[Retric]

The theory behind these devices is even minimal assistance over a long day makes a difference. Try holding your arms strait out for 10 seconds and it's easy, 10 minutes and it becomes really difficult.

Now picture something that reduces your load by 80% you still need to provide some upward assistance so lowering your arms is still effortless, but holding your arms out is also much less effort. For an easy example, sitting underwater provides this kind of support but it also clearly does not reduce range of motion.

[dx034]

Does that mean that lowering your arms with the vest becomes harder? In that case it'll probably take workers a while to build new muscles? Or how does the vest distinguish holding body weight vs the worker lowering their arms.

[Retric]

This gets complicated because you can vary the amount of support based on the angle the arms are at. Anyway, there is no need to account for extra weight simply supporting someone's arms can make a large difference. But, you get into a lot of trade offs.