Over the course of two months, researchers trained macaque monkeys to lift more and more weight, until they were able to do the equivalent of a one-armed pull-up. When the researchers stimulated a bundle of nerves in the spinal cord known as the reticulospinal tract (RST), they saw increases in the resulting neuronal electrical signals in the monkeysâ€™ arm muscles as training progressed, while they did not see the same consistent upward trend in the musclesâ€™ responses to stimulation of the corticospinal tract (CST). The results suggest that RST connectivity may play a critical role in muscle strengthening. Published in The Scientist, September 2020. Writing by Jef Akst.