EVIDENCE FOR A NONLINEAR RELATIONSHIP BETWEEN LEG STRENGTH AND GAIT SPEED

Although the relationship between strength and physical performance in older adults is probably non-linear, few empirical studies have demon strated that this is so. In a population-based sample of adults aged 6 0-96 years (n = 409), leg strength was measured in four muscle groups (knee extensor, knee flexor, ankle plantar flexor, ankle dorsiflexor) of both legs using an isokinetic dynamometer. A leg strength score was calculated as the sum of the four strength measurements in the right leg. Usual gait speed n as measured over a 15.2 metre course. With a l inear model, leg strength explained 17% of variance in gait speed. Non -linear models (quadratic and inverse) explained significantly more va riance (22%). The nature of the non-linear relationship was that, in s tronger subjects, there mas no association between strength and gait s peed, while in weaker subjects, there mas an association. Body weight and age also explained significant amounts of variance in gait speed, while ses and height did not. The results supported the hypothesis of a non-linear relationship between leg strength and gait speed that is similar for older men and women. This finding represents a mechanism f or how small changes in physiological capacity may have substantial ef fects on performance in frail adults, while large changes in capacity have little or no effect in healthy adults.