Background: A better understanding of the effects of the lockdown on lifestyle behaviors may help to guide the public health response to COVID-19 at a national level and to update the global strategy to respond COVID-19 pandemic. The aim of the study was to examine the effects of the COVID-19 lockdown on device-measured physical activity (PA), sedentary time, sleep and self-regulation; and to determine whether PA and sleep are related to self-regulation problems during the lockdown. Methods: PA, sedentary time and sleep were assessed using accelerometry in the week in which the Spanish national state of alarm was declared (n = 21). Parents reported preschooler’s self-regulation difficulties (internalizing and externalizing) before (n = 268) and during the lockdown (n = 157) by a validated questionnaire. Results: Preschoolers showed a decrease in total PA (mean difference [MD] = −43.3 min per day, 95% CI −68.1 to −18.5), sleep efficiency (MD = −2.09%, 95% CI −4.12 to −0.05), an increase in sedentary time (MD = 50.2 min per day, 95% CI 17.1 to 83.3) internalizing (MD = 0.17, 95% CI 0.06 to 0.28) and externalizing (MD = 0.33, 95% CI 0.23 to 0.44) problems. Preschoolers who met the World Health Organization recommendations for PA had lower internalizing scores than non-active peers (MD = −1.28, 95% CI −2.53 to −0.03). Conclusions: Our findings highlight the importance of meeting PA recommendations to reduce psychosocial difficulties during a lockdown situation.

IMPORTANCE Although the associations between cardiorespiratory fitness (CRF) and health in adults are well understood, to date, no systematic review has quantitatively examined the association between CRF during youth and health parameters later in life.OBJECTIVES To examine the prospective association between CRF in childhood and adolescence and future health status and to assess whether changes in CRF are associated with future health status at least 1 year later.DATA SOURCES For this systematic review and meta-analysis, MEDLINE, Embase, and SPORTDiscus electronic databases were searched for relevant articles published from database inception to January 30, 2020. STUDY SELECTIONThe following inclusion criteria were used: CRF measured using a validated test and assessed at baseline and/or its change from baseline to the end of follow-up, healthy population with a mean age of 3 to 18 years at baseline, and prospective cohort design with a follow-up period of at least 1 year.DATA EXTRACTION AND SYNTHESIS Data were processed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Random-effects models were used to estimate the pooled effect size. MAIN OUTCOMES AND MEASURES Anthropometric and adiposity measurements and cardiometabolic health parameters.RESULTS Fifty-five studies were included with a total of 37 563 youths (46% female). Weak-moderate associations were found between CRF at baseline and body mass index (r = -0.11; 95% CI, -0.18 to -0.04; I 2 = 59.03), waist circumference (r = -0.29; 95% CI, -0.42 to -0.14; I 2 = 69.42), skinfold thickness (r = -0.34; 95% CI, -0.41 to -0.26; I 2 = 83.87), obesity (r = -0.15; 95% CI, -0.23 to -0.06; I 2 = 86.75), total cholesterol level (r = -0.12; 95% CI, -0.19 to -0.05; I 2 = 75.81), high-density lipoprotein cholesterol (HDL-C) level (r = 0.11; 95% CI, 0.05-0.18; I 2 = 69.06), total cholesterol to HDL-C ratio (r = -0.19; 95% CI, -0.26 to -0.13; I 2 = 67.07), triglyceride levels (r = -0.10; 95% CI, -0.18 to -0.02; I 2 = 73.43), homeostasis model assessment for insulin resistance (r = -0.12; 95% CI, -0.18 to -0.06; I 2 = 68.26), fasting insulin level (r = -0.07; 95% CI, -0.11 to -0.03; I 2 = 0), and cardiometabolic risk (r = -0.18; 95% CI, -0.29 to -0.07; I 2 = 90.61) at follow-up. Meta-regression analyses found that early associations in waist circumference (β = 0.014; 95% CI, 0.002-0.026), skinfold thickness (β = 0.006; 95% CI, 0.002-0.011), HDL-C level (β = −0.006; 95% CI, −0.011 to −0.001), triglyceride levels (β = 0.009; 95% CI, 0.004-0.014), and cardiometabolic risk (β = 0.007; 95% CI, 0.003-0.011) from baseline to follow-up dissipated over time. Weak-moderate associations were found between change in CRF and body mass index (r = -0.17; 95% CI, -0.24 to -0.11; I 2 = 39.65), skinfold thickness (r = -0.36; 95% CI, -0.58 to -0.09; I 2 = 96.84), obesity (r = -0.21; 95% CI, -0.35 to -0.06; I 2 = 91.08), HDL-C level (r = 0.05; 95% CI, 0.02-0.08; I 2 = 0), low-density lipoprotein cholesterol level (r = -0.06; 95% CI, -0.11 to -0.01; I...