Bioenergetics: Aerobic Pathway

Last time, we discussed how the body generates energy for physical activity via the anaerobic pathway. Now, we will discuss how the body generates energy via aerobic pathways.

Another product of the phosphagen system is AMP. AMP stimulates glycolysis, the next energy-producing system. Glycolysis not as fast as single step phosphagen system. But glycolysis can produce more ATP, due to higher levels of availability of the substrate glycogen stored in the muscle or via glucose in the blood, vs CP. One interesting fact is that skeletal muscle has about 6 times concentration of CP than ATP, so can make more ATP initially, in addition to the ATP already stored in the body.

The third way to get ATP to be used as energy is the oxidative system. At rest and during low-intensity activities, both carbohydrates and fats are utilized in the oxidative system to create ATP to sustain these activities. As intensity increases, there is a shift in substrate preference from fats to carbohydrates. Regarding fats, triglycerides are stored both in fat cells, and to a limited extent, also in muscle cells. Actually, fat oxidation through the aerobic oxidative system has much more capacity for ATP synthesis, and thus, energy, when compared to the protein and carbohydrate substrates. One triglyceride molecule can yield over 300 ATP.

Basically, there is an inverse pattern between rate of ATP production vs capacity for ATP production. Let’s consider three running activities – 100 meter dash, 400 meter relay, and a marathon .For a sprint, this will be primarily engaging the phosphagen system, and the fast glycolysis. The rate of ATP production will be high, but capacity will be low. Thus, the reason why we cannot sprint for that long of a distance. As we move onto a 400 meter relay, energy via the phosphagen system will be depleted, and will be of no use until the substrates are repleted. Thus, glycolysis will provide most of the energy. The substrates (phosphagens and glycogen, respectively) for these systems need to be replenished for physical activity to continue at the same intensity or longer duration. Lastly, the oxidative system takes over when we run a marathon, which requires a prolonged energy source. In the oxidative system, the rate of ATP production is lower compared to the first two systems, but the capacity is large.

The biochemical reactions occurring in both the anaerobic and aerobic pathways create by-products which are not able to be used by the body for physical activity. Light activity during post-exercise period increases rate of recovery by clearing those by-products which induce muscle fatigue in the body.