When categorizing types of exercise, running is typically considered an aerobic activity; it's highly effective at burning fat and, as a type of cardiovascular activity, it works your heart and circulatory system. On the other hand, many athletes think of muscle-building exercises as strictly anaerobic, strength-training activities. In truth, many forms of exercise offer both types of workout. Just like weight training, regular running increases muscle mass. Expect to see particular change along your legs.
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Lower and Upper Leg Muscles
The motion of running primarily works your lower leg muscles, particularly your calves. Long-distance running generally develops lean and muscular legs with pronounced calves. If you have highly developed quadriceps, endurance running will bring the emphasis down lower on your leg and produce a more balanced physique. On the other hand, the explosive movement used to start off a sprint also relies on the quadriceps.
Fast-twitch and Slow-twitch Muscle
Humans have two types of muscle fibers: fast-twitch, or type II; and slow-twitch, or type I. For activities such as distance running, you typically rely on slow-twitch muscle fibers, which allow you to maintain less intensive movements over a longer period. By contrast, the fast-twitch muscles are useful for sudden, forceful movements, such as breaking into a sprint. Your leg muscles may have more fast or slow-twitch fibers, regardless of your exercise habits; most individuals are born with a greater amount of one or the other. However, regular practice at a particular type of activity, such as running, will develop the corresponding muscle-fiber type.
Leg Muscle Issues
Running puts a lot of stress on the calf muscles and requires relatively little of the muscles along the front of the leg. As a result, it's relatively common for runners to develop shin splits, a strain along the shin. Sometimes the stress even causes micro-fractures along the tibia. You can avoid the problem by building up your running practice gradually. A major cause of the problem among beginners is setting your training goal too high, too soon. Whenever you run, you should also take the time to stretch your leg muscles, warm them up and cool them down afterwards.
A minority of runners choose to practice without shoes, following the tradition of ancient peoples, before the advent of footwear. The Harvard University Skeletal Biology Lab studies the striking patterns of the foot against the ground among barefoot runners. Evidence is inconclusive as to the ideal barefoot running style. Nonetheless, the lab hypothesizes the forefoot and mid-foot striking appear to mitigate stress injuries. Instead of focusing the work at the calf muscle, the stride pattern appears to work the foot muscles more intensively. Before adopting a new running pattern or shedding your shoes, consult with a doctor or qualified specialist.