They found 21 young, healthy heterosexual couples to engage in amorous congress (defined as foreplay and sexual relations where at least one person has an orgasm) while hooked up to a SenseWear armband. The study designers were interested in how many calories these young men and women would burn during the act.
The answer? Around 85 kilocalories (otherwise known as "calories"), which is equivalent to the amount found in one egg. To compare, researchers also asked the participants to run a half hour on the treadmill. Here, the men and women burned an average of 213 to 276 Calories. That's a lot more than they did getting down.
So, while you might not be able to rationalize skipping out on the gym because of your late-night sexy time, researchers did find that having sex is a funner way to burn off extra calories. Um, we don't need a science degree to have figured that out. (i09)