EXPLAINER: Sex is no substitute for exercise, studies reveal

Researchers debunked the belief that a typical sexual encounter burns hundreds of calories.

You may be sweaty. Your heart may be racing. You may even wake up the next morning with muscles you forgot you had.

But no, sex is not a replacement for going to the gym.

The popular idea that an enthusiastic night in bed can substitute for a proper workout sounds convenient, but studies suggest the calorie math simply does not work that way.

A widely cited 2013 study published in the peer-reviewed journal PLOS ONE measured the energy expenditure of 21 young heterosexual couples during sexual activity and compared it with a 30-minute moderate-intensity treadmill workout.

Researchers from Université du Québec à Montréal and Université de Montréal found that men burned an average of 4.2 calories per minute during sex, compared with 9.2 calories per minute on the treadmill. Women burned 3.1 calories per minute during sex, compared with 7.1 calories per minute during the workout.

In other words, minute for minute, the treadmill burned more than twice as many calories.

The difference becomes even clearer when looking at the entire sessions.

According to the same PLOS ONE study, men burned an average of 101 calories during sexual activity, while women burned about 69 calories. During the 30-minute treadmill workout, men burned an average of 276 calories and women 213 calories.

Using those averages, a man would need about 66 minutes of sexual activity to burn the same number of calories as the 30-minute treadmill session. For women, it would take roughly 69 minutes.

And that assumes the average calorie-burning rate could be maintained throughout.

There is another important detail often lost when the research circulates online: the sexual encounters measured in the study averaged about 25 minutes and included foreplay, intercourse and at least one orgasm.

Overall, researchers measured sexual activity at an average intensity of 5.8 METs, putting it within the moderate-intensity range. They concluded that sex can, at times, constitute significant exercise—but their own measurements show it generally burned substantially fewer calories than the treadmill workout.

The belief that a typical sexual encounter effortlessly burns hundreds of calories has also been challenged by researchers.

A separate 2013 paper published in the New England Journal of Medicine specifically listed the claim that one bout of sexual activity burns 100 to 300 calories per participant among commonly repeated obesity myths.

Researchers calculated that a 70-kilogram man engaging in sexual activity at an intensity of 3 METs would burn about 3.5 calories per minute, roughly comparable to walking at a moderate pace.

Using an average sexual encounter of about six minutes, the researchers estimated an expenditure of around 21 calories. They noted that the same man would have burned roughly a third of that energy simply watching television during the same period, leaving an estimated additional expenditure of only around 14 calories.

None of this means sex is physically meaningless.

Sex can raise heart rate and energy expenditure, while particularly vigorous encounters may demand considerably more effort. Duration, body weight, intensity and how physically active each partner is can also dramatically change the amount of energy burned.

But calorie burning isn’t the only reason exercise matters.

A proper fitness routine can be deliberately designed to improve cardiovascular endurance, muscular strength, mobility, balance and specific muscle groups. Sexual activity is generally too variable in duration and intensity to reliably provide the same training stimulus.

So enjoy sex for what it is—not as a loophole for skipping your workout.

Because according to the research, replacing that 30-minute workout would require considerably more time in bed than most people might imagine.

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