Effect of age on center of mass motion during human walking.

The objective of this study was to investigate the effects of age and speed on body center of mass (COM) motion over a gait cycle. Whole body kinematics and ground reactions were recorded for 21 healthy young (21-32 y) and 20 healthy older adults (66-81 y) walking at 80%, 100% and 120% of preferred speed. The limb-induced COM accelerations and the work done on the COM by the limbs were computed. Despite walking with similar gait speeds, older adults did significantly (p<0.05) less positive work on the COM during push-off but then performed more positive work on the COM during midstance. As a result, older adults induced lower tri-axial COM accelerations via the trailing limb and higher vertical COM acceleration via the leading limb during double support. Older adults also reduced the mediolateral COM acceleration induced by the leading limb during the last third of double support. The forward and vertical components of the limb-induced COM accelerations were highly correlated (p<0.005) but were not correlated to the mediolateral component during double support, at any speed. Together, these results suggest that older adults use the leading limb to compensate for reduced vertical support and work done by the trailing limb. Further, older adults seem to adapt their gait patterns to reduce mediolateral COM accelerations. These findings are relevant for understanding the factors that underlie walking performance and lateral balance in old age.