No matter how fit your horse is, when he is at rest the muscles should not feel hard. Hard, dense muscles indicate pain and trigger points. Healthy muscles have an elastic feel when palpated.
Trigger points can cause weakness and lack of coordination, so often, riders will push to strengthen those areas. Know that you can’t strengthen muscles that are in spasm. The muscle fibers are contracted. What will happen is that the muscles surrounding the affected muscles will take up the slack, further weakening the muscles with trigger and stress points.
Muscles with trigger points fatigue more quickly than healthy muscles. And the muscles surrounding muscles with trigger points also become fatigued as they tighten and work too hard.
One of the signs that you can look for to identify spasms before you mount is twitching and trembling. Be on the lookout while you are grooming your horse.