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With benefits like a revved up metabolism, improved cardiovascular fitness, and increased fat burn, it's no wonder interval training has become so popular. But when it comes to figuring out how often you should try high-intensity interval training (HIIT), it's important to consider your fitness levels and goals.

What Is Interval Training?

HIIT combines two effective fat-burning methods, interval training and high-intensity training, for a highly effective (and popular) cardio training style. HIIT alternates periods of moderate-to-high intensity exercise (sometimes called "bursts") with periods of low-intensity activity or complete rest. But don't expect it to be easy—when performed correctly, HIIT can provide a seriously sweaty strength workout. And if you're new to HIIT, routines should be incorporated gradually to avoid injury.

How Interval Training Can Help Your Fitness Goals

Improve Cardiovascular Health

Interval training can help strengthen the heart to increase circulation, decrease cholesterol and fat levels, and lower the risk of heart disease.Eight weeks of a combination of high intensity interval training and conventional training reduce visceral adiposity and improve physical fitness: a group-based intervention. Giannaki CD, Aphamis G, Sakkis P. The Journal of Sports Medicine and Physical Fitness, 2015, Jan.; 0022-4707. Running sprint interval training induces fat loss in women. Hazell TJ, Hamilton CD, Olver TD. Applied Physiology, Nutrition, and Metabolism, 2014, Mar.;39(8):1715-5320. Both aerobic endurance and strength training programmes improve cardiovascular health in obese adults.Schjerve IE, Tyldum GA, Tjønna AE, et al. Clinical Science. 2008 Nov;115(9):283-93.

Fitness pro and Greatist expert Jen Cassetty says that although cardio is good for the heart, interval training should not be performed often if improving cardiac health is the main goal. Interval training isn’t ideal for daily workout routines and puts strain on the cardio-respiratory system, so try opting for more traditional cardio sessions.

Lose Weight or Tone Up

Studies suggest interval training not only revs up the metabolism, but it is also very effective in reducing body fat, especially around the abdomen.High-intensity intermittent exercise and fat loss. Boutcher SH. Journal of obesity, 2010, Nov.;2011():2090-0716. However, don't assume steady state aerobic exercise is entirely ineffective. Strength coach and Greatist expert Matt Delaney says that lower intensity ("steady state") cardio is also effective at fat loss and can be performed in conjunction with interval training on alternating days to allow for proper muscle recovery.

Maintain Muscle Mass

Want the burn without losing muscle? Proceed with caution. Performing too much cardio can potentially cancel out muscle gains by leaving the body without enough calories to grow and sustain muscles. Greatist expert and trainer Noam Tamir and Cassetty recommend not doing interval training very often to avoid overtraining muscles or losing existing muscle mass. But incorporating interval training and additional strength training into an exercise routine can help build leaner, more defined muscles.

Interval Training for All Fitness Levels

Workout Newbie (active zero to two times per week)

If you're just starting out, the key is to incorporate HIIT slowly. Interval training can put a great deal of strain on the heart because of its intensity, so it needs to be introduced gradually and carefully. Cassetty says people have to be conditioned for physical stress during a workout first. Those who don’t work out often need to get their hearts and muscles warmed up before undergoing bursts of intense cardio. Consider doing steady-state, low-intensity cardio (i.e., jogging on a treadmill or using an elliptical) the day before you start interval training.

And interval training may not be for everyone. Delaney says people who are very overweight or have a history of heart problems should avoid interval training when starting a fitness program. People over 40 should also complete a physical examination before undergoing an intense exercise program like interval training. And a small percentage of people are also at risk for injury and health complications when starting intense workout regimes.Exercise: a risk for sudden death in patients with coronary heart disease. Cobb LA, Weaver WD. Journal of the American College of Cardiology, 1986, Jan.;7(1):0735-1097. Chronobiological considerations for exercise and heart disease. Atkinson G, Drust B, George K. Sports medicine (Auckland, N.Z.), 2006, Nov.;36(6):0112-1642. Bottom line: If you think you fall into one of those categories, it's best to check with a doctor first.

Workout Regular (active two to four times per week)

For those who already lead moderately active lives, Tamir suggests adding interval training two to three times per week for heart health, along with a day of long-duration (low-intensity) cardio. In terms of weight loss, try two to three days of HIIT workouts, plus a metabolic resistance and strength training session (circuit training). Tamir adds that the latter approach is probably one of the most optimal ways to lose weight.

Workout Guru (active four to seven times per week)

For an added challenge, those at more advanced fitness levels can increase the frequency and intensity of the bursts during interval training. Delaney advises varying the work-to-rest ratio when performing interval training. Tamir suggests interval training two to three days per week, plus two long duration cardio sessions for heart health; or two to three strength training sessions for weight loss. And if you want to make an interval training session more difficult, simply decrease the amount of rest time.

Your Interval Training Game Plan

So, how many times a week should you hit it? (Sorry, we had to). Follow the chart below for a personalized interval training plan. These recommendations are based on research and opinions from our Greatist experts, but keep in mind that some may prefer more or less interval training depending on their individual fitness goals.

Tamir emphasizes the importance of quality over quantity, avoiding high-intensity, back-to-back days of interval training to prevent overtraining muscles and decreased energy. For those looking for more of these short and powerful workouts, he advises performing interval training two to three times a week for all fitness levels, and three to four times for those looking to increase oxygen uptake (or VO2 max). Delaney believes in a solid 1:1 interval training-to-cardio ratio where one day of interval training is followed by a day of steady state, lower-intensity cardio.

Be aware of personal comfort levels, and increase the frequency and intensity of interval training sessions gradually as the body adapts. Because the rules of “how often" depend on individual starting points and goals, Cassetty recommends that the frequency, intensity, or time of each interval training session be increased by 10 percent after each week until the goal is reached.

Interval Training Workout Plan Originally published August 2011. Updated June 2015.

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