Responses to exercise

In a nutshell

During exercise your muscles need lots of energy, this causes muscle cells to respire more. To respire more, your body needs more oxygen and this is achieved by increasing your heart rate, breathing rate and breathing volume. If the oxygen is not delivered quickly enough, your muscle cells will respire anaerobically. This process produces lactic acid and can cause painful cramps. Once exercise is completed, the body will need to repay the oxygen to the muscle cells.

Increasing the rate of respiration

During exercise, your muscles must contract a lot. In order to do this, the muscle cells need a lot energy from respiration. To increase the rate of respiration, the cells require more oxygen. 

Therefore, your body must deliver more oxygen to your muscle cells. To achieve this, your heart rate, breathing rate and breathing volume (how deep your breaths are) will increase. 

Increasing your breathing rate and volume will increase the amount of oxygen that enters the blood. This means that there will be more oxygenated blood. Your heart will then have to beat faster in order to pump this oxygenated blood around the body and to the muscle cells.

Anaerobic respiration

During intense exercise, your body can't supply your muscle cells with enough oxygen. In this case, your muscles will respire anaerobically. Anaerobic respiration will produce lactic acid. This will build up in the muscles and cause painful cramps.

​$$glucose\rightarrow lactic\ acid$$​​

Anaerobic respiration produces less energy than aerobic respiration as it is less efficient. If your muscles respire anaerobically for a long period of time they can become very fatigued.

Oxygen debt

Definition

Oxygen debt is the amount of oxygen your body needs after exercise. During exercise your body couldn't provide your muscle cells with enough oxygen so they were respiring anaerobically. When you stop exercising, your body must 'repay' the oxygen to the muscle cells.

This is why you still breathe heavily after exercise as your body is trying to transport more oxygenated blood to your muscle cells.

Note: Higher tier students need to know that blood flowing through the muscles will carry the lactic acid to the liver where it is broken down into glucose.