When guys who lift weights do a one-arm shoulder press, using heavier weights (up to 70% of their max) makes several key shoulder and back muscles work a lot harder than using just a light 6 kg dumbbell.

If you're a guy who lifts weights and does overhead presses, doing the front version might fire up your front shoulder and chest muscles more than the back version — so it could be better for building those areas.

When competitive male bodybuilders do overhead presses with a free barbell instead of a machine, their side and rear shoulder muscles work harder because they have to balance the weight themselves.

If you're a guy who lifts weights, doing the back-overhead press might fire up your rear shoulder and triceps muscles more than the front version when you're lowering the weight.

When healthy guys do shoulder presses, standing with dumbbells makes their shoulder muscles work harder (based on electrical activity), even though they can lift heavier weights when sitting with a barbell.

When guys lift weights overhead using a shaky bar with weights swinging off it, their core and shoulder muscles have to work harder than when using a regular, steady bar.