Improvement of isokinetic knee extensor strength and reduction of postural sway in the elderly from long-term Tai Chi exercise

Objectives: To compare isokinetic strength of leg muscles and foot center of pressure (COP) as a measure of sway between long-term Tai Chi practitioners and controls. Design: Cross-sectional study. Setting: Community setting. Participants: Twenty subjects in the Tai Chi group and 19 subjects in the control group (age, >55y). Intervention: Subjects in Tai Chi group had practiced Tai Chi for a minimum of 3 years. Main Outcome Measures: Concentric and eccentric strength of knee extensors and flexors at 60degrees/s and 120degrees/s, and foot COP displacement during quiet stance with eyes open or closed. Results: People in the Tai Chi group had significantly higher knee extensor strength at all speeds tested (P<.013), and smaller foot COP excursions for both eyes open and eyes closed conditions (P<.05) than people in control group. No significant difference existed in knee flexors between the 2 groups (P<.713). The COP excursions correlated significantly with the eccentric strength of knee extensors (P<.07) but not with the concentric strength of knee extensors (P<.14) or with the isokinetic strength of knee flexors at most of the speeds (P<.27). Conclusion: These findings support the hypothesis that the maintenance of eccentric strength of postural muscles in the lower extremities, which is beneficial for maintaining good postural stability, is helped through the long-term practice of Tai Chi.