Effect of submaximal isometric wrist extension training on grip strength

Gripping force is produced by co-contraction of forearm flexors and extensors. Activation of extensors is important for stabilizing the wrist during gripping. However, forearm muscle function is complicated and the neurophysiological mechanism responsible for the gain in gripping force is unclear. Therefore, the purpose of this study was to investigate whether increasing forearm extensor activation with isometric wrist extension training has an effect on gripping force. Thirteen healthy subjects participated in this study. Maximal voluntary contraction of gripping was measured using a piezosensor (MVC(grip)) and EMG of forearm muscles at every wrist angle (from 70A degrees flexion to 80A degrees extension with 10A degrees intervals) were measured simultaneously at baseline, 4 weeks, and 8 weeks after training. Training consisted of 30 repetitions equal to 70% MVC of isometric wrist extension for 8 weeks (5/week) on the right side. Gripping force was measured on both sides using a grip dynamometer without wrist angle restriction. Gripping force, EMG, maximal wrist extension force, and wrist angle-gripping force curve were investigated after training. After training, maximal wrist extension force increased significantly. Gripping force on the trained side also increased significantly. The training changed wrist angle at peak of MVC(grip). EMG activation of forearm extensors increased and that of flexors decreased during gripping. These results suggest that wrist extension training leads to an increase in gripping force and changes the balance of EMG activation between forearm flexors and extensors during gripping. Therefore, this training method should be useful as a therapeutic strategy for increasing grip strength.