It could be that since one leg is shorter than the other (with it being abnormally shorter than on a normal human since we are not perfectly symmetrical) the mechanics of exercises like squats make his body compensate for this abnormality by putting more pressure on the longer leg. I believe Jay knows this also, if you notice his bodybuilding training is iso-lateral (for example he leg curls with each leg individually rather than doing both at the same time) to prevent his longer leg from getting too large compared to his shorter leg. It can also be noticed on Ronnie's bench press where his right arm, shoulder and pec carry most of the weight. Once he increased the weight, and his joints got weaker on his left side this assymetry might have led to his current nerve damage, since his left side did not get as much resistance training (a substantial amount).
