i think phil heaths triceps may have partly been due to a decade and a half of dribbling a basketball for hours a day at times. dribbling is like all triceps. expecially if your playing against someone who is pretty good and fast, then you could be dribbling pretty hard too.
all those years of super high repeptition dribbling may have somehow "primed" his triceps in a way (so to speak), so that they respond much better than they woudl have,