That may not mean much to a lot of people, but it's a measure of lung activity.
For a chap of my size, I should be blowing 650 litres per minute. At the doctors this morning, I managed only 270. Then I rode to work. In the rain.
OK, so I've been much worse - on at least one memorable occasion when a v keen junior doctor disagreed with me and obviously wasn't going to be happy until I'd blown in the damn meter, when it didn't register (scale tends to start at 60).
On the one hand, it's a really sh1te way of measuring asthma, for a variety of reasons which I could bore you with for the next week.
On the other hand, it's pretty remarkable that I can get to work in 30mins with a deeply inadequate amount of oxygen tickling my alveoli.
On the third hand, should I be riding in the rain at all?