Interval Training

Medical Editor:

Are you pressed for time? Are you interested in improving your aerobic capacity and exercise performance in less than one-fifth the time of traditional endurance training? If so, then interval training is just what the exercise physiologist ordered. Indeed, research proves that you can improve your endurance and recovery from intense bouts of exercise with just one hour per week of interval training compared with five hours per week of traditional endurance training! Athletes know the magic of intervals; they use them all the time to improve their performance, and they know that intervals help speed up recovery so they can get going quickly after a blast of energy (like a sprint). In this article, I'll review what interval training is, describe the benefits and the studies that prove it works, and then show you how to design an interval-training program.

What is interval training?

Interval training is a method of training where you increase and decrease the intensity of your workout between aerobic and anaerobic training. Interval training in Sweden, where some say it originated, is known as fartlek training (Swedish for "speed play"). The protocol for interval training is to push your body past the aerobic threshold for a few moments and then return to your aerobic conditioning level with the objective of improving your performance (speed, strength, and endurance). The aerobic threshold is the intensity where your body switches from burning a greater percentage of fat to a greater percentage of carbohydrate and is generally 85% of your maximum heart rate (train below 85% and it's considered aerobic exercise; train above 85% and it's anaerobic exercise).

How are interval-training sessions designed?

Interval training can be personalized to the individual in almost every facet. The idea is to set up work to active-recovery ratios (work:active-recovery) in intervals of minutes. For instance, let's say you usually train comfortably at 6 mph on the treadmill. So, after your warm up and a few minutes at 6 mph, you sprint for one minute at 7.5 mph and then jog again at 6 mph for three minutes (1:3 ratio: a total of four minutes). You continue these intervals for your entire workout and then cool down for about five minutes.

How do I determine how hard to work?

Heart rate is a good indicator of how hard you're working, and it's easy to measure, so it's an ideal method for setting up and monitoring intervals. Here's an example. Say your heart rate is 70% of your predicted maximum when you jog at 6 mph. After you warm up and spend a few minutes at that pace, you increase the speed for your work interval to 7 mph, which might be 85% or even 90% of heart rate max, and then you cut back on the speed to 6 mph at a heart rate of 70% of max for your active-recovery. Below is a sample 28-minute interval workout (excluding warm-up and cooldown). Keep in mind that you can spend the entire workout doing them or vary it and do just some of the work intervals, and note that the time of each interval in this example always adds up to four minutes.

Warm-up: five minutes at 5-6 mph

Interval 1: three minutes at 6 mph (70% of max heart rate)

Interval 2: one minute at 7 mph (80% of max heart rate)

Interval 3: three minutes at 6 mph

Interval 4: one minute at 7 mph

Interval 5: three minutes at 6 mph

Interval 6 - harder: one minute at 7.5 mph (85% of max heart rate)

Interval 7: three minutes at 6 mph

Interval 8: one minute at 7.5 mph

Interval 9: three minutes at 6 mph

Interval 10: one minute 7.5 mph

Interval 11: three minutes at 6 mph

Interval 12: one minute 7.5 mph

Interval 13: three minutes at 6 mph

Interval 14: last push -- one minute at 8 mph (90% of heart rate max)

Cooldown: five minutes at 5-6 mph, then walk

Some athletes train as high as 100% of heart rate maximum. I don't recommend that beginners go above 85%-90%. 1:3 work:active-recovery ratios are the standard starting point. Remember to stay well-hydrated during the entire exercise.

Medically Reviewed by a Doctor on 1/28/2014


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