When I was an apprentice (never finished, thinking about going back in) I got hurt mostly by trying to be a hard ass or being afraid of asking for help. The journeyman I worked with most of the time wouldn't tolerate much whining. I have herniated discs/surgery in the back but that could also be from the office job I got afterwards. If you keep your core muscles (ab, back, iliac) in good shape that is absolutely key.
