Resistance training is a type of exercise that causes your muscles to work against resistance. It is also called strength training because the goal is to make your muscles stronger. A classic example is weight-lifting. But a new study shows that before you can strengthen the muscles in your arm, you have to strengthen the nerve pathways from your brain to your arm.

Researchers at the Institute of Neuroscience at Newcastle University in the United Kingdom worked with two monkeys to get a better understanding of how resistance training works. They measured changes that occur in the motor cortex of the brain and in two pathways that carry motor signals from the brain, through the spinal cord, and out to the muscles of the upper arm. The motor cortex is the part of your brain that controls muscle movement. The two tracks are the corticospinal tract (CST) and the reticulospinal tract (RST).

The study is published in The Journal of Neuroscience. The investigators trained monkeys to pull a weighted handle with one arm. Over 12 weeks, the investigators gradually increased the weight on the handle to improve muscle strength in the arm. To check the progress of the strengthening exercise, they stimulated the motor cortex of the monkeys and measured how well nerve signals passed down the CST and RST. They found that although the CST did not change, the RST nerve signals increased gradually over the training period. At the end of the study, although RST tracks go to both sides of the body, only the tracks to the exercised arm got stronger.

The researchers concluded that the RST is more important than the CST for strengthening arm muscles, and that before the muscles actually grow and become stronger, this nervous system pathway must change and adapt to exercise. The monkeys needed a stronger nerve pathway before they could get stronger arm muscles.

Although the research was done in monkeys, it probably applies to humans also. So, if you have started strength training and you are wondering when you will see bigger muscles don’t give up. You are probably getting results in your brain. Those big, strong muscles should follow eventually.

Source: Study titled “Cortical, Corticospinal, and Reticulospinal Contributions to Strength Training,” led by researchers at Institute for Neuroscience, Newcastle University, UK, and published in The Journal of Neuroscience, July, 2020