Metabolic Conditioning - the WOD

Biking, running, swimming, rowing, speed skating and cross-country skiing are collectively known as “metabolic conditioning.” In the common vernacular they are referred to as “cardio.” CrossFit’s third fitness model, the one that deals with metabolic pathways, contains the seeds of the CrossFit “cardio” prescription.


To understand the CrossFit approach to “cardio” we need first to briefly cover the nature and interaction of the three major pathways. Of the three metabolic pathways the first two, the phosphagen and the glycolytic, are “anaerobic,” and the third, the oxidative, is “aerobic.” We needn't belabor the biochemical significance of aerobic and anaerobic systems; suffice it to say that understanding the nature and interaction of anaerobic exercise and aerobic exercise is vital to understanding conditioning. Just remember that efforts at moderate to high power and lasting less than several minutes are anaerobic and efforts at low power and lasting in excess of several minutes are aerobic. As an example, the sprints at 100, 200, 400, and 800 meters are largely anaerobic, and events such as 1,500 meters, the mile, 2,000 meters and 3,000 meters are largely aerobic.

Aerobic training benefits cardiovascular function and decreases body fat—all good. Aerobic conditioning allows us to engage in low-power extended efforts efficiently (cardio/respiratory endurance and stamina). This is critical to many sports. Athletes engaged in sports or training where a preponderance of the training load is spent in aerobic efforts witness decreases in muscle mass, strength, speed and power. It is not uncommon to find marathoners with a vertical leap of only several inches! Furthermore, aerobic activity has a pronounced tendency to decrease anaerobic capacity. This does not bode well for most athletes or those interested in elite fitness.

Anaerobic activity also benefits cardiovascular function and decreases body fat! In fact, anaerobic exercise is superior to aerobic exercise for fat loss! Anaerobic activity is, however, unique in its capacity to dramatically improve power, speed, strength and muscle mass. Anaerobic conditioning allows us to exert tremendous forces over brief time intervals. One aspect of anaerobic conditioning that bears great 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 volumes of aerobic exercise! The method by which we use anaerobic efforts to develop aerobic conditioning is “interval training.”

Basketball, football, gymnastics, boxing, track events under one mile, soccer, swimming events under 400 meters, volleyball, wrestling and weightlifting are all sports that require the vast majority of training time spent in anaerobic activity. Long-distance and ultra-endurance running, cross-country skiing, and 1,500+ meter swimming are all sports that require aerobic training at levels that produce results unacceptable to other athletes or the individual concerned with total conditioning and optimal health. We strongly recommend that you attend a track meet of nationally or internationally competitive athletes. Pay close attention to the physiques of the athletes competing at 100, 200, 400 and 800 meters and the milers. The difference you are sure to notice is a direct result of training at those distances.

Interval Training

The key to developing the cardiovascular system without an unacceptable loss of strength, speed and power is interval training. Interval training mixes bouts of work and rest in timed intervals. The table below gives guidelines for interval training. We can control the dominant metabolic pathway conditioned by varying the duration of the work and rest interval and number of repetitions. Note that the phosphagen pathway is the dominant pathway in intervals of 10-30 seconds of work followed by rest of 30-90 seconds (load:recovery 1:3) repeated 25-30 times. The glycolytic pathway is the dominant pathway in intervals of 30-120 seconds of work followed by rest of 60-240 seconds (load: recovery 1:2) repeated 10-20 times. And finally, the oxidative pathway is the dominant pathway in intervals of 120-300 seconds of work followed by rest of 120-300 seconds (load:recovery 1:1). The bulk of metabolic training should be interval training.

One example of an interval that CrossFit makes regular use of is the Tabata Interval, which is 20 seconds of work followed by 10 seconds of rest repeated eight times. Dr. Izumi Tabata published research that demonstrated that this interval protocol produced remarkable increases in both anaerobic and aerobic capacity.

Courtesy of CrossFit Inc.