What's the first thing that comes to mind when you think about the words twitch and muscle? Spasms, perhaps. You'd hardly be alone in thinking that. But when it comes to fitness, it's most commonly ...

This article was originally featured on The Conversation. Usain Bolt, the world’s fastest human, ran a 100-meter sprint at a speed of 23.35 miles per hour (37.57 kilometers per hour). That’s ...

Your running speed partly comes down to factors you can't control, like genetics, and partly relies on your training. When you purchase through links on our site, we may earn an affiliate commission.