How Exercise Affects the Respiratory System

What Is the Effect of Exercise on the Respiratory System?

The main effect of exercise on the respiratory system is a rapid rise in ventilation, the amount of air moved in and out of the lungs each minute, matched to the extra oxygen the muscles need and the extra carbon dioxide they produce. At the same time, more blood flows through the lungs, and gas exchange across the alveoli speeds up.

Why the body needs more air

Muscles turn fuel into usable energy through cellular respiration, which consumes oxygen and releases carbon dioxide. At rest the whole body uses about 250 milliliters of oxygen per minute. During hard exercise that figure can climb more than tenfold in a healthy young adult, and even higher in endurance athletes. The respiratory system must bring in that oxygen and remove the carbon dioxide fast enough to keep the blood chemistry steady.

Short-term and long-term effects

The effects fall into two groups. Short-term or acute effects happen within seconds to minutes of starting exercise: faster and deeper breathing, more blood through the lungs and greater oxygen unloading in the muscles. Long-term effects, or training adaptations, build up over weeks to months of regular activity and mostly concern the breathing muscles, the heart and the muscles themselves rather than the lungs.

Explained simply

Think of the body as a fire in a stove. When the fire burns harder, it needs more air flowing in and makes more smoke to send up the chimney. Exercise turns the fire up, so the lungs act like a bigger bellows, pushing more fresh air in and more stale air out with every breath.

How Does the Respiratory System Respond to Exercise?

The respiratory system responds to exercise in stages: breathing jumps up within seconds of starting, rises more gradually over the next few minutes, settles at a steady level during moderate effort and climbs steeply again during very hard effort. After exercise it drops quickly at first and then slowly returns to resting levels.

The stages of the breathing response

1. Anticipation: breathing may increase slightly even before movement starts, driven by the brain preparing for activity.
2. Fast rise at onset: within the first few seconds, ventilation jumps sharply, long before blood chemistry has had time to change.
3. Gradual rise: over the next few minutes, ventilation keeps rising toward a level matched to the work rate.
4. Steady state: during moderate exercise, ventilation levels off and stays matched to oxygen use and carbon dioxide output.
5. Extra rise above the threshold: at high intensity, ventilation rises faster than oxygen use, as described below.
6. Recovery: after stopping, ventilation falls quickly, then declines slowly while the body repays its oxygen debt.

Deeper first, then faster

At low and moderate intensities, the main change is a larger tidal volume, the air moved per breath, which can grow from about 0.5 liter to roughly half of the vital capacity. Once tidal volume nears this limit, the respiratory rate rises, from about 12 to 20 breaths per minute at rest to around 40 to 50 at maximal effort in adults. Deeper breaths are more efficient, because a smaller share of each breath is wasted in the dead space of the airways.

Above the ventilatory threshold

As exercise gets harder, muscles rely more on fast, oxygen-free energy pathways and produce lactic acid. The blood buffers the acid with bicarbonate, which releases extra carbon dioxide, and the rising acidity stimulates the respiratory chemoreceptors. Ventilation then rises out of proportion to oxygen use, the point where breathing becomes noticeably heavy and talking gets difficult.

What Controls Breathing During Exercise?

Breathing during exercise is controlled by several signals working together: commands from the motor areas of the brain, feedback from receptors in the working muscles and joints, and fine-tuning by chemoreceptors that sense carbon dioxide, oxygen and acidity in the blood. The breathing centers in the brainstem combine these signals, as explained on our control of breathing page.

Central command

When the motor cortex sends signals to the muscles to move, it sends parallel signals to the breathing centers. This feed-forward command explains why breathing rises the moment exercise starts, and even slightly beforehand, before any change in blood gases.

Signals from muscles and joints

Sensory receptors in moving limbs detect movement, stretch and the build-up of chemicals in working muscle. Their signals travel to the brainstem and add to the drive to breathe. Studies in which limbs are moved passively show that movement alone can raise breathing.

Chemical fine-tuning

The central chemoreceptors in the medulla and the peripheral chemoreceptors in the carotid and aortic bodies make small corrections that keep arterial carbon dioxide close to its normal level of about 40 mmHg. Remarkably, during moderate exercise the average levels of oxygen and carbon dioxide in arterial blood barely change, which shows that ventilation is matched to metabolism with great precision. Rising temperature and potassium in the blood may also add to the drive during hard work.

What Happens in the Lungs and Blood During Exercise?

During exercise the lungs receive much more blood, open up capillaries that were partly closed at rest and exchange gases faster, while the blood unloads more oxygen in the muscles. These changes let oxygen uptake rise many times over without a fall in arterial oxygen in most healthy people.

More blood through the lungs

The heart's output can rise from about 5 liters per minute at rest to 20 liters or more at maximal effort, and every drop of it passes through the pulmonary circulation. The lung vessels handle this by opening extra capillaries, especially near the top of the lungs, and by widening those already open. Pulmonary artery pressure therefore rises only modestly, and air and blood become more evenly matched, as described on our ventilation-perfusion ratio page.

Faster gas exchange

With more capillaries open, the surface area for diffusion grows, and the lungs' diffusing capacity rises. A red blood cell crosses a lung capillary faster during exercise, in roughly a third of a second instead of about three-quarters of a second at rest. Because oxygen loading is normally complete early in the transit, healthy lungs usually still fill the blood with oxygen in time. Some highly trained endurance athletes are an exception: at very high work rates, their blood can leave the lungs slightly less saturated.

Greater oxygen unloading in the muscles

Working muscle is warmer, more acidic and richer in carbon dioxide. These conditions shift the oxygen-hemoglobin dissociation curve to the right, the Bohr effect, so hemoglobin releases more of its oxygen. Blood returning from hard-working muscle may hold only a small fraction of its oxygen, compared with about three-quarters at rest. The extra carbon dioxide is carried back to the lungs mainly as bicarbonate, as explained on our carbon dioxide transport page.

How Do the Breathing Muscles Work During Exercise?

During exercise the diaphragm and external intercostal muscles contract harder to enlarge the chest, and breathing out, which is passive at rest, becomes active with help from the abdominal and internal intercostal muscles. In very hard work, accessory muscles in the neck join in as well.

Breathing in

The diaphragm remains the main muscle of inhalation and moves further with each breath. The external intercostal muscles lift the ribs more strongly, and at high ventilation the sternocleidomastoid and scalene muscles raise the upper rib cage. The full set is described on our muscles of respiration page.

Breathing out

At rest, exhalation happens mostly by elastic recoil of the lungs and chest wall. During exercise, the abdominal muscles push the abdominal organs up against the diaphragm, and the internal intercostals pull the ribs down, emptying the lungs further and faster. This active exhalation also helps the next breath in, because the stretched diaphragm starts from a more effective length. The mechanics of breathing page explains the pressure changes behind each breath.

The cost of breathing

Breathing muscles need oxygen too. At rest they use only a tiny share of the body's oxygen, but at maximal exercise they can use about 10 to 15% of the total in fit people. They also compete with the leg and arm muscles for blood flow during the hardest efforts.

Breathing while running

During running, many people fall into a rhythm in which breaths lock to strides, a pattern called locomotor-respiratory coupling. Above moderate intensity, most people also switch from nose breathing to breathing through the mouth and nose together, because the nasal passages offer more resistance to high airflow; see nose breathing vs mouth breathing.

What Are the Benefits of Exercise on the Respiratory System?

The main benefits of regular exercise on the respiratory system are stronger and more fatigue-resistant breathing muscles, more efficient breathing at any given workload and less breathlessness during everyday activities. Most of the gain in fitness, however, comes from changes in the heart, blood and muscles rather than from bigger lungs.

Training adaptations

• Stronger breathing muscles: the diaphragm and intercostals gain endurance, with more oxidative fibers and capillaries, like other trained muscles.
• Lower ventilation at the same pace: a trained person breathes less air to run or cycle at a given speed, because their muscles produce less lactic acid at that intensity.
• Higher ventilatory threshold: the point where breathing becomes heavy shifts to a faster pace.
• Higher maximal ventilation: trained people can move more air at peak effort, partly because they can work harder.
• Less breathlessness: everyday tasks take a smaller share of maximal capacity, so they feel easier.

What does not change much

In adults, the size of the lungs, the number of alveoli and the structure of the airways change very little with training. Vital capacity may rise slightly through stronger muscles, but the main reason maximal oxygen uptake rises is a larger stroke volume of the heart, more capillaries in muscle and more mitochondria in muscle cells. Swimmers and divers often have larger lung volumes, which may reflect both training from childhood and natural selection into the sport.

The cardiorespiratory system

The heart and lungs work as one oxygen delivery chain, which is why fitness is often called cardiorespiratory fitness. Our page on the respiratory and circulatory system explains how they share the task. In healthy people the lungs rarely limit exercise; the heart's pumping capacity and the muscles' ability to use oxygen are usually the limiting links.

How Do Altitude, Age and Air Quality Change Breathing During Exercise?

Altitude, age and the air itself all change how the respiratory system copes with exercise: thin air lowers the oxygen available, aging gradually reduces lung and chest elasticity, and cold, dry or polluted air can irritate the airways.

Altitude

At high altitude each breath holds fewer oxygen molecules, because the partial pressure of oxygen in the air is lower. Ventilation at any workload is higher, and maximal oxygen uptake falls. Over days to weeks the body adapts, partly by breathing more and later by making more red blood cells, as described on our breathing at high altitude page.

Age

With aging, the lungs lose some elastic recoil, the chest wall stiffens and the breathing muscles weaken slightly, so maximal ventilation and oxygen uptake decline slowly. Physically active older adults keep much more of their capacity than inactive people of the same age, mainly through the heart and muscle adaptations described above.

Cold, dry and polluted air

Heavy breathing through the mouth bypasses the warming and humidifying role of the nasal cavity. Large volumes of cold, dry air can dry and cool the airway lining, and in sensitive people this can trigger airway narrowing. Polluted air also delivers more particles to the airways when ventilation is high, because far more air passes through the lungs per minute.

Children

Children breathe faster and with smaller breaths than adults during exercise, and their ventilation per unit of oxygen used is slightly higher. Their lungs are still growing, adding alveoli through early childhood, a process described on our development of the respiratory system page.

Common Conditions That Affect Breathing During Exercise

Several conditions limit breathing during exercise, mostly by narrowing the airways, reducing lung elasticity or impairing gas exchange. Our respiratory diseases section covers them in more detail, and breathlessness that is unusual or out of proportion to effort should be checked by a doctor.

• Exercise-induced bronchoconstriction: temporary narrowing of the airways during or after exercise, common in people with asthma and also seen in some athletes without other symptoms.
• COPD: narrowed airways trap air in the lungs during fast breathing, a process called dynamic hyperinflation, which makes each breath harder.
• Pulmonary fibrosis: stiff lungs and a thickened respiratory membrane limit both breath size and oxygen uptake.
• Exercise-induced laryngeal obstruction: the larynx partly closes during hard breathing, causing noisy inhalation that can be mistaken for asthma.
• Heart conditions and anemia: these reduce oxygen delivery and cause breathlessness even when the lungs are healthy.

Fast, deep breathing that goes beyond the body's needs is described on our hyperventilation and hypoventilation page.