There are three main energy systems that fuel all human activity. Almost all changes that occur in the body due to exercise are related to the demands placed on these energy systems. Furthermore, the efficacy of any given fitness regimen may largely be tied to its ability to elicit an adequate stimulus for change within these three energy systems.

Energy is derived aerobically when oxygen is utilized to metabolize substrates derived from food and liberates energy. An activity is termed aerobic when the majority of energy needed is derived aerobically. These activities are usually greater than ninety seconds in duration and involve low to moderate power output or intensity. Examples of aerobic activity include running on the treadmill for twenty minutes, swimming a mile, and watching TV.

Energy is derived anaerobic ally when energy is liberated from substrates in the absence of oxygen. Activities are considered anaerobic when the majority of the energy needed is derived anaerobically. These activities are of less than two minutes in duration and involve moderate to high power output or intensity. There are two such anaerobic systems, the phosphagen system and the lactic acid system. Examples of anaerobic activity include running a 100-meter sprint, squatting, and doing pull-ups.

Our main purpose here is to discuss how anaerobic and aerobic training support performance variables like strength, power, speed, and endurance. We also support the contention that total conditioning and optimal health necessitates training each of the physiological systems in a systematic fashion.

It warrants mention that in any activity all three energy systems are utilized though one may dominate. The interplay of these systems can be complex, yet a simple examination of the characteristics of aerobic vs. anaerobic training can prove useful.

Aerobic training benefits cardiovascular function and decreases body fat. This is certainly of significant benefit. Aerobic conditioning allows us to engage in moderate/low power output for extended period of time. This is valuable for many sports. Athletes engaging in excessive aerobic training witness decreases in muscle mass, strength, speed, and power. It is not uncommon to find marathoners with a vertical leap of several inches and a bench press well below average for most athletes. Aerobic activity has a pronounced tendency to decrease anaerobic capacity. This does not bode well for athletes or the individual interested in total conditioning or optimal health.

Anaerobic activity also benefits cardiovascular function and decreases body fat. Anaerobic activity is unique in its capacity to dramatically improve power, speed, strength, and muscle mass. Anaerobic conditioning allows us to exert tremendous forces over a very brief time. Perhaps the aspect of anaerobic conditioning that bears greatest consideration is that anaerobic conditioning will not adversely affect aerobic capacity! In fact, properly structured, anaerobic activity can be used to develop a very high level of aerobic fitness without the muscle wasting consistent with high volume aerobic exercise!

Basketball, football, gymnastics, boxing, track and field events under one mile, soccer, swimming events under 400 yards, volleyball, wrestling, and weightlifting are all sports that require the majority of training time spent in anaerobic activity. Long distance and ultra-endurance running, cross-country skiing, and 1500+ yard swimming are all sports that require aerobic training at levels that produce results unacceptable to other athletes or individuals concerned with total conditioning or optimal health.

The CrossFit approach is to judiciously balance anaerobic and aerobic exercise in a manner that is consistent with the athlete’s goals. Our exercise prescriptions adhere to proper specificity, progression, variation, and recovery to optimize adaptations.