Fitness trends evolve. In the ’80s, it was all about aerobics; today, science points toward interval training as the exercise style du jour. Personal trainers and fitness scientists agree: incorporate periods of high-speed and high-intensity cardio into your exercise regimen, and you’ll take your workout to a whole new level. You’ll pack more effective training into less time and be in the best shape of your life.
What Is Interval Training?
Interval training is the repetition of high-speed, high-intensity exercise followed by periods of rest or low activity. It’s a training style athletes in nonendurance sports (think track events, rather than marathon running) often use to build strength and speed.
Interval training isn’t specific to any type of exercise. You can work in intervals using a treadmill, riding an exercise or outdoor bike, running outside, or lifting weights. (Bodybuilders use the technique of alternating power lifting with lighter weights to increase muscle mass efficiently.) As long as it’s an exercise that allows you to vary your intensity, you can apply interval training to it.
By alternating between high and low intensities, you move your heart rate to the anaerobic range, at which your body burns more calories for fuel, and then immediately bring it back down to recover. The anaerobic threshold (AT) is synonymous with the lactate threshold (LT), the intensity level at which lactic acid starts to build up in the bloodstream, potentially leading to severe muscle soreness or even acidosis. Sounds bad, right? But when you exercise below the LT, any lactate your muscles produce is flushed out of your body before it can accumulate. Interval training relies on your body’s ability to temporarily exceed that threshold (between 90 and 95 percent of your maximum heart rate) and then recover, removing blood lactate during lower-intensity intervals. So you’re really cheating your body into doing more work without registering the stress.
Why Mix It Up?
As long as it’s done safely, interval training boasts a wide range of benefits beyond your normal workout routine.
- Cardio conditions your heart muscle, and anaerobic intervals turn your workout into super-cardio. The work you do lowers your resting pulse and increases your stroke volume, the amount of blood your heart pumps on each beat. And an efficient heart is a younger heart, since it has to do less work and accumulates less wear and tear. Other cardiovascular benefits are lower blood pressure and cholesterol levels.
- You’ll boost speed and strength, though not endurance. According to Patrick J. O’Shea, Ed.D, professor emeritus of exercise and sports science at Oregon State University, there are two types of muscles in the body. Slow-twitch muscles supply endurance, drawing on oxygen to burn fat. Fast-twitch muscles are for strength and power; you use them for explosive bursts of energy in sprinting, jumping, and lifting. Glycogen is their main source of energy, and since the body has a limited supply of this fuel, fast-twitch muscles fatigue quickly, usually within three minutes. They’re what you exercise during interval training, improving speed and power.
- High-intensity cardio has been shown to boost resting metabolism. Though researchers are still substantiating this concept, the prevailing thought is that you train your body to burn fuel during your workout—even more in the anaerobic range—and it just keeps going throughout the day.
- Because you’re reaching a higher level of efficiency by exceeding your AT, you’ll be able to have shorter workouts with greater results. An interval training routine should last no longer than 20 or 30 minutes, since your body is doing a lot of work within that period. For clock-watchers at the gym—those of us who have kids to pick up, meetings to attend, and paperwork to handle—interval training is a great solution to the time crunch.
- Intense exercise boosts endorphin production and promotes restful sleep. You’ll be able to tap into that “runner’s high” that can keep you cheerful even when the rest of your day doesn’t go so well, and you’ll sleep better at night.
