Sex Differences

Author: Craig Coghlin CPT (Canfit Pro), CFC (CSEP)
Typically, women have been regarded as being the weaker sex. But is this really an accurate assumption? Do there exist any similarities when you take into account body size?

Neuromuscular Responses

In many studies, women have been found to be up to 60% weaker than men in the upper body, and up to 30% weaker in the lower body. Yet everyone knows that in stature, men are usually quite bigger. Thus, many studies have been done comparing strength relative to body weight, or relative to fat-free body mass. When expressed relative to body weight, women still tend to be about 5-15% weaker in the lower body, but when this is compared relative to fat-free mass, much of the difference disappears. Therefore it becomes apparent that there are similar qualities of muscle between men and women.

Substantial differences still exist, though, when comparing upper body strength relative to either body weight or fat-free body mass. This could be due to the fact that women tend to carry their essential fatty mass around the hips (childbirth), which implies more muscle in this area. When use-patterns are studied, it is discovered that women typically employ upper body muscle mass less frequently as compared to men. Yet for some females, upper body strength exceeds that of the average man. This points out the importance of neuromuscular recruitment and motor unit firings.

Muscle fibre types are typically similar as well, with the only difference being that women possess a smaller cross sectional area for their muscle fibres than that of a man.

Cardiovascular Responses

Maximal heart rate is typically similar between sexes, although women tend to have a higher heart rate response. Also, cardiac output (the amount of blood the heart can shoot out in a minute) is nearly identical. It is known that women have smaller hearts because of their smaller body size, and thus have a reduced blood volume. This explains why the heart rate response must
be higher in women to maintain the same cardiac output (cardiac output = heart rate X stroke volume).

Women also have a lower amount of hemoglobin (the thing that carries oxygen in the blood). This results in a lower arterial oxygen content, and thus reduced oxidative potential for the muscle. Therefore, less oxygen can be delivered, resulting in lower VO2 Max levels.

Respiratory Response

The differences here are obviously due to body size. For the same workload, women must work harder to maintain similar power outputs due to having to work at a higher percentage of their VO2 Max. Lung sizes in women are smaller, again due to body size; therefore they cannot breathe in the same amount of air as a man.

Metabolic Responses

Some studies have concluded that a female’s VO2 Max is only 70-75% of that of a male’s beyond puberty. However, this could simply be due to the fact that on average, women lead a less active lifestyle. In highly trained females, the difference is usually due to a greater fat mass, and lower hemoglobin levels.

Although when comparing relative to body weight or fat-free mass, differences still exist between males and females. Is this simple genetics? Or does this have something to do with evolution? Historically, women were generally discouraged from participating in athletic activities, and encouraged to play with dolls and play dress-up. As society slowly became more active, women were still looked upon as being weaker, being instructed to run shorter distances, do modified pushups, and avoid many “dangerous” sports. Has this put women at an evolutionary athletic disadvantage? Only time will tell as women’s sports are greatly increasing in popularity and the caliber of female athletes continues to increase by an astonishing amount.

Wilmore, Jack H., and Costill, David L. 1999. Physiology of Sport and Exercise. Second Edition. Human Kinetics. Champaign, IL.