Thank you, gcoe.

Running on sand sounds a nice idea. Don't have that easily to hand here, but hopefully have plenty of opportunities on forthcoming holidays. Out of interest, why is it better to run on firm sand? Presumably there's less impact on the non-firm stuff but I guess you are also landing/taking off different because, in effect, you are on a moving surface...

I am over 30 but have been a semi-regular runner (semi-regular, but not all that good at it!) since childhood.