The Three Metabolic Pathways - From CrossFit RVA

Published October 15, 2012

Excellent article on the three metabolic pathways and how you use them in your workouts. "A few nights ago I was talking with Justin W and DP about the recent “Grace" (Clean and Jerk 135 lbs- 30 reps for time) we did. They both had phenomenal times for the workout, but Justin brought up that he can go straight through 20 reps, but then has to drop the bar. From that point he felt like his breaks were too long, and that if he could get back on the bar faster, he could improve his time. Well, it just so happens that there is a reason that Justin has to put the bar down at 20 reps or so, and it's not that he is not trying hard enough. Tapping into, and improving the efficiency of our energy sources is one of the main tenants of Crossfit. So let's look at the 3 main energy pathways that were tapped into during Justin's experience, and how they affected him. 1. Phosphagen or Creatine phosphate or Phosphocreatine depending on whom you’re asking, is a short duration energy pathway that gets activated when ATP is needed rapidly. As you can see from the chart above it peaks out in 5-10 seconds 2. Glycolytic is the second pathway. This is generally referred to as the anaerobic pathway. It’s anaerobic because it does not use oxygen. This pathway peaks in about 60 seconds. 3. Oxidative phosphorylation is the final energy pathway. This is generally defined as the aerobic pathway because it utilizes oxygen as a final electron acceptor after moving electrons down a chain of proteins in the mitochondria to produce massive amounts of ATP. (Note: As you can see from the chart above, all three pathways are generally working all the time, until energy stores are exhausted in the case of the Phosphocreatine and Glycolytic pathways. Not only TIME but INTENSITY determines which energy pathways is utilized to the greatest degree. If you’re pounding through high-intensity metcon, your body needs a lot of energy quickly, using Phosphocreatine and Glycolytic pathways. If you’re jogging, your body will begin by using phosphocreatine and glyolytic pathways, but quickly taper into the oxidative pathway, which produces plenty of energy over long periods of time.) These 3 pathways make up our body's quick energy systems. These energy systems are what we are trying to tax during our workouts. Now back to Justin's story. Justin was able to do his first 20 clean and jerks in 60 seconds, at which point he put the bar down and had to huff in the air for 5-10 seconds before he could continue on. He completed his last 10 reps in 45 seconds, taking breaks to breathe. Now that we have taken a look at the energy pathways that Justin was using this makes sense. He was able to get his first 20 reps in 60 seconds because he was drawing energy straight out of those first two pathways, once they were exhausted; he had to breathe in order to create more ATP (energy). Although we don't try to encourage you by yelling out motivators like “Exhaust that Glycolytic pathway" or “make sure you burn the hell out of that Phosphocreatine", training energy pathways is one of the primary goals of Crossfit. In this way, we are able to see you do more work in a given period of time, which shows that you have increased the efficiency of one or more of those pathways. As an example, Justin used to do 15 clean and jerks in the first 60 seconds of Grace, now he can do 20. He can do that because he has increased his body efficiency at using those first two energy pathways. Hopefully I didn't get too far into the physiological weeds here, but next time you bend over and gasp for breath you will know why!

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