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Interval Training Workouts

Intervals training workouts that vary exercise intensity help build fitness fast

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Updated May 16, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

A female running in the city.
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Interval training has been used by athletes for years to build fitness. Interval training combines short, high intensity bursts of speed, with slow, recovery phases, repeated during one exercise session. An early form of interval training, "Fartlek" (a Swedish term meaning 'speed play') was casual and unstructured. A runner would simply increase and decrease his pace at will.

Today, athletes use more structured interval training workouts and HIT (High Intensity Training) to build speed and endurance. This variation of interval training and speed work can be a simple or sophisticated routine, but the basics are still the same as the original fartlek training.

What is Interval Training?

Interval training is built upon alternating short, high intensity bursts of speed with slower, recovery phases throughout a single workout. The interval workouts can be highly sophisticated and structured training that is designed for an athlete based upon his or her sport, event and current level of conditioning. An interval training workout may even be designed based upon the results of anaerobic threshold testing (AT) that includes measuring the blood-lactate of an athlete during intense exercise.

How Interval Training Works

Interval training works both the aerobic and the anaerobic system. During the high intensity efforts, the anaerobic system uses the energy stored in the muscles (glycogen) for short bursts of activity. Anaerobic metabolism works without oxygen, but the by-product is lactic acid. As lactic acid builds, the athlete enters oxygen debt, and it is during the recovery phase that the heart and lungs work together to "pay back" this oxygen debt and break down the lactic acid. It is in this phase that the aerobic system is using oxygen to convert stored carbohydrates into energy.

It's thought that by performing high intensity intervals that produce lactic acid during practice, the body adapts and burns lactic acid more efficiently during exercise. This means athletes can exercise at a higher intensity for a longer period of time before fatigue or pain slows them down.

The Benefits of Interval Training

Interval training adheres to the principle of adaptation. Interval training leads to many physiological changes including an increase in cardiovascular efficiency (the ability to deliver oxygen to the working muscles) as well as increased tolerance to the build-up of lactic acid. These changes result in improved performance, greater speed, and endurance.

Interval training also helps avoid injuries associated with repetitive overuse, common in endurance athletes. Intervals also allow an athlete to increase training intensity without overtraining or burn-out. Adding intervals to a workout routine is also a great way add cross training to an exercise routine.

Interval Training Burns More Calories

According to the American College of Sports Medicine, more calories are burned in short, high intensity exercise. If you are counting calories burned, high intensity exercise such as intervals are better than long, slow endurance exercise, but you may pay a price. There are risks inherent in high intensity training, so it's important to know both the the benefits and dangers of high intensity training.

Interval Training Workout Routines

Designing the right interval training routine can be sophisticated or casual. Elite athletes may go to sports performance lab to have blood lactate and exercise metabolism testing performed to determine the best interval training routine. On the other end of the spectrum, you can use the casual "speed play" interval training (fartlek). With this routine, simply pay attention to how you feel and set your intensity and duration accordingly.

If you want something a bit more structured, you can use a basic interval training workout routine. Keep in mind that interval training is extremely demanding on the heart, lungs and muscles, and it's important to have an OK from your physician before you start interval training. You should also have a solid base of overall aerobic fitness before performing high intensity training of any kind.

Beginners should start with short intervals (under 30 seconds), fewer repeats and more rest. Elite athletes can up the intensity, time and frequency of training. Few athletes benefit from performing intervals more than two times per week.

Interval Training Safety Tips

  • Warm Up before starting intervals
  • Assess current conditioning and set training goals that are within your ability
  • Start slowly. (for example: walk 2 minutes/ run 2 minutes) In general, longer intervals provide better results
  • Keep a steady, but challenging pace throughout the interval
  • Build the number of repetitions over time
  • Bring your heart rate down to 100-110 bpm during the rest interval
  • To improve, increase intensity or duration, but not both at the same time
  • Make any changes slowly over a period of time
  • Train on a smooth, flat surface to ensure even effort
  • You can also use circuit training as a form of interval training

Advanced Interval Training Workouts
You can vary your work and recovery intervals based on your goals. Four variables you can manipulate when designing your interval training program include:

  • Intensity (speed) of work interval
  • Duration (distance or time) of work interval
  • Duration of rest or recovery interval
  • Number of repetitions of each interval

Common Interval Training Workouts

It is recommended that you consult an athletic trainer, coach or personal trainer prior to designing an interval training program.

Sources

ACSM Fit Society Page. American College of Sports Medicine [www.acsm.org] Winter 2009-2010.

Hoyt, Trey. Skeletal muscle benefits of endurance training: mitochondrial adaptations. American Medical Athletic Association Journal, Fall 2009.

Roels, et al. Effects of Hypoxic Interval Training on Cycling Performance. Medicine & Science in Sports & Exercise. January 2005.

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