In some instances, an animal may completely refuse to engage in certain tasks because it is too painful. Muscle Spasms result from strain. A knot forms around the muscle as the body responds to the pain. The muscle function is impaired and the body demands a rest for its injured part. The mule's body is only acting as ours would to protect itself.
Lactic acid builds up and the spasm results in soreness and pain.
This soreness and pain is designed to limit movement so that healing will occur. All this spasmatic reaction to an injury greatly limits the range of motion. As the rider continues to ask the mule to engage in the motion, the more the mule's body reacts in pain and the more it tells the mule to rest that part until it is healed. The mule begins to show symptoms of avoidance of movement because it is too painful. Laird's treatment involves finding the spasm.