Assessment of muscle activity using elastic resistance in strength exercise
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Strength exercise is associated with many positive health effects. However, many people do not have the opportunity to use conventional strength exercise equipment. Studies have shown that elastic resistance can induce similar levels of muscle activity as when exercising with isotonic resistance. The exercises previously investigated is however limited, and few studies have investigated whether muscle activation differ in the different phases of a contraction. In this study, face pulls, rowing, lateral pull-down, flies, reversed flies, and squat was performed by 29 subjects to assess the muscle activity level with elastic vs. isotonic resistance. Muscle activity was measured for three muscles in each exercise, using surface electromyography (EMG). The root-mean-square EMG signal was normalized to the maximal EMG (i.e., EMGmax) elicited during a maximal voluntary contraction. A linear encoder was also used so that any differences in muscle activity between the specific phases of a contraction could be assessed. The load used during the two modalities was matched using a 10 repetition maximum protocol. A significant main effect of exercise modality on muscle activity was found in 12 of the 18 combinations (three muscles in six exercises). Among these, eight combinations showed a significantly higher muscle activity using isotonic resistance, and four with elastic resistance. In the remaining six combinations, no significant differences were found. Significant interaction effects were found in 16 of the 18 combinations, i.e., muscle activity was affected by contraction phase. Overall, the absolute difference in muscle activity between elastic and isotonic resistance was small and not likely to have any physiological relevance. In conclusion elastic bands seem to be a feasible alternative to conventional strength exercise equipment for everyone interested in the benefits associated with strength exercise.