This is interesting. I have a theory on this ( and since i can't sleep right now because of 19tren-tfo / beastdrol cycle, i will share it )
Sex while not only giving a great cardiovascular workout can also have the HIIT principal applied to it by modifying the duration and speed at which you thrust your intended target This can give a great overall total body workout and as such should be approached with the same amount of focus and energy that your normal weight lifting sessions enjoy. Furthermore, busting your nut is not only highly amusing and enjoyable, but causes stimulation of the testes which are the main producers of TESTOSTERONE allowing to increase muscle mass while also recieving a great pump.
This is what happens when I can't sleep. I will be ordering some NEED2SLEEP very very soon, damn every other week pay periods!
that actualy makes.. alot of sense