Metabolic Conditioning, or ‘Cardio’

The past couple of weeks we have been taking a deeper look at the underlying foundations and methodology employed by CrossFit. This week, we will explore the idea of Metabolic Conditioning, or “Cardio,” something widely misunderstood by many. As mentioned in past, most of this info comes from CrossFit Journal, which can be found at

Metabolic Conditioning, or “Cardio”

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 two major pathways, anaerobic and aerobic. 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 remarkably 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 most of the 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.

View 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. Some of the best resources on interval training come from Dr. Stephen Seiler. His articles on interval training and the time course of training adaptations contain the seeds of CrossFit’s heavy reliance on interval training. The article on the time course of training adaptations explains that there are three waves of adaptation to endurance training. The first wave is increased maximal oxygen consumption. The second is increased lactate threshold. The third is increased efficiency. In the CrossFit concept, we are interested in maximizing first-wave adaptations and procuring the second systemically through multiple modalities, including weight training, and avoiding completely third-wave adaptations. Second- and third-wave adaptations are highly specific to the activity in which they are developed and can be detrimental to the broad fitness that we advocate and develop.

A clear understanding of this material has prompted us to advocate regular high-intensity training in as many training modalities as possible through largely anaerobic efforts and intervals while deliberately and specifically avoiding the efficiency that accompanies mastery of a single modality. It is at first ironic that our interpretation of Dr. Seiler’s work was not his intention, but when our quest of optimal physical competence is viewed in light of Dr. Seiler’s more specific aim of maximizing endurance performance, our interpretation is powerful.

Dr. Seiler’s work, incidentally, makes clear the fallacy of assuming that endurance work is of greater benefit to the cardiovascular system than higher-intensity interval work. This is especially important: With interval training we get all of the cardiovascular benefit of endurance work without the attendant loss of strength, speed and power.

Next week, we will discuss the role of gymnastics and weightlifting, and where they fit in in this spectrum.


Please reach out with any questions, and as always, continue to man up & lift your life!

The information provided in this article is for educational purposes only. Rabbi Fitness LLC is not a doctor. The contents of this article should not be taken as medical advice. It is not intended to diagnose, treat, or cure any health problem– nor is it intended to replace the advice of a physician. Always consult your physician or qualified health professional on any matters regarding your health and/or engagement in physical activity, especially if you (or your family) have a history of high blood pressure, heart disease, or if you have ever experienced chest pain when exercising or have experienced chest pain in the past month when not engaged in physical activity, smoke, have high cholesterol, are obese, or have a bone or joint problem that could be made worse by a change in physical activity.

Here at Rabbi Fitness LLC, our goal is to improve the lives of busy men becoming the best version of themselves with optimal strength, energy & superior health to engage & attack life with all their being! Call 516-331-0235 or email This email address is being protected from spambots. You need JavaScript enabled to view it.