It's no secret that sprinters and distance runners have different body types. It's pretty easy to tell them a part just by glancing at them, but why is that? They're both runners after all. Why do sprinters and distance runners look so different?
We're going to take a deep dive into what makes a sprinter's build and a distance runner's build so different and how that helps each of them perform in their respective disciplines.
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Above are photos of two of the worlds best runners, Shalane Flanagan Olympic medalist and NYC Marathon Champion and Shelly-Ann Fraiser-Price 2x Olympic gold medalist in the 100m. As you can see they're built very differently. Let's take a look at why that is.
Fast twitch Muscles and Anaerobic Running
The physical demands of sprinters and distance runners are vastly different. Sprinters are fast twitch muscle dominant and work in an anaerobic zone when training. The combination of the two gives them a bulkier build than their distance runner counterparts.
Sprinters need to be able to produce and utilize high levels of ground reaction forces in a very short amount of time. Research shows that at top end speed sprinters are producing 4-5x their body weight of pressure with every step and they're doing this with just milliseconds of contact time on the ground. It requires a lot of ankle, foot and leg strength to be able to do this well. The shorter the sprint distance the more dense the athlete will be. This is because of the principals of anaerobic training.
Anaerobic means simply "without air" and refers to the body utilizing energy without the presence of oxygen. It is an energy system that uses glucose and glycogen stores to fuel the body. There's a lot to unpack with anaerobic training vs aerobic training but for this blog post it's just important to know that anaerobic activities are considered anything that takes under two minutes to perform and they result in the building of dense fast twitch muscles.
Slow twitch Muscles and aerobic Running
Distance runners have long lean muscles because of the nature of their training. They spend a long time in aerobic training zones and don't put nearly as much force into the ground when running.
Aerobic means "with air" and consists of more than two minutes of consistent movement. After about 30 minutes of consistent moderately paced exercise our body runs out of carbohydrate (glucose and glycogen) stores and turns to fats and proteins to create sustainable energy. When the body runs out of fats for a fuel source it begins to break down muscle fibers to create energy. This is what makes slow twitch muscle fibers long and lean.
For more on fat burning while running: Running For Fat Burn.
Now don't get it twisted; distance runners are strong in their own right and they need to be lifting weights in order to be injury free and build speed. However, their resistance training is geared more towards reinforcing their joints and tendons than force production and turn over speed. That being said, it takes far lighter weights to get the job done.
It's important to keep in mind that running is a full body exercises. Although a runner's lower half is taking on the brunt force of the ground their torso and arms are stabilizing and balancing the body and need to be trained similarly to their lower body.
Can specific training build fast or slow twitch muscles?
The short answer is, sort of. We are all born with predetermined muscle fibers and although research shows that you can increase your fast and slow twitch fiber counts by altering your training you will never be able to completely overturn which way your body naturally leans. If you are predominately fast twitch you can absolutely be a good distance runner, but it's highly unlikely that you'll ever be elite and vice versa.
If you're unsure of where you land don't sweat it! As cheesy as this is... follow your gut. There is something in our DNA that helps guide us to our respective distances. In all my years as a coach I've rarely seen athletes want to run a distance that their body wasn't naturally built for.
In summary: Sprinters and Distance Runners have different needs
There's a lot going on in the body when you're performing any type of running.
Sprinters needs are very different than distance runners needs and because of that their build is different. The training modes needed for each distance and predetermined muscle fiber counts play a big role in both sprinting and distance running performance. all of these factors are why these two types of runners look so different.
For more check out these resources and references:
Faster top running speeds are achieved with greater ground forces not more rapid leg movements Weyand, et. al , J Appl Physiol 89: 1991–1999, 2000.
The Cooper Institute, www.cooperinstitute.org