During easy and steady runs when you want a calmer, more even effort, fewer side stitches, and a breath rhythm that keeps your sense of exertion from spiking.
Runners naturally tend to sync breath to stride, a coupling called locomotor-respiratory entrainment. A 3:2 pattern is an odd ratio (three steps in, two out), so your exhale alternates between the left and right foot strike instead of always falling on the same side. Because the exhale coincides with the moment of greatest ground impact and core instability, always exhaling on one foot may load that side more heavily; alternating is proposed to spread the load and reduce side stitches (exercise-related transient abdominal pain), whose exact cause is still debated. Steady diaphragmatic breathing also keeps ventilation efficient and effort feeling controlled.
Locomotor-respiratory coupling itself is well documented. The specific claim that alternating the exhale foot reduces injuries or side stitches is plausible but not strongly proven, the causes of side stitches remain uncertain. Treat cadence breathing as a useful, low-risk pacing and comfort tool rather than a proven injury preventer.
Rhythmic breathing in running is old folk practice, but the structured odd-ratio approach was popularised by Budd Coates (a national-class runner and coach) in his 2013 book 'Running on Air', which built on the idea of coupling breath to stride and deliberately alternating which foot the exhale lands on.
Practice the 3:2 rhythm while walking first, then on very easy runs until it becomes automatic. Add 2:1 for tempo runs and hills once 3:2 feels natural. Don't hold any pattern rigidly during hard intervals or races, let your breathing free up as you approach maximal effort.
Why an odd number of steps?
An odd total (like 3 in, 2 out) makes your exhale land on alternating feet instead of the same one every stride, which spreads impact and may cut down side stitches.
Should I breathe through my nose or mouth?
Nose on easy runs if you can, it paces you naturally. As effort climbs, add mouth breathing; don't starve yourself of air just to stay nasal.
What if I can't hold the rhythm?
That's usually a sign to slow down. The cadence should fit the pace, not the other way around.
Safety
Breathwork is a complement to (not a replacement for) professional medical care. If you have a heart, respiratory, or blood-pressure condition, are pregnant, or feel unwell, check with a clinician before practising breath-hold techniques.