Not enough shoulder flexibility for squats?

Dnia 2008-01-02 Jim Janney napisa³(a):
> Andrzej Rosa <bakters.DeleteThis@yahoo.com> writes:
>
>> Dnia 2007-12-31 Uncle Bob napisa³(a):
>>> "Andrzej Rosa" <bakters.DeleteThis@yahoo.com> schreef:
> [...]
>>>
>>> The shoulders are attached to the humerus, not the hands. When the bar
>>> wobbles, the hands move wrt the lower arm, which means there is movement at
>>> the wrist joint.
>>
>> There is none of it. You grip the bar in the middle and the bar has too
>> much inertia to actually wobble at the fulcrum of your grip point.
>> Dumbbells on the other hand do tend to wobble if you don't grip them
>> tight. They can, because they have less rotational inertia (I mean an
>> equivalent of mass in rotational motion traditionally denoted as "I",
>> however it translates to English).
>
> It's been a long time since I studied physics, but I think my
> textbooks called that the "moment of inertia",

I didn't dare to use literal translation from my mother tongue, but it
looks like I could in this case.

> although "rotational
> inertia" actually makes more sense. And I think you're correct that
> the longer bar will be more stable because of this. However, I think
> Pete is also correct that trying to control a longer bar from the
> center gives a correspondingly poorer mechanical advantage;

Compared with what? With two-armed press? Sure. With one-armed
dumbbell pull? Sure. With one-armed kettlebell press? Sure.

But not with one-armed dumbbell press.

> think of
> working a lever from the wrong end, and note that the tightrope walker
> uses both hands, spaced well apart.

Because they need to balance _themselves_. They use inertia of a bar
to press or pull against, so they can regain balance in case they start
losing it. They can do it, because a long bar has high moment of
inertia, but to actually use it they need two hands.

A bar you press overhead also has higher moment of inertia than a
dumbbell, so it isn't easy to unbalance it. In practice it means that
with a bar you don't need to press so precisely to keep it balanced as
you need with a dumbbell.

> So we have two opposing trends, and I don't know which one would
> ultimately dominate.

Infinitely long bar would be impossible to unbalance (due to infinite
moment of inertia), so it would work like a machine press.

> I suspect that lifters actually correct by
> moving their bodies under the balance point,

It takes too much time. If you are "chasing" a bar, you are in trouble.


> but since I don't do
> overhead lifts this is all theoretical on my part.

Give some thought to learning a bent-press. I started working toward it
to fix my shoulder, and it stayed fixed ever since.

--
Andrzej Rosa 1127R
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