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An interesting figure from a new Australian study in the European Journal of Applied Physiology:
The subjects in the study did eight weeks of heavy weight training — using only one leg (their dominant one). As you can see, they dramatically increased strength in both legs. This effect is well known, but I still think it’s pretty cool! The goal of this particular study was to try to figure exactly how this happens, using magnetic pulses to the brain to help assess the role of the nervous system. They did indeed find a significant reduction in “corticospinal inhibition” in both legs, suggesting that the training improves the transmission of the signal from the brain to the muscle, and this improvement applies to both sides of the body.
The point? Well, as the researchers note, it’s something to bear in mind if you have an injury in one leg or one arm. You might be able to keep the injured limb strong without even exercising it. Of course, you have to balance that against the risk of creating physical imbalances. I guess the ideal would be to train enough to increase strength without actually putting on muscle. As the researchers conclude, clinical trials of this approach are needed.