Why do working muscles need oxygen

Energy comes from foods rich in carbohydrate, protein and fat. However, ATP is not stored to a great extent in cells. So once muscle contraction starts, the making of more ATP must start quickly. Since ATP is so important, the muscle cells have several different ways to make it. These systems work together in phases.

The three biochemical systems for producing ATP are, in order:. All muscle cells have a little ATP within them that they can use immediately — but only enough to last for about 3 seconds! So all muscle cells contain a high-energy compound called creatine phosphate which is broken down to make more ATP quickly.

Creatine phosphate can supply the energy needs of a working muscle at a very high rate, but only for about 8—10 seconds. Fortunately, muscles also have large stores of a carbohydrate, called glycogen, which can be used to make ATP from glucose. This means that oxygen is very important, and as you exercise, energy requirements go up — so you need more oxygen. Oxygen is first absorbed by the blood as it passes through the lungs, binding to a special protein called hemoglobin contained within red blood cells.

Now tied to hemoglobin, oxygen is pumped by the heart through the vascular system to the rest of the body. The oxygen is then released into the cells where it is used in the breakdown of molecules to create needed energy.

Muscles performing work require increasing amounts of energy as the workload increases, which correspondingly requires more and more oxygen. We breathe more when we exercise to help remove the large amount of carbon dioxide CO 2 that is produced by the working muscles. As carbon dioxide levels increase, hydrogen ions are also produced, which reduces the pH of the system, which is very tightly regulated through chemoreceptors in the brain and carotid arteries.

Figure 1. We observe that the VO 2 oxygen uptake increases as intensity increases and drops upon stopping the exercise. Oxygen deficit is defined as the difference between the oxygen intake of the body during the early stages of exercise and during a similar duration in a steady state of exercise. EPOC is an abbreviation for excess post-exercise oxygen consumption also known as oxygen debt and refers to the amount of oxygen required to restore your body to its normal, resting level of metabolic function.

To understand this effect, think about how you breathe heavy for a while after you have finished a hard run. However, it is important to note that the heavier breathing required by the body in the EPOC stage is not delivering more oxygen — but instead eliminating excess carbon dioxide in order to maintain a healthy pH balance.

Muscles can produce energy without oxygen in a process called anaerobic metabolism. The only fuel that can be burned anaerobically is carbohydrate, being converted into a substance called pyruvate through glycolysis and then into blood lactate via anaerobic metabolism. Oxygen and glucose are your 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. 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 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. As you begin to exercise, you use up these reserves, and oxygen-hemoglobin saturation in your bloodstream drops sharply.