Pandemic footprints on children’s health: how COVID-19 reshaped BMI, fitness and suspected myopia in rural Chinese primary-school students

Table of Contents

1. Key Highlights
2. Introduction
3. Study design and what was measured
4. What changed in body size: BMI rises concentrated in younger children
5. Task-specific shifts in physical fitness: sprint, rope-jumping and flexibility
6. Suspected myopia rose, concentrated in specific age-sex strata
7. Behavioral and biological pathways: how lockdown produced these outcomes
8. How these findings compare with other studies
9. Practical recommendations for schools, families and policymakers
10. Practical exercises and session templates schools can adopt
11. Limitations to weigh when interpreting results
12. Research gaps and priorities
13. What schools and health systems should measure going forward
14. Final synthesis: targeted, practical steps to reduce long-term harm
15. FAQ

Key Highlights

• Between 2019 (pre-pandemic) and 2020 (home-based schooling), children aged 6–11 in a rural Zhejiang primary school showed higher BMI—especially boys aged 6–10 and girls aged 7–8—task-specific changes in fitness (improved rope-jumping, mixed flexibility declines, stable sprint times), and a significant rise in suspected myopia concentrated in select age–sex groups.
• Differences were age- and sex-specific: girls aged 7 and 11 and boys aged 10 experienced the largest relative increases in suspected myopia; flexibility fell mainly among the youngest children; rope-jumping improved for most ages likely due to home-friendly exercise routines.
• Findings point to targeted, age-sensitive interventions—promoting daily MVPA, structured indoor exercise options, protected outdoor time and routine vision screening—to mitigate lasting effects from prolonged home confinement.

Introduction

School closures and months of home confinement during the COVID-19 emergency remapped children’s daily lives—classrooms shifted online, playgrounds closed, and family routines reorganized around screens and indoor space. This transformation unfolded during a critical developmental window: ages 6–11, when growth, motor skill acquisition and ocular development are particularly sensitive to environmental inputs. A repeated cross-sectional screening of a rural primary school in Lishui City, Zhejiang Province, compared physiological and vision markers in November 2019 and November 2020. The results show a complex pattern: increases in body mass index concentrated in younger children, task-specific shifts in physical fitness with notable gains in rope-jumping but declines in flexibility for the youngest groups, and a measurable uptick in suspected myopia in several age–sex strata.

These patterns illuminate how behavioral changes tied to home confinement—reduced outdoor time, altered physical education practices, and increased near-screen activities—translate into distinct biological and functional outcomes. The screening data provide a rare simultaneous look at both fitness and visual acuity across primary-school ages, and suggest practical directions for schools, public health authorities and families to reduce lasting harms from prolonged disruptions.

The sections that follow explain the study design and what was measured, walk through the detailed findings, interpret mechanisms linking behavior to outcomes, compare these results with international observations, and translate evidence into concrete recommendations for school curricula, parental practice and policy.

Study design and what was measured

Researchers analyzed anonymized school health-screening records from a public primary school in a rural municipality (Lishui City, Zhejiang). Two annual screening waves—November 2019 (pre-pandemic) and November 2020 (during pandemic-related home-based learning)—provided repeated cross-sectional snapshots of children aged 6–11.

Measured outcomes

• Anthropometry: height, weight, body mass index (BMI) and WHO BMI-for-age z-scores (BAZ).
• Physical fitness: 50 m sprint time (s), 1-minute rope-jumping count (number of skips), sit-and-reach (cm) for flexibility.
• Visual acuity: unaided distance visual acuity using the Chinese standard logarithmic chart; suspected myopia defined as unaided VA < 5.0 in either eye.

Sample and analytic approach

• Sample sizes screened were N = 1,183 (2019) and N = 1,120 (2020); complete-case analytic counts varied by measure (maximum 1,069 in 2019 and 1,116 in 2020).
• Analyses used factorial regression models (Year × Age × Sex) adjusted for age and sex with class-level cluster-robust standard errors.
• For myopia (a binary outcome), modified Poisson regression estimated prevalence ratios (PRs); the Benjamini–Hochberg procedure controlled the false discovery rate across multiple tests.

Why this design matters The repeated cross-sectional approach offers a practical way to detect population-level shifts when longitudinal cohort tracking is not possible. Using standardized national fitness protocols and consistent examiners across years reduced measurement variability. However, unaided visual acuity screening—while feasible for school-wide surveillance—cannot substitute for cycloplegic refraction, which remains the gold standard for diagnosing refractive error.

What changed in body size: BMI rises concentrated in younger children

The screening recorded a clear increase in BMI in 2020 compared with 2019, but the effect was not uniform across ages or sexes.

Key patterns

• Boys aged 6–10 showed consistent, statistically significant increases in BMI (ranging about +1.27 to +2.30 kg/m^2), and their BMI-for-age z-scores rose substantially (+0.83 to +1.51 SD units for ages 6–9).
• Girls aged 7–8 also experienced significant BMI increases (+1.17 to +2.25 kg/m^2) with z-score increases of roughly +0.51 to +1.18 SD units.
• Older children (girls 9–11, boys 10–11) showed no consistent, significant BMI z-score increases.

Interpreting the rise The observed pattern reflects how home confinement differentially affects cohorts. Younger children typically rely on structured school routines for daily movement—playground free play, recess, PE sessions and active commuting. When those are curtailed:

• Sedentary time increases.
• Opportunities for moderate-to-vigorous physical activity (MVPA) decrease.
• Access to organized sports and outdoor play shrinks, particularly in settings where homes or local outdoor spaces are limited.

Dietary patterns also shifted during lockdowns in many contexts—greater snacking, irregular meal patterns, and increased availability of calorie-dense foods at home. These behavioral shifts can accelerate weight gain over a relatively short period.

Real-world example Several international reports from early pandemic periods documented similar trends: household surveys in multiple countries showed increased sedentary hours and snacking among children; longitudinal surveillance in some regions detected higher rates of weight gain among primary-school children during periods of restriction.

Implications Weight gain in early childhood is consequential: higher BMI at ages 6–9 tracks into adolescence and adulthood and raises the lifetime risk of cardiometabolic conditions. Interventions must prioritize younger primary-school children for weight-management strategies, combining daily activity targets with dietary guidance.

Task-specific shifts in physical fitness: sprint, rope-jumping and flexibility

The pandemic period produced heterogeneous outcomes across fitness domains. The effects were not global declines; rather, performance changed differently by task.

50 m sprint: broadly unchanged

• No statistically robust change in sprint times across age-sex strata after correcting for multiple tests.
• Physical explanation: sprinting performance in this age range depends strongly on growth-related increases in stride length and neuromuscular development. Even with reduced structured activity, natural maturation may preserve short-sprint capacity across one year, and sprinting needs relatively less continuous practice than other discrete skills.

Rope-jumping: widespread improvement, with younger boys as exceptions

• Rope-jumping counts in 1 minute increased significantly in 2020 across many age groups (notably ages 7–9 and 11 for both sexes), with gains approximately +12 to +23 jumps/min in several strata.
• Exceptions: boys aged 6 and 10 showed declines in rope-jumping performance.
• Likely driver: rope-jumping requires minimal space and equipment and was widely promoted as a home-friendly PE activity during school closures. Families and home-based curricula could adopt rope-jumping more readily than team sports or field-based activities. Additionally, rope-jumping improves coordination and muscular endurance—skills that respond quickly to frequent short practice sessions.

Sit-and-reach (flexibility): declines concentrated among the youngest

• Flexibility declined in boys aged 6 (−7.94 cm) and girls aged 6–7 (−3.59 and −5.71 cm), while girls aged 10 showed an increase (+4.44 cm).
• Young children’s flexibility can be sensitive to changes in daily movement variety and stretching opportunities. Reduced unstructured play and less guided physical education could limit activities that maintain dynamic flexibility and hamstring extensibility.

Why performance varied by task

• Accessibility and feasibility during lockdown: rope-jumping could be done indoors; sprinting required more continuous space to train effectively; flexibility maintenance requires guided stretching and mobility routines that young children may not engage in without adult facilitation.
• Developmental stage: younger children have not yet consolidated motor patterns; missing guided practice has a larger relative effect than in older children who may have already established basic motor competence.
• Gendered preferences and activities: boys and girls may have differed in what home activities they chose or were encouraged to do, influencing observed sex differences in some outcomes.

Policy-relevant insight Fitness is multidimensional. Measures that can be maintained during confinement—jump rope, calisthenics, guided indoor games—should be prioritized in home-based PE. Schools should include simple, space-efficient routines that preserve coordination and flexibility for young children.

Suspected myopia rose, concentrated in specific age-sex strata

The screening found an overall increase in the prevalence of suspected myopia from 2019 to 2020, but the rise was uneven.

Notable prevalence ratios (2020 vs 2019), after multiple-test correction

• Girls aged 7: PR = 1.83 (95% CI 1.29–2.59), q = 0.009
• Girls aged 11: PR = 1.41 (95% CI 1.10–1.81), q = 0.020
• Boys aged 10: PR = 1.24 (95% CI 1.07–1.43), q = 0.020
• Boys aged 6: PR = 0.65 (95% CI 0.49–0.88), q = 0.020 (a notable decrease)

Additional strata showed nominal increases that did not survive FDR adjustment. Sensitivity analyses—excluding age 11 or applying weighting to standardize age-sex distributions—produced consistent results: an overall elevated risk of suspected myopia in 2020 remained.

Measurement caveat Suspected myopia was determined by unaided distance visual acuity (VA < 5.0 in either eye). School-based VA screening is practical but not definitive: it cannot replace cycloplegic refraction. Without cycloplegia, accommodation can mask hyperopia or masquerade as myopia in some cases, leading to possible misclassification where asthenopia or uncorrected refractive hyperopia confounds VA. Nonetheless, a consistent change in unaided VA across a population suggests altered visual stressors and warrants attention.

Mechanisms linking pandemic behaviors to myopia progression

• Reduced outdoor time: outdoor light exposure increases retinal dopamine release, a biochemical brake on axial elongation. Less time outdoors removes this protective signal.
• Increased near work and screen time: prolonged near-focus and sustained accommodative demand can encourage eye growth patterns associated with myopia progression.
• Home-based learning: continuous hours of close-up digital study without sufficient breaks intensified near work in many children worldwide.

Why specific ages and sexes?

• The sensitive window for emmetropization and axial growth spans early school years. Small increases in near work during these critical periods can produce measurable increases in myopia incidence.
• Gender differences may reflect behavioral patterns—some studies indicate girls spend more time in near work or are more engaged in indoor quiet activities—though cultural factors and family routines also interact.
• The decline among boys aged 6 may reflect sampling variability or differential patterns of activity for that cohort in this particular school; sensitivity analyses recommended.

Real-world countermeasures Countries and school systems that prioritized daily outdoor recess or structured outdoor breaks for children reported lower rates of myopia onset in intervention trials. Simple measures—prescribed outdoor play, visual rest breaks, and limiting continuous screen time—are effective, affordable public-health interventions.

Behavioral and biological pathways: how lockdown produced these outcomes

The observed patterns follow two broad, interlinked pathways.

1. Behavioral displacement of activity

• Home confinement increased sedentary behavior and reduced MVPA. For younger children who attain much of their daily movement through school-recess and PE, the relative loss was larger. Lower mechanical loading and cardiovascular stimulation impede neuromuscular and motor-skill development that underpins strength, flexibility and cardiorespiratory fitness.

2. Visual environment and ocular growth

• Outdoor light exposure acts through retinal dopamine to constrain axial elongation. Less exposure reduces this physiological brake.
• Increased near work and screen exposure increase accommodative load and may promote axial elongation through mechanical or biochemical routes.

These pathways operate simultaneously. For example, fewer outdoor activities both reduce physical fitness stimulus and remove protective visual inputs. The co-occurrence of increased BMI and suspected myopia suggests that lifestyle shifts during confinement have multi-system effects.

How these findings compare with other studies

Cross-national and local studies reported mixed but generally concerning signals during the pandemic:

• Japan and Austria: reports described slower run times and reduced motor competence among young children during emergency periods.
• Portugal: declines in motor competence among primary-grade children were documented in lockdown studies.
• China (other provinces): several studies documented increased myopia incidence and progression tied to home-based online learning.

What sets this study apart is the simultaneous assessment of fitness and visual acuity across a broad age range (6–11) in a single rural school, allowing age- and sex-stratified comparisons. The positive change in rope-jumping, contrasting with declines in flexibility, illustrates how the content of at-home activity programs shapes outcomes. Where home-based PE emphasized jump rope and calisthenics—activities requiring little space—students could maintain or improve those specific capacities.

Practical recommendations for schools, families and policymakers

The findings point to pragmatic, scalable actions that reduce the risk of persistent harms from prolonged confinement.

For schools and education authorities

• Integrate short, daily home-friendly PE modules into online curricula: jump rope, dynamic stretching, calisthenics and balance drills. These require minimal equipment and can be performed in limited indoor spaces.
• Preserve scheduled outdoor time when safe and feasible. Structured outdoor recess or classroom-led outdoor breaks (20–30 minutes, multiple times per day where possible) protect vision and boost activity.
• Train teachers to incorporate guided stretching and mobility routines targeting flexibility, particularly for younger grades.
• Maintain routine vision screening and follow-up. School screenings are essential signals, but suspicious cases require cycloplegic refraction by eye care professionals.

For parents and caregivers

• Aim for at least 60 minutes of moderate-to-vigorous physical activity daily for children, consistent with WHO guidance. Break this into several short sessions if continuous time is unavailable.
• Prioritize two hours per day of outdoor time when infection-control rules permit, using parks, gardens or supervised outdoor play.
• Limit continuous near-screen or near-work periods to approximately 30 minutes, inserting visual-rest breaks (20–20–20 rule: every 20 minutes, look at an object 20 feet away for 20 seconds) and stand-up movement breaks.
• Use home routines to preserve stretching and mobility: short guided sessions after waking and before bedtime maintain flexibility.
• Keep food environments supportive: reduce high-sugar snack availability, maintain family meals and emphasize balanced nutrition.

Public health and policy actions

• Develop and disseminate evidence-based home-PE guidance—accessible video modules and family guidance emphasizing rope-jump, mobility, and short cardio workouts.
• Fund catch-up physical education resources for students returning to school: additional PE sessions and motor-skill remediation especially for the youngest cohorts.
• Strengthen school vision programs with standard protocols for referral to optometry/ophthalmology and ensure access to cycloplegic refraction where indicated.
• Target resources to rural areas and lower-resource schools where home space and outdoor access may be limited.

Implementation examples

• District-level programs can issue “PE at home” kits (jump rope, printed exercise cards, video links) and schedule virtual supervised group sessions.
• Community health teams can partner with schools to run outdoor activity days with social distancing.
• Eye health campaigns can combine school screening with parent educational materials on limiting continuous screen time and encouraging outdoor play.

Practical exercises and session templates schools can adopt

Below are practical, evidence-informed elements that can be incorporated into home-based or hybrid PE programs.

Short daily routines (10–15 minutes)

• Warm-up (2 minutes): standing march, arm circles.
• Jump-rope sets (3–6 minutes): intervals of 30–60 seconds jumping, 30–60 seconds rest; repeat 4–6 times.
• Dynamic mobility (3–4 minutes): leg swings, hip circles, toe touches.
• Flexibility cooldown (2–3 minutes): guided sit-and-reach, gentle hamstring stretches.

Structured mini-sessions to build flexibility (10 minutes, 3× weekly)

• Active games that promote dynamic range: animal walks, reaches, and playful partner stretches.
• Teacher-guided short flexibility circuits using simple props (towel for assisted stretches).

Vision-friendly study schedule for online learning

• Study blocks of 25–30 minutes with a 5–10 minute movement/visual-rest breakpoint.
• At least two 20–30 minute outdoor breaks per day when practical.
• Create ergonomically appropriate study spaces with good ambient lighting.

These activities require little cost and can be adjusted for space constraints and safety.

Limitations to weigh when interpreting results

The study provides useful signals but has limitations that affect generalization and causal interpretation.

• Single-school, rural sample: findings reflect local circumstances and may not generalize to urban or nationally representative populations.
• Repeated cross-sectional design: some children could appear in both waves; cohorts were not fully independent. This raises the potential for correlated measures across years without full longitudinal control.
• Visual acuity screening vs. cycloplegic refraction: unaided VA can misclassify refractive status. Without cycloplegia, accommodative error can overestimate apparent myopia.
• Unmeasured behavioral variables: outdoor time, screen time, dietary intake and household activity patterns were not directly measured; inferred mechanisms rely on existing literature.
• Potential secular changes and measurement variability: examiner-related differences or minor protocol deviations could contribute to small between-year differences, though efforts were made to standardize procedures.
• Cross-sectional data preclude definitive causal claims linking home confinement to the observed changes.

Despite these limitations, the age- and sex-specific patterns align with plausible behavioral mechanisms and with findings from other settings, giving weight to the conclusions.

Research gaps and priorities

To build on these findings and guide policy, several research priorities emerge.

• Multisite longitudinal studies: tracking representative cohorts across urban and rural schools to quantify generalizability and long-term tracking of BMI, fitness and refractive error.
• Objective behavior measurement: use accelerometers, light sensors and screen-use logs to quantify the causal chain linking activity, outdoor exposure and myopia progression.
• Intervention trials: randomized or quasi-experimental evaluations of home-based PE programs (e.g., rope-jumping curricula, outdoor-break prescriptions) to test efficacy in preserving fitness and preventing myopia.
• Vision diagnostics in school settings: pragmatic studies comparing unaided VA screening, autorefraction, and cycloplegic refraction in the same populations to determine best practice for school screening programs.
• Developmental timing: research that pinpoints sensitive windows (by month, not just by year) for motor and ocular development would refine age-targeted interventions.

What schools and health systems should measure going forward

• Routine surveillance: continue annual school-based fitness and vision screening using standardized protocols; add brief behavioral questionnaires on outdoor time and screen use.
• Early-warning indicators: track BMI-for-age z-scores and rates of deterioration in sit-and-reach among the youngest grades; rising rates should trigger programmatic responses.
• Referral pathways: establish clear referral mechanisms from school screening to community pediatricians, dietitians, and eye care professionals for confirmatory testing and treatment.

Final synthesis: targeted, practical steps to reduce long-term harm

The pandemic’s disruption to children’s daily life produced mixed effects: some fitness components were preserved or improved (rope-jumping), while others—flexibility in the youngest children and BMI increases—worsened, and suspected myopia rose among selected age-sex groups. The heterogeneity matters: responses must be tailored by age and sex and must address both physical activity and visual environments.

Concrete, evidence-aligned steps:

• Prioritize younger primary grades for activity catch-up and targeted monitoring.
• Promote home-friendly, space-efficient daily activity modules—jump rope, dynamic mobility and short cardio bursts.
• Reintroduce and protect outdoor time in school schedules as a measured public-health priority.
• Strengthen vision screening programs and ensure timely access to diagnostic refraction.
• Combine physical-activity promotion with healthy dietary guidance to control rapid BMI increases.

Protective measures are feasible and affordable. Simple changes in school timetabling, teacher training and parent guidance can preserve motor development and vision health when large-scale disruptions recur.

FAQ

Q: How reliable are the reported increases in suspected myopia? A: The screening used unaided distance visual acuity, a standard and practical school-based method. It is a reliable surveillance tool but cannot replace cycloplegic refraction for clinical diagnosis. Population-level increases in unaided VA impairment suggest altered visual stressors and warrant confirmatory testing with cycloplegia for individuals flagged during screening.

Q: Should parents be alarmed about BMI increases observed during the pandemic year? A: The increases—particularly among younger children—are concerning because early childhood BMI elevation tends to persist. Parents should act by increasing daily physical activity opportunities, improving dietary patterns, and using structured routines that limit sedentary and snacking behaviors. Small, consistent changes can reverse short-term gains.

Q: Why did rope-jumping performance improve despite lockdowns? A: Jump rope is space- and equipment-efficient and was widely recommended in home-based PE guidance. Regular short practice sessions can quickly improve coordination and muscular endurance, which explains improvements in many age groups. This demonstrates that well-chosen home activities can preserve or enhance specific skills.

Q: Why did flexibility decline mainly among the youngest children? A: Younger children rely more on structured and guided play to develop flexibility and motor skills. Without school-based stretching, games and guided activities during home confinement, flexibility—particularly hamstring extensibility measured by sit-and-reach—can decline more rapidly in this group.

Q: What practical steps reduce myopia risk when children study online? A: Encourage regular outdoor time (ideally accumulating around 1–2 hours daily when feasible), limit continuous near-screen sessions to 25–30 minutes with movement and visual-rest breaks, ensure good ambient lighting during study, and schedule routine eye checks. Schools should incorporate visual-rest guidance into online lesson plans.

Q: Are the study results generalizable beyond this one rural school? A: The study offers context-specific evidence from a rural area; patterns align with reports from other countries and regions, but generalization to urban settings or other communities requires caution. Larger, multi-center studies would determine how representative these findings are at regional or national scales.

Q: If schools close again, what should administrators prioritize? A: Maintain daily structured physical activities that students can do at home, preserve or create outdoor time options where safe, provide teacher-led virtual PE sessions emphasizing mobility and flexibility, and continue vision screening programs with clear referral pathways.

Q: What further assessments should be added to school screenings? A: Adding brief standardized behavioral questions about outdoor time, screen time and sleep to screenings would improve interpretation and enable targeted interventions. For vision, establishing periodic access to confirmatory cycloplegic refraction for high-risk students strengthens clinical follow-up.

Q: How quickly can children recover lost fitness or reverse early BMI increases? A: Young children respond well to consistent increases in activity and improved diet. With structured increases in MVPA and healthier meals, improvements in BMI and fitness measures can be observed over months. However, earlier intervention yields faster recovery and reduces the risk of longer-term tracking.

Q: What research will clarify the long-term consequences of the pandemic on child health? A: Longitudinal cohort studies that follow children through adolescence, with objective measures of activity, light exposure and refractive error, will clarify persistence of the observed changes and their health consequences. Randomized interventions testing home-friendly activity programs and outdoor-time prescriptions will establish effective mitigation strategies.