i would say the pecs..many pro bodybuilders career have ended cuz they tore pecs while benching heavy..notable victims are ernie taylor,kevin levrone,alex fedrov and the latest being markus ruhl..pec tears have resulted in retirements of alot pros too..ernie retired last year and kevin levrone till the end of his career was troubled by his pec tear,alex federovs chest looks like its torn permanently..