I get (what i think it) tendinitis in my left arm after practices (Bracialis area.) I think it's from putting that "side pressure" motion with my arm.
I recently bought something called the "Arm Aid." Just got it in this week, and tried it once.
Revolutionary tool to fix RSI, forearm pain, tendonitis & tennis elbow
I hope it does the trick....seems legit, but we will see. It feels good to use it (a good pain)
This contraption won't help my wrist tendons strengthen, but it may help you with your tendinitis.