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If you've ever taken a biology course, you may have heard of the process called "cellular respiration" in which your body produces energy. But how does it work? And how does understanding this improve my fitness goals?
If you've ever taken a biology course, you may have heard of the process called "cellular respiration" in which your body produces energy. But how does it work? And how does understanding this improve my fitness goals?
It's important to first understand that cellular respiration takes place in every cell (as they all need energy) in the mitochondria, notably the "powerhouse" of the cell. The more mitochondria you have, the more energy you can produce. Sounds simple enough. You can increase your body's mitochondria count through nutrition, exercise, and sleep. With more healthy mitochondria, you can effectively prevent or delay the onset of numerous diseases (study linked here).
So now that we've got the importance of mitochondria settled, let's talk about how it gets the needed elements to perform cellular respiration. Glucose, the body's primary source of energy, is created when your body breaks down carbohydrates and fats into simple sugars, fructose, galactose, and glucose. Your digestive system will rely more on carbohydrates as this source because fats are much more complex; it takes more energy (that your body is trying to save) to break down fats than simple or even complex carbohydrates, so it will usually store them as adipose tissue throughout the body for a last resort. Once your digestive system breaks down the food you've eaten, glucose will be absorbed in the digestive linings and sent to the bloodstream. As a response to the glucose in the blood, your pancreas releases a hormone, insulin. Insulin, also critical in muscle growth, helps deliver glucose to the cells. The heart, famous for pumping blood throughout the body, will also aid this transportation to every cell. Once the glucose reaches the extracellular region, the phospholipid bilayer will let it in, package it in a vacuole, and deliver the energy source to the mitochondria.
Now, cellular respiration begins. Glucose alone cannot produce enough chemical energy. Oxygen is added. In aerobic exercise, just as the name ("aer" = "air) suggests, cellular respiration creates energy to fuel the activity. The ultimate output of cellular respiration (besides carbon dioxide which you will breathe out, and water, which you may go towards sweat, in addition to other bodily processes that require H20) is ATP -- adenosine triphosphate. ATP has stored potential chemical energy in it's phosphate bonds that your muscles can utilize to keep you moving, your heart pumping, your stomach digesting, etc.
Then, the leftover NADH, AKA nicotinamide adenine dinucleotide for those that were curious, from both glycolysis and the Krebs Cycle, and FADH2 go to the Electron Transport Chain. NADH reverts to NAD+; FADH2 reverts to FAD2+; ADP (two phosphates as opposed to three) + P creates ~32 ATP molecules; and all the remaining H+ molecules combine with Oxygen to form H2) molecules.
First, glucose is converted to pyruvic acid in the process of "glycolysis." This produces 2 net ATP/molecule of glucose.
Next, pyruvic acid goes into the Krebs Cycle. Here, acetyl Co-A (Co meaning coenzyme) will break off into Co-A and citrate. NAD+ will convert to NADH, taking an H from the citrate; FAD2+ will convert to FADH2, taking two Hydrogens from the citrate; carbon dioxide is released with remaining carbons. All in all, 2 ATP and roughly 6 NADH, 3 FADH2, and 4 CO2 are outputted from the Krebs Cycle.
In total, 36 ATP are produced per 1 glucose molecule. It is then ejected from the mitochondrial membrane, travels through the cell's cytoplasm, and is sent out of the cell and "is consumed for energy in processes including ion transport, muscle contraction, nerve impulse propagation, substrate phosphorylation, and chemical synthesis." The energy stored in phosphate bonds is released when ATP loses one P and turns back into ADP.
Why is this important when exercising?
Why is this important when exercising?
Well, this can be critical for proper fueling and breathing. Through eating short diffusion carbohydrates (simple sugars) roughly 30 minutes before exercising, your mitochondria will have lots of glucose to produce energy. For longer excursions, fuel the night before with pastas and breads so that the glucose will be stored in the muscle's and the liver's glycogen. When your long run or bike ride begins, your body will draw to these stores and produce ATP. You will "hit a wall" if you do not fuel properly, as your body will have to turn to fat reserves -- a conversion process that takes a lot more energy and time and will therefore not supply enough energy fast enough.
Everyday processes (i.e. breathing) take lots of energy, but organized physical activity require adequate fuel.
Of course, everything on a case-by-case bias, and no this is not a reason to eat an entire bag of candy before your next run (fueling properly means fueling smart); be sure to consider your type of activity when planning when and what to eat. Going on a longer run tomorrow morning? Eat a more carb-heavy dinner tonight. Weight lifting this afternoon? Eat a more balanced lunch with complex carbohydrates for continuous energy and plenty of protein for muscle building. Etc., etc., you get the idea. In the end, it really comes down to your needs. But now, hopefully, you can look at your next Oreo or bowl of rice and understand how that helps keep you alive and moving to do whatever you desire.
Written By: Siena
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