This past week, I had the opportunity to participate in an exercise physiology study that examined metabolic and cardiorespiratory output across intervals of high-intensity exercise. The study was specifically recruiting high-level crossfitters since interval training at high intensity is the underlying structure of most advanced training programs. I was stoked to participate because I have done interval training at high intensity nearly every day for the past 25 years in track, gymnastics, and now crossfit.

Turns out it shows. Here is a picture of the setup.

Rev-ing up

First, I was outfitted with a mask that measured gas exchange–the amount of oxygen inhaled and the amount of carbon dioxide exhaled. I also had a series of highly sensitive electrodes to measure stroke volume–amount of blood pumped from one ventricle of the heart with each beat–and other measures of cardiac output. From here, I was asked to sit still in a chair while the experimenters took some measures of metabolites, namely lactate which rapidly accumulates with high-intensity exercise, as well as gas exchange and cardiac output.

After this period, I was asked to do a 4-minute warmup on a resistance (spinning) bike followed by four, thirty second intervals of a full-blown sprint with 90 seconds of rest in between. Sounds easy, right? No! About halfway through each sprint, I thought that I was being tricked and that the resistance had increased. Turns out, it hadn’t. I just hit a glycolytic wall that got progressively worse and extremely enduring the last 10 seconds. It reminded me of the “proverbial wall” a runner hits during the last 100 meters of a 400 meter race.

I also had some measures of body composition taken in the BodPod (a Star Trek-like medical machine) before the bike. My body fat is low–10.1%–which I have always known, but I have never experienced side effects most common of having low body fat.

Here is a snapshot of my metabolic and cardiorespiratory output during the four sprints on the bike. Clearly, I recover quickly and efficiently. Within a 90 second period, my lactate levels were more than halfway cleared and by 4 minutes into my 7 minute cool down, my heart rate, breathing, and gas exchange were back to resting levels. Further, I had a fatigue rate of 62% across the 30 second intervals whereas most people are in the 80’s. I’m also able to maintain power upon transitioning from glycolytic to aerobic (fat-based) reserves which most people can’t do. How did we know this? We know this from RER or respiratory exchange ratio. In the beginning, my numbers were 1.3 or higher which is an indication that I am solely burning glucose. About three quarters of the way into the sprint, at the time that I hit the proverbial wall and felt a real burn, my RER dropped below 1.0 indicating that I was utilizing both fat and glucose.


Sure, these results may be genetic but I am fairly confident that my daily strength and conditioning and competition routine that I have adopted for 2-3 hours a day for the past 25 years was the likely contributor.