Seated Chest Press vs Smith Machine Bench Press

On Feb 13, 11:16 pm, Bartleby <arroy... RemoveThis @hotmail.com> wrote:
>
>
> "The full effect of gravity" is present whether an object is moving
> horizontally or vertically.

In a general sense, sure.

But imagine a tug-of-war, with both sides evenly matched. Now you
come in and pull at a direction perpendicular to both forces, on
either side. Assuming you have enough force applied, don't you think
you would have an effect? Hence my akido analogy.

> I don't get your aikido metaphor. If I am standing and pushing against
> someone who is standing and pushing against me, I am
> exerting force more or less horizontally. I can understand how
> deflecting my opponent's force would be potentially advantageous, but
> I don't see the relationship to the issue being discussed

Well, any analogy will rip if you stretch it far enough. I meant only
to illustrate by way of comparison the notion that the direction of
the force applied is an important consideration. But we can forget
this akido example if it will only introduce more complexity to the
discussion.

> The same gravitational force applies whether I am lifting a weight
> vertically or horizontally.

Semantics here: yes, it applies "equally" in the sense that you plug
in the same number for gravity no matter the equation (unless you get
very far away from the earth, of course, but we're not talking about
such cases), but no, it does not apply "equally" because its effect
can be skewered by the force applied against it.

Again, I have in mind, to use yet another illustration, the tug-of-
war: pushing up a weight against gravity would be analogous to the two
sides tugging 180 degrees away from each other; pushing forward a
weight against gravity would be (roughly) analogous to a third party
coming along tugging 90 degrees to both parties.

> I can lift far more free weight
> vertically as in a deadlift or a squat or a shoulder press than I can
> by pushing a weight out horizontally, but that does not
> mean that gravitational force is lessened by moving a weight upwards.
> You want to compare apples with apples so let's
> eliminate the machines entirely.

Um, no, we can't eliminate the machines because, well, the question is
precisely why one machine is easier than the other despite the muscles
being worked the same way. Obviously, when you talk about a deadlift
compared to a shoulder press -- or even the squat -- you're talking
about very different things.

> Not true. Please cite verbatim a physics text which says this.

If I tell you "sdfdf" means "lkjhf" and you say no it doesn't, it's up
to you to provide the proof.

> Would you agree that 45 degrees is a midpoint between straight up and
> straight out? Something
> has to go up to get to 45 degrees. I don't use machines all that
> much, but I know that there are different
> machines, e.g., Strive, HammerStrength, etc. There are cams and
> levers that differentiate
> one (well-maintained) machine from the next and which don't exist with
> free weight exercises.
> These factors make it difficult to compare free weight lifts with
> machines - or even between different
> kinds of machines.. I would never assume I could do a free weight
> lift with the same weight I move
> on a machine - whether the machine has me lifting vertically or
> horizontally. This goes beyond the
> contribution of stabilizer muscles.

We're not comparing free-weight exercises here to machine-stabilized
ones. We are very clearly one machine with another. And, what's
more, I am comparing mechanically equivalent machines, where leverage
is concerned. I have been saying that, all else being equal, the
direction of force exerted against gravity makes a significant
difference.

> I do not mean to suggest that machines can't be helpful.

They certainly have their place, even if for nothing else than for the
sake of variety!

> Some machines are harder to use than others. Strive, for example,
> suposedly
> allows you to focus on where your sticking point is - at the outset,
> midway or near the end.

Yes, some machines are harder to use, as exercises, than others, which
would purport to model the same exercise.

I'm talking about *mechanically equivalent* ones.

> I used a HammerStrength incline bench press tonight. I'm glad the
> machine helped to support the
> weight as I was pushing out out and slightly up. I was not working
> against 100 -n% gravity!

Note that that's an incline press machine. Quite a different "muscle
motion" than what's being discussed.

> Simply stated, in the
> bottom position the lever is rotated out of the horizontal and not all
> of the weight force of the plates was directed
> against me. As I moved the weight up and the lever arm moved towards
> the horizontal, more of the weight was
> directed against me. If you spotted me doing a flat bench and helped
> out a lot at the bottom position and gradually
> lessened your assistance as my arm extended and the weight went up, I
> could do a mighty fine bench press (for me)
> - but that does not mean that gravity is minimized by lifting a weight
> vertically!

Be that as it may, we're not talking about the incline press, but the
flat bench press. Our issue concerns why a seated chest press machine
is easier to use than one where the user is laying down on his back.

> If you could provide mechanically equivalent machines where the lever
> arms are reducing the
> weight directed against the lifter by the same percentage throughout
> the phases of the lift and
> where the same muscle groups are equally engaged,you would see that it
> would be irrelevant
> whether one is pushing out or up. Gravitational force is an
> unvarying constant.

And that's just the crux of the matter: would mechanically equivalent
machines be equally easy/difficult? I say no, you say yes. You say
yes because gravity is constant; I say no because while gravity itself
is constant, its "potency" can be "diluted" by the direction against
which it is contested.

Remember, gravity is being worked against here. Gravity would only be
constant in "bottom-line terms" if the weight is simply being dropped
to the earth. We are, however, lifting that weight, and the direction
of our lift/work/push matters.

Tell you what. I'm going to ask a physics professor or two. I'll
report back when I get an answer, whether I'm right or wrong. I
promise.

On Feb 14, 7:21 am, Tom Anderson <t....RemoveThis@urchin.earth.li> wrote:
>
> I'd say it was three-billy-goats-and-a-bridge territory myself, but hey.

Heh, more like two apples, two oranges, a banana, and innumerable
keystrokes and dead neurons.

> Okay, thanks. You're wrong.
>
> That's just not how physics works. Whatever the angle of the string, you
> have to apply the same force to it to lift the weight.

The pulleys make the job easier. That's why you have pulleys.
Machines make life easier.

Because it's easier, there is less force used per inch/feet/drop of
sweat/whatever.

That's why a free-weight exercise will be harder than one performed in
a machine.

> The crux of the problem relates to bending a force through an angle: if
> you're pushing horizontally but moving a weight up,

AHA!

I'm not envisioning the weight being moved up. I'm envisioning that
weight being moved forward. In the seated version.

No wonder you keep returning to pulleys! Indeed, how else to apply
force through an angle!

Anyway, the last time you raised this issue (though not so
explicitly), I mentioned that both machines could be engineered to be
mechanically equivalent such that their pulley actions are not
different at all....

> is that as difficult
> as moving a weight up (like i say) or horizontally (like you say)? A
> pulley is a good way of setting up a system like that, which is why
> pulleys keep getting mentioned. The same goes for levers.

Again, if you engineer both machines, the prone and the seated
versions, to be "mechanically equivalent," the "pulley action" would
not be different between them, and hence "cancel out" as variables
explaining why one offered more difficulty than the other.

Now I might still turn out to be wrong on that final score, but that
final score is what I'm arguing -- not over pulleys and how they work,
et cetera et cetera et cetera...which is why I'd mentioned that in
contesting me you have to contest from *within* my argument, not from
without it, or else we wind up having two different, though related,
conversations: "Watt's on first? Hu's on second?"

> If you like, i could have phrased my question with a lever instead of a
> pulley. Or with some hydraulic pistons, or two axles with a universal
> joint. They're all entirely equivalent.

Yes, and *both* machines have them such that there is no mechanical
difference between them. With no mechanical difference between them,
we can get down to my argument that direction of force against gravity
is the determinant in exercise difficulty.

Can you just forget about pulleys and levers? I don't mean that they
don't exist in these machines -- rather, that they exist in such a
state between the two machines such that they "cancel out" as
factors. What don't you get about that?

Now maybe it's physically impossible to construct such machines,
machines with different user positions to be mechanically equivalent
-- maybe there's just no way in this universe that two machines could
be made such that their mechanical actions are so equivalent to one
another such that they cancel out in any work-comparison with one
another. I can't imagine why not, but if that's your argument, then
that's that.

But you haven't said that. You keep going back to pulleys and geegaws
of this sort when I keep saying that they can be made mechanically
equivalent so that they are no longer a point of difference between
the two machines. It's like I'm saying I don't want fries with that
and you keep asking whether I would like ketchup with my fries...are
you really saying that the fries just come with the order regardless
of what I want?

Again, there are no pulleys, etc. involved here. Not because they
don't exist, but because they're *mechanically equivalent* such that
they factor one another out as differences between the two machines.

> Well, that's been clear for quite a while.

So why not talk to me about what I'm talking about -- since you're
replying to me -- instead of continuing to go on about oranges to my
apples??

> I'm generalising. I thought it was obvious that the fine detail of the
> linkage between the handles and the weights didn't matter (provided
> there's no mechanical advantage), but i guess it's not.

It's obvious it doesn't matter.

There is no mechanical advantage between mechanically equivalent
machines.

You (and the others) keep bringing up mechanical advantage with
pulleys and so forth, when I keep saying that there is no mechanical
advantage between mechanically equivalent machines.

> tom
>
> --
> Orange paint menace