The Barak et al 2026 study of infant suck biomechanics + clinical correlates rests on assumptions which lack an evidence base or biological plausibility
This series of NDC (Neuroprotective Developmental Care) analyses of new research in the fields of breastfeeding, lactation, and infant care acknowledge the tremendous amount of work that goes into each new study and it's publication, celebrating the passion authors have for advancing knowledge in the clinical care of parents with infants. The series also claims the importance of respectful dissent and debate, which is fundamental to the advancement of science and the care of families. Our small team at The NDC Institute: Home of the Possums Programs hope that researchers whose work Pam analyses and critiques accept the sincere respect from which we offer differing perspectives, as together we serve the shared value of contributing to better outcomes for families.
Overview
The Barak et al 2026 study is significant, because it aims to investigate links between the clinical presentation of breastfeeding pairs and ultrasound measures of the biomechanics of infant suck, an area vital to clinical assistance for breastfeeding problems but which has still received little research attention. In 2022 Douglas et al published a case series of five mother-baby pairs, also investigating the link between clinical presentation and ultrasound measures of the biomechanics of infant suck. That earlier pilot study applied ultrasound pre- and post-measures to evaluate the intra-oral effect of an intervention which aimed to enhance positional stability in mother-infant fit and hold).
The authors of the Barak et al cross-sectional study evaluate 21 mother-infant pairs, infant ages 3-6 weeks, using ultrasound measurements of a breastfeed, the Numeric Assessment Scale for nipple pain. The authors state that they have shown that
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Mean milk transfer rate (measured by pre and post weighs and durations of a single feed) is an indicator of breastfeeding quality
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Gastroesophageal reflux symptoms are linked with breastfeeding quality. (This may be a translation error as infants show clinical signs but are unable to describe symptoms).
The authors conclude: "Clinicians are encouraged to assess breastfeeding quality in cases of reflux symptoms."
Methodology problem #1. Omitted variable bias
Barak et al 2026 fail to consider correlations between clinical presentations of fit and hold and biomechanics of suck using ultrasound measures, ignoring Douglas et al 2022. Barak et al state only that they assess all mother-baby pairs with the infant in cradle hold.
Methodology problems #2. Multiple assumptions, which lack an evidence base or biological plausibility
Barak et al 2026 make multiple assumptions which align with popular understandings but which lack an evidence-base, and also lack biological plausibility. Some examples are detailed in the table below.
| Barak et al 2026 claim | Analysis |
|---|---|
| "Tongue mobility plays a critical role" in breastfeeding. | Ultrasound and MRI findings which explore the role of tongue movement in the complex biological system of a breastfeeding mother-baby pair are explored in depth in Douglas et al 2022. The tongue's role is commonly misunderstood. For example, the tongue doesn't lateralise, rise halfway up the oral cavity, or compress milk pores. The tongue moulds around available intra-oral nipple and breast tissue. |
| Martinelli Lingual Frenulum Protocol for Infants is a valid and reliable tool to diagnose tongue-tie. | As a tool for determining presence of ankyloglossia, the LFPI been shown by Dhar et al 2026 to have "limited clinical validation with feeding difficulties", with very low certainty of evidence including "poor validation methodology, inconsistency in results, and serious imprecision in measurements". The LFPI tool integrates subjective signs which lack clinical relevance and which have not been demonstrated to help with ankyloglossia screening, such as tongue posture during crying, gloved finger assessment of tongue movement, and lip posture during breastfeeding. |
| "Biomechanically, inadequate attachment or poor tongue mobility may lead to inefficient milk transfer and a variety of compensatory responses by the infant, such as increased vacuum, biting and nipple compression." | The gestalt model of infant suck and the mechanobiological model of nipple pain and damage more credibly explain each of these signs cf theories relating to poor tongue mobility. |
| "Oxytocin plays a central role in the milk ejection reflex, and stress or acute pain can disrupt its release," which is hypothesised to affect milk transfer rates. | Despite its popularity, this theory is not corroborated by the evidence. |
| "Biomechanically, a small change in nipple diameter could indicate restricted tongue elevation, which plays a key role in bolus propulsion and milk duct compression. Such restriction may impair the infant’s milk flow control and swallow efficiency, which has been proposed to contribute to aerophagia and reflux-like symptoms in previous studies". | These claims lack biological plausibility, misunderstanding nipple diameter changes in infant suck during breastfeeding. |
| "The anterior portion of the tongue primarily stabilizes the breast against the palate and moves en bloc with the mandible in a limited superior–inferior direction, contributing to the establishment of a baseline intraoral vacuum. The mid-posterior portion of the tongue then moves on a superior–inferior axis. In the superior (‘tongue up’) position, the nipple tip is compressed against the hard palate, closing the nipple pores. As the tongue moves inferiorly (‘tongue down’), intraoral vacuum increases, drawing the nipple towards the hard–soft palate junction and enabling milk transfer into the oral cavity." "Studies demonstrated that the anterior part of the tongue moves en bloc with the mandible in a limited superior–inferior direction, while the mid-posterior part undulates independently in a peristaltic-like motion. The coordinated inferior–superior motion of the mid-posterior tongue is associated with intraoral pressure changes and the efficiency of milk removal from the breast". | Whilst work by Professor Donna Geddes and her team are cited by Barak et al concerning the application of ultrasound measures, the authors ignore Douglas et al 2022 co-authored by Professor Geddes, which critiques Barak et al's description of sucking. For example, their description confuses the mid tongue (which is visible on clinical examination) with the posterior tongue (which lies under the soft palate and is not visible on clinical examination), and which have different actions during sucking. This is consistent with the same error concerning movement the mid and posterior parts of the tongue found in Watson Genna et al's interpretations of suck during breastfeeding. There is no peristaltic movement in the infant tongue during breastfeeding, as the anterior and mid tongues move up and down enbloc, but there is an anterior-posterior rocking motion of the posterior tongue. Perhaps the extension of the cervical spine during Barak et al 2026 and Watson Genna 2024 ulstrasound analysis has confused interpretation of the movement of the mid and posterior tongues, so that the authors conflate the two? |
| A pre- and post-breastfeed weigh compared with duration of the feed is a reliable measure of the infant's breastfeeding performance over time. | No single feed cannot be generalised as a measure of breastfeeding success over time, since volumes transferred in a single breastfeed are highly variable. Pre- and post- test weighs are only reliable measures when used over a 24 hour period. |
| "Poor tongue mobility and poor lip seal were identified as possible causes of aerophagia, a condition in which a large volume of air is swallowed by the infant. Aerophagia shares symptoms with Gastro-Esophageal Reflux (GER), a common parental complaint." | There is no credible evidence-base or biological rationale linking aerophagia induced reflux with breastfeeding difficulties, as infants don't swallow much air during breastfeeding, even when encountering difficulty (Mills et al 2020). |
| Barak et al evaluate infant reflux signs using the Infant Gastroesophageal Reflux Questionnaire- revised (I-GERQ-R) 12-item questionnaire, filled by the primary caregiver. The authors find that higher I-GERQ-R scores, indicating more severe reflux symptoms, were associated with smaller changes in nipple diameter during feeding. The I-GERQ-R aims to track symptoms and screening for symptom burden in infants, demonstrating high sensitivity. | The diagnostic validity of the I-GERQ-R for identifying GERD is limited. It has weak correlation with objective measures like pH-impedance studies. Furthermore, age-dependent normal values show that symptoms of GER identified by I-GERQ-R decrease with age; Van Lennep et al 2024 show that a score of ≥16, previously considered suggestive of GERD, may be common in healthy young infants, especially those 0-4 months old age range. A study by Carabelli et al 2024 showed no correlation between I-GERQ-R scores and oesophageal impedance abnormalities or nocturnal crying, concluding that I-GERQ-R scores don't accurately predict reflux in infants with persistent crying. This indicates that I-GERQ-R scores alone may not accurately predict reflux in infants with persistent crying. |
Summary
The authors conclude "that time-based milk transfer assessements and US measurements into clinical practice may enhance diagnostic precision and therapeutic strategies. Clinicians are encouraged to assess breastfeeding quality in cases of reflux symptoms," but their study is unable to draw that conclusion due to the contestable assumptions and omitted variable bias upon which it has been built.
Recommended resources
How babies breastfeed: the biomechanics of infant suck (short animation)
How babies breastfeed: the biomechanics of infant suck - video and animation
Ultrasound and vacuum studies elucidate the biomechanics of the infant suck cycle in breastfeeding
Research demonstrates the variability, stability, and resilience of a woman's milk ejections
References
Barak D, Bart O, Hoffnung LA. Integrating ultrasound biomechanics and clinical assessments to examine breastfeeding function: novel insights into tongue mobility, milk transfer, and reflux symptoms. International Breastfeeding Journal. 2026;2026:https://doi.org/10.1186/s13006-13026-00856-13003.
Carabelli G, Binotto I, Armano C, et al. Study on Nocturnal Infant Crying Evaluation (NICE) and Reflux Disease (RED). Children (Basel). 2024;11(4):450. Published 2024 Apr 8. doi:10.3390/children11040450
Douglas PS, Perrella SL, Geddes DT. A brief gestalt intervention changes ultrasound measures of tongue movement during breastfeeding: case series. BMC Pregnancy and Childbirth. 2022;22(1):94. DOI: 10.1186/s12884-12021-04363-12887.
Douglas PS, Geddes DB. Practice-based interpretation of ultrasound studies leads the way to less pharmaceutical and surgical intervention for breastfeeding babies and more effective clinical support. Midwifery. 2018;58:145–155.
Douglas PS, Keogh R. Gestalt breastfeeding: helping mothers and infants optimise positional stability and intra-oral breast tissue volume for effective, pain-free milk transfer. Journal of Human Lactation. 2017;33(3):509–518.
Genna CW, Saperstein Y, Siegel SA, Laine AF, Elad D. Quantitative imaging of tongue kinematics during infant feeding and adult swallowing reveals highly conserved patterns. Physiological Reports. 2021;9:e14685.
Mills N, Lydon A-M, Davies-Payne D, Keesing M, Mirjalili SA, Geddes DT. Imaging the breastfeeding swallow: pilot study utilizing real-time MRI. Laryngoscope Investigative Otolaryngology. 2020;5:572-579.
Van Lennep M, Lansink F, Benninga MA, van Wijk MP. Age-dependent normal values for the 'Infant Gastroesophageal Reflux Questionnaire Revised'. Eur J Pediatr. 2024;183(1):445-452. doi:10.1007/s00431-023-05281-w