Exercise and Oxygen Debt

When we are relaxing, there is a relatively low demand for energy because we aren’t moving. However, when we exercise, the demand for energy increases due to more muscle contraction. Our bodies have to respond to this increased demand for energy.

The Effects of Exercise

When we exercise, we have to use our muscles much more than usual. This means that the rate of cellular respiration must increase. As aerobic respiration requires oxygen, we will need to get more oxygen and glucose to our muscles.

To achieve this, there is an increase in:

  • Breathing rate – We breathe more frequently. However, this will cause us to use our respiratory muscles more than usual, which will require more energy
  • Breathing volume – We take in more oxygen with each breath
  • Heart rate – We can pump oxygen to the cells at a faster rate

Although, sometimes we still cannot supply enough oxygen to the muscles, especially if we are exercising hard. So instead, anaerobic respiration takes place in the muscles.

Measuring the effects of exercise

The two main ways to measure the effects of exercise on the body are:”

MeasurementDefinitionHow to measure it
Heart rate Number of times the heart beats per minute Press the index finger and middle finger on the inside of your other wrist (located on the thumb side of your wrist)
Respiratory rate (Breathing rate) Number of breaths taken per minute Count how many times the chest rises per minute

Oxygen Debt

When we are doing vigorous exercise, our cells may need to use anaerobic respiration, which is far less efficient than aerobic respiration. However, if there isn’t enough oxygen available, efficiency becomes less important and anaerobic respiration becomes our primary option.

The main problem with anaerobic respiration is that the oxidation of glucose is incomplete. This causes lactic acid to build up in the muscles. You might recognise this from the burning sensation you feel in your muscles during vigorous exercise.

  • Lactic acid buildup stops muscles from contracting efficiently

As soon as we finish exercising, our liver gets rid of the lactic acid by reacting it with oxygen. So, the more lactic acid is built up, the more oxygen will be required to get rid of it. This is called oxygen debt.

We repay this oxygen debt when we continue to breathe heavily even after stopping vigorous exercise. The lactic acid is transported from the muscles to the liver, where it is converted to glucose.