Undergraduate Honors Theses

Thesis Defended

Fall 2011

Document Type



Integrative Physiology

First Advisor

roger M. Enoka, Ph.D.


Older adults use more muscle activity than younger adults when performing the same motor task. There is evidence to suggest that age alters the spinal and cortical pathways that control coordinated movements between agonist and antagonist muscles. The purpose of the current work was to investigate the changes in presynaptic inhibition across young and old adults at rest and during isometric plantar flexion. The results of the study indicate that young adults were able to modulate the presynaptic inhibition pathway to a greater extent than old adults. The young adults demonstrated a significant decrease in the D1 conditioned soleus H-reflex at rest and during a plantar flexion contraction at 10% of maximum (rest: 48.2% ±16.0% of test H-reflex, P=0.001; plantar flexion: 52.9% ±25.0%; P=0.001), whereas the old adults only displayed a significant decrease in the H-reflex at rest (rest: 88.0 ±10.4% of test H-reflex, P=0.022; plantar flexion: 102 ±18.6%, P= 0.97). Additionally, there were greater levels of activity, although statistically insignificant, in the antagonist muscle (tibialis anterior) in old adults during plantar flexion (young plantar flexion: 4.9 ±3.7% MVC; old plantar flexion: 7.8 ±3.5% MVC), further supporting the notion that older adults rely more on descending commands than incoming sensory feedback when performing different physical tasks. This work provides further insight on the decline in neural function and can inform clinical work an future mechanistic studies.