Age-related changes in lower trunk coordination and energy transfer during gait.

The effects of aging on lower trunk (trunk-low-back joint-pelvis) coordination and energy transfer during locomotion has received little attention; consequently, there are scant biomechanical data available for comparison with patient populations whose upper body movements may be impaired by orthopaedic or neurologic disorders. To address this problem, we analyzed gait data from a cross-sectional sample of healthy adults (n = 93) between 20 and 90 yr old (n = 44 elderly, >50 yr old; n = 49 young, <50 yr old). Gait characteristics of elders were mostly typical: gait speed of elders (1.13 +/- 0.20 m/s) was significantly (P = 0.007) lower than gait speed of young subjects (1.20 +/- 0.18 m/s). Although elders had less low-back (trunk relative to pelvis) range of motion (ROM; P = 0.013) during gait than young subjects, no age-related differences were detected in absolute trunk and pelvis ROM or peak pitch angles during gait. Despite similar upper body postures, there was a strong association between age and pelvis-trunk angular velocity phase angle (r = 0.48, P < 0.001) with zero phase occurring at approximately 55 yr of age; young subjects lead with the pelvis while elderly subjects lead with the trunk. Age related changes in gait speed and low-back ROM were unable to explain the above findings. The trunk-leading strategy used by elders resulted in a sense reversal of the low-back joint power curve and increased (P = 0.013) the mechanical energy expenditure required for eccentric control of the lower trunk musculature during stance phase of gait. These data suggest an age-related change in the control of lower trunk movements during gait that preserves upper body posture and walking speed but requires a leading trunk and higher mechanical energy demands of lower trunk musculature-two factors that may reduce the ability to recover from dynamic instabilities. The behavioral and motor control aspects of these findings may be important for understanding locomotor impairment compensations in aging humans and in quantifying falls risk.