Relationship between hip abductor rate of force development and mediolateral stability in older adults

Objective: To examine the relationship between hip abductor rate of force development (RFD) and performance of reactive and voluntary balance tasks in older adults. Design: Descriptive study using correlation and regression analyses. Setting: University research laboratory. Participants: A volunteer sample of 30 community-dwelling men and women over the age of 65 years. Interventions: Not applicable. Main Outcome Measures: Measures of hip abductor RFD, center of pressure (COP) displacement during compensatory stepping, and scores on 1-leg standing (OLS), and tandem gait tests. Hip abductor RFD was defined as the time required to go from 10% of maximum force to 60% of maximum force (10%-60% RFD) or to 90% of maximum force (10%-90% RFD). Results: Hip abductor RFD did not correlate with COP displacement during compensatory stepping, but did correlate significantly with OLS and tandem gait variables (P <.05). In predicting OLS scores, age (beta=-.485, P <.05) and 10% to 60% RFD (beta=-.354, P <.05) were significant predictors. In predicting tandem gait scores, 10% to 90% RFD (beta=384, P<.05) was the only significant predictor in the final regression model. Conclusions: Hip abductor RFD, tested under voluntary conditions, correlated with performance of clinical tests that challenge lateral stability. Our results support the idea that voluntary and reactive balance tasks involve different types of neuromuscular control.