Tim Downie wrote:

Interesting, but is it true? I'd need some convincing that we would
contort into a less efficient position when trying to increase
effort. I'd be more inclined to concede that it might *look* like
it's less efficient.

Most people trying to twist open a tight container will hold it
towards their dominant side, a little below shoulder height, twisting
their spine, neck and shoulders.

I am convinced that the correct place is in one's centre, at about hip
height, and that the twisting movement required can be generated at
the hips.

Hmmm, what gives you this conviction? Ya see, if I was a betting man and
had to choose between what "feels right" or someone's "idea" of what is the
most efficient way, I'd plump for what "feels right" most of the time.

What feels right is learned. What's the right way to hold a pen, use a
screwdriver, type on a keyboard, lift sleeping child or open a door?

If you were to do a study with openable jars (or at least ones that could
only be opened with a deal of difficulty), you might be able to show that
one technique worked more often than another. Just observing how people
attempt to open an unopenable jar doesn't really prove anything other than
the fact that different people use different approaches.

Except that certain ways of doing things are demonstrably stronger than
others.

Daniele