The Symmetrical Tonic Neck Reflex (STNR)

Introduction

In 1 sentence (quick summary)

The symmetrical tonic neck reflex (STNR) is an archaic reflex essential for the motor organization of the baby, but if it persists, it can disrupt posture, coordination, and the ability to sit still.

In 30 seconds (general public)

The STNR appears around 6 months and links the baby’s head movements to symmetrical reactions of the upper and lower body: when the head lifts, the arms extend and the legs bend; when it lowers, the arms flex and the legs extend. This pattern prepares the transition from crawling to creeping. However, if it remains active beyond the expected age, it can cause postural issues, clumsiness, or learning difficulties.

In 3 minutes (parents/educators)

The symmetric neck reflex, or STNR, is one of the last major archaic reflexes to appear. It establishes around 6 months, when the baby begins to sit up. It plays a crucial role in the emergence of creeping, stimulating the tonic alternation between arms and legs. It allows the baby to dissociate the upper and lower body, but it must disappear for voluntary movement to take over.

If it is not integrated, this reflex prevents proper sitting posture, makes arm-leg coordination difficult, and disrupts overall motor organization, impacting even school learning.

Mechanism of the reflex

The STNR is activated by flexion or extension movements of the head.

• <p>Head backward (extension): arms extend, legs bend.</p>
• <p>Head forward (flexion): arms flex, legs extend.</p>

It is a tonic postural reflex, meaning it modulates muscle tone according to the position of the head. It is controlled by the brainstem, the vestibular system, and proprioceptive loops.

The STNR appears around 6 months, peaks between 6 and 8 months, and then gradually integrates until 11-12 months, paving the way for stable voluntary posture, particularly autonomous sitting.

Symptoms of an active STNR

A persistent symmetrical tonic neck reflex can generate visible disturbances:

• <p>Difficulty staying seated without collapsing or arching.</p>
• <p>Asymmetrical or tense posture while writing.</p>
• <p>Balance or arm-leg coordination issues.</p>
• <p>Tendency to look up or down while moving arms.</p>
• <p>Aversion to manual supports (difficulty supporting oneself on the arms).</p>

In adults or older children, this can manifest as postural pain, instability while sitting, or difficulty coordinating reading, writing, and trunk maintenance.

Impacts on coordination, balance, posture

Sitting posture

A child with an active STNR will struggle to keep their back straight without support. They may alternate between exaggerated arching and collapsing, or sit on their knees on the chair to stabilize their pelvis better.

Coordination

This reflex disrupts coordination between the upper and lower body. For example, when a child lowers their head to write, their arms involuntarily flex, causing excessive tension and choppy writing.

Balance and gross motor skills

When walking or running, the natural arm-leg alternation can be altered. The child may have a stiff gait, avoid stairs, or struggle with biking or swimming.

Developmental stages and integration

The STNR follows a clear cycle:

If the baby does not crawl and goes straight to “hands and feet” or standing without a phase on the ground, the STNR may not be integrated.

Practical examples of an active STNR

• <p>✍️ Writing: the child lowers their head → their arms flex → they tense their hand → their writing becomes illegible.</p>
• <p>📚 Reading: they read with their head tilted → their back collapses → their concentration drops.</p>
• <p>🪜 Stairs: they do not properly alternate left/right leg.</p>
• <p>🧘 Sports or yoga: difficulty in dissociating head movement from limb movement.</p>

Connection with other archaic reflexes

ATNR – Asymmetrical Tonic Neck Reflex

The ATNR acts according to head rotation; if it remains active alongside the STNR, it prevents any fine bilateral coordination (eye-hand, writing, cross-motor skills).

<a target="_blank" rel="noopener noreferrer nofollow" class="text-primary underline cursor-pointer" href="/en/r/73f80176-59c8-4529-8675-2a28b72f4a9c">👉 Read the article on the ATNR →</a>

Moro Reflex

Often present in associated sensory disorders, the Moro disrupts posture following vestibular stimulation.

<a target="_blank" rel="noopener noreferrer nofollow" class="text-primary underline cursor-pointer" href="/en/r/bb390833-1a13-48f5-8888-7d64493fe5c1">👉 Read the article on the Moro reflex →</a>

These reflexes can be present together. Their joint assessment is essential for complete integration.

Conclusion

The symmetrical tonic neck reflex (STNR) is a structural milestone in gross motor skills. It helps the baby to sit up, but must extinguish for voluntary gestures to take over. When it persists, it creates disharmony between posture, coordination, and attention, often invisible but profound.

➡️ Fortunately, gentle, playful, and repeated exercises can help integrate it even late — in children as well as adults.

Further exploration

🔗 Reflex <a target="_blank" rel="noopener noreferrer nofollow" class="text-primary underline cursor-pointer" href="/en/r/73f80176-59c8-4529-8675-2a28b72f4a9c">Asymmetrical Tonic Neck Reflex (ATNR)</a> →

<a target="_blank" rel="noopener noreferrer nofollow" class="text-primary underline cursor-pointer" href="/en/r/bb390833-1a13-48f5-8888-7d64493fe5c1">🔗Moro Reflex →</a>

<a target="_blank" rel="noopener noreferrer nofollow" class="text-primary underline cursor-pointer" href="/en/r/f794320f-e613-44c2-85b9-75f0e68e367f">🔗Galant Reflex →</a>