Abstract
Biomechanical research has shown that pull forces are largely generated by leg extension and by leaning (using one's body mass). However, this pulling technique requires sufficient friction in the foot floor interface. When pulling tasks are performed on slippery surfaces the center of gravity must be kept over the feet, thereby increasing the trunk's role in force generation. The purpose of this study was to investigate using electromyography (EMG) the muscle recruitments in the torso when pulling tasks are performed on slippery versus non-slippery surfaces. It was hypothesized that if a lifting belt acts to stiffen the torso, this would reduce the muscle activities detected with the EMG. Twelve subjects pulled at 40% of their maximal exertion values in four postures, with a lifting belt either tight or very loose, and under good footing conditions or extremely slippery footing conditions. When averaged across subjects all EMG activities increased under the slippery conditions. These increases ranged between 25 and 131 percent, although for some muscles the response to the slippery conditions was mediated by the pulling posture. The lifting belt had no effect on any of the muscle activities and created no differential muscle response due to the footing conditions or the pulling postures employed.
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