When you start to exercise, your body has to make some changes in order to keep up the level of exercise.


The muscles start to produce more CO2 as they work harder

To get rid of the extra CO2 you start to breathe deeper and faster

Your heart rate increases to pump more oxygen around the body

Your arterioles widen to stop your blood pressure increasing

Blood is diverted away from inactive organs (stomach/liver) and towards the working muscles through vasoconstriction and vasodilation

When the muscles contract they squeeze blood back towards your heart

The heart contracts even stronger to pump more blood with each beat


The body has also developed ways of dealing with the negative effects of exercise:

  • Blood is directed closer to the skin to help loose heat through radiation and prevent us overheating
  • We sweat more during exercise to help cool us down. The sweat evaporates which uses heat in doing so


Recovering from Exercise

When you stop exercising, it takes a while for your body to return back to its normal, resting state. This is to help clear away the waste products of exercise, such as Carbon Dioxide and lactic acid.

  • Your heart rate will slowly fall, The fitter you are, the quicker it will return to normal
  • Breathing rate will slowly return to normal, your body needs extra Oxygen following exercise to help get rid of lactic acid
  • It can take up to 48 hours to replenish your stores of glycogen
  • Muscles often suffer small micro tears during exercise and need to be repaired over the next 48 hours
  • Overall, the amount of time your body takes to recover will depend on how fit you are and how hard the exercise was!


Heart rate graph


This graph shows the difference between the heart rate of a fit person who exercises regularly and someone who does not exercise. You can see the following:

  • The fit person has a lower resting heart rate before they begin to exercise
  • The fit persons heart rate rises more slowly
  • The maximum heart rate reached by the fit person is a lot lower than the unfit person
  • The fit persons heart rate drops quicker when they finish exercise
  • The heart rate of the fit person returns to their resting heart rate in a quicker time

Aerobic Exercise

Aerobic exercise is submaximal exercise which gets your heart rate and breathing rate up, over a sustained period. For example, jogging, swimming, cycling. Aerobic exercise is excellent for the health of your heart and lungs. If you perform aerobic exercise regularly your body adapts is the following ways:

  • Makes more red blood cells so more Oxygen can be transported in the blood
  • Your arteries become wider and more elastic so that your blood pressure falls
  • Your heart grows bigger (hypertrophies) and the walls become thicker so it can pump more blood with each beat. This means it doesn't have to beat so fast!
  • More capillaries grow within your muscles so that more O2 can get there quicker
  • Your heart rate returns to normal more quickly following exercise
  • More capillaries also grow around the alveoli in your lungs so more O2 is taken into the blood and more CO2 is released
  • Your diaphragm and intercostal muscles become stronger so they can make your chest cavity bigger meaning you can breathe in more air with each breath


When you notice yourself becoming fitter, it is because of all of these adaptations!

Exercise also causes adaptations within your muscles, joints, bones and energy systems:

  • Your muscles grow larger (hypertrophy) and stronger
  • Your tendons grow bigger and stronger
  • Your body gets better at burning fat - even when you aren't exercising
  • Your muscles get better at using oxygen
  • Your VO2 max increases
  • Ligaments and cartilage at your joints grow thicker and stronger
  • Bones become stronger