My horse had the same thing before I started him conditioning for barrels. It only took about a week. I long trotted alot instead of walking or running everywhere. I don't have any hills.On my property we have a few mile trail.walk those alot.helps temindously!!But I probly ride 2 or more hours(not all on barrles) and 5 to 6 days a week so that might have contributed.