A Review of Preschool Children’s Physical Activity and Sedentary Time Using Objective Measures

Context

Identifying current physical activity levels and sedentary time of preschool children is important for informing government policy and community initiatives. This paper reviewed studies reporting on physical activity and time spent sedentary among preschool-aged children (2–5 years) using objective measures.

Evidence acquisition

Databases were searched for studies published up to and including April 2013 that reported on, or enabled the calculation of, the proportion of time preschool children spent sedentary and in light- and moderate to vigorous–intensity physical activity. A total of 40 publications met the inclusion criteria for physical activity and 31 met the inclusion criteria for sedentary time. Objective measures included ActiGraph, Actiwatch, Actical, Actiheart, and RT3 accelerometers, direct observation, and Quantum XL telemetry heart rate monitoring. Data were analyzed in May 2013.

Evidence synthesis

Considerable variation in prevalence estimates existed. The proportion of time children spent sedentary ranged from 34% to 94%. The time spent in light-intensity physical activity and moderate to vigorous–intensity physical activity ranged from 4% to 33% and 2% to 41%, respectively.

Conclusions

The considerable variation of prevalence estimates makes it difficult to determine the “true” prevalence of physical activity and sedentary time in preschool children. Future research should aim to reduce inconsistencies in the employed methodologies to better understand preschoolers’ physical activity levels and sedentary behavior.

Introduction

Optimizing time spent being physically active and minimizing sedentary time are important foci for children’s health from a very young age.1, 2 Recommended amounts of physical activity for preschool children (i.e., those aged 2–5 years who have not yet started school) have been operationalized into public health guidelines.

The National Association for Sport and Physical Education (NASPE) in the U.S. recommends that preschool-aged children participate in at least 60 minutes of structured and 60 minutes of unstructured physical activity (intensity of physical activity not specified) each day and should not be sedentary for more than 60 minutes at a time except when sleeping.³ In Australia, the United Kingdom, and Canada, recently endorsed guidelines suggest preschool children should (1) be physically active for at least 3 hours every day (accumulated throughout the day including light-, moderate-, and vigorous-intensity physical activity); (2) spend less than 1 hour per day using electronic entertainment media; and (3) not be sedentary, restrained, or kept inactive for more than 1 hour at a time (with the exception of sleeping).4, 5, 6, 7

Accurately quantifying preschool children’s participation in these health behaviors is important for informing government policy and community initiatives: first, for determining the necessity of a focus on this age group (i.e., if most young children are highly active then they would be less of a priority compared with other groups), and second, for monitoring the effectiveness of any existing strategic government initiatives targeting these behaviors. However, little is known about the proportion of preschool children meeting physical activity and sedentary recommendations, as few countries have conducted national prevalence surveys in this age group.

Lack of prevalence information may be attributed to the challenges associated with assessing these behaviors in young children.⁸ Population prevalence surveys typically employ self- or proxy-report questionnaires,⁹ and capturing these behaviors in young children using these subjective techniques may result in problems with the data such as recall bias, lack of comprehension, and socially desirable responses.¹⁰ In addition, use of different survey measures also makes it difficult to compare across samples.

Objective measures such as heart rate telemetry and direct observation techniques have traditionally provided more valid and reliable measures of young children’s physical activity and sedentary time than proxy reports.¹¹ However, the development of motion sensors has provided the field with a viable alternative. Accelerometers enable objective estimates of young children’s physical activity¹² and more recently have also been used to assess time spent sedentary.¹³ Accelerometers, heart rate telemetry, and direct observation capture the intensity of movement and can therefore provide estimates of young children’s time spent sedentary and in light-, moderate-, and vigorous-intensity physical activity.¹³

There is considerable conjecture over which accelerometer data cut-points accurately reflect various intensities of activity among preschool children, which has previously been described thoroughly in papers.8, 13 Several validated preschool-age cut-points exist in the literature, and these cut-points are considerably different from one another. The variability in applied cut-points has been shown to have a strong influence on the interpretation of moderate to vigorous–intensity physical activity prevalence estimates.¹⁴

Four review papers8, 14, 15, 16 have been published that synthesize aspects of preschool children’s objectively assessed physical activity. However, none of the reviews reported the percentage of time children spent in light-intensity physical activity or in moderate- or vigorous-intensity physical activity, none reported the percentage of time children spent sedentary, and none synthesized evidence from studies using only objective measures of physical activity, including heart rate telemetry and direct observation. Reporting prevalence estimates using the percentage of time spent in these various intensities of activity is important for standardizing different amounts of wear time between participants and studies, and making estimates between different measures more comparable. Consideration of young children’s participation in light-intensity physical activity and time spent sedentary, particularly prolonged sitting, are important given that these behaviors are a part of the public health recommendations.4, 5, 6

It is also important to distinguish between time spent in light-intensity physical activity and moderate to vigorous–intensity physical activity for two reasons: (1) emerging evidence suggests that engagement in light-intensity physical activity may elicit health benefits in older children17, 18, 19; and (2) it may be easier to reduce sedentary time by incorporating light-intensity physical activity rather than moderate to vigorous–intensity physical activity in preschool children. Additionally, reporting young children’s participation in physical activity and sedentary behavior using objective techniques other than accelerometry is vital given that considerable variability exists in accelerometer cut-points validated in preschool children.¹³

The inclusion of other objective measures enables the comparison of these estimates to accelerometer studies using different cut-points. Therefore, the aim of this paper was to review studies reporting on, or allowing the calculation of, the percentage of time spent in light- and moderate to vigorous–intensity physical activity and being sedentary among preschool children (aged 2–5 years) using a range of objective measures.