I think everyone has a weak bodypart, my biceps, hams and calves for me. mostly due to more red fiber in those areas, high fatigue fibers which won't grow as big as white fiber. My biceps never get sore. Even thou i'm a pler, I am making strength and mass gains but not in those areas. Granted I don't concentrate on biceps for pl, but it's been like that before i switched from BB. and i've been training for almost 20 years. The only thing that did help was a giant set or "Holistic set" 5, 12, 40 reps then repeat and repeat again. 80%,60% 40% no rest inbetween. you'll probably have to drop weight at each set to do this.