After a year, the drug helped muscles recover faster after exercise because it boosted a hormone that makes mitochondria work better.

The drug didn’t make muscles stronger or change how much energy they used during exercise — only how fast they recovered afterward, which points to mitochondria being the target.

In a 12-month randomized, double-blind, placebo-controlled trial, tesamorelin improved mitochondrial oxidative capacity in obese adults with reduced growth hormone secretion, as measured by enhanced phosphocreatine recovery after exercise, with improvements strongly associated with increased IGF-I levels.