I'm actually writing this for my dad.
My dad is 52 years old, and had ripped his bicep (muscle, tendon, or ligament it attaches to, i'm not sure) many years ago. In the process of aging, he's lost a lot of strength. One of the things he's come to notice, is that one arm has become much stronger than the other.
To the point where one is curling 45's easy and the other is straining on 35's.
1) How should he go about training his arms? He's always stayed balanced in doing the same weight and reps in both arms, but, is it time to consider breaking that?
2) How can he strengthen the injured arm, at this age?