Risk of falling: Predictors based on reduced strength in persons previously affected by polio

Objectives: To examine the contributions of sensorimotor factors to postural control and falling in people with prior polio and to determine whether these contributions differ from those found in normal populations. Design: Survey and case-control study. Setting: A falls and balance laboratory in Australia. Participants: Forty persons with prior polio (age range, 28-71y) and 38 age- and sex-matched control subjects. Interventions: Not applicable. Main Outcome Measures: Lower-limb muscle strength, sway, vision, lower-limb sensation, reaction time, foot-tapping speed, and falls. Results: Compared with the control subjects, the prior polio subjects performed similarly in sensory tests but worse in tests that involved a motor component. Within the prior polio group, lower-limb strength was strongly associated with postural sway on a compliant surface and explained more of the variance in sway than in control subjects. Prior polio subjects who fell multiple times had reduced lower-limb strength, slower reaction time, lower foot-tapping speed, and increased sway compared with those who fell less often. However, the rate of decline in lower-limb strength within the prior polio group did not exceed normal, age-related changes. Conclusions: This investigation of prior polio subjects provides an appropriate model for studying muscle weakness as a falls risk factor. Weakness was directly associated with falls, and had an indirect effect mediated through increased sway.