Recently, several sports journals have published articles claiming that women have greater endurance than men. The cite the fantastic swimming records of Penny Dean of California who set the record for men and women for a single crossing of the English Channel in 7 hours and 40 minutes, and Cynthia Nichols of Canada who set the record for a double crossing at 19 hours and 12 minutes. The authors base their claim on the fact that women store more energy as fat in their bodies, and the extra fat may be the reason for their great endurance, but it is the insulating properties of fat, rather than the fuel-contributing effect that gave them an advantage. Loss of body heat is a major problem in channel swimming.
Muscles get most of their energy from fat and sugar.
Having extra fat can help you to exercise longer when you exercise at an extremely slow pace. However, when you exercise more intensely, the limiting factor in endurance exercise is the amount of sugar that can be stored inside of a muscle. When a muscle runs out of its stored sugar supply, it hurts and you will have difficulty using it. In spite of their increased percentage of body fat, women's muscles use the same percentage of fat and sugar as men's muscles do through all intensities of exercise. The extra fat that most women carry slows them down.