There is conflicting evidence as to whether vigorous exercise  is more or less beneficial than moderate exercise. Some studies have shown that vigorous exercise executed by healthy individuals can effectively increase opioid peptides aka endorphins, a naturally occurring opiate that in conjunction with other neurotransmitters is responsible for exercise induced euphoria and has been shown to be addictive), positively influence hormone production increase testosterone and growth hormone,benefits that are not as fully realized with moderate exercise.

Exercise differ by the duration and intensity of muscular contractions involved, as well as by how energy is generated within the muscle. Initially during aerobic exercise, glycogen is broken down to produce glucose, which is then broken down with the help of oxygen to generate energy. In the absence of these carbohydrates, fat metabolism is initiated instead. The latter is a slow process,Moderate pace is an aerobic exercise, but sprinting is not. Playing singles tennis, with near-continuous motion, is generally considered aerobic activity.

When overall fitness is an occupational requirement, as for athletes, combat services, and police and fire personnel, aerobic exercise alone may not provide a well balanced exercise program. In particular, muscular strength, especially upper-body muscular strength, may be neglected. Also, the metabolic pathways involved in anaerobic metabolism glycolysis and lactic acid fermentation that generate energy during high intensity, low duration tasks such as sprinting, are not exercised at peak rates. Aerobic exercise is, however, an extremely valuable component of a balanced exercise program and is good for cardiovascular health.