Myostatin is a protein that acts as a cap on muscle mass. Therefore, blocking myostatin may allow athletes to rapidly increase muscle – though at present this is not known to have ever been done in humans.  

Animals with naturally-occurring mutations in the gene show dramatic “double muscling.” The Belgian Blue bull shown here is one species that has been selected for its mutant myostatin gene, and hence remarkable strength. Mice lacking myostatin and with an added follistatin gene have a shocking 400% the muscle mass of nomal mice (and look like tiny bodybuilders too).

Such gene therapy for athletes isn’t yet available, and the prospects at the moment remain theoretical. But since so many aspects of our physique – from eyesight to strength, endurance to pain tolerance – contribute to athleticism, the arms race of doping won’t lose steam any time soon.