Time to task failure of the contralateral untrained limb after high load-low repetition eccentric and low load-high repetition resistance training

Abstract Aims: Cross-training is the process whereby training of one limb gives rise to enhancements in the performance of the opposite, untrained limb and may be dependent on type of muscle contractions performed. The aim of this study was to investigate whether unilateral resistance training using eccentric contraction is more effective than concentric resistance training to improve time to task failure in the contralateral untrained limb. Methods:Subjects completed 12 weeks of resistance training consisting of 36 sessions, using unilateral leg exercise. Sustained isometric knee extension performed at 50% of maxmal force until task failure for the contralateral untrained leg. Surface electromyography (EMG) signals were simultaneously recorded from contralateral untrained quadriceps (vastusmedialis, rectus femoris, and vastuslateralis). Results: Time to task failure of the contralateraluntrained leg and associated EMG activitiessignificantly increased after 12 weeks ofunilateral resistance training(p<0.05). However, percent increase in time to task failure and EMG amplitude after eccentric resistance training was significantly higher than concentric resistance training (p<0.05). Conclusion: This study concluded that unilateral eccentric resistancetraining is superior to concentric resistance training to increase time to task failure in the contralateral untrained limb.摘要 研究目的：交叉训练（cross-training）指对单侧肢体进行训练后，可使对侧未接受训练的肢体运动表现得到提升的过程，其效果可能取决于所采用的肌肉收缩类型。本研究旨在探讨采用离心收缩（eccentric contraction）的单侧抗阻训练，是否比向心抗阻训练（concentric resistance training）更能有效提升未训练对侧肢体的任务失败时间。 研究方法：受试者完成为期12周、共计36次的单侧腿部抗阻训练。随后对未接受训练的对侧肢体进行持续等长膝关节伸肌收缩测试，收缩负荷设定为最大肌力的50%，直至任务失败。同时记录未训练对侧股四头肌（股内侧肌、股直肌及股外侧肌）的表面肌电图（surface electromyography, EMG）信号。 研究结果：12周单侧抗阻训练后，未训练对侧肢体的任务失败时间及相关肌电活动均显著提升（p<0.05）。然而，离心抗阻训练组的任务失败时间及肌电振幅的提升百分比均显著高于向心抗阻训练组（p<0.05）。 研究结论：本研究得出结论，在提升未训练对侧肢体的任务失败时间方面，单侧离心抗阻训练的效果优于向心抗阻训练。