Exercise and metabolism
How the body responds to exercise
During exercise, muscles contract more and need more energy, so they respire faster. This means they need more oxygen and produce more carbon dioxide. To supply more oxygenated blood to the muscles and remove the carbon dioxide, the body increases:
- — the blood is pumped round faster.
- — more breaths per minute.
- — deeper breaths, taking in more air each time.
Key terms
Anaerobic respiration and muscle fatigue
During long periods of vigorous activity, the body can't supply oxygen to the muscles fast enough, so they start to respire . This produces , which builds up in the muscles.
The muscles become — tired and less able to contract efficiently. They may also start to ache or cramp.
Key terms
Oxygen debt (Higher tier)
After exercise, you keep breathing hard for a while. This is because of the : the amount of extra oxygen the body needs after exercise to react with the lactic acid that has built up and remove it from the cells.
Blood flowing through the muscles carries the lactic acid to the liver, where it is converted back into . Heart rate and breathing stay high until the oxygen debt has been repaid.
Key terms
Metabolism
is the sum of all the reactions in a cell or the body. The energy released by respiration is used for many enzyme-controlled metabolic reactions, including:
- converting glucose into , (in animals) and
- forming from one molecule of glycerol and three molecules of fatty acids
- using glucose and to form amino acids, which are then used to make
- itself
- breaking down excess proteins to form , which is excreted