Date of Award
Spring 2023
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Exercise Science
Program
Exercise and Rehabilitation Science
First Advisor
Hunter, Sandra K.
Second Advisor
Sundberg, Christopher W.
Third Advisor
Ng, Alexander V.
Abstract
The mechanisms for the loss in limb muscle power output in old (60-79 years) and very old adults (≥80 years) and whether these mechanisms differ between older men and women are not well-understood. The aims of the thesis are to 1) compare peak power output of the knee extensor muscles between young, old, and very old adults and 2) determine the physiological mechanisms for the age-related loss of power in men compared with women. 31 young (22.9±3.0 years, 16 men), 83 old (70.4±4.9 years, 44 men), and 16 very old adults (85.8±4.2 years, 7 men) performed maximal isokinetic contractions at 15 different velocities (0-450°/s) to identify peak power output across the torque-velocity relationship. Voluntary activation (VA) and contractile properties were assessed with transcranial magnetic stimulation and electrical stimulation of the femoral nerve. Old and very old men and women generated less power than young across all velocities (p<0.01). Compared with young men (673±163 W), peak power output was ~42% lower in old (399±119 W, p <0.01) and ~67% lower in very old (225±51 W, p<0.01). For women, peak power output was ~49% lower in old (223±45 W, p<0.01) and ~60% lower in very old (170±40 W) compared with young (428±79 W, p<0.01). Factors within the muscle were the most highly associated variables with peak power for both sexes including; lean thigh tissue mass (men: R^2 =0.53, p<0.01; women: R^2=0.34, p<0.01), potentiated twitch amplitude (men: R^2=0.60, p<0.01; women: R^2=0.55, p<0.01), and rate of twitch torque development (men: R^2=0.69, p<0.01; women: R^2=0.57, p<0.01). In contrast, VA was weakly associated with peak power output for women (R^2=0.13, p=0.01) and not associated at all for men (R^2=0.03, p=0.18). Muscle activation (% peak EMG amplitude) of the vastus lateralis during the maximal power contraction was not associated with peak power output for men (R^2=0.01, p=0.37) or women (R^2=0.00, p=0.88). These data suggest that the age-related loss in power of the knee extensor muscles is due primarily to factors within the muscle for both men and women, and that impaired neural activation may play a minor role in the loss in power output for women.