Interval Training

  • Author:
    Richard Weil, MEd, CDE

  • Medical Editor: William C. Shiel Jr., MD, FACP, FACR
    William C. Shiel Jr., MD, FACP, FACR

    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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What are the physiological effects of interval training, and how do they increase fitness and performance?

Imagine that your muscles are engines that burn fuel (fat and carbohydrate) to keep you going, and in that engine there are two energy systems, aerobic (more fat-burning) and anaerobic (more carbohydrate-burning). Athletes and others who play sports that demand stopping and starting, or individuals who participate in endurance events that include hills or a sprint at the end, require that the muscles switch quickly between both systems. For example, say you're on a long-distance bike ride and you come to a large hill. Along the flat road your heart rate is at the low end of your training range and you're working aerobically and burning lots of fat (comparable to the active-recovery of your interval training session), but then you hit a very large hill. Now your heart rate increases and you start breathing harder (the work interval of your interval session), and so your muscles must make the switch to the anaerobic system where you burn more carbohydrate than fat. If you've put your time in with interval workouts, then at the top of the hill you'll catch your breath quickly and be ready to go. But if you haven't been doing intervals, your recovery will be sluggish (your muscles don't make the switch back to aerobic metabolism) and your performance will be compromised. In a nutshell, interval training trains your muscles to switch quickly between the two energy systems to keep you going, and the results are awesome.

How do I know if I should do intervals?

There are several reasons why you might do intervals.

  1. Recovery is the best indication of fitness, and intervals dramatically improve recovery. Next time you climb a hill while running or biking, or climb a flight of stairs, or sprint down the field, check your recovery time. If you find yourself bent over catching your breath instead of getting right on with it, consider intervals. In just a few weeks, your recovery will improve.
  2. Intervals might help you break a weight-loss plateau. There are no studies that I am aware of to prove that intervals break weight-loss plateaus, but many individuals have reported this to me and I have seen it happen myself. I can't explain exactly why it works, nor does it work for everyone, but it's certainly worth the effort if your weight loss has stalled. At the very least, you will improve your fitness.
  3. Intervals might be just the thing if you're bored with your routine. First off, it's a new activity. Second, you experience results quickly (within a week or two), and nothing is more motivating and exciting than near-instant gratification!
Medically Reviewed by a Doctor on 6/30/2015

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