In a normal population the self-selected hand position to produce maximal grip strength is about 30 degrees of wrist extension. When wrist extension dips below 25 degrees optimum power drops. For men when the wrist is extended the grip strength is greatest in a neutral position. As a male turns his palm upwards (supination) the application of force becomes less. In men and women both in a pronated hand down position the grip strength is the weakest. What is interesting; women (unlike men), when tested for grip strength, are equally strong in a neutral and supinated position.
Undirected a women may choose to supinate her hand to achieve maximum force.