Neural control of postural sway: Relationship to strength measures in young and elderly adults

Age-related changes in postural sway are well-established, and studied from a control perspective using an inverted pendulum model. The purpose of the present work was to expand previous research in this area by investigating relationships between sway-related control parameters and musculoskeletal measures of muscle function and health. Eleven female older adults and eight female young adults completed blood draw, grip, leg extension, and balance tests. Serum levels of skeletal muscle-specific troponin T (sTnT), a biomarker for muscle health, were obtained from blood samples. Maximal grip force and leg extension torque were obtained from dynamometer tests. Center of pressure parameters were derived from force platform records obtained during eyes open and eyes closed balance tests. Sway control parameters were derived from an inverted pendulum model with PID-feedback control. Regression analyses were used to quantify the relationship between model parameters and grip strength, leg strength, and sTnT. Model integral gain (K_i) was observed to significantly predict grip strength in the eyes open condition. In the eyes closed condition, model derivative gain (K_d) was observed to significantly predict sTnT, and both proportional (K_p) and noise (K_n) model gains were observed to significantly predict grip and leg strength measures. Collectively, the relationship between control (K_i, K_d, K_p) and musculoskeletal health (strength, sTnT) parameters suggests a compensation mechanism, which may have served to minimize effects of reduced muscle function on sway amplitude, overshoot, and accuracy. Most associations were observed during eyes closed conditions, suggesting that visual input plays a larger role in regulating balance than the proposed compensation mechanisms. This work highlights the potential use for both strength and sTnT tests as biomarkers for postural control and balance impairment in older adults.