As noted earlier in this series of papers (37), the pediatric obesity epidemic has focused attention on levels of physical activity (PA) and sedentary behavior (SB) in early childhood. There is evidence that low levels of habitual PA and high levels of habitual SB predispose young children to increased body fatness (28). Widespread and increasing use of preschool child care in the United States (1,12) and elsewhere (4,8,30), combined with the evidence that features of the preschool can influence habitual PA significantly (13), evidence that PA can influence obesity risk, and that PA is readily measurable using objective methods in preschoolers (9,17,23,25,28), have led to an emerging interest in the levels of PA and SB of children while within child care centers.
Two US studies conducted in the late 1980s used direct observation of PA of preschool children within child care centers (2,20). Both studies reported that children spent very little time in moderate- to vigorous-intensity PA (MVPA). Baranowski et al. (2), for example, found that the 19 children observed spent almost all of their time in Children's Activity Rating Scale (CARS) (26) levels 1 and 2, representing SB. These early studies provided cause for concern. However, rapid secular trends in obesity prevalence, in child care use, in the nature of child care, and probably in habitual levels of PA (19) make the generalizability of older studies to contemporary child care questionable.
Both the nature and scale of preschool have changed dramatically in most developed countries in the last two decades. In most countries in western Europe, for example, >90% of preschool children attend some form of child care now (4,30) compared with <20% in the mid 1990s, so child care has moved rapidly from the preserve of a small and probably unrepresentative minority of the population to almost the entire population. Moreover, there has been a rapid trend toward incorporating child care into the educational domain, at least in western Europe. In Scotland, for example, the national education curriculum extends from age 3 yr, and child care now aims toward school readiness and outcomes such as basic literacy and numeracy (28,30); this trend might have encouraged more SB (associated with traditional desk-based school teaching). In addition, the increasing availability and popularity of media (VHS then DVD) and an increasing emphasis on "health and safety" (with the perception that physically active play might increase risk of accidents) might also have promoted more SB within some child care settings. On the other hand, greater awareness of the benefits of PA (34) might have counteracted such influences to some degree. It is also theoretically possible to have both high levels of SB and high levels of PA, although increasing sedentariness has generally been associated with reductions in PA in preschoolers (18,29). Typical levels of PA in preschoolers in contemporary child care are therefore unclear. It is important to summarize evidence on levels of PA within child care from more recent studies to enhance the generalizability of findings to the contemporary child care environment.
Several reviews have recently summarized evidence on objectively measured levels of PA in preschool children (16,23,28), but these considered habitual PA, not PA within the child care setting. In addition, several studies reported on objectively measured levels of PA among preschool children during particular periods of childcare, notably recess (8,15,20), but these studies, although valuable, do not address the issues of usual levels of PA and adequacy of PA within the child care setting during a typical day. The aim of the present review, therefore, was to provide a critical summary of recent evidence on levels of objectively measured PA while preschool children are within the child care setting.
A literature search was carried out for relevant evidence in MEDLINE, PubMed, and SportDiscus. The search period was from January 2000 (with the intention of including early accelerometry studies) to October 2008. The following search terms were used: physical activity, physical inactivity, exercise, accelerometry, heart rate monitoring, sedentary behavior, play, physical education, childhood, and early childhood. Articles identified as being of potential relevance were screened by reading each abstract and by reading the articles where necessary. Articles identified as relevant were searched for relevant references manually, and a request for additional relevant references was made to speakers and attendees at the symposium "Role of Child Care in the Young Child's Physical Activity" at the American College of Sports Medicine Annual Meeting in May 2008. Recent reviews on other aspects of PA in the preschool child (9,16,23) were also searched manually for evidence eligible for the current review.
Study inclusion and exclusion criteria.
To meet its aim, the present review included evidence only from studies that used objective measurement of PA and/or SB during child care time in 3- to 6-yr-olds. Duplicate publications and studies published only in abstract form were excluded. Studies that reported habitual PA data only (or from which PA data during child care could not be extracted, e.g., ) were excluded, and studies that focused only on specific periods of child care, such as recess, were also excluded on the grounds of lack of relevance to the specific aim of the present study. Studies that took place in the child care setting, but altered the child care timetable or children's behavior (usually to carry out a methodological investigation), were excluded because these would not provide valid evidence on usual child care PA. A list of excluded papers and reasons for exclusion is available from the author. The rationale for exclusion of studies that used subjective methods (child report, parent, or carer proxy report) is that such studies cannot provide estimates of levels of PA with confidence (25,31). Several studies reviewed here used more than one objective method in the same sample, increasing confidence in their conclusions as to the adequacy of levels of PA (29); these were considered as separate studies but only counted once when summarizing study sample sizes. The nature of the scientific question being considered by the present review meant that observational studies that aimed to assess usual levels of PA within child care formed most of the included evidence. The major exception was that inclusion of baseline (before intervention) data from intervention studies was considered appropriate where such data were available (1,30,35).
Assessment of adequacy of PA levels at child care.
Authors of studies that were eligible for the present review occasionally referred to PA recommendations-comparing levels of PA observed in their study participants with recommendations-when considering whether levels of PA measured in their studies were "adequate." However, many studies did not or could not make such comparisons, for example, because accelerometry cut points were not available to estimate the intensity of PA or because recommendations for MVPA were not available at the time the study was being conducted and reported. School-age children should accumulate at least 60 min of MVPA every day (11,34), and at least in the UK, this recommendation is used by default for preschool children (11). In the United States, the National Association for Sport and Physical Education (NASPE) (22) recommends that preschoolers should "Accumulate at least 60 minutes/day of structured PA and at least 60 minutes/day of unstructured PA and should not be sedentary for more than 60 minutes except while sleeping." The NASPE recommendation does not specify intensity of PA, and uncertainty in the intensity of PA in some eligible studies, combined with a lack of emphasis on MVPA in the NASPE recommendation, made it difficult to compare the adequacy of PA against the NASPE recommendation, and so no such judgment was made by the author in the present review. An additional problem is in extrapolating typical levels of PA in child care during the sampling or observation periods to a "full" child care day. Intensity of PA was also not available from some studies (notably those that used pedometers). In the evidence summary provided here, three approaches were therefore taken to dealing with the problem of judging the adequacy of PA levels; summary data on the volume of PA from each study are provided as "Results" in the evidence tables-in their original form-so that the reader can make judgments about their adequacy; the judgments made by authors of the original studies are also summarized in the Results section; the author has, in addition, expressed levels of MVPA or step counts as a standard 8-h child care day to make it easier to make judgments about the adequacy of MVPA and easier to compare between the diverse body of eligible studies.
Some authors of eligible studies did not or could not make judgments about the adequacy of PA in their samples. Others made relative judgments (by comparing levels of PA at child care with other periods). Some considered it undesirable if the preschool children failed to reach 60 min·d−1 of MVPA, during a full day in child care-where a full day was measured (7,12,17,24)-or if the typical level of PA during shorter stays at the nursery was insufficient to reach 60 min of MVPA if extrapolated during an entire day. Some authors have considered that levels of activity as measured by accelerometry, direct observation, or step count should be no lower during child care than in the typical time spent outside child care (4,7,17,30). In other words, it is widely accepted among researchers that child care should not restrict the children's opportunities for PA or suppress their PA levels. Several authors compared PA during child care time versus PA in time spent outside child care (in the same child) as an index of the adequacy of PA in child care (7,17,30). Some studies concluded that PA at child care was inadequate if levels of PA, step count, and/or MVPA were significantly lower at child care than in comparison groups of children not attending child care (4,7,8,17).
Avoidance of bias in studies reviewed.
The studies reviewed here, and summarized in Tables 1 and 2, used accelerometry, direct observation, and/or pedometers. Studies of accelerometry generally used the Actigraph accelerometer with the "age-specific" cut points for preschoolers of Sirard et al. (33) to measure MVPA with either 15-s (approximately 800 counts per 15 s being equivalent to MVPA) or 30-s epochs (1) or with the age-independent cut point of 3200 counts per minute of Puyau et al. (27) to measure MVPA with 1-min epochs. The studies of direct observation reviewed here used either the OSRAC-P, the preschool version of the Observational System for Recording Physical Activity (OSRAP) (6), as described earlier in this series of papers (25) or the-similar-CARS (five-point scale) (26).
The objective methods-which form the recent evidence base on levels of PA at child care-are not prone to bias in the assessment of the amount/intensity of PA (10,25,31). However, bias might have been introduced into the assessments of PA if measurements had been made at particularly inactive child care centers, or in particularly inactive children, or in particularly inactive periods of the day (such as daytime naps). In the eligible studies reviewed here, the authors had the specific aim of determining the usual levels of PA within child care and so acknowledged such potential sources of bias consistently. Study designs attempted to minimize bias by random selection of participating children, random selection of child care centers, and random selection of days and times of measurements (5,17,24,30,35). Stratified sampling to provide reasonably representative observations during the child care day was also used widely in the studies reviewed here, as was measurement during the entire child care day in many studies (4,7,17,21,30,35). In summary, the eligible studies reviewed here seem to have a low risk of bias in their assessments of absolute amounts of the amount of PA/MVPA during the child care day.
The literature search found 12 published articles, of 96 different child care centers, and >1900 individual children. Studies that used Actigraph accelerometry are summarized in Table 1; all of the six individual studies that used the Actigraph to estimate MVPA levels concluded that levels of PA during child care time were low. In all of the studies child care time, even when extrapolated during a full day, would not have provided 60 min of MVPA (Table 1).
Studies that used direct observation and pedometers are summarized in Table 2. Individual studies concluded fairly consistently that levels of MVPA were low, and Table 2 supports these conclusions: three of the four studies that used direct observation found that typical levels of MVPA were usually much lower than the 60-min·d−1 recommendation when expressed over a full day at child care.
Summary and interpretation of study findings
The individual studies reviewed here (Tables 1 and 2) generally concluded that levels of objectively measured PA were low within childcare, and most also reported very high levels of objectively measured SB. The evidence review and synthesis is supportive of individual study conclusions and suggests that low levels of PA are common across many child care settings, robust to a range of different objective methods, and across several populations. When >60% of published studies are consistent in their conclusion, confidence in the conclusion is usually considered "high" (16,32,34). In one of the studies (5), slightly higher levels of MVPA were observed than in most of the other studies. The quality of the evidence summarized could be considered to be high because (a) various measures were taken to minimize child care sampling bias and (b) objective and validated measures were used to quantify levels of PA.
Comparisons with other evidence.
Older evidence from studies that used direct observation of PA in US child care settings also suggested that levels of PA were very low (2,20). It is possible that, despite dramatic changes in the nature and scale of child care for preschoolers, common features within the child care setting have acted, and still act, as barriers to PA. New barriers to PA within child care may also have emerged. Studies of objectively measured habitual PA among preschool children generally report relatively low levels of habitual PA (28), so the problem of low PA of preschoolers is not unique to the child care setting.
Review and evidence limitations.
Some of the studies reviewed here were unable to provide quantitative evidence as to the adequacy of amount and/or intensity of the PA observed, some methods (e.g., pedometers) being unable to measure the intensity of PA, and other methods were not amenable to quantification of MVPA at present, in the absence of cut points from calibration studies (e.g., use of the Actigraph with ankle placement) (39). Nevertheless, Tables 1 and 2 illustrate a good deal of consistency of findings between studies in their summary data. In several studies, significant differences in PA within child care were observed within or between child care centers (e.g., (12)). The factors that influence PA to bring about such variation are beyond the scope and aim of the present review and are considered in detail by subsequent papers in the present symposium series (36,37). The present review included studies that varied markedly in sample size, that is, both the number of child care centers and the number of children. Significant heterogeneity between studies is likely, and no formal attempt was made to explore this or to combine data in meta-analysis; the issue of sources of variation in PA at child care centers was beyond the scope of the present review that aimed only to summarize the usual levels of PA within child care. No formal assessment of publication bias was undertaken.
Evidence of variability in PA levels between and within child care settings provides some hope that identifiable and modifiable features of the child care setting exist and that future interventions that address these features might help promote higher levels of PA in child care than are typical at present. Preschool PA research is now focused on finding evidence that will help promote higher levels of PA of children both inside and outside child care (5,8,15,36,37). Evaluation of future interventions to promote PA in child care should use objective methods of PA measurement (31), and evaluation of both processes and outcomes of interventions will be essential (30,35,38). In view of the importance and the wide range of benefits of increasing PA in childhood (34), the typically low level of PA of preschoolers at child care settings is a major concern.
Salary funding was from the Scottish Higher Education Funding Council. The author's research on PA in preschool children has been supported by the British Heart Foundation, Sport Aiding Medical Research for Kids (SPARKS), the Scottish Government Health Department Chief Scientist Office, and the Yorkhill Children's Foundation.
The author has no conflicts of interest to declare.
The results of the present study do not constitute endorsement by the American College of Sports Medicine.
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