Relationship between postural sway on an unstable platform and ankle plantar flexor force steadiness in community-dwelling older women

Background: Force steadiness is evaluated as force variability during constant force exertion around a target level. Ankle plantar flexor force steadiness is reported to be related to postural sway on an unstable platform in healthy young adults; however, this relationship in older adults is unclear. Research question: This study aimed to investigate whether ankle plantar flexor force steadiness was related to postural sway on stable and unstable platforms in older adults. Methods: Twenty-six community-dwelling older women participated in this study (72 +/- 6 years). Maximal isometric strength and force steadiness at 5%, 20 %, and 50 % of the maximal strength of ankle plantar flexion were assessed. Postural sway in the anteroposterior direction during bipedal standing was measured on stable and unstable platforms. Results: The results showed that force steadiness at any intensity level and maximal isometric strength were not related to postural sway on the stable platform. Force steadiness at 20 % of maximal strength alone was significantly correlated with postural sway on the unstable platform (rho = 0.441, p < 0.05). Significance: These results indicate that the ability to control muscle force could be important for postural stability on an unstable platform in older adults.