Oscar’s Training Articles – Metabolic Pathways

What is fitness? One of our definitions of fitness in CrossFit is about being balanced in all three metabolic pathways. We have 3 different metabolic pathways that provide our bodies with energy. These mechanisms are more and less active at different times depending on the duration and or intensity of the activity. The pathways are the phosphagen pathway, the glycolytic pathway, and the oxidative pathway. They are all the dominant producer of energy (ATP=adenosine triphosphate) at different times depending on what the task is at hand.

For very short bursts of energy the phosphagen pathway is main supplier of energy. It can support a very high power output for a short period of time without using oxygen. Some examples of athletes that excel in this pathway are baseball players, football players, sprinters, throwers and etc. In CrossFit we tap into this system by doing lower repetitions at higher weights and sprints. For example shorter sprints, heavy deadlifts, squats, snatches, clean&jerks, and etc. Athletes who lack capacity in this pathway is usually long distance runners, tri-athletes, and etc.

The glycolytic pathway supports energy for moderately high power activities that last several minutes. It can produce energy both anaerobically and aerobically. Athletes that thrive in this pathway are usually field sport athletes, fighters, mid-distance sprinters, and etc. This pathway is dominant in CrossFit WODs like “Diane”, “Karen”, “Grace”, “Isabel”, “Helen”, “Fran” and etc.

The third and last metabolic pathway is the oxidative pathway. This system provides energy for lower intensity activities over a longer period of time. Athletes with well-developed oxidative pathways are long distance runners, tri-athletes, cross country skiers, and etc. We develop this system in CrossFit through longer rows, runs, “Murph”, “Cindy”, “Mary”, and most hero WODs (20+min).

Many athletes focus on one thing only and become specialists in their pathway. A power lifter that can squat 800lbs has exceled in the phosphagen system. A sub 2.5H marathon runner has an excellent oxidative capacity. Both of these athletes can do some extraordinary things, however, they have both severely compromised their fitness by becoming a specialist in their pathway. The powerlifter might be strong but if he cannot run 800m without getting into cardiac arrest then he is not fit. The marathon runner will fly through 800m of running but when he is faced with a heavy barbell he will fail. Our goal is to become as well rounded as possible in all pathways. We want to be able to lift heavy, run for long periods of time and crush “Fran”. These system are always working together, no one system ever turns off completely, one is just more dominant than the other. Which is how lifting heavy can improve your running and conditioning can improve your lifting. Now you might be wondering, -“How do I improve my capacity in these pathways?” That’s simple. Come to TNT and be ready to work hard. The programming methodically rotates these pathways. “CrossFit is about constantly varied training, but that doesn’t mean the training is random” (Dave Castro). So don’t pick your WODs based on preference, hit all of them with focus and intensity, even the 10K Row and 40min AMRAP :)


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Oscar Isacsson, CSCS, USAW-L1SP
CrossFit TNT Coach