How should I breathe when running?

Breathe through both your mouth and your nose, take deep breaths that move your belly and not just your chest, and don't try to control it too much. At easy pace, your breathing will settle into a rhythm on its own.

A lot of beginners worry about getting breathing "right". For most people, the right breathing is the one that doesn't feel strained. If you can speak in full sentences, your breathing is fine.

Mouth, nose or both

Both. Nose-only breathing works at very easy paces, and some people like it as a pace check. But as soon as you run harder, your body needs more air than your nose can deliver, so open your mouth. There's no benefit in forcing nose-only breathing at hard efforts.

Belly breathing

Shallow chest breaths use only the top part of your lungs. Try to let your stomach expand as you inhale and relax as you exhale. You can practice lying down for a minute, then notice it when you run. Relaxing your shoulders and jaw helps.

Rhythmic breathing

If you like structure, you can match breaths to steps. A common pattern is breathing in for three steps and out for two at easy to moderate effort, and then 2 in, 2 out when you speed up. The odd count means you exhale on alternate feet, which some runners say spreads out the impact and helps with side stitches (see how to stop side stitches).

If counting stresses you out, skip it. The research on specific patterns is thin.

If you still can't catch your breath

Usually the pace is the issue, not the technique. Slow down and add walking breaks, as described in why you get out of breath when running.

League of Fitness scores runs synced from Apple Health by intensity and heart rate zones, so a comfortable run where you can still talk counts as the effort it was. You don't need to push the pace for it to be worth logging.

If you notice wheezing, tightness in your chest, or breathlessness that feels out of proportion to the effort, talk to a doctor. Exercise-induced asthma is common and easy to treat.