In dystonia are the muscles subjected to the involuntary contraction ever damaged from the involuntary contraction?

Bulk up. In all the dystonias i've seen, i can't think of one where the abnormal contraction itself caused muscle injury. Usually, the muscle bulks up due to repeated "exercise" from the dystonia. Over time there can be damage to adjacent joints. For example, torticollis can damage the neck joints over the years due to extra wear and tear. Dystoniascan cause the muscle to hurt, but not damage.