an interesting article on myth about weight losing

Heard about this all over the media - sex only burns 21 Cal (or kcal) on average?
The original paper looks into different myths regarding weight losing. Part of this article touches on the subject of sexercise. It calculated the amount of energy needed for sex using the average energy expendature per hour times the average length of sex (only 6 minutes! - Bohlen JG, Held JP, Sanderson MO, Patterson RP. Heart rate, rate-pressure product, and oxygen uptake during four sexual activities. Arch Intern Med 1984;144:1745-1748) This gives the shocking number 21 Cal per sexual activity!

We might as well spend 20 minutes watching TV, we burn the same amount of energy...

Original source - http://www.nejm.org/doi/full/10.1056/NEJMsa1208051#t=articleDiscussion
published on new england journal of medicine.