The first being that we should use armrests as they support our upper limbs and reduce the amount of load down to our lower back when in a seated posture. The second being that we should not use armrests as they create risk factors such as shoulder shrugging, contact stress on the forearm and leaning postures.

Should I use armrest or not?

Traditionally, OH&S requirements encourage the use of armrests on the chair as they act to support the elbows and arms. ... Your arms are not load bearing joints, so leaning on your elbow, supporting your body weight over the course of a work week ultimately with result in neck and shoulder complaints.

Are armrests bad for shoulders?

This means that the position of the armrests are wider than their shoulder breadth so to use the armrests the user would need to move their elbow away from their torso (resulting in shoulder abduction aka an awkward posture). And, of course this is considered to be an ergonomic risk for the shoulder and upper back.