Ipsilateral and contralateral corticospinal response to unilateral strength training are similar for both the dominant and non-dominant limb

Introduction: It has been proposed that the cross-transfer of strength is greatest when motor training is completed by the dominant limb (in right handers only). The objective here was to investigate the effect of limb dominance on the cross-transfer of strength and corticospinal excitability and inhibition following right or left limb unilateral strength training in right handed participants. Methods: Twenty-two healthy right-handed males and females were randomized into a control, right-hand training or left-hand training group. All participants were tested for dynamic strength (1-RM) and muscle thickness. Transcranial magnetic stimulation (TMS) was used to assess corticospinal excitability and intracortical inhibition of the contralateral and ipsilateral motor cortex. The training groups competed 3 weeks of supervised wrist extension training beginning at 70% of their 1-RM, for 4 sets of 6–8 repetitions, which was externally paced (3 s concentric phase and 4 s eccentric phase). Results: Following unilateral resistance training, both groups exhibited significant strength gain in the trained limb and the extent of the cross-transfer of strength was substantial and not different between groups. TMS revealed that both groups displayed bilateral increases in corticospinal excitability, indicating that unilateral training affects both the contralateral ‘trained’ and ipsilateral ‘untrained’ motor cortices, independent of which limb is trained in strongly right handed individuals, but increased corticospinal excitability was not correlated with improved performance. Interestingly, intracortical inhibition was only reduced in the trained motor cortex; however, there were no differences between groups following training. Discussion: The present data does not provide evidence for the role of increased corticospinal excitability underpinning the crosstransfer of strength, however the magnitude of the cross-transfer of strength is not limited by limb dominance; rather, it appears to be dependent upon the motor control requirements of the task prescribed.