by Gabe Mirkin, M.D.
Interval training means that you alternate bursts of intense exercise with slow exercise until you feel tired. Short intervals are defined as lasting less than 30 seconds each, while long intervals usually last more than two minutes each. The most efficient, time-saving and health-benefiting way to exercise is to use short intervals (Scan J Med & Sci in Sports, Jan 2014).
You can do many more short intervals than long intervals because they do not cause much muscle damage and you do not build up significant amounts of lactic acid in less than 30 seconds.
Long intervals can cause so much muscle damage and such high levels of lactic acid that you can do very few of them in a workout. They also take longer to recover before you can do your next interval workout. Competitive athletes need to do long intervals as well as short intervals, but if you are not competing in sports, you don’t ever need to do long intervals.
The faster you go in an interval workout, the greater the gain in your ability to take in and use oxygen, and the faster you can ride or run. In one study, short intervals improved one-hour race times the most (Med Sci Sports Exerc, May 1999;31(5):736-41). This study compared 30-second all-out, 5-minute all-out, and 40-min all-out bouts of cycling. In 10 weeks of twice-a-week, effort-matched trials, they found that short interval training was more effective than long intervals in improving mean power output and VO2max (the maximal amount of oxygen you can take in and use per minute). VO2 max is the best laboratory measure of how fast a cyclist can ride or a runner can run over a distance.
How to Do A Short Interval Workout
• Warm up by jogging, cycling or swimming slowly for 5-10 minutes
• Pick up the pace for 30 seconds or less, until you feel a burning or tightness in your muscles or shortness of breath
• Then exercise very slowly until you recover your breath and your muscles feel fresh
• Alternate these 30-second-or-less sprints with slow recoveries until your muscles start to feel heavy or tight
• Cool down by moving very slowly for at least 5-10 minutes.
Apply these concepts to any sport or activity that requires continuous motion. For example, if you are riding a bicycle, warm up slowly for 5-10 minutes. Then increase your speed and the pressure on the pedals for 5-20 pedal strokes. Slow down and recover, then repeat.
As you become stronger, work up to 50 pedal stroke intervals, or whatever you can do in 30 seconds or less. Do not start your next interval until your legs feel fresh again, the burning has gone away and you are no longer short of breath. When your leg muscles start to feel stiff and heavy, stop the workout for the day and spend 5-10 minutes cooling down by exercising at a very slow pace.
Rest Periods Between Short Intervals
It makes little difference how long you exercise at a reduced pace between your short intervals. The shorter the rest between intervals, the longer it takes to recover from the next interval (Med and Sci in Sports and Ex, August 2005). When an athlete trains for competition, it is far more important how fast he can run each interval compared to how long he has to rest to recover between each interval. I have seen Olympic champions at every distance, particularly the shorter events, coming back to do their next interval when they feel they have recovered enough, not after they have waited a prescribed recovery time.
Athletes learn their ideal interval rest durations through trial and error. They may want to rest until their pulse drops to a comfortable rate, or until they are breathing at a normal rate, or until their muscles lose soreness and feel fresh. Competitive athletes can use either active and passive recoveries (moving slowly or standing still) between intervals (Eur J Appl Physiology, March 2005;93(5–6):694–700). Active recovery drops lactic acid levels toward normal faster than passive recovery (Med and Sci in Sports and Ex, Apr 1, 1996;28(4):450-456).
Rules for Short Interval Training
Athletes train by “stress and recover”. On one day, they take a hard workout which damages their muscles. On the next day, they feel sore so they take easy workouts, and when the extreme soreness goes away, they take a hard workout again. You should do the same.
• If you are doing interval training properly, your muscles will feel sore on the next day, so do not do intervals on consecutive days. Always allow at least 48 hours between interval workouts, and 72 hours is probably better.
• Plan to go easy on your recovery days; do not plan to take off. If your sore muscles feel better after a 5-10 minute warm up, exercise at a very low intensity. Stop exercising if you feel discomfort.
• If your sore muscles do not feel better after a 5-10 minute warmup, take the day off.
• You can do your next interval workout two or three days later, or when your muscles feel fresh again. Never attempt an interval workout if your legs still feel heavy or hurt after you warm up.
Advantages of Short Interval Training
Interval training workouts take far less time than conventional workouts that maintain a steady pace at lower intensity. We have known for many years that high-intensity training improves performance and is necessary for competitive athletes in all sports. Now researchers are finding that these short bouts of intense exercise offer tremendous health benefits for everyone. See Interval Training Helps Your Heart, Intervals Lower Blood Sugar, Lactic Acid is Good For You, Intervals for Everyone.
Caution: Intense exercise can cause heart attacks in people with blocked arteries leading to their hearts, so before you start interval training, check with your doctor.