Composite variable of lower extremity muscle strength and balance ability for evaluating risks of mobility limitation and falls in community-dwelling older adults

Ground reaction force (GRF) in sit-to-stand (STS) movement is used mainly for evaluating lower extremity muscle strength. We attempted to evaluate not only lower extremity muscle strength, but also balance ability from GRF in STS movement. This study aimed to investigate the relationship between GRF variables, including composite variables, which are the combination of parameters representing lower extremity muscle strength and balance ability, and mobility limitation and falls. This study included 381 community-dwelling older adults (73.8 ± 5.3 years; 45.9% men). We measured the maximal rate of force development over 87.5 ms/body weight (RFD8.75/w) and peak reaction force/body weight (F/w) to evaluate lower extremity muscle strength. We also measured lateral load sway divided by the change in vertical load/second (vx/vw) to evaluate balance ability. We then created composite variables of these variables. To perform logistic regression analysis separated by gender, three groups based on the tertile of each variable were used. Composite variables that comprised the Rv score, which was the combination of RFD8.75/w and vx/vw, and Fv scores, which combined F/w and vx/vw, were especially effective for evaluating the risk of mobility limitation in both genders. In evaluating the fall risk, the Rv and Fv scores of the poor group in women only showed significantly higher odds ratios of 2.74 (95% CI: 1.21 - 6.20) and 3.02 (95% CI: 1.31 - 6.96), respectively. These results suggest that the composite variables, Rv and Fv scores, are superior for evaluating risks of mobility limitation and falls, rather than each single variable.