I don’t know about the rest of the dopers, but I tend to find that with standard weightlifting apparatus (the one you do benchpresses with - barbell?) I find it easier to lift the further apart the weights are from each other. So basically if both weights of say 20KG are each placed near the end of either side of the bar, it becomes easier to lift (even with one arm).
However, the closer the weights are to each other on the bar, the harder it becomes to lift. Why is the concentration of the same weight on the same bar more difficult to lift? Technically, wouldn’t the same force be required as “normally” lifting it up?
If you don’t understand what I mean, imagine a long pole. Imagine on each side of the pole there are large weights of equal size. Now my proposition (if you can call it that) is that the closer the weights become to each other (in other words, sliding them towards each other at equal lengths), the harder it will be to lift for the same person using the same technique. Why is that?
With weights closer to the end of the barbell, the barbell has a greater rotational inertia. The force to lift would be the same, but slight imbalances in lifting would be dampened more.
In short, spreading the weight to the ends just makes the bar more stable and easier to control, but just as heavy.
I think scotth is right. If the weights are close together, you have to do a lot of adjusting during the lift to keep the bar parallel to the floor, which probably uses muscles that are less-often worked out (and therefore weaker). When the bar is more stable, you only have to use the larger, stronger muscles, since inertia is keeping the bar where you need it to be.
I’m certain there are physiologists on the boards that can identify the muscles involved, and tell us all whether I’m full of it.
In benchpressing, there is a difference between having the weights at least shoulder width apart, and within the shoulders or at the shoulders. My personal guess is that once it is wider than the shoulders, it won’t matter much how much wider it gets.
Completely untested in any rigorous way, I’d be interested if other people find that to be true or false.
scotth is correct WRT having a greater angular moment of inertia. (BTW that gives more stability but if you lose equilibrium it is also much more difficult to correct for the same reason, and you’ll probably drop one end.) But with all due respect to Saltire (IANAP) I think the added difficulty in having the weights close together has more to do with the added effort and conflicting forces needed to both lift and stabilize the bar rather than any characteristics of the muscles used to do so.
Although I’ve never actually seen this, the most stable lift would be with a bar that is severely bent, putting the weights below the hands, therefore putting the center of gravity of the bar below the support point. That’s what tightrope walkers do with those long poles, they are lowering their center of gravity to add stability. OTOH, one reason people use free weights instead of machines is to challenge more muscles in controlling the weight.