By June 8, 1951, a total of 74 human runs had been made on the decelerator, 19 with the subjects in the backward position, and 55 in the forward position. Stapp, one of the most frequent volunteers on the runs, sustained a fracture of his right wrist during the runs on two separate occasions, also broke ribs, lost fillings from his teeth and bleeding into his retinas that caused temporary vision loss; in one run he survived forces up to 38 g.