# RULA upper arm angle

I want to perform a RULA based analysis on a set of participants and in order to calculate the RULA score I would need the upper arm(shoulder) angle. My question is would the upper arm angle be based of the trunk or the vertical axis?

For example, if the person had a bent back and if he was not aligned with the vertical axis, then the upper arm angle would be calculated with respect to the back or the vertical axis?

In the RULA assessment sheet: https://i0.wp.com/www.ergo-plus.com/wp-content/uploads/RULA-2.jpg the vertical axis and the back are both aligned with each other. But what if they were not? With what other line, ie, the back or the vertical axis, we would obtain the upper arm angle?

I have so far tried both the methods and both yield decent results but I dont really know which one would be the one RULA actually suggests to use!

Thank You!