Why do breathing rates remain high after exercise?

The human respiratory system is adapted to allow air to pass in and out of the body, and for efficient gas exchange to happen. Exercise and smoking both affect the lungs and circulatory system.

The body's respiratory rate remains elevated following exercise, a phenomenon known as Excess Post-Exercise Oxygen Consumption, or EPOC. EPOC occurs as the body works to return its systems to homeostasis, or the resting state that preceded exercise. The additional oxygen consumption is used to replenish energy stores, return oxygen and hormone levels in the bloodstream to normal, and restore body temperature, ventilation and heart rate. EPOC may last several minutes to up to 24 hours, depending on what type of exercise was performed 1.

Replenishing the body's energy stores requires the use of more energy. During EPOC, the body replaces creatine phosphate and adenosine triphospate, or ATP, fuels that are used in quick bursts of activity. It expends energy to convert the waste product lactic acid to pyruvate, a viable fuel source. In addition, glycogen stores within individual muscles are restocked.

• Replenishing the body's energy stores requires the use of more energy.
  
• In addition, glycogen stores within individual muscles are restocked.

Balancing Oxygen and Hormones in the Bloodstream

Two changes occur in the bloodstream during exercise that require EPOC 2. The body draws upon oxygen in the blood for energy when working out. Therefore, following activity it must replenish these stores. Secondly, hormones that flood the bloodstream during exercise must be restored to normal levels.

• Two changes occur in the bloodstream during exercise that require EPOC 2.
  
• Secondly, hormones that flood the bloodstream during exercise must be restored to normal levels.

Heat is produced during exercise, which elevates the body's core temperature 2. In the period of EPOC, the body requires additional energy to activate its cooling systems. Ventilation and heart rate, which are both working overtime during EPOC to replenish energy stores and serve the needs of the bloodstream, require increased energy themselves. As the overall post-exercise system requirements are met, breathing and heart rates gradually return to normal 1.

Get the Most Out of EPOC

EPOC is highest following certain types of physical activity. For someone who is trying to lose weight and decrease body fat percentage, a lengthier EPOC will be beneficial to reaching overall goals. Aerobic activity followed by resistance training in the same session has been found to have higher rates of EPOC than resistance training followed aerobics. High Intensity Interval Training, exercising in short bursts of intense activity, places increased demands on the body during EPOC. Supersetting, or performing weight training exercises back-to-back with minimal rest between sets, has also been shown to boost energy expenditure in EPOC.

• EPOC is highest following certain types of physical activity.
  
• Aerobic activity followed by resistance training in the same session has been found to have higher rates of EPOC than resistance training followed aerobics.

By Nicole Vulcan Updated April 29, 2019

If you just started working out, you may be concerned about all the spluttering and gasping for air that you're doing. Don't worry though — that heavy breathing is happening for a very good reason. And as you get fitter, expect those effects not to subside completely, but to stop being quite so dramatic.

During exercise, your breathing increases to deliver more oxygen to your hard-working muscles.

When you work out, your muscles move from a resting state to an active one, and they need more oxygen to do their work. Your body accomplishes this by forcing more oxygen-rich blood to flow through your body. During exercise, your breathing rate increases, and you also take in more air with each individual breath. Your lungs take in that increased oxygen, which mixes with your blood, and then goes to your heart, a highly effective pump that delivers blood to the rest of your body. Your body produces more heat during exercise as well. An increase in blood flow also allows the skin to dissipate heat more effectively.

When you first start a workout, you'll probably notice that you start breathing heavier right away. After about three minutes, however, you'll probably notice that your breathing tends to even out. If you maintain the same level of intensity throughout the rest of the workout, you can expect your breathing to stay at about the same rate as it was during about the third minute. If you increased your intensity, however, you can expect your breathing rate to go up again.

At some point, however, you're going to be breathing as fast and hard as your body can, and your muscles will be using the maximum amount of oxygen that they can. That's called your VO2 max. When you've reached that point, you probably won't be able to exercise any harder. If you're a beginner or novice to exercise, chances are you won't be able to maintain that maximum intensity for very long. Fitter people tend to have higher VO2 max levels than people who are not in such good condition. Fit people take in more oxygen with each breath, and their bodies are also more efficient at using the oxygen received.

Doing any type of moderate-intensity cardio at least three or four times a week is going to help you achieve a higher VO2 max. Aim to work at 65 to 85 percent of your maximum heart rate for at least 20 minutes, three times a week, suggests sports coach Brian Mac. An easy way to calculate your maximum heart rate — or the max number of times your heart can beat in a minute's time — is to subtract your age from 220. Then multiply that number by .65 and .85 to arrive at the ideal range for your workouts. Another way to increase your VO2 max is high-intensity interval training, in which you alternate between exercise at near-max intensity and slower "rest" intervals. After a five-minute warm-up, try sprinting for 30 seconds and then walking or jogging for 30 seconds, for a total of six rounds.

During vigorous exercise, muscles are not supplied with enough oxygen. This means that cells have to respire anaerobically. Anaerobic respiration involves no oxygen. This leads to a build-up of lactic acid in the muscles and creates an oxygen debt. Lactic acid causes muscle fatigue and prevents muscles from contracting efficiently. In order to remove the lactic acid, it needs to be oxidised. The increased breathing rate allows more oxygen to enter the body and help to remove the lactic acid. 

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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

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.