Special Test

Biceps Femoris Reflex

Last updated on: November 7, 2024

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The Biceps Femoris Reflex or Lateral Hamstring Reflex is elicited by striking the biceps femoris tendon just above its insertion above the knee joint. This reflex is mediated by tibial portion of the sciatic nerve, primarily by the S1 nerve root.

How to perform the Biceps Femoris Reflex?

With the patient sitting, recumbent, or lying on the opposite side and the knee moderately flexed, the examiner’s fingers are placed over the tendon on the lateral posterior aspect of the knee and tapped. The response is knee flexion. The Lateral Hamstring Reflex may also be elicited by tapping the head of the fibula (fibular reflex).

See Also: Deep Tendon Reflex Testing

This reflex is mediated by tibial portion of the sciatic nerve, primarily by the S1 nerve root. The external hamstring reflex is sometimes helpful in sorting out whether an absent ankle jerk is due to peripheral neuropathy or radiculopathy. If due to neuropathy, the external hamstring will usually be preserved, but in radiculopathy, it may be depressed in concert with the ankle reflex.

Reflex Name	Biceps Femoris Reflex
Muscle	Biceps femoris
Patient Position	Prone with the knee flexed to approximately 20°
Position of Examiner	Standing next to the patient. The thumb is placed over the biceps femoris tendon just proximal to the joint line.
Evaluative Procedure	The thumb is tapped with a reflex hammer.
Innervation	Tibial, common peroneal
Nerve Root	L5, S1, S2, (S3)

References & More

DeJong’s The Neurologic Examination – 8th Edition
Van de Crommert HW, Faist M, Berger W, Duysens J. Biceps femoris tendon jerk reflexes are enhanced at the end of the swing phase in humans. Brain Res. 1996 Sep 23;734(1-2):341-4. PMID: 8896845. Pubmed