How Interval Training Works

Interval training “teaches” your body how to work at higher intensities for longer periods of time without fatigue. It’s an effective way to improve your physical fitness because you are challenging your body to do more than it is accustomed to, which causes it to adapt and become more fit. Without such challenges, fitness levels plateau and improvement stagnates.

Interval training refers to workouts that include brief periods of higher intensity exercise interspersed with periods of less-intense exercise or rest. For example, swimmers might swim one lap as fast as possible, then swim a lap or two at a more moderate pace. Runners may sprint for one minute, then jog for two minutes. Aerobic classes might alternate between 60- to 90-second all-out drills and several minutes of slower-paced recovery exercise. The high-intensity phase should feel difficult, while the recovery phase should feel fairly light to somewhat difficult.

High-intensity exercise is physically and psychologically demanding; that level of activity is impossible to sustain for more than a short time without becoming exhausted. The rest periods or low-intensity breaks allow the body to recover so the next high-intensity period can begin without undue fatigue. Athletes typically alternate training days with days of rest or moderately paced exercise.

If you want to add interval training to your exercise program, increase your training distance or speed by no more than 10 percent per week. Doing too much, after all, can lead to overuse and potential injuries. Do not increase the distance or speed at all if signs of over-training or injury exist. Signs of over-training include: fatigue, depression, irritability, insomnia, increase in resting heart rate, muscle pain, joint pain, overuse injuries and an unexplained decline in athletic performance.

For example, if you are exercising for weight loss, you can walk at a faster pace and burn calories more quickly than at a slower pace. Or, you can walk at the slower pace but increase the distance to burn more calories.

Interval training that includes a significant number of high-intensity exercise periods may cause a temporary increase in your resting metabolic rate, thus increasing the number of calories you burn at rest.

Because the high-intensity periods can be uncomfortable and potentially injurious, interval training is not for everyone, especially beginners and/or de-conditioned individuals. Consult with a health/fitness professional before beginning an interval program.