Cross-Exercise: Which Training Program is Better?

A Review by Alyssa Bialowas

Cross-education training is defined as a neurophysiological phenomenon where there is an increase in strength in an untrained limb following unilateral strength training in the opposite, contralateral limb. This can also be called cross-exercise, contralateral training or inter-limb transfer, however the most commonly used and the term most researched would be cross-education.

Previous studies have proved that strength increases in the contralateral limb after performing unilateral strength exercises with the ipsilateral limb, however the training load required to achieve the cross-training has yet to be determined (duration, frequency, intensity, rest, and type of exercise or training). Cross education can also be seen in the transfer of skills from one limb to another.

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The Study

Researchers conducted a meta-analysis to deduce which unilateral strength training load would enable the biggest strength increases in the contralateral limb. An electronic search was performed on five different databases, and was divided into four stages –

Identification
Screening
Selection
Inclusion

In selected studies, effect size and confidence interval limits at 95% were calculated using the standardized mean change difference between the pre- and post-intervention measurements in both experimental and control groups.

The Results

A final sample of 10 studies were included in this search, which included a total of 409 participants. The results from the study indicate an interaction between the characteristics of the training programs and the increase in recorded contralateral strength. Isometric, concentric, eccentric or mixed training proved to have an influence on contralateral effect, with increased statistical significance in eccentric protocols. The type of training (sets of repetitions) had a strong influence, and no statistically significant correlations between speed of execution were found.

The studies found with the most strenuous training (lots of muscle fatigue and failure) produced the lowest results on contralateral strength increases. Training programs with multiple sets of repetitions obtained strength improvements in the opposite limb.

Takeaway

High-speed eccentric exercises are more effective in producing inter-limb transfer of strength. The effects of cross-education may depend more on volume of training and frequency of training than on training load in individual sessions.

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