Muscular strength and power generating ability decline with advancing age. Older adults adapt their lower limb motor patterns to cope with these declines in muscle function. When mechanical demands approach limits of lower limb muscular capacity, motor patterns must be adapted to produce a desired movement. The term “motor pattern” is used to broadly represent the kinematic and kinetic profile of a person accomplishing a given task. Generally, these adaptations involve higher reliance on stronger proximal muscles to compensate for limitations or weakness of distal muscles. Three studies were conducted to examine factors affecting differences between older and young adults in lower extremity mechanics for walking and cycling. In the first two studies, the effects of physical activity status, walking speed, and step length on lower extremity motor patterns of older and young adults were examined. As walking speed and step length increased, lower extremity muscular effort, as reflected by joint moments and power, increased. Differences in motor patterns between older and young participants, were preserved for multiple speed and step length conditions. In general, older adults showed higher reliance on hip musculature to compensate for lower muscle strength of plantarflexors. Moreover, sedentary and older groups, who had lower leg strength, exhibited similar lower limb motor patterns during walking. Likewise, physically active and young participants, who had higher lower extremity strength, displayed similar lower limb motor patterns. Consistent with the 2008 Physical Activity Guidelines for Americans, these results suggest that adopting and maintaining a physically active life-style can help maintain walking abilities in older adults. When cycling at a submaximal intensities, both older and young participants showed higher reliance on muscles about the knee and had higher rates of energy cost for higher power outputs and cadences. Older adults had higher rates of energy cost and higher co-activation of thigh antagonistic muscles during cycling than young adults. The higher antagonist co-activation likely contributes to older adults higher energy cost. Considering all study outcomes, differences in motor patterns used by older and young adults were more apparent for walking than cycling. The less prominent age-related differences in cycling are likely related to its non-weight bearing characteristic, heavier reliance on hip and knee muscular effort, and the kinematically constrained nature of the cycling task.