Screen Time and Body Image in Icelandic Adolescents: Sex-Specific Cross-Sectional and Longitudinal Associations.

Studies of adolescent body image and screen use are mostly limited to girls, and longitudinal data are scarce. We examined cross-sectional and longitudinal associations between these variables in mid-adolescent boys and girls. Data was collected when participants were at age 15 and 17, by questionnaire and objective measurements (n = 152 had complete data). Sex-specific linear regression was used to explore cross-sectional and longitudinal associations of self-reported screen use (total use, and time spent in gaming, TV/DVD/internet-based watching and internet use for communication) and body image, adjusting for vigorous physical activity, symptoms of depression, and body composition. Screen time was negatively associated with body image at both time points, although more strongly at age 15, and for girls only. Gaming and TV/DVD/internet watching was more strongly associated with body image than internet use for communication. Girls with above median screen time at both ages had 14% lower body image score at age 17 than girls with below median screen time at both time points. Our results suggest that screen use is likely to play a role in the development of body dissatisfaction among adolescent females. Limiting screen time may, therefore, help to mitigate body dissatisfaction in adolescent girls.

Less physical activity and more varied and disrupted sleep is associated with a less favorable metabolic profile in adolescents.

BACKGROUND: Sleep and physical activity are modifiable behaviors that play an important role in preventing overweight, obesity, and metabolic health problems. Studies of the association between concurrent objective measures of sleep, physical activity, and metabolic risk factors among adolescents are limited. OBJECTIVE: The aim of the study was to examine the association between metabolic risk factors and objectively measured school day physical activity and sleep duration, quality, onset, and variability in adolescents. MATERIALS AND METHODS: We measured one school week of free-living sleep and physical activity with wrist actigraphy in 252 adolescents (146 girls), aged 15.8±0.3 years. Metabolic risk factors included body mass index, waist circumference, total body and trunk fat percentage, resting blood pressure, and fasting glucose and insulin levels. Multiple linear regression adjusted for sex, parental education, and day length was used to assess associations between metabolic risk factors and sleep and activity parameters. RESULTS: On average, participants went to bed at 00:22±0.88 hours and slept 6.2±0.7 hours/night, with 0.83±0.36 hours of awakenings/night. However, night-to-night variability in sleep duration was considerable (mean ± interquartile range) 0.75±0.55 hours) and bedtime (0.64±0.53 hours) respectively. Neither average sleep duration nor mean bedtime was associated with any metabolic risk factors. However, greater night-to-night variability in sleep duration and bedtime was associated with higher total body and trunk fat percentage, and less physical activity was associated with higher trunk fat percentage and insulin levels. CONCLUSION: Greater nightly variation in sleep duration and in bedtime and less physical activity were associated with a less favorable metabolic profile in adolescents. These findings support the idea that, along with an adequate amount of physical activity, a regular sleep schedule is important for the metabolic health of adolescents.

Less screen time and more physical activity is associated with more stable sleep patterns among Icelandic adolescents.

OBJECTIVES: Emerging evidence suggests that inconsistent sleep may affect physical and psychological health. Thus, it is important to identify modifiable determinants of sleep variability. Screen time and physical activity are both thought to affect sleep, but studies of their relationship to sleep variability using objective measures are lacking. We examined cross-sectional associations between these variables in mid-teen adolescents using objectively measured sleep and activity. METHODS: Wrist-worn accelerometers were used to measure one week of sleep and activity in 315 tenth grade students (mean age 15.8y) from six Reykjavík compulsory schools. Participants reported their daily hours of screen time. Regression analysis was used to explore associations of screen time and physical activity with variability in duration, quality, and timing of sleep, adjusting for DXA-measured body fat percentage, parental education, and physical activity or screen time. RESULTS: Screen time, especially game playing, was associated with variability in duration, timing, and quality of sleep, most strongly with variation in bedtime. Physical activity was inversely associated with variability in duration, timing, and quality of sleep, most strongly with variation in the number of awakenings. Boys had less stable sleep patterns and higher screen time than girls, and sex-specific associations of screen time with sleep variability parameters were significant for boys only. CONCLUSIONS: Less screen time and more physical activity were independently associated with less sleep variability among mid-teen adolescents. Our results indicate that encouraging youngsters toward an active lifestyle with limited screen use may be important to achieve more consistent sleep.

Longitudinal Change in Adolescent Bedtimes Measured by Self-Report and Actigraphy.

INTRODUCTION: Sleep is often quantified using self-report or actigraphy. Self-report is practical and less technically challenging, but prone to bias. We sought to determine whether these methods have comparable sensitivity to measure longitudinal changes in adolescent bedtimes. METHODS: We measured one week of free-living sleep with wrist actigraphy and usual bedtime on school nights and non-school nights with self-report questionnaire in 144 students at 15 y and 17 y. RESULTS: Self-reported and actigraphy-measured bedtimes were correlated with one another at 15 y and 17 y (p < .001), but reported bedtime was consistently earlier (>30 minutes, p < .001) and with wide inter-method confidence intervals (> ±106 minutes). Mean inter-method discrepancy did not differ on school nights at 15 y and 17 y but was greater at 17 y on non-school nights (p = .002). Inter-method discrepancy at 15 y was not correlated to that at 17 y. Mean change in self-reported school night bedtime from 15 y to 17 y did not differ from that by actigraphy, but self-reported bedtime changed less on non-school nights (p = .002). Two-year changes in self-reported bedtime did not correlate with changes measured by actigraphy. CONCLUSIONS: Although methods were correlated, consistently earlier self-reported bedtime suggests report-bias. More varied non-school night bedtimes challenge the accuracy of self-report and actigraphy, reducing sensitivity to change. On school nights, the methods did not differ in group-level sensitivity to changes in bedtime. However, lack of correlation between bedtime changes by each method suggests sensitivity to individual-level change was different. Methodological differences in sensitivity to individual- and group-level change should be considered in longitudinal studies of adolescent sleep patterns.

Above average increases in body fat from 9 to 15 years of age had a negative impact on academic performance, independent of physical activity.

AIM: The associations between body fat levels and physical activity with academic performance are inconclusive and were explored using longitudinal data. METHODS: We enrolled 134/242 adolescents aged 15, who were studied at the age of nine and agreed to be followed up from April to May 2015 for the Health behaviours of Icelandic youth study. Accelerometers measured physical activity, body mass indexes (BMI) were calculated and dual-energy X-ray absorptiometry scans assessed the participants' body composition at nine and 15. Their language and maths skills were compared to a growth model that estimated the academic performances of children born in 1999. RESULTS: Higher than normal body fat levels between the ages of nine and 15 were negatively associated with maths performance, but the same association was not found for Icelandic language studies. These were Pearson's r = -0.24 (p = 0.01) for BMI and Pearson's r = -0.34 (p = 0.01) for the percentage of body fat. No associations were found with changes in physical activity. CONCLUSION: Children who put on more body fat than normal between the ages of nine and 15 had an increased risk of adverse academic performance that was independent of changes in physical activity.

Less screen time and more frequent vigorous physical activity is associated with lower risk of reporting negative mental health symptoms among Icelandic adolescents.

OBJECTIVE: Few studies have explored the potential interrelated associations of screen time and physical activity with mental health in youth, particularly using objective methods. We examined cross-sectional associations of these variables among Icelandic adolescents, using objective and subjective measurements of physical activity. METHODS: Data were collected in the spring of 2015 from 315 tenth grade students (mean age 15.8 years) in six elementary schools in metropolitan Reykjavík, Iceland. Participants reported, via questionnaire, on demographics, weekly frequency of vigorous physical activity, daily hours of screen time and mental health status (symptoms of depression, anxiety and somatic complaints, self-esteem and life satisfaction). Total physical activity was measured over one week with wrist-worn accelerometers. Body composition was determined by DXA-scanning. Poisson regression analysis was used to explore independent and interactive associations of screen time and physical activity with mental health variables, adjusting for gender, body fat percentage and maternal education. RESULTS: Less screen time (below the group median of 5.3 h/day) and more frequent vigorous physical activity (≥4x/week) were each associated with reporting fewer symptoms of depression, anxiety, low self-esteem, and life dissatisfaction. No significant associations were observed between objectively measured physical activity and mental health outcomes. Interactive regression analysis showed that the group reporting both less screen time and more frequent vigorous physical activity had the lowest risk of reporting symptoms of depression, anxiety, low self-esteem, and life dissatisfaction. CONCLUSIONS: Reports of less screen time and more frequent vigorous physical activity were associated with lower risk of reporting mental health problems among Icelandic adolescents. Those who reported a combination of engaging in less screen time and more frequent vigorous physical activity had the lowest risk, suggesting a synergistic relationship between the two behaviors on mental health outcomes. Our results support guiding youth towards more active and less sedentary/screen-based lifestyle.

[Physical activity and sleep in Icelandic adolescents].

INTRODUCTION: Physical activity and sleep are major determinants of overall health. According to international recommendations, adolescents should engage in moderate to vigorous physical activity for at least 60 min each day and sleep eight to ten hours each night. The association between physical activity and sleep in adolescents is not well known. The aim of the study was to estimate a) the proportion of Icelandic adolescents that achieves recommended physical activity and sleep, b) if there is an association between physical activity and sleep patterns, and c) sex differences in physical activity and sleep. MATERIAL AND METHODS: A total of 411 adolescents from the 10th grade in six schools in Reykjavik were invited to participate in a cross-sectional study in the spring of 2015. Valid data was obtained from 106 boys and 160 girls. Objective and subjective measures of physical activity and sleep were made by wrist-worn accelerometers and a questionnaire. RESULTS: Almost half of the participants fulfilled the physical activity recommendations according to the questionnaire. Although 51.1% reported usually getting enough sleep, only 22.9% achieved the recommended sleep length according to objective assessment. No associations were observed between sleep and subjective physical activity. Girls had higher accelerometer-measured physical activity than boys on non-school days (p<0.01), but weekly averages were not different between sexes. Girls and boys did not differ in subjective or objective measures of sleep. CONCLUSION: The behavior of Icelandic adolescents does not reflect recommended amount of sleep and physical activity. Only 22.9% obtained the recommended sleep length and just 11.3% fulfilled recommendations of both sleep and physical activity.

Cross-sectional study of randomly selected 18-year-old students showed that body mass index was only associated with sleep duration in girls.

AIM: This study investigated the associations, by sex, between sleep and adiposity, dietary habits, cardiorespiratory fitness and metabolic risk in 18-year-old students. METHODS: We carried out a cross-sectional study of 199 randomly chosen, healthy 18-year-old students (53% girls) in Iceland's capital region. The data collection took place in the winter months of 2012 to 2015. The anthropometric measurements were body mass index, waist circumference and body fat percentage. Sleep duration and dietary habits were self-reported. Cardiorespiratory fitness was measured on a stationary bicycle. A subsample of 152 participants gave blood samples. RESULTS: A quarter of the adolescents failed to reach the minimum recommended sleep duration of seven hours per night on weekdays. In girls, the average sleep score was associated with body mass index and waist circumference, after adjusting for cardiorespiratory fitness and unhealthy eating scores. In boys, the average sleep score was not associated with anthropometric measurements, but cardiorespiratory fitness was an independent predictor (p < 0.001). No associations were found between average sleep scores and metabolic profiles in either sex. CONCLUSION: Sleep duration and adiposity only appeared to be associated in girls and were independent of cardiorespiratory fitness and unhealthy eating. Sleep duration was not related to metabolic risk.

Sleep deficiency on school days in Icelandic youth, as assessed by wrist accelerometry.

AIMS: The purpose of this study was to objectively measure, with wrist-worn actigraphy, free-living sleeping patterns in Icelandic adolescents, and to compare sleep duration, sleep quality and clock times between school days (SchD) and non-school days (NSchD) and the association between sleep and body mass index (BMI). METHODS: A cross-sectional study on 15.9-year-old (±0.3) adolescents from six schools in Reykjavík, Iceland, took place in the spring of 2015. Free-living sleep was measured on 301 subjects (122 boys and 179 girls) over seven days using wrist-worn actigraphy accelerometers. Total rest time (TRT), total sleep time (TST), sleep quality markers, and clock times for sleep were quantified and compared between SchD and NSchD and between the sexes, using paired and group t-tests as appropriate. Linear regression was used to assess the association between sleep parameters and BMI. RESULTS: On SchD, TST was 6.2 ± 0.7 h, with sleep efficiency (SLE) of 87.9 ± 4.4% for the group. On NSchD, TST increased to 7.3 ± 1.1 h (p < 0.001), although SLE decreased to 87.4 ± 4.7% (p < 0.05). On SchD and NSchD, 67% and 93% had bed times after midnight, respectively, and on SchD 10.7% met sleep recommendations (8 h/night). There was no association between BMI and average sleep parameters. CONCLUSION: The majority of Icelandic adolescents did not get the recommended number of hours of sleep, especially on SchD. While TST increased on NSchD, many participants still did not achieve the recommendations. These findings provide information on the sleep patterns of adolescents and may serve as reference for development of policies and interventions to promote better sleep practices.

The Impact of Sport Participation on Bone Mass and Geometry in Male Adolescents.

PURPOSE: Exercise is an effective approach for developing bone mass and adolescence is a key period to optimize bone health. However, sports-specific training may have different effects on bone outcomes. This study examined the differences on bone outcomes between osteogenic (football) and nonosteogenic (swimming and cycling) sports and a control group in male adolescents. METHODS: One hundred twenty one males (13.1 ± 0.1 yr) were measured: 41 swimmers, 37 footballers, 29 cyclists, and 14 controls. Dual energy X-ray absorptiometry measured bone mineral density (BMD) and bone mineral content at lumbar spine, right and left hip, and total body. Hip Structural Analysis evaluated bone geometry at the femoral neck. Quantitative ultrasound evaluated bone stiffness at both feet. RESULTS: Footballers had significantly higher BMD at total body less head (7%-9%), total hip (12%-21%), and legs (7%-11%) compared with all groups and significantly higher BMD at the femoral neck than controls (14%). Cyclists had higher BMD at the trochanter (10%) and bone mineral content at the arms (10%) compared with controls. Geometrical analysis showed that footballers had significantly higher cross-sectional area (8%-19%) compared with all groups, cross-sectional moment of inertia (17%) compared with controls and section modulus compared with cyclists (11%) and controls (21%). Footballers had significantly higher bone stiffness compared with all groups (10%-20%) at the dominant foot and (12%-13%) at the nondominant foot compared with swimmers and controls. CONCLUSIONS: Adolescent male footballers exhibited higher bone density, geometry, and stiffness compared with swimmers, cyclists and controls. Although swimmers and cyclists had higher bone outcomes compared with controls, these differences were not significant.

Health Behavior and Metabolic Risk Factors Associated with Normal Weight Obesity in Adolescents.

OBJECTIVE: To explore health behaviors and metabolic risk factors in normal weight obese (NWO) adolescents compared with normal weight lean (NWL) peers. DESIGN AND METHODS: A cross-sectional study of 18-year-old students (n = 182, 47% female) in the capital area of Iceland, with body mass index within normal range (BMI, 18.5-24.9 kg/m2). Body composition was estimated via dual energy X-ray absorptiometry, fitness was assessed with maximal oxygen uptake (VO2max) during treadmill test, dietary intake through 24-hour recall, questionnaires explained health behavior and fasting blood samples were taken. NWO was defined as normal BMI and body fat >17.6% in males and >31.6% in females. RESULTS: Among normal weight adolescents, 42% (n = 76) were defined as NWO, thereof 61% (n = 46) male participants. Fewer participants with NWO were physically active, ate breakfast on a regular basis, and consumed vegetables frequently compared with NWL. No difference was detected between the two groups in energy- and nutrient intake. The mean difference in aerobic fitness was 5.1 ml/kg/min between the groups in favor of the NWL group (p<0.001). NWO was positively associated with having one or more risk factors for metabolic syndrome (Odds Ratio OR = 2.2; 95% confidence interval CI: 1.2, 3.9) when adjusted for sex. High waist circumference was more prevalent among NWO than NWL, but only among girls (13% vs 4%, p = 0.019). CONCLUSIONS: High prevalence of NWO was observed in the study group. Promoting healthy lifestyle with regard to nutrition and physical activity in early life should be emphasized regardless of BMI.

Importance of physical health and health-behaviors in adolescence for risk of dropout from secondary education in young adulthood: an 8-year prospective study.

BACKGROUND: Education and health constitute two interlinked assets that are highly important to individuals. In Iceland, prevalence of dropout from secondary education poses a considerable problem. This 8-year prospective study assesses to what extent poor physical health and negative health-behaviors of Icelandic adolescents predict increased odds of dropout from secondary education. METHODS: The sample included n = 201 Icelandic children who participated at age 15 (baseline) and again at age 23 (follow-up). Data included objective measurements of physical health and questionnaires assessing health-behaviors, education status, parental education, neighborhood characteristics, self-esteem, and depression. Independent t-tests and chi-square were used to assess differences in physical health and health-behaviors at follow-up stratified by education status. Ordinal regression models were conducted to assess whether physical health and health-behaviors at age 15 predicted increased odds of dropout from secondary education at age 23, independent of gender, parental education and psychological factors. RESULTS: At age 23, 78 % of girls and 71 % of boys had completed a secondary education. Completion of a secondary education was associated with significant health benefits, especially among women. Women without a secondary education had lower fitness, more somatic complaints, higher diastolic blood pressure, less sports participation, and poorer sleep, whilst men without a secondary education watched more television. In logistic regression models somatic complaints during adolescence were associated with 1.09 (95 % CI: 1.02-1.18) higher odds of dropout from secondary education in young adulthood, independent of covariates. Health-behaviors associated with higher dropout odds included smoking (3.67, 95 % CI: 1.50-9.00), alcohol drinking (2.57, 95 % CI: 1.15-5.75), and time spent watching television (1.27, 95 % CI:1.03-1.56), which were independent of most covariates. Finally, mother's higher education was strongly associated with significantly lower dropout odds (OR 0.54, 95 % CI: 0.34-0.88) independent of father's education and psychological factors, whilst high self-esteem was independently associated with lower dropout odds (OR 0.91, 95 % CI: 0.85-0.98). CONCLUSIONS: Completion of a secondary education yields substantial physical health benefits for young women, but not for men. Importantly, somatic complaints and negative health-behaviors among adolescent boys and girls adversely impact their educational outcomes later in life, and may have widespread consequences for their future prospects.

Lean soft tissue contributes more to bone health than fat mass independent of physical activity in women across the lifespan.

OBJECTIVES: To investigate the association between lean soft tissue (LST) and fat mass (FM) on bone health variables in women across the lifespan, while taking into account the influence of objectively measured habitual physical activity (PA). STUDY DESIGN: A total of 104 women, 37 young (23.3 ± 2.6 years), 28 middle-age (49.2 ± 5.4 years), and 39 old (68.3 ± 6.4 years) participated in this cross-sectional study. All underwent a DXA scan and wore a pedometer for 7 days. MAIN OUTCOME MEASURES: Bone mineral content (BMC) and BMD of the whole body (WB), lumbar spine (LS) and proximal femur (PF), and body composition (FM and LST) were assessed with DXA and PA (steps/day) was assessed from 7 day pedometer counts. RESULTS: LST was significantly and positively associated with PF and LS BMD (r = 0.34; 0.67, p < 0.05), and WB, PF and LS BMC (r range = 0.41-0.59, p < 0.05) in all age groups and WB BMD in the middle-age group (r = 0.72, p < 0.05) independent of PA, FM, and hormonal status. FM was not positively associated with any bone variable in any age group when adjusted for PA, LST, and hormonal status. PA was significantly associated with WB BMD in the middle-age group (r = 0.60, p < 0.05), independent of LST, FM, and hormonal status. CONCLUSIONS: LST contributes more to bone health in women across the lifespan than FM, independent of PA and hormonal status.

Effects of a 6-month multimodal training intervention on retention of functional fitness in older adults: a randomized-controlled cross-over design.

BACKGROUND: Older adults have the highest rates of disability, functional dependence and use of healthcare resources. Training interventions for older individuals are of special interest where regular physical activity (PA) has many health benefits. The main purpose of this study was to assess the immediate and long-term effects of a 6-month multimodal training intervention (MTI) on functional fitness in old adults. METHODS: For this study, 117 participants, 71 to 90 years old, were randomized in immediate intervention group and a control group (delayed intervention group). The intervention consisted of daily endurance and twice-a-week strength training. The method was based on a randomized-controlled cross-over design. Short Physical Performance Battery (SPPB), 8 foot up-and-go test, strength performance, six min walking test (6 MW), physical activity, BMI and quality of life were obtained at baseline, after a 6-month intervention- and control phase, again after 6-month crossover- and delayed intervention phase, and after anadditional 6-month follow-up. RESULTS: After 6 months of MTI, the intervention group improved in physical performance compared with the control group via Short Physical Performance Battery (SPPB) score (mean diff = 0.6, 95 % CI: 0.1, 1.0) and 8-foot up-and-go test (mean diff = -1.0 s, 95 % CI: -1.5, -0.6), and in endurance performance via 6-minute walking test (6 MW) (mean diff = 44.2 meters, 95 % CI: 17.1, 71.2). In strength performance via knee extension the intervention group improved while control group declined (mean diff = 55.0 Newton, 95 % CI: 28.4, 81.7), and also in PA (mean diff = 125.9 cpm, 95 % CI: 96.0, 155.8). Long-term effects of MTI on the particpants was assesed by estimating the mean difference in the variables measured between time-point 1 and 4: SPPB (1.1 points, 95 % CI: 0.8, 1.4); 8-foot up-and-go (-0.9 s, 95 % CI: -1.2, -0.6); 6 MW (18.7 m, 95 % CI: 6.5, 31.0); knee extension (4.2 Newton, 95 % CI: -10.0, 18.3); hand grip (6.7 Newton, 95 % CI: -4.4, 17.8); PA (-4.0 cpm, 95 % CI: -33.9, 26.0); BMI (-0.6 kg/m2, 95 % CI: -0.9, -0.3) and Icelandic quality of life (0.3 points, 95 % CI: -0.7, 1.4). CONCLUSIONS: Our results suggest that regular MTI can improve and prevent decline in functional fitness in older individuals, influence their lifestyle and positively affect their ability to stay independent, thus reducing the need for institutional care. TRIAL REGISTRATION: This study was approved by the National Bioethics Committee in Iceland, VSNb20080300114/03-1.

Adiposity and aerobic fitness are associated with metabolic disease risk in children.

To examine the relative association of physical activity, cardiorespiratroy fitness (CRF), and adiposity with risk for metabolic disease in prepubescent children. Forty-six prepubescent children (age, 9.4 ± 1.7 years; 24 males) were assessed for adiposity (%fat) via dual-energy X-ray absorptiometry, CRF with a peak graded exercise test, and physical activity using pedometers. Metabolic disease risk was assessed by a composite score of the following factors: waist circumference (WC), mean arterial pressure (MAP), triacylglycerol (TAG), total cholesterol to high-density lipoprotein cholesterol ratio (TC/HDL-C ratio), glucose, and insulin. Adiposity was correlated with metabolic disease risk score, as well as homeostasis model assessment of insulin resistance (HOMA-IR), TAG, TC/HDL-C ratio, WC, insulin, and MAP (r range = 0.33 to 0.95, all p < 0.05). Physical activity was negatively associated with metabolic disease risk score, as well as HOMA-IR, TAG, WC, insulin, and MAP (r range = -0.32 to -0.49, all p < 0.05). CRF was inversely associated with metabolic disease risk score and HOMA-IR, TAG, TC/HDL-C ratio, WC, insulin, and MAP (r range = -0.32 to -0.63, all p < 0.05). Compared across fitness-physical activity and fatness groups, the low-fit-high-fat and the low-activity-high-fat groups had higher metabolic risk scores than both low-fat groups. Regression analyses revealed sexual maturity (ß = 0.27, p = 0.044) and %fat (ß = 0.49, p = 0.005) were the only independent predictors of metabolic disease risk score, explaining 4.7% and 9.5% of the variance, respectively. Adiposity appears to be an influential factor for metabolic disease risk in prepubescent children, and fitness is protective against metabolic disease risk in the presence of high levels of adiposity.

Adiposity, activity, fitness, and C-reactive protein in children.

PURPOSE: The purpose of this study was to examine the relative association of physical activity, cardiorespiratory fitness (CRF), and adiposity with C-reactive protein (CRP) in prepubescent children. METHODS: Forty-five prepubescent children (age = 9.4 ± 1.6 yr; 26 boys) were assessed for adiposity (percent fat) via dual-energy x-ray absorptiometry, CRF with a peak graded exercise test, physical activity using pedometers, and systemic inflammation via serum CRP. RESULTS: Adiposity was positively correlated with CRP (body mass index, r = 0.61; percent fat, r = 0.59, P < 0.001), whereas step count and CRF were inversely associated with CRP (r = -0.49 and -0.37, respectively, all P values < 0.05). Compared across fitness or physical activity and adiposity groups, the low-fit/high-fat and the low-activity/high-fat groups had higher CRP than both low-fat groups. There was also a main effect of physical activity (P < 0.01) but not fitness on CRP. Regression analyses revealed that percent fat (ß = 0.59, P = 0.002) and physical activity (ß = -0.35, P = 0.011) were the only independent predictors of CRP, explaining 16.0% and 10.0% of the variance, respectively. CONCLUSIONS: Adiposity is positively related to serum CRP in prepubescent children, independent of the effects of fitness or physical activity. In addition, physical activity is inversely associated with CRP levels. This research identified habitual physical activity and adiposity as focal points for the design of interventions attempting to reduce chronic systemic inflammation in children.

Effect of caffeine on quadriceps muscle pain during acute cycling exercise in low versus high caffeine consumers.

This experiment examined the effect of a moderate dose of caffeine on quadriceps muscle pain during a bout of high-intensity cycling in low- versus high-caffeine-consuming males. College-age men who were low (< or =100 mg/day; n = 12) or high (> or =400 mg/day; n = 13) habitual caffeine consumers ingested caffeine (5 mg/kg body weight) or a placebo in a counterbalanced order and 1 hr later completed 30 min of cycle ergometry at 75-77% of peak oxygen consumption. Perceptions of quadriceps muscle pain, as well as oxygen consumption, heart rate, and work rate, were recorded during both bouts of exercise. Caffeine ingestion resulted in a statistically significant and moderate reduction in quadriceps muscle-pain-intensity ratings during the 30-min bout of high-intensity cycle ergometry compared with placebo ingestion in both low (d = -0.42) and high (d = -0.55) caffeine consumers. The results suggest that caffeine ingestion is associated with a moderate hypoalgesic effect during high-intensity cycling in college-age men who are low or high habitual caffeine consumers, but future work should consider better defining and differentiating pain and effort when examining the effects of caffeine during acute exercise.

Change in body mass index is a stronger predictor of change in fat mass than lean mass in elderly black and white women.

The aim of this study was to determine the relation between change in body mass index (BMI) and changes in fat mass (FM), lean soft tissue (LST), and percentage body fat (%Fat) in elderly (67.6 +/- 6.0 years) women varying in race (53 black, 144 white) who underwent measurements of BMI, FM, LST, and %Fat at baseline and after 2 years. The group did not markedly change body composition over 2 years (BMI = -0.1 +/- 1.5 kg/m(2), P = 0.53; FM = 0.0 +/- 2.8 kg, P = 0.95; LST = -0.4 +/- 1.7 kg, P < 0.001; %Fat = 0.3 +/- 2.0%, P = 0.06). Change in BMI predicted change in FM (r = 0.90, SEE = 1.19 kg FM, P < 0.001) but was less predictive of change in %Fat (r = 0.64, SEE = 1.54%Fat, P < 0.001). Change in BMI was curvilinearly related to change in LST adjusted for change in height (R = 0.76, SEE = 1.10 kg LST, P < 0.001). Change in BMI more strongly predicts change in FM than LST and could be used to monitor change in FM in community-dwelling women.

Predictors of fatness and physical fitness in nine-year-old Icelandic school children.

INTRODUCTION: In recent years, the prevalence of overweight and obese children has increased in Iceland, as in most Westernized countries. The main objectives of this study were to assess predictors of fitness and fatness of 9-year-old school children in Iceland. METHODS: In total, 488 subjects (73.3% participation rate) from 18 randomly selected primary schools participated in this cross-sectional study. Height, weight, sum of four skinfolds and other anthropometric measures were performed on all children. Fitness was assessed via a maximal cycle ergometer test in 229 children and of those, 177 wore Actigraph accelerometers to measure physical activity over five consecutive days. Questionnaires regarding family background and lifestyle were completed by 361 mothers and 332 fathers. RESULTS: The main findings from our study showed fatness, area of living and sex, as well as background variables, such as fathers' smoking and income, and number of sport practices attended per week were important predictors of fitness (best-fit model: R-sq=0.48, p<0.0001). In addition, parental body mass index (BMI), mothers' smoking and physical activity and children's objective measure of physical activity were found to be important predictors of children's fatness (best-fit model: R-sq=0.23, p<0.0001). CONCLUSION: These results provide information about predictors of fitness and fatness of 9-year-old children and emphasize the inverse association between the two. Further, our results suggest that mothers have a stronger influence on children's weight than fathers but the opposite may be true for fitness.

The relation of fatness to insulin is independent of fitness in 9- but not 15-yr-olds.

PURPOSE: To explore the relationship between varying aerobic fitness (fitness), fatness, and fasting insulin levels in healthy children. METHODS: A population-based sample of 9-yr-old (9YO, 47 boys, 56 girls) and 15-yr-old (15YO, 53 boys, 51 girls) Icelandic children. Body fatness was evaluated via body mass index, waist circumference adjusted for height (waist adj), and sum of four skinfolds. Fitness was assessed with a graded maximal cycle ergometer test. Fasting insulin was measured using an ECLIA. RESULTS: Fasting insulin correlated to all fatness measures (9YO, r = 0.43-0.46, P < 0.001; 15YO, r = 0.30-0.37, P < 0.003) and fitness (9YO, r = -0.29, P = 0.003; 15YO, r = -0.32, P = 0.001). Adjustment for fitness did not affect the relations between fatness and fasting insulin in 9YO (r = 0.33-0.37, P < 0.001); however, only waist adj remained significantly related to fasting insulin (r = 0.24, P = 0.016) in 15YO. Children in the upper half of fitness and fatness split on the median did not differ in fasting insulin from children in the upper half of fitness but lower half of fatness. Fatness was related to fasting insulin in 9YO (r = 0.51-0.54, P = 0.001) and 15YO (r = 0.31-0.35, P = 0.011-0.028) in the lower half of fitness, but no association was observed in the upper half of fitness in either group. CONCLUSION: Fatness has a greater association with fasting insulin than fitness, especially among 9YO; however, fitness attenuates the adverse relation of fatness to fasting insulin in 15YO but does not change it in 9YO. In both age groups, being fitter and fatter does not result in greater fasting insulin than being fitter and leaner, and fatness is primarily associated with fasting insulin in lower-fit children.