Intensity-Dependent Effects of Unilateral, Fatiguing, Isometric Muscle Contractions on Ipsilateral and Contralateral Muscular Performance in Female Subjects.

Kwak, M, Benitez, B, Succi, PJ, Mitchinson, CJ, and Bergstrom, HC. Intensity-dependent effects of unilateral, fatiguing, isometric muscle contractions on ipsilateral and contralateral muscular performance in female subjects. J Strength Cond Res 39(7): e854-e861, 2025-This study examined time to task failure (TTF), performance fatigability (PF), and cross-over effects on the contralateral, unexercised hand after unilateral handgrip holds to failure (HTF) at 40 and 60% maximal voluntary isometric contractions (MVIC). Ten female subjects completed a pre-MVIC on both hands, sustained HTFs at randomly ordered percentages of 40 and 60% MVIC on the dominant hand, and a post-MVIC on both hands. Analyses included a paired samples t test and repeated measures analysis of variances. The TTF ( p < 0.001) and PF ( p = 0.002) were significantly greater for 40% MVIC HTF compared with 60% MVIC HTF. After 60% MVIC HTF, post-MVIC was significantly greater than pre-MVIC for the nonexercised hand ( p = 0.021), but not for 40% MVIC HTF ( p = 0.796). The longer sustained time for accumulation of metabolites at 40% MVIC HTF may have influenced the greater PF compared with 60% MVIC HTF. The significant increase in MVIC force on the contralateral, unexercised hand (cross-facilitation) after the unilateral handgrip HTF at 60% MVIC, but not 40% MVIC, may be attributed to the central effects. This study may inform a possible mechanism underlying the cross-education effect of unilateral, fatiguing isometric muscle contractions, which may be beneficial for training and rehabilitation settings.