Age-Related changes in joint power during gait: Adaptations in middle-aged adults to maintain walking speed.

Across the adult lifespan, gait speed is thought to be maintained through midlife and starts to decrease after age 60. Reducing the piston-like drive of the gastrocnemius during push-off (ankle joint power burst A2) is a change that decreases gait speed and increases stability in older adults. As physiological systems begin to decline during midlife, middle-aged adults may adjust their joint powers to minimize destabilization while maintaining a gait speed comparable to that of younger adults. The purpose is to quantify changes in joint powers during gait as a function of advancing age; younger (ages 20-35), middle-aged (ages 50-64), and older adults (ages 65-79). Participants walked at their self-selected speed, for ten trials, along a 15 m walkway. Joint powers for the hip, knee, and ankle were calculated. Older adults walked slower (1.33 m/s) than the younger and middle-aged groups (1.44 and 1.44 m/s, respectively). Middle-aged and older adults had lower ankle energy generation (A2) than younger adults. Middle-aged adults had lower ankle energy absorption (A1) than the other two age groups. Lower A2 reduces the piston-like push-off during late stance presumably to reduce the associated instability. However, the reduced energy generation did not decrease speed in middle-aged adults because energy absorption was reduced during mid-stance (A1). The reduced absorption allowed the body to rotate forward over the ankle faster and maintain gait speed despite reduced energy generation during push-off. Thus, middle-aged adults flexibly adapted both energy generation and absorption to maintain gait speed, a novel finding.