Pure's mutations

After working a lot in mines, a little area with some people, miners get a disease which transforms them. This disease is very contagious, today all workers have this (except children which are cure by medicinal plants). It could be explained by workers lives all time together and medicinal plants are rare.

The transformation progress by steps: Members become stronger, some hairs appear on it and they shrink a little. Muscles are very developed.
 * 1) Arms
 * 2) Chest
 * 3) Head
 * 4) Chest