Ever wonder how many calories you burn during sex? Thanks to new research from the University of Montreal - and 21 couples we now know more about than our best friends - we have the answer.

Men burn 100 calories in the average sheets session, while women expend 69. The typical romp lasts 25 minutes from the start of foreplay to the end of the deed, but that's just an average - the times varied widely in the study, and ranged between 10 and 57 minutes. The longer the session, the more calories burned.

At this point you're probably thinking, "How the heck did they find this out?" And it's true that previous studies on the topic generally required sex in a lab with electrodes, cables, cuffs, and a mask worn over the mouth - which, as you can imagine, limited pleasure for all but the most sexually adventurous subjects. But new technology allows the same information to be calculated from an unassuming armband that can be worn at home, leading to more realistic data.

In addition to having their lovemaking monitored by the sex equivalent of a Fitbit, subjects also ran on a treadmill for 30 minutes to compare sexercise to actual exercise. For women, running at a moderate pace burned more than twice as many calories per minute, 213 total. When asked which was more pleasurable - sex or the treadmill - 95% of women said sex, 5% reported that both were equally enjoyable, and no one said the treadmill (there was no write-in option for "You really had to ask?").

"The level of intensity that is exerted from sexual activity could be higher than that of walking at [3 miles per hour] but less than that of jogging at [5 miles per hour]," the researchers write in the study, which was published by the journal PLOS ONE . "Taken together, these results suggest that sexual activity may potentially be considered, at times, as a significant exercise."

Back to the original question: To calculate how many calories you burn the next time you have sex, multiply the time in minutes by 3.1 (for women) or 4.2 (for men).