Dysdiadochokinesia (DDK) is the medical term for an impaired ability to perform rapid, alternating movements (i.e., diadochokinesia).
The term is from Greek δυς dys "bad", διάδοχος diadochos "working in turn", κίνησις kinesis "movement".
A simpler method using this same concept is to ask the patient to demonstrate the movement of trying a doorknob or screwing in a light bulb.
When testing for this condition in legs, ask the patient to tap your hand as quickly as possible with the ball of each foot in turn.
[5] Dysdiadochokinesia has been linked to a mutation in SLC18A2, which encodes vesicular monoamine transporter 2 (VMAT2).