Tsukuba, Japan—Different types of exercise encourage the formation of different types of muscle fibers, or the cells that make up your muscles. Slow twitch muscle fibers support endurance activities ...

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 ...

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.