Unilateral or bilateral resistance training? Effect on muscle mass and strength



From Ergo Log


Strength athletes can perform many exercises in two different ways: left and right separately [unilateral] or left and right simultaneously [bilateral]. It doesn’t matter which version you choose when it comes to the amount of muscle mass you build up from the exercise, write Brazilian sports scientists in an article that will soon be published in the Journal of Strength and Conditioning Research. But when it comes to strength it’s a different matter.


The researchers performed an experiment with three groups of young, active women. Each group consisted of just over a dozen women, and two of these groups trained their upper leg muscles twice a week on a leg extension machine for a period of 12 weeks. A third group of women did not train, and functioned as control group.


One of the training groups trained in the traditional way – with both legs together, or as sports scientists like to call it, bilaterally. The second group trained the legs separately or, to use the jargon, unilaterally.


In terms of muscle mass, it made no difference how the women trained. The women who had trained their left and right legs separately built up just as much muscle mass in their quadriceps as the women who had trained both legs at the same time.

The women who had trained their legs bilaterally built up slightly more strength in each leg than the women who had done their leg extensions unilaterally.

On the other hand, the women who had trained their legs unilaterally ended up with slightly more maximal strength in each leg than the women who had done bilateral leg extensions.

“If the training aim is to optimize the increase in force produced for each lower limb separately, unilateral training may be recommended”, the researchers concluded. “This may imply in improved performance in daily activities and in athletic performance during unilateral movements, such as kicking and running.”


“Although unilateral training enabled the use of heavier training loads, there were no greater superior gains in muscle mass compared to bilateral training for 12 weeks.”


J Strength Cond Res. 2015 Aug 29. [Epub ahead of print].


Source: http://www.ergo-log.com/unilateral-bilateral-resistance-training.html

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