Relationship between verbal command volume and magnitude of muscle contraction.

The purpose of this study was to investigate the hypothesized correlation between volume of a verbal command and magnitude of a resulting voluntary isometric muscular contraction, using a withdrawal-reinstatement (ABAB) research design. Nineteen volunteer male subjects between the ages of 18 and 30 years performed isometric contractions of the triceps brachii muscles in response to prerecorded verbal commands. With a volume increase of 22 decibels A scale, subjects averaged an 8 percent increase in muscle contraction strength, a difference that was significant at the .05 level. Through an awareness and use of the effects of voice volume on muscular contraction, the therapist may be able to improve the accuracy and consistency of examination methods, and increase the efficacy and efficiency of therapeutic procedures.