Loading video... VIDEO: A new study shows that humans express a powerful hormone during exercise and that treating mice with the hormone improves physical performance, capacity and fitness. Researchers say the findings present... view more Credit: USC Leonard Davis School of Gerontology A new study shows that humans express a powerful hormone during exercise and that treating mice with the hormone improves physical performance, capacity and fitness. Researchers say the findings present new possibilities for addressing age-related physical decline. The research, published on Wednesday in Nature Communications, reveals a detailed look at how the mitochondrial genome encodes instructions for regulating physical capacity, performance and metabolism during aging and may be able to increase healthy lifespan.