– Energy Transport Systems

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As far as I’m concerned the human body has 5 methods for producing energy. Glycolysis, lactic acid pathway, aerobic respiration, lipid metabolism, and protein metabolism.

If I were to go exercise what method would these systems take on? Surely they don’t all occur at the same time and which method is most efficient?

In: Biology

Glycolysis is the first step in all respiration, whether aerobic or anaerobic. You’re constantly doing it as necessary to maintain enough ATP and ADP to run your cells.

When you’re idle or lightly exerting yourself, it’s all aerobic respiration. It’s efficient, which is a key part of powering our huge brain and huge legs.

The problem is that it’s slow. You need to inhale a bunch of oxygen, transport it into the middle of your cells, do a bunch of crazy chemical reactions, get the byproducts out of your cells, and transport the carbon dioxide to your lungs. Most of the time, this comfortably powers your body and provides a nice reserve of energy-storing ATP in your bloodstream.

When you exercise, you quickly consume all that ATP in your blood. Eventually, you overload your aerobic respiration – you literally can’t breathe fast enough to get enough oxygen in and enough carbon dioxide out.

That’s when your anaerobic respiration kicks in. This process is faster and doesn’t require oxygen or produce CO2. The downsides are that it’s not very efficient, and it converts an important chemical for aerobic respiration into useless lactic acid, which later needs to be converted into CO2.

Metabolism deals with getting that glucose into your bloodstream from food. During digestion, your body will salvage many chemicals from food you eat, but others will be metabolized into glucose or stored as fat in lipid cells.

If you don’t eat enough food to replenish your blood glucose, well, you’ll get hungry. Your body is OK with maintaining a low level of energy stores – after all, our caveman ancestors couldn’t hunt three meals a day. The human body disregards a brief diet.

Eventually, if you’re chronically malnourished, your body realizes that food isn’t coming, and it needs to hit the reserves. You literally begin eating yourself, a process called catabolism. You start with reserves of glycogen in your liver, then in your muscles. If you’re still not getting enough calories, your body starts eating the lipids in your fat cells, and you lose weight! Yay!

This is why it’s important to diet and exercise together – your fat cells are reserved for desperate circumstances – that is, weeks of undernourishment. You need to trigger this process by spending way more energy than you ingest, long enough that your body thinks you’re in a famine.

If you keep dieting or overexerting yourself after the point where your body fat is depleted, your body’s only option is to catabolize your muscles, and you start to wither. Don’t do this – not only is this dangerous, but the byproducts are toxic.

By the way, catabolic processes aren’t fast enough to keep up with respiration. Once your blood glucose and glycogen reserves are totally depleted, and there’s nothing in your blood that can be easily converted to glucose, you collapse of exhaustion.