Abstract
In a 1977 study, task performance was shown to decline with exposure to combined vertical vibration, as opposed to single sinusoidal vibration. In the current study, electromyography was used to capture muscle activity of the back during single and combined whole-body vertical vibration to explore this phenomenon. Fourteen, right-handed males were exposed to four vertical vibration conditions (no vibration, 2.5 Hz, 5.0 Hz, and vibration combining 2.5 Hz with 5.0 Hz) while sitting upright. Subjects performed a four-limb task during testing. The participants were able to respond cyclically to the 2.5 Hz and 5 Hz vibration conditions when encountered independently, but only responded to the 2.5 Hz component of the combined vibration condition. Responding only at 2.5 Hz to a combined signal would allow the energy at 5.0 Hz to be dissipated elsewhere in the body, possibly explaining the performance decrement noted previously. This study has revealed a significant musculoskeletal control system limitation.