Question

Given that your cells undergo lactic acid fermentation when they don't have enough oxygen, why does muscle function decrease when there is less oxygen than the cells need? Explain

Answer 1

Lactic acid fermentation

In lactic acid fermentation, NADH, transfers its electrons directly to pyruvate, generating lactate as a byproduct. Lactate, which is just the deprotonated form of lactic acid, gives the process its name. The bacteria that make yogurt carry out lactic acid fermentation, as do the red blood cells in your body, which don’t have mitochondria and thus can’t perform cellular respiration. Lactic acid fermentation has two steps: glycolysis and NADH regeneration. During glycolysis, one glucose molecule is converted to two pyruvate molecules, producing two net ATP and two NADH. During NADH regeneration, the two NADH donates electrons and hydrogen atoms to the two pyruvate molecules, producing two lactate molecules and regenerating NAD+. Muscle cells also carry out lactic acid fermentation, though only when they have too little oxygen for aerobic respiration to continue—for instance, when you’ve been exercising very hard. When you exercise, your respiratory rate increases. This is true regardless of whether you exercise by stationary methods such as weight lifting, or by a traveling method such as jogging or biking. Clearly, an active body needs more oxygen than a body at rest. The reason for this lies in the complex chemical processes in your muscles and your bloodstream.

Your body needs oxygen at all times. Oxygen and glucose are the body's basic energy building blocks. It requires them to make your heart pump blood, to keep your lungs inhaling and exhaling, and to allow every other organ and cell to function. Every one of these activities uses up energy that must be replaced in part by taking in more oxygen. When you exercise, your muscles move more vigorously than when you are at rest. Their metabolic rate increases. They need more energy, so they produce more of the chemical energy molecule ATP. You need oxygen to produce ATP, so the more ATP you produce, the more oxygen your body requires. Oxygen reaches your muscles and other parts of the body by means of your bloodstream. Oxygen dissolves into the plasma, where most of it -- about 98.5 percent, according to information from Eastern Kentucky University -- becomes attached to hemoglobin molecules. While you're resting, only about 20 to 25 percent of the hemoglobin molecules give up their oxygen to your tissues. A lot of oxygen remains in the bloodstream in reserve.

Cellular respiration is the process in which your muscles use oxygen to produce ATP energy. The process is simple. Your body obtains oxygen from the ambient air you breathe. It enters the bloodstream and is carried to your muscles, where some of it is used immediately, and the rest is stored by a compound called myoglobin. Whether you’re exercising or not, the oxygen in your body is used to break down glucose and create the fuel for your muscles called ATP. During exercise, your muscles have to work harder, which increases their demand for oxygen. This is why your breathing and heart rates increase: To help pull more oxygen into your bloodstream. As you exercise, the oxygen that reaches your muscles never leaves, but rather converts the available glucose into ATP. So what occurs when your body runs out of oxygen or your other systems simply can’t deliver it to your muscles quickly enough? Your muscles begin converting glucose into lactic acid instead of energy, anaerobic exercise takes over, power output drops and fatigue sets in. Unfortunately, anaerobic exercise can only sustain temporarily before your muscles run out of energy completely and become fatigued. Oxygen also plays a huge role in the recovery process because it helps restore pre-exercise ATP levels and helps your liver break down lactic acid into simple carbohydrates. This is why so many high-level athletes do “cooldowns.” Cooldowns get more oxygen into the body after intense exercise where it can expedite the recovery process. No matter how you look at it, the more oxygen you have in your body during and after exercise, the better you will perform and the faster you will recover. Incorporate O⁺recreational oxygen before your next workout to give your body the oxygen support it needs to recover better and faster.

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