Humans are pretty quick. In 2009, Usain Bolt flew down the track at over 23 mph; in 2014, Dennis Kimetto, the marathon world record-holder, cruised along at 12.8 mph — about a 4:42-per-mile pace — for 26.2 miles. Scientists are uncovering what makes the Bolts and Kimettos of the world tick, and how we evolved to do both. That knowledge is redefining what’s possible and may help you speed up, too.
Muscle Fiber Types
Muscle fibers come in two general types, fast- and slow-twitch, and everyone has a mix of both. Fast-twitch fibers are for short, powerful bursts; they contract quickly but also fatigue quickly. Slow-twitch fibers have more mitochondria — the cells’ powerhouses that use oxygen to make energy — so they don’t fatigue as easily and are ideal for longer activities.
As you’d suspect, sprinters have more fast-twitch fibers, while endurance athletes have more slow-twitch. Although partly genetic, there’s some evidence we can train in order to change the proportion of fibers our muscles have. For example, distance running at a slow pace may increase a person’s percentage of slow-twitch fibers.
