Inter-hand transfer of the effects of unilateral isometric resistance training for wrist flexion and extension

Objective To investigate the effects on one hand of training the other with isometric wrist extension and flexion training and its underlying mechanism. Methods Twenty healthy young girls were recruited and randomized into a training group and a control group with 10 subjects in each, using a random number table. The subjects in the training group were accepted isometric training of the wrist extensors and flexors on the right side once every other day, 4 days a week for 6 weeks according to a pre-programmed protocol, while those in the control group had no intervention. Peak torque and surface electromyography (sEMG) were recorded and assessed before and after 6 weeks of training. Results In the training group, the average peak torque of right wrist flexion and extension were both significantly higher than before training (within-group comparison) and higher than in the control group (between-group comparison) after 6 weeks of training. The average peak torques of the left wrist in the training group in flexion and extension were (12.9±2.0) Nm and (6.4±1.3) Nm after training, both significantly higher than before the training and stronger than the control group. In the sEMG traces during wrist extension, after training the ascend velocity of the right extensor carpi ulnaris and the integrated area of the left extensor carpi ulnaris in the training group were significantly smaller than before training and in the control group. Conclusion Unilateral isometric resistance training of the wrist muscles can transfer to the contralateral side, probably by altering muscle recruitment. Key words: Contralateral recruitment; Electromyography; Maximal voluntary contraction; Muscle strength training; Wrist strength