Interjoint coordination and the personal lift-assist device.

It has been suggested that interjoint coordination may serve to reduce joint stress and muscular demand and to maintain balance during dynamic lifting tasks, thus having implications for safe lifting practices. Before recommending the use of an on-body ergonomic aid, the Personal Lift-Assist Device (PLAD), it is important to determine any effects this device may have on interjoint coordination. Principal component analyses were applied to relative phase angle waveforms, defining the hip-knee and lumbar spine-hip coordination of 15 males and 15 females during a repetitive lifting task. When wearing the PLAD, users lifted with more synchronous hip-knee and lumbar spine-hip coordination patterns (P < .01). Furthermore, increases in load caused less synchronized interjoint coordination at both the hip-knee and lumbar spine-hip during the up and down phases of the lift (P < .01) for all conditions. No significant main effects of sex or significant interactions were observed on any of the outcome variables.