They used a 1 Rep Max type intensity calculation (which is very common) and to get that baseline they used an isometric contraction with a joint angle of 50deg

They used a 1 Rep Max type intensity calculation (which is very common) and to get that baseline they used an isometric contraction with a joint angle of 50deg. So basically you put someone on the machine, set the angle, tell them what to do and give them ~3 tries to do a bicep curl as hard as they can. Since the “weight” isn’t allowed to move, it’s just down to how hard each individual can pull. I’m pretty sure they used a machine like a biodex that is basically a load cell/resistance unit that you can setup for different movements and contraction types. It works based on an arm coming off a rotational unit. So direct load cell measurements are torque. Torque can then be used to calculate other things depending on what you’re doing. The results are interpreted and that sets the individual’s Maximum Voluntary Contraction Isometric Torque, which again is basically just 1RM on this machine.