Association between ankle muscle strength and postural sway in older adults

Our study aimed to investigate the relationship between the strength of ankle muscles and postural sway in older adults during upright standing tasks of varying difficulty. Forty-three elderly participants (20 women) performed maximal isometric contractions and three distinct postural tasks: normal quiet stance (60 s), tandem stance (20 s), and one-legged stance (10 s) on a pressure platform. Postural sway was comprehensively assessed, considering center of pressure velocity, peak-to-peak amplitude, and standard deviation of center of pressure displacement in both anterior/posterior and medio/lateral directions. Additionally, weight distribution asymmetry in both directions served as a quantifiable index. Surface electromyographic (EMG) activity of the Tibialis Anterior, Medial Gastrocnemius, Rectus Femoris, and Semitendinosus was recorded during the postural tasks. Throughout the balance tasks, isometric plantar and dorsiflexion torque exhibited a consistent decrease as posture variables increased (p < 0.001). Narrowing the base of support led to significant increases in all postural variables and EMG activity (p < 0.01), with a more pronounced effect on ankle muscles compared to hip muscles (p < 0.0005). In the normal quiet stance (r = .683) and tandem stance (r = .641), greater center of pressure velocity correlated with a more symmetrical weight distribution between the legs. These results suggest that ankle muscle strength serves as a reliable predictor of static balance control, particularly in postures involving a narrow stance. Therefore, the enhancement of plantar flexors and dorsiflexors, rather than an exclusive focus on symmetrical weight distribution, is more likely to contribute to improved static balance control in older adults.