The effects of walking speed on obstacle crossing in healthy young and healthy older adults.

The effects of walking speed and age on the peak external moments generated about the joints of the trailing limb during stance just prior to stepping over an obstacle and on the kinematics of the trailing limb when crossing the obstacle were investigated in 10 healthy young adults (YA) and 10 healthy older adults (OA). The peak hip and knee adduction moments in OA were 21-43% greater than those in YA (p<or= 0.046). The angular velocity of hip flexion from toe-off to when the toe was over the obstacle in OA was 20% less than that in YA (p=0.048). Eight external peak moments about the hip, knee, or ankle increased significantly with speed in both groups (p<or=0.01); the largest in the sagittal plane was 62% for knee flexion (p<or=0.0001). Toe-obstacle clearance was not affected. Trailing foot placement was affected by speed, but not by age. Speed produced a small change ( approximately 1 degrees ) in knee abduction-adduction, the only joint angle affected (p=0.022). The greater magnitudes of hip and ankle adduction moments occurring in the trailing limb of OA place larger demands on the hip and ankle abductors of the trailing limb to maintain dynamic balance when stepping over the obstacle with the leading limb.