Greater bilateral deficit in leg press than in handgrip exercise might be linked to differences in postural stability requirements.

Bilateral deficit is defined as the difference in the summed force between contracting muscles alone and contracting contralateral homologous muscles in combination. The purpose of the study was to investigate how postural stability influences bilateral deficit by comparing an exercise requiring more postural stability (the leg press) with an exercise requiring less postural stability (the handgrip). Eight participants volunteered for the study (3 males, 5 females). Maximal strength was determined by a 1-repetition maximum for the leg press (weight machine) and handgrip (dynamometer) exercises. Electromyography was used to measure activation of the effectors (flexor carpi ulnaris for the handgrip and vastus lateralis for the leg press) and the core muscles (rectus abdominis and external obliques). Bilateral deficit was greater in the leg press (-12.08 +/- 10.22%) than the handgrip (-0.677 +/- 5.00%; p < 0.05). Muscle activation of the effectors and core muscles was not significantly different between unilateral and bilateral conditions for either exercise. However, core muscle activation was significantly greater during the leg press (48.30 +/- 19.60 microV) than during the handgrip (16.50 +/- 8.10 microV; p < 0.05) exercise. These results support the hypothesis that an exercise requiring more postural stability (e.g., the leg press) will have a larger deficit and greater activation of core muscles than an exercise requiring less postural stability (e.g., the handgrip). Since the bilateral deficit was only apparent for the leg press exercise, we conclude that postural stability requirements might influence the magnitude of bilateral deficit.