which muscle groups should be concentrated on that assist on increasing overhead press?
bench press is all chest, whereas overhead press is more shoulders.
Absolutely, conversely if you didn't do any bench presses it would be twice as hard to increase the weight of the overhead press.
Bench press is not ALL chest. It involves the front part of your deltoid (I forget the exact name) but it does involve a lot of triceps and shoulders as well as your chest. So getting stronger on bench can very well increase your OH press. Just keep adding weight progressively on each, and they will go up.
