A high degree of aerobic fitness, requires a well adapted ability to take in, carry and utilize oxygen. Laboratory measurements are most accurate, but expensive. Estimates may be made of your fitness level as depicted in charts presented later. Anaerobic exercies is usually of short duration and produces lactic acid. 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.