Unilateral Exercise Improves Endurance On Both Sides

Did you know if you do exercise or skills on one side of your body, it can carry over to the non-worked side? A recent study examined gene expression in the rested side of the human body.

Remember years ago hearing about the benefits to strength when you strength train just one side of your body? Even if you don’t work one arm at all, but work the other, the arm you don’t exercise will get stronger. If you don’t remember, it was a pretty big deal at the time with far reaching implications, particularly for therapies in people with damaged limbs. One application for most of us is that if we get an injury or even just have a sore joint going into the gym, we can still work to maintain strength on the injured limb while we recover.

Strength isn’t the only thing that can be gained from working one side and not the other. If you were to analyze the handwriting of your non-dominant hand you would see that it is quite similar to the writing of your dominant hand. If you were a criminal, a forensic handwriting analyst might catch you even if you only wrote with your non-dominant hand while committing crimes. This might seem trivial to most of us, but it’s actually pretty important. It means not only does strength transfer from one side of the body to the other, but so does skill and technique, even for fine motor skills like writing.

For the first time ever, a recent study in Plos One researched gene expression in resting muscles when the other side was exercised. Specifically, they studied the genes that control endurance factors like burning fat for fuel. What they discovered was pretty fascinating.

Not only do strength and skill transfer from one side of the body to the other, but so does activation of the genes that determine short-term endurance factors. For as long as days after exercise, the side that is not targeted can show genes active that support enhanced endurance. This is likely due to circulatory factors (stuff in your blood) that activate these genes remotely, for example free fatty acids (the fat that circulates in your blood for use as fuel), adrenaline, and so forth. If these factors really are responsible for increased gene expression, then it may be true that exercising for endurance can improve endurance in all the muscles of your body so long as the workout is challenging enough. This makes sense also in clients I’ve had who experienced an increase in running endurance after fasting, even if they did not lose any weight. The activity of their aerobic system is heightened to compensate for lack of energy intake.

This study, like the ones that preceded it, has critical uses for people with immobilized limbs. You won’t win any powerlifting or marathon competitions from the changes you get by working only one side of the body, but you can help in healing and the subsequent recovery of full ability later.

One aspect of these results that should be fleshed out even further is if chronic endurance exercise can make long-term improvements to muscles, even if they are worked out in other ways. Could combat athletes who do a lot of cardio, which often has a lower body focus, rely more on strength training in the upper body without needing specific endurance training there to develop champion level muscular endurance? Could we benefit from daily endurance work on non-consecutive limbs and get a greater benefit overall than in bilateral (working both sides) exercise? As you can see, the answers to these questions could make any athlete better.


1. Milène Catoire, et. al., Pronounced Effects of Acute Endurance Exercise on Gene Expression in Resting and Exercising Human Skeletal Muscle, Plos One, 7:11 (2012)

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