Mostly working with them as described before about going up and down hills, disengaging small circles under lead and so on, will help pop muscles. Fitting is about the best thing to also start with. Changing or improving feeds and establish a diet to fit your yearling!
Sherri: Many halter classes start in the Weanling class, typically 6 months, then goes to Yearling, 2 year, 3 year, 4 and older.. Later on, theres also Broodmare halter! Stallions will have their own catagory as well.
Dixon's Red Hot Ember