Date of Award

Spring 1-1-2012

Document Type


Degree Name

Doctor of Philosophy (PhD)


Integrative Physiology

First Advisor

Alaa A. Ahmed

Second Advisor

Roger Enoka

Third Advisor

William C. Byrnes

Fourth Advisor

Brian L. Tracy


My dissertation is based on the overarching hypothesis that uphill and downhill walking are far more challenging than level walking for old adults and thus represent critical barriers to their independence and quality of life. In a series of five experiments/analyses, I studied the muscular actions and biomechanics of uphill and downhill walking in young and old adults to understand the factors that underlie the loss of uphill and downhill walking ability with age.

My first objective was to understand how advanced age affects the muscular actions of uphill and downhill walking. In my first two studies, I determined which muscle recruitment strategies young adults employ to walk uphill and downhill across a range of speeds and also showed that: 1) a disproportionate recruitment of hip vs. ankle muscles leads to gluteus maximus (a hip extensor) activity approaching the maximum isometric capacity of old adults at steep uphill grades and 2) neural changes with advanced age contribute notably more than muscle weakness to this reliance on hip muscles.

My second objective was to understand how advanced age affects the biomechanics of uphill and downhill walking. In my third study, I discovered that, in contrast to level walking and akin to a 4-wheel drive automobile, both the leading and trailing legs of young adults contribute progressively more to power generation with steeper uphill grade and to power absorption with steeper downhill grade. In my fourth study, I found that old adults exhibit impaired trailing leg propulsive function compared to young adults walking at the same speed during both level and uphill walking. Old adults compensate by performing greater positive work than young adults during the subsequent single support phase. Finally, in my fifth study, I used motion analysis and inverse dynamics techniques to quantify ankle, knee, and hip joint kinetics (moments and powers) and gained joint-level insights into the age-related muscular limitations restricting uphill walking ability in old adults.

Overall, my findings point to specific targets (e.g., propulsive forces) for biomechanical interventions that might improve the uphill and downhill walking ability of old adults, and thus enhance their quality of life.