When men and women undergo the same type of intensive training, men typically gain more muscle size. The reason for this disparity has to do with the ratio of Type I and Type II muscle fibers. Women have an equal amount of Type I and Type II fibers, while men have a disproportionate amount of Type II fibers. Type II fibers are the fast-twitch fibers that are used for power, whereas Type I muscle fibers are slow twitch and used for aerobic purposes. This fact prevents women from experiencing the same muscle growth as men even when performing the same workout.
Fat Storage and Decomposition
Men have a lower body fat percentage than women. A healthy range for men is 10 to 15 percent, whereas women hover between 20 and 25 percent body fat. When the body accumulates excess fat, male bodies store it in their abdominal region while women store it in their hip area.
The simple distribution of fat gives men an advantage with mobilizing and decomposing it. According to researchers Chantal Vella and Len Kravitz, in a 2002 study, fat that is stored in the abdominal region is more open to epinephrine stimulation than fat in the hip area. Men have additional advantage in that their resting metabolism is higher than that of women.
Lung and Heart Capacity
Men have been shown to have a better beginning level VO2 max, which is the maximum amount of oxygen the body can take in during maximum effort. The average untrained male will have a resting VO2 max of 3.5 liters per minute, while an untrained female will have at 2.0 liters per minute. This differential is due in part to the physical size disparities between men and women as well as women having a higher body fat percentage. With regards to the body's ability to deliver oxygen, women have a lower blood hemoglobin level than men which can impact oxygen delivery to the body.
Muscular Strength and Power
Due to the higher number of Type II muscle fibers, lower body fat percentage and greater VO2 max, men have greater muscular strength and power. Because of the increased Type II fibers, men have greater muscle mass, especially in the upper body, which is the source of their greater strength. The advantages in power come from the muscle fibers and VO2 measurements. On the average, men have significantly greater amounts of peak power and overall power when adjusted for body weight.