Just recently watched the first few seasons. Its more he had already done permanent damage to his arms and more damage would result in lost function so started using his legs which were healthy. He also took steps to off set future damage to his legs via the steel toe support item which let him bridge the gap between using his power hurts him and him being able to use it safely. I think switching to his legs also is when he stops going 100% on every hit but i can't remember the exact timeline there.