When we exercise, the volume of air pumped by the lungs can be as much as 16 times higher the amount pumped at rest. Oxygen consumption can increase from 250 ml to 5000 ml per minute and breathing frequency can rise from 12-16 to 40-50 breaths each minute. So it's no surprise that we runners obsess a little over breathing. But is there a "best" way to breathe? And can training your breathing improve performance or reduce injury risk?

"The key objective during exercise is to exchange as much air – oxygen and carbon dioxide – as possible," says Professor Alison McConnell, a respiratory physiologist at Brunel University and author of Breathe Strong, Perform Better. And that means breathing through the mouth. "The mouth offers the path of least resistance," she explains. "The idea that you should try to breathe only through your nostrils, which have a high resistance, during exertion is nonsense." Which presumably makes those little sticking plasters you put across your nose bridge, to open the nostrils more a waste of time? "The scientific literature doesn't support any performance benefit from the use of nasal dilators," she says.

A series of studies from the University of Arizona demonstrates that the more demanding the activity, the more we switch to mouth or, more correctly, nose and mouth (oronasal) breathing, because it feels easier. At rest, 70% of total ventilation (the movement of air into and out of the lungs) was via nasal airways – at 90% of maximal intensity, the contribution had dropped to 27%. "This response is pure physics," says McConnell. "Airflow is greatest via the route of least resistance."

Ventilation is mainly determined by tidal volume (the amount of air in a single breath) – but as exercise intensity increases, the number of breaths taken also rises. And while breathing may be a subconscious, involuntary action, we have conscious control of the muscles that assist with both inhalation and exhalation.

The most important breathing muscle is the diaphragm – a dome-shaped muscle that divides the thoracic (chest) cavity from the abdominal cavity. "When the diaphragm contracts during inhalation, it shortens and flattens, pushing downwards into the abdomen, which bulges outwards - this expands the chest, creating a pressure gradient which allows the lungs to fill," explains McConnell. When people talk about "belly breathing", it's this action of the diaphragm to which they are referring. "The term belly breathing is a misnomer," she adds. "You are not filling the abdomen with air when you belly breathe, you are simply pushing the diaphragm down into the abdomen to expand the lungs."

To see how to use your diaphragm properly, lie on your back with your knees bent. Place your thumbs lightly on the lowest rib on each side, with your fingers spread across your belly, fingertips almost touching. If you are using the diaphragm correctly, as you breathe in you should see your ribs move outwards and apart (your fingertips will move away from each other) - your abdomen will also bulge outwards. If there is little movement, or if the chest rises instead, your breathing is less efficient than it could be.

"Taking frequent, shallow breaths is inefficient, and tends to have a detrimental effect on performance," says McConnell. She suggests two to ensure that you are controlling your breathing. Firstly, learn how to breathe rhythmically during movement (more of that in a moment). And secondly, improve your inspiratory (inhalation) muscle function. McConnell invented a inspiratory muscle training device called POWERbreathe® back in 1990, which she dubbed "dumbbells for your diaphragm".

The theory behind inspiratory muscle training is based on research showing that during hard exercise, these muscles can use 14-18% of the oxygenated blood being pumped out by the heart each minute, shortchanging the working muscles. "In addition to this metabolic demand, the respiratory muscles can trigger a reflex, the metaboreflex, during intense or prolonged exercise that limits blood flow to the exercising muscles," explains McConnell.

A study in the British Journal of Sports Medicine found that four weeks of combined endurance training and inspiratory muscle training improved 5km run performance by 4.3% more than endurance training alone. "Inspiratory muscle training can help in two ways," says McConnell. "Firstly, it reduces your perception of breathing effort, so you don't get so uncomfortable and breathless during exercise. Secondly, it can raise the threshold at which the metaboreflex limits blood flow to your leg muscles."

So what about rhythmic breathing? This is to do with synchronizing or "entraining" your breaths with your movement – in this case, your foot strike.

"At foot strike, there is a tendency for everything to move downwards because of gravity and momentum," says McConnell. "This gives an inspiratory advantage by pulling the diaphragm downwards, helping it to expand the lungs, so an inhalation at this point can capitalise on that.Of course, you can't sync every step with a new inhalation, or you'd be breathing too frequently, so the idea is to take the breath in 'sips' that coincide with the foot strike."

I find that I do this spontaneously when I'm working all-out – such as during track repeats. It almost feels as if the foot strike is driving the breathing rather than the other way around.

While breath-movement entrainment is very strong in quadrupeds such as horses, dogs and antelopes, it is relatively weak in humans. Animals tend to lock into a 1-1 rhythm (one breath phase - an inhalation or exhalation - per foot strike) because the diaphragm is horizontal as opposed to vertical, putting them at a mechanical disadvantage if they don't entrain. In humans, entrainment might be useful but it is by no means essential. That said, most elite athletes do it, so there must be some advantage.

"Getting into a rhythm can minimise the potential conflict of breathing at an inappropriate time – for example, inhaling when the abdominal organs are pushing the diaphragm upwards," believes McConnell.

And could this also help with that most common of runner's afflictions – a stitch? Possibly. McConnell believes that at least some stitches arise as a result of diaphragmatic overload: the diaphragm is trying to perform its role as a breathing muscle and as a core stabiliser, and simply can't cope. "A lack of rhythmicity might irritate the diaphragm by tugging and stretching the connective tissue in this region of the body," she explains. "Training yourself to use the diaphragm more efficiently, combined with rhythmic breathing, could reduce the risk of stitch."

Some researchers have contended that synchronising breathing with stride rate may reduce the oxygen cost of running – improving economy – and while this makes sense intuitively, it hasn't been shown directly. However, it has been found that faster runners, and those with a higher level of fitness, are more likely to entrain than less experienced and less fit runners, so there could be a link between entrainment and economy.

A good drill to try is to take as many foot strikes per phase as you can (in-two-three, four, out, two, three four, for example), to gain control and mastery of your breathing. This is similar to the so-called hypoxic breathing drills many swimmers use.

Budd Coates, a running coach and author of a new book called Running on Air extols the virtues of a specific form of rhythmic breathing, in which you synchronise your exhalations with alternate feet, allegedly reducing injury risk.

As a young athlete, Coates observed that his exhalations always coincided with his left foot landing – and that this was the side of his body that suffered repeated injuries. He developed an asymmetrical breathing rhythm – using a shorter exhalation than inhalation – after reading research that stated impact stress in running was highest when the foot strikes the ground at the start of an exhalation. "This is because when you exhale, your diaphragm and the muscles associated with the diaphragm relax, creating less stability in your core. Less stability at the time of greatest impact makes a perfect storm for injury," he writes.

Coates claims that his rhythmic breathing method enabled him to outrun injury and improve his performance. I've been playing with the technique for a few weeks now, and find the 3-2 pattern (inhale for three footstrikes, exhale for two) achievable and fairly comfortable, but it hasn't made any difference to my ongoing foot niggle as yet. Does McConnell think Coates's theory holds water?

"The underlying principles are sound," says McConnell. "Foot strike presents the biggest challenge to the stabilising muscles, and when you are working hard, the respiratory role of the trunk musculature takes precedence over its stabilising role." But she warns that getting too obsessed with counting and ratios can be counterproductive. "My advice is to aim is to entrain running cadence and footstrike cadence in a way that feels comfortable to you. And bear in mind that this will vary according to speed and terrain." In other words, go with the flow.