VO2max part II - Fat x Sugar

Hello everyone, this is VO2max Part II and I want to focus on the concept of the “crossover point”. In part I, I mentioned that the crossover point referred to the exercise intensity at which glucose and fat contribute equally to energy production (50%/50%). However, the type of diet regularly adopted strongly influences the crossover point. For example, two distinct situations can be identified. The graph on n the left shows the contribution of fat and carbohydrate to energy production as exercise intensity increases for subjects on a high-carb/low-fat (HCLF) diet. We can see that even though the energy derived from fat reduces, whereas the energy derived from carbs increase as the intensity of exercise goes up. It is interesting that the two lines (blue line fat and red line carb) never touch each other for HCLF. In other words, there is an elusive crossover point. This is because the abundance of carbohydrate is so high that it will always be the predominant source of energy for exercise. In fact, even at its highest point, the energy derived from fat does not surpass 40 to 45%. Now, look at the graph on the right that depicts subjects on a low-carb/high-fat (LCHF) diet. We notice that, even though the energy derived from fat reduces as the intensity of exercise increases, a clear crossover point can be identified, and it happens at ~85% of VO2max. This is in clear contrast with the figure on the left in which the elusive “crossover point” happens at ~50% of the VO2max. This again shows that the macronutrient composition of the diet largely determines whole-body substrate preference. This last graph displays my VO2max test data showing that my crossover point was also at 85% of VO2max, which is consistent with the high rate of fat oxidation typical of someone adapted to a low-carbohydrate diet. I also want to draw the attention to the fact that I plotted both the percentage of VO2max and my heart rate in bpm on the x axis. This allows me to use HR as an indication of the exercise intensity at which my body shifts substrate preference. Interestingly, I did a test on the track using the Garmin watch and it tells me that my lactate threshold is around 160 bpm, which is right where there is a sharp increase in energy derived from glucose on the graph. These are just some of the useful information anyone can use to identify training zones for endurance training and/or to prescribe exercise for anyone. That’s it for now. Thanks for watching and I’ll see you in the next.