Quick question - sitting up/down on bench when lifting

[famoushamish]

I have a quick question that I really had trouble finding an answer to with Google because when I include 'sit up' in my query, I get tons of links about situps.

When you are using a heavy barbell or dumbbells lying down on a bench and you are starting or finishing each set, how do you raise/lower your body with weights safely?
It is fine when I am using light weights - I can just sit back up OK. With the barbell, I tend to roll it down my chest to my quads and then sit up/down - but not sure if that is best or not.
with dumbbells, I tend to hold them in my stomach and sit up/down, but that sometimes hurts my back a bit, so I am assuming that is not the best way. I tried dropping them today, but that felt really awkward and tends to attract stares as people are startled by the noise.

[sicpsnake]

As far as the barbell goes: wat. Just put it back on the rack and sit up normally.

With dumbbells raise your knees up to the weight and let the weight of the dumbbells force you upright. If you are having a hard time picturing it YouTube Matt ogus dumbbell bench press

[famoushamish]

As far as the barbell goes: wat. Just put it back on the rack and sit up normally.

The bench press at my gym tends to be pretty busy, so I often use a regular bench and one of the fixed/preloaded (not sure what to call them) barbells (I am not lifting enough that I need heavier weights). So when I am doing the bench press I often don't have a rack to put it back on. Should I stop doing that and just wait for it to be available?

With dumbbells raise your knees up to the weight and let the weight of the dumbbells force you upright. If you are having a hard time picturing it YouTube Matt ogus dumbbell bench press

Thanks, will check that out - I am having some trouble visualizing this.