Don't know if I'm understanding you correctly, but the forces occuring in spokes and hub during (rim) braking are very similar to those experienced while JRA. While JRA the wheel has to carry its portion of the rider's weight in a pure vertical orientation, when braking this angle changes from the vertical to something pointing backwards, and the force increase somewhat. The amount the angle changes and how much the force increase depends on how hard the braking is. But basically the wheel don't see any difference between braking or a heavier rider coasting.