Effect of arm swing on single-step balance recovery.

Balance recovery techniques are useful not only in preventing falls but also in many sports activities. The step strategy plays an important role especially under intense perturbations. However, relatively little is known about the effect of arm swing on stepping balance recovery although considerable arm motions have been observed. The purpose of this study was to examine how the arms influence kinematic and kinetic characteristics in single-step balance recovery. Twelve young male adults were released from three forward-lean angles and asked to regain balance by taking a single step under arm swing (AS) and arm constrained (AC) conditions. It was found that unconstrained arms had initial forward motion and later upward motion causing increased moment of inertia of the body, which decreased falling angular velocity and allowed more time for stepping. The lengthened total balance time included weight transfer and stepping time, although duration increase in the latter was significant only at the largest lean angle. In contrast, step length, step velocity, and vertical ground reaction forces on the stepping foot were unaffected by arm swing. Future studies are required to investigate optimal movement strategies for the arms to coordinate with other body segments in balance recovery and injury reduction.