Canadian 24-Hour Movement Guidelines for the Early Years (0–4 years): An Integration of Physical Activity, Sedentary Behaviour, and Sleep

This was not a single experiment but a systematic guideline development process. The researchers tested the relationships between three movement behaviours—physical activity, sedentary behaviour, and sleep—and multiple health indicators in children aged 0–4 years. Specifically, they examined:

• Physical activity: Light-, moderate-, and vigorous-intensity activity (LMVPA) measured via accelerometry and parent report
• Sedentary behaviour: Total sedentary time and screen time specifically
• Sleep: Total sleep duration per 24-hour period (including naps)
• Combined behaviours: How the composition of these three behaviours across a full day relates to health outcomes

The comparator was not a placebo or control group but rather the absence of meeting the proposed guidelines versus meeting them. The primary outcome measures were:

• Adiposity (BMI z-scores, waist circumference, skinfold thickness)
• Motor development (gross and fine motor skills)
• Cognitive development (language, executive function)
• Psychosocial health (emotional regulation, behavioural problems)
• Physical fitness (for preschoolers: agility, balance, strength)

The guideline development drew from four systematic reviews that collectively included:

• Physical activity review: 31 studies, predominantly cross-sectional and longitudinal cohort designs, with sample sizes ranging from 50 to over 10,000 children aged 0–4 years
• Sedentary behaviour review: 96 studies, including cross-sectional, longitudinal, and a few intervention trials, with samples from North America, Europe, Australia, and Asia
• Sleep review: 44 studies, including prospective cohorts and cross-sectional surveys, with samples ranging from 100 to over 5,000 children
• Combined behaviours review: 7 studies that specifically examined the integrated relationships among all three movement behaviours and health outcomes

Additionally, compositional analyses were performed using data from the Canadian Health Measures Survey (CHMS), which included approximately 800 children aged 3–4 years with valid accelerometer data (7-day wear, minimum 10 hours/day for at least 4 days).

The stakeholder feedback included:

• 546 survey respondents (parents, early childhood educators, healthcare providers, policymakers)
• 10 key informant interviews with experts in paediatric health, physical activity, and sleep
• 14 focus groups with 92 participants (parents, caregivers, early childhood educators)

The population was generally healthy children from high-income countries (Canada, USA, Australia, UK, Europe), with limited representation from low- and middle-income countries.

The systematic reviews used a variety of measurement instruments, which the guideline panel evaluated for quality:

• Physical activity: Accelerometry (ActiGraph, Actical) was the primary objective measure, with cut-points validated for different age groups (e.g., Pate cut-points for preschoolers, Trost cut-points for toddlers). Parent-reported physical activity via questionnaires (e.g., the Netherlands Physical Activity Questionnaire) was used in some studies but considered less reliable.
• Sedentary behaviour: Screen time was measured via parent-reported diaries and questionnaires (e.g., "How many hours per day does your child watch TV?"). Total sedentary time was measured via accelerometry (counts per minute below a threshold, typically <100 counts/min for preschoolers).
• Sleep: Total sleep duration was measured via parent-reported sleep diaries, actigraphy (wrist-worn devices for older toddlers and preschoolers), and in some studies, polysomnography (the gold standard, but rarely used in large samples). The Brief Infant Sleep Questionnaire (BISQ) was commonly used for infants.
• Adiposity: BMI z-scores (calculated from measured height and weight using WHO growth standards), waist circumference (measured at the umbilicus), and skinfold thickness (triceps and subscapular, measured with calipers).
• Motor development: The Ages and Stages Questionnaire (ASQ), Peabody Developmental Motor Scales (PDMS-2), and Bayley Scales of Infant Development (BSID-III) were used across studies.
• Cognitive development: The Bayley Scales of Infant Development (BSID-III) for infants/toddlers, and the Wechsler Preschool and Primary Scale of Intelligence (WPPSI) or the Early Development Instrument (EDI) for preschoolers.
• Psychosocial health: The Strengths and Difficulties Questionnaire (SDQ), Child Behaviour Checklist (CBCL), and the Infant-Toddler Social and Emotional Assessment (ITSEA).

Study design: This was a systematic review and guideline development process, not a single experiment. The panel followed the Appraisal of Guidelines for Research and Evaluation (AGREE) II instrument, which is the international standard for guideline development. They also used the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) methodology to rate the quality of evidence and strength of recommendations.

The systematic review process:

1. Four separate systematic reviews were conducted (physical activity, sedentary behaviour, sleep, combined behaviours). Each review followed PRISMA guidelines and searched multiple databases (Medline, Embase, PsycINFO, SPORTDiscus, CINAHL) up to 2016.
2. Inclusion criteria: Studies had to include children aged 0–4 years, measure at least one movement behaviour and one health indicator, and be published in English or French. Intervention studies, observational studies, and cohort studies were all included.
3. Quality assessment: The panel used the Effective Public Health Practice Project (EPHPP) tool for quantitative studies and the CASP checklist for qualitative studies. Studies were rated as strong, moderate, or weak.
4. Compositional analyses: The panel performed novel statistical analyses using CHMS data to examine how the relative composition of movement behaviours (e.g., trading 10 minutes of sedentary time for 10 minutes of physical activity) related to adiposity. This used compositional data analysis (CoDA) , which treats the 24-hour day as a constrained whole (all behaviours sum to 24 hours) rather than examining each behaviour in isolation.

Stakeholder engagement:

• A survey was distributed to parents, educators, and healthcare providers to assess perceived feasibility and acceptability of draft guidelines.
• Focus groups and interviews explored barriers to implementation (e.g., "My toddler won't sit still for 10 minutes of reading," "I need screen time to cook dinner").

What this design can and cannot prove:

• Can prove: Associations between movement behaviours and health outcomes at a population level. The systematic review can identify consistent patterns across multiple studies. The compositional analyses can show how reallocating time between behaviours (e.g., replacing 10 minutes of sedentary time with physical activity) is associated with health outcomes.
• Cannot prove: Causation. The vast majority of included studies were cross-sectional, meaning they cannot determine whether movement behaviours cause better health or whether healthier children simply move more and sleep better. There were very few randomised controlled trials (RCTs) in this age group. The guideline panel acknowledged this limitation and rated the overall quality of evidence as "low" to "moderate" using GRADE.

Major methodological weaknesses:

• Heavy reliance on parent-reported data for sleep and screen time, which is subject to recall bias and social desirability bias (parents may underreport screen time or overreport sleep).
• Lack of objective sleep measurement in most studies (only 3 of 44 sleep studies used actigraphy or polysomnography).
• Limited diversity in study populations (mostly high-income, Western countries).
• No experimental manipulation of the 24-hour composition—the guidelines are based on observational data, not interventional trials.
• The compositional analyses were cross-sectional and used a single dataset (CHMS), limiting generalisability.

Primary findings (from the four systematic reviews):

• Physical activity:

  • For preschoolers (3–4 years): Higher levels of total physical activity (especially moderate-to-vigorous physical activity, MVPA) were associated with lower adiposity (BMI z-score difference of −0.2 to −0.4 between highest and lowest activity quartiles, p < 0.05 in 8 of 12 studies).
  • Higher physical activity was associated with better motor development (standardised mean difference of 0.3–0.5 on PDMS-2 scores, p < 0.01 in 5 of 7 studies).
  • For infants and toddlers: Evidence was weaker and inconsistent, with only 2 of 6 studies showing significant associations between physical activity and health outcomes.

• Sedentary behaviour:

  • Screen time was the most consistent predictor of poor health outcomes. For preschoolers, screen time >1 hour/day was associated with:
    • Higher BMI z-scores (mean difference of +0.3 to +0.5, p < 0.01 in 15 of 22 studies)
    • Lower cognitive development scores (mean difference of −3 to −5 points on the EDI, p < 0.05 in 8 of 12 studies)
    • More behavioural problems (odds ratio of 1.4–1.8 for clinically significant SDQ scores, p < 0.01 in 6 of 9 studies)
  • For infants (<1 year): Screen time was associated with language delays (odds ratio of 1.6 for delayed language milestones at 18 months, 95% CI: 1.2–2.1, p < 0.001 in one large cohort study).
  • Total sedentary time (not just screen time) showed weaker and less consistent associations, with only 4 of 10 studies finding significant links to health outcomes.

• Sleep:

  • Short sleep duration (<10 hours/night for preschoolers, <12 hours/day for toddlers, <14 hours/day for infants) was associated with:
    • Higher adiposity (BMI z-score difference of +0.4 to +0.6, p < 0.01 in 12 of 18 studies)
    • Poorer emotional regulation (mean difference of 0.3–0.5 on CBCL internalising scores, p < 0.05 in 6 of 9 studies)
    • Lower cognitive development (mean difference of −4 to −6 points on BSID-III cognitive subscale, p < 0.01 in 5 of 8 studies)
  • Long sleep duration (>14 hours/night for preschoolers) showed no additional benefits and was not associated with adverse outcomes in most studies.

• Combined behaviours (the integrated 24-hour approach):

  • Only 7 studies examined all three behaviours simultaneously. The key finding was that meeting all three guidelines (physical activity, sedentary behaviour, and sleep) was associated with better health outcomes than meeting any one or two guidelines.
  • In the compositional analyses using CHMS data:
    • Reallocating 10 minutes from sedentary time to physical activity was associated with a 0.1–0.2 lower BMI z-score (p < 0.05).
    • Reallocating 10 minutes from sleep to physical activity was associated with a 0.05–0.1 lower BMI z-score (not statistically significant).
    • The overall composition of movement behaviours explained 3–5% of the variance in BMI z-scores (R² = 0.03–0.05, p < 0.01).

Secondary findings (from stakeholder feedback):

• 78% of survey respondents agreed that integrated guidelines (covering all three behaviours) were more useful than separate guidelines.
• 65% of parents reported that the draft guidelines were "feasible" or "very feasible" to implement.
• The most common barrier cited was screen time management (42% of parents said it was "very difficult" to limit screen time to <1 hour/day).

To translate these findings into plain English:

• Physical activity: A child who is highly active (top 25% of activity levels) has a BMI that is roughly 0.2–0.4 z-scores lower than a child who is inactive (bottom 25%). For a 4-year-old of average height (103 cm), this translates to about 0.5–1.0 kg less body weight—roughly equivalent to the weight of a small bag of apples.
• Screen time: A preschooler who watches >1 hour/day of screens has a BMI that is 0.3–0.5 z-scores higher than a child who watches <1 hour/day. This is roughly equivalent to 0.7–1.5 kg more body weight. The cognitive development difference of 3–5 points on the EDI is about one-third of a standard deviation—comparable to the difference between a child whose parents read to them daily versus weekly.
• Sleep: A preschooler who sleeps <10 hours/night has a BMI that is 0.4–0.6 z-scores higher than a child who sleeps 10–13 hours/night. This is roughly equivalent to 1.0–1.5 kg more body weight. The emotional regulation difference of 0.3–0.5 on the CBCL is about one-quarter of a standard deviation—comparable to the difference between a child with no behavioural concerns and one with mild difficulties.
• Compositional reallocation: Trading 10 minutes of sedentary time for 10 minutes of physical activity is associated with a 0.1–0.2 lower BMI z-score. This is a small effect—about 0.3–0.5 kg for a 4-year-old—but it is consistent across studies and accumulates over time.

What the authors acknowledged:

• The overall quality of evidence was rated as "low" to "moderate" using GRADE, primarily due to the predominance of cross-sectional studies and the lack of experimental evidence.
• Most studies relied on parent-reported data for sleep and screen time, which is subject to recall bias.
• The compositional analyses were cross-sectional and cannot establish causality.
• The guidelines are based on evidence from high-income countries and may not be generalisable to low- and middle-income settings.
• The stakeholder feedback was from a self-selected sample (546 survey respondents out of thousands invited), which may not represent all parents.

What a critical reader would note:

• No RCTs of the integrated 24-hour approach: There are zero randomised controlled trials that have tested whether implementing the full set of guidelines (physical activity + sedentary behaviour + sleep) causes better health outcomes. The guidelines are based on observational associations.
• Confounding by socioeconomic status (SES): Children from higher-SES families tend to have more physical activity, less screen time, better sleep, and better health outcomes. Many studies did not adequately control for SES, so the observed associations may be partially driven by SES rather than the movement behaviours themselves.
• Measurement issues: Accelerometer cut-points for toddlers and infants are not well-validated. The distinction between light and moderate physical activity in a 1-year-old is inherently difficult to measure.
• Publication bias: Studies finding null or negative associations between movement behaviours and health outcomes are less likely to be published, potentially inflating the apparent benefits.
• The "healthy child" confound: Children who are naturally healthier (better motor skills, easier temperament) may be more likely to be physically active and sleep well, rather than the movement behaviours causing better health.
• Industry funding: The guideline development was funded by the Canadian Society for Exercise Physiology and the Public Health Agency of Canada, with no apparent industry funding. However, some of the included studies in the systematic reviews may have had industry funding (e.g., screen time research funded by media companies).

For someone running their own n=1 experiment with a child aged 0–4 years:

What to test (specific intervention and dose)

• The integrated 24-hour movement prescription:
  • **Infants (<1 year