It is high intensity and has a greater inherent risk of injury. Unconditioned individuals have a lower anaerobic threshold than the aerobically trained athlete. The highly trained male athlete may approach the high 70's to low 80's. Training, therefore, enhances the ability of the body, and muscle cells in particular, to better handle oxygen. Muscle must be able to use oxygen efficiently to keep anaerobic metabolism at a given level of effort to a minimum.
Cardiac output is a major determinant of oxygen uptake.
This is one of the major factors causing the approximately 7 percent decline with each decade of life, after age 30 of course. Muscle training and utilization of oxygen at the end organ, muscle, is the second factor that affects oxygen uptake. The A-V oxygen difference comes about as a combination of arterial oxygen content, shunting of blood to muscles and the muscle extraction of oxygen. Training results in a more efficient heart and an increase in the maximum stroke volume. An increase in VO2 results in an ease in the stress of a given workload.