Electronic Thesis and Dissertation Repository


Master of Science




Dr. Timothy Doherty


This study investigated the relationship between motor unit (MU) properties and the strength and power of two lower limb muscles in healthy young and old adults. Twelve older adults (mean age, 77 ± 5 yrs) and twelve young adults (mean age, 24 ± 3 yrs) were studied. MU properties of the tibialis anterior (TA) and vastus medialis (VM) muscles were determined using decomposition-enhanced spike-triggered averaging (DE-STA). Motor unit number estimates (MUNE) of the TA were significantly reduced (p>0.05) in older adults (102 ± 76) compared to young adults (234 ± 109), primarily as a result of significantly larger surface-detected motor unit potentials (S-MUP) in older adults. Although VM S-MUP values were larger in older adults (60 ± 31 μV) compared to young (48 ±42), the difference was not significant. Maximal strength and power were significantly larger in both the TA and knee extensors of young adults compared to old. Maximal power output displayed greater deficits than isometric strength in both lower limb muscles of older adults. Results from this study indicate that there are changes in MU properties with age, and that this effect may be greater in the TA muscle. Further, power, especially in the knee extensors, may be a more sensitive measure of neuromuscular health than isometric strength, and should be the focus of exercise programs in elderly subjects.