Tracking of bone mass from childhood to puberty: a 7-year follow-up. The CHAMPS study DK.

Bone mass in childhood is highly influenced by puberty. At the same age, bone mass was higher for pubertal than pre-pubertal children. A high level of tracking during 7 years from childhood through puberty was shown, indicating that early levels of bone mass may be important for later bone health. INTRODUCTION: Bone mass development in childhood varies by sex and age, but also by pubertal stage. The objectives of this study were to (1) describe bone mass development in childhood as it relates to pubertal onset and to (2) determine the degree of tracking from childhood to adolescence. METHODS: A longitudinal study with 7 years of follow-up was initiated in 2008 to include 831 children (407 boys) aged 8 to 17 years. Participants underwent whole body dual-energy X-ray absorptiometry (DXA) scanning, blood collection to quantify luteinizing hormone levels, and Tanner stage self-assessment three times during the 7-year follow-up. Total body less head bone mineral content, areal bone mineral density, and bone area were used to describe development in bone accrual and to examine tracking over 7 years. RESULTS: Bone mass in pubertal children is higher than that of pre-pubertal children at the same age. Analysing tracking with quintiles of bone mass Z-scores in 2008 and 2015 showed that more than 80% of participants remained in the same or neighbouring quintile over the study period. Tracking was confirmed by correlation coefficients between Z-scores at baseline and 7-year follow-up (range, 0.80-0.84). CONCLUSIONS: Bone mass is highly influenced by pubertal onset, and pubertal stage should be considered when examining children's bone health. Because bone mass indices track from childhood into puberty, children with low bone mass may be at risk of developing osteoporosis later in life.

The inter- and intrarater reliability and agreement for field-based assessment of scapular control, shoulder range of motion, and shoulder isometric strength in elite adolescent athletes.

OBJECTIVES: To investigate the intra- and interrater reliability and agreement for field-based assessment of scapular control, shoulder range of motion (ROM), and shoulder isometric strength in elite youth athletes. DESIGN: Test-retest reliability and agreement study. SETTING: Eight blinded raters (two for each assessment) assessed players on field during two testing sessions separated by one week. PARTICIPANTS: 162 elite youth handball players with or without a history of previous shoulder pain within the preceding six months. MAIN OUTCOME MEASURES: Kappa (κ) and prevalence-adjusted bias-adjusted kappa (PABAK) coefficients for scapular control reliability, and 95% limits of agreement (LOA) for ROM and strength agreement. RESULTS: Scapular control demonstrated substantial to almost perfect reliability (κ 0.67 to 0.84, PABAK from 0.68 to 0.88). Mean strength values ranged from 0.9 N/kg to 1.6 N/kg, and LOAs ranged from -0.7 N/kg to 0.8 N/kg. Rotational strength revealed additionally systematic bias between and within rater. No or acceptable systematic bias were evident for ROM and abduction strength measures. Mean values and LOAs for ROM ranged between 39.9° to 52.3°, and from -12.6° to 9.9°, respectively. CONCLUSIONS: Scapular control and ROM can be assessed on the field with acceptable reliability. The threshold for reliable measurements of isometric strength using handheld-dynamometers is high.

Retinal vascular diameters in relation to physical activity in Danish children - The CHAMPS Eye Study.

Our objective was to determine associations between retinal vascular caliber and physical activity (PA) in a school-based child cohort. In a prospective study, we created a childhood cumulative average PA-index using objectively measured PA (accelerometry) assessed at four periods between 2009 and 2015. Cumulative exposure to PA intensities was estimated. Cross-sectional examinations on biomarkers, anthropometry, and ophthalmological data including retinal fundus photographs were performed in 2015. Semi-automated measurements of retinal vascular diameters were performed and summarized into central retinal arteriolar and venular equivalents (CRAE, CRVE). We included 307 participants. Mean age in 2015 was 15.4 years (0.7). The mean CRAE and CRVE were 156.5 µm (2.8) and 217.6 µm (7.7), respectively. After adjusting for age, gender, and axial length, more time in PA was independently related to thinner retinal venules (ß-coefficient = -1.25 µm/%, 95% confidence interval = -2.20, -0.30, P < .01). Sedentary time was associated with wider venules (P < .01). Furthermore, birthweight (ß-coefficient = 0.56 µm/%, 95% confidence interval = 0.18, 0.95, P < .01) was associated with CRVE. Blood pressure was associated with thinner retinal arterioles (ß-coefficient = -0.19 µm/mmHg, 95% confidence interval = -0.36, -0.01, P = .04). We concluded that children with higher PA in childhood had thinner retinal venular caliber. Our results suggest that PA during childhood positively impacts the retinal microcirculation and that retinal vascular analysis may be a possible assessment to detect microvascular impairments in children with an increased risk of future cardiovascular disease.

The SMS, Phone, and medical Examination sports injury surveillance system is a feasible and valid approach to measuring handball exposure, injury occurrence, and consequences in elite youth sport.

Current methods of sports injury surveillance are limited by lack of medical validation of self-reported injuries and/or incomplete information about injury consequences beyond time loss from sport. The aims of this study were to (a) evaluate the feasibility of the SMS, Phone, and medical Examination injury surveillance (SPEx) system (b) to evaluate the proportion of injuries and injury consequences reported by SPEx when compared to outcomes from a modified version of the Oslo Sports Trauma Research Centre (OSTRC) Overuse Injury Questionnaire. We followed 679 elite adolescent handball players over 31 weeks using the SPEx system. During the last 7 weeks, we also implemented a modified OSTRC questionnaire in a subgroup of 271 players via telephone interviews. The weekly response proportions to the primary SPEx questions ranged from 85% to 96% (mean 92%). SMS responses were received from 79% of the participants within 1 day. 95% of reported injuries were classified through the telephone interview within a week, and 67% were diagnosed by medical personnel. Comparisons between reported injuries from SPEx and OSTRC demonstrated fair (κ = 39.5% [25.1%-54.0%]) to substantial prevalence-adjusted bias-adjusted kappa (PABAK = 66.8% [95% CI 58.0%-75.6%]) agreement. The average injury severity score difference between SPEx and the OSTRC approach was -0.2 (95% CI -3.69-3.29) of possible 100 with 95% limits of agreement from(-14.81-14.41). These results support the feasibility and validity of the SPEx injury surveillance system in elite youth sport. Future studies should evaluate the external validity of SPEx system in different cohorts of athletes.

Validity of the SMS, Phone, and medical staff Examination sports injury surveillance system for time-loss and medical attention injuries in sports.

The accurate measurement of sport exposure time and injury occurrence is key to effective injury prevention and management. Current measures are limited by their inability to identify all types of sport-related injury, narrow scope of injury information, or lack the perspective of the injured athlete. The aims of the study were to evaluate the proportion of injuries and the agreement between sport exposures reported by the SMS messaging and follow-up telephone part of the SMS, Phone, and medical staff Examination (SPEx) sports injury surveillance system when compared to measures obtained by trained on-field observers and medical staff (comparison method). We followed 24 elite adolescent handball players over 12 consecutive weeks. Eighty-six injury registrations were obtained by the SPEx and comparison methods. Of them, 35 injury registrations (41%) were captured by SPEx only, 10 injury registrations (12%) by the comparison method only, and 41 injury registrations (48%) by both methods. Weekly exposure time differences (95% limits of agreement) between SPEx and the comparison method ranged from -4.2 to 6.3 hours (training) and -1.5 to 1.0 hours (match) with systematic differences being 1.1 hours (95% CI 0.7 to 1.4) and -0.2 (95% CI -0.3 to -0.2), respectively. These results support the ability of the SPEx system to measure training and match exposures and injury occurrence among young athletes. High weekly response proportions (mean 83%) indicate that SMS messaging can be used for player measures of injury consequences beyond time-loss from sport. However, this needs to be further evaluated in large-scale studies.

Handball load and shoulder injury rate: a 31-week cohort study of 679 elite youth handball players.

BACKGROUND: Knowledge of injury patterns, an essential step towards injury prevention, is lacking in youth handball. AIM: To investigate if an increase in handball load is associated with increased shoulder injury rates compared with a minor increase or decrease, and if an association is influenced by scapular control, isometric shoulder strength or glenohumeral range of motion (ROM). METHODS: 679 players (14-18 years) provided weekly reports on shoulder injury and handball load (training and competition hours) over 31 weeks using the SMS, phone and medical examination system. Handball load in a given week was categorised into (1) <20% increase or decrease (reference), (2) increase between 20% and 60% and (3) increase >60% relative to the weekly average amount of handball load the preceding 4 weeks. Assessment of shoulder isometric rotational and abduction strength, ROM and scapular control was performed at baseline and midseason. RESULTS: An increase in handball load by >60% was associated with greater shoulder injury rate (HR 1.91; 95% CI 1.00 to 3.70, p=0.05) compared with the reference group. The effect of an increase in handball load between 20% and 60% was exacerbated among players with reduced external rotational strength (HR 4.0; 95% CI 1.1 to 15.2, p=0.04) or scapular dyskinesis (HR 4.8; 95% CI 1.3 to 18.3, p=0.02). Reduced external rotational strength exacerbated the effect of an increase above 60% (HR 4.2; 95% CI 1.4 to 12.8, p=0.01). CONCLUSIONS: A large increase in weekly handball load increases the shoulder injury rate in elite youth handball players; particularly, in the presence of reduced external rotational strength or scapular dyskinesis.

Upper extremity injuries in Danish children aged 6-12, mechanisms, and risk factors.

Although injuries to the upper extremity are most costly, the picture of the upper extremity injury problem remains incomplete. This study is the first to describe the etiology and mechanisms of upper extremity injuries in Danish children. A 2.5-year observational prospective cohort study was conducted to record upper extremity injuries in 1048 children. Data were weekly collected by sending a text message. A total of 176 upper extremity injuries were reported (128 acute injuries). Of the acute upper extremity injuries, 55% were sprains, 47% occurred in the hand/wrist, and 53% of cases were caused by a fall. When corrected for exposure to physical activity, this resulted in an acute upper extremity injury incidence density of 0.18 per 1000 h of physical activity. The odds of sustaining an upper extremity injury was higher in the older children (HR: 1.84, 95% CI: 1.10-3.09), a tendency was found suggesting that girls are at increased acute upper extremity risk compared to boys (HR: 1.40 95% CI: 0.97-2.04). The findings that most injuries occur after a fall, that injury risk increases over age and that girls seem to be at increased injury risk provides essential information to guide future childhood injury prevention.

Do number of days with low back pain and patterns of episodes of pain have similar outcomes in a biopsychosocial prediction model?

PURPOSES: We used two different methods to classify low back pain (LBP) in the general population (1) to assess the overlapping of individuals within the different subgroups in those two classifications, (2) to explore if the associations between LBP and some selected bio-psychosocial factors are similar, regardless which of the two classifications is used. METHOD: During 1 year, 49- or 50-year-old people from the Danish general population were sent fortnightly automated text messages (SMS-Track) asking them if they had any LBP in the past fortnight. Responses for the whole year were then classified into two different ways: (1) In relation to the number of days with LBP in the preceding year (0, 1-30, and >30), (2) In relation to the frequency and duration of episodes of LBP (more or less never pain, episodic, and more or less constant pain). Some bio-psychosocial factors, collected with a questionnaire at baseline 9 years earlier, were entered into regression models to investigate their associations with the subgroups of the two classifications of LBP and the results compared. RESULTS: The percentage of agreement between categories of the two classification systems was above 68 % (Kappa 0.7). Despite the large overlap of persons in the two classification groups, the patterns of associations with the two types of LBP definitions were different in the two classification groups. However, none of the estimates were significantly different when the variables were compared across the two classifications. CONCLUSION: Different classification systems of LBP are capable of bringing forth different findings. This may help explain the lack of consistency between studies on risk factors of LBP.

Longitudinal influence of musculo-skeletal injuries and extra physical education on physical fitness in schoolchildren.

The aims of this study were to investigate if (A) injuries and (B) increased physical education (PE) influenced the development of physical fitness in schoolchildren. Simultaneously, to investigate if a possible PE effect was modified by sport participation outside school hours. This was a longitudinal controlled school-based study. Six schools with 270 min of PE (extra PE) and four schools with 90 min of PE were followed up for 2.5 years. In total, 1054 children were included for analysis (normal PE = 443, extra PE = 611). Development in fitness was analyzed using composite z-scores from six fitness tests measured four times. Information of injury and sport was derived from weekly automated mobile phone text messages surveying the presence of musculo-skeletal pain and organized sport participation. Injury and extra PE both influenced the development of physical fitness. Injury decreased development of physical fitness with -1.01 composite z-score units (95% CI: -1.57; -0.45). Extra PE increased physical fitness development with 0.80 (95% CI: 0.49; 1.10) composite z-score units. The influence of injury was not dependent on extra PE. No modifying effect was found by mean weekly sport participation outside school hours. In conclusion, extra PE had a positive effect, whereas injuries had a negative effect on physical fitness development in schoolchildren.

Self-reported previous knee injury and low knee function increase knee injury risk in adolescent female football.

Knee injuries are common in adolescent female football. Self-reported previous knee injury and low Knee injury and Osteoarthritis Outcome Score (KOOS) are proposed to predict future knee injuries, but evidence regarding this in adolescent female football is scarce. The aim of this study was to investigate self-reported previous knee injury and low KOOS subscale score as risk factors for future knee injuries in adolescent female football. A sample of 326 adolescent female football players, aged 15-18, without knee injury at baseline, were included. Data on self-reported previous knee injury and KOOS questionnaires were collected at baseline. Time-loss knee injuries and football exposures were reported weekly by answers to standardized text-message questions, followed by injury telephone interviews. A priori, self-reported previous knee injury and low KOOS subscale scores (< 80 points) were chosen as independent variables in the risk factor analyses. The study showed that self-reported previous knee injury significantly increased the risk of time-loss knee injury [relative risk (RR): 3.65, 95% confidence (CI) 1.73-7.68; P < 0.001]. Risk of time-loss knee injury was also significantly increased in players with low KOOS subscale scores (< 80 points) in Activities of Daily Living (RR: 5.0), Sport/Recreational (RR: 2.2) and Quality of Life (RR: 3.0) (P < 0.05). In conclusion, self-reported previous knee injury and low scores in three KOOS subscales significantly increase the risk of future time-loss knee injury in adolescent female football.

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

The aims of this prospective school cohort study were to describe the epidemiology of diagnosed back pain in childhood, classified as either nontraumatic or traumatic back injury, and to estimate the association with physical activity in different settings. Over 2.5 years, 1240 children aged 6-12 years were surveyed weekly using mobile text messages to ask about the presence or absence of back pain. Pain was clinically diagnosed and injuries were classified using the International Classification of Diseases version 10. Physical activity data were obtained from text messages and accelerometers. Of the 315 back injuries diagnosed, 186 injuries were nontraumatic and 129 were traumatic. The incidence rate ratio was 1.5 for a nontraumatic back injury compared with a traumatic injury. The overall estimated back injury incidence rate was 0.20 per 1000 physical activity units (95% confidence interval 0.18-0.23). The back injury incidence rates were higher for sports when exposure per 1000 physical activity units was taken into consideration and especially children horse-riding had a 40 times higher risk of sustaining a traumatic back injury compared to the risk during non-organized leisure time physical activity. However, the reasonably low injury incidence rates support the recommendations of children continuously being physically active.

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.

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.

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.

Sugar-sweetened beverages consumption in relation to changes in body fatness over 6 and 12 years among 9-year-old children: the European Youth Heart Study.

BACKGROUND/OBJECTIVES: In parallel with the obesity epidemic, consumption of sugar-sweetened beverages (SSB) has risen over the same period. Our aim was to investigate associations between the consumption of SSB in childhood and adolescence with subsequent changes in body fatness in early adulthood. SUBJECTS/METHODS: A longitudinal study of 9-year-old children (n=283) enrolled in the Danish part of the European Youth Heart Study with a 6-year and 12-year follow-up. Data were collected at ages 9, 15 and 21 years. Multivariate regression analyses with adjustment for potential confounders were used to evaluate the effect of SSB consumption at 9 and 15 years and change in SSB consumption from 9-15 years on subsequent change in body fatness until 21 years. RESULTS: Subjects who consumed more than one serve of SSB daily at age 15 years had larger increases in body mass index (BMI) (ß=0.92, P=0.046) and waist circumference (WC) (ß=2.69, P=0.04) compared to non-consumers over the subsequent 6 years. In addition, subjects who increased their SSB consumption from age 9-15 years also had larger increases in BMI (ß=0.91, P=0.09) and WC (ß=2.72, P=0.04) from 15-21 years, compared to those who reported no change in consumption. No significant association was observed from 9-21 years. CONCLUSION: This study provides new evidence that SSB consumption in adolescence and changes in SSB consumption from childhood to adolescence are both significant predictors of change in body fatness later in early adulthood.

Overuse and traumatic extremity injuries in schoolchildren surveyed with weekly text messages over 2.5 years.

The objectives of this prospective cohort study were to report the incidence, prevalence, and duration of traumatic and overuse injuries during a period of 2.5 years and to estimate the odds of injury types. In all, 1259 schoolchildren, aged 6-12, were surveyed each week with an automated mobile phone text message asking questions on the presence of any musculo-skeletal problems and participation in leisure-time sport. Children were examined and injuries classified as overuse or traumatic. The overall injury incidence and prevalence were 1.2% and 4.6% per week, with 2.5 times more overuse than traumatic injuries in lower extremities, and mean injury duration of 5.3 and 4.8 weeks, respectively. A reverse pattern was found for upper extremities, with 3.1 times more traumatic than overuse injuries and mean durations of 3.3 and 5.2 weeks, respectively. Grade level, school type, leisure-time sport, and seasonal variation were associated with the risk of sustaining lower extremity injuries. Only grade level was associated with upper extremity injuries. The magnitude of overuse and traumatic limb injuries emphasizes the need for health professionals, coaches, and parents to pay special attention in relation to the growing and physically active child.

Aerobic fitness testing in 6- to 9-year-old children: reliability and validity of a modified Yo-Yo IR1 test and the Andersen test.

This study analysed the reliability and validity of two intermittent running tests (the Yo-Yo IR1 test and the Andersen test) as tools for estimating VO(2max) in children under the age of 10. Two groups, aged 6-7 years (grade 0, n = 18) and 8-9 years (grade 2, n = 16), carried out two repetitions of a modified Yo-Yo IR1 test (2 × 16 m) and the Andersen test, as well as an incremental treadmill test, to directly determine the VO(2max). No significant differences were observed in test-retest performance of the Yo-Yo IR1 test [693 ± 418 (±SD) and 670 ± 328 m, r (2) = 0.79, CV = 19%, p > 0.05, n = 32) and the Andersen test (988 ± 77 and 989 ± 87 m, r (2) = 0.86, CV = 3%, p > 0.05, n = 31). The Yo-Yo IR1 (r (2) = 0.47, n = 31, p < 0.002) and Andersen test performance (r (2) = 0.53, n = 32, p < 0.001) correlated with the VO(2max). Yo-Yo IR1 performance correlated with Andersen test performance (r (2) = 0.74, n = 32, p < 0.0001). In conclusion, the Yo-Yo IR1 and the Andersen tests are reproducible and can be used as an indicator of aerobic fitness for 6- to 9-year-old children.

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.

High-level physical activity in childhood seems to protect against low back pain in early adolescence.

BACKGROUND: The evidence on the impact of physical activity on back pain in children and adolescents has been contradicting. It has also been shown that the physical activity cannot accurately be estimated in children using questionnaires. PURPOSE: The aim of this study was to establish if physical activity in childhood had any impact on back pain reporting in early adolescence (3 years later), using an objective instrumental measurement of physical activity. STUDY DESIGN: Prospective cohort study. PATIENT SAMPLE: Representative random sample of Danish children from the city of Odense sampled at age 9 years and followed-up at age 12 years. OUTCOME MEASURES: The 1-month period prevalence of back pain (neck pain, mid back pain, and low back pain) was established using a structured interview. METHODS: Physical activity was assessed with the MTI-accelerometer. The accelerometer provides a minute-by-minute measure of the physical activity performed. An overall measure of physical activity and time spent in high activity were studied in relation to back pain using logistic regression. The analyses were performed on the total sample and then stratified on back pain (yes/no) at baseline. RESULTS: High physical activity (HPA) levels seem to protect against future low back pain and appear to actually "treat" and reduce the odds of future mid back pain. When comparing the least active children to the most active children, the least active had a multivariate odds ratio of 3.3 of getting low back pain and 2.7 of getting mid back pain 3 years later. When stratified on back pain at baseline, this effect on mid back pain was especially noticeable in children who had had mid back pain already at baseline, with an odds ratio of 7.2. CONCLUSIONS: HPA in childhood seems to protect against low back pain and mid back pain in early adolescence. Larger prospective studies with repetitive follow-ups and preferably intervention studies should be performed, to see if these findings can be reproduced.

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).