Bonking occurs when muscles are functionally depleted of glycogen, the carbohydrate energy that the body stores. Even at the worst stroke, the muscles are not completely empty of glycogen, leaving between 10% and 30% of the original supply. However, the shortage of available energy means that muscles cannot continue to work effectively. Perhaps a complete stroke can be described as total glycogen depletion of muscles and liver.
Glycogen is the primary source of fuel for endurance athletes. This severe glycogen depletion does not occur during short-term, high-intensity exertion, but occurs during continuous exercise at about 70 to 85 percent of maximum VO2 that is maintained for periods of more than about two hours. The short answer is that having sex refers to low blood sugar (hypoglycemia) and simply running out of fuel for the body and brain. Have you ever done a long training session or race on a bike or running and suddenly “hit the wall” or exploded?.