stand off wrote:
In this workout, the athletes use a different fuel source every couple reps. First 2 reps are purely using fat for energy. then for the next 2 it's aerobic at the lactate threshold. then at the end it's purely anaerobic using the glycolytic energy system.
......
You are WRONG. The first two reps of his workout, based on % of VO2 max, fall into the aerobic threshold range where fatty acids are the primary substrate.
You know nothing of exercise physiology. The first rep uses fat and the next two use aerobic? Didn't realize aerobic was a fuel source and using fat wasn't aerobic... I mean seriously. You're mistaken and need to be clearer with your words. Carbs and fat are the fuel sources, aerobic and glycolytic are ATP generation pathways. Glycolytic is by definition anaerobic? For fast glycolysis, yes, but not for slow glycolysis. Regardless, the last rep isn't even close to using purely anaerobic energy.
If you listened to the video, the last rep was supposed to be at 2k-3k race effort. The contribution from the glycolytic system is less than 20% of the total energy demands for that pace. The fast glycolytic system is really good for up to 1 minute at max effort, and a bit longer with a more controlled effort (~2 minutes), but beyond that aerobic energy sources are dominant.
Even if the first rep was at marathon pace, the primary fuel source would still be carbohydrates. For most easy runs, about half of the calories still come from carbs. Jogging uses more calories from fat than carbs, but if they're jogging in between reps and using fat for fuel, they must be wasting their time, right? Nonsense.