Sex has often been called the best form of aerobic exercise. To calculate the exact aerobic benefit, I shall try and see how many calories one burns during an average sexual encounter. Every piece of data used for the calulations is an average measurement. Tantric sex is not included, however the appropriate formulae are.

#### Constants

- The average length of a male member is 6 inches or .16 meters with a standard deviation of about
^{3}/_{4} inches.
- The average adult male is 73.5 kilos and 1.75 meters tall
- The average adult female is 61.25 Kilos and 1.62 meters tall.
- An average session of sex will last for 30 minutes, of which, 66 percent, or 20 minutes will involve actual coitus, penetration or movement leading to orgasm on the part of one or both parties.
- The average male head weighs 10 pounds, or 4.5 kilos.
- The average female head weighs 9 pounds, or 4.08 kilos.

#### Equations

#### Example

The common missionary, or male-superior position of intercourse shall serve as an example to calculate the consumption of calories by a male during sex. First, we assume an average displacement per thrust of 12 centemeters. Due to physical constraints, it is often not possible to insert the entire male member into the female. 12 centemeters is thus a good working average. Due to changes in technique and rhythm, I will assume one .12 m coital thrust every half second.

So far, we have a displacement of 12 cm every half second. Now, we must find the force of the thrust to derive the work.

Let us start with the velocity of said coital thrust. Velocity is distance / time. If the distance is .12 meters, and time is .5 seconds, the velocity is .24 m/s.

Next, the acceleration is needed. Acceleration is velocity / time. Thus, .24 m/s divided by .5 seconds is .48 m/s^{2}.

Force = mass x acceleration. Assuming an average, 73.5 Kilo man, the force in newtons would be 35.28. However, that is wrong, as the entire human body does not move during coitus. Assuming that the head, torso, and pelvic region move during sex, the total moving mass is much closer to ^{2}/_{3}rds of the total body mass. Thus, We must multiply 49 Kilos by the acceleration of .48 m/s^{2}

Finally, calculating the total work is possible. Work is force x displacement. So, 23.52N x .12 m of displacement is 2.8224 Newton-meters (Nm). Since coital thrusting happens for about 20 minutes during the average sexual encounter, we take 300 seconds times 2.8224 Newtons and get 846.72 Nm.

Since 1 Nm is 0.238846 calories, we find that 846.72 Nm is 202.24 calories. A man burns 202 calories for every 20 minutes of copulation.

For the female-superior position, one can simply switch the average male mass with the average female mass. This comes out to 706 Nm, or 168.5 calories.

To further these calculations, assume a female head weighs 4.08 kilos. The male head is 4.5 kilos. Assume he or she can, on average, engulf three inches (.0726 meters) of a male member.

We then find that for a ten minute blowjob, a male spends 14.7 calories and a female spends 13.4 calories. This number is probably higher, given that the entire torso tends to move during fellatio.

Sources:

- http://sexualrecords.com/
- The Handy Science Answer Book The Carnegie Library, 1994.
- Research in the first person
- The Definitive Penis Size Survey
- The very useful onlineconversion.com