When pronation or supination is a problem in the forearm, it's usually due to a limitation of rotation, rather than an excess. Normal forearm rotation is about 75 degrees pronation and 85 degrees supination. Many daily activities are performed in an arc of 50 degrees of pronation and 50 degrees of supination. If rotation is limited by more than 30 degrees of pronation or supination, more shoulder rotation is required, which can be problematic if the condition is chronic.