Respiratory System During Exercise of Differing Intensities and Recovery

Exercise Intensity and the Respiratory System

The respiratory rate is the number of breaths taken per minute and tidal volume is the volume of air in each breath.
At rest, an average adult’s respiratory rate is 12-20 breaths per minute and tidal volume is approximately 500ml.
However, with increased exercise intensity, both respiratory rate and tidal volume increase to deliver more oxygen to working muscles and to remove the buildup of carbon dioxide.

Aerobic respiration is the method our bodies use to convert glucose and oxygen into energy, carbon dioxide, and water. This occurs during exercise of low to moderate intensity.
Anaerobic respiration occurs when the demand for oxygen exceeds the supply, typical during high intensity exercise. In this case, the body creates energy through the breakdown of glucose without the use of oxygen, creating lactic acid.

VO2 Max, or maximal oxygen uptake, is the maximum amount of oxygen an individual can utilise during intense exercise. It’s a measure of a person’s cardiovascular fitness and aerobic endurance.
During low to moderate intensity exercise, oxygen supply can meet demand and VO2 remains within its maximum limit.
During high intensity exercise, oxygen demand exceeds supply and the working muscles must rely on anaerobic respiration, despite the fact that the VO2 has reached its maximum.

During the recovery period after exercise, the breathing rate and tidal volume remain elevated to remove excess carbon dioxide, to repay the body’s oxygen debt and to cool down the body.
Gradually, as the body’s need for oxygen returns to resting levels, both respiratory rate and tidal volume will also slowly return to their resting values.

Oxygen debt, also known as Excess Post-exercise Oxygen Consumption (EPOC), refers to the amount of oxygen needed to restore the body to its resting metabolic state. Oxygen is needed to break down the lactic acid produced during anaerobic respiration.
During the recovery period, there is a high demand for oxygen to repay this debt which is why the respiratory system remains active post-exercise.

The breathing rate remains high during recovery to expel carbon dioxide, a by-product of aerobic and anaerobic respiration, from the body.
The body also works to remove lactic acid, produced during anaerobic respiration, from the muscles. This is transported in the bloodstream to the liver where it is converted back to glucose.

A proper cool down after exercise includes lightweight aerobic activity and stretching exercises. The purpose is to gradually bring breathing and heart rates down to their resting states and to promote recovery.
Skipping the cool down can lead to dizziness and slow the removal of waste products from the muscles, prolonging recovery and possibly leading to muscle soreness.