Contralateral effects of unilateral resistance training: a meta-analysis

Abstract

It is often claimed that strength training of one limb increases the strength of the contralateral limb, but this has not been demonstrated consistently, particularly in well-controlled studies. The aim was to quantitatively combine the results of other studies on the effects of unilateral training on contralateral strength in humans to provide an answer to this physiological question. We analyzed all randomized controlled studies of voluntary unilateral resistance training that used training intensities of at least 50% of maximal voluntary strength for a minimum of 2 wk. Studies were identified by computerized and hand searches of the literature. Data on changes in strength of contralateral and control limbs were extracted and statistically pooled in a meta-analysis. This approach allows conclusions to be based on a statistically meaningful sample size, which might be difficult to achieve in other ways. Seventeen studies met the inclusion criteria, and 13 provided enough data for statistical pooling. The contralateral effects of strength training reported in individual studies varied from -2.7 to 21.6% of initial strength. The pooled estimate of the effect of unilateral resistance training on the maximal voluntary strength of the contralateral limb was 7.8% (95% confidence interval: 4.1-11.6%). This was 35.1% (95% confidence interval: 20.9-49.3%) of the effect on the trained limb. Pooling of all available data shows that unilateral strength training produces modest increases in contralateral strength.

Asymmetry Assessment Using Surface Topography in Healthy Adolescents

“…Many studies that have reported muscle asymmetry and strength, have associated these features with the increase of unilateral training [43][44][45]. Similar to this, we expected that thickness asymmetries would be attributed to the increased use of one hand over the other in everyday activities.…”

“…For the overall sample, a clear majority also exhibited thickness in the left oblique area, as well as in the right shoulder. The right shoulder and the left oblique can be connected as a pair of contralateral muscles [44,46]. For example, the usage of the right shoulder activates the left side obliques.…”

Unilateral practice of a ballistic movement causes bilateral increases in performance and corticospinal excitability

“…It will also be important to establish the precise characteristics of training that are required to cause bilateral excitability increases. In particular, the potential for training involving high-force contractions (i.e., strength training) to influence ipsilateral cortical excitability should be investigated, given the similarities between strength and ballistic task characteristics and the frequent observation of a cross-transfer in strength performance with unilateral training (e.g., 3,28).…”

“…This contralateral strength training effect is a form of cross-transfer that has been known since 1894 (36). Meta-analysis indicates that the average size of the strength increase in the untrained limb is ϳ8% of its pretraining strength, or 35-50% of the strength gain of the trained limb (3,28). The relatively small functional improvements involved have resulted in skepticism regarding the potential clinical benefits of the contralateral strength training effect for conditions such as hemiparesis (3).…”

Effects of Lumbar Resistance and Stabilization Complex Exercises on Extremity Muscle Strength and Endurance of Normal Adults

“…Results indicate that such training on one side will affect the other side of the body. Thus, the approach is also called cross-training or opposite-side effect training 5) .…”