My horse always gets beat up as he changes pasture/paddock. It lasts for a few months as they decide on the pecking order of things and then he's completely fine.
For him, working on ground work and establishing OUR relationship has helped him to deal with pasture bullies and become more outgoing and playful in a nice way (he can be a real jerk sometimes to his herd mates.)
But that's just what works for us, not sure if it will be a universal thing but thought I would contribute.
"Strength is the ability to use a muscle without tension"