Breathe in, fill out

sir – Your leading article (June 14) enjoins us to “breathe in” before boarding a railway carriage in order to fit more people in.

Breathing in increases the volume of the body by the amount of air inspired – typically anything between half a litre and three litres.

If everybody boarding a crowded train breathed in, there would be far less room available, not more. Professor David Allison

New Malden, Surrey