Chances are you breathe through your mouth regularly, certainly under stress, during meetings, or behind a screen. Mouth breathing bypasses your nose's natural filter system, disrupts your sleep, and costs more energy than you realise. Your nose produces nitric oxide: a molecule that kills bacteria, widens blood vessels, and relaxes your airways. Breathing through your mouth skips all of that. This exercise helps clear your nose again and restore nasal breathing as your default. Breathe out calmly. Then pinch your nose shut and walk as many paces as you can, until you feel a clear urge to breathe. Then breathe in slowly and steadily through your nose. Is your nose still blocked? Then breathe out gently through pursed lips, as if blowing up a balloon. Stop walking and breathe calmly for at least 1 minute. Repeat this 6 times. You often feel the effect right away. That comes from the nitric oxide your nose produces the moment you breathe through it. Tip: humming increases your nitric oxide level fifteenfold. Silent humming works just as well, and no one needs to know you're optimising your airways during that dull meeting.

This week, try to take 9 out of every 10 breaths through your nose, including during light exertion.