Date of Award
Master of Science (MS)
Clinical and Translational Rehabilitation Health Science
Hunter, Sandra K.
Ng, Alexander V.
Hoeger Bement, Marie
Aging is accompanied by reductions in strength and contraction velocity, and increased fatigability of limb muscles during high-velocity dynamic contractions. These age-related changes affect functional tasks and are well described for the lower limb, with less known about the upper limb muscles. The aims of the thesis were to compare in young and old men and women: (1) maximal torque and power of the elbow flexor muscles across a range of isokinetic velocities, and (2) the neural (supraspinal) and muscular mechanisms of fatigue induced by high-velocity dynamic contractions of the elbow flexor muscles. 28 young (23.2 ± 2.6 years) men (n = 14) and women (n = 14) and 33 (72.6 ± 5.6 years) old men (n = 18) and women (n = 15) with the elbow flexor muscles performed: (1) maximal isokinetic contractions at 15 velocities to assess strength and power (0-450°/s), and (2) a dynamic fatiguing task involving 80 fast, maximal-effort contractions with a load equivalent to 20% of maximal voluntary isometric torque (MVIC). Before and after the fatiguing task the following were assessed: voluntary activation using motor cortical stimulation as a measure of supraspinal fatigue, and contractile properties evoked with electrical stimulation as a measure of muscular mechanisms. The elbow flexor muscles of the old adults were weaker and less powerful than young adults across all the velocities assessed (P<0.01), although voluntary activation was similar between the age groups (P>0.05). Some young and old adults were not able attain higher contraction velocities, primarily driven by the women. Old adults were more fatigable than young adults (P<0.001, 15% difference) with now sex differences (P>0.05). Old adults exhibited a larger reduction in voluntary activation (P=0.036, 7.5% age difference) and greater increase in relaxation in the old adults (55%) than the young (36%) following the fatiguing task. The elbow flexor muscles of old men and women were weaker and less powerful than young, but this was not due to differences in voluntary activation. The greater fatigability of elbow flexor muscles in the old adults however, was due to both supraspinal mechanisms and slowing of the muscle that occurs with aging.
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