I worked in a factory setting for a decade and battled with pain right from the start. I discovered that it was much worse when i wasn't drinking enough water. We were also taught by our in-house therapists to do stretches at regular intervals, which helped. They also taught us the need to be stronger than our work and encouraged us to exercise in addition to the physical labor we were doing. Sufficient rest is also critical.
With window cleaning I'm trying to apply those lessons along with principles of ergonomics like maintaining good posture, switching sides, not using excessive force, and keeping the body in a more neutral position as much as possible. One reason I'm actually excited to enter the world of wfp is to add more variety of movement into the day. Rather than exclusively squeegeeing, i can use some different muscle groups while poling.
Nevertheless, I encounter pain on nearly every job already. Thankfully, i discovered a site that I've linked to before on trigger points. It mentioned that most carpal tunnel diagnosis are not really carpal tunnel at all, but instead referred trigger point pain. If you find and relieve the trigger point, you can eliminate the pain. This had been a godsend for me as I've found it to be the most effective remedy yet.