Running may look tedious and exhausting, but it has many benefits for your body. Running is a form of high-intensity, cardiovascular exercise that raises your heart and respiration rates. It can help you reach or maintain your ideal body weight while also improving your health and fitness, according to Vanderbilt University. In general, running for extended periods of time will tone the muscles of your legs without making them bulky.
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Effect of Running on Legs
Most people run as an endurance activity that they maintain for 20 or more minutes per session. Your calves, quadriceps, hamstrings and glutes are all active during the activity. This activity works on your muscular endurance, not building strength or size of the leg muscles. Muscular endurance is defined as the ability of a muscle group to execute repeated contractions over a period of time sufficient to cause muscular fatigue, according to the American College of Sports Medicine. Strength building is a different method of training muscles and has a different purpose.
Bodybuilders are a group of athletes that train for muscular size, or hypertrophy. Hypertrophy training is a form of resistance training, not endurance or cardio training. When trying to build the size of your legs, or any muscle group, it takes consistent weight training over an extended period of time. Typically you will perform three to six sets of six to 12 repetitions per exercise with 30 to 90 seconds of rest between sets.
For health and moderate weight-loss/fitness improvements, run three days per week for 30 to 45 minutes at a moderate to high intensity. If you want to see significant health, fitness and weight-loss changes, increase your frequency to four days each week and up the duration of two of your runs to 60 to 90 minutes. To avoid bulking your leg muscles, perform leg workouts two days per week on nonconsecutive days. Choose one exercise for each muscle group and do three sets of 12 to 15 reps per exercise.
Genetics and gender play a role in whether your legs get bulky from running or just toned. If you naturally build muscle easily, it is possible that your legs may get slightly bigger from running. However, it is unlikely that you will see large muscular growth from an endurance activity. Also, men tend to put muscle on more easily than women. Each person adapts to training differently, so watch the changes to your body and adapt your training to reach your goals.