Collapsing weakness “Collapsing weakness”, the phenomenon in which a limb collapses from an instructed position with a light touch, is a common finding in patients with functional weakness. It is often associated with power that comes and goes or “intermittency”. This should be not be described as “intermittency of effort” since you cannot directly assess someone’s effort. Normal power can often be achieved transiently with encouragement, for example by saying to the patient, “At the count of three, stop me from pushing down…”. Alternatively, gradually increase the force applied to the limb starting gently and building imperceptibly up to normal force. An inability to understand the instruction, pain in the relevant joint, being generally unwell, and a misguided eagerness of some patients to “convince the doctor” may cause a false result. These concerns have been vindicated in the small number of validity studies of this sign which have found that it is a rather poor discriminator between functional and disease related symptoms.7