Adam Pulford

On aerobic glycolysis vs anaerobic glycolysis. This terminology has existed since the beginning of times and ingrained in every physiology, biochemistry and medical textbook. According to this terminology, aerobic glycolysis is the oxidation of glucose to pyruvate in cytosol then to Acetyl-CoA in mitochondria in the presence of oxygen. Anaerobic glycolysis is the reduction of pyruvate to lactate under “anaerobic conditions”. However this terminology is wrong as lactate is the real end-product of “both” glycolysis. Over the last 50 years Dr. George Brooks has worked on this and proven it. The ratio of lactate to pyruvate at rest is ~30-40 and at high intensity exercise is up to 500. So, even during resting conditions, the production of lactate is significantly higher than the production of cytosolic pyruvate…Hence, glycolysis should be just that, glycolysis… This wrong terminology has penetrated into so many fields in medicine and biology as well as exercise physiology and training leading to terms like “aerobic threshold” and “anaerobic threshold”. Simply, they don’t exist as they are portrayed, since both metabolic events are under fully aerobic conditions and also lactate is the main end-product over cytosolic pyruvate. The pure anaerobic threshold is the change from glycolysis to ATP-PC system during sprinting where anaerobic conditions are the predominant. In a world with so many training zones and philosophies, at least we should agree in the “modern” principles of muscle bioenergetics during exercise. We should make an effort to move on and get rid of 50+ year old inaccurate concepts like “anaerobic threshold” and “aerobic threshold” 🙏

A few comments regarding #zone2 training: When I started the Zone 2 concept ~30 years ago, it was successful with elite athletes but back in the days, nobody talked about fitness, longevity, mitochondrial function or metabolic health. Back then it was more about improving aerobic capacity and already by doing lactate testing, I could see the connection with mitochondrial function quite well. Then, 18 years ago when I started measuring FATox and CHOox rates in the lab and matched blood lactate with FATox, things started to click even stronger as I could see more scientific and applied evidence that Zone 2 worked quite well. Both lactate and Fat are mitochondrial substrates and therefore, good surrogates to assess mitochondrial function. I kept using this methodology as well as Zone 2 training with athletes and patients and in 2017 I published the methodology with my colleague Dr. George Brooks. Without ANY doubt, I can see after thousands of metabolic tests in almost 30 years and with all kinds of people, that Zone 2 increases FATox + lactate clearance capacity the most compared to other zones (my understanding of zones) and improves fitness quite a bit, if Zone 2 is determined and applied correctly. My Zone 2 usually coincides with FATmax. However, there are different interpretations of Z2 these days. Not judging them at all…I, like almost 30 years ago, still apply the Z2 concept with some of the best athletes in the world as well as with patients and fitness enthusiasts and still works quite well. Furthermore, a very important concept that many tend to forget about my training methodology is Zone4, which is high glycolytic training (about LT) which is also key to improve performance and also health. Ask my athletes how many intervals at Z4 do and how hard they are…It hurts a lot 😬 With the hype around Zone 2 nowadays, I just wanted to write this to give my perspective with the hope it helps 😉. Thanks for reading 🙏