Age-related change in knee extensors and flexors rate of force development and its relation to postural stability

Introduction The ability to develop force rapidly, assessed as the rate of force development (RFD), in the knee extensors declines significantly with increasing age with negative impact in controlling posture 1. Little research has examined the age-related change in knee flexors RFD and its association with postural control. The aim of this study was to examine whether knee extensors and flexors RFD changes differently across lifespan and the relationship between knee flexors RFD and postural control, in both men and women. Methods Traditional centre of pressure (COP) and stabilogram parameters were examined on hard and soft surfaces with eyes open and closed. The RFD of knee extensors and flexors was assessed in static knee extension and flexion. Three groups of healthy volunteers, aged 18-30 (YG), 40-50 (MG) and 60-77 (OG) years, with 10 males and 10 females in each were recruited from local populations. General linear model multivariate analysis with group and gender as fixed factors were performed to compare the between group RFD differences, and bivariate correlations were used to examine the relationship between RFD and COP. Testing procedures were approved by the Human Research Ethics Committee of the University and written informed consent was obtained from the subjects. Results Significant lower RFD was found in OG compared with YG and MG in knee extensors (p \u3c 0.001 and p \u3c 0.05) and flexors (p \u3c 0.01 and p \u3c 0.001) RFD. The ability to develop force rapidly was higher in males than females in all age-groups (p \u3c 0.001). Both MG and YG were significantly different from OG in COP mean distance in anterior-posterior (AP) direction (p \u3c 0.05) and COP mean velocity in AP and medial-lateral (ML) directions (p \u3c 0.001). Moderate negative correlations were found between COP mean velocity in ML and knee extensors (r = -0.30 to -0.37, p = 0.05) and flexors (r = -0.32 to -0.40, p = 0.05 to 0.01) in all posture testing conditions. Discussion/conclusion Results showed significant age-related decreases in RFD of knee extensors and flexors. However, the ability to develop force is maintained until the fifth decade. The increased amount of postural sway in ML appears to be the best marker for risk of falling 2. Both knee extensors and flexors RFD showed significant negative correlations with COP mean velocity in ML. It appeared that the higher RFD the better the postural control performance. It is suggested that RFD be further examined for its validity as a good indicator in postural control, particularly in the knee flexors