Updated on Monday, Oct. 28, at 11:17 a.m. ET.
Does sex count as exercise? Good news: It might.
A new study finds that, in young people, sex burns an average of 4.2 calories a minute for men and 3.1 calories a minute for women. That intensity is moderate, the researchers reported online Oct. 24 in the open-access journal PLOS ONE. In other words, sex is better exercise than a walk, but not quite as good as a jog.
"These results suggest that sexual activity may potentially be considered, at times, as a significant exercise," the researchers wrote.
Sex as exercise?
Whether sex gets to count as a workout is a long-debated topic. A popular myth holds that a typical session of sex burns between 100 and 300 calories, but no one has ever directly measured the calories burned.
A few brave couples have had sex for science, however. Famed sex researchers William Masters and Virginia Johnson observed couples having sex and noted that heart rates reached as high as 180 beats per minute. For comparison, between 85 and 119 beats per minute count as moderate-intensity exercise for a 50-year-old. [Infographic: How Many Calories Am I Burning?]
In 1984, a study of 10 intrepid married couples published in the journal Archives of Internal Medicine used heart rate and blood pressure monitoring, a fast-responding oxygen gas analyzer and electrocardiography to determine that, for men, self-stimulation increased heart rate by 37 percent. Man-on-top sex increased it by 51 percent.
One problem with these studies, however, is that the couples had to get busy in the lab, hooked up to wires and tubes — imagine the difficulty of reproducing a, ahem, typical sex session. Fortunately, new technology provides a way around this monitoring problem.
Using a wearable armband called SenseWear, University of Quebec at Montreal researchers tracked the energy expenditures of couples as they had sex in their homes. The researchers recruited 21 heterosexual couples ages 18 to 35, choosing to focus on young people because energy expenditures vary widely across age.
Each person first completed a 30-minute moderate-intensity treadmill workout to provide a baseline measure of their calorie expenditure during exertion. They were then sent home with armbands and instructions to have sex four times over the course of the next month while wearing the sensors.
The SenseWear bands use accelerometers, temperature sensors and galvanic skin response sensors to come up with an accurate measurement of calories expended. Galvanic skin response refers to an increase of electrical conductivity that occurs when a person sweats.
Let's get physical
The recorded sex sessions lasted for an average of 24.7 minutes, with the shortest lasting 10 minutes and the longest stretching out over 57 minutes. Men expended more energy getting busy than women, even after controlling for men's greater body mass. On average, a sexual encounter cost men 101 calories, or 4.2 calories per minute. That's compared with 276 calories, or 9.2 per minute, on the treadmill.
Women expended an average of 69 calories during a session of sex, averaging 3.1 calories per minute. Again, the numbers weren't as high as a sweat-it-out session on the treadmill, during which women expended an average of 213 calories, or 7.1 per minute.
Still, the researchers said, people found sex pleasant (duh) and thus might be more likely to get horizontal than to schlep to the gym. Sex may also be a better way to burn calories than housework, though more research is needed: A study released in October in the journal BMC Public Health found that people overestimated how many calories they were burning while sweeping floors and vacuuming.
Editor's Note: This article was updated to correct the name of the university from University of Montreal to the University of Quebec at Montreal.
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Stephanie Pappas is a contributing writer for Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz.