If you are starting or increasing a running program, you probably know that running is great for your cardiovascular fitness and overall health but you might wonder if running gives you muscular, or runner's legs. The answer is a qualified yes — because running primarily uses your legs, you will develop sport-specific muscles over time.
However, the type of running you do makes a big difference — long-distance running builds leaner muscles, while sprinting adds bulk. By understanding the effect of running on each of your main leg muscle groups you can tailor your fitness plan to build muscle where you want it.
The short answer is that running will give you muscular legs. But how much bulk you add depends on whether you prefer powerful sprinting to long-distance endurance running.
Fast- vs. Slow-Twitch Muscles
Depending on whether you are jogging or sprinting, you utilize one of two types of muscle fiber: slow-twitch or fast-twitch. Long-distance running uses slow-twitch fibers, which are not as strong as fast-twitch but have a good oxygen supply and can work for long periods of time without tiring.
By contrast, fast-twitch muscle is stronger but tires quickly, so it works when you are sprinting. The bulging leg muscles of sprinters are due to more fast-twitch muscles, while the lean legs of distance runners are composed of mostly slow-twitch muscles.
Lean vs. Powerful Quads
The quadriceps is one of the largest muscle groups in your body. Composed of four muscles, your quads lift and extend the knee while running. In a fast run, the quads engage more strongly to lift your knee higher and thus extend your stride, which is why sprinters have such powerful quadriceps.
Endurance running, on the other hand, makes fewer demands on the quadriceps, because it is a forward motion driven from the hip. Long-distance running is an excellent way to build lean muscle in your quads, says Men's Journal, and balance your thigh.
Bare Feet for Your Calves
Your calf muscles play an essential role in propelling you each step forward, meaning that you will develop muscular, toned calves with regular running. However, excessive speed-work, or sprinting at the end of runs can lead to injury as you push off from your toes, which stresses the calf.
Running barefoot can help strengthen your calves, as does hill-running. Bare Foot Running suggests massaging your calf muscles regularly to break down the scar tissue; which will, in turn, make your calf muscles stronger.
Strong and Flexible Hamstrings
The hamstrings are the prime mover in long-distance running. The hamstrings get very strong with regular running but they can also become tight, which can cause injuries through muscular imbalance. That's why Harvard Health Publishing recommends working all the major muscles of the lower body together — the glutes, hamstrings and quads —to prevent imbalance.
By varying your running training you can develop muscular legs safely. For example, if you are a long-distance runner, include some sprint work or hill training to improve your quad and calf strength; if you are a sprinter, do some long runs to keep your hamstrings strong and flexible.