Unilateral leg resistance training improves time to task failure of the contralateral untrained leg

Abstract

Background: Cross-training is the process whereby training of one limb gives rise to enhancements in the performance of the opposite, untrained limb, most likely due to neural adaptations at the level of the motor cortex and/or spinal cord. Objective: To investigate whether unilateral resistance training can affect the ability of untrained homologous muscle in the contralateral limb to maintain force output over a sustained contraction. Methods: Fifteen healthy subjects completed 12 weeks of resistance training consisting of 36 sessions, using the unilateral leg press exercise. Sustained isometric knee extension performed at 50% of maximal force until task failure on both the ipsilateral trained leg and contralateral untrained leg. Surface electromyography (EMG) signals were recorded from the trained and contralateral untrained quadriceps (vastus medialis, rectus femoris, and vastus lateralis). Results: Time to task failure of the contralateral untrained leg was significantly increased after 12 weeks of unilateral resistance training (p < .05). Moreover, the EMG amplitude of the contralateral untrained quadriceps was significantly higher during the post training sustained contractions with respect to pre training condition (p < .05). Conclusions: Unilateral resistance training of the quadriceps can increase the ability of homologous muscle in the contralateral limb to maintain force output.

Keywords

• EMG
• cross training
• sustained contraction