Crimping is the one climbing grip technique that isolates the most stress on your finger tendon/joints. Thumb lock crimping puts a lot of hanging weight solely on your finger joints. The proper crimp form is to open hand crimp the holds. The open hand crimp is when you are on a hold with the first four digits on, the thumb either adjacent to the digits or keeping it off the hold completely. Most importantly keeping the palm open. This prevents putting your weight on the finger tendons.