Loudness of verbal commands affect the Voluntary motor response. It seems the more intensity of verbal command, the more muscle contraction force. The purpose of thisstudy was to investigate the hypothesized effect of verbal command loundness onmagnitude of a resulting voluntary isometric contraction of triceps brachi muscle. Thirthy five female subjectsbetween ages of 18-30 performed four isometric contractions of the right triceps branchi muscle in response to fluctuations of verbal command in four stages with one-minute rest between stages. The muscle contraction force was measured at each stage by digital dynamometer. The intensity ofverbal commands in four stages was 66, 88,66, 88 decibels, respectively. Statistical analysis showed that increasing voice volume between first and second stage increased the muscle isometric force significantly (P<0.05) and decreasing voice volume approximately 22 db between second and third stage had significant effect on muscle force. But increasing voice volume between third stage did not have any significant effect on muscle force. Therefore the verbal command repetitions caused decrease of the primary effect.

Keywords: Key Words: 1) Acoustic stimulation 2) Muscle Contraction 3) Exercisetherapy 4) verbal Command

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