Correlates of Physical Activity in Children with Chronic Physical Illness and Physical-Mental Multimorbidity
Introduction to Multimorbidity and Physical Activity in Children
Approximately 25 \% of children and adolescents live with chronic physical illnesses (PI) such as asthma, juvenile arthritis, diabetes, epilepsy, or cerebral palsy.
These conditions heighten their risk of experiencing physical, psychosocial, and emotional health challenges.
Multimorbidity (MM), defined as a co-occurring mental illness, is frequently experienced by 40 \% to 50 \% of children with chronic physical illnesses.
Children with multimorbidity are a particularly vulnerable population heavily relying on public health and healthcare systems.
Studies on high-cost users reveal that a small fraction ( 5 \% ) of children account for roughly 60 \% of healthcare costs, predominantly due to chronic illness and often multimorbidity.
There's an observed increase in mental health care service use among children and youth, and it is plausible that children with multimorbidity disproportionately contribute to this trend.
Engagement in Physical Activity (PA):
Despite growing evidence of complex healthcare needs, a significant gap exists in understanding PA engagement among children with multimorbidity.
PA in children with chronic physical illnesses can improve aerobic capacity and internalizing symptoms, and it's a recognized strategy for secondary disease prevention.
However, children with chronic physical illnesses typically engage in insufficient levels of PA.
Specific knowledge about PA levels in children with multimorbidity is scarce, highlighting a critical literature gap.
Unique Challenges Faced by Children with Multimorbidity:
Compared to typically developing children or those with only a physical illness, children with multimorbidity often experience unique challenges, including physical pain, decreased physical health-related quality of life, poorer social relationships, and worse psychological well-being.
Given the broad benefits of PA for both physical and mental health, understanding its role in the context of childhood multimorbidity is crucial.
Known Correlates of PA in General Population:
Systematic reviews indicate PA engagement is influenced by demographic, health, psychosocial, behavioral, and environmental factors.
Consistently related factors in typically developing children include being male, younger age, greater perceived athletic or physical competence, stronger parental and peer support, higher motor proficiency, participation in community sports, warmer seasons, and easier access to facilities.
Research is limited on these factors' influence in children with chronic physical and/or mental illnesses.
PA Correlates in Specific Populations (comparative research):
Physical disabilities: Unique influences of physical limitations and health remain important, alongside psychosocial and environmental factors.
Adolescents with psychiatric disorders: PA was not explained by general population correlates (sex, BMI, SES); instead, the type of psychiatric illness was a factor.
This discrepancy underscores the potential for different correlates in children with and without multimorbidity, justifying focused examination.
Study Objectives:
To estimate the levels of PA in children with multimorbidity (MM) and those with a physical illness only (PI).
To identify demographic, health, psychological/cognitive/emotional, behavioral, familial, and environmental correlates of PA among children with PI and children with MM.
Methodologies
Participants and Study Design:
Utilized baseline data from the ongoing Multimorbidity in Children and Youth Across the Life Course (MY LIFE) study.
A prospective cohort study following 263 children aged 2 to 16 years (mean age: 9.8 years, SD = 4.0 ; 47.7 \% female).
Participants were recruited from outpatient clinics at a Canadian academic pediatric hospital.
Eligibility criteria: physician-diagnosed chronic physical illness (expected to last \ge 12 months, cause functional limitations, dependencies, and require additional healthcare) and parents with adequate English proficiency.
Sampling Method:
Recruitment occurred across various pediatric subspecialty clinics including dermatology, endocrinology, gastroenterology, hematology, immunology, neurology, respiratory, and rheumatology.
Study Procedures:
Baseline appointments were conducted between August 2017 and November 2019, with follow-up appointments scheduled at 6 , 12 , and 24 months.
Parents and youth aged \ge 10 years completed computer-assisted self-report questionnaires.
Research assistants collected biological samples and fitted accelerometers.
Written informed assent was obtained from participants aged \ge 7 years, and written informed consent was obtained from parents of all enrolled participants and youth aged \ge 16 years.
The study received ethical approval from the Hamilton Integration Research Ethics Board.
Measures:
Multimorbidity Assessment:
The Mini International Neuropsychiatric Interview for Children and Adolescents (MINI-KID) was used to identify children with multimorbidity.
This diagnostic interview tool aligns with criteria from both the Diagnostic and Statistical Manual of Mental Disorders (5th ed., DSM-V) and the International Classification of Diseases, Tenth Revision (ICD-10).
The parent version of MINI-KID was administered over the telephone.
It demonstrated good test–retest reliability ( K = 0.71 ) and convergent validity ( \beta = 0.67 ).
Eight specific MINI-KID modules were administered to screen for major depressive episode, generalized anxiety disorder, separation anxiety disorder, social anxiety disorder, specific phobias, attention-deficit hyperactivity disorder, oppositional defiant disorder, and conduct disorder.
Participants meeting diagnostic criteria for any mental illness were classified as having multimorbidity (MM), while others were classified as having a physical illness only (PI).
Physical Activity (PA) Measurement:
PA was objectively assessed using ActiGraph GT3X activity monitors, worn on the right hip for 7 days during all waking hours (excluding water-based activities like showering or swimming).
Raw data collected at 30 Hz were converted to 3 -second epochs for analysis.
Parents kept a log to record wear time. Non-wear time was defined as any time indicated in the log or consecutive zero counts exceeding 60 minutes.
A wear time criterion of \ge 10 hours per day for \ge 3 days was set to ensure data representativeness (between-day reliability \approx 87 \% ).
Evenson cut points were used to determine average daily moderate-to-vigorous physical activity (MVPA) for all children to allow for age-group comparisons, with strong accuracy (Area Under the Curve (AUC) ranging from 0.70 to 0.90 for ages 5 to 15 years).
Pate cut points were additionally applied for children aged 2 to 4 years to assess adherence to early years PA guidelines.
All accelerometer data underwent cleaning and processing using ActiLife Software.
Demographic and Health Covariates:
Parents reported information on the child's age, sex, immigration status (child and parent), race, parental relationship status, and household income.
The World Health Organization Disability Assessment Schedule (WHODAS) 2.0 (12-item, parent-reported) assessed health disability components across cognition, mobility, self-care, getting along, life activities, and participation. Scores ranged from 0 ("none") to 4 ("extreme or cannot do"), with higher sums indicating greater functional limitations. The WHODAS 2.0 showed partial measurement invariance.
Body Mass Index (BMI) percentiles were calculated from measured standing height and weight, based on World Health Organization growth reference data.
Psychological/Cognitive/Emotional Covariates:
The Strengths and Difficulties Questionnaire (SDQ) (parent-reported for children aged 3 to 16 years) assessed emotional symptoms, conduct problems, hyperactivity/inattention, peer relationship problems, and pro-social behaviors (25 items, 3-point scale). It provided externalizing and internalizing scores, with higher scores reflecting greater problems. Mean test–retest reliability was 0.62 .
The Self-Perception Profile for Children (SPPC) was administered to youth aged \ge 10 years, measuring perceived scholastic, social, athletic competence, physical appearance, behavioral conduct, and global self-worth. Higher scores indicated more positive perceptions. The SPPC demonstrated internal consistency ( \alpha = 0.83-0.95 ).
The parent-reported KIDSCREEN-27 evaluated health-related quality of life (HRQL) across physical well-being, psychological well-being, autonomy and parents, support, and school environment (5-point scale). Raw scores were transformed into T-scores (mean 50 , SD = 10 ), with higher scores signifying better HRQL. It has robust reliability, validity, and sensitivity.
Behavioral Covariates:
Involvement in community sports was assessed using two items from the Ontario Child Health Study (OCHS) for youth \ge 10 years, asking about frequency of participation in organized and unorganized sport or PA outside of school in the past 12 months. Scores ranged from 2 to 10 , with higher scores indicating greater participation.
Familial Covariate:
Family functioning was assessed using the General Functioning subscale of the McMaster Family Assessment Device (FAD). Parents rated 12 items on a 4 -point scale, pertaining to communication, problem-solving, involvement, and control. Higher total scores reflected better family functioning. The FAD showed good reliability (Cronbach’s \alpha = 0.86 ).
Environmental Covariate:
Seasonality was a categorical variable (winter, spring, summer, or fall), defined by the National Research Council Canada based on the first day of accelerometer wear.
Missing Data:
Out of 263 total participants, 140 yielded valid accelerometer data ( \ge 10 hours of wear time on \ge 3 days).
Missing accelerometer data were not associated with a positive MINI-KID screen or other independent variables.
However, children aged \ge 10 years were slightly more likely to have missing accelerometer data ( 50.4 \% ) compared to children aged < 10 years ( 43.8 \% ).
Statistical Analyses:
The proportion of children meeting PA guidelines was calculated by age group.
Ages 5 to 16 years: \ge 60 minutes of average daily MVPA (Evenson cut points).
Ages 3 to 4 years: \ge 180 minutes of average daily PA (any intensity) and \ge 60 minutes of MVPA daily (Pate cut points).
Children aged < 3 years: \ge 180 minutes of average daily PA (any intensity) (Pate cut points).
Bivariate correlational analyses using Spearman rho ( \rho ) correlations were performed to examine associations with average daily MVPA, as many correlates were skewed.
Average MVPA minutes per day were calculated as the sum of MVPA minutes on valid wear days divided by the number of valid wear days using Evenson cut points for consistent comparison across all age groups.
Kruskal–Wallis tests were used to assess seasonal differences in MVPA.
Analyses were stratified by multimorbidity status (MM vs. PI) and age (dichotomized into 2-9 years and 10-16 years).
All statistical analyses used IBM SPSS Version 25 , with significance set at p < .05 .
Sample size calculations, originally for planned longitudinal analyses of the MY LIFE study, indicated 80 \% power to detect non-linear trajectories of mental health over four data collection waves.
Results
Descriptive Statistics of the Sample:
The average age of children in the study was 9.4 years ( SD = 4.2 ).
The majority were male ( 51.4 \% ) and had a "normal" BMI ( 66.4 \% ).
Most parents reported that both they ( 86.4 \% ) and their child ( 95.0 \% ) were born in Canada.
A high proportion of parents were White ( 87.1 \% ), married or in a common-law relationship ( 86.4 \% ), and had an annual household income below CAD \$119,000 ( 52.1 \% ).
Physical Activity Guideline Adherence:
Ages \ge 5 years:
41.2 \% of children with Multimorbidity (MM) met PA guidelines.
46.5 \% of children with Physical Illness only (PI) met PA guidelines.
Ages < 5 years:
No children with MM ( 0 \% ) met PA guidelines.
14.3 \% of children with PI met PA guidelines.
Average Daily MVPA (all ages, n=140 ): Children with MM averaged 56.59 minutes ( SD = 22.58 ), while children with PI averaged 55.97 minutes ( SD = 20.06 ).
Correlational Analyses (Spearman Rho with Average Daily MVPA):
Children with Multimorbidity (MM, n=55 ):
Age: Negatively correlated ( \rho(53) = -0.45, p = .001 ), indicating older children engaged in less MVPA.
BMI percentile: Negatively correlated ( \rho(48) = -0.28, p = .04 ).
Child-rated self-perceived behavioral conduct: Negatively correlated ( \rho(24) = -0.45, p = .02 ).
Parent-rated physical health-related quality of life: Positively correlated ( \rho(51) = 0.56, p < .001 ).
Parent-rated peer support (HRQL): Positively correlated ( \rho(52) = 0.27, p = .04 ).
Season: MVPA did not significantly differ across seasons (H = 3.52 , df = 3 , p = .318 ).
Children with Physical Illness only (PI, n=85 ):
Age: Negatively correlated ( \rho(83) = -0.40, p < .001 ), indicating older children engaged in less MVPA.
Sex (female): Negatively correlated ( \rho(83) = -0.26, p = .01 ), suggesting females engaged in less MVPA.
Child-rated self-perceived social competence: Positively correlated ( \rho(31) = 0.42, p = .02 ).
Child-rated self-perceived athletic competence: Positively correlated ( \rho(31) = 0.48, p = .005 ).
Parent-rated physical health-related quality of life: Positively correlated ( \rho(83) = 0.34, p = .001 ).
Frequency of participation in community sport: Positively correlated ( \rho(31) = 0.41, p = .02 ).
Family functioning: Positively correlated ( \rho(83) = 0.26, p = .02 ).
Season: MVPA significantly differed by season (H = 9.27 , df = 3 , p = .026 ), with the highest MVPA in spring and lowest in fall.
Discussion
Overall PA Levels: Approximately half of the children in the MY LIFE study met Canadian PA Guidelines. However, their average daily MVPA was 5 to 13 minutes lower compared to a nationally representative sample.
This aligns with prior systematic reviews showing insufficient PA engagement in children with chronic physical diseases.
Common Correlates across Groups:
Age: Consistently correlated negatively with MVPA in both MM and PI groups, meaning older children tend to be less active. This is a consistent finding in research on typically developing children as well.
Physical Health-Related Quality of Life (HRQL): Positively correlated with MVPA in both groups. This is congruent with previous research suggesting that health problems can interfere with PA participation.
Correlates Specific to Multimorbidity (MM) Group:
BMI percentile: Negatively correlated with MVPA in the MM group. The lack of correlation for BMI with PA in children with PI (and previous studies of physical disabilities) might be explained by limitations at all body sizes.
Self-perceived behavioral conduct: Negatively correlated with MVPA. Poorer perceptions of behavioral conduct (e.g., viewing restless or aggressive behaviors as inappropriate) might reflect higher levels of high-energy, externalizing behaviors that could be inversely related to structured MVPA.
Peer support (HRQL): Positively correlated with MVPA, suggesting the importance of peer relationships and support specifically for children with MM.
Sex and Season: Unlike the PI group, sex and season were not significant correlates for children with MM. The sex imbalance in the MM group ( 36.4 \% female) might limit the ability to confidently rule out a sex association.
Correlates Specific to Physical Illness only (PI) Group:
Sex (female): Negatively correlated with MVPA, suggesting female children with PI engaged in less MVPA.
Self-perceived social and athletic competence: Positively correlated with MVPA, consistent with findings in typically developing children. Higher perceived athletic ability motivates participation, and PA is often a social activity.
Participation in community sport: Positively correlated with MVPA, reinforcing the role of organized activities in fostering PA.
Family functioning: Positively correlated with MVPA. Higher family functioning scores may indicate increased parental support for PA, which is consistently linked to child PA.
Season: MVPA significantly differed by season, being highest in spring and lowest in fall, likely due to differences in time spent outdoors.
Discrepancies and Implications of Differences:
The differences in significant correlates between the PI and MM groups (e.g., sex, social/athletic competence, community sport, family functioning, and season for PI but not MM) suggest that children with multimorbidity may face unknown barriers that preclude their participation in leisure-time PA, even if these factors are present.
Strengths of the Study:
This is the first study to objectively describe PA and its correlates specifically in children with MM.
The use of accelerometry provided objective PA volume data.
Reliable and valid assessments of multimorbidity were applied.
The sample's breadth across various physical illnesses provided considerable generalizability.
Limitations of the Study:
A significant portion of the sample (just over half) did not provide valid accelerometer data, potentially leading to underpowered analyses and a bias towards more physically active children.
Missing accelerometer data may not have been random (e.g., older children were more likely to have missing data).
The study could not qualify the type or context of PA children engaged in.
The study's primary design focus on multimorbidity development meant it did not include all potential PA correlates or a comparison group of healthy children.
Implications and Future Directions for Interventions and Research:
The study demonstrates that children with physical illness, with or without multimorbidity, are insufficiently active, and their PA engagement is influenced by multi-level developmental variables.
Intervention strategies should consider:
Targeting older children through community sport/athletic programming to cultivate peer support and social competence.
Creating mastery motivational climates to improve movement skills and self-perceptions, given the association between self-perceptions and PA in both groups.
Prioritizing family-centered care due to the positive correlation between physical HRQL and PA in both groups.
Future research is needed to:
Explore the causal direction of these associations using prospective data.
Investigate unmeasured variables such as motor skills and more specific parental support for PA.
Examine different patterns, intensities, types, and contexts of PA to clarify which activities children feel able or unable to participate in.
Introduction to Multimorbidity and Physical Activity in Children
Approximately 25 \% of children and adolescents are affected by chronic physical illnesses (PI) such as asthma (a chronic respiratory condition), juvenile arthritis (an autoimmune inflammatory disease), diabetes (a metabolic disorder), epilepsy (a neurological disorder characterized by seizures), or cerebral palsy (a group of disorders affecting movement and muscle tone).
These persistent conditions significantly elevate their risk of experiencing a wide array of physical, psychosocial, and emotional health challenges. These can include pain, fatigue, social isolation, anxiety, depression, and difficulties with daily functioning and academic performance.
Multimorbidity (MM), specifically defined here as the co-occurrence of a chronic mental illness alongside a chronic physical illness, is a prevalent issue, affecting an estimated 40 \% to 50 \% of children with chronic physical illnesses.
This subgroup of children with multimorbidity represents a particularly vulnerable population, placing substantial demands on public health and healthcare systems due to their complex and often intersecting health needs.
Research on high-cost healthcare users indicates that a disproportionately small fraction ( 5 \% ) of children accounts for a significant majority (approximately 60 \% ) of total healthcare costs, primarily driven by the long-term management of chronic illness, and very often, the added complexity of multimorbidity.
There has been a discernible rise in the utilization of mental health care services among children and youth in recent years, and it is highly plausible that children with multimorbidity contribute disproportionately to this increasing trend, given their heightened prevalence of co-occurring mental health conditions.
Engagement in Physical Activity (PA):
Despite the accumulating evidence highlighting the complex and extensive healthcare needs of children with multimorbidity, there remains a critical lacuna in the literature regarding their patterns and levels of physical activity engagement.
Physical activity in children with chronic physical illnesses has been demonstrated to offer substantial benefits, including improvements in aerobic capacity (cardiovascular fitness) and reductions in internalizing symptoms (such as anxiety and depression). It is, moreover, a well-recognized and effective strategy for secondary disease prevention and overall health promotion.
Notwithstanding these benefits, children with chronic physical illnesses generally exhibit insufficient levels of PA, consistently falling below recommended guidelines.
Crucially, specific and detailed knowledge concerning PA levels and their unique correlates in the distinct population of children with multimorbidity is notably scarce, underscoring a significant gap in current literature.
Unique Challenges Faced by Children with Multimorbidity:
When compared to their typically developing peers or even children with only a single physical illness, children with multimorbidity frequently contend with a confluence of unique and exacerbated challenges. These include more severe and chronic physical pain, a considerably decreased physical health-related quality of life, poorer quality and fewer social relationships, and generally worse psychological well-being.
Given the broad-ranging and well-established benefits of physical activity for both mitigating physical symptoms and fostering positive mental health outcomes, understanding its precise role and dynamics within the complex context of childhood multimorbidity is of paramount importance for developing targeted interventions.
Known Correlates of PA in General Population:
Extensive systematic reviews investigating physical activity engagement in the general pediatric population consistently indicate that PA levels are multifactorially influenced by a combination of demographic, health, psychosocial, behavioral, and environmental factors across various ecological levels.
Factors that are consistently and robustly related to higher PA engagement in typically developing children include being male, younger age, possessing greater perceived athletic or physical competence, receiving stronger support from both parents and peers, exhibiting higher levels of motor proficiency, active participation in organized community sports, occurrences during warmer seasons, and having easier and more frequent access to appropriate recreational facilities.
However, remarkably limited research has explored the specific influence of these established factors in children who live with chronic physical and/or mental illnesses, suggesting that the dynamics might differ significantly in these specialized populations.
PA Correlates in Specific Populations (comparative research):
In children with physical disabilities, unique influences stemming from their specific physical limitations and overall health status continue to play a pivotal role in dictating PA levels, alongside the more general psychosocial and environmental factors.
In adolescents diagnosed with psychiatric disorders, it has been observed that physical activity engagement was not readily explained by correlates typically found in the general population (such as sex, Body Mass Index, or socioeconomic status); instead, the specific type and severity of the psychiatric illness emerged as a more significant explanatory factor.
This significant discrepancy in observed correlates between the general population and specific clinical groups highlights the potential for distinct and unique correlates in children with and without multimorbidity, thereby strongly justifying a focused and dedicated examination of this particular population.
Study Objectives:
To rigorously estimate and compare the levels of physical activity in children with multimorbidity (MM) and those with a physical illness only (PI).
To systematically identify and analyze the demographic, health, psychological/cognitive/emotional, behavioral, familial, and environmental correlates of PA specifically among children with PI and children with MM, to uncover any unique distinctions between these two groups.
Methodologies
Participants and Study Design:
This study utilized comprehensive baseline data meticulously collected from the ongoing "Multimorbidity in Children and Youth Across the Life Course (MY LIFE)" study.
The MY LIFE study is designed as a prospective cohort study, which rigorously follows 263 children, aged from 2 to 16 years (with a mean age of 9.8 years and a standard deviation, SD = 4.0 ; 47.7 \% female participants), over an extended period to observe the development and progression of multimorbidity.
Participants were systematically recruited from various outpatient clinics situated within a major Canadian academic pediatric hospital, ensuring a diverse range of physical illnesses.
Detailed eligibility criteria included a physician-diagnosed chronic physical illness, defined as a condition expected to persist for \ge 12 months, cause functional limitations, lead to dependencies on healthcare, and necessitate additional healthcare services. Furthermore, parents were required to have adequate English proficiency to complete study questionnaires.
Sampling Method:
Recruitment efforts were strategically diversified across a broad spectrum of pediatric subspecialty clinics. These included dermatology (skin conditions), endocrinology (hormonal disorders), gastroenterology (digestive system disorders), hematology (blood disorders), immunology (immune system disorders), neurology (nervous system disorders), respiratory (lung and breathing conditions), and rheumatology (musculoskeletal and autoimmune conditions), allowing for a comprehensive representation of chronic physical illnesses.
Study Procedures:
Baseline appointments, which involved extensive data collection, were systematically conducted between August 2017 and November 2019. Subsequent follow-up appointments were meticulously scheduled at 6 , 12 , and 24 months to capture longitudinal changes.
Both parents and youth aged \ge 10 years were tasked with completing a series of computer-assisted self-report questionnaires, designed to gather demographic, health, and psychosocial information efficiently and accurately.
Trained research assistants were responsible for collecting biological samples (e.g., blood, saliva) for future analyses and for expertly fitting participants with ActiGraph accelerometers, which objectively measure physical activity.
Written informed assent, signifying agreement to participate, was obtained from participants aged \ge 7 years, while comprehensive written informed consent was obtained from parents of all enrolled participants and from youth aged \ge 16 years who were legally capable of consenting independently.
The entire study protocol, including recruitment and data collection, received full ethical approval from the Hamilton Integrated Research Ethics Board, ensuring adherence to the highest standards of research ethics.
Measures:
Multimorbidity Assessment:
The presence of multimorbidity (MM) was rigorously identified using the Mini International Neuropsychiatric Interview for Children and Adolescents (MINI-KID), a structured diagnostic interview regarded as a gold standard in psychiatric diagnosis.
This widely validated diagnostic interview tool is meticulously aligned with the diagnostic criteria specified in both the Diagnostic and Statistical Manual of Mental Disorders (5th ed., DSM-V) and the International Classification of Diseases, Tenth Revision (ICD-10), ensuring robust and consistent psychiatric diagnoses.
The parent version of the MINI-KID was administered over the telephone by trained personnel, allowing for a comprehensive parental assessment of their child's mental health status.
The instrument demonstrated commendable test–retest reliability ( K = 0.71 ), indicating consistency over time, and strong convergent validity ( \beta = 0.67 ), showing it accurately measures what it intends to measure.
Eight specific MINI-KID modules were strategically administered to screen for a range of common mental health disorders, including major depressive episode, generalized anxiety disorder, separation anxiety disorder, social anxiety disorder, specific phobias, attention-deficit hyperactivity disorder (ADHD), oppositional defiant disorder, and conduct disorder.
Participants who met the diagnostic criteria for any of these specified mental illnesses were consequently classified as having multimorbidity (MM), whereas those who did not meet these criteria were classified as having a physical illness only (PI).
Physical Activity (PA) Measurement:
Physical activity was objectively and precisely assessed using ActiGraph GT3X activity monitors, which are tri-axial accelerometers designed to capture real-time movement data. These devices were worn on the right hip for a continuous period of 7 days during all waking hours, with the exception of water-based activities such as showering or swimming, where removal was necessary.
Raw acceleration data, collected at a high frequency of 30 Hz (30 readings per second), were subsequently converted into 3 -second epochs (short time intervals) for detailed analysis, allowing for fine-grained measurement of activity intensity.
Parents were requested to meticulously maintain a log to accurately record accelerometer wear time. Non-wear time was stringently defined as any period indicated in the parent log as not being worn, or any continuous sequence of zero counts extending beyond 60 minutes, implying the device was removed.
A strict wear time criterion of \ge 10 hours per day for \ge 3 valid days was established to ensure that the collected data were representative of the participant's typical physical activity patterns, supported by a between-day reliability of approximately 87 \% .
Evenson cut points, a widely accepted method, were employed to determine average daily moderate-to-vigorous physical activity (MVPA) minutes for all children, facilitating consistent age-group comparisons and demonstrating strong accuracy (Area Under the Curve (AUC) ranging from 0.70 to 0.90 for ages 5 to 15 years).
Additionally, Pate cut points were specifically applied for younger children aged 2 to 4 years to assess their adherence to early years PA guidelines, which differ in intensity and duration from older children's recommendations.
All raw accelerometer data underwent a rigorous process of cleaning and processing using specialized ActiLife Software, ensuring data quality and readiness for statistical analysis.
Demographic and Health Covariates:
Parents provided comprehensive self-reported information on several key demographic variables, including the child's exact age, sex, immigration status (for both the child and parent), race/ethnicity, parental relationship status, and estimated annual household income bracket.
The World Health Organization Disability Assessment Schedule (WHODAS) 2.0 (12-item, parent-reported version) was utilized to assess various components of health disability across six domains: cognition (understanding and communicating), mobility (moving around), self-care (hygiene, dressing, eating), getting along (interacting with others), life activities (home, school/work), and participation (community involvement). Scores for each item ranged from 0 ("none") to 4 ("extreme or cannot do"), with higher cumulative sums indicating greater levels of functional limitations and disability. The WHODAS 2.0 demonstrated partial measurement invariance, suggesting its utility across different groups.
Body Mass Index (BMI) percentiles, a measure of relative weight for height and age, were meticulously calculated from objectively measured standing height and weight according to standardized procedures, using World Health Organization growth reference data specific to pediatric populations.
Psychological/Cognitive/Emotional Covariates:
The Strengths and Difficulties Questionnaire (SDQ) (parent-reported for children aged 3 to 16 years) was administered to assess a broad range of psychosocial attributes, including emotional symptoms (e.g., anxiety, depression), conduct problems (e.g., aggression, rule-breaking), hyperactivity/inattention (e.g., restlessness, difficulty concentrating), peer relationship problems (e.g., few friends, bullying), and pro-social behaviors (e.g., kindness, sharing). It consists of 25 items rated on a 3 -point scale. This instrument provided valuable externalizing (conduct and hyperactivity) and internalizing (emotional and peer problems) scores, with higher scores consistently reflecting greater reported problems. The mean test–retest reliability of the SDQ was 0.62 .
The Self-Perception Profile for Children (SPPC) was specifically administered to youth aged \ge 10 years, offering a multi-dimensional measure of perceived competence and self-worth. It assessed self-perceptions across scholastic competence (academic ability), social competence (social skills, friendships), athletic competence (sports ability), physical appearance, behavioral conduct (acting appropriately), and global self-worth. Higher scores on the SPPC consistently indicated more positive self-perceptions in these domains. The SPPC demonstrated strong internal consistency ( \alpha = 0.83-0.95 ).
The parent-reported KIDSCREEN-27, a widely recognized instrument, was employed to evaluate health-related quality of life (HRQL) across five crucial dimensions: physical well-being, psychological well-being, autonomy and relationship with parents, social support and peers, and school environment. Items were rated on a 5 -point Likert scale. Raw scores were then transformed into standardized T-scores (with a mean of 50 and a standard deviation, SD = 10 ), where higher T-scores consistently signified better HRQL. The KIDSCREEN-27 is known for its robust reliability, validity, and sensitivity across pediatric populations.
Behavioral Covariates:
Involvement in community sports was specifically assessed using two targeted items derived from the Ontario Child Health Study (OCHS) for youth \ge 10 years. These items inquired about the frequency of participation in both organized (e.g., team sports, clubs) and unorganized (e.g., informal play, active recreation) sport or physical activity outside of school settings during the preceding 12 months. Scores ranged from 2 to 10 , with higher scores indicating greater overall participation in these activities.
Familial Covariate:
Family functioning, a key aspect of the child’s social environment, was comprehensively assessed using the General Functioning subscale of the McMaster Family Assessment Device (FAD). Parents rated 12 items on a 4 -point scale, pertaining to critical dimensions such as communication patterns, problem-solving abilities, affective involvement among family members, and control structures within the family unit. Higher total scores on this subscale consistently reflected better overall family functioning. The FAD demonstrated good reliability (Cronbach’s \alpha = 0.86 ).
Environmental Covariate:
Seasonality was classified as a categorical variable, distinguishing between winter, spring, summer, or fall. This classification was determined based on the precise first day of accelerometer data wear, using definitions provided by the National Research Council Canada, acknowledging the potential impact of weather and outdoor opportunities on physical activity.
Missing Data:
Out of a total of 263 participants enrolled in the study, 140 ultimately yielded valid accelerometer data, successfully meeting the stringent criteria of \ge 10 hours of wear time on \ge 3 days. This represents a significant portion of missing data, which could influence the generalizability of findings.
Importantly, analyses revealed that missing accelerometer data were not statistically associated with a positive MINI-KID screen (i.e., having multimorbidity) or with other independent variables, suggesting that missingness was not directly linked to the primary outcome or key predictors.
However, a notable observation was that children aged \ge 10 years were slightly more prone to having missing accelerometer data ( 50.4 \% ) compared to their younger counterparts aged < 10 years ( 43.8 \% ). This age-related difference in data completeness highlights a potential bias where older, possibly less compliant or more sedentary, children might be underrepresented in the valid PA data.
Statistical Analyses:
The proportion of children successfully meeting established physical activity guidelines was meticulously calculated and reported according to distinct age groups, reflecting the varied recommendations for different developmental stages.
For children aged 5 to 16 years, adherence was defined as accumulating \ge 60 minutes of average daily MVPA, determined using Evenson cut points.
For children aged 3 to 4 years, adherence required \ge 180 minutes of average daily PA (of any intensity) and, specifically, \ge 60 minutes of MVPA daily, assessed using Pate cut points relevant for early years guidelines.
For the youngest participants, children aged < 3 years, the guideline was set at \ge 180 minutes of average daily PA (any intensity), also utilizing Pate cut points.
Bivariate correlational analyses employing Spearman's rho ( \rho ) correlation coefficient were systematically performed to examine the strength and direction of associations with average daily MVPA. This non-parametric test was chosen because many of the explanatory variables (correlates) exhibited skewed distributions, making it more appropriate than Pearson's correlation.
Average MVPA minutes per day were consistently calculated as the sum of MVPA minutes on valid wear days divided by the total number of valid wear days, exclusively using Evenson cut points for all age groups to ensure uniformity and direct comparison across the entire sample.
Kruskal–Wallis tests, a non-parametric alternative to one-way ANOVA, were specifically utilized to assess potential statistically significant seasonal differences in average daily MVPA, given the categorical nature of the season variable and likely non-normal distribution of MVPA.
To investigate differences more keenly, all primary analyses were meticulously stratified by multimorbidity status (MM vs. PI) and by age (dichotomized into 2-9 years and 10-16 years). This stratification allowed for a nuanced understanding of specific correlates within these distinct subgroups.
All statistical analyses were rigorously conducted using IBM SPSS Version 25 , with the level of statistical significance set a priori at p < .05 . All reported p -values reflect two-tailed tests.
Sample size calculations, originally conducted for the planned longitudinal analyses of the MY LIFE study, indicated that the study possessed 80 \% statistical power to detect meaningful non-linear trajectories of mental health over the four scheduled data collection waves, assuring the robustness of the broader study design.
Results
Descriptive Statistics of the Sample:
The average age of children included in the analyzed subset of the study was 9.4 years ( SD = 4.2 ), indicating a broad age range encompassing early childhood through adolescence.
The majority of the participants were male ( 51.4 \% ) and a significant proportion ( 66.4 \% ) were classified as having a "normal" Body Mass Index (BMI), suggesting that severe obesity was not a dominant characteristic of the overall sample.
Most parents reported that both they ( 86.4 \% ) and their child ( 95.0 \% ) were born in Canada, indicating a predominantly Canadian-born cohort.
A high proportion of parents identified as White ( 87.1 \% ), were married or in a common-law relationship ( 86.4 \% ), and reported an annual household income below CAD \$119,000 ( 52.1 \% ), providing insight into the socioeconomic and demographic profile of the study participants.
Physical Activity Guideline Adherence:
The rates of adherence to recommended PA guidelines varied significantly by age group and multimorbidity status.
Ages \ge 5 years:
Only 41.2 \% of children struggling with Multimorbidity (MM) successfully met the established PA guidelines, indicating a substantial proportion are insufficiently active.
A slightly higher, but still concerning, 46.5 \% of children with Physical Illness only (PI) met the PA guidelines, suggesting that chronic physical illness alone is associated with lower PA.
Ages < 5 years:
Alarmingly, no children ( 0 \% ) within the MM group met the PA guidelines in this younger age bracket, highlighting a critical activity deficit for this highly vulnerable group.
A small fraction, 14.3 \% of children with PI, met the PA guidelines, underscoring challenges in early childhood PA even without co-occurring mental health conditions.
Average Daily MVPA (all ages, n=140 ): Children with Multimorbidity (MM) engaged in an average of 56.59 minutes ( SD = 22.58 ) of MVPA per day, while children with Physical Illness only (PI) averaged 55.97 minutes ( SD = 20.06 ). These averages are strikingly similar between the two groups, despite differences in guideline adherence, suggesting a general trend of suboptimal activity levels.
Correlational Analyses (Spearman Rho with Average Daily MVPA):
These analyses specifically explored the associations between various factors and average daily MVPA, stratified by multimorbidity status.
Children with Multimorbidity (MM, n=55 ):
Age: A statistically significant negative correlation was found ( \rho(53) = -0.45, p = .001 ), unequivocally indicating that older children within the multimorbidity group engaged in considerably less MVPA. This is a moderate, clinically meaningful inverse relationship.
BMI percentile: A modest but significant negative correlation emerged ( \rho(48) = -0.28, p = .04 ), suggesting that children with higher BMI percentiles in the MM group tended to have lower MVPA levels.
Child-rated self-perceived behavioral conduct: A notable negative correlation was observed ( \rho(24) = -0.45, p = .02 ), implying that children who perceived their own behavioral conduct more negatively (i.e., reported more behavioral problems) tended to have lower MVPA.
Parent-rated physical health-related quality of life: A strong and statistically highly significant positive correlation was identified ( \rho(51) = 0.56, p < .001 ), clearly demonstrating that children whose parents reported better physical HRQL engaged in substantially more MVPA.
Parent-rated peer support (HRQL): A weaker, yet statistically significant, positive correlation was found ( \rho(52) = 0.27, p = .04 ), suggesting that greater perceived peer support for the child was associated with higher MVPA in the MM group.
Season: In contrast to the PI group, MVPA levels in children with MM did not significantly differ across seasons (H = 3.52 , df = 3 , p = .318 ), indicating their physical activity was less impacted by climatic variations.
Children with Physical Illness only (PI, n=85 ):
Age: Similar to the MM group, a strong and highly significant negative correlation was observed ( \rho(83) = -0.40, p < .001 ), confirming that older children with only a physical illness also engaged in markedly less MVPA.
Sex (female): A significant negative correlation was present ( \rho(83) = -0.26, p = .01 ), suggesting that female children in the PI group consistently engaged in less MVPA compared to their male counterparts.
Child-rated self-perceived social competence: A statistically significant positive correlation was found ( \rho(31) = 0.42, p = .02 ), indicating that children who perceived themselves as more socially competent tended to engage in more MVPA, likely through social physical activities.
Child-rated self-perceived athletic competence: A robust and highly significant positive correlation was evident ( \rho(31) = 0.48, p = .005 ), demonstrating that children with higher perceived athletic ability were significantly more active.
Parent-rated physical health-related quality of life: A statistically significant positive correlation was identified ( \rho(83) = 0.34, p = .001 ), reaffirming that better parental reports of physical HRQL were linked to higher MVPA in the PI group.
Frequency of participation in community sport: A significant positive correlation was observed ( \rho(31) = 0.41, p = .02 ), strongly suggesting that greater engagement in organized community sports directly translates to higher overall MVPA levels.
Family functioning: A modest but statistically significant positive correlation was found ( \rho(83) = 0.26, p = .02 ), indicating that better family functioning was associated with higher MVPA in children with PI.
Season: In distinct contrast to the MM group, MVPA levels significantly differed by season in the PI group (H = 9.27 , df = 3 , p = .026 ). Post-hoc analyses would likely show the highest MVPA occurring in spring and the lowest in fall, reflecting seasonal outdoor activity patterns.
Discussion
Overall PA Levels: Approximately half of the children participating in the MY LIFE study, encompassing both PI and MM groups, marginally met the Canadian Physical Activity Guidelines. However, a crucial finding was that their average daily MVPA was noticeably lower, specifically 5 to 13 minutes less, compared to what is typically observed in a nationally representative sample of healthy children. This consistent shortfall in activity highlights a pervasive challenge.
This finding is entirely congruent with prior extensive systematic reviews that have consistently documented insufficient physical activity engagement among children diagnosed with various chronic physical diseases, emphasizing a broader public health concern.
Common Correlates across Groups:
Age: The negative correlation between age and MVPA was a consistent and robust finding, observed in both the Multimorbidity (MM) and Physical Illness only (PI) groups. This means that as children in both cohorts grew older, there was a predictable and significant decline in their engagement in moderate-to-vigorous physical activity. This pattern is not unique to children with chronic conditions; it is a well-established and consistent trend observed in longitudinal research on typically developing children as well, highlighting a universal challenge of maintaining activity levels through adolescence.
Physical Health-Related Quality of Life (HRQL): A positive correlation between physical HRQL and MVPA was similarly found in both groups. This relationship suggests that children who, according to parental reports, experience better physical health and fewer physical limitations (higher HRQL) are more likely to be physically active. This is entirely congruent with existing research, which posits that chronic health problems, pain, and functional limitations can significantly interfere with a child's ability and willingness to participate in regular physical activity.
Correlates Specific to Multimorbidity (MM) Group:
BMI percentile: A unique negative correlation with MVPA was observed exclusively in the MM group, indicating that children with multimorbidity who had higher BMI percentiles tended to be less physically active. The absence of this correlation for BMI with PA in children with PI (and in some previous studies of physical disabilities) might be explained by the idea that physical limitations or health challenges can constrain physical activity enjoyment or opportunity across all body sizes in the PI group, whereas the added burden of mental health conditions in the MM group may exacerbate the negative impact of higher BMI on activity.
Self-perceived behavioral conduct: A negative correlation was found between self-perceived behavioral conduct and MVPA. This suggests that children with MM who view their own behaviors more negatively (e.g., struggling with restlessness, impulsivity, or aggressive behaviors) may be less likely to engage in structured MVPA. This could reflect a higher prevalence of high-energy, externalizing behaviors that might be inversely related to sustained, organized physical activity participation, or it might indicate underlying issues that make participation difficult.
Parent-rated peer support (HRQL): This was positively correlated with MVPA, specifically for children with MM, suggesting that the presence of strong and encouraging peer relationships and social support is particularly crucial for promoting physical activity in this vulnerable group. Peer support may provide motivation, opportunities, and a sense of belonging that helps overcome internal and external barriers to activity.
Sex and Season: Notably, unlike the PI group, sex (male/female) and season were not identified as statistically significant correlates for children with MM. The sex imbalance in the MM group (only 36.4 \% female) might partially limit the statistical power to confidently rule out a sex association. Furthermore, the lack of seasonal effect could imply that factors related to their complex multimorbidity might override external environmental influences on their activity patterns, or they might engage in more indoor, less seasonally dependent activities.
Correlates Specific to Physical Illness only (PI) Group:
Sex (female): A negative correlation was found with MVPA, unequivocally suggesting that female children within the PI group consistently engaged in less MVPA compared to their male counterparts. This aligns with general population trends where girls tend to be less active during adolescence.
Self-perceived social and athletic competence: These factors were positively correlated with MVPA, consistent with findings in typically developing children. Higher perceived athletic ability likely motivates greater participation in sports and physical activities, while stronger self-perceptions of social competence can facilitate engagement in physical activities that are inherently social (e.g., team sports, group play).
Participation in community sport: A robust positive correlation with MVPA was observed, strongly reinforcing the well-established role of organized community activities and sports programs as a powerful mechanism for fostering and maintaining higher levels of physical activity in children, even those with chronic physical illnesses.
Family functioning: A positive correlation between better family functioning and MVPA was evident. Higher scores on family functioning may serve as an indicator of increased parental support for physical activity, active family lifestyles, or better management of the child's illness, all of which are consistently linked to higher levels of child physical activity.
Season: In contrast to the MM group, MVPA significantly differed by season for the PI group, with activity being highest in spring and lowest in fall. This seasonal variation is likely attributable to fluctuations in weather conditions, which directly influence opportunities for outdoor physical activity and preferences for certain types of recreation.
Discrepancies and Implications of Differences:
The observed differences in significant correlates between the PI and MM groups (e.g., sex, social/athletic competence, community sport involvement, family functioning, and seasonal effects being significant for PI but not for MM) are highly significant. They strongly suggest that children living with multimorbidity may confront a distinct and potentially more profound set of unknown barriers. These barriers may critically impede their participation in leisure-time physical activity, even when factors typically associated with higher PA in other populations (like strong family functioning or athletic competence) are present. This highlights the unique complexity of promoting PA in the context of co-occurring physical and mental illnesses.
Strengths of the Study:
This investigation stands as the pioneering study that has objectively described physical activity levels and empirically identified its specific correlates in children with documented multimorbidity, filling a crucial gap in pediatric health research.
The rigorous use of accelerometry provided objectively measured physical activity volume data, circumventing the inherent biases and inaccuracies often associated with self-report or parental report measures of activity.
The application of reliable and externally validated diagnostic assessments for multimorbidity, such as the MINI-KID, ensured the accuracy and clinical relevance of the classifications used for the study groups.
The diverse sample, recruited from various pediatric subspecialty clinics and encompassing a broad spectrum of chronic physical illnesses, allowed for considerable generalizability of the findings to a wide range of children with complex health needs.
Limitations of the Study:
A notable limitation was that a substantial proportion of the eligible sample (just over half) did not provide sufficient valid accelerometer data to be included in the analyses. This attrition could potentially lead to underpowered statistical analyses for detecting subtle effects and introduces a risk of bias, possibly overestimating activity levels if children who are less active or less compliant were more likely to have missing data.
Moreover, the data indicated that missing accelerometer data may not have been entirely random; specifically, older children were more likely to have missing data. This non-random missingness further increases the risk of bias and could limit the generalizability of findings, particularly for adolescents.
The study's design, reliant on accelerometry, could not qualify the precise type, context, or organized nature of the physical activities children engaged in (e.g., whether it was structured sport, active play, or daily chores). This lack of qualitative detail limits understanding of preferred or accessible activities.
Furthermore, the study's primary design focus on the development and impact of multimorbidity over time meant that it did not include all potential correlates of physical activity (e.g., specific motor skills, detailed measures of parental support for PA) or a direct comparison group of healthy children, which would have provided a broader contextual understanding.
Implications and Future Directions for Interventions and Research:
The study conclusively demonstrates that children with chronic physical illness, irrespective of whether they also experience multimorbidity, are largely insufficiently active. Furthermore, their engagement in physical activity is influenced by a complex interplay of multi-level developmental variables, necessitating multifaceted intervention approaches.
Intervention strategies should prudently consider:
Developing targeted interventions for older children, leveraging community sport and athletic programming. These programs should aim not only to promote physical activity but also to intentionally cultivate peer support and enhance social competence, addressing key correlates found in PI and MM groups.
Fostering mastery motivational climates within physical activity settings, which emphasize individual improvement and personal bests rather than competitive outcomes. This approach could significantly improve movement skills and bolster children's self-perceptions of competence, which were shown to be positively associated with PA in both groups.
Prioritizing family-centered care approaches, given the consistent and positive correlation between physical HRQL and physical activity in both study groups. Interventions should actively involve families in promoting activity, managing health, and supporting the child's overall well-being.
Future research is critically needed to:
Employ rigorous prospective data collection and advanced longitudinal analyses to explore the causal direction and temporal relationships of these identified associations, moving beyond simple correlations to understand mechanisms.
Investigate additional unmeasured variables that may significantly influence PA, such as specific motor skills, environmental factors like neighborhood walkability, and more nuanced or specific measures of parental support for physical activity.
Conduct detailed qualitative and quantitative studies to examine different patterns, intensities, types, and contexts of physical activity, explicitly clarifying which activities children with multimorbidity feel able or unable to participate in, and what specific barriers or facilitators exist in those contexts.