I am 17 years old, I have skinny wrists and I do karate.
I hurt my wrist each time I spar with a punch bag.
I thought getting large muscles in my wrists would improve this.
How can I get bigger wrist muscles? :cool:

To be honest, getting "bigger wrist muscles"... isn't really the way to go.

If you hurt your wrist each time you spar, wrap your wrist with tape. I used to do this when I did kickboxing.

If you want to strengthen your wrist/forearms, grab a pair of dumbbells (not too heavy).

Sit on a chair (or weight bench), grab the dumbbell with your right hand, place your right elbow on your right thigh, so you make a perpendicular angle with your forearm and your biceps. Then, roll your fist towards you, so you're doing a mini-curl with your wrist.

Probably you are not punching the right way with unnatural angle of wrist.. anyway it is possible to punch that way and get without injury

You should train your grip . Because when gripping hard it is harder to rotate your wrist.. your wrist hurts because of the impact on your rotation of the wrist

I'm not saying you should punch with a hard grip..

And do many straight punches a day.. you can't train like a bodybuilder forearm or something and expect to not get hurt...

Because when you train straight pucnech your wrist is straight and it gets use to that position and your tendons will deal with the impact

There is also a way of stretching wich I do not recommend.. streching only makes your wrist get use to changing angles that is the problem

Only I would recommend pushups on the wrists that aikido guys do and armwrestlers

Something like your knuckles facing the floor.. it can be painful at the beignng

But it will harden your bone and maybe grove it because bones groves when it is understress it expands and even gets harder

So yea do wateva