Why do males tend to have better cardiorespiratory fitness than females?

A. Males tend to have higher levels of hemoglobin in their blood.

B. Females tend to have higher levels of hemoglobin in their blood.

C. Males tend to have higher levels of body fat than females.

D. Females tend to have more lean muscle mass than males.

A is the correct answer - men have higher hemoglobin levels than women. Another factor not mentioned here is that men tend to have better cardiorespiratory fitness because they are bigger physiologically and therefore have bigger heart sizes and lung capacity. A man's heart can pump more blood - and therefore more oxygen - per beat.