We'll be honest – we never actually believed a roll in the hay equated with a full-on cardio session, but when you hear it enough times, you do start to use it as a reason to ditch that evening's gym session, right?
But if your other half has been using the no-pants-dance as an excuse to take a time-out from training during the week, you may want to tell them they've been wasting their time.
According to a study published in the New England Journal of Medicine, for a man who weighs 154 lbs – or 11 stone – a 60-minute sex session will burn 210 calories which is the equivalent of walking at – wait for it – a moderate pace.
And if you think 60 minutes sounds pretty damn ambitious, you're not alone.
Commenting on the stamina of our other halves, the scientists explained: "Given that the average bout of sexual activity lasts about six minutes, a man in his early-to-mid-30s might expend approximately 21 calories during sexual intercourse."
Adding insult to injury, they continued: "Of course, he would have spent roughly one third that amount of energy just watching television, so the incremental benefit of one bout of sexual activity with respect to energy expended is plausibly on the order of 14 calories."
14 measly calories? Sounds like those lads need to work a little harder…