Upper extremity kinematic and kinetic adaptations during a fatiguing repetitive task (original) (raw)
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Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology, 2013
Different functional roles for the hands have been demonstrated, however leg control is not as well understood. The purpose of the present study was to evaluate bilateral knee neuromuscular control to determine if the limb receiving greater attention would have more well-tuned control compared to an unattended limb. Surface electrodes were placed on seven muscles of each limb, before standing on two force platforms. Visual feedback was given of the forces and moments of the ''focus limb,'' but not the ''unattended limb.'' Static isometric forces were matched with their focus limb, requiring their unattended limb to push in the opposite direction, using a combination of forward-backward-medial-lateral shear forces while muscle activity was collected bilaterally. There was a significant main effect for limb task (p = 0.02), with the medial hamstrings being more specific (p = 0.001) while performing the unattended limb and the lateral hamstring being more well-tuned (p = 0.007) while performing the focus limb task. The focus limb's medial and lateral gastrocnemius were principally active in the forwards direction, but only the unattended limb's lateral gastrocnemius was active in the backwards direction. Findings suggest unique neuromuscular control strategies are used for the legs depending on limb task.
Muscular and kinematic adaptations to fatiguing repetitive upper extremity work
Applied Ergonomics, 2019
Repetitive work is common in the modern workplace and the effects are often studied using fatigue protocols; however, there is evidence that the manner in which fatigue develops impacts the kinematic and muscular response to reduced physical capacity. The purpose of this study was to simultaneously evaluate muscular and kinematic adaptations during fatiguing, repetitive work until exhaustion. We measured muscle activity in 13 muscles in the shoulder and trunk, and captured full body kinematics while participants completed simulated, repetitive work tasks. Every 12 min, reference data were collected to quantify fatigue. This sequence continued until they reached the termination criteria. Participants displayed significant signs of muscle fatigue, loss of strength and increased perceived fatigue (p < 0.05). Analysis revealed a significant effect of time on posture and muscle activity that was both task and time dependent, and variable both between and within individuals. Participants were able to compensate for reduced physical capacity and maintain task performance through coordinated compensation strategies.
Forschende Komplementärmedizin / Research in Complementary Medicine, 2008
We commend the authors for attempting an in-depth literature review of such a diverse field as Specialised Kinesiology. Their recommendations for the tools that can be used in methods of analysis in future studies are well advised. The title of their paper, however, suffers from design flaws and is deceptive. This paper is primarily a review of Touch for Health Kinesiology and its family of techniques, which should be distinctly differentiated from Applied Kinesiology as defined by the International College of Applied Kinesiology.
Journal of PHYSIOLOGICAL ANTHROPOLOGY and Applied Human Science, 2002
T o i n v e s t i g a t e t h e b e h a v i o r o f mechanomyogram (MMG) and electromyogram (EMG) signals in the time and frequency domains during sustained isometric contraction, MMG and surface EMG were obtained simultaneously from four muscles: upper trapezius (TP), anterior deltoid (DL), biceps brachii (BB), and brachioradialis (BR) of 10 healthy male subjects. Experimental conditions consisted of 27 combinations of 9 postures [3 shoulder angles (SA): 0°, 30°, 60° and 3 elbow angles (EA): 120°, 90°, 60°] and 3 contraction levels: 20%, 40%, and 60% of maximum voluntary contraction (MVC). Subjective evaluations of fatigue were also assessed using the Borg scale at intervals of 60, 30, and 10 sec at 20%, 40%, and 60% MVC tests, respectively. The mean power frequency (MPF) and root mean square (RMS) of both signals were calculated. The current study found clear and significant relationships among physiological and psychological parameters on the one hand and SA and EA on the other. EA's effect on MVC was found to be significant. SA had a highly significant effect on both endurance time and Borg scale. In all experimental conditions, significant correlations were found between the changes in MPF and RMS of EMG in BB with SA and EA (or muscle length). In all four muscles, MMG frequency content was two or three times lower than EMG frequency content. During sustained isometric contraction, the EMG signal showed the wellknown shift to lower frequencies (a continuous decrease from onset to completion of the contraction). In contrast, the MMG spectra did not show any shift, although its form c hang ed (gen era lly r em ai ni ng ab ou t co nstant). Throughout the contraction, increased RMS of EMG was found for all tests, whereas in the MMG signal, a significant progressive increase in RMS was observed only at 20% MVC in all four muscles. This supports the hypothesis that the RMS amplitude of the MMG signal produced during contraction is highly correlated with force production. Possible explanations for this behavioral difference between the MMG and EMG signals are discussed.
Motor control and kinetics during low level concentric and eccentric contractions in man
Electroencephalography and Clinical Neurophysiology - Electromyography and Motor Control, 1996
Motor unit (MU) recruitment patterns were studied in 6 female subjects during dynamic contractions at relative workloads corresponding to 10% maximum voluntary contraction. The contractions consisted of a 20 ° elbow flexion (concentric contractionl and extension (eccentric contraction) and MU action potential trains were recorded from the brachial biceps muscle. The mean angular velocity of the dynamic contractions was 10°/s, during which a total of 119 MUs were identified. Additionally, a few contractions were studied at 20°/s during which 30 MUs were identified, and 9 MUs during the 4(/°/s contraction. About 60% of the identified MUs were active during the concentric as well as the eccentric phase for each of the velocities. Mean firing rate decreased significantly when the contraction changed from concentric to eccentric, whereas the number and properties of identified active MUs were similar, This emphasizes firing rate modulation as important during low level dynamic contractions rather than selective recruitment of different types of MUs in the concentric versus the eccentric phase. Similar kinetic demands occur frequently in occupational tasks, especially during monotonous work. The present data indicate that only a limited pool of MUs are being recruited during such tasks. Extensive recruitment of these MUs may cause fatigue and start a potentially vicious circle leading to work-related muscle disorders.
A review of occupationally-relevant models of localised muscle fatigue
International Journal of Human Factors Modelling and Simulation, 2015
Localised muscle fatigue (LMF) is a complex phenomenon that can differ between individuals, tasks, and muscles. Several muscle fatigue models (MFMs) have been developed in prior research. MFMs have potential practical value in ergonomics, given that LMF can impair performance, serve as a surrogate measure of injury risk, and may act as a causal factor for work-related musculoskeletal disorders. Existing MFMs are reviewed here, and which are broadly classified as either 'empirical' or 'theoretical'. Two specific MFMs, considered most ergonomically-relevant, were directly compared and some important differences in predictions were found. Identifying such differences is suggested as a useful approach, both for developing testable hypotheses and in guiding subsequent model development or refinement. Other potential approaches for improving future MFMs are also discussed, including expansion of model structure to account for individual differences (e.g., age, gender, and obesity), task related parameters, and variability in motor unit composition.
Journal of Electromyography and Kinesiology, 2013
Previous studies have associated amplitude and frequency characteristics of the electromyogram (EMG) to the risk of developing musculoskeletal disorders (MSDs) with repetitive tasks. However, few studies have investigated whether EMG variability and between-muscle activity characteristics may be associated with MSD risk. Twenty-six healthy volunteers (13 men, 13 women) performed a repetitive pointing task at shoulder height until scoring 8 on a Borg CR-10 scale. Electromyographic (EMG) signals were recorded from six neck/shoulder muscle sites. EMG amplitude (RMS), variability and mutual information (MI) among muscle pairs were computed. Muscle fatigue was evidenced by increased EMG RMS of four muscles (Upper Trapezius (UT): +17%; supraspinatus (SUPRA): +28%; middle deltoid: +13%; biceps brachii: +38%) and increased SUPRA variability. Correlations between minute 1 patterns and endurance time indicated that in women, initially high variability in UTR (r = 0.79) and SUPRA (r = 0.71) predicted higher endurance, whereas in men, initially low MI in LT-UT (À0.69) and in LT-SUPRA (À0.77) pairs predicted high endurance. Significant correlations suggest that variability and between-muscle patterns may be associated with fatigue and injury mechanisms, in a gender-specific way. Differing fatigue mechanisms between genders could help explain gender differences in injury mechanisms.