Array
Usain Bolt is the fastest human in the world, but only up to 200m. His huge legs, packed with fast-twitch muscle fibres, allow explosive acceleration but they can’t sustain prolonged aerobic exertion, making them dead weights over longer distances. Usain Bolt has never actually run a mile, but most experts think he’d struggle to get a time under 4min 30s.
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.