Training with unilateral resistance exercise increases contralateral strength

1 School of Physiotherapy, The University of Sydney, Lidcombe; and 2 Prince of Wales Medical Research Institute, University of New South Wales, Randwick, Australia Submitted 11 May 2005 ; accepted in final form 10 July 2005 Evidence that unilateral training increases contralateral strength is inconsistent, possibly because existing studies have design limitations such as lack of control groups, lack of randomization, and insufficient statistical power. This study sought to determine whether unilateral resistance training increases contralateral strength. Subjects ( n = 115) were randomly assigned to a control group or one of the following four training groups that performed supervised elbow flexion contractions: 1 ) one set at high speed, 2 ) one set at low speed, 3 ) three sets at high speed, or 4 ) three sets at low speed. Training was 3 times/wk for 6 wk with a six- to eight-repetition maximum load. Control subjects attended sessions but did not exercise. Elbow flexor strength was measured with a one-repetition maximum arm curl before and after training. Training with one set at slow speed did not produce an increase in contralateral strength (mean effect of –1% or –0.07 kg; 95% confidence interval: –0.42–0.28 kg; P = 0.68). However, three sets increased strength of the untrained arm by a mean of 7% of initial strength (additional mean effect of 0.41 kg; 95% confidence interval: 0.06–0.75 kg; P = 0.022). There was a tendency for training with fast contractions to produce a greater increase in contralateral strength than slow training (additional mean effect of 5% or 0.31 kg; 95% confidence interval: –0.03–0.66 kg; P = 0.08), but there was no interaction between the number of sets and training speed. We conclude that three sets of unilateral resistance exercise produce small contralateral increases in strength. cross education; training volume; training speed; elbow flexors; neural adaptations Address for reprint requests and other correspondence: J. Munn, School of Physiotherapy, The Univ. of Sydney, PO Box 170, Lidcombe NSW, 1825 Australia (e-mail: J.Munn{at}fhs.usyd.edu.au )