Take it from someone who had tendonitis, if ur hand gets tired in anyway stop and rest, stretch it a bit and come back later... dont over do it and although my hand is better now I still get the odd pain now and then and when I do I rest and its fine.. STOP when ur hand gets tired because its then ur muscels and tendons start to cramp up and its then they get prone to injury.. I had to stop playing guitar for 6 months so be carefull peeps...