How Interval Training Works

By: Thorin Klosowski
Men exercising for healthy lifestyles.
Alternating between intervals of higher- and lower-paced exercise can help you burn fat.
Sri Maiava Rusden/Photodisc/Getty Images

If you exercise on a regular basis, then chances are you've looked for alternate methods to change your routine or shave some time off your workout. One of these methods is interval training, which, as the name suggests, means alternating intense and light cardiovascular activity. Variances on this technique take time off your workout by burning calories quickly while helping you build stamina and endurance [source: Mayo Clinic]. It also improves the efficiency of mitochondria -- the tiny organelles that allow your muscles to use oxygen to create energy -- which may allow you to burn fat more quickly than with a continuous workout [source: Reynolds].

Interval training can be integrated into most cardiovascular exercises but is commonly used in running, swimming and cycling. The exercises are meant to increase strength in the lungs and heart. The chance to increase stamina and endurance is appealing to athletes, but it can be a means to lose weight and get in shape for the average person as well. According to one study, people who participated in a cycling interval training regiment lost three times as much weight as those who cycled at a steady pace [source: Aubrey].


No change to a workout is worthwhile if it doesn't improve on the one you're doing now. Interval training operates differently than continuous workouts because the pause in strenuous activity helps reduce the accumulation of lactic acid, which is one cause of muscle pain. This buildup doesn't happen with interval training because the cool-down periods give your body a chance to redistribute the accumulated lactic acid. You will still experience delayed onset muscle soreness (DOMS), which is caused by muscles being stressed in ways they aren't used to, but you won't experience the immediate burning pain that you would with continuous exercise [source: WebMD].

In the next section, we'll take a look at the ways your can integrate interval training into your exercise.


Interval Training Workouts

Interval training does come with a few ground rules. Experts recommend that you don't train with interval training on consecutive days, which means you'll want to start with an every-other-day exercise plan. If you still want to work out everyday, you shouldn't work the same muscles as you do when you use interval training. For instance, if you're running, you'll want to work out your upper body instead on the days in between. You can do interval training on other muscle groups if you want, as long as you switch every other day.

Before you start, you need to stretch in the same ways you would before your normal workout. For most cardiovascular activities, this means low-impact, quick stretches that get blood circulation going. Once you're ready, it's time to enter the world of interval training.


The goal of interval training is to get your heart rate up to about 85 percent of its maximum for short bursts of time [source: Aubrey]. Depending on your experience and health, these bursts can last anywhere from a few seconds to a few minutes. This could mean switching from a hard run to an average jog, or from a brisk jog to a fast walk. You'll want to change up the duration of rest and activity every once and a while, both to keep your workout from getting dull and to keep your body from getting used to a standard.

You can apply the ideas of interval training to nearly any cardiovascular workout. This means if you prefer cycling, running, stair-climbing, swimming or even walking, you can incorporate interval training into it. It's best to start on the easy end of things. For instance, when you start, you may only want to incorporate the intense interval for 30 seconds, but as you warm up to it, you can add more and more time. Your rest periods will be based on your own body, so paying attention to your heart rate is key. Once you get back down to a moderate level, just above your normal resting rate, it's time to crank it up again.

Gyms often offer circuit interval training classes led by an instructor who changes up the exercises as well as the speed and rate of a workout. This prohibits your body from getting used to a specific movement and builds multiple muscles in one workout.

If interval training doesn't sound extreme enough for your workout, you might consider upping the ante a bit. We'll take a look at one way to do this in the next section.


High-intensity Interval Training Workouts

Action blur of woman running
With high-intensity interval workouts, you don't let your heart rate get all the way back down to resting.
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Experienced exercisers and athletes might find standard interval training to be a bit lackluster for their needs. If this is the case, you'll find in high-intensity interval training (HIIT) a means to build high endurance and stamina for longer bike rides, runs and other strenuous activities. HIIT improves the ways your body burns fat, meaning athletes can work longer before having to tap their carbohydrate stores [source: Jaret]. High-intensity workouts push your body so it has to spend the rest of the day consuming oxygen and energy just to recover. You won't want to do these workouts more than three times a week.

HIIT tends to follow the same basic premise of interval training with one exception: The rate of intense workout should push your heart rate up near its maximum and not let it drop all the way back down to its resting pace during the workout. Still, as with traditional interval training, strenuous exercise followed by a pause helps build muscle faster and more efficiently.


There are several ways to complete a high-intensity workout. One method is a four-minute workout where you train for 20 seconds at your maximum, then rest for 10 seconds, then 20 seconds back on, 10 seconds off -- until you've completed this cycle for eight rounds. You can even change the workout types in this method, moving from your legs to arms to abs in each cycle. Most high-intensity interval training workouts are similar to this one, and you can change and edit your own workout as you see fit.

These high-intensity workouts are a way to quickly lose weight and get cardio fitness into your larger workout regiment without cutting into your time too much.

We've covered the methods and ways interval training works, but we'll take a look at the benefits and downsides of using this workout technique in the next section.


Benefits of Interval Training

Interval training has been proven as an effective way to improve endurance and lose weight. We've already covered a few of the reasons why: Its short duration and its ability to allow the muscle to remove lactic acid before the build-up, but there are more benefits to these workouts -- as well as a few disclaimers.

As we've already mentioned, you'll burn the same amount of calories -- if not more -- using interval training techniques than you would simply by doing continuous training at one pace. You'll also decrease your chance for injury because you won't be wearing out the same muscles over and over again in repetition. As long as you follow the 24-hour cycle, you shouldn't have a greater chance of trouble with cardio injuries like runner's knee, shin splints or cramps [source: Mayo Clinic]. If you're already working out, it may be easy to modify your workout set to include interval training every other day. Along with many other cardiovascular exercises, it can be done nearly anywhere either with or without equipment, depending on your preference.


However, as with any exercise technique, interval training isn't perfect. It's usually recommended that you have at least a little bit of exercise experience before starting this technique so you're aware of your body's limits. It's also easy to overdo it at first, which might make first-timers want to quit before giving it a real chance. If this is the case, you'll want to slow down and allow yourself a bit more time to recover from the intense bursts. Although you're supposed to "feel the burn" for the rest of the day, it shouldn't dissuade you from ever doing it again. You'll also want to be aware of your surroundings if you're running at maximum speed, so be sure to do it in a location you know well.

As with most cardiovascular exercises, interval training isn't known for its muscle-building proficiency. It's an excellent way to lose weight, burn calories, stay in shape and increase stamina, but it won't help you bulk up. Although it's most often associated with cardiovascular workouts, the technique can also be applied to weight-lifting to build muscle.

The main problem with interval training is that even though it can be effective for those with heart disease, high blood pressure and COPD, it's difficult to measure how long sessions should last, and it's also easy to overdo. If you have a history of any of these conditions, be sure to talk to a doctor first. Consider setting yourself up with a personal trainer who can closely monitor your heart rate to make sure you don't overexert yourself [source: Jaret].

Continue on to the next page to find out more about exercise and other related topics.


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