Is there any significance to my body motion observation?

Uh, your statement didn’t hold true for me, at least not as described so I can only say that there is no ‘significance’.

As for the restrictions the body has on movement, it’s protective and keeps everything where it should be so we aren’t big flesh puddles.

@asmonet ~ ha ha me neither
I just tried it

Doesn’t it just mean your muscles get tired of keeping your arm raised?

Your earlier stopping point would be the point where the force of gravity is equal to the force those muscles exert in a resting state. After having done this two or three times, those muscles will become tired, and at what used to be the stopping point, gravity will still be stronger than the muscles. So the stopping point lowers.

That’s my guess.

@asmonet , @mcbealer What happened when you tried what I said. Did you find that you could stop anywhere or did your arm just drop all the way? I have tried this in person with people and had my results replicated.

@Fyrius , If you just let your arm drop there should not be any muscle fatigue involved.

are we raising our entire arm or just the hand?

You can bend either at the elbow or at the shoulder. The result is the same.

I did it with my arm extended at shoulder height. Basically, my hand just dropped down to my side.

Oh, I should have mentioned that you have to do it with your elbow bent. The elbow in fact will naturally be in one of its two stopping points.

@LostInParadise: Yes there should.

I’d like you to try something for me.
Find something heavy that you can hold in one hand. A dumbbell would be ideal. Failing that, try a carton of milk, a bag of sugar, a bucket of sand, whatever. Now, while holding this heavy thing in your hand, raise it to shoulder level – or you can put the weight on something of the appropriate height, then grab it and hold it, if you want – then lower it slowly. As slowly as you can. Repeat this a few times. I think you will find this tiring as heck.
This is actually much like what people advise you to do with weight lifting exercises you’re not strong enough to carry out the normal way. Get the weight high enough somehow, then lower it as slowly as possible. Makes good, easier practise for the real thing.
It’s called “negative” lifting, apparently.

Doing this with just the weight of your arm is of course a lot less taxing on the muscles, but on a lower level, it’s the exact same thing.

@Fyrius , That is just my point. Using a heavy weight just reinforces what I am saying. If you just let your arm drop with a weight in it you will still hit the stopping points.

When I see weight lifters on television lifting really heavy weights, there are one or two resting places where they pause before lifting the weight over their heads. They are hitting the stopping points.

I’m not sure if we’re talking about the same thing. If you let your arm drop with a weight in it, wouldn’t the stopping point be where it slaps against your thigh?
Reading back to your opening post, I still think your stopping point as described there would be the point where the force gravity exerts on your arm stops being greater than the stretch-inertia your muscles exert on it in a relaxed state.

“When I see weight lifters on television lifting really heavy weights, there are one or two resting places where they pause before lifting the weight over their heads.”
You mean like this?
I think that’s a matter of completely different things. This guy brings the barbell up in one swing, then pauses for a bit, then presses it over his head in another motion. Between the first and second movement, he needs to get his arms from above the bar to below the bar. Before he’s done this he can’t direct his force properly to get the barbell further up.
The “stopping point” in your arm lowering experiment is completely different from the “stopping point” in a clean&press.

For that matter, I’m pretty convinced your unified “stopping point” concept doesn’t really exist as such. When you lower your arm, the “stopping point” will vary based on muscle fatigue. There’s no anatomical significance to this position.
When you throw a ball, the various part of your arm don’t stop moving where they do because they reach a “stopping point”, but because the muscles are coordinated to work together as effectively as possible, and while some could move further that would make the throw less strong.
The stopping points of an elbow will just be the point where the joint won’t move further (which is a property of the joint) and the point where the lower arm bumps into the upper arm.
You will also find a “stopping point” in your legs when you try for example to do a split, but that in turn is because the maximum length of your leg muscles is finite and won’t stretch beyond a certain point.

It seems you’re looking for one single anatomical explanation for resembling but fundamentally disparate phenomena. There is no such thing. Each kind of stopping point has its own explanation.

@Fyrius , We are at an impasse.
I’m not sure if we’re talking about the same thing. If you let your arm drop with a weight in it, wouldn’t the stopping point be where it slaps against your thigh?

No, if you have your elbow bent in a comfortable position, I maintain that you will reach a stopping point. I think the only way I can properly explain what I am saying is to use a video.