which demand more control (i.e. sit and stance). Furthermore, slower onsets to initiate the pelvis rotation to move from sit-to-stance illustrate a decrease in pelvic preparatory movement in the LBP group.

The effect of changes in joint angle on the characteristics of physiological tremor - Corrected Proof

Benoit Carignan, Jean-François Daneault, Christian Duval — 2012-05-18

Abstract: Introduction: Physiological tremor, as a whole, can be influenced by changes in muscle activity. However, the origin of low-frequency physiological tremor oscillations has yet to be conclusively determined. It is possible that by experimentally manipulating muscular activity, a better determination of the origin of those low-frequency oscillations can be achieved. It was demonstrated that changes in joint angle modify characteristics of muscular activity. As such, we hypothesize that changes in wrist-joint angle will alter the characteristics of low-frequency physiological tremor oscillations.Objective: Assess the influence of changes in joint angle of the wrist on characteristics of physiological finger tremor.Methods: Physiological finger tremor was recorded (n=25) using a laser displacement system while the arm and hand were supported. The relative angle between the dorsum of the hand and the forearm was altered between conditions (135°, 180°, 225° and 270°), while the hand and the finger remained parallel to the ground. EMG of the extensors and flexors were also recorded.Results: Tremor amplitude was significantly altered by changes in wrist-joint angle. This was especially the case for lower frequency oscillations. In addition, electromyography properties of forearm muscles were also significantly modified by changes in wrist-joint angles.Conclusions: This study demonstrates that changes in wrist-joint angle modify the characteristics of physiological finger tremor. This should be taken into account when interpreting tremor data as well as when developing tools to minimize tremor.

Biomechanical and metabolic responses to seat-tube angle variation during cycling in tri-athletes - Corrected Proof

Maria Cristina Bisi, Mattia Ceccarelli, Federico Riva, Rita Stagni — 2012-05-18

Abstract: One of the most physically demanding parts of triathlon is the transition from cycling to running. Many tri-athletes believe that increasing seat-tube angle (STA) can bring advantages in the following running part. The aim of this study was to evaluate the effects of inverting the support of the seat, for increasing STA, on the metabolic response and on the muscle activation pattern, maintaining a controlled kinematic. Moreover, a muscle-skeletal model was applied to evaluate the hypothesis that increasing STA changes force-producing capabilities of muscles crossing the hip.Ten tri-athletes cycled at two different power levels and with two different STA’s. Gas exchange data, kinematics and surface electromyography (sEMG) were acquired during the tests. sEMG was measured from eight muscles of the right side of the body. A model of muscle mechanics and energy expenditure was applied to estimate variations of force production capabilities and muscle energy consumption between the two STA configurations.Inverting the support of the seat showed no significant effects on kinematic, Oxygen consumption, muscle activations and muscle power production capabilities. Nevertheless, an interesting advantage can be the tendency to less activate gastrocnemius and biceps femoris: this could lead to minor muscle fatigue during the following running phase.

Bulk movement included in multi-channel mechanomyography: Similarity between mechanomyography of resting muscle and that of contracting muscle - Corrected Proof

Takashi Kawamoto, Nobutoshi Yamazaki — 2012-05-14

Abstract: Although mechanomyography (MMG) reflects local vibrations from contracting muscle fibers, it also includes bulk movement: deformation in global soft tissue around measuring points. To distinguish between them, we compared the multi-channel MMG of resting muscle, which dominantly reflected the bulk movement caused by arterial pulsations, to that of the contracting muscle. The MMG signals were measured at five points around the upper arms of 10 male subjects during resting and during isometric ramp contraction from 5% to 85% of maximal voluntary contraction (MVC) of the biceps brachii muscle. The characteristics of bulk movement were defined as the amplitude distribution and phase relation among the five MMG signals. The bulk movement characteristics during the rest state were not necessarily the same among the subjects. However, below 30Hz, each subject’s characteristics remained the same from the rest state (0% MVC) to the contracting state (80% MVC), at which the bulk movement mainly originates from muscle contraction activity. Results show that the MMG of the low frequency domain (<30Hz) includes bulk movement depending on the mechanical deformation characteristics of each subject’s body, for a wide range of muscle contraction intensities.

The effects of exercise on limb proprioceptive signals - Corrected Proof

Sylvie Fortier, Fabien A. Basset — 2012-05-14

Abstract: The definition of proprioception in the literature is equivocal, therefore it is desirable for communication and comprehension purposes that all authors who use proprioception and its related terms reach a consensus as to their meaning. This review aims to clarify these terms and to improve the understanding of the proprioceptive system. Over the years, many different views have been put forward on the origin of proprioception. The present-day view is that, in the absence of vision, we are able to determine the location of our limbs by signals of both peripheral and central origin. Nonetheless, recent research findings argue that the centrally generated sense of effort may not be well-suited to signal position sense and suggest revising the sense of effort hypothesis. This paper enlightens the latest views on the role of peripheral afferents and central signals involved in the proprioceptive system. It also describes the most common experimental protocols used to evaluate proprioception. The paper’s final section describes in detail the effect of different muscle contraction types on kinaesthetic sense—in particular, on the sense of limb position.

Analytical decomposition can help to interpret ankle joint moment–angle relationship - Corrected Proof

Ruoli Wang, Eva W. Broström, Anna-Clara Esbjörnsson, Elena M. Gutierrez-Farewik — 2012-05-09

Abstract: Moment–angle relationship (dynamic joint stiffness) – the relationship between changes in joint moment and changes in joint angle – is useful for demonstrating interaction of kinematics and kinetics during gait. However, the individual contributors of dynamic joint stiffness are not well studied and understood, which has thus far limited its clinical application. In this study, ankle dynamic joint stiffness was analyzed and decomposed into three components in thirty able-bodied children during the stance phase of the gait. To verify the accuracy of the decomposition, the sum of decomposed components was compared to stiffness computed from experimental data, and good to very good agreement was found. Component 1, the term associated with changes in ground reaction force moment, was the dominant contribution to ankle dynamic joint stiffness. Retrospective data from eight children with juvenile idiopathic arthritis and idiopathic toe-walking was examined to explore the potential utility of analytical decomposition in pathological gait. Compared to controls, component 1 was the source of highest deviation in both pathological groups. Specifically, ankle dynamic joint stiffness differences can be further identified via two sub-components of component 1 which are based on magnitudes and rates of change of the ground reaction force and of its moment arm, and differences between the two patient groups and controls were most evident and interpretable here. Findings of the current study indicate that analytical decomposition can help identify the individual contributors to joint stiffness and clarify the sources of differences in patient groups.

Architectural differences between the hamstring muscles - Corrected Proof

Eleftherios Kellis, Nikiforos Galanis, George Kapetanos, Konstantinos Natsis — 2012-05-08

Abstract: The purpose of this study was to understand the detailed architectural properties of the human hamstring muscles. The long (BFlh) and short (BFsh) head of biceps femoris, semimembranosus (SM) and semitendinosus (ST) muscles were dissected and removed from their origins in eight cadaveric specimens (age 67.8±4.3years). Mean fiber length, sarcomere length, physiological cross-section area and pennation angle were measured. These data were then used to calculate a similarity index (δ) between pairs of muscles. The results indicated moderate similarity between BFlh and BFsh (δ=0.54) and between BFlh and SM (δ=0.35). In contrast, similarity was low between SM and ST (δ=0.98) and between BFlh and SM (δ=1.17). The fascicle length/muscle length ratio was higher for the ST (0.58) and BFsh (0.50) compared with the BFlh (0.27) and SM (0.22). There were, however, high inter-correlations between individual muscle architecture values, especially for muscle thickness and fascicle length data sets. Prediction of the whole hamstring architecture was achieved by combining data from all four muscles. These data show different designs of the hamstring muscles, especially between the SM and ST (medial) and BFlh and BFsh (lateral) muscles. Modeling the hamstrings as one muscle group by assuming uniform inter-muscular architecture yields less accurate representation of human hamstring muscle function.

Effect of degree of knee osteoarthritis on balancing capacity after sudden perturbation - Corrected Proof

Rita M. Kiss — 2012-05-07

Abstract: This study aimed to assess equilibrium ability after sudden perturbation in patients with moderate and severe unilateral knee osteoarthritis (OA), with regard to age, gender, and lateral dominance.Our clinical trial included 45 female and 45 male healthy elderly subjects, 24 female and 24 male patients with moderate OA (mOA), and 24 female and 24 male patients with severe OA (sOA). Subjects were divided in two age groups: 65–69 and 70–74years.Using an oscillatory platform, we conducted provocation tests and determined the Lehr’s damping ratio (D), which represents balancing capacity after sudden perturbation.D values determined for standing on both legs were similar to those of healthy individuals on the dominant limb or for OA patients on the non-affected limb; they were significantly lower for healthy individuals on the non-dominant limb and OA patients on the affected limb. For healthy subjects and mOA patients, D was significantly decreased with age and influenced by gender. sOA patients presented lower D values than other groups under all conditions, which were not influenced by age or gender.Our results demonstrate that OA patients were less capable of responding to perturbations, possibly indicating that they have an increased risk of falling.

Independent activation in adjacent lumbar extensor muscle compartments - Corrected Proof

Marilee M. Nugent, Paul J. Stapley, Theodore E. Milner — 2012-05-03

Abstract: The purpose of this study was to examine compartmentalization in human lumbar spine extensors. Structure and innervation of these muscles would suggest the possibility of more segmentally specific biomechanical functions than have been found in previous studies examining muscle activation patterns during simple spine bending and twisting tasks. We selected specialized tasks to more effectively investigate the degree of independent control possible within lumbar spine extensors. We recorded surface electromyograms (SEMG) from the right posterior lumbar region during performance of two segmentally specific bellydance skills by seven novice and five trained subjects. These movements were performed at two frequencies (0.5 and 1Hz). Cross-correlations were performed between pairs of rectified, low-pass filtered (6Hz) SEMG signals to determine temporal lags between rhythmic bursts. Results showed a difference in the timing of muscle activation above and below the third lumbar vertebra. Temporal asynchrony was independent of either skill level or tempo, suggesting a hard-wired capacity for independent control of adjacent muscle compartments. The results have implications for understanding trunk control in the context of postural stability and postural adaptation during locomotion, as well as for lower back functional assessment and rehabilitation.

Biomechanics – Review of approaches for performance training in spinal manipulation - Corrected Proof

J.J. Triano, M. Descarreaux, C. Dugas — 2012-04-30

Abstract: Motor skills development is an inherent part of clinical training in health disciplines. The conscious use of educational theory to ground learning is receiving increasing attention across health care education. There are three distinct, yet overlapping, stages of motor skill learning; the cognitive, the integrative or associative, and the autonomous; in which a contextual framework for learning content may be structured. The learning is associated with a mapping of changes within the central nervous system by the interactive mechanisms of adaptation, use-dependent plasticity and operant reinforcement.Successful skill learning requires a sufficient amount of practice and the implementation of relevant feedback strategies in the form of knowledge of performance (KP) or knowledge of results (KR). There is a natural maturation of skills that may be accelerated by feedback. Several factors contribute to stronger skills development. “Mixture-of-experts” models systematically sequence tasks into logical blocks of theory, practice and student reflection on performance. Feedback should involve both KP and KR that compares performance to a tangible standard. Rehearsals should balance use of simulators and volunteer simulated patients to provide the full range of safe and effective learning opportunities prior to students accepting a role as care givers to the public in any clinical setting.

Electromyography variables during the golf swing: A literature review - Corrected Proof

Sérgio Marta, Luís Silva, Maria António Castro, Pedro Pezarat-Correia, Jan Cabri — 2012-04-30

Abstract: The aim of the study was to review systematically the literature available on electromyographic (EMG) variables of the golf swing. From the 19 studies found, a high variety of EMG methodologies were reported. With respect to EMG intensity, the right erector spinae seems to be highly activated, especially during the acceleration phase, whereas the oblique abdominal muscles showed moderate to low levels of activation. The pectoralis major, subscapularis and latissimus dorsi muscles of both sides showed their peak activity during the acceleration phase. High muscle activity was found in the forearm muscles, especially in the wrist flexor muscles demonstrating activity levels above the maximal voluntary contraction. In the lower limb higher muscle activity of the trail side was found. There is no consensus on the influence of the golf club used on the neuromuscular patterns described. Furthermore, there is a lack of studies on average golf players, since most studies were executed on professional or low handicap golfers.Further EMG studies are needed, especially on lower limb muscles, to describe golf swing muscle activation patterns and to evaluate timing parameters to characterize neuromuscular patterns responsible for an efficient movement with lowest risk for injury.

Between-day reliability of a method for non-invasive estimation of muscle composition - Corrected Proof

Boštjan Šimunič — 2012-04-30

Abstract: Tensiomyography is a method for valid and non-invasive estimation of skeletal muscle fibre type composition. The validity of selected temporal tensiomyographic measures has been well established recently; there is, however, no evidence regarding the method’s between-day reliability. Therefore it is the aim of this paper to establish the between-day repeatability of tensiomyographic measures in three skeletal muscles.For three consecutive days, 10 healthy male volunteers (mean±SD: age 24.6±3.0years; height 177.9±3.9cm; weight 72.4±5.2kg) were examined in a supine position. Four temporal measures (delay, contraction, sustain, and half-relaxation time) and maximal amplitude were extracted from the displacement–time tensiomyogram. A reliability analysis was performed with calculations of bias, random error, coefficient of variation (CV), standard error of measurement, and intra-class correlation coefficient (ICC) with a 95% confidence interval.An analysis of ICC demonstrated excellent agreement (ICC were over 0.94 in 14 out of 15 tested parameters). However, lower CV was observed in half-relaxation time, presumably because of the specifics of the parameter definition itself. These data indicate that for the three muscles tested, tensiomyographic measurements were reproducible across consecutive test days. Furthermore, we indicated the most possible origin of the lowest reliability detected in half-relaxation time.

Biomechanical assessments of the effect of visual feedback on cycling for patients with stroke - Corrected Proof

Sang-I Lin, Chao-Chen Lo, Pei-Yi Lin, Jia-Jin J. Chen — 2012-04-26

Abstract: Stroke patients exhibit abnormal pattern in leg cycling exercise. The aim of this study was to investigate the effects of visual feedback on the control of cycling motion in stroke patients from kinesiological, kinematic and kinetic aspects. The cycling performance derived from cycling electromyography (EMG), cycling cadence, and torque of forty stroke subjects was evaluated under conditions with and without visual feedback of cycling cadence. Kinesiological indices, shape symmetry index (SSI) and area symmetry index (ASI) were extracted from EMG linear envelopes to evaluate the symmetry of muscle firing patterns during cycling. Roughness index (RI) was calculated from cycling cadence to represent cycling smoothness from kinematic aspects. Averaged cycling power (Pav), the product of cadence and torque, was used to represent force output. The rectus femoris EMG showed significantly greater ASI with visual feedback, however, the difference in SSI between the two conditions was not significant. For the biceps femoris, there was a significant decrease in SSI with visual feedback, while the ASI was not affected significantly by the task conditions. The cycling smoothness was better and the average power generated was larger when visual feedback was provided. This study found that the addition of visual feedback improved both neuromuscular control and overall performance. Such improvement is likely to be the result of better control of the rectus femoris muscle activation and coordination of both legs.

Patient-centered outcomes of high-velocity, low-amplitude spinal manipulation for low back pain: A systematic review - Corrected Proof

C.M. Goertz, K.A. Pohlman, R.D. Vining, J.W. Brantingham, C.R. Long — 2012-04-25

Abstract: Low back pain (LBP) is a well-recognized public health problem with no clear gold standard medical approach to treatment. Thus, those with LBP frequently turn to treatments such as spinal manipulation (SM). Many clinical trials have been conducted to evaluate the efficacy or effectiveness of SM for LBP. The primary objective of this paper was to describe the current literature on patient-centered outcomes following a specific type of commonly used SM, high-velocity low-amplitude (HVLA), in patients with LBP. A systematic search strategy was used to capture all LBP clinical trials of HVLA using our predefined patient-centered outcomes: visual analogue scale, numerical pain rating scale, Roland-Morris Disability Questionnaire, and the Oswestry Low Back Pain Disability Index. Of the 1294 articles identified by our search, 38 met our eligibility criteria. Like previous SM for LBP systematic reviews, this review shows a small but consistent treatment effect at least as large as that seen in other conservative methods of care. The heterogeneity and inconsistency in reporting within the studies reviewed makes it difficult to draw definitive conclusions. Future SM studies for LBP would benefit if some of these issues were addressed by the scientific community before further research in this area is conducted.

Hip and knee joint kinematics during a diagonal jump landing in anterior cruciate ligament reconstructed females - Corrected Proof

2012-04-20

Abstract: Anterior cruciate ligament (ACL) injury is a common injury encountered by sport medicine clinicians. Surgical reconstruction is the recommended treatment of choice for those athletes wishing to return to full-contact sports participation and for sports requiring multi-directional movement patterns. The aim of ACL reconstruction is to restore knee joint mechanical stability such that the athlete can return to sporting participation. However, knowledge regarding the extent to which lower limb kinematic profiles are restored following ACL reconstruction is limited. In the present study the hip and knee joint kinematic profiles of 13 ACL reconstructed (ACL-R) and 16 non-injured control subjects were investigated during the performance of a diagonal jump landing task. The ACL-R group exhibited significantly less peak knee joint flexion (P=0.01). Significant between group differences were noted for time averaged hip joint sagittal plane (P<0.05) and transverse plane (P<0.05) kinematic profiles, as well as knee joint frontal plane (P<0.05) and sagittal plane (P<0.05) kinematic profiles. These results suggest that aberrant hip and knee joint kinematic profiles are present following ACL reconstruction, which could influence future injury risk.

Association between history and physical examination factors and change in lumbar multifidus muscle thickness after spinal manipulation in patients with low back pain - Corrected Proof

2012-04-19

Abstract: Understanding the clinical characteristics of patients with low back pain (LBP) who display improved lumbar multifidus (LM) muscle function after spinal manipulative therapy (SMT) may provide insight into a potentially synergistic interaction between SMT and exercise. Therefore, the purpose of this study was to identify the baseline historical and physical examination factors associated with increased contracted LM muscle thickness one week after SMT. Eighty-one participants with LBP underwent a baseline physical examination and ultrasound imaging assessment of the LM muscle during submaximal contraction before and one week after SMT. The relationship between baseline examination variables and 1-week change in contracted LM thickness was assessed using correlation analysis and hierarchical multiple linear regression. Four variables best predicted the magnitude of increases in contracted LM muscle thickness after SMT. When combined, these variables suggest that patients with LBP, (1) that are fairly acute, (2) have at least a moderately good prognosis without focal and irritable symptoms, and (3) exhibit signs of spinal instability, may be the best candidates for a combined SMT and lumbar stabilization exercise (LSE) treatment approach.

Influence of the intensity of a conditioning contraction on the subsequent twitch torque and maximal voluntary concentric torque - Corrected Proof

2012-04-18

Abstract: This study aimed to clarify the influence of the intensity of a conditioning contraction on subsequent isometric twitch and maximal voluntary concentric torques. Subjects (n=12men) performed voluntary isometric plantar flexion for six seconds as a conditioning contraction, at intensities of 40%, 60%, 80% and 100% of a maximal voluntary isometric contraction (MVIC). Before and immediately after the conditioning contraction, isometric twitch and maximal voluntary concentric (180°/s) plantar flexion torques were determined. Surface electromyograms were recorded from the triceps surae muscles and M-wave amplitudes and root-mean-square values of the electromyographic signals (RMSEMG) were calculated. The isometric twitch torque increased significantly after conditioning contraction at all intensities (P<0.05), whereas maximal voluntary concentric torque increased significantly only at 80% and 100% MVIC conditions (P<0.05). It is concluded that during a six second conditioning contraction, the effect of the intensity of a conditioning contraction on subsequent torque development is different between an isometric twitch and maximal voluntary concentric contractions, with the latter being less affected.

The basis for spinal manipulation: Chiropractic perspective of indications and theory - Corrected Proof

Charles N.R. Henderson — 2012-04-18

Abstract: It is reasonable to think that patients responding to spinal manipulation (SM), a mechanically based therapy, would have mechanical derangement of the spine as a critical causal component in the mechanism of their condition. Consequently, SM practitioners routinely assess intervertebral motion, and treat patients on the basis of those assessments.In chiropractic practice, the vertebral subluxation has been the historical raison d’etre for SM. Vertebral subluxation is a biomechanical spine derangement thought to produce clinically significant effects by disturbing neurological function. This paper reviews the putative mechanical features of the subluxation and three theories that form the foundation for much of chiropractic practice. It concludes with discussion of subluxation as an indicator for SM therapy, particularly from the perspective that subluxation may be one contributory cause of ill-health within a “web of causation”.

Organization of physiological tremors and coordination solutions to postural pointing on an uneven stance surface - Corrected Proof

Mei-Chun Guo, Jeng-Feng Yang, Chien-Ting Huang, Ing-Shiou Hwang — 2012-04-13

Abstract: The study investigated the destabilization effect on multi-segment physiological tremors and coordinative control for a postural-suprapostural task under different stance conditions. Twenty volunteers executed postural pointing from a level surface and a seesaw balance board; meanwhile, physiological tremors of the whole postural system and fluctuation movements of fingertip/stance surface were recorded. In reference to level stance, seesaw stance led to much fewer tremor increments of the upper limb and less fluctuation movement of the fingertip than tremor increment of the lower limb and rolling movement of the stance surface. Tremor coupling between the adjacent segments organized differentially with stance surface. In reference to level stance, seesaw stance reinforced tremor coupling of the upper limb but enfeebled the coupling in the arm-lumbar and calf-foot complexes. Stance-related differences in physiological tremors could be explained by characteristic changes in the primary and secondary principal components (PC1 and PC2), with relatively high communality with segment tremors of the lower and upper limbs, respectively. Seesaw stance introduced a prominent 4–8Hz spectral peak in PC1 and potentiated 1–4Hz and 8–12Hz spectral peaks of PC2. Structural reorganization of physiological tremors with stance configuration suggests that seesaw stance involves distinct suprapostural and postural synergies for regulating degree of freedom in joint space.

The role of spinal manipulation in addressing disordered sensorimotor integration and altered motor control - Corrected Proof

Heidi Haavik, Bernadette Murphy — 2012-04-09

Abstract: This review provides an overview of some of the growing body of research on the effects of spinal manipulation on sensory processing, motor output, functional performance and sensorimotor integration. It describes a body of work using somatosensory evoked potentials (SEPs), transcranial magnetic nerve stimulation, and electromyographic techniques to demonstrate neurophysiological changes following spinal manipulation. This work contributes to the understanding of how an initial episode(s) of back or neck pain may lead to ongoing changes in input from the spine which over time lead to altered sensorimotor integration of input from the spine and limbs.

Vertebral artery strains during high-speed, low amplitude cervical spinal manipulation - Corrected Proof

W. Herzog, T.R. Leonard, B. Symons, C. Tang, S. Wuest — 2012-04-09

Abstract: Spinal manipulative therapy (SMT) has been recognized as an effective treatment modality for many back, neck and musculoskeletal problems. One of the major issues of the use of SMT is its safety, especially with regards to neck manipulation and the risk of stroke. The vast majority of these accidents involve the vertebro-basilar system, specifically the vertebral artery (VA) between C2/C1. However, the mechanics of this region of the VA during SMT are unexplored. Here, we present first ever data on the mechanics of this region during cervical SMT performed by clinicians. VA strains obtained during SMT are significantly smaller than those obtained during diagnostic and range of motion testing, and are much smaller than failure strains. We conclude from this work that cervical SMT performed by trained clinicians does not appear to place undue strain on VA, and thus does not seem to be a factor in vertebro-basilar injuries.

Balance of hip and trunk muscle activity is associated with increased anterior pelvic tilt during prone hip extension - Corrected Proof

Hiroshige Tateuchi, Masashi Taniguchi, Natsuko Mori, Noriaki Ichihashi — 2012-03-30

Abstract: Prone hip extension has been used as a self-perturbation task to test the stability of the lumbopelvic region. However, the relationship between recruitment patterns in the hip and trunk muscles and lumbopelvic kinematics remains unknown. The present study aimed to examine if the balance of hip and trunk muscle activities are related to pelvic motion and low back muscle activity during prone hip extension. Sixteen healthy participants performed prone hip extension from 30° of hip flexion to 10° of hip extension. Surface electromyography (of the gluteus maximus, semitendinosus, rectus femoris, tensor fasciae latae, multifidus, and erector spinae) and pelvic kinematic measurements were collected. Results showed that increased activity of the hip flexor (tensor fasciae latae) relative to that of hip extensors (gluteus maximus and semitendinosus) was significantly associated with increased anterior pelvic tilt during hip extension (r=0.52). Increased anterior pelvic tilt was also significantly related to the delayed onset timing of the contralateral and ipsilateral multifidus (r=0.57, r=0.53) and contralateral erector spinae (r=0.63). Additionally, the decrease of the gluteus maximus activity relative to the semitendinosus was significantly related to increased muscle activity of the ipsilateral erector spinae (r=−0.57). These results indicate that imbalance between the agonist and antagonist hip muscles and delayed trunk muscle onset would increase motion in the lumbopelvic region.

Ultrasound-guided insertion of intramuscular electrodes into suboccipital muscles in the non-human primate - Corrected Proof

2012-03-23

Abstract: The head–neck system is highly complex from a biomechanical and musculoskeletal perspective. Currently, the options for recording the recruitment of deep neck muscles in experimental animals are limited to chronic approaches requiring permanent implantation of electromyographic electrodes. Here, we describe a method for targeting deep muscles of the dorsal neck in non-human primates with intramuscular electrodes that are inserted acutely. Electrode insertion is guided by ultrasonography, which is necessary to ensure placement of the electrode in the target muscle. To confirm electrode placement, we delivered threshold electrical stimulation through the intramuscular electrode and visualized the muscle twitch. In one animal, we also compared recordings obtained from acutely- and chronically-implanted electrodes. This method increases the options for accessing deep neck muscles, and hence could be used in experiments for which the invasive surgery inherent to a chronic implant is not appropriate. This method could also be extended to the injection of pharmacological agents or anatomical tracers into specific neck muscles.

David A. Winter, Ph.D., P.Eng. - Corrected Proof

Sandra Olney — 2012-03-23

David A. Winter, Ph.D., P.Eng., referred to as “the Muybridge of the 20th century” died on February 7, 2012 in his 82nd year after several months’ battle with cancer. He was Distinguished Professor Emeritus of the University of Waterloo, Waterloo, Canada, where he made extensive contributions to biomechanics, motor control and electromyography in the kinesiology of human posture and movement.

Visceral responses to spinal manipulation - Corrected Proof

Philip S. Bolton, Brian Budgell — 2012-03-22

Abstract: While spinal manipulation is widely seen as a reasonable treatment option for biomechanical disorders of the spine, such as neck pain and low back pain, the use of spinal manipulation to treat non-musculoskeletal complaints remains controversial. This controversy is due in part to the perception that there is no robust neurobiological rationale to justify using a biomechanical treatment of the spine to address a disorder of visceral function. This paper therefore looks at the physiological evidence that spinal manipulation can impact visceral function. A structured search was conducted, using PubMed and the Index to Chiropractic Literature, to construct of corpus of primary data studies in healthy human subjects of the effects of spinal manipulation on visceral function. The corpus of literature is not large, and the greatest number of papers concerns cardiovascular function. Authors often attribute visceral effects of spinal manipulation to somato-autonomic reflexes. While this is not unreasonable, little attention is paid to alternative mechanisms such as somato-humoural pathways. Thus, while the literature confirms that mechanical stimulation of the spine modulates some organ functions in some cohorts, a comprehensive neurobiological rationale for this general phenomenon has yet to appear.

Electromyographic models to assess muscle fatigue - Corrected Proof

Miriam González-Izal, Armando Malanda, Esteban Gorostiaga, Mikel Izquierdo — 2012-03-22

Abstract: Muscle fatigue is a common experience in daily life. Many authors have defined it as the incapacity to maintain the required or expected force, and therefore, force, power and torque recordings have been used as direct measurements of muscle fatigue. In addition, the measurement of these variables combined with the measurement of surface electromyography (sEMG) recordings (which can be measured during all types of movements) during exercise may be useful to assess and understand muscle fatigue. Therefore, there is a need to develop muscle fatigue models that relate changes in sEMG variables with muscle fatigue. However, the main issue when using conventional sEMG variables to quantify fatigue is their poor association with direct measures of fatigue. Therefore, using different techniques, several authors have combined sets of sEMG parameters to assess muscle fatigue. The aim of this paper is to serve as a state-of-the-art summary of different sEMG models used to assess muscle fatigue. This paper provides an overview of linear and non-linear sEMG models for estimating muscle fatigue, their ability to assess power loss and their limitations due to neuromuscular changes after a training period.

Trunk muscle activation during stabilization exercises with single and double leg support - Corrected Proof

2012-03-21

Abstract: The aim of this study was to analyze trunk muscle activity during bridge style stabilization exercises, when combined with single and double leg support strategies. Twenty-nine healthy volunteers performed bridge exercises in 3 different positions (back, front and side bridges), with and without an elevated leg, and a quadruped exercise with contralateral arm and leg raise (“bird-dog”). Surface EMG was bilaterally recorded from rectus abdominis (RA), external and internal oblique (EO, IO), and erector spinae (ES). Back, front and side bridges primarily activated the ES (approximately 17% MVC), RA (approximately 30% MVC) and muscles required to support the lateral moment (mostly obliques), respectively. Compared with conventional bridge exercises, single leg support produced higher levels of trunk activation, predominantly in the oblique muscles. The bird-dog exercise produced greatest activity in IO on the side of the elevated arm and in the contralateral ES. In conclusion, during a common bridge with double leg support, the antigravity muscles were the most active. When performed with an elevated leg, however, rotation torques increased the activation of the trunk rotators, especially IO. This information may be useful for clinicians and rehabilitation specialists in determining appropriate exercise progression for the trunk stabilizers.

Spinal manipulation epidemiology: Systematic review of cost effectiveness studies - Corrected Proof

Z.A. Michaleff, C.-W.C. Lin, C.G. Maher, M.W. van Tulder — 2012-03-19

Abstract: Background: Spinal manipulative therapy (SMT) is frequently used by health professionals to manage spinal pain. With many treatments having comparable outcomes to SMT, determining the cost-effectiveness of these treatments has been identified as a high research priority.Objective: To investigate the cost-effectiveness of SMT compared to other treatment options for people with spinal pain of any duration.Methods: We searched eight clinical and economic databases and the reference lists of relevant systematic reviews. Full economic evaluations conducted alongside randomised controlled trials with at least one SMT arm were eligible for inclusion. Two authors independently screened search results, extracted data and assessed risk of bias using the CHEC-list.Results: Six cost-effectiveness and cost–utility analysis were included. All included studies had a low risk of bias scoring ⩾16/19 on the CHEC-List. SMT was found to be a cost-effective treatment to manage neck and back pain when used alone or in combination with other techniques compared to GP care, exercise and physiotherapy.Conclusions: This review supports the use of SMT in clinical practice as a cost-effective treatment when used alone or in combination with other treatment approaches. However, as this conclusion is primarily based on single studies more high quality research is needed to identify whether these findings are applicable in other settings.

Reliability and validity of measuring scapular upward rotation using an electrical inclinometer - Corrected Proof

W. Steven Tucker, R. Lyndsey Ingram — 2012-03-19

Abstract: The aim of this study was to assess the reliability and validity of a modified two-dimensional electrical inclinometer to measure scapular upward rotation during static humeral elevation. Numerous techniques have been proposed to qualitatively and quantitatively measure upward rotation of the scapula. These techniques are limited by expense or an inability to be synchronized with other measurements, such as muscle activity and force output. For validity testing, static scapular upward rotation was measured separately with a digital protractor and electrical inclinometer while participants were at rest and 60°, 90° and 120° of humeral elevation in the scapular plane. For reliability testing, either 20min before or 20min after validity testing, participants performed the testing positions while measurements were taken with the electrical inclinometer only. Significant correlations existed between the modified electrical inclinometer and digital protractor at all four positions (r>0.996, p<0.001). The electrical inclinometer demonstrated good to excellent intra-rater reliability (ICC3,1>0.892, 95%CI: 0.785–0.988 and SEM<1.8°). These results support the use of the electrical inclinometer to measure scapular upward rotation. These findings provide clinicians and researchers with a practical instrument that can accurately measure scapular upward rotation in synchrony with other measurements, such as electromyography and isokinetic data.

Kinesiological research: The use of surface electromyography for assessing the effects of spinal manipulation - Corrected Proof

Greg Lehman — 2012-03-16

Abstract: Decreasing an elevated muscle tone is an often cited benefit of spinal manipulation. Spinal manipulation is theorized to disrupt an assumed pain-spasm-pain cycle that sufferers of low back pain may be experiencing. The current research has mostly investigated the short term influence of a single spinal manipulation on paraspinal muscle activity either at rest (e.g. standing or prone) or during simple movements (e.g. forward bend). The higher quality experiments to date have typically reported both reductions in muscle activity during lying prone or during the fully flexed position of forward bend. The only study measuring the long term influence of spinal manipulation has failed to document any change in muscle activity as measured with surface electromyography. Both manually delivered manipulations and manipulations delivered via a mechanical adjusting device have been associated with changes in muscle activation. Changes in muscle activity at muscles distant from the spinal joints manipulated (e.g. muscles in the upper limbs) have been documented following a single spinal manipulation however rather than the typical reduction in muscle activity an increase in resting activation has been reported. The state of muscle dysfunction (e.g. palpably tender or subjectively taut) may be a factor in achieving a myoelectric response to spinal manipulation. Currently, the clinical significance of short term changes in electromyographic amplitude following manipulation is unknown.

Grip pattern and finger coordination differences between pianists and non-pianists - Corrected Proof

Luciane Fernanda Rodrigues Martinho Fernandes, Ricardo Machado Leite de Barros — 2012-03-15

Abstract: The aim of this study was to assess differences of grip pattern and finger coordination in pianists and non-pianists, using hand tasks that were unrelated to pianistic practice. Eleven pianists with more than 10years of intensive practice were compared to 14 non-pianists. Both groups performed four tasks with their right hand: (1) gross grip at fast velocity; (2) gross grip at slow velocity; (3) hook grip at fast velocity; and (4) hook grip at slow velocity. The three-dimensional coordinates were reconstructed using a kinematic analysis system, and the flexion and extension angles of the metacarpophalangeal joints were calculated. The phase diagrams were qualitatively and quantitatively appraised in order to identify differences between the groups. Principal component analysis was used to assess differences between pianists and non-pianists in terms of the reproducibility and regularity of palmar grip cycles. Coefficients of correlation between the joint angles were used to analyze finger coordination during the tasks. The pianists showed better reproducibility and regularity in the palmar grip pattern, as well as finger movements that were more coordinated when performing different hand tasks.

Performance based objective outcome measures and spinal manipulation - Corrected Proof

Steven R. Passmore, Martin Descarreaux — 2012-03-14

Abstract: This paper provides a general overview of performance based outcome measures used in an attempt to objectively measure the ramifications of spinal manipulation. While not a systematic or exhaustive review it serves to categorize, and provide insight into the background, successes and shortcomings of measurement techniques used. The outcome measures are drawn from the full spectrum of approaches to research and are broken down into the following sections: (1) biomechanically constrained motor performance measures, (2) neurologically constrained performance measures and (3) perceptual, perceptual motor, and complex task constrained performance measures. The paper concludes with some future research directions to enhance the understanding of the impact of spinal manipulation, and how to objectively measure its mechanical and physiological effects on the human system.

Muscle loading and activation of the shoulder joint during humeral external rotation by pulley and variable resistance - Corrected Proof

Heikki Peltonen, Jari Arokoski, Mauri Kallinen, Teemu Pullinen — 2012-03-09

Abstract: Background: The aim of the study was to evaluate differences in the loading of glenohumeral joint muscles between a cable pulley machine (CP) and variable resistance machine (VR) during axial humeral external rotation.Methods: Eleven healthy male subjects took part in the study. Intramuscular electromyography from five muscles of the shoulder (medial deltoid, supraspinatus, infraspinatus and upper part of the trapezius), torque and power output was measured at different rotation angles and with different loads (10%, 50% and 100% of 1RM). Also the compressive and shear force in the glenohumeral joint was analyzed at the horizontal level at angles of rotation. External rotation was performed with a self-selected velocity on the scapular plane.Findings: In the CP the range of movement became narrower than in the VR with increasing workload (P<0.05). The activity of the infraspinatus did not grow in the CP after 50% load, while it did in the VR (P<0.01). The upper part of the trapezius was activated less in the CP than in the VR (P<0.01) machine when using 50% and 100% loads. In comparison with the CP, the shear forces that pull the head of the humerus in a posterior direction were more evenly distributed in the VR than in the CP at different angles of rotation (P<0.001).Interpretation: The VR seems to make a broader range of motion possible, lager activation the primary external rotators and evenly distributed shear forces than the CP. However, performing the exercise with VR and high load also activates the upper part of the trapezius.Relevance: These findings can be used in the development of exercise designs, methods and equipment for shoulder injury rehabilitation.

Whole-body vibration increases upper and lower body muscle activity in older adults: Potential use of vibration accessories - Corrected Proof

2012-03-09

Abstract: The current study examined the effects of whole-body vibration (WBV) on upper and lower body muscle activity during static muscle contractions (squat and bicep curls). The use of WBV accessories such as hand straps attached to the platform and a soft surface mat were also evaluated. Surface electromyography (sEMG) was measured for the medial gastrocnemius (MG), vastus lateralis (VL), and biceps brachii (BB) muscles in fourteen healthy older adults (74.8±4.5years; mean±SD) with a WBV stimulus at an acceleration of 40ms−2 (30Hz High, 2.5mm or 46Hz Low, 1.1mm). WBV increased lower body (VL and MG) sEMG vs baseline (no WBV) though this was decreased with the use of the soft mat. The addition of the bicep curl with hand straps had no effect on lower body sEMG. WBV also increased BB sEMG vs baseline which was further increased when using the hand straps. There was no upper body effect of the soft mat. This study demonstrates WBV increases both lower and upper body muscle activity in healthy older adults. Moreover, WBV accessories such as hand straps attached to the platform or a soft surface mat may be used to alter exercise intensity.

Biomechanical characterization of cervical spinal manipulation in living subjects and cadavers - Corrected Proof

Bruce Symons, Sarah Wuest, Timothy Leonard, Walter Herzog — 2012-03-09

Abstract: Background: Cervical spinal manipulative therapy (cSMT) is a common therapeutic modality used in the treatment of neck pain and headaches. Cadaveric necks have been used as a model for assessing the effects of cSMT on vertebral artery mechanics. However, there have been no previous studies comparing the biomechanical indices of cSMT performed in living subjects versus cadavers.Methods: The preload force, peak force and duration of cSMT performed by two chiropractors were recorded in 28 subjects with and without neck pain, and in five cadavers.Results: There were no statistical differences in terms of the preload, peak force and duration of cSMT in living subjects with versus without neck pain. However, all three parameters differed statistically in living subjects versus cadavers; and both preload and peak forces were significantly higher for cadaveric cSMT; the average peak force was 190.3±85.5N (mean±SD) in living subjects, versus 283.9±53.6N in cadavers. Furthermore, the duration was significantly faster for cadaveric cSMT (175±100ms in living subjects versus 120±30ms in cadavers. These observations were consistent for both chiropractors.Conclusions: When performed in cadavers, cSMT tends to be more “aggressive” in terms of all biomechanical indices used to describe cSMT.

Does a ‘tight’ hamstring predict low back pain reporting during prolonged standing? - Corrected Proof

Sean M. Raftry, Paul W.M. Marshall — 2012-03-09

Abstract: The purpose of this study was to investigate the relationship between hamstring passive stiffness and extensibility in asymptomatic individuals with the reporting of low back pain during 2-h prolonged standing. Twenty healthy participants with no history of low back pain (mean±SD, age 22.6±2.7years, height 1.74±0.09m, weight 76.2±14.8kg). Low back pain (VAS score; mm) was continuously monitored during 2-h prolonged standing. Hamstring extensibility, passive stiffness, and stretch tolerance were measured before and after prolonged standing using an instrumented straight leg raise (iSLR). Ten participants reported a clinically relevant increase (Δ VAS>10mm) in low back pain during prolonged standing. Hamstring extensiblity (leg°max), passive stiffness (Nm.°−1), and stretch tolerance (VAS; mm) were no different between pain developers and non-pain developers. No changes in hamstring measures were observed following 2-h prolonged standing. No relationship was observed in this study between measures of hamstring extensibility and the reporting of low back pain during prolonged standing. There is no evidence to recommend hamstring extensibility interventions (i.e. passive stretching) as a means of reducing pain reporting in occupations requiring prolonged standing.

Imitation of a bimanual task in preschool- and school-age children: A hierarchical construction - Corrected Proof

Lazhar Labiadh, Marie-Martine Ramanantsoa, Eveline Golomer — 2012-03-05

Abstract: The present study examined the development of bimanual interaction during the imitation of a live demonstration. To this end, children of five different age groups observed an adult model performing in an object manipulation task consisting to open a box with one hand, taking out an object with the other hand, and closing the box again, before they were asked to imitate this motor task under different imitation conditions. The children’s responses were videotaped, coded in dichotomous data, and then transformed in percentage scores. The main results showed that all children were able to imitate/attain the goal of the task. However, differences were observed for the different imitation conditions, which were also reflected in some age effects, while hand dominance was a strong constraint on imitation. Also, practice did not seem to increase the likelihood of model imitation. These findings confirm that imitation is a reconstruction mechanism hierarchically organized.

Relationship between back muscle endurance and voluntary activation - Corrected Proof

Emily Bottle, Paul H. Strutton — 2012-03-05

Abstract: There is some evidence that the Biering-Sorensen endurance test can discriminate low back pain sufferers from healthy individuals and can predict future back pain. This test relies on the subject’s ability to voluntarily drive the back muscles. This neural drive, termed voluntary activation (VA) can be measured using the twitch interpolation technique. The aim of the current study was to investigate the relationship between back muscle endurance and VA.Twenty-one healthy volunteers (10 males) participated. Bilateral electromyographic recordings were obtained from erector spinae and rectus abdominis. Back extensor torque was recorded using a dynamometer. The protocol consisted of measurement of VA (using magnetic stimulation of the brain and assessment of the sizes of the evoked twitches) and measurement of endurance.There was a linear correlation (r2=1, P<0.01) between voluntary torque and VA. The mean (SEM) endurance time was 174.9 (12.8)s. There was no correlation between endurance and VA at either 100% MVC (r2=0.01, P=0.72) or at 50% MVC (r2=0.11, P=0.16).These findings indicate that the endurance of the back muscles, as assessed using this widely utilised test does not appear to be related to a subject’s ability to drive their back muscles voluntarily either maximally or submaximally.

Comparison of electromyography and joint moment as indicators of co-contraction - Corrected Proof

Brian A. Knarr, Joseph A. Zeni, Jill S. Higginson — 2012-03-01

Abstract: Antagonistic muscle activity can impair performance, increase metabolic cost, and increase joint stability. Excessive antagonist muscle activity may also cause an undesirable increase in joint contact forces in certain populations such as persons with knee osteoarthritis. Co-contraction of antagonistic muscles measured by electromyography (EMG) is a popular method used to infer muscle forces and subsequent joint forces. However, EMG alone cannot completely describe joint loads that are experienced. This study compares a co-contraction index from EMG to a co-contraction index calculated from simulated muscle moments during gait.Co-contraction indices were calculated from nine healthy, able-bodied subjects during treadmill walking at self-selected speed. Musculoskeletal simulations that tracked experimental kinematics and kinetics were generated for each subject. Experimentally measured EMG was used to constrain the model’s muscle excitation for the vastus lateralis and semimembranosus muscles. Using the model’s excitations as constrained by EMG, muscle activation and muscle moments were calculated. A common co-contraction index (CCI) based on EMG was compared with co-contraction based on normalized modeled muscle moments (MCCI). While the overall patterns were similar, the co-contraction predicted by MCCI was significantly lower than CCI.Because a simulation can account for passive muscle forces not detected with traditional EMG analysis, MCCI may better reflect physiological knee joint loads. Overall, the application of two co-contraction methods provides a more complete description of muscle co-contraction and joint loading than either method individually.

Effect of exercise-induced fatigue on postural control of the knee - Corrected Proof

H. Hassanlouei, L. Arendt-Nielsen, U.G. Kersting, D. Falla — 2012-02-27

Abstract: Muscle fatigue is associated with reduced power output and work capacity of the skeletal muscle. Fatigue-induced impairments in muscle function are believed to be a potential cause of increased injury rates during the latter stages of athletic competition and often occur during unexpected perturbations. However the effect of fatigue on functionally relevant, full body destabilizing perturbations has not been investigated. This study examines the effect of muscle fatigue on the activation of the quadriceps and hamstrings to fast, full body perturbations evoked by a moveable platform. Surface electromyographic (EMG) signals were recorded from the knee extensor (vastus medialis, rectus femoris, and vastus lateralis) and flexor muscles (biceps femoris and semitendinosus) of the right leg in nine healthy men during full body perturbations performed at baseline and immediately following high intensity exercise performed on a bicycle ergometer. In each condition, participants stood on a moveable platform during which 16 randomized postural perturbations (eight repetitions of two perturbation types: 8cm forward slides, 8cm backward slides) with varying inter-perturbation time intervals were performed over a period of 2–3min. Maximal voluntary knee extension force was measured before and after the high intensity exercise protocol to confirm the presence of fatigue. Immediately after exercise, the maximal force decreased by 63% and 66% for knee extensors and flexors, respectively (P<0.0001). During the post-exercise postural perturbations, the EMG average rectified value (ARV) was significantly lower than the baseline condition for both the knee extensors (average across all muscles; baseline: 19.7±25.4μV, post exercise: 16.2±19.4μV) and flexors (baseline: 24.3±20.9μV, post exercise: 13.8±11.0μV) (both P<0.05). Moreover the EMG onset was significantly delayed for both the knee extensors (baseline: 132.7±32.9ms, post exercise: 170.8±22.9ms) and flexors (baseline: 139.1±38.8ms, post exercise: 179.3±50.9ms) (both P<0.05). A significant correlation (R2=0.53; P<0.05) was identified between the percent reduction of knee extension MVC and the percent change in onset time of the knee extensors post exercise. This study shows that muscle fatigue induces a reduction and delay in the activation of both the quadriceps and hamstring muscles in response to rapid destabilizing perturbations potentially reducing the stability around the knee.

Combined effects of fatigue and temperature manipulation on skeletal muscle electrical and mechanical characteristics during isometric contraction - Corrected Proof

2012-02-22

Abstract: Peripheral fatigue and muscle cooling induce similar effects on sarcolemmal propagation properties. The aim of the study was to assess the combined effects of muscle temperature (Tm) manipulation and fatigue on skeletal muscle electrical and mechanical characteristics during isometric contraction. After maximum voluntary contraction (MVC) assessment, 16 participants performed brief and sustained isometric tasks of different intensities in low (TmL), high (TmH) and neutral (TmN) temperature conditions, before and after a fatiguing exercise (6s on/4s off at 50% MVC, to the point of fatigue). During contraction, the surface electromyogram (EMG) and force were recorded from the biceps brachii muscle. The root mean square (RMS) and conduction velocity (CV) were calculated off-line. After the fatiguing exercise: (i) MVC decreased similarly in all Tm conditions (P<0.05), while EMG RMS did not change; and (ii) CV decreased to a further extent in TmL compared to TmN and TmH in all brief and sustained contractions (P<0.05). The larger CV drop in TmL after fatigue suggests that TmL and fatigue have a combined and additional effect on sarcolemmal propagation properties. Despite these changes, force generating capacity was not affected by Tm manipulation. A compensatory mechanism has been proposed to explain this phenomenon.

The effect of anterior cruciate ligament rupture on the timing and amplitude of gastrocnemius muscle activation: A study of alterations in EMG measures and their relationship to knee joint stability - Corrected Proof

David M. Klyne, Susan L. Keays, Joanne E. Bullock-Saxton, Peter A. Newcombe — 2012-02-22

Abstract: Changes in hamstring and quadriceps activity are well known in individuals with anterior cruciate ligament deficiency (ACLD) to potentially compensate for knee joint instability. However, few studies have explored gastrocnemius activity or its relationship to knee stability. The purpose of this study was therefore to examine the activation characteristics of medial gastrocnemius (MG) in ACLD subjects and relate any changes to knee joint laxity. Two subject cohorts were assessed: those with unilateral ACLD (n=15) and uninjured control subjects (n=11). Surface EMG of the left and right MG were recorded during a controlled single leg hop on each limb. Onset and offset of MG activation relative to take-off, during flight and landing were calculated as well as muscle activity (RMS). Passive antero-posterior knee laxity was measured with a KT1000 arthrometer during a maximal manual displacement test. Medial gastrocnemius activity on the injured side of ACLD participants demonstrated significantly prolonged activation in preparation to hop, minimal muscle inactivity prior to take-off, and increased duration of overall muscle activity when compared to the uninjured side and control subjects (p<0.05). Significant positive correlations were found between passive knee joint laxity and prolonged activation prior to knee bend. RMS of the muscle signal was not significantly different between limbs. Overall, MG on the ACLD side demonstrated longer activation, with minimal rest during the hop test, which may be an attempt to maintain knee stability. Furthermore, the strong relationship between knee laxity and prolonged muscle activation suggests that individuals with a loss of knee stability are more reliant on active control of the gastrocnemius muscle.

An algorithm for defining the onset and cessation of the flexion-relaxation phenomenon in the low back musculature - Corrected Proof

Sangeun Jin, Xiaopeng Ning, Gary A. Mirka — 2012-02-20

Abstract: The flexion-relaxation phenomenon (FRP) in the low back provides insights into the interplay between the active and passive tissues. Establishing a reliable algorithm for defining the lumbar angle at which the muscles deactivate and reactivate was the focus of the current paper. First, the EMG data were processed using six different smoothing techniques (no smoothing, moving average, moving standard deviation, Butterworth low pass filter at 0.5Hz, 5Hz, and 50Hz) herein called the processed EMG (pEMG). The FRP points were then defined using four thresholds (pEMG less than 3% MVC, pEMG less than 5% MVC, pEMG less than 2 times FRP pEMG, and pEMG less than 3 times FRP pEMG). Finally, a duration requirement was tested (no duration requirement, pEMG data must maintain threshold requirement for 50 data points). Each combination of smoothing, threshold, and duration were applied through a computer program to each muscle for all trials and established an EMG-off and EMG-on angle for each muscle. These estimates were compared to the gold standard of expert-identified EMG-off and EMG-on angles and the root mean square error (RMSE) between this gold standard and the predictions of the algorithms served as the dependent variable. The results showed that the most important factor to produce low values of RMSE is to utilize a Butterworth low pass filter of 5Hz or less and, if this is employed, there is no value to a duration requirement. The results also suggest that using the “3 times FRP pEMG” threshold technique may provide further improvements in these predictions.

Spinal manipulative therapy and somatosensory activation - Corrected Proof

J.G. Pickar, P.S. Bolton — 2012-02-20

Abstract: Manually-applied movement and mobilization of body parts as a healing activity has been used for centuries. A relatively high velocity, low amplitude force applied to the vertebral column with therapeutic intent, referred to as spinal manipulative therapy (SMT), is one such activity. It is most commonly used by chiropractors, but other healthcare practitioners including osteopaths and physiotherapists also perform SMT. The mechanisms responsible for the therapeutic effects of SMT remain unclear. Early theories proposed that the nervous system mediates the effects of SMT. The goal of this article is to briefly update our knowledge regarding several physical characteristics of an applied SMT, and review what is known about the signaling characteristics of sensory neurons innervating the vertebral column in response to spinal manipulation. Based upon the experimental literature, we propose that SMT may produce a sustained change in the synaptic efficacy of central neurons by evoking a high frequency, bursting discharge from several types of dynamically-sensitive, mechanosensitive paraspinal primary afferent neurons.

Effect of high-load and high-volume resistance exercise on the tensiomyographic twitch response of biceps brachii - Corrected Proof

2012-02-17

Abstract: The purpose of the present study was to assess the ability of TMG in detecting mechanical fatigue induced by two different resistance exercises on biceps brachii: high-volume (HV), and high-load (HL). Sixteen healthy subjects (age 25.1±2.6years; body mass 79.9±8.9kg; height 179±7.4cm) performed arm-curl in two different protocols (HV: 8×15×10kg, HL: 5×3×30kg). Tensiomyography was used to assess muscle response to both exercise protocols. The contractile capacity of biceps brachii significantly varied by means of the effects of potentiation and fatigue mechanisms that take place at different exercise phases. The most significant changes correspond to values of maximum radial displacement of muscle belly (Dm), sustained contraction time (Ts), relaxation time (Tr), and contraction velocity (Vc). The behavior of these parameters is, in general, similar in both exercise protocols, but they show subtle differences among them. During the first set, in both protocols, values for Vc increase, along with a decrease in Tr, Ts, and Dm values. Fatigue onset was evident from changes in such parameters, with HL being the first in showing these mechanisms. Tensiomyography has been shown to be highly sensitive in detecting fatigue-induced changes.

Assessment of eccentric exercise-induced muscle damage of the elbow flexors by tensiomyography - Corrected Proof

2012-02-15

Abstract: Exercise induced muscle damage (EIMD) impairs maximal torque production which can cause a decline in athletic performance and/or mobility. EIMD is commonly assessed by using maximal voluntary contraction (MVC), creatine kinase (CK) and muscle soreness. We propose as an additional technique, tensiomyography (TMG), recently introduced to measure mechanical and muscle contractile characteristics. The purpose of this study was to determine the validity of TMG in detecting changes in maximal torque following EIMD. Nineteen participants performed eccentric elbow flexions to achieve EIMD on the non- dominant arm and used the dominant elbow flexor as a control. TMG parameters, MVC and rate of torque development (RTD) were measured prior to EIMD and repeated for another six consecutive days. Creatine kinase, muscle soreness and limb girth were also measured during this period. Twenty four hours after inducing EIMD, MVC torque, RTD and TMG maximal displacement had significantly (p<0.01) declined by 37%, 44% and 31%, respectively. By day 6 MVC, RTD and TMG recovered to 12%, 24% and 17% of respective pre-EIMD values. In conclusion, as hypothesised TMG maximal displacement significantly followed other standard EIMD responses. This could therefore be useful in detecting muscle damage from impaired muscle function and its recovery following EIMD.

Influence of amplitude cancellation on the accuracy of determining the onset of muscle activity from the surface electromyogram - Corrected Proof

2012-02-13

Abstract: The purpose of the study was to quantify the influence of amplitude cancellation on the accuracy of detecting the onset of muscle activity based on an analysis of simulated surface electromyographic (EMG) signals. EMG activity of a generic lower limb muscle was simulated during the stance phase of human gait. Surface EMG signals were generated with and without amplitude cancellation by summing simulated motor unit potentials either before (cancellation EMG) or after (no-cancellation EMG) the potentials had been rectified. The two sets of EMG signals were compared at forces of 30% and 80% of maximum voluntary contraction (MVC) and with various low-pass filter cut-off frequencies. Onset time was determined both visually and by an algorithm that identified when the mean amplitude of the signal within a sliding window exceeded a specified standard deviation (SD) above the baseline mean. Onset error was greater for the no-cancellation conditions when determined automatically and by visual inspection. However, the differences in onset error between the two cancellation conditions appear to be clinically insignificant. Therefore, amplitude cancellation does not appear to limit the ability to detect the onset of muscle activity from the surface EMG.