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Clinical exam · Nervous system

Pronator drift !

  • Maneuver

With the arms outstretched and the eyes closed, an arm that turns in and sinks shows subtle weakness of the motor pathway.

Updated 2026-11-01

See it in 3D: Motor cortex · Spinal cord

What it is

Pronator drift is a quick, sensitive test for mild upper motor neuron weakness. With the arms held out in front, palms up, the weak arm turns inwards (pronates) and sinks, because the pronators and flexors overpower the supinators and extensors. It detects lesions that strength grading can miss and is the 'A' of BE-FAST.

The anatomy it tests

  • Tests the corticospinal tract from the motor cortex (precentral gyrus) to the cervical cord.
  • Damage to this tract weakens the arm's extensors and supinators most, so the arm pronates and bends.
  • Closing the eyes removes visual correction of the arm's position.

How to do it

  1. Patient seated or standing.
  2. Ask the patient to hold both arms straight out in front at shoulder height, palms up and fingers together.
  3. Ask the patient to close the eyes and hold the position for about 20 to 30 seconds.
  4. The examiner watches whether one arm turns inwards, bends at the elbow or sinks.
  5. A light downward tap on both arms can be given to see whether they return to place.

What a positive result means

  • Positive: one arm pronates and sinks; suggests an upper motor neuron lesion of the opposite hemisphere, such as a stroke.
  • Upward or outward drift with finger movements: proprioceptive loss (parietal or dorsal column lesion).
  • Sinking without pronation may come from pain or weakness of another cause.
  • A negative test does not rule out a small lesion.

Usefulness and limits

  • Sensitive for mild upper motor neuron lesions and easy to teach.
  • Shoulder pain, poor understanding or poor effort give false positives.

Test yourself

Think of the answer, then tap the question to see it.

What does an outstretched arm that turns in and sinks with the eyes closed indicate?

Mild upper motor neuron weakness in the opposite hemisphere, for example from a stroke.

Why is the patient asked to close the eyes?

To remove visual correction, so that drift from weakness or from loss of position sense becomes visible.

What does upward drift of the arm with finger movements suggest?

Loss of proprioception, from a parietal or dorsal column lesion, rather than weakness.

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See it in 3D

The structures of Durgical's 3D anatomy where it is found.

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Educational content on the clinical exam; it is learned and practised under supervision. It does not replace assessment by a health professional and is not for self-diagnosis.

Sources: 16.4 The Sensory and Motor Exams (OpenStax, Anatomy and Physiology 2e, 2022); How To Assess Muscle Strength (MSD Manual Professional Edition, 2024); Signs and Symptoms of Stroke (Centers for Disease Control and Prevention (CDC), 2024).

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