Ground contact characteristics of Tai Chi gait.

BACKGROUND To date, no direct measurement has been done that quantitatively characterizes the foot-ground contact during Tai Chi Chuan movements. The goal of this study was to quantify the biomechanical characteristics of foot-ground contact during a Tai Chi gait (TCG), one of the basic but common Tai Chi Chuan movements. METHODS The ground reaction force profiles, center of pressure (COP) and plantar pressure patterns under the stance foot of TCG were directly measured in a sample of 10 healthy young individuals. RESULTS The medial force reached a peak value of 12 +/- 2% body weight (BW) during early stance. The vertical force reached and maintained a peak value of 109 +/- 2% BW during single stance, and shifted within a range of 10% and 70% BW during double stance phases. There was a uniformly small rate of loading in all three directions throughout stance. The peak plantar pressure was fairly constant throughout stance in the rear-foot region (maximum value of 0.27 +/- 0.07 kPa/kg), but changed from 0 to 0.16 +/- 0.04 kPa/kg in the fore-foot region. The peak pressure difference between the fore-foot and rear-foot regions was less than 0.06 +/- 0.01 kPa/kg during single stance and the second double stance. The maximum plantar contact area during TCG was 60 +/- 9% of the foot area. The foot COP displaced largely during the early and late part of the stance and maintained fairly stationary during single stance. The maximum COP displacement in the medial-lateral direction was 64 +/- 8% of foot width. CONCLUSIONS TCG had a low impact force, a fairly evenly distributed body weight between the fore-foot and rear-foot regions, and a large medial-lateral displacement of the foot COP.