Early motor development has long been used by healthcare providers and parents as an indicator of progress of neurological development during infancy, 1 and it is a particular focus of monitoring infants born preterm. 2 Current theories of early motor development suggest that the acquisition of new motor abilities arises from the interaction of multiple elements of the infant, the environment, and the task at hand through a process of exploration of movement options and selection of the optimal solution in a given context. 3 An understanding of early motor development will be enhanced by exploring the potential influence of factors associated with the caregiving environment and infant preferences. Such factors include the use of infant equipment and predominant play positions. The broad purpose of our investigation was to understand more about how infants born preterm spend their days and to understand how some of their activities are related to early motor development.
We began by reviewing what is known about the relationship between both infant equipment use and positioning and early motor development among infants born at term. We then planned a study on a sample of infants born preterm who were at high risk for neuromotor disorders. Because parental perception of the health and well-being of infants during the first year of life is largely influenced by the acquisition of early motor milestones, 4 this is an important area for investigation. Infants born preterm have a different pattern of early motor development than infants born at term. 5 Further understanding about how these variations relate to daily routines will be useful to therapists working with infants born preterm and their families. We review below what is known about the relationship between both infant equipment use and positioning and early motor development and identify gaps in knowledge.
Despite the large variety of infant equipment available to parents, little is known about the influence of devices such as jolly jumpers, infant seats, “exersaucers,” and swings on early motor development. Two divergent influences are possible: The use of equipment might enhance early motor development, or the use of equipment might impede optimal motor development. Positioning also has the potential to either enhance or impede the acquisition of motor abilities among infants. Although the supine and side-lying sleeping positions, recommended by the American Academy of Pediatrics to reduce the incidence of sudden infant death syndrome, have been found to be associated with early delays in prone motor development of infants born at term who were healthy in a study conducted in the United States, 4 infants who sleep in these positions have been found to attain normal motor milestones in later infancy. 4,6 Little research evidence is available about the influence of positioning while awake (either imposed by a caregiver or selected by an infant) on motor development in infancy. Wakeful positioning, and not sleep position, is of interest in our inquiry.
In samples of infants developing typically, those using walkers and those not using walkers did not differ in age of independent walking, 7–9 although infants using walkers have been identified to have delayed prone development, 7,10 delayed acquisition of independent rolling, 10 and poorer quality of locomotion 8 (eg, reduced knee flexion, increased hip flexion, and greater lateral displacements of the center of gravity) than infants who did not use a walker. In several more recent studies, infants developing typically having used a walker demonstrated later acquisition of sitting, crawling, and walking than infants who did not use a walker, 11 and the quality of movement among infants who used walkers was observed to be similar to that of children with cerebral palsy. 12 Specifically, these infants demonstrated equinus foot positions and developed contractures of the gastrocnemii.
Aside from walkers, little is known about the influence of other infant equipment on motor development. In recent work on 43 infants at low risk at eight months of age, 13 the authors determined that the time of total equipment use (as measured through parental survey) and infant motor development (as measured by the Alberta Infant Motor Scale) were negatively related (r = −0.50, p = 0.001). Whether the slower rates of motor development preceded higher equipment use or higher equipment use preceded a slower rate of motor development remained unsolved. Another limitation of that preliminary investigation 13 was the ceiling effect of available time categories for parents’ responses; the longest response option was “>60 minutes”; however, many mothers reported using selected infant equipment for two to four hours per day.
Little is known about the influence of positioning while awake on early motor development. In a pilot study on 26 four-month-old infants born at term, Bridgewater and Sullivan 14 reported that greater time in supine and side-lying was negatively associated with the child's ability to prop on the elbows. Conversely, greater time in prone at this age was associated with less mature midline abilities in supine. This pilot work provides some preliminary insight into the importance of context-specific positional experience for the acquisition of early motor abilities; however, the sample comprised only healthy infants born at term and was limited to investigation at four months, an age at which the caregiver largely determines the infant's play positions.
It is useful to know whether and how a variety of infant equipment and play positions relate to motor development among infants born preterm. Some infants born preterm are at risk for neuromotor disorders;15 however, little is known about how these infants typically spend their days and how environmental factors such as equipment use and positioning potentially modify the motor behavior of these infants. In a sample of 10 infants born preterm who were healthy (ie, a subgroup not at high risk for neuromotor disorder), use of a seating device experimentally demonstrated that infants who used the seat slept more, were quieter, and exhibited fewer motor behaviors associated with prematurity, such as clonus, startles, and twitches. 16 Otherwise, the potentially beneficial and harmful effects of a variety of types of infant equipment and variations in positioning on subgroups of infants born preterm at greater risk for adverse neuromotor outcomes has not been clarified.
There were two main purposes of this study. First, we aimed to determine the relationship between both total duration of equipment use and the duration of use of different pieces of infant equipment and motor development, as a whole and with respect to different aspects of development in prone, supine, sitting, and standing in a sample of infants attending a developmental follow-up clinic. Second, we wanted to determine variations in motor development associated with parental reports of their infant's predominant play positions. We anticipated that this information would contribute to decision making among therapists working with high-risk infants and their families.
Ethics approval was obtained from the Review Board for Health Sciences Research Involving Human Subjects at the University of Western Ontario and the Clinical Research Committee at St. Joseph's Health Centre before participants were recruited for this study. The parents of infants born preterm scheduled to attend the Developmental Follow-up Clinic of the Neonatal Intensive Care Unit at St. Joseph's Health Centre in London, Ontario, when their infants were eight months of age (age corrected for prematurity) were contacted between July 2000 and May 2001 for consideration of participation in this research project. Eight months was selected for this investigation because it is the time of one of the regularly scheduled clinic visits and a time of great variability in motor development. 17 A letter of information describing the project and a consent form were mailed to families 10 days before the appointment date. Infants were eligible for this study if their birth weight was under 1500 g or if they had had a complicated neonatal course with clinical findings placing them at high risk for developmental sequelae. Infants with known chromosomal or musculoskeletal malformations or anomalies were excluded.
After we obtained informed consent, descriptive data of both caregivers and infants were obtained through chart review by the clinic physical therapists. Forty-eight parents with their 60 infants were recruited; most infants were accompanied to the clinic by their mothers. Fifty-nine of the infants lived with their biological mothers, and one lived with foster parents. Mothers averaged 29.7 years of age (SD = 4.9;N = 47; the age of the foster mother was not recorded). The median number of children in the families was two with a range of one to eight.
The 28 male and 32 female infants were born at an average of 28.7 weeks’ gestation (SD = 2.3); average weight at birth was 1208 g (SD = 311). Thirty-seven were singletons, 20 were twins, and three were from a set of triplets. They required an average of 11.5 days of ventilation (SD = 18.6) and 21.4 days of supplemental oxygen (SD = 30.2). None of the infants had neonatal seizures. One infant was identified as having periventricular leukomalacia (PVL), and 15 were diagnosed with intraventricular hemorrhage (IVH: I = seven, II = five, III = two, and IV = one). Three infants were discharged home from the Neonatal Intensive Care Unit on supplemental oxygen. No infants were identified as having visual or hearing impairments at the eight-month clinic visit; at that point the average age, corrected for prematurity, was 8.08 months (SD = 0.41). Neurological status was classified by the clinic physician as “normal,” “suspect,” or “abnormal” at the end of the visit using a combination of classic neurodevelopmental examinations 18–20 and gestalt perception. 21 Five infants were classified as neurologically abnormal, 30 as suspect in their neuromotor development, and 25 as normal.
During the clinic visit, parents were asked to respond to a series of questions about the activities their infants had engaged in during the month preceding the clinic visit; one of two physical therapists conducted these verbal interviews. Parents were asked, “What equipment, if any, has your baby used in your home while awake over the past month?” A list including the following options was read out: jolly jumper, walker, exersaucer, seat, automatic swing, sling, backpack/snugglie, carried in arms/on lap, or other. We modified a survey instrument used in a previous study 13 by adding the item of “carried” because we believe that carrying has the potential to limit opportunities for exploration through infant-initiated movement, and clinical experience informed us that parents of infants born preterm seemed to report carrying their infants frequently. When a parent responded that they did use a piece of equipment, they were asked, “What is the average time per day that your baby used the equipment?” Because many mothers in the previous study 13 reported the highest value of “>60 minutes”, we elected to collect data on duration of daily equipment use continuously through open-ended responses instead of a fixed response set.
Parents were also asked about their infants’ favorite (ie, most frequently assumed) and least favorite (ie, least frequently assumed) play positions (of supine, prone, sitting, standing, none, or other) and the average length of time their infants would play in the position at any one time. To determine a temporal relationship between both equipment use and positioning and early motor development, we asked parents to consider the period of one month before the eight-month clinic visit. The interview questions are contained in the Appendix.
Each infant was also assessed at the clinic visit using the Alberta Infant Motor Scale (AIMS), a standardized observational and norm-referenced measure of infant motor development from birth through to independent walking. 17 The AIMS contains 58 items examined in prone, supine, sitting, and standing. Each item in the infant's current motor repertoire is scored as either “observed” or “not observed,” and a score is determined by adding together the number of items below that of the least mature observed item and the number of observed items. During test development, interrater and test-retest reliability coefficients were determined to be 0.98 and 0.99, respectively. The AIMS also demonstrated high concurrent validity with the gross motor scale of the Peabody Scales of Motor Development (r = 0.94) and the psychomotor index of the Bayley Scales of Infant Development (r = 0.85) among infants aged eight to 13 months. Interrater reliability between each of the physical therapists and the principal author (who participated in the reliability and validity testing and the norming of the AIMS) was determined on a small sample (n = 7 and n = 5) of eight-month-old infants at study onset. The intraclass correlation coefficients (2,1) were 0.95 (95% confidence interval, 0.73–0.99) and 0.98 (95% confidence interval, 0.87–0.99).
The order of the parental survey and the assessment of infant motor development varied according to the clinic schedule and optimal timing for infant observations. The AIMS data were summarized for the total sample. Pearson's correlation coefficient was calculated to determine the strength of the relationship between the duration of both total and individual equipment use and the AIMS total and subscale scores for the sample as a whole. One-way analyses of variance were conducted on the AIMS scores of infants whose parents reported different favorite and least favorite play positions. A sample of 60 parent-infant dyads was targeted for recruitment, providing a power of 0.90 to detect correlations of greater than or equal to 0.40 significant at a two-tailed α level of 0.05 when using the total sample. 22 An α level of 0.05 was selected for this exploratory study.
The AIMS total and subscale scores for the total sample are contained in Table 1. Before investigating the relationship between duration of equipment use and motor development, stepwise linear regression was used to determine if any of the perinatal variables were associated with AIMS scores and therefore needed to be considered as covariates. None of the following variables were significantly associated with the AIMS scores in this sample: birth weight, gestational age at birth, days of ventilation, days of oxygen supplementation, presence of IVH, or discharge home on oxygen. Because there was only one infant with PVL, the effect of this variable on motor development could not be analyzed in this sample.
Duration of Equipment Use and Motor Development
Total daily duration of equipment use averaged 4.1 hours (SD = 2.7) with a range 0.75 to 14.2 hours. Table 2 contains details of the number of children using various pieces of infant equipment (or being carried) and the median duration and the range of duration of use among all infants in the sample.
Statistically significant correlations between duration of individual and total equipment use and AIMS subscale and total scores are contained in Table 3. Higher use of a swing was associated with lower total AIMS scores and lower scores in the prone and sit subscales. Greater use of carrying throughout the day was associated with lower sit subscale scores. Higher overall use of equipment was associated with lower sit and stand subscale scores.
The statistically significant bivariate correlations were plotted on a scatter plot to check for outliers. Visual inspection of the plot of duration of swing use and AIMS prone and sit subscale and total scores resulted in the identification of one outlying point. For most of the sample, reported swing use (n = 13) was under 60 minutes. One exception was a child who reportedly used the swing for two hours a day. At the eight-month clinic visit, he was judged to be neurologically abnormal and, correspondingly, had low AIMS scores. With this infant removed, the correlation between duration of swing use and AIMS prone and sit subscale scores and total score dropped to −0.24, −0.16, and −0.21, respectively (all statistically nonsignificant).
A similar procedure was used to inspect the plot of duration of both carrying and total equipment use and AIMS sit subscale score, as well as duration of total equipment use and the AIMS stand subscale score. In these cases, no outlying points were determined.
Play Position and Motor Development
Mothers reported their infants’ favorite play positions as being sitting (n = 23), supine (n = 15), prone (n = 9), and standing (n = 9); four mothers reported no one position to be favorite. Among the respondents, the average time that infants were reported to be in their favorite positions was 46 minutes (SD = 38). Table 4 contains the means and standard deviations of the AIMS total scores by favorite play position. Total scores differed by reported favorite position (F = 8.75, df = 4, p < 0.001). Infants whose parents stated that standing was their favorite play position obtained statistically significantly higher AIMS scores than infants in the other positions (p < 0.01). Infants whose parents stated that prone was their favorite play position obtained higher AIMS scores than infants whose parents reported supine to be the favorite play position (p = 0.009).
Least favorite positions were reported to be prone (n = 24), supine (n = 15), sitting (n = 8), and standing (n = 1). Ten mothers reported that their infants had no least favorite position, and two reported “other” least favorite positions (being held and being in the car seat). The average time that infants were reported to be in their least favorite positions was five minutes (SD = 9). Table 5 contains the means and standard deviations of the AIMS total scores by least favorite play position (data from one child whose least favorite position was standing and two who reported “other” are not included in the table). Infants whose parents stated that supine was their least favorite play position obtained statistically significantly higher AIMS scores than infants whose parents stated that there was either no least favorite position (p = 0.002) or that prone was the least favorite (p < 0.001). Infants whose parents stated that sitting was their least favorite play position obtained higher AIMS scores than infants whose parents reported prone to be the least favorite play position (p = 0.006).
In this study of infants born preterm attending a developmental follow-up clinic, the reported duration of carrying was negatively associated with motor competency in the sit subscale of the AIMS. As a group, infants in this sample were reported by their parents to predominantly play in the sitting and supine positions; the least favorite play position was reported to be prone. The relevance of determining equipment use and predominant play positions and the potential long-term implications of altered patterns of early motor activity are discussed.
Equipment Use and Early Motor Development
Compared with a sample of infants of the same age but at low risk, 13 more families in the current study reported using a seat (63% vs 49%), a swing (23% vs 13%), and a walker (10% vs 2%). Slightly fewer families in the current study reported using a jolly jumper (23% vs 28%).
Once obvious outlying points were removed, the main finding about relationships between equipment use and motor development was between the duration of carrying and the sit subscale of the AIMS. That is, more carrying, as reported by parents, was associated with less ability to sit. In the previous study, we did not ask families about how much their child was being carried throughout the day; however, we were struck by the fact that 90% of parents in the current study reported carrying their infants for a median value of two hours per day with a range of up to 10 hours! Carrying was reported with equal frequency across the three groups of children (23 of 25 in the normal group, 27 of 30 in the suspect group, and 4 of 5 in the abnormal group). Although we attempted to build in a temporal element in this study (ie, we asked about carrying and use of infant equipment in the month prior to attending clinic, at which time motor development was assessed), we cannot determine whether carrying interfered with the acquisition of independent sitting or whether lack of this motor competency led parents to carry their infants for long periods throughout the day. Whatever the case, carrying clearly is a major activity—and therefore potentially has a large impact—in the lives of these families. We believe that this issue should be explored with families attending developmental follow-up clinics with their infants.
For parents reporting a daily duration of carrying of greater than, for example, two hours, it might be helpful to determine why they carry their infants as much as they do. One possibility is a child who “demands” to be in the upright position but who is not yet able to sit independently. As children become more cognitively aware of their environments, they typically want to interact socially more frequently. A child who does not yet have the motor competency to maintain sitting might benefit from the use of a variety of infant equipment such as high chairs, other infant seats, and exersaucers. It is interesting to note that more parents reported using infant seats in this study (63%) than in the study of a sample of infants at low risk for neuromotor disorders (49%). Families frequently use exersaucers; 50% and 57% of the families in the current and previous studies, respectively, reported using this equipment. Given the child's current abilities in sitting, adaptations could be made to progress from more to less support to encourage independent sitting. Infant seats, highchairs, and exersaucers can be adapted for varying degrees of support, thereby providing graded opportunities to develop antigravity control. Parents could also be informed about how to assist their infants in acquiring independent sitting through exposure to increasingly challenging play activities in this position.
Although increased carrying was negatively related to the ability to sit for the group data, there were a small number of infants who had advanced motor competencies. One parent reported carrying her child to ensure his safety, and we speculate that this might have been the case for more mothers. For infants fitting this description, parents might be advised to use a playpen for some of the daytime activities to ensure safety and the development of infant-parent independence.
Although the statistically significant finding with respect to the negative association between use of an infant swing and aspects of motor development was attributable to one outlying point, a greater proportion of families in the current study reported using a swing compared with the previous study. 13 Anecdotally, parents often use a swing to sooth an irritable child; the swing is most frequently used under six months of age. This suggests that therapists should follow up on potential reasons for high use after six months of age and provide guidance on other ways to decrease irritability and to develop antigravity postural control in sitting.
Other than carrying and the use of a swing, no other negative relationships were found between use of equipment and motor development. This contrasts with the overall results of the previous study on infants at low risk 13 and suggests that infant equipment might be recommended more frequently to families attending developmental follow-up clinics, certainly if their infants are classified as neurologically abnormal and possibly if their infants are classified as suspect. Therapists routinely prescribe adaptive equipment for children with identified neurological impairments 23 but might not regularly consider use of equipment to enhance antigravity postural control for infants without definitive diagnoses.
Play Positions and Early Motor Development
As a group, infants in this sample were reported by their parents to prefer predominantly the play positions of sitting and supine. We perceive infants who spend more time in these positions to have fewer opportunities for self-initiated gross motor exploration than infants who spend more time in either prone or standing. Parents reported the infants’ least favorite play position to be prone. None of the infants in this sample had a medical condition that would cause them to be uncomfortable in the prone position. Knowledge of the recommendation to put infants in supine or side-lying for sleep has been found to be associated with an avoidance of the prone position for play among parents of infants one to six months of age. 24 It is possible that the perceived preference of sitting and supine positions reported by parents of eight-month-old infants has been influenced by the earlier recommendations for the sleeping position. Therapists might discuss with parents the appropriateness of “supine for sleep” to reduce the incidence of sudden infant death syndrome and “prone for play” to provide the infant with a variety of play positions during awake time. 24
The variation in AIMS score by predominant play position is not startling. Infants presumably prefer to play in positions that reflect their motor competencies. Although this result per se might not be particularly useful in the clinical setting, these findings highlight the importance of knowing each infant's preference if a focus of therapeutic intervention is to enhance the acquisition of specific motor competencies. For example, if a goal of intervention with a specific infant is to enhance trunk rotation, a competency that some infants born preterm do not readily attain, 25 it will be useful to know if that infant prefers sitting or prone. By working first in a favorite position and then progressing to a position to which the infant is less inclined (if deemed to be necessary for acquisition of a motor competency), greater success with intervention might be anticipated. One can be assured that the interaction between the infant and therapist or the parent will be more pleasant! If one of the major competencies of a good clinician is to engage the child, 26 explicitly determining a child's most and least favorite positions will be helpful in planning direct interventions.
Physical therapists should also consider the role of prevention and promotion of health, wellness, and fitness 27 when working with infants born preterm and their families. To our knowledge, the motor performance, fitness, and physical activity patterns of adolescents and adults who were born preterm and are without neurological impairments have not been investigated; however, some research evidence on infants and children is available to highlight the possibility that physical outcomes might not be optimal for those born early. 28–32 Some children who had been born early eg, those who were small for gestational age or had bronchopulmonary dysplasia have been identified to have smaller muscle mass, 28 lower anaerobic muscle performance, 29–31 and lower aerobic fitness 32 than children who had been born at term. Although not investigated in children with a preterm birth, motor performance in childhood has been found to be related to child-rearing habits and the family environment. 33,34 The precise origins of variations in motor performance in children born early ie, whether anatomic, metabolic, neurological, or environmental remains to be clarified. 29
This related research evidence, coupled with our findings that some infants born preterm preferred sitting and supine play positions and were slow to acquire age-appropriate antigravity postural control (unpublished data, 2002) suggests that parents could be counseled earlier in their infants’ lives about the importance of having higher expectations of their infants’ motor development. 35 Specific handling techniques and caregiving practices that expose infants to postural challenges have been shown to be associated with motor advancement 36 and could be recommended. In their study of neuromotor abilities of children with low birth weights, Keller et al 28 stated that they “cannot exclude the possibility that factors such as parental overprotection, fear of deleterious effects of exercise, or impaired exercise performance might have induced hypoactivity during the first years of life” and influenced motor performance in mid childhood. Therapists could provide education to clarify age-appropriate developmental expectations, reduce prematurity stereotyping, and promote age-appropriate movement activities.
The question about whether use of infant equipment enhances or impedes motor development remains unanswered; the potential influence likely varies across infants. Recall bias with respect to parents’ abilities to report the average duration of equipment use and duration of time in favorite and least favorite positions is a potential problem in this study. In future work, this aspect could be improved through the use of a log book as recommended by Bridgewater and Sullivan;14 however, it must be acknowledged that completion of a log book likely influences parental choices regarding infant equipment use and play positions. As a therapeutic strategy, this might be positive in that parents would have a heightened awareness of the possibilities for enhancing their infants’ motor development. Also, this investigation focused on play positions alone and not the specific play activities. Given the importance of play in overall child development, this is an area for future research. Contributions of other parent and child variables to choices about daily activities that affect early motor development are also topics for subsequent investigations.
Infant equipment might be used for some infants born preterm to enhance motor abilities; decisions need to be made individually in the context of many child and family factors. Determining an infant's favorite play position is anticipated to assist with intervention. Because variations in motor development were not explained by gestational age at birth, birth weight, or associated medical or comorbid conditions in this sample, there is a role for further investigation of the influence of environmental factors such as parental expectations and caregiving practices on early motor development and longer-term physical outcomes.
We thank the staff of the Developmental Follow-up Clinic for participating in this work. Lynn Lane, Lynn Whittey, and Donna Sharpe recruited participants, and Gillian Salvarakis, physical therapist, conducted some of the data collection. Drs Carlyle, Fox, Lee, and Pusey reviewed a previous version of this manuscript. Keeley Haggins and Melissa Lauzon (PT, BSc candidates at the time of this study) participated in an early phase by setting up the data file and entering the data of the first participants.
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Interview by Physical Therapist
Different families use different pieces of equipment with their babies at home. What equipment, if any, has your baby used in your home while awake during the past month? What is the average time per day that your baby uses the equipment? TABLE