There are significant changes in gait across the life span, but particularly after the age of 70 years. This article reviews the physiology of gait and the motor control challenges during gait. The kinematics (motion) and the kinetics (moment and power) of normal gait of a database of healthy young and older adults are compared. Older subjects generate significantly lower peak ankle plantar flexor power during gait. The clinical significance of the reduction in ankle plantar flexion power is discussed.