UMass Amherst KIN 430 - BiomechLabG (4 pages)

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BiomechLabG



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BiomechLabG

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Pages:
4
School:
University of Massachusetts Amherst
Course:
Kin 430 - Biomechanics

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Biomechanics Laboratory G Muscle Force Electromyography Introduction One of the major forces influencing human movement is muscle force The central nervous system modulates the force produced by muscle via two mechanisms recruitment varying the number of active motor units and rate coding varying the stimulation frequency of active motor units The electrical potentials associated with recruitment and rate coding can be measured using electromyography EMG techniques and this gives an indication of the activation of the muscle The mechanical effects of muscle force production can be quantified as the torque they produced about the joints Previous researchers have shown that in isometric static contractions there is a direct relationship between EMG signal amplitude and muscle force or torque production the higher the EMG amplitude the greater the force or torque produced by the muscle In some muscles the relationship between EMG amplitude and force appears to be nearly linear first dorsal interosseous muscle see bottom of the page while in other muscles a non linear relationship has been reported deltoid muscle see bottom of the page In the case of the non linear trends the amplitude of the EMG signal increases disproportionately more than muscle force i e the line curves upwards The most common explanation is 1 muscles which rely on both recruitment and rate coding over the full force range yield linear EMG force relations while 2 muscle which fully recruit all motor units at submaximal force have to rely on rate coding exclusively in the higher force range yielding a disproportionate increase in EMG amplitude at higher forces EMG can be measured easily and non invasively but direct muscle force measurement in humans is rarely possible it is too invasive However in the case of incremental isometric muscle contractions such as in holding increasingly heavy weights muscle force should change proportionally with the torque that must be produced to support the weights



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