Integrated Metabolism and Hybrid Electric Motors

Anaerobic metabolism arises as a result of the development of aerobic metabolism and vice versa. It is a myth that the aerobic system turns off while the anaerobic system turns on. Sprinters too often neglect their aerobic / oxidative metabolism. We need to rethink metabolism in an integrated manner and no longer in “pathways” (See Box 2)! Metabolic energy systems are very complex and many new terms such as ATP, glycolysis, phosphocreatine, lactate, lactic acid, alactate (without lactate), and intramuscular triglycerides (lipid).

To better understand integrated metabolism, it is useful to compare our bodies to a complex hybrid electric engine. Even this is certainly an oversimplification, but useful in understanding how we use energy during a marathon.  A complex hybrid car engine uses a combination of a gasoline internal combustion engine and a battery powered electric drive system. The batteries are powered by the gasoline engine and produces electricity for later use. In our case the internal combustion engine is our ability to use glucose and fat to make energy in the form of ATP. We also possess two electric batteries that make ATP, the phospho-creatine system and the anaerobic lactate system. It is important that these engines batteries are interdependent and work together.  Our engines use all the potential electrical and thermal energies synchronously. The electric motor is the anaerobic metabolism while the gas engine is the aerobic metabolism whose maximum power is the famous VO2max. These motors are interdependent because we can only mobilize energy at 100% of our VO2max if we produce enough power from our two electric motors. From a physiological standpoint, our pistons (shortening and lengthening of our muscle fibers) operate thanks to two electric motors. These two electric motors are powered by batteries, a small phosphocreatine high-power battery (anaerobic alactate glycolysis) whose disadvantage is that it is quickly discharged, and a large lactate battery (anaerobic lactate glycolysis). The lactate battery is self-limiting and controlled by the muscular acidity level and has nothing to with lactic acid. The anaerobic phosphocreatine system is the fastest and most powerful and is not affected per se by the acidity level. As its name suggests, this system works without oxygen, and doesn’t produce lactate and lasts for about 6 to 15 seconds.  The anaerobic lactate system works without oxygen, produces lactate and last for about 2 minutes. We have known for a bit more than a decade that these batteries, (anaerobic alactate and lactate) are recharged as soon as the runner “lifts” his foot.

Indeed, creatine phosphate is reconstituted by oxygen consumption and lactate is converted back into pyruvate which provides energy to the engine. This is the principle of optimal speed variation that will result in a faster performance on average than constant speed. Our bodies truly are hybrid vehicles in the diversity of its engines and their operations. The oxygen supply of the combustion engine is performed by the heart which distributes in a circuit which in turn feeds both engines (thermal and electrical) nutriments and oxygen. It also allows for the recycling of metabolites produced by these engines for internal recycling. The only major difference between the human engine and that of a machine, is that the electric motor cannot work alone, even on a 100-meter sprint! Indeed, even for the efforts of 10 seconds (100 meters run by elite runners), 30% of the energy is provided by the combustible heat engine in the same proportions as a 3000-meter effort (Figure 27). A sprinter reaches 100% VO2max from the 3rd second of the race and fights to stay there to the end. Hence the interest for a sprinter like Usain Bolt to possess a high VO2max.