The Effect of Hill Sprints on Leg Muscles

Hill sprints are an anaerobic strength-training exercise designed to improve muscle strength and efficiency and reduce the risk of injury. A typical hill sprint workout consists of several eight- to 12-second speed bursts up a 4- to 15-percent grade with a one-minute walking recovery after each sprint. In an interview with "Men's Journal," NFL performance coach Keats Snideman suggests completing hill sprints at somewhere near 95 percent intensity. First-time hill sprinters, warns Brad Hudson, should avoid jumping in too fast. Hill sprints significantly stress both muscles and connective tissues, and should be taken easy at first to avoid injury.

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Aerobic vs. Anaerobic

In general, running is an aerobic activity, meaning it rhythmically works large muscle groups for an extended period of time, inspiring your muscles to burn both carbohydrates and fat. Hill sprints, on the other hand, are an anaerobic exercise that build up your leg muscles while burning only carbohydrates. Hill sprints are a strength-training exercise that indirectly improves endurance, in some ways more like weight reps than regular running. As coach Snideman advises, "Rest long enough between sprints so you can go as fast in the next rep as you did in the last."

The Anaerobic Threshold

Mark A. Jenkins, M.D., an NCAA trainer for Rice University, notes that the muscles quickly burn through their short-term energy stores, and lactic acid begins to build up in the muscles. This is called the anaerobic threshold. Anaerobic training pushes that threshold to a higher and higher percentage of your peak performance. This means that as you do hill sprint workouts, you will be training your body to go further and further using the more efficient aerobic pathways in the future. As Jenkins notes, "Continually pushing yourself into a lactate burdened state makes your body adapt."

Injury Resistance

Hill sprints, like any good strength-training exercise, strengthen the muscles they target over time. Stronger muscles are less likely to give out during intense workouts. In an interview with, Olympic coach Brad Hudson pointed out this quality about hill sprints. "Your first session will stimulate physiological adaptations that serve to better protect your muscles and connective tissues from damage in your next session," he said.

Stride Power

According to coach Hudson, hill sprint workouts also "increase the power and efficiency of the stride," developing your ability to cover more ground with the same number of strides. Hill sprints build muscle strength that comes in handy in race situations. They foster optimal muscle efficiency, speed and resistance to muscular fatigue.

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