Your time is precious — and limited. So when it comes to working out, it’s not uncommon to wonder: what exercise burns the most calories?

Exercise scientists have rigorously studied the amount of energy people expend during different types of exercise, and they’ve determined which workouts are best for burning calories. The thing to keep in mind: the more muscles you engage and the harder (and longer) you push those muscles, the more energy your body will churn through, says Dr. Tim Church, an exercise researcher and a professor of preventative medicine at Pennington Biomedical Research Center at Louisiana State University. So in order to maximize the number of calories you’ll burn, “you want an exercise that uses both lower and upper body muscle groups and is performed at a high intensity,” Church says.

You might therefore expect something along the lines of CrossFit or Tabata-style interval training to burn the most calories. And you may be right.

A study on one popular CrossFit workout called the “Cindy” — in which a person does a series of pull-ups, push-ups and squats in as many rounds as possible — found that it burned an average of 13 calories per minute. The workout lasts 20 minutes, so exercisers burned an average of 260 calories in total. While perfect apples-to-apples studies aren’t available, some Tabata research has shown that one of these workouts — composed of 4-minute training blocks that mix maximum-intensity bouts of resistance and aerobic training with short periods of rest — burns 14.5 calories per minute, or 280 calories during a 20-minute workout.

These per-minute calorie averages beat out many traditional forms of exercise. “But there’s such a variety within these classes and the people doing them that scores are all over the map,” says John Porcari, author of the Tabata study and a professor of exercise and sports science at the University of Wisconsin, La Crosse. For example, some people in his Tabata study burned up to 360 calories during the 20-minute workout, or 18 calories per minute.

Yet “per-minute” calorie burn isn’t always the best way to assess a workout’s energy demands, Porcari says. The total time spent training and a person’s willingness to stick with a workout are also important factors. “You can crank like the dickens for 30 seconds and burn a lot of calories,” he says. So if you’re extremely short on time, high-intensity interval training (HIIT) is probably your best option. But in the real world, Porcari says, many people won’t be comfortable (or capable of) engaging in regular or extended bouts of high-intensity training.

He says a “more fair” way to assess an exercise’s true energy demands is to ask people to do it at a pace that is comfortable for them. And when it comes to vigorous, calorie-burning exercises that people are comfortable doing for extended periods of time, running usually comes out on top. “When you look at the literature, running tends to burn more calories than other modalities,” he says.

According to an online calorie estimator from the American Council on Exercise, a 115-pound person running for 30 minutes at a slow-to-moderate pace (a 10-minute mile) would burn about 260 calories: the same amount people who did CrossFit typically torched in 20 minutes, according to the research. A 175-pound person would burn nearly 400 calories during that same 30-minute run. Pick up the pace, and you can achieve an even greater rate of calorie burn.

You may be wondering whether more intense forms of exercise lead to a higher rate of calorie expenditure even after training is finished — or a so-called “afterburn effect.” Research from Colorado State University has shown that, yes, intense exercise does keep a person’s metabolism humming longer than mild exercise. But this afterburn effect tends to peter out quickly — within a few hours — and it accounts for a small fraction of the total calories a person expends during and after exercise.

Also, a workout’s length — not just its intensity — helps to keep a person’s metabolism elevated after training, finds a review from the University of New Mexico. So if your goal is to burn the maximum amount of energy, you’ll want to find an exercise that is vigorous and that you can stick with for a long stretch of time.

For a lot of people, that mode is running. For others, it may be fast stationary cycling or Tabata or using an elliptical. The research suggests all are more or less comparable if you’re able to put in the time and keep up the intensity.

The bottom line? The best workout for burning calories is “the one you actually do,” Church says. You can find extreme forms of exercise that maximize per-minute calorie burn. But if you don’t stick with them or do them regularly, they’re not much good to you.