The playing of most musical instruments is not a natural activity for the human body. The demands on posture, muscle tension, dexterity, and endurance can be immense. And, if the body doesn't stand up to the strain, it could mean a few months of musical inactivity.
Warm up for at least ten minutes before starting a practice or playing session – a bit of finger stretching is highly recommended; take a five-minute break every half hour or so – get up, stretch a bit, and make sure you have proper circulation in your hands; if it hurts, stop playing – trying to play through the pain will only aggravate the problem; make sure that your posture is as upright and as comfortable as possible – try to avoid sitting with a bent back; try to keep the tension and pressure in your hands and arms as low as possible – musicians often exert more pressure on the strings than what is needed.
Slouching a real back-breaker