That assumes all the weight is at the end of the arm, which it isn't in this case.

I do have a weight on my shoulder: my arm. Holding your arm up for a long time is hard anyway. A human arm weights 8 pounds.

> When you carry a bottle, you keep passing it from one hand to another

That's a good point.

> inability to do so will make it very challenging in probably less than 20min

That seems a bit extreme.

Anyway grip is the part that fails, not the shoulder strength.