The Cross-education Effect: Is There An Asymmetrical Transfer Of Strength Between Dominant And Non-dominant Limbs?

The cross-education effect has been described as an increase in muscle strength in the untrained limb from training the opposite limb. It has been hypothesized that the transfer effect is asymmetrical; in other words, training the dominant limb would elicit a greater cross-education effect than training the non-dominant limb. However, there is a paucity of studies that address this topic, and the few available reports are equivocal in observing this asymmetrical transfer of strength. PURPOSE: To compare the magnitude of the cross-education effect in strength between dominant and non-dominant limbs. METHODS: One hundred and twenty-two participants (18-35 years) were randomized to one of three groups: 1) training on the dominant arm only (n = 40), 2) training on the non-dominant arm only (n = 39), and 3) non-exercise time-matched control group (n = 43). Participants in training groups completed 6 weeks (18 training sessions) of unilateral elbow flexion exercise starting with a one-repetition maximum (1RM) test (≤ 5 attempts), followed by four sets of elbow flexion exercise using a weight corresponding to an 8-12 repetition maximum. The main outcome was maximum unilateral concentric strength (i.e., 1RM) of the individual’s untrained arm, measured at pre- and post-training. Changes in 1RM strength were compared using the Bayes Factor for Informative Hypotheses (BAIN). Specifically, the analysis of covariance (ANCOVA) function of BAIN was utilized with the pre-value of 1RM serving as the covariate. Data are presented as mean changes and 95% credible intervals. RESULTS: We found no support for the asymmetrical transfer of strength between limbs (posterior probability of 0.64). The group training the dominant arm [Δ 1.4 (1.1, 1.8) kg] and the group training the non-dominant arm [Δ 1.2 (0.93, 1.61) kg] both observed a cross-education effect. Both of these were greater than a non-exercise control group [Δ -0.18 (-0.5, 0.13) kg]. CONCLUSIONS: We found a similar cross-education effect in strength when training the dominant and non-dominant limb. Therefore, those looking to investigate or obtain benefits from the cross-education effect may not need to be concerned with which arm is trained.