Associations between Subtalar Muscle Strength and Balance Performance in Healthy Young and Old Adults

Background: Associations between lower limb muscle strength and balance performance in adults have previously been reported. However, the function of the foot muscles for postural control has not been understood, yet. Objective: The purpose of the present study was to investigate associations between pronator and supinator muscle strength, subtalar range of motion (ROM) and postural stability while standing under various conditions in young versus old adults. Methods: Using a custom-built apparatus equipped with a force transducer and an electrogoniometer, maximum voluntary isometric subtalar pronator and supinator strength as well as ROM tests were administered to 30 young (mean age: 25.1 years) and 30 old (mean age: 65.2 years) volunteers. Total active subtalar ROM, peak pronator and peak supinator torques were measured. While standing on a force plate, limits of stability (LOS) were determined during anterior–posterior (AP) and medio-lateral (ML) leaning tasks. Furthermore, sway distance and velocity during single-legged standing were measured. Correlation and regression analyses were conducted. Results: In both age groups, subtalar pronator muscle strength was related to AP-LOS (young: r = 0.36; old: r = 0.49). In young adults, subtalar supinator muscle strength was associated with ML-LOS (r = 0.41). The regression analyses revealed that summed subtalar muscle strength predicts 13 and 20% of the variance of AP-LOS in young and old adults, respectively. Summed subtalar muscle strength was found to predict 18% of the variance in ML-LOS in young but not in old adults. There were no correlations and no predictors found concerning subtalar muscle strength and postural sway during single-legged standing for both age groups. Conclusions: Longitudinal studies have to proof whether pronator muscle strength training might positively affect balance performance during AP leaning, specifically in old adults.