Muscle fatigue, important determinants of muscle strength

3 Pages

Health + Exercise Science
Course Code
HES 319
Brian Tracy

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21 April Muscle Fatigue Muscle fatigue can be defined as an activity-related impairment of the physiologic processes that are involved in the production of muscle force We can study muscle fatigue for different types of muscular activity Sustained maximal contractions Repetitive maximal contractions Sustained sub-maximal isometric contractions until voluntary failure Repetitive sub-maximal isometric contractions until voluntary failure Muscle fatigue can be caused by changes in physiological mechanics at many different sites in the neuromuscular system Central drive to the motor neurons Activation of motor units and muscles Neuromuscular propagation Excitation-contraction coupling Availability of energy substrates The intracellular milieu, or environment The contractile apparatus Blood flow to the muscle – supply decreases with muscle force, venous outflow decreases During sustained submaximal contractions, the force does not change, but the EMG from the muscle increases This is due to an increased neural drive, or neural command, to the muscle that is not translated into changes in force This suggests that mechanisms distal to the sarcolemma are being altered during fatigue Muscle fibers begin to fail, therefore there must be increased output from the brain Muscle fatigue can be caused by failure of neuromuscular transmission There is a fairly large decrease in the force from repetitive nerve stimulation There is a lesser decrease in the force from intermittent muscle stimulation This suggests that the activation signal is not being fully transmitted to the contractile apparatus This effect is probably only significant during long periods of frequent activation of the motor units Transcranial magnetic stimulation Activates all of the corticospinal neurons in the cortex Can test the contribution of “central” mechanisms to fatigue Extra force elicited by a
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