The time course of cross-education during short-term isometric strength training

Abstract

Purpose: This study examined the time course of contralateral adaptations in maximal isometric strength (MVC), rate of force development (RFD), and rate of electromyographic (EMG) rise (RER) during 4 weeks of unilateral isometric strength training with the non-dominant elbow flexors. Methods: Twenty participants were allocated to strength training (n = 10, three female, two left hand dominant) or control (n = 10, three female, two left hand dominant) groups. Both groups completed testing at baseline and following each week of training to evaluate MVC strength, EMG amplitude, RFD and RER at early (RFD 50 , RER 50 ) and late (RFD 200 , RER 200 ) contraction phases for the dominant ‘untrained’ elbow flexors. The training group completed 11 unilateral isometric training sessions across 4 weeks. Results: The contralateral improvements for MVC strength (P < 0.01) and RFD 200 (P = 0.017) were evidenced after 2 weeks, whereas RFD 50 (P < 0.01) and RER 50 (P = 0.02) showed significant improvements after 3 weeks. Each of the dependent variables was significantly (P < 0.05) greater than baseline values at the end of the training intervention for the trained arm. No changes in any of the variables were observed for the control group (P > 0.10). Conclusions: Unilateral isometric strength training for 2–3 weeks can produce substantial increases in isometric muscle strength and RFD for both the trained and untrained arms. These data have implications for rehabilitative exercise design and prescription.