Wright, K. D., Graham, S. M., Moir, G. L., & Connaboy, C. (2012). The effects of additional load on the occurrence of bilateral-deficit: mechanical or neural factors? Presentation 2178 at the 59th Annual Meeting of the American College of Sports Medicine, San Francisco, California; May 29-June 2, 2012.

"Bilateral deficit (BD) is the reduction in the maximal voluntary force output from a synchronous bilateral contraction, when compared to the combined force outputs in biomechanically similar unilateral contractions (Bobbert et al., 2006). A number of theories for the occurrence of BD have been suggested; (1) an inhibition in neural drive or (2) differences in the mechanics between bilateral and unilateral jumping. If BD is principally a neural phenomenon, then a change in load should not affect the relative magnitude of BD observed. However, if there is a mechanical basis for BD then a difference will present in the observed BD between unloaded and loaded conditions."

This study examined the effects of an additional load of 10% body-weight (BW) on the occurrence of bilateral deficit in physically active students (M = 22; F = 4). Ss performed a series of counter-movement jumps under both unloaded and loaded (body weight plus 10%) conditions: 3 x unilateral left leg jumps, 3 x unilateral right leg jumps, and 3 x bilateral jumps. Thirty seconds rest was taken between jumps, with five minutes between sets of jumps. Ss were randomly assigned to one of two groups. Group 1 performed unloaded followed by loaded condition. Group 2 performed loaded followed by unloaded condition. Vertical jump height was determined using a jump mat. Analysis used the percentage difference (%diff) in jump height between the combined unilateral and bilateral jumps for the unloaded and loaded conditions.

No effect for jump order was observed. A significant reduction in bilateral deficit was observed in the jump heights recorded during the unloaded and loaded conditions.

Implication. A significant reduction in the difference between unilateral and bilateral vertical jumps resulted from the addition of extra load. This study shows that an alteration in an activity results in different mechanics.

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