Sex may feel like a workout sometimes, but just how many calories are you actually burning under the sheets?

Researchers first posed that question in 1984, in a paper published in the Archives of Internal Medicine concluding that sex equated to light-to-moderate exercise. Several more studies since then have found similar conclusions.

In other words, if you're looking to burn a lot of calories over a short period of time, hit the gym, not the bed.

That said, there are some ways to boost the physical intensity of sex to shed a few more calories than you otherwise might. There are also other benefits to having sex than just pleasure and calorie loss.

The number of calories sex burns

There are no large scale studies on how many calories sex burns. Though there are several small ones where researchers have found ways to estimate the amount.

Some of the most recent data we have is from 2013, when researchers from the University of Quebec in Montreal published their study of 21 young, healthy heterosexual couples to see how much energy they expended over four different sex sessions.

The study, published in PLOS One, found that during the average sexual activity session – which the researchers defined as foreplay, intercourse, and at least one partner's orgasm – men burned 101 calories, and women burned 69.1 calories.

Factoring in how long each session lasted, the researchers concluded that the men burned, on average, 4.2 calories per minute compared to 3.1 calories per minute for women.

This was significantly less than when the same participants exercised on a treadmill, where men burned 9.2 calories/minute and women burned 7.1 calories/minute – more than twice as much as sex.

Co-author of the study Antony Karelis, PhD, professor in the Department of Exercise Science at the University of Quebec, Montreal, says "there is some kind of energy expenditure [during sex] but it's not that big."

Another study published in 2013 in the New England Journal of Medicine concluded similar results that a man in his 30s might only burn 21 calories during intercourse if he's having sex for 6 minutes.

Five to six minutes is about the average duration of sexual intercourse – not including foreplay, of course. And, of course, calorie expenditure is individualized, meaning you may burn slightly more or fewer calories than these study participants.

But, if your steamy encounters last about as long as an infomercial, then you should not rely on sex either to burn a significant amount of calories or to get in your recommended amount of weekly exercise.

How to burn more calories during sex

Let's get the obvious out of the way, first: Whoever is on top is probably doing most of the movement and will likely be expending more energy.

So, if you're looking to burn a few more calories during sex, take charge and get on top, or have you and your partner take turns so you can both benefit. Breaking a sweat is a good indication that you're putting in work, says Karelis.

You can also make the sex session last longer in hopes of burning more calories, but that's easier said than done.

As for different positions, "it would be incredibly difficult for people to change sex in such a substantial way that it would be equivalent to a workout," says Debby Herbenick, PhD, professor of sexual and reproductive health at the Indiana University School of Public Health and author of "The Coregasm Workout: The Revolutionary Method for Better Sex Through Exercise."

Herbenick adds that "there are endless sex positions, and I recommend that people choose the ones that are pleasurable for them and their partner, not the one that will burn five or 10 more calories."

Exercise itself can enhance arousal, according to Herbenick. She says people can exercise in ways that boost their own arousal, and then take those lessons learned to the bedroom and enhance their own sexual experience.

Alternatively, you can do some exercise with your partner before sex as some real calorie-burning foreplay, and then focus on simply enjoying sex.

The benefits of sex beyond calorie burning

If you're feeling disappointed that sex doesn't burn as many calories as you'd hoped, remember that sex has plenty of other health benefits.

Additionally, Karelis notes research has shown that having sex regularly reduces your risk of heart disease and is even associated with living longer-especially if you're orgasming regularly.

These benefits seem even better than burning calories, no?

Karelis hopes more research will be done in the near future so we can learn more about calorie expenditure and other health aspects regarding sex. There's still a lot to learn.