Although female athletes are capable of extraordinary achievement, a number of studies have investigated performance differences between male and female endurance athletes. Their findings are quite interesting.
One study evaluated the amount of energy used by the respiratory muscles in male and female athletes. Respiratory muscles are muscles found in the rib cage and diaphragm that are critical for breathing. The researchers measured the amount of energy respiratory muscles consumed in male and female athletes during maximal exercise intensities. The more oxygen consumed the harder these muscles are working. They found that respiratory muscles in females worked harder than those of males at maximal exercise intensities. As a result, women needed greater blood flow to respiratory muscles than men.
Although the researchers did not speculate why this occurred, a recent report provides answers. The same researchers looked at the dynamics of breathing in highly trained male and female athletes performing at maximal exercise intensity. They noted that airway passages in females are smaller than the passages in males. This explains why females have to breathe harder to get the amount of oxygen necessary to sustain maximal performance. As my wife would say, "women always have to work harder than men".