does 100m build muscle up to get big legs?

Answer 1

yes, but what part of your legs are you on about?? clycling is a better excerise for building muscle on your legs and running will just put pressure on your knees and that aint good

Answer 2

if you are new to sprinting and haven't been weight training you may see some slight growth, mainly from increased cellular hydration. with out placing a constantly increasing load on the muscle(s) gains will be minimal as there is no reason for the muscles to continue to adapt and grow larger.

if you were squating and sprinting you would see much more growth vs sprinting alone.