Brain-Based Solutions™ for the Flexor
Withdrawal Reflex

A Physiological Protective Response (Part 3 of 5)




The nociceptive or flexor withdrawal reflex (FWR) is a cord-mediated reflex intended to protect the body from damaging stimuli.

The classic example is the reflexive response of the offended part after touching something hot, and withdrawing that body part from the hot object. The heat, for example, stimulates noxious receptors in the skin, triggering the primary afferents that travel to the cord and brain.

The sensory input synapses ipsilaterally in the cord’s gray matter and ultimately the anterior horn cells with facilitation of the associated physiological flexors that cause withdrawal; other neurons cause facilitation of the contralaterally related and associated physiological extensors, pushing away from the stimulus.

There is also a simultaneous and reciprocal contralateral response—a crossed cord reflex (part 4 of 5). Other interneurons instantaneously relay the sensory information up to the cerebellum, midbrain, and cortex to integrate the nociceptive response and the consequential protective movement.


The Reflex


All human physiological reflexes have a predictable display. Therefore, either they work according to their original design or they are pathological. There are no other choices. If a reflex displays itself in ways other than according to its pre-programmed format it can be considered “other-than-human,” with a concomitant increased the risk of injury. Reflex error always requires treatment.









Mechanism of Display

The FWR is the manifestation of a painful (i.e., nociceptive) stimulus. As a result, the limb protects itself and the rest of the body—a survival response—by withdrawal. (In this case, we will only focus on lower extremity’s response to nociception, but there is also an upper body response, as well.)

















proximal rectus femoris contralaterally; this is opposite of what one would expect. (For more about the influence on the proximal and distal aspects of the bi- or multi- articular muscle, see the “Spinal Pattern Generator” videos from


The results of the entire neurological examination indicated that Michael was deafferentated through his cervicodorsal spine and left shoulder girdle and he was not ventilating properly, affecting his left cerebellum.

The Fix


Coupled chiropractic manual manipulation of Michael’s left cervicodorsal spine and left shoulder girdle, together with certain specific physiological exercises to rehabilitate the structure and nervous system in order to normalize his FWR.

The Result


According to Michael’s original diagnosis, increasing the afferentation to his left cerebellum normalized his flexor withdrawal response. Now, stroking the sole of his foot with a sharp object caused the proper physiological response—the facilitation of the proximal ipsilateral rectus femoris and the inhibition of the proximal rectus femoris contralaterally. This response is more human-like.



This erroneous FWR display is significant. It suggests that a painful (nociceptive) stimulus to either of Michael’s feet might (figuratively) cause him to collapse onto the stimulus (discussed in the “Spinal Pattern Generator” videos). The examination indicated that his nervous system was originally unable to update fast enough to maintain upright posture. Actually, if Michael were to receive a stimulus that was significant enough to maintain his capacity for upright posture, his lower body flexors would inhibit increasing his probability of falling. Michael had other therapies and left the office able to respond nominally.

This short article tackles the flexor withdrawal reflex (FWR) and one way to effectively influence its erroneous display.


The FWR is a protective response. It helps move away from perceived danger while maintaining posture and balance.It can be challenging to observe a dysfunctional FWR and this inappropriate display can lead to the realization of pain in various ways.

Case Study


Michael (54y) came in complaining of twitching in his left hip for the past 3-4 days. He had no idea how the twitching started, but said he had been under a lot of personal and professional stress the past two weeks.

Schematic Flexor Withdrawal Reflex FWR.P
Schematic Babinski Stimulation.PNG

As a result of noxious stimulation, one would expect physiological withdrawal on the side of stimulation and positive support contralaterally. That is, we would expect to observe physiological flexion of the thigh on the hip ipsilateral to stimulation and physiological extension of the thigh on the hip contralateral to that same type of stimulation (i.e., the positive support to resist falling down). (For more information, read “Examining Multiarticular Muscles; Analyzing Their Role in Functional Joint Integrity”.)




What We Found

One aspect of Michael’s examination indicated that stroking the sole of either foot with a sharp object caused the inhibition of the proximal rectus femoris ipsilaterally with an erroneous facilitation of the

A very important clinical note: when testing with FRA you have 4-5 seconds per test because of the way the withdrawal reflex decays in the cord. It is maintained for protective reasons.

Also, whenever one FRA is stimulated it supersedes any other FRA independent of their timing.

Consider that again: The normal response to stroking the sole of the foot with a sharp object should cause a physiological withdrawal of the involved lower extremity and extension of the lower extremity contralaterally, increasing resistance to fall.