The arm troughs are designed to handle the maximum forces that the KINARM Exoskeleton can exert, so that won’t be a problem for you. That said, most people with no impairments will be able to overpower the robots and likely overheat the motors (which will shut off automatically). If you have a specific subject population that has generally low strength then you should be able to take some measurements from them.
Any time you try this sort of experiment it will be important to build in reasonable safeties so that no subject is hurt, ex. reasonable ramp up and down times on forces and some sort of limits for the test angles on the shoulder and elbow so you can tell if someone is overpowering the system or being over powered.
If you’d like some more specific advice please let me know.