Interval training is an advanced technique for getting fit fast. If you haven’t already, first look over the exercise overview.

Many experts say twenty minutes of interval has the same training effect as over an hour of regular aerobic exercise, and there’s some science to support that view. That may be. I get a great workout doing intervals, but I find I also need to do at least some aerobic exercise (a long bike ride on weekends, for example) to feel fit. But for a maximal training effect in a minimal period of time, it’s hard to beat intervals.

You shouldn’t attempt interval training unless you’re already fit aerobically. For instance, if you want to do intervals while out for a walk, first be sure you’re comfortable walking for twenty minutes at a 4-miles-an-hour (15 minutes a mile) pace. As with any exercise, don’t do intervals if they make you hurt. Unless you’re already an athlete, don’t do intervals running up or down hills.

At its simplest, interval training is doing moderate exercise for about twenty minutes. During this period, every three minutes, exercise all-out for 30-45 seconds and then return to the moderate pace. At the next three-minute mark, go all out for 30-45 seconds, then moderate pace. Rinse and repeat.

Most people doing this type of approach use their usual aerobic exercise as the base: walking/running, swimming, bicycle riding, etc. If you have access to level ground, probably the easiest is walking and running. If your patch of level ground is short, do the “walk-back” approach: run for 30 seconds and then walk back to the starting point. Keep repeating: running in the first direction for 30 seconds and then walking back.

If you want to get started and you’re already reasonably fit, go for a 20-minute walk and see how you feel. The next time you’re out for a walk, run for 20-30 seconds every three minutes. Your goal is to become so out of breath you have to stop running, so you slow down to a walk. At the next three-minute point run for 20-30 seconds and then walk. Keep up this pattern for the 20-minute walk. In the ensuing weeks and months as you become more fit, you can increase the speed of your run and/or run for 40-45 seconds before slowing to a walk.

One of my favorite interval approaches is called “10-20-30,” although it should actually be called “30, 20, 10.” You start out walking at a normal pace for 30 seconds. Then do a moderate jog for 20 seconds, and then run all out for 10 seconds. Repeat this sequence six times. Then walk at a normal pace for two minutes. Finally, do the 10-20-30 sequence six more times. It’s a great workout and only takes 14 minutes. Highly recommended. Here’s a video of this approach. But they only do five sets each, so the total is just twelve minutes. Awesome!