Dynamic stability in elders: momentum control in locomotor ADL.

BACKGROUND Momentum must be controlled in stable locomotor activities, including sit-to-stand and gait. The relationship of momentum control and balance maintenance in elders or in a balance-impaired population has not been studied. Although decreased locomotor speed has long been reported among elders, the literature is lacunar concerning the mechanical mechanisms underlying this slowing. The purpose of this study was to describe the whole body and upper body linear and angular momentum for healthy elders during sit-to-stand and gait and compare them to a group of balance-impaired elders who have bilateral vestibular hypofunction (BVH). METHODS Ten elders with BVH were matched to 10 healthy elders aged 67-90. Linear and angular momentum were calculated for sit-to-stand and for free speed and paced gait. Means and 95% confidence intervals were used to compare groups. RESULTS Elders with BVH used significantly less linear and angular momentum to rise from a chair than healthy elders and showed excessive lateral momentum during gait, despite walking at a slower velocity. CONCLUSIONS Healthy elders limit momentum generation by decreasing gait velocity, apparently because they lack sufficient strength or balance control to safely dissipate the momentum that a faster, less controlled gait engenders. Elders with BVH further limit momentum in locomotor activities to decrease their risk of falling, but are apparently unable to control lateral momentum during gait. Excessive lateral momentum in gait among balance-impaired elders leads to loss of balance, a frequent occurrence in this patient population.