Respiratory Responses to Exercise
Two of the major functions of the respiratory system (the lungs and the tubes through which air pass into and out of the body) are to:
1. Provide oxygen (O2) to the tissues of body via the lungs
2. Eliminate carbon dioxide (CO2) from the tissues of the body via the lungs
As with the cardiovascular system (heart, blood and blood vessels) greater demand is placed on these key functions with certain types of exercise.
As exercise commences pulmonary ventilation (breathing) increases in direct proportion to the intensity and metabolic needs of the exercise. This is shown on the adjacent graph. Note that pulmonary ventilation is expressed in terms of litres of air inhaled and exhaled per minute (L/min)).
Ventilation increases to meet the demands of exercise through the following two methods:
1. An increase in ‘tidal volume’ which refers to the quantity of air that is inhaled and exhaled with every breath. This is similar to ‘stoke volume’ in the cardiovascular system.
2. An increase in the ‘respiration or breathing rate’ which refers to how many times a person completes an inhalation and exhalation every minute. This is similar to ‘heart rate’ in the cardiovascular system.
If the exercise is intense, breathing rates may increase from a typical resting rate of 15 breaths per minute up to 40 – 50 breaths per minute.
The most commonly used measure of respiratory function with exercise is known as VO2 (volume of oxygen uptake). VO2 refers to the amount of oxygen taken up and used by the body.
With continuous exercise (≥ 1 minute in duration) such as aerobic fitness, longer duration anaerobic fitness and to a lesser degree muscular endurance training, VO2 increases linearly with increases in exercise intensity. This is due to an increasing reliance on oxygen to help provide energy as exercise continues.
As the intensity of exercise continues to increase a person reaches a maximum point above which oxygen consumption will not increase any further. This point is known as VO2 max and is shown on the following graph.
Training types with moderate – high intensity, longer duration (≥ 1 minute) and have short or no rests throughout create what is known as 'EPOC'. EPOC stands for 'Excess Post-exercise Oxygen Consumption', and relates to the bodies need to keep consuming oxygen at a greater than resting rate once exercise has finished to make up for an oxygen 'debt' that is created when exercise commences. We'll explain this a little more in relation to the following graph.
As longer duration exer
The size of the deficit largely determines the time that will be spent in recovery to ‘re-pay’ the oxygen debt.
Respiration rate and depth remain elevated during this recovery period in order to expel carbon dioxide and return the acid–base balance of the muscles to neutral.
During intense sessions focusing on muscular endurance and/or anaerobic fitness respiration rate and depth may remain elevated for 20-40 minutes after the workout.
When it comes to exercise the respiratory and cardiovascular systems are largely geared to the intake and supply of oxygen for energy and removal of the waste products carbon dioxide and lactate.
For these reasons we expect the greatest response of these systems to occur with training that relies on oxygen for energy and produces significant amounts of carbon dioxide and lactate.
For this reason the response of the respiratory system to these training types will be minimal. Breathing rates will rise slightly during a warm up, there may be a slight peak in breathing rate shortly after each set and breathing rate will return to normal within a few minutes of finishing the training session.
The respiratory system response becomes greater as exercise increases in duration and the demand for oxygen becomes more prevalent.
With muscular hypertrophy training we will see greater peaks in breathing rates at the end of each set than we would for strength training as lactate starts to accumulate requiring oxygen to help metabolise it.
It may take 10-20 minutes post exercise for the breathing rate to return to normal with hypertrophy training because of this.
Breathing rates will have larger peaks at the end of each work interval due to limited recovery time. Breathing rates will compound over the total duration of the session and stay elevated for longer post workout. Similar responses will occur for anaerobic fitness training.
Training to improve aerobic fitness results in responses from the respiratory system that are very similar to the responses of the cardiovascular system for aerobic fitness.
Breathing increases up to ‘steady state’ where the supply of oxygen and expulsion of carbon dioxide meets the demands of the exercise.
Breathing rates remain relatively constant once steady state has been reached (as long as the intensity of the exercise
remains constant), or fluctuate if the intensity fluctuates, much like the heart rate response to fluctuating intensities.
Breathing rates return to normal within 10-20 minutes after a primarily aerobic fitness session, as the respiratory system is not ‘overstressed’.
The largest peaks in breathing rate and the longest periods of EPOC will occur with training for muscular endurance and anaerobic fitness.
These types of training with prolonged periods of high intensity work and limited recovery put the greatest demands on the respiratory and cardiovascular systems, and therefore have the greatest acute response.
