Changes in physical activity and the association between pain and physical activity - a longitudinal analysis of 17,454 patients with knee or hip osteoarthritis from the GLA:D® registry.

OBJECTIVE: Investigate change in physical activity following an 8-week education and exercise therapy program for patients with knee/hip osteoarthritis, focusing on those with low physical activity level. Furthermore, to evaluate associations between changes in pain intensity and physical activity. METHOD: Data from the Good Life with osteoArthritis in Denmark (GLA:D®) registry, at baseline, immediately after completion, and 12 months after entering the program was used. Measures of interest were UCLA activity scale (1-10) and Visual Analog Scale for pain intensity (0-100 mm). Changes in physical activity levels (low 1-4, moderate 5-6, and high 7-10) over three time points were investigated. Asymmetric fixed effects regression models were used to evaluate the association between clinically relevant change in pain (≥15 mm) and change in physical activity level from baseline to 12 months. RESULTS: 37% with low activity level at baseline (n = 4,836) and 69% of all patients (n = 17,454) reached or maintained at least a moderate physical activity level at follow-ups. Surprisingly, both an improvement (ß = 1.44, P < 0.001) and a worsening (ß = 1.18, P < 0.001) in pain intensity was associated with increased physical activity in low activity patients. For all patients a similar trend was observed (ß = 0.51, P < 0.001 and ß = 0.11, P = 0.215, respectively). CONCLUSION: In low active knee or hip OA patients, a third of patients participating in an education and exercise therapy program reached and maintained at least a moderate physical activity level for 1 year. The improvement in physical activity was not dependent on pain reduction.

Machine learning augmented near-infrared spectroscopy: In vivo follow-up of cartilage defects.

OBJECTIVE: To assess the potential of near-infrared spectroscopy (NIRS) for in vivo arthroscopic monitoring of cartilage defects. METHOD: Sharp and blunt cartilage grooves were induced in the radiocarpal and intercarpal joints of Shetland ponies and monitored at baseline (0 weeks) and at three follow-up timepoints (11, 23, and 39 weeks) by measuring near-infrared spectra in vivo at and around the grooves. The animals were sacrificed after 39 weeks and the joints were harvested. Spectra were reacquired ex vivo to ensure reliability of in vivo measurements and for reference analyses. Additionally, cartilage thickness and instantaneous modulus were determined via computed tomography and mechanical testing, respectively. The relationship between the ex vivo spectra and cartilage reference properties was determined using convolutional neural network. RESULTS: In an independent test set, the trained networks yielded significant correlations for cartilage thickness (ρ = 0.473) and instantaneous modulus (ρ = 0.498). These networks were used to predict the reference properties at baseline and at follow-up time points. In the radiocarpal joint, cartilage thickness increased significantly with both groove types after baseline and remained swollen. Additionally, at 39 weeks, a significant difference was observed in cartilage thickness between controls and sharp grooves. For the instantaneous modulus, a significant decrease was observed with both groove types in the radiocarpal joint from baseline to 23 and 39 weeks. CONCLUSION: NIRS combined with machine learning enabled determination of cartilage properties in vivo, thereby providing longitudinal evaluation of post-intervention injury development. Additionally, radiocarpal joints were found more vulnerable to cartilage degeneration after damage than intercarpal joints.

T2* and quantitative susceptibility mapping in an equine model of post-traumatic osteoarthritis: assessment of mechanical and structural properties of articular cartilage.

OBJECTIVE: To investigate the potential of quantitative susceptibility mapping (QSM) and T2* relaxation time mapping to determine mechanical and structural properties of articular cartilage via univariate and multivariate analysis. METHODS: Samples were obtained from a cartilage repair study, in which surgically induced full-thickness chondral defects in the stifle joints of seven Shetland ponies caused post-traumatic osteoarthritis (14 samples). Control samples were collected from non-operated joints of three animals (6 samples). Magnetic resonance imaging (MRI) was performed at 9.4 T, using a 3-D multi-echo gradient echo sequence. Biomechanical testing, digital densitometry (DD) and polarized light microscopy (PLM) were utilized as reference methods. To compare MRI parameters with reference parameters (equilibrium and dynamic moduli, proteoglycan content, collagen fiber angle and -anisotropy), depth-wise profiles of MRI parameters were acquired at the biomechanical testing locations. Partial least squares regression (PLSR) and Spearman's rank correlation were utilized in data analysis. RESULTS: PLSR indicated a moderate-to-strong correlation (ρ = 0.49-0.66) and a moderate correlation (ρ = 0.41-0.55) between the reference values and T2* relaxation time and QSM profiles, respectively (excluding superficial-only results). PLSR correlations were noticeably higher than direct correlations between bulk MRI and reference parameters. 3-D parametric surface maps revealed spatial variations in the MRI parameters between experimental and control groups. CONCLUSION: Quantitative parameters from 3-D multi-echo gradient echo MRI can be utilized to predict the properties of articular cartilage. With PLSR, especially the T2* relaxation time profile appeared to correlate with the properties of cartilage. Furthermore, the results suggest that degeneration affects the QSM-contrast in the cartilage. However, this change in contrast is not easy to quantify.

Does adiposity mediate the relationship between physical activity and biological risk factors in youth?: a cross-sectional study from the International Children's Accelerometry Database (ICAD).

BACKGROUND/OBJECTIVES: To model the association between accumulating 60 daily minutes of moderate-to-vigorous physical activity and a composite score of biological risk factors into a direct and an indirect effect, using abdominal obesity as the mediator. SUBJECTS/METHODS: Cross-sectional data from the International Children's Accelerometry Database (ICAD) including 6-18-year-old children and adolescents (N=3412) from 4 countries providing at least 3 days of accelerometry-assessed physical activity. A standardized composite risk score was calculated from systolic blood pressure and fasting blood samples of insulin, glucose, triacylglycerol and inverse HDL-cholesterol. Abdominal obesity was assessed by the waist-circumference:height ratio. Two-stage regression analysis, allowing for exposure-mediator interaction, was used for the effect decomposition. RESULTS: Participants achieving 60 daily minutes of moderate-to-vigorous physical activity had a 0.31 (95% CI: -0.39, -0.23) standard deviations lower composite risk score than those achieving less than 60 min. Modelling the associations suggested that 0.24 standard deviations (95% CI: -0.32, -0.16) was attributed to the direct effect and -0.07 (95% CI: -0.11, -0.02) to the indirect effect indicating that 22% of the total effect was mediated by central adiposity. Modelling 30 and 90 min of moderate-to-vigorous physical activity per day resulted in changes in the direct but not the indirect effect. CONCLUSIONS: One hour of daily moderate-to-vigorous physical activity was associated with clinically relevant differences in metabolic control compared to engagement in less than this minimally recommended amount. The majority of the difference was explained by the direct effect of physical activity.International Journal of Obesity advance online publication, 31 October 2017; doi:10.1038/ijo.2017.241.

Motor competence and cardiorespiratory fitness have greater influence on body fatness than physical activity across time.

We investigated the longitudinal associations among physical activity (PA), motor competence (MC), cardiorespiratory fitness (VO2peak ), and body fatness across 7 years, and also analyzed the possible mediation effects of PA, MC, and VO2peak on the relationships with body fatness. This was a seven-year longitudinal study with three measuring points (mean ages [in years] and respective sample size: 6.75±0.37, n=696; 9.59±1.07, n=617; 13.35±0.34, n=513). PA (moderate-to-vigorous PA-MVPA and vigorous PA-VPA) was monitored using accelerometers. MC was assessed by the "Körperkoordinationstest für Kinder-KTK" test battery. VO2peak was evaluated using a continuous running protocol until exhaustion. Body fatness was determined by the sum of four skinfolds. Structural equation modeling was performed to evaluate the longitudinal associations among PA, MC, VO2peak, and body fatness and the potential mediation effects of PA, MC, and VO2peak . All coefficients presented were standardized (z-scores). MC and VO2peak directly influenced the development of body fatness, and VO2peak mediated the associations between MVPA, VPA, MC, and body fatness. MC also mediated the associations between MVPA, VPA, and body fatness. In addition, VO2peak had the largest total association with body fatness (ß=-0.431; P<.05), followed by MC (ß=-0.369; P<.05) and VPA (ß=-0.112; P<.05). As PA, MC, and VO2peak exhibited longitudinal association with body fatness, it seems logical that interventions should strive to promote the development of fitness and MC through developmentally appropriate physical activities, as the synergistic interactions of all three variables impacted body fatness.

Estimation of articular cartilage properties using multivariate analysis of optical coherence tomography signal.

OBJECTIVE: The aim was to investigate the applicability of multivariate analysis of optical coherence tomography (OCT) information for determining structural integrity, composition and mechanical properties of articular cartilage. DESIGN: Equine osteochondral samples (N = 65) were imaged with OCT, and their total attenuation and backscattering coefficients (µt and µb) were measured. Subsequently, the Mankin score, optical density (OD) describing the fixed charge density, light absorbance in amide I region (Aamide), collagen orientation, permeability, fibril network modulus (Ef) and non-fibrillar matrix modulus (Em) of the samples were determined. Partial least squares (PLS) regression model was calculated to predict tissue properties from the OCT signals of the samples. RESULTS: Significant correlations between the measured and predicted mean collagen orientation (R(2) = 0.75, P < 0.0001), permeability (R(2) = 0.74, P < 0.0001), mean OD (R(2) = 0.73, P < 0.0001), Mankin scores (R(2) = 0.70, P < 0.0001), Em (R(2) = 0.50, P < 0.0001), Ef (R(2) = 0.42, P < 0.0001), and Aamide (R(2) = 0.43, P < 0.0001) were obtained. Significant correlation was also found between µb and Ef (ρ = 0.280, P = 0.03), but not between µt and any of the determined properties of articular cartilage (P > 0.05). CONCLUSION: Multivariate analysis of OCT signal provided good estimates for tissue structure, composition and mechanical properties. This technique may significantly enhance OCT evaluation of articular cartilage integrity, and could be applied, for example, in delineation of degenerated areas around cartilage injuries during arthroscopic repair surgery.

Objectively measured physical activity in Danish after-school cares: Does sport certification matter?

Inactivity and more sedentary time predominate the daily activity level of many of today's children. In Denmark, certified sport after-school cares have been established in order to increase children's daily physical activity (PA) level. This cross-sectional study aimed to investigate the activity level among participants in certified sport after-school cares vs regular after-school cares. The study was carried out in 2011 in 10 after-school cares (5 sport/5 regular) throughout Denmark, whereof 475 children aged 5-11 years participated. PA level was assessed using Actigraph GT3X and GT3X+ activity monitors worn by the children for at least 8 consecutive days. Anthropometry and cardiorespiratory fitness were measured as well. A multivariate regression analysis was carried out to check for the differences in the PA level across the two care systems. However, there did not appear to be any differences in overall PA or in time-specific day parts (e.g., during after-school care). The activity levels were quite similar across after-school cares and were mutually high during time spent in the care facility.

Effects of extra school-based physical education on overall physical fitness development--the CHAMPS study DK.

First, this study aimed to investigate if four extra physical education (PE) lessons per week improved children's development in physical fitness. Second, to investigate if the extra PE lessons improved development in physical fitness for children with lower levels of fitness at baseline. This study was a longitudinal controlled school-based study. The study population consisted of 10 Danish public schools with children in preschool to fourth grade (cohorts 0-4) with 2.5-year follow-up. Six schools had extra PE and four schools had normal PE. In total 1247 children were included (normal PE = 536, extra PE = 711). Development in fitness was analyzed using a composite z-score from six fitness tests. Multilevel mixed-effects linear regression was used to examine the association between school type and development in fitness. Extra PE increased the total development of composite z-score units among children enrolled in cohort 4 and borderline in cohort 3 with 1.06 (95% confidence interval 0.48-1.65) and 0.52 z-score units (-0.06 to 1.09), respectively. Children in the lower 50 percentiles increased their development with 0.47 (0.08-0.85) z-score units. Extra PE in schools improved development in fitness for cohort 4 and borderline for cohort 3 among all children. Extra PE improved fitness development across all cohorts among children with low fitness levels.

Associations between bicycling and carotid arterial stiffness in adolescents: The European Youth Hearts Study.

The aim of the study was to investigate the associations between bicycling and carotid arterial stiffness, independent of objectively measured moderate-and-vigorous physical activity. This cross-sectional study included 375 adolescents (age 15.7 ± 0.4 years) from the Danish site of the European Youth Heart Study. Total frequency of bicycle usage was assessed by self-report, and carotid arterial stiffness was assessed using B-mode ultrasound. After adjusting for pubertal status, body height, and objectively measured physical activity and other personal lifestyle and demographic factors, boys using their bicycle every day of the week displayed a higher carotid arterial compliance {standard beta 0.47 [95% confidence interval (CI) 0.07-0.87]} and distension [standard beta 0.38 (95% CI -0.04 to 0.81)]. Boys using their bicycle every day of the week furthermore displayed a lower Young's elastic modulus [standard beta -0.48 (95% CI -0.91 to -0.06)]. Similar trends were observed when investigating the association between commuter bicycling and carotid arterial stiffness. These associations were not observed in girls. Our observations suggest that increasing bicycling in adolescence may be beneficial to carotid arterial health among boys.

Musculoskeletal extremity injuries in a cohort of schoolchildren aged 6-12: a 2.5-year prospective study.

The objectives of this prospective school cohort study were to describe the epidemiology of diagnosed musculoskeletal extremity injuries and to estimate the injury incidence rates in relation to different settings, different body regions and injury types. In all, 1259 schoolchildren, aged 6-12, were surveyed weekly during 2.5 years using a new method of automated mobile phone text messaging asking questions on the presence of any musculoskeletal problems. All injuries were clinically diagnosed. Physical activity was measured from text messaging and accelerometers. A total number of 1229 injuries were diagnosed; 180 injuries in the upper extremity and 1049 in the lower extremity, with an overall rate of 1.59 injuries per 1000 physical activity units [95% confidence interval (CI) 1.50-1.68]. Upper extremities accounted for a rate of 0.23 (95% CI 0.20-0.27) and lower extremities accounted for 1.36 (95% CI 1.27-1.44). This study has added a wide overall perspective to the area concerning incidence and incidence rates of musculoskeletal extremity injuries in schoolchildren aged 6-12 years, including severe and less severe, traumatic, and overuse injuries. The understanding of injury epidemiology in children is fundamental to the acknowledgement and insurance of the appropriate prevention and treatment.

The effects of physical activity and exercise on brain-derived neurotrophic factor in healthy humans: A review.

The purpose of this study was to summarize the effects of physical activity and exercise on peripheral brain-derived neurotrophic factor (BDNF) in healthy humans. Experimental and observational studies were identified from PubMed, Web of Knowledge, Scopus, and SPORT Discus. A total of 32 articles met the inclusion criteria. Evidence from experimental studies suggested that peripheral BDNF concentrations were elevated by acute and chronic aerobic exercise. The majority of the studies suggested that strength training had no influence on peripheral BDNF. The results from most observational studies suggested an inverse relationship between the peripheral BDNF level and habitual physical activity or cardiorespiratory fitness. More research is needed to confirm the findings from the observational studies.

Prospective association of adiposity and cardiorespiratory fitness with cardiovascular risk factors in healthy children.

This study aimed to examine the prospective association of three different measures of adiposity and cardiorespiratory fitness (CRF) with 2-year change in cardiovascular disease (CVD) risk factors in children. Two-year longitudinal data in schoolchildren aged 7-11 years (n = 365-729) was used. Total body fat (TBF) from dual-energy x-ray absorptiometry, body mass index (BMI), waist circumference (WC), CRF, blood samples, and blood pressure were obtained in 2008 and 2010 in the Childhood Health, Activity, and Motor Performance School Study in Denmark (CHAMPS study-DK). Greater adiposity at baseline was associated with increased CVD risk factor levels at follow-up. The magnitudes of associations were similar regardless of adiposity measure [TBF%: ß 0.30, 95% confidence interval (CI): 0.21-0.39; BMI: ß 0.24, 95% CI: 0.14-0.33; WC: ß 0.20, 95% CI: 0.10-0.31], and no evidence of nonlinear relationships was observed. We found less strong associations of CRF with increase in CVD risk factor levels after adjusting for adiposity; however, increasing CRF was still favorably associated with decrease in CVD risk factor levels among boys. Results suggest that any effort to shift the population distribution of adiposity downward would be valuable for early CVD prevention. The association of CRF with CVD risk factors was largely explained by adiposity, particularly among girls.

Secular trends in physical fitness in Danish adolescents.

It is important to monitor changes over time in aerobic fitness and obesity in order to target interventions when health deteriorates. We analyzed data from three population studies of adolescents carried out in 1983, 1997, and 2003. Participants were 1050 adolescents from the whole country of Denmark in 1983, 410 in 1997, and 418 in 2003, the two latter cohorts from the City of Odense. VO(2max) was estimated from maximal power output (MPO) in a cycle test with progressively increasing workload. Estimated VO(2max) for boys and girls was 52 and 41 mL/min/kg, respectively, both in 1983, 1997, and 2003 with no difference between the three cohorts. However, body mass index (BMI) increased 10% in the upper decentile of the distribution since 1983. MPO decreased over time, but validation studies showed that this was not due to decreased VO(2max) . The cohort from 1983 was tested twice by school teachers and experienced scientists, and the scientists found higher MPO than school teachers in the same subjects, which emphasize the importance of good validation studies.

Objectively measured habitual physical activity in 1997/1998 vs 2003/2004 in Danish children: the European Youth Heart Study.

Based on two cross-sectional studies conducted in 8-10-year-old third-grade children living in the municipality of Odense, potential differences were examined in the level of habitual physical activity (HPA) in Danish children between 1997/1998 and 2003/2004. HPA was assessed objectively by accelerometry. Primarily, overall differences were analyzed as gender and day type specific (i.e. Mon-Thu vs Fri-Sun) levels in HPA. Secondarily, differences were analyzed across socioeconomic gradients defined according to parents' occupation. Data were expressed as total counts per registered time. During the period 1997/1998-2003/2004, no significant differences were observed in the level of HPA during Mon-Thu or Fri-Sun or across socioeconomic gradients. Post hoc analyses indicated a slightly more favorable ratio between the percentages of time spent in light and moderate intensity levels during Mon-Thu in 2003/2004 when compared with 1997/1998. Gender differences in the level of HPA were found to be more distinct during Mon-Thu than during Fri-Sun. This study does not support the idea that Danish children are becoming less physically active. However, a limited statistical power should be considered when interpreting differences across socioeconomic gradients. Boys were found to be more physically active than girls, especially during the weekdays (Friday not included).

Semi-automated International Cartilage Repair Society scoring of equine articular cartilage lesions in optical coherence tomography images.

BACKGROUND: Arthroscopic optical coherence tomography (OCT) is a promising tool for the detailed evaluation of articular cartilage injuries. However, OCT-based articular cartilage scoring still relies on the operator's visual estimation. OBJECTIVES: To test the hypothesis that semi-automated International Cartilage Repair Society (ICRS) scoring of chondral lesions seen in OCT images could enhance intra- and interobserver agreement of scoring and its accuracy. STUDY DESIGN: Validation study using equine cadaver tissue. METHODS: Osteochondral samples (n = 99) were prepared from 18 equine metacarpophalangeal joints and imaged using OCT. Custom-made software was developed for semi-automated ICRS scoring of cartilage lesions on OCT images. Scoring was performed visually and semi-automatically by five observers, and levels of inter- and intraobserver agreement were calculated. Subsequently, OCT-based scores were compared with ICRS scores based on light microscopy images of the histological sections of matching locations (n = 82). RESULTS: When semi-automated scoring of the OCT images was performed by multiple observers, mean levels of intraobserver and interobserver agreement were higher than those achieved with visual OCT scoring (83% vs. 77% and 74% vs. 33%, respectively). Histology-based scores from matching regions of interest agreed better with visual OCT-based scoring than with semi-automated OCT scoring; however, the accuracy of the software was improved by optimising the threshold combinations used to determine the ICRS score. MAIN LIMITATIONS: Images were obtained from cadavers. CONCLUSIONS: Semi-automated scoring software improved the reproducibility of ICRS scoring of chondral lesions in OCT images and made scoring less observer-dependent. The image analysis and segmentation techniques adopted in this study warrant further optimisation to achieve better accuracy with semi-automated ICRS scoring. In addition, studies on in vivo applications are required.

Arthroscopic optical coherence tomography provides detailed information on articular cartilage lesions in horses.

Arthroscopy enables direct inspection of the articular surface, but provides no information on deeper cartilage layers. Optical coherence tomography (OCT), based on measurement of reflection and backscattering of light, is a diagnostic technique used in cardiovascular surgery and ophthalmology. It provides cross-sectional images at resolutions comparable to that of low-power microscopy. The aim of this study was to determine if OCT is feasible for advanced clinical assessment of lesions in equine articular cartilage during diagnostic arthroscopy. Diagnostic arthroscopy of 36 metacarpophalangeal joints was carried out ex vivo. Of these, 18 joints with varying degrees of cartilage damage were selected, wherein OCT arthroscopy was conducted using an OCT catheter (diameter 0.9 mm) inserted through standard instrument portals. Five sites of interest, occasionally supplemented with other locations where defects were encountered, were arthroscopically graded according to the International Cartilage Repair Society (ICRS) classification system. The same sites were evaluated qualitatively (ICRS classification and morphological description of the lesions) and quantitatively (measurement of cartilage thickness) on OCT images. OCT provided high resolution images of cartilage enabling determination of cartilage thickness. Comparing ICRS grades determined by both arthroscopy and OCT revealed poor agreement. Furthermore, OCT visualised a spectrum of lesions, including cavitation, fibrillation, superficial and deep clefts, erosion, ulceration and fragmentation. In addition, with OCT the arthroscopically inaccessible area between the dorsal MC3 and P1 was reachable in some cases. Arthroscopically-guided OCT provided more detailed and quantitative information on the morphology of articular cartilage lesions than conventional arthroscopy. OCT could therefore improve the diagnostic value of arthroscopy in equine orthopaedic surgery.

Hemodynamic variables during exercise in childhood and resting systolic blood pressure levels 6 years later in adolescence: the European Youth Heart Study.

The aim of this study was to analyze whether systolic blood pressure (SBP), heart rate (HR) and rate pressure product (RPP) during exercise in childhood can predict resting SBP levels in adolescence independent of resting SBP and conventional cardiovascular risk factors. We studied this in a sample of Danish children followed longitudinally for 6 years. The study comprised 226 children randomly sampled at age 9, who had their blood pressure and HR measured during ergometer exercise to exhaustion and was reassessed in adolescence. SBP and RPP during exercise in stage two of the test were positively associated with future resting SBP, independent of resting SBP in childhood (P=0.045 and P=0.013, respectively). After additional adjustment for conventional cardiovascular risk factors the associations with SBP and RPP during stage two on future resting SBP only slightly materially change, although only RPP remained significant (P=0.059 and P=0.012, respectively). No significant independent associations were observed for HR during exercise, but associations were in the same direction. Our results supports that measuring SBP and RPP, during a standard acute ergometer exercise test in children, improves the prediction of future SBP levels during rest in adolescence independent of resting SBP and conventional cardiovascular risk factors.

Sources of variation in habitual physical activity of children and adolescents: the European youth heart study.

The present study examined the influence of gender, maturity state, seasonality, type of measurement day and socioeconomic status (SES) on habitual physical activity in 8-10-year-old children and 14-16-year-old adolescents (n=1318). Physical activity was assessed objectively by accelerometry. The results showed a significant effect of the type of measurement day on physical activity with a general pattern of lower activity levels in weekends compared with weekdays. Furthermore, higher physical activity levels were observed during the months of spring/summer compared with the months of autumn/winter for the 8-10-year-olds, whereas no significant effect of months was observed for the 14-16-year-olds, possibly due to exam preparations and lack of physical activity registration during the months of summer for this cohort. SES was unrelated to physical activity in the 8-10-year-olds, whereas an inverse association was observed in the 14-16-year-olds. However, a post hoc analysis provided strong evidence that this latter result was biased by the accelerometers inability to pick up bicycling activities. Finally, boys were more physically active compared with girls, and maturity state was unrelated to physical activity. The results could prove useful for working out strategies to prevent inactivity and for adjusting for temporal sources of variation in physical activity in future studies.

Tracking of objectively measured physical activity from childhood to adolescence: the European youth heart study.

A number of studies have investigated tracking of physical activity from childhood to adolescence and, in general, these studies have been based on methods with some degree of subjectivity (e.g., questionnaires). The aim of the present study was to evaluate tracking of physical activity from childhood to adolescence using accelerometry, taking into account major sources of variation in physical activity. Both a crude and an adjusted model was fitted, and, in the adjusted model, analyses were corrected for seasonal variation, within-week variation, activity registration during night time sleep, within instrumental measurement error, and day-to-day variation in physical activity. In all, 208 subjects were included in the crude analyses. Stability coefficients estimated from the crude model were low (i.e., 0.18 and 0.19 for boys and girls, respectively) and only borderline significant. However, in the adjusted model highly significant stability coefficients of 0.53 and 0.48 for boys and girls, respectively, were observed. It was concluded that physical activity behavior tends to track moderately from childhood to adolescence.

Secular trends in cardiorespiratory fitness and body mass index in Danish children: The European Youth Heart Study.

AIM: To examine the secular trends in cardiorespiratory fitness (CF) and body fatness in Danish children. Trends were analyzed overall and across socioeconomic status (SES). METHODS: Two cross-sectional studies conducted on 589 and 458 third-grade Danish children in 1997-1998 and 2003-2004, respectively. CF was determined by a maximal cycle-ergometer test. The lowest sex-specific quartile of CF in the study from 1997 to 1998 was used as a cut-point for low CF. Body mass index (BMI) cut-points were used to describe overweight, and SES was divided into two groups according to parents' occupation. RESULTS: This study showed a secular decline in CF in girls overall. Increased CF, BMI, and prevalence of overweight were observed in boys with high SES, in boys with low SES, and in girls with low SES, respectively. However, after additional Bonferroni's correction, none of the statistical analyses performed across socioeconomic gradients reached significant P-values. CONCLUSION: CF declined in girls overall. Although not statistically significant after additional Bonferroni's correction, results in general showed less favorable trends in low SES children. Thus, trying to describe secular trends in CF and body fatness overall without any regard to SES might disguise social-caused differences. However, further studies are needed in order to verify this hypothesis.