Effects of Tai Chi on joint proprioception and stability limits in elderly subjects

The objectives of this study were to examine whether elderly Tai Chi practitioners have developed better knee joint proprioception and standing balance control than control subjects. Tai Chi and control subjects (N = 21 each, aged 69.4 +/- SD 5.5 and 72.3 +/- 6.1 yr, respectively) were matched with respect to age, sex, and physical activity level. Passive knee joint repositioning was used to test joint proprioceptive acuity. Control of body sway during static standing and subjects' intentional weight shifting to eight different spatial limits of stability within their base of support were conducted using force platform measurements. Tai Chi practitioners were found to have better knee joint proprioceptive acuity, in that they made less absolute angle error (2.1 +/- 1.2 degrees ) than control subjects (4.0 +/- 3.4 degrees, with P = 0.023) in passive knee joint repositioning. No significant difference was found in the anteroposterior and mediolateral body sway during static standing (P > 0.05). However, Tai Chi practitioners initiated voluntary weight shifting in the limits of stability test more quickly (reaction time: 0.8 +/- 0.2 s for Tai Chi practitioners) than control subjects (1.1 +/- 0.3 s; P = 0.008). Moreover, they could lean further without losing stability (maximum excursion: 5.2 +/- 0.6% for Tai Chi practitioners and 4.6 +/- 0.5% for control subjects; P = 0.001) and showed better control of their leaning trajectory (directional control: 75.9 +/- 10.0% for Tai Chi practitioners and 68.5 +/- 6.9% for control subjects; P = 0.008). These results demonstrate that long-term Tai Chi practitioners had improved knee joint proprioception and expanded their limits of stability during weight shifting in stance.