Breathing and respiratory training
Evidence: limited
For most runners the respiratory system is not the performance limiter, so the room for breathing work to help is small. Training the breathing muscles has a real but modest effect that depends on the test used and shrinks as fitness rises. Nasal breathing and branded breathing techniques are largely unproven for performance. One genuine mechanism, breathing-muscle fatigue stealing blood flow from the legs at high intensity, is well established, but it does not translate into a reliable training recommendation.
Not medical advice
This is a general knowledge base, not medical advice. Breathlessness, wheeze or a cough on running can have medical causes; if breathing troubles you when you run, see a doctor rather than reaching for a breathing gadget. See exercise-induced bronchoconstriction.
Runners worry about their breathing because it is the most obvious sensation of hard effort. Feeling out of breath is not the same as breathing being the thing that holds you back, and for most runners it is not.
Breathing is rarely the limiter
In healthy, untrained people the respiratory system has spare capacity. The work of breathing costs under about 10% of oxygen uptake, and the lungs are not what caps performance (Amann 2012). The heart, blood and muscles set the ceiling, and they adapt far more to training than the lungs do, which is why the respiratory system is not where most runners should look for gains. See cardiovascular and respiratory adaptations.
There is a real exception at the sharp end. In highly trained athletes working above roughly 85% of maximum, the respiratory system can begin to contribute to fatigue, through a fall in the oxygen saturation of the blood, through the high oxygen cost of hard breathing (around 15% of the total), and through a reflex worth understanding in its own right. When the diaphragm and the other breathing muscles fatigue during heavy sustained exercise, they trigger what is called the respiratory-muscle metaboreflex. It constricts blood vessels and diverts blood flow away from the working legs, which worsens leg fatigue and how hard the effort feels (Dempsey et al. 2006). Taking over the work of breathing in an experiment delays fatigue, and pre-fatiguing the breathing muscles hastens it. This is the strongest reason to think training the breathing muscles might help, though it is a mechanism seen mainly in fit athletes at high intensity, not proof of a race benefit.
Inspiratory and respiratory muscle training
The breathing muscles can be trained, usually with a handheld device that adds resistance to breathing in. Doing so reliably makes them stronger; whether that strength turns into faster running is the uncertain step. A meta-analysis in healthy people found that respiratory muscle training improved endurance on constant-load and intermittent tests by roughly 16 to 18%, but produced no significant improvement on a conventional VO₂max-style ramp test, and the benefit was larger in less-fit people and shrank as fitness rose (Illi et al. 2012). A review focused on athletes similarly found reliable gains in breathing-muscle strength and a positive but training-dependent effect on some performance measures (HajGhanbari et al. 2013). The effect is real but modest, it depends heavily on which test you measure it with, and it is smallest in exactly the trained runners most drawn to it. The underlying trials are small and mostly unblinded, so the true effect is probably at the low end.
Nasal breathing
Nasal-only breathing is widely promoted for endurance, and the evidence does not support a performance benefit. In a small study of recreational runners who had already trained with nasal breathing for months, breathing through the nose alone produced no difference in VO₂max, time to exhaustion or peak lactate, so it did not raise maximal capacity (Dallam et al. 2018). It did lower ventilation and slightly lower oxygen uptake at a submaximal intensity, a modest gain in ventilatory economy, but the study had 10 subjects, no control group and no performance outcome, and the runners were already adapted, so it says nothing about switching without preparation. A narrative review by the same group reaches the honest bottom line: nasal breathing raises airway resistance and slows the breathing rate and may improve ventilatory efficiency, but these effects have been examined so rarely that the literature is thin and no performance benefit is established (Dallam & Kies 2020). Nasal breathing does warm and humidify air before it reaches the airways, which can be a comfort in the cold, but that is not the same as running faster. See cold-weather running.
Breathing techniques and masks
Branded breathing methods such as Buteyko and ‘breathe light’ training, and prescribed rhythmic breathing patterns, are marketed to runners, but no credible study shows they improve running performance. The honest position is an absence of evidence rather than weak support, so they should be treated as unproven. So-called altitude or elevation training masks do not simulate altitude at all: they add resistance to breathing in, so at best they are a form of respiratory muscle training, with the same modest and uncertain evidence, and they do nothing to reproduce the low oxygen of real altitude. A face covering does have one genuine and separate use, trapping heat and moisture to blunt the airway’s response to very cold air (Stenfors et al. 2022, and see cold airways), but that is protecting the airways in the cold, not training them or standing in for height.
The bottom line
For nearly all runners, breathing is not the limiter, and the training that raises the ceiling is the ordinary aerobic work that improves the heart, blood and muscles. Breathing-muscle training is a small and largely marginal add-on with the least to offer trained runners, while nasal breathing and breathing gadgets are, on current evidence, not worth counting on for speed. If breathing is genuinely hard on easy runs, that is a reason to see a doctor about asthma or airway narrowing, not to buy a mask.