Faster, longer, further… fatter? Knocking out a particular gene in muscle lets mice run twice as far as normal. Knocking out the same gene in fat cells allows the animals to put on weight without developing type-2 diabetes.The discoveries could lead to new treatments for diabetes or for invigorating muscles in elderly people and in those with wasting diseases, say Johan Auwerx of the Federal Polytechnic School of Lausanne, Switzerland, and colleagues. Auwerx warns that cheats may exploit the potential for increase athletic performance, however.Auwerx and his colleagues used a targeted virus to knock out the gene that makes a protein called nuclear receptor corepressor 1 NCoR1 in the muscle of mice. Without NCoR1, mitochondria, which power cells, keep working at full speed. “Effectively, the mice go further, faster, on the same amount of gas,” says Auwerx.