Any possibility for a thin, lean 50 year old on a low protein diet building some muscle ? I do use a parallel bar 2-3 times a week (3 or 4 reps of 15). Is there

Any possibility for a thin, lean 50 year old on a low protein diet building some muscle ? I do use a parallel bar 2-3 times a week (3 or 4 reps of 15). Is there a regimen that does not use weights and bars that one can do at home to build some strength and muscle.