Make sure you're hitting mainly with the knuckles on your index and middle finger. If you hit with your lower knuckles, you're more likely to injure your hand and wrist.
A lot of times pressure on the kneecap while kneeling is due to either a tight calf muscle or a tight front of your thigh. Stretching those areas regularly can...
Massages are actually really hard on your thumb joints if you don't take it easy. A lot of massage therapists actually don't even make it 3-5 years in their industry...
