Niels Wedderkopp

Physical activity levels and patterns of 9- and 15-yr-old European children.

PURPOSE The purpose of this study was to assess physical activity levels and patterns from children participating in the European Youth Heart Study (EYHS). Very limited physical activity data exist that have been collected from representative samples of children and even fewer data collected where physical activity has been measured using objective methods. METHODS Subjects were 2185 children aged 9 and 15 yr from Denmark, Portugal, Estonia, and Norway. Physical activity data were obtained using MTI (formerly CSA) accelerometers. The primary outcome variable was established as the childs activity level (accelerometer counts per minute). Children wore the accelerometer for 3 or 4 d, which included at least 1 weekend day. RESULTS Boys were more active than girls at age 9 (784 +/- 282 vs 649 +/- 204 counts.min-1) and 15 yr (615 +/- 228 vs 491 +/- 163 counts.min-1). With respect to time engaged in moderate-intensity activity, gender differences were apparent at age 9 (192 +/- 66 vs 160 +/- 54 min.d-1) and age 15 (99 +/- 45 vs 73 +/- 32 min.d-1). At age 9, the great majority of boys and girls achieved current health-related physical activity recommendations (97.4% and 97.6%, respectively). At age 15, fewer children achieved the guidelines and gender differences were apparent (boys 81.9% vs girls 62.0%). CONCLUSIONS Accelerometers are a feasible and accurate instrument for use in large epidemiological studies of childrens activity. Boys tend to be more active than girls, and there is a marked reduction in activity over the adolescent years. The great majority of younger children achieve current physical activity recommendations, whereas fewer older children do so-especially older girls.

Reexamination of validity and reliability of the CSA monitor in walking and running.

PURPOSE To evaluate the reliability and validity of the CSA (model 7164) accelerometer (MTI) in a wide walking-running speed range in laboratory and field. METHOD Twelve male subjects performed three treadmill walking/running sessions and one field trial with the same continuous protocol involving progressively increasing velocities at 5 min per interval from 3 to 6 km x h(-1) (walking) and 8 to 20 km x h(-1) (running). In the field trial, this protocol was terminated after 35 min (14 km.h(-1)), but the trial then extended with 5-km running at a freely chosen velocity. In both scenarios, two CSAs were mounted on each hip and the step frequency measured at each velocity. Oxygen uptake VO(2) x kg(-1) was measured on the last two treadmill sessions. Correlation analyses were performed for mean CSA output relationship with speed, VO(2) per kilogram, and step frequency. RESULTS In all trials, CSA output rose linearly (R2 = 0.92, P < 0.001) with increasing speed until 9 km.h-1 but remained at approximately 10000 counts.min-1 during running, thus underestimating VO(2) per kilogram at speeds > 9 km x h(-1). Estimation errors increased with speed from 11% (P < 0.01) at 10 km x h(-1) to 48% (P < 0.001) at 16 km x h(-1), when assuming a linear relationship. Freely chosen velocities in the field trial ranged from 10.9 to 16.3 km.h-1. No difference in the CSA-speed relationship was observed between the two scenarios. Differences in CSA output between subjects could partially be attributed to differences in step frequency (R = -0.34 (P = 0.02) for walking and R = -0.63 (P < 0.001) for running). CONCLUSION CSA output increases linearly with speed in the walking range but not in running, presumably due to relatively constant vertical acceleration in running. Between-subject reliability was related to step frequency because CSA data are filtered most at higher movement frequencies. Epidemiological CSA data should thus be interpreted with these limitations in mind.

Back pain reporting pattern in a Danish population-based sample of children and adolescents.

Study Design. A cross-sectional survey of 806 pupils in Odense, Denmark was performed. This survey included children and adolescents ages 8 to 10 and 14 to 16 years obtained through two-stage cluster sampling from schools stratified according to school type, location, and socioeconomic character of the uptake area. Objectives. To establish the 1-month prevalence of neck, middle back, and low back pain and the consequences this disorder may have in relation to age and gender. Summary of Background Data. The differences in definitions of back pain and the variety of age groups included in previous studies make it difficult to draw clear conclusions about the onset of pain for various spinal regions in the young. Methods. Information on back pain within the preceding month, obtained through a standardized interview of 481 children and 325 adolescents, was categorized according to area of pain, age, and gender. The consequences of back pain also were studied. Results. The 1-month prevalence of back pain was 39%. Thoracic pain is most common in childhood, whereas thoracic pain and lumbar pain are equally common in adolescence. Neck pain and pain in more than one area of the spine are rare in both age groups. No gender differences were found. Of those who had back pain, 38% also reported some type of consequence, usually either visits to a medical physician or diminished physical activities. Conclusions. For clinical and research purposes, neck pain, middle back pain, and low back pain in childhood should be regarded as three specific entities. In future research the data for different age groups should be reported separately.

Comparison of two intervention programmes in young female players in European handball--with and without ankle disc.

Introduction: The prevention of injuriesin all sports calls for a structured plan. The plan consists, as earlier described, of four steps. We have previously presented studies incorporating all four steps. The studies have shown that it is possible to prevent most injuries in young female players in European handball by applying a training programme combining the use of an ankle disc with functional strength training. In the previous studies we were not able to discriminate whether the preventive effect was due to the functional strength training or the training with the ankle disc. The aim of this study was to compare a programme with ankle disc and functional strength training with a programme with functional strength training only.

Secular trends in physical fitness and obesity in Danish 9-year-old girls and boys: Odense School Child Study and Danish substudy of the European Youth Heart Study.

Introduction:  Low physical fitness and obesity have been shown to be associated with cardiovascular disease (CVD) risk. Obesity is on the increase in many countries, but little is known about physical fitness trends. Monitoring of changes in fitness and obesity in the population is important for preventive strategies, and the aim of this study was to analyse the secular trends in fitness and body composition in Danish children.

Longitudinal associations of cycling to school with adolescent fitness

OBJECTIVE To investigate whether change in transport to school from non-cycling to cycling was associated with change in cardio-respiratory fitness (CRF) over a six-year follow-up. METHODS Participants were 384 children (9.7 (0.5) years) who participated in the Danish arm of the European Youth Heart Study in 1997 and who were followed up 6 years later. CRF was assessed by a maximal cycle ergometer test and travel to school was investigated by questionnaire at both time points. Linear regression models were used to investigate associations between CRF and change in mode of travel to school between baseline and follow-up. RESULTS Higher CRF was significantly associated with cycling to school in children and adolescents of both sexes. Longitudinal regression models showed that a change in travel mode from non-cycling to cycling was a significant predictor of CRF at follow-up (P<0.001) after adjustment for potential confounders. Participants who did not cycle to school at baseline, but who had changed to cycling at follow-up, were significantly fitter (0.33 W kg(-1)) than those who did not cycle to school at either time point (P=0.001), a difference of 9%. CONCLUSION Cycling to school may contribute to higher cardiovascular fitness in young people.

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.

Injury risk in Danish youth and senior elite handball using a new SMS text messages approach

Objective To assess the injury incidence in elite handball, and if gender and previous injuries are risk factors for new injuries. Methods Cohort study of 517 male and female elite handball players (age groups under (u)16, u-18 and senior). Participants completed a web survey establishing injury history, demographic information and sports experience, and provided weekly reports of time-loss injuries and handball exposure for 31 weeks by short message service text messaging (SMS). Injuries were further classified by telephone interview. Results The weekly response rate ranged from 85% to 90% illustrating the promise of the SMS system as a tool in injury surveillance. Of 448 reported injuries, 165 injuries (37%) were overuse injuries and 283 (63%) traumatic injuries. Knee (19%) and ankle (29%) were the most common traumatic injuries. The injury incidence during match play was 23.5 (95% CI 17.8 to 30.4), 15.1 (95% CI 9.7 to 22.2), 11.1 (95% CI 7.0 to 16.6) injuries per 1000 match hours among senior, u-18 and u-16 players, respectively. U-18 male players had an overall 1.76 (95% CI 1.10 to 2.80) times higher risk of injury compared to females. Having had two or more previous injuries causing absence from handball for more than 4 weeks increased the risk of new injury in the u-16 group (IRR: 1.79 (95% CI 1.03 to 3.11)–2.23 (95% CI 1.22 to 4.10)). Conclusion The incidence of time-loss injuries in elite handball was higher during match play than previously reported in recreational handball. Previous injuries were a risk factor for new injuries among u-16 players. Male players had a significant higher injury rate in the u-18 group.

Association between back pain and physical fitness in adolescents.

Study Design. A cross-sectional study of 9413 adolescents. Objectives. To study the associations between back pain, physical activity, and physical fitness. Summary of Background Data. A high physical fitness level, and especially muscle endurance in the back muscles, is associated with lower risk of back pain, but little is known about other types of physical fitness and back pain in adolescents. Methods. A cross-sectional study of 3956 boys and 5457 girls 17 years of age. The associations between self-reported back pain and different types of physical fitness and self-reported physical activity were analyzed in high schoolchildren in Denmark. Results. Back pain was reported by 43% of the girls and 37% of the boys. Back pain was associated with low isometric muscle endurance in the back extensors, and the highest quartile had a lower risk of back pain (odds ratio = 0.71; 95% confidence interval, 0.62–0.82) within the last month. No associations were found to aerobic fitness, functional strength, flexibility, or physical activity level after adjustment for muscle endurance. More girls than boys experienced back pain, and it was more common in taller adolescents. Conclusion. Children with high isometric muscle endurance were less likely to report back pain. No other measures of physical fitness or level of self-reported physical activity were linked to back pain reporting.

Reliability and Validity of the Computer Science and Applications Accelerometer in a Mechanical Setting

Accelerometry has been proposed as an objective method for measurement of physical activity. Intra- and inter-instrument reliability and validity of the Computer Science and Applications (CSA) Model 7164 accelerometer, along with the nature of the analogue filter in the device, was studied with sinusoidal movements in a mechanical setting. Six CSA units were tested with 17 different frequencies (0.5 - 4 Hz) on 3 radius settings (0.022 - 0.049 m), yielding 51 different acceleration settings (0.1 - 19.7 m· sec-2). Intra-instrument reliability was relatively good (mean CV of 4.4%), although questionable on extreme values of acceleration (less than 1 m · sec-2 and higher than 16 m · sec-2). Analyses on inter-instrument reliability revealed both overall systematic bias and acceleration-specific differences between units, approaching unit error magnitudes of 20% from the mean of all 6 units. The correlation between CSA output and acceleration (i.e., validity) was significant but the relation was clearly nonlinear. Applying equations to cancel the frequency-dependent filtering restored this linearity (R2 = 0.97). In conclusion, the CSA exhibits reasonable intra-instrument reliability but that large unit differences call for unit-specific calibration or alternatively statistical adjustment. Linearity between CSA output and acceleration is achieved only by correcting for movement frequency filtering.