Background: Efficient trunk control is crucial in infant motor development when infants first learn how to move against gravity. Traditional assessments of trunk control commonly treat the trunk as one unit but the Segmental Assessment of Trunk Control (SATCo) assesses trunk control segment by segment. Good reliability and validity of the SATCo have been proved in children with neuro-disability but not yet validated in young infants. The present study was to examine if the SATCo was reliable, valid and responsive for infants aged 4 to 9 months. Methods: Infants born at full-term and at less than 30 weeks of gestation were recruited and assessed using the SATCo monthly from 4 to 9 months of age (corrected for prematurity). Intra-class correlation coefficients (ICC) were used to examine intra- and inter-rater reliability between 2 raters. The ability of the SATCo to demonstrate differences between the full-term and preterm infants was examined using the Mann Whitney U test. The responsiveness of the SATCo on the full-term infants was tested using the Friedman test. Results: Twenty full-term (mean gestation = 38.7 weeks; birthweight = 3019.9 g) and 20 preterm infants (mean gestation = 27.2 weeks; birthweight = 989.6 g) were recruited. The intra and inter-rater reliability of the SATCo levels on full-term infants was good (all ICC > 0.75), except inter-rater reliability at 6 months. The preterm infants scored significantly lower in reactive trunk control at 8 months (Mann Whitney U = 102.0, p = 0.016) but this was the only difference noted. A significant developmental trend was shown in the static, active and reactive trunk control of the full-term infants (Chi-square = 81.4, 75.6 and 79.5 respectively, all p < 0.001. Conclusions: The SATCo was reliable and responsive in assessing trunk control in young infants aged from 4 to 9 months. Care should be exercised when testing infants aged 5 to 6 months, who are more likely to use subtle hand support, and for those who have already achieved independent sitting. The SATCo could differentiate the reactive trunk control between the full-term and preterm infants at 8 months but not earlier. Psychometric properties of the SATCo in infants with motor disorders requires further investigation. Keywords: Postural balance, Trunk control, Reliability, Validity, Responsiveness, Psychometric, Infants Background typically developing infants but is commonly delayed Efficient postural control of the trunk (trunk control) in children with motor impairments . allows an individual to perform a variety of tasks in Assessment of trunk control in infants and young an upright, vertical posture without loss of balance children can include kinematic and kinetic measures and plays a significant role in motor development as , but these are generally limited to research labora- an infant learns to move against gravity [1, 2]. Trunk tories and are not clinically practical. Thus, a devel- control emerges in the first 12 months after birth for opmental assessment in the clinic usually incorporates an assessment of trunk control . However, the main limitation of these developmental assessments is * Correspondence: email@example.com that the trunk is considered as a single unit, without Department of Rehabilitation Sciences, The Hong Kong Polytechnic consideration of the different trunk segments . University, Hung Hom, Kowloon, Hong Kong Full list of author information is available at the end of the article © The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Pin et al. BMC Pediatrics (2018) 18:182 Page 2 of 8 Thus differentiation cannot be made to determine characteristics in typically developing young infants the relationship between upright segmental trunk before testing on infants with neurodisability. control and achievement of the major motor mile- The present study focused on determination of the stones.Asanexample,doesaninfant need tohave reliability, construct validity and responsiveness of gained assured control when upright at the lower the SATCo in young infants. According to the con- thoracic, upper or lower lumbar segment in order to sensus statement from the COSMIN initiative (COn- crawl on all-fours or to sit independently? The con- sensus-based Standards for the selection of health ventional developmental assessment thus neither cor- Measurement INstruments) , reliability is defined relates development of trunk control with overall as the consistency of the measurement from the out- motor development nor, importantly for infants or come measure in the absence of real changes among children with motor impairments, how development the assessors (both intra- and inter-rater reliability) of neutral vertical control in specific trunk segments . Construct validity represents whether the out- could contribute to better motor function. An atyp- come measure is able to demonstrate differences be- ical motor developmental profile has been identified tween relevant groups . Responsiveness refers to in preterm infants; imbalance of flexor and extensor theabilityof theoutcome measuretodetectchanges muscle strength has been postulated as contributing over time . This study was to investigate whether to poor trunk control in upright positions in the the SATCo: first 18 months of corrected age [4–6]. However, the contribution of any segmental influence to this pro- (1) was reliable in assessing trunk control in typically file is unknown. developing full-term (FT) infants from 4 to The Segmental Assessment of Trunk Control 9 months of age; (SATCo) provides in-depth segment by segment as- (2) could differentiate between preterm (PT) and FT sessment of trunk control . The child’s trunk con- born infants aged from 4 to 9 months (all ages were trol is examined by progressively reducing the corrected for prematurity in the remaining text); support from the shoulder girdle to assess head con- and trol, through support at the axillae (upper thoracic), (3) could demonstrate changes over time in the FT inferior scapula (mid-thoracic), lower ribs (lower thor- infants from 4 to 9 months of age. acic), below ribs (upper lumbar), pelvis (lower lum- bar) and no support to assess full trunk control . Methods Trunk control is tested under 3 different conditions Participants in sitting: maintenance of a neutral vertical posture The FT infants were recruited via personal contact or with no movement (static control), maintenance of by word of mouth. The inclusion criteria were infants the neutral vertical posture during voluntary head or born at or after 37 weeks of gestation with no con- reaching movements (active control) and recovery of cerns expressed by parents or family doctor about the neutral posture after a disturbance of balance by their prenatal and perinatal histories, or postnatal de- a nudge (reactive control) . The preliminary results velopment. The PT infants were recruited from a of the SATCo showed a high inter-rater reliability neonatal intensive care unit in one of the seven clus- (Intra-class correlation, ICC ≥ 0.8) [3, 7]and moderate ter hospitals in Hong Kong and via a private internet to good correlations with other established motor as- parental group whose infants were all born prema- sessments (r from 0.65 to 0.88) . Nevertheless, in turely. PT infants were included if born at or less the psychometric study of the SATCo by Butler and than 30 weeks of gestation. Both PT and FT infants colleagues , just eight typically developing infants with known congenital abnormalities and syndromes, (aged 3 to 9 months) and one infant with neurodeve- such as Down syndrome, were excluded. As lopment delay (aged 18-months) were tested. A very co-morbidities from prematurity, such as chronic lung small number out of 31 children with cerebral palsy disease, intra-ventricular haemorrhage, necrotising en- was recruited in the other SATCo psychometric study terocolitis, and retinopathy of prematurity are com- . Although the SATCo is a promising outcome mon, infants with these co-morbidities were not measure of segmental trunk control, its psychometric excluded but this information was noted for any fu- properties in infants and young children should be ture analyses. This research study was conducted in fully examined since psychometric evaluation of an accordance with the Declaration of Helsinki. Ethics outcome measure is population-specific . As there approvals were granted from the Departmental Re- is no previous study focussing solely on the psycho- search Committee, Department of Rehabilitation Sci- metric properties of the SATCo in young infants, it ences, The Hong Kong Polytechnic University would be reasonable to evaluate the psychometric (HSEARS20140214001) and Joint Chinese University Pin et al. BMC Pediatrics (2018) 18:182 Page 3 of 8 of Hong Kong- New Territories East Cluster Clinical indication of the age and name of the infant to re- Research Ethics Committee (2014.193). Parents of all duce the bias of scorings by PBB. This method has participating infants signed an informed consent prior been previously validated by a psychometric study of to the assessment. the SATCo . For the intra-rater reliability, 10% of the video-recordings was randomly drawn from a hat Measures and procedure by a research assistant, who also ensured that no 2 All FT and PT infants were longitudinally followed up video-recordings came from the same infant. These from 4 to 9 months old and assessed using the video-recordings were independently re-scored by the SATCo monthly by the first author (TWP) at the in- same two authors without any knowledge of previous fants’ homes. A monthly visit was considered appro- SATCo scores given. The two scorings took place at priate to capture the rapid gross motor development least 4 weeks apart to minimise recall bias. In order in young infants without putting an excessive burden to take rank orders of measurements of the study in- on the study families with the home visits. The fants into consideration, more rigorous intra-class SATCo testing was conducted according to the pub- correlation coefficients (ICC) was used to analyse the lished criteria, although the infants were allowed to intra- and inter-rater reliability, despite the fact that wear thin unrestrictive clothing instead of being trunk theSATCo is ordinaldata. The sum of the 3 nu- naked during testing . The infants’ trunk control merical values from the SATCo of each infant was was scored as ‘present’, ‘absent’ or ‘not tested’ at each used to calculate the ICC of inter-rater reliability. trunk segmental level under each of the three condi- Intra-class correlation coefficients were used to exam- tions (static, active and reactive). The infants’ per- ine intra- and inter-rater reliability. If the coefficient formance was videotaped with two cameras set on is less than 0.5, it is considered to have poor reliabil- tripods at 45° and 90° to the infant respectively. ity; the coefficient between 0.51 and 0.75 represents A sample size of 11 infants was required to achieve moderate reliability; and the coefficient greater than 80% power and α = 0.15 with 2 observations per sub- 0.75 represents good reliability . ject and an effect size of 0.2 (H =0.7 and H =0.9) To examine if the SATCo could differentiate the PT o 1 . Twenty FT infants were targeted for this study infants from their FT peers, the three SATCo scores and 20 PT infants also targeted for comparison in the of the PT and FT infants from 4 to 9 months old validity component. were compared using the Mann Whitney U test. The SATCo levels of the PT and FT infants from the first Data analyses author (TWP) were used. The Friedman test was used In order to statistically analyse the SATCo levels, a to examine the responsiveness of the SATCo on the number was assigned for each trunk segmental level FT infants, i.e. changes over time . All statistical where control was being learnt: 1 for head control, 2 significance levels were set at p ≤ 0.05. No adjustment for upper thoracic level, 3 for mid-thoracic, 4 for to the significance level was made. lowerthoracic, 5for upperlumbar, 6for lowerlum- ber and 7 for full trunk control. The number 8 was Results used if full trunk control was demonstrated; this was Twenty FT infants (mean gestation = 38.7 weeks, SD 1.0; the same process as in the previous psychometric mean birthweight = 3019.9 g, SD 370.7; 60% males) study of the SATCo . Each infant thus had 3 nu- were recruited and assessed between June 2014 and merical values indicating their respective segmental May 2015. Twenty PT infants were recruited and levels of learning static, active and reactive control assessed from December 2014 to July 2016 (mean for each month. For example, if the infant had 5, 4 gestation = 27.2 weeks, SD 1.7; mean birthweight = and 3, this implied that static trunk control was be- 989.6 g, SD 237.0; 45% males) (Appendix). Two data ing learned at upper lumbar level, active trunk con- points were missing (1.6%) in the FT group (n =1 sick trol at lower thoracic and reactive trunk control at infant and n = 1 family away) and 9 (7.5%) in the PT mid thoracic. group (n = 4 late start of data collection, n =2 family To examine the intra- and inter-rater reliability of away, n = 2 unable to be tested due to constant crying theSATCo,the first(TWP) andsecond(PBB) au- andstrugglingduringthe test, and n =1 sick infant). thors independently graded the FT infants. PBB is the As expected, there were significant differences in author of the SATCo  and TWP is a paediatric gestation age (t = − 25.5, p < 0.001) and birthweight physiotherapist with over 25 years of clinical experi- (t = − 20.6, p < 0.001) between the two groups but no dif- ence. TWP had a one-week training with PBB prior ference was found in gender (Chi square = 0.90, p =0.342) to the present study to establish consensus. The or number of infants with birthweight appropriate for ges- video-recordings were anonymously coded with no tation (Chi Square = 0.36; p= 0.500). Pin et al. BMC Pediatrics (2018) 18:182 Page 4 of 8 Reliability Table 2 Comparison of the median SATCo segmental levels between the preterm and full-term born infants Both examiners (TWP and PBB) independently scored a a 118 video-recordings of the FT infants (n =20 for Preterm Full-term each month, but only 18 at 9 months of age). Both SATCo at 4 m Static 5 (1–5) 5 (4–5) N = 17 preterm examiners re-scored 17 of these 118 video-recordings p 0.670 N = 20 full-term (n =2 for 4 months; n =3 for 5 and 6 months; n =4 Active 4 (1–5) 4.5 (3–5) for 7 months; n =3 for 8 months; n =2 for 9 months). p 0.308 Table 1 shows the intra- and inter-rater reliability of Reactive 4 (1–5) 4 (3–5) the SATCo scores of the FT infants. The intra-rater p 0.220 reliability for both examiners was good with the ICC consistently well above 0.75 with all p < 0.001 (Table 1). SATCo at 5 m Static 5 (4–6) 5 (4–6) N = 19 preterm The inter-rater reliability was also good with the ICC p 0.075 N = 20 full-term above 0.75, except at 6 months when the ICC was 0.641, Active 5 (3–6) 5 (4–6) with all p ≤ 0.015 (Table 1). p 0.629 Reactive 5 (3–5) 5 (4–6) Construct validity p 0.304 No significant difference was found between the PT and SATCo at 6 m Static 6 (4–7) 6 (4–7) FT groups in the SATCo segmental levels from 4 to N = 18 preterm p 0.403 N = 20 full-term 9 months (all p > 0.05), except for reactive trunk control Active 6 (5–6) 6 (4–7) at 8 months (Mann Whitney U = 102.0, p = 0.016) p 0.856 (Table 2). A borderline significant difference was found in static trunk control at 8 months (Mann Whitney U = Reactive 5 (4–6) 5 (4–6) 121.5, p = 0.058) and in reactive trunk control at p 0.509 9 months (Mann Whitney U = 111.5, p = 0.057). SATCo at 7 m Static 6 (5–8) 6.5 (5–8) For the responsiveness of the SATCo, a significant time N = 20 preterm p 0.467 N = 20 full-term effect was shown in the static, active and reactive segmen- Active 6 (4–7) 6 (5–8) tal trunk control of the FT infants (Chi-square = 81.4, 75.6 p 0.126 and 79.5 respectively, all p <0.001) (Fig. 1). Paired Reactive 6 (4–7) 6 (5–7) p 0.305 Table 1 Intra- and Inter-rater reliability of SATCo SATCo at 8 m Static 7 (5–8) 8 (6–8) N = 18 preterm ICC 95% CI p 0.058 N = 20 full-term Intra-rater reliability (n = 17) Active 6.5 (5–8) 7.5 (5–8) Examiner 1 (first author, TWP) p 0.082 Static control 0.987 0.964, 0.995 Reactive 5.5 (5–8) 7 (6–8) Active control 0.982 0.949, 0.993 p 0.016 Reactive control 0.985 0.985, 0.994 SATCo at 9 m Static 8 (4–8) 8 (7–8) Examiner 2 (second author, PBB) N = 19 preterm p 0.091 N = 18 full-term Static control 0.976 0.935, 0.991 Active 8 (4–8) 8 (7–8) Active control 0.978 0.938, 0.992 p 0.184 Reactive control 0.964 0.900, 0.987 Reactive 7 (3–8) 7 (6–8) Inter-rater reliability (2 examiners on 1 occasion) p 0.057 4 months (n = 20) 0.895 0.736, 0.959 Ages corrected for the preterm born infants. Numbers in brackets = range of SATCo scores 5 months (n = 20) 0.761 0.397, 0.905 The numbers represent medians of the SATCo trunk segmental level at which 6 months (n = 20) 0.641 0.094, 0.858 control was being learnt: 1 = head control, 2 = upper thoracic level, 3 = mid- thoracic, 4 = lower thoracic, 5 = upper lumbar, 6 = lower lumber, 7 = full trunk 7 months (n = 20) 0.967 0.917, 0.987 control, and 8 = full trunk control achieved. Please note that the SATCo is an ordinal scale and the learning levels shown in this table were the medians of 8 months (n = 20) 0.812 0.524, 0.925 each group of infants at each month. The non-integral numbers reported in 9 months (n = 18) 0.873 0.660, 0.952 the table were purely for statistical purposes. In real life situations, no half- level would be credited to the infants All ICC significant at p ≤ 0.015 at two-way mixed effects model on average measures with absolute consistency definition n number of infants at each month Pin et al. BMC Pediatrics (2018) 18:182 Page 5 of 8 Fig. 1 Developmental trend of trunk control from 4 to 9 months of age in full-term infants. S- static control, A- active control, R- reactive control. Numbers on the y-axis are the SATCo trunk segmental level at which control was being learnt (1 = head control, 2 = upper thoracic level, 3 = mid-thoracic, 4 = lower thoracic, 5 = upper lumbar, 6 = lower lumber, 7 = full trunk control, and 8 = full trunk control achieved). The solid line represents the medians of the group at each age group. The boxes and the whiskers represent the spread of the data within that age group. The asterisks represent outliers in that age group comparisons at each month, i.e. 4 with 5 months, 5 with Reliability 6 months, and so on, showed a significant time effect in For FT infants aged from 4 to 9 months, the the static, active and reactive trunk control of the infants inter-rater reliability of the SATCo was good from 4 at all ages (all p < 0.05), with the exception of a border- to 9 months, with an exception at 6 months which line significance in the active control between 4 and showed only fair reliability (Table 1). The intra-rater 5months(Chi-square=3.6, p = 0.058) and reactive reliability was shown to be good (Table 1). These re- control between 8 and 9 months (Chi-square = 3.6, sults are comparable with the previously reported re- p = 0.058). liability [3, 7]. Although the ICC for the inter-rater reliability was in general over 0.75, except at 6 months, the confidence intervals (CI) were relatively Availability of data and materials wide at 5, 8 and 9 months. Most of the FT infants The raw data and data sets used and analyzed in the aged 8 to 9 months were able to sit independently present study are available from the corresponding without any hand support and achieved full trunk author on reasonable request. control under the three conditions in the SATCo (Table 2). These infants were able to move off the Discussion testing bench if not restrained. It was challenging to The SATCo emphasises a segmental assessment of keep these active infants on the testing bench with trunk control, making it unique among other devel- the correct starting position for sufficient time to test opmental assessments and assessments of trunk con- static, active and reactive full trunk control. The fail- trol . Thepresent studyhas expanded on previous ure to recognise subtle hand support by the child, work [3, 7] by specifically examining its reliability, such as one hand resting on the lap especially during construct validity and responsiveness in young in- the test for reactive control, was the most common fants aged from 4 to 9 months. problem, and was identified as a common testing Pin et al. BMC Pediatrics (2018) 18:182 Page 6 of 8 error in the previous psychometric study of the with increasing demand on their trunk control in a SATCo . These factors may have contributed to vertical posture such as standing [4, 6]. A larger sam- thewideCIat5,8and9months andthe lower ple size of infants for a longer follow-up duration inter-rater reliability at 6 months. However, despite may verify this speculation. At present, it is reason- the wide CI, over 75% of the results between the 2 able to conclude that the SATCo is able to differenti- examiners were in total agreement and discrepancy of ate the PT and FT infants at 8 months of (corrected) more than 2 segmental levels between the 2 exam- age but not earlier in their reactive trunk control. iners was only 6.7% in total. These findings are in The construct validity of the SATCo for infants agreement with previous findings on school-aged chil- against another valid outcome measure, such as de- dren with cerebral palsy . velopmental assessments, requires further investiga- These results suggest that the SATCo is appropri- tion before its full clinical use for young infants. ate for typically developing infants aged 4 to 9 months of age, with care particularly with respect Responsiveness to hand support with infants aged at 5 and 6 months The results of the Friedman test showed that the SATCo and for those infants who have already achieved in- was responsive in demonstrating the changes in static, ac- dependent sitting. It could be helpful for an extra tive and reactive segmental trunk control in the FT infants assistant, if available, to watch vigilantly for subtle over time from 4 to 9 months of age (Fig. 1). High or max- hand support or other compensations that the child imal SATCo scores were demonstrated at 8 to 9 months might use during the test to potentially improve the and contrasted clearly with the scores at 4 to 5 months of reliability of the SATCo. If possible, training in the agefor theinfants (Fig. 1). Furthermore, it appears that SATCo with more experienced users could help to neutral vertical trunk control develops cephalo-caudally avoid these pitfalls. and, among the three types of trunk control, reactive con- trol appears to be the last to become established in infants Construct validity of this age range (Fig. 1). The SATCo was able to differentiate PT from FT infants in their reactive trunk control at 8 months of age but Study limitations not at other ages. It has been postulated that an imbal- This study consisted of a relatively small sample size of ance in the development of flexor and extensor muscle both FT and PT infants, despite the fact that sample size strength in PT infants may adversely impact their trunk was calculated a priori. Caution should be taken when control [4–6]. These previous studies demonstrated the interpreting the present results, especially for some of significant differences between the PT and FT infants by the reliability data with a wider CI. assessing their gross motor skills in various positions [4–6]. The present study specifically assessed the seg- Conclusions mental trunk control in an upright position. All infants The SATCo has been shown to be a generally reliable aged 4 to 6 months, regardless FT or PT, spend the ma- outcome measure for examining segmental trunk con- jority of their time in reclined positions and thus the de- trol of young infants aged from 4 to 9 months. Wide mand on their vertical trunk control would be similar CIs were found at 5, 8 and 9 months of age and re- for both groups of infants (Table 2). This was reflected duced reliability at 6 months. Thus, close attention by the lack of a significant difference in the SATCo should be taken during testing of infants who have scores at this young age range. From 7 months onwards, already achieved independent sitting and are more most of the FT infants were fully mobile on the floor likely to fidget and move and at ages where an infant and were able to sit independently. The demand of their may use subtle hand support, for example around 5 trunk control would thus be very different from the PT to 6 months. TheSATCo wasabletodifferentiate be- infants, who were still at the stage of mastering inde- tween PT and FT infants in their reactive trunk control at pendent sitting and floor ambulation. This has been 8 months of (corrected) age but not earlier as would be an- reflected in the significant difference in reactive trunk ticipated from the reclined postures used by all infants at a control at 8 months between the two groups of infants. younger age. In the FT infants, trunk control was shown to The borderline significant difference in active trunk con- develop in a cephalo-caudal direction and to become fully trol at 8 months may be due to the small sample size of established around 8 to 9 months of age: reactive trunk the present study. control emerged after static and active control at each It is also possible that the majority of the PT in- monthly SATCo test. Further investigations of the psycho- fants in the present study were neurologically intact metric properties of the SATCo in infants with infants (Appendix); any subtle difficulties with trunk neuro-disability is recommended before it is widely used in control might only become apparent at an older age clinical and research settings. Pin et al. BMC Pediatrics (2018) 18:182 Page 7 of 8 Appendix Table 3 Characteristics of the preterm infants GA BW Gender AGA IVH ROP CLD NEC PT001 26.6 1070 M Yes Yes PT003 29 1300 M Yes PT004 28.1 1310 F Yes PT005 26.7 908 M Yes Yes (left grade 2) Yes PT006 26 890 M Yes Yes (left grade 2) Yes PT007 27.4 940 F Yes Yes (left grade 1) Yes PT008 27.6 675 M No Yes (left grade 2) Yes Yes PT009 25 790 F Yes 0 Yes PT011 28.9 1225 M Yes 0 PT012 26.1 800 F Yes 0 Yes PT013 26.3 780 F Yes Yes (right grade 2) Yes PT014 25.6 745 M Yes Yes Yes PT015 26.6 950 F Yes Yes PT016 28.6 1080 M Yes Yes (right grade 4, left grade 3) Yes PT017 26.9 1000 F Yes 0 Yes Yes PT018 23.6 558 F Yes 0 Yes Yes PT019 30 1220 F Yes Yes (left grade 1) Yes Yes PT020 30 1210 F Yes Yes PT021 29.6 1440 F Yes PT022 26 900 M Yes Yes AGA weight appropriate for gestation age, BW birthweight, CLD chronic lung disease, CP cerebral palsy, GA gestation age, IVH intra-ventricular haemorrhage, NEC necrotising enterocolitis, ROP retinopathy of prematurity This infant was diagnosed with cerebral palsy at 8 months corrected age Fok TF, So HK, Wong E, Ng PC, Chang A, Lau J, et al. Updated gestations age specific birth weight, crown-heel length, and head circumference of Chinese new- borns. Arch Dis Child Fetal Neonatal Ed. 2003;88:F229–36 Abbreviations Committee, Department of Rehabilitation Sciences, The Hong Kong FT: Full-term; PT: Preterm; SATCo: Segmental Assessment of Trunk Control Polytechnic University (HSEARS20140214001) and Joint Chinese University of Hong Kong- New Territories East Cluster Clinical Research Ethics Committee Acknowledgements (2014.193). Parents of all participating infants signed an informed consent The authors would thank Miss Joyce HL Choi for her assistance in data before data collection on their infants. collection and management, and all the infants and their parents who participated in this study. Competing interests The authors declare that they have no competing interests. Funding This work was fully supported by The Hong Kong Polytechnic University Departmental Research Fund (Project no.UA-2G awarded to TWP). Publisher’sNote Springer Nature remains neutral with regard to jurisdictional claims in Availability of data and materials published maps and institutional affiliations. The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request. Author details Department of Rehabilitation Sciences, The Hong Kong Polytechnic Authors’ contributions University, Hung Hom, Kowloon, Hong Kong. Health, Exercise and Active TWP designed the study, collected, analysed and interpreted the data, wrote Living, Manchester Metropolitan University, Manchester, UK. Department of the manuscript and was fund-holder of this study. PBB designed the study, Paediatrics, Prince of Wales Hospital, Shatin, Hong Kong. Physiotherapy acted as the blinded assessor, analysed, interpreted the data, and significantly Department, Prince of Wales Hospital, Shatin, Hong Kong. contributed to writing the manuscript. HMC designed the study, recruited study infants, analysed and interpreted the data. SLS designed the study, recruited Received: 1 November 2017 Accepted: 18 May 2018 study infants, analysed and interpreted the data. All authors read and approved the final manuscript. Ethics approval and consent to participate References This research study was conducted in accordance with the Declaration of 1. Hadders-Algra M, Carlberg EB, editors. Postural control: a key issue in Helsinki. Ethics approvals were granted from the Departmental Research developmental disorders. London: Mac Keith Press; 2008. Pin et al. BMC Pediatrics (2018) 18:182 Page 8 of 8 2. Shumway-Cook A, Woollacott MH. Motor control: translating research into clinical practice. 5th ed. Philadelphia: Wolters Kluwer; 2016. 3. Butler PB, Saavedra S, Sofranac M, Jarvis SE, Woollacott MH. Refinement, reliability, and validity of the segmental assessment of trunk control. 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Published: May 31, 2018