Effect of loading parameters on motor performance during a dynamic weight-shift task

- Ground reaction forces were measured during a dynamic weight-shift task.
- Motor performance and motor skill acquisition were measured in 12 healthy adults.
- Performance accuracy was affected by both the weight-load size and frequency.

Controlling weight shift (WS) is essential to performing motions safely and smoothly during daily and athletic activities. This study investigated the impact of loading parameters on the motor performance and difficulty level of a dynamic WS task performed while standing. Twelve healthy young adults (21.2 ± 0.9 years, 53.5 ± 7.4 kg) were asked to match the target and their weight loads using visual feedback displayed on a computer monitor. Motor performance was estimated by assessment of loading accuracy and pace of motor skill acquisition, measured as a proxy of difficulty level, was estimated by assessment of learning rate. As predicted, both loading accuracy values decreased with increasing target frequency. Notably, the interaction of loading size and frequency had a significant effect on loading accuracy, which was increasingly impaired as the weight load increased at frequencies greater than 0.5 Hz. Moreover, the pace of motor skill acquisition in a dynamic WS task while standing was affected by the weight-load speed independently of the weight-load size. These results indicate that loading accuracy is affected by both the weight-load size and frequency and that 0.5 Hz is a critical frequency at which the difficulty level increases during dynamic WS tasks while standing in healthy youths. These findings suggest that the adequacy of the initial settings used regarding loading size and frequency is an important consideration in rehabilitative and athletic training aimed at evaluating and improving WS while standing.