Playing guitar is mentally, as well as physically quite challenging. A guitar player needs to look after both her/his hands. The idea is to keep it loose and economise the movements on both hands. The more effort and energy it take to play something, the sloppier it’s going to sound and more susceptible to injuries. Repetitive stain injury (RSI) and tendinitis are not very common, but both are possibilities for performing guitarists or anyone who practices for long hours.
If your work is physically challenging and puts a lot of strain on the hands, require a lot of grip strength, you need to take extra care of your hands. Make sure to properly warm up, stretch and provide adequate rest between the practice sessions. I used to box when I was a teenager and at one point realised, I can’t do both guitar and boxing. Injuries and pain on the hand from boxing hindered my guitar practice immensely. I had to pick between being a no name boxer or somewhat of an accomplished musician and the choice was very easy for me.
The following video provides some of the stretching exercises I do before and during a practice/performance. Notice how the stretches and hand exercises are slightly different for the strumming hand. Make sure to perform these if you are practising for long hours and preferably before each practice session.