My dad doesn't want me to lift more than 20kg (44 lbs) in any exercise because I'm 14. I know a lot of teenagers don't take this seriously and do bad form just to lift more weight, but I don't wish to do that.
The problem is that I can easily do more than 15 reps with 20kg in almost every machine and as we know what I'm targeting here when doing more than 15 reps is mainly resistance, I know I won't become Schwarzenegger (I don't take steroids); but, I know I can get a little more muscular and mainly increase my strength, so the question is:
Can I only use one arm on machines without damaging my muscles (or something like that) yet still target the muscles in a correct way? For example on Lat Pulldowns (obviously with one hand grip) or Inclined Bench Press Machines.
Meaning that I would still lift no more than 20 but just with one arm, so in theory I would be able to lift about 35-40 with the 2 arms.