Sensory processing
The ATNR: The Fencing Reflex, and What It Means When It Stays
Turn a newborn's head and one arm extends while the other bends. Why that happens, when it should stop, and what an obligatory response blocks.
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The asymmetric tonic neck reflex — the ATNR, or the “fencing position” — is what happens when a calm newborn lying on their back has their head turned to one side: the arm and leg on the side the face is turned toward extend, and the opposite arm and leg bend. It appears around 35 weeks of gestation and typically integrates by 3 to 4 months.1 It has a job while it lasts: it brings the hand into the infant's visual field as the head turns, which supports early hand-eye coordination.1 The distinction that matters clinically is between an OBLIGATORY response, where the limbs lock into the position and stay, and a facultative one, where the tendency is there but can be overcome. An obligatory ATNR persisting past 4 to 6 months is the one with documented consequences.
What the ATNR is
Turn a calm, supine newborn's head to one side and a predictable thing happens: the arm and leg on the side the face is turned toward extend, and the arm and leg on the other side bend. The posture looks like a fencer's stance, which is where the common name comes from.1
What it is for. The ATNR brings the hand into the infant's visual field as the head turns, which supports the development of hand-eye coordination. It also promotes sensory awareness of body laterality, and may support the cross-lateral movement patterns needed for crawling.1
When it appears, and when it fades
| Point | What is expected1 |
|---|---|
| Around 35 weeks of gestation | The reflex appears. |
| By 3 to 4 months of age | Typically integrates. |
| Beyond 4 to 6 months | An obligatory response at this point has documented consequences for motor development. |
How a clinician checks it
The infant is supine and calm. The examiner gently rotates the head to one side and holds it there for 10 to 15 seconds, then repeats to the other side — both sides are tested, because asymmetry between them is itself information.1
Obligatory or facultative. This is the distinction that changes what the finding means. In an obligatory response the limbs assume the position and remain fixed there. In a facultative one the tendency is present but can be overcome.1 The documented consequences below attach to the obligatory kind.
What an obligatory ATNR prevents
An obligatory ATNR persisting beyond 4 to 6 months stops an infant from holding a symmetric posture, and the consequences are specific and sequential.1
What it blocks
- Bringing both hands to the midline — a prerequisite for two-handed play
- Reaching across the body to grasp
- Rolling, and then sitting and crawling, which build on symmetric posture
Where this stops. This is a documented consequence of an obligatory response in infancy, not a general claim about school-age difficulty. A retained reflex does not automatically mean impairment,2 and the broader association between retained reflexes and later academic performance is correlational. A 2026 systematic review of 14 studies in children aged 3 to 11 without neurodevelopmental diagnoses found consistent negative associations with motor outcomes and with reading, spelling and mathematics, and concluded that the available evidence “remains limited and heterogeneous”.3
If you have been told your child has a retained ATNR
An obligatory ATNR in an infant who is not reaching midline is a reason to see a doctor or a pediatric therapist, and soon. A facultative one in a school-age child is a different conversation, and the questions worth asking are on the parent article.
Frequently asked questions
What is the fencing reflex?
It is the common name for the asymmetric tonic neck reflex, or ATNR. When a calm newborn's head is turned to one side, the arm and leg on that side extend and the opposite arm and leg bend, producing a posture that looks like a fencer's stance.
When should the ATNR go away?
It appears around 35 weeks of gestation and typically integrates by 3 to 4 months of age.
What is the difference between an obligatory and a facultative ATNR?
In an obligatory response the limbs assume the position and stay locked in it. In a facultative response the tendency is there but can be overcome. The documented consequences for motor development attach to the obligatory kind.
Does a retained ATNR cause handwriting problems?
Retained reflexes have been associated with handwriting difficulty in group studies, but association in a group does not establish cause in an individual child, and occupational therapy guidance states that a retained reflex does not automatically mean impairment.
Sources
- Chamarthi VS, Gunasekaran V, Daley SF. Primitive Reflexes: Comprehensive Neurological Assessment Across the Lifespan. In: StatPearls. StatPearls Publishing; updated 2026. ncbi.nlm.nih.gov/books/NBK554606 (PMID 32119493). Checked August 25, 2026.
- American Occupational Therapy Association. Practice guidance on reflex integration programs and occupational outcomes. Checked August 19, 2026.
- Provazník A, Musálek M, Bob P, Větrovský T, Malambo C, Silva AF, Anderson D. Persisting primitive reflexes and motor and cognitive development in children: a systematic review. Acta Psychologica. 2026;266:106915. doi:10.1016/j.actpsy.2026.106915 (PMID 42061063).
Medical disclaimer. This page is for general educational purposes and does not constitute medical advice, diagnosis, or treatment. Sensory and motor concerns are best assessed by an occupational or physical therapist who can evaluate your individual child.