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Verbal instruction increases electromyographic (EMG) activity in the first three repetitions of an exercise, but its effect on an entire exercise set until failure is unknown. Once there are changes in motor unit recruitment due to fatigue, the effect of verbal instructions can change during different intervals of a set. This study analyzed whether verbal instruction emphasized the contraction of back muscles (i.e., myoelectric activity) during initial, intermediate, and final exercise repetitions performed until failure. Twenty participants with little or no experience in strength training performed a seated row exercise with and without verbal instruction. Surface electrodes were fixed over the latissimus dorsi, teres major, biceps brachii, and posterior deltoid muscles. Myoelectric activity was computed by mean amplitude and by the median frequency. We analyzed data with repeated measures MANOVA and found that, with verbal instruction, there was increased EMG mean amplitude in the latissimus dorsi (15.21%, p=0.030) and reduced EMG mean amplitude in the posterior deltoid (14.39%, p=0.018) on initial repetitions. Other muscle EMG amplitudes did not change. On intermediate repetitions, there was reduced signal amplitude only in the posterior deltoid (15.03%, p=0.022). The verbal instruction did not interfere with signal amplitude on final repetitions nor in the median frequency throughout the series. Verbal instruction seems to have little effect on increasing myoelectric activity of these targeted muscles in an entire set of a resistance training.

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