Pubertal increment in insulin resistance is negatively related to lumbar bone mineral density in 18-year-old males.

Transient insulin resistance seen during puberty is expected to favour body growth, but our results show that increment in insulin resistance even in physiological ranges during puberty might compromise lumbar spine bone mineral density accrual independently of body composition parameters, and therefore adult bone quality might be challenged. INTRODUCTION: Insulin resistance (IR) might have a compromising effect on growing bone, and therefore adult bone quality might be challenged. The aim of the present study was to identify whether increases in IR during puberty contribute to bone mineral characteristics in males independently of body composition parameters. METHODS: This is a retrospective cohort-based longitudinal observational study. Data from 85 subjects were included. Boys were studied annually during their pubertal years (12 years at baseline) and at follow-up at the age of 18 years. Anthropometry, bone age, fasting blood samples, body composition, total body, and lumbar spine bone mineral characteristics were measured. Insulin resistance was determined by homeostatic model assessment of IR (HOMA-IR). Multiple regression analysis was performed to determine the effect of changes in HOMA-IR during pubertal years as a longitudinal predictor to fixed bone mineral outcome variables at the age of 18 years. All models were adjusted to potential clinically justified confounding variables. RESULTS: After adjustment to baseline bone indices and body composition-related predictors, the pubertal increment in the HOMA-IR was a negative independent predictor of lumbar spine bone mineral areal density (ß = - 0.202, p = 0.005) and lumbar spine bone mineral apparent density (ß = - 0.235, p = 0.005) in 18-year-old males. CONCLUSIONS: Pubertal increment in IR has a potential diminishing effect on lumbar spine bone mineral density accrual independently of body composition parameters. Further studies are needed to clarify whether monitoring HOMA-IR during puberty may identify subjects at increased risk of low peak bone mass and possible osteoporosis in the future.

European fitness landscape for children and adolescents: updated reference values, fitness maps and country rankings based on nearly 8 million test results from 34 countries gathered by the FitBack network.

OBJECTIVES: (1) To develop reference values for health-related fitness in European children and adolescents aged 6-18 years that are the foundation for the web-based, open-access and multilanguage fitness platform (FitBack); (2) to provide comparisons across European countries. METHODS: This study builds on a previous large fitness reference study in European youth by (1) widening the age demographic, (2) identifying the most recent and representative country-level data and (3) including national data from existing fitness surveillance and monitoring systems. We used the Assessing Levels of PHysical Activity and fitness at population level (ALPHA) test battery as it comprises tests with the highest test-retest reliability, criterion/construct validity and health-related predictive validity: the 20 m shuttle run (cardiorespiratory fitness); handgrip strength and standing long jump (muscular strength); and body height, body mass, body mass index and waist circumference (anthropometry). Percentile values were obtained using the generalised additive models for location, scale and shape method. RESULTS: A total of 7 966 693 test results from 34 countries (106 datasets) were used to develop sex-specific and age-specific percentile values. In addition, country-level rankings based on mean percentiles are provided for each fitness test, as well as an overall fitness ranking. Finally, an interactive fitness platform, including individual and group reporting and European fitness maps, is provided and freely available online (www.fitbackeurope.eu). CONCLUSION: This study discusses the major implications of fitness assessment in youth from health, educational and sport perspectives, and how the FitBack reference values and interactive web-based platform contribute to it. Fitness testing can be conducted in school and/or sport settings, and the interpreted results be integrated in the healthcare systems across Europe.

Arterial Structure in 18-Year-Old Males Is Dependent on Physical Activity at 12 Years and Cumulative Cardiorespiratory Fitness From Puberty to Late Adolescence.

PURPOSE: To evaluate the long-term effect of body composition, physical activity, and cardiorespiratory fitness (CRF) from puberty on arterial health in late adolescent males. METHODS: The cumulative burden of physical activity (measured with accelerometer), CRF (VO2peak0.82), and body composition (body mass index, fat mass, and fat percentage) from puberty to late adolescence (sum of 4 time points from 12 to 18 y) was assessed in 102 males. Additional analysis on the first (T1) and last (T4) time points was performed. Intima-media thickness (IMT), carotid-femoral pulse wave velocity, and augmentation index adjusted to heart rate of 75 beats per minute (bpm) as dependent variables were measured at T4 and analyzed in multivariable regression models adjusted for known risk factors including maturation, blood pressure, and smoking habits. RESULTS: T1 and cumulative body composition measures were independently associated with IMT, while cumulative (ß = -0.011, P = .036) and T4 (ß = -0.0.031, P = .001) CRF revealed independent associations with IMT. Individuals with moderate to vigorous physical activity >60 minutes per day at T1 showed relationship (ß = -1.091, P = .026) with IMT independently of late adolescent physical activity. No significant relationship was present for arterial function. CONCLUSION: Arterial structure in adolescent males is associated with physical activity at 12 years while relationship with CRF can be seen in late adolescence and cumulatively from puberty to late adolescence.

Session Rating of Perceived Exertion Is Different for Similar Intensity and Duration Prescribed Low-Intensity Sessions and Has a Different Effect on Performance in Young Cross-Country Skiers.

ABSTRACT: Pind, R, Purge, P, Mäestu, E, Vahtra, E, Hofmann, P, and Mäestu, J. Session rating of perceived exertion is different for similar intensity and duration prescribed low-intensity sessions and has a different effect on performance in young cross-country skiers. J Strength Cond Res 37(1): 187-193, 2023-The aim of this study was to analyze whether the rating of perceived exertion (RPE) and the resulting internal load (sRPE) could differ among subjects when volume and intensity are matched in young cross-country (XC) skiers. Second, we analyzed whether subjects with a high or low RPE response and sRPE have different adaptation after a 1-week low-intensity high-volume training period. Well-trained national level XC skiers (n = 13) aged 13.4 ± 1.9 years took part in a 1-week training period with double poling performance tested pretraining and after 1-week training. All subjects trained under a similar training program. Rating of perceived exertion was measured after each training session on a 10-point scale, and the total training load was calculated by the sRPE method by multiplying training session's duration and the RPE. Subjects were divided into Glow (n = 6) or Ghigh (n = 7) groups based on median rating of RPE (3.78 ± 1.24) in low-intensity trainings. Total training load in low-intensity trainings was higher in Ghigh compared with Glow (4,010 ± 765 vs. 2,499 ± 193 arbitrary units, respectively), although total training time with (16.3 ± 0.8 hours vs. 16.0 ± 0.6 hours) or without (13.1 ± 0.9 hours vs. 13.3 ± 0.7 hours, p > 0.05, respectively to Glow and Ghigh) high-intensity sessions was not different. No significant differences were found for time spent in different heart rate zones between the 2 groups. Increases in performance were significant for both groups (p< 0.05), while the effect was large in Ghigh (+12.5%; ES = 0.74), and medium in Glow (+10.7%; ES = 0.34). Differences in the internal load and the further quantification of training load for different target intensity sessions could provide important practical information to stimulate expected adaptation in young endurance athletes.

Long-Term Rowing Performance Development in Male Olympic and World Championship Medal Winners Compared With Nonmedalists.

ABSTRACT: Mäestu, J, Lelle, R, Mäestu, E, Pind, R, Vahtra, E, Purge, P, and Mikulic, P. Long-term rowing performance development in male Olympic and World Championship medal winners compared with nonmedalists. J Strength Cond Res 37(9): e521-e526, 2023-The purpose of this study was, first, to investigate individual longitudinal 2,000 m rowing ergometer performance (2,000 erg) development of world class male rowers from the beginning of their career until reaching the elite level and to compare ELITE performance development with those who did not reach podium places and, second, to provide 2,000 erg milestones for talent prediction in rowing. Individual annual 2,000 erg performances of 54 male rowers were analyzed from age 15 and throughout their career. Olympic or World Championships medal winners (ELITE; n = 11) were compared with those who did not reach international podium places. Two thousand erg increased ( p ≤ 0.05) until the age of 24 in ELITE, while plateaued earlier for less successful rowers. No differences in the rate of performance improvement were found between ELITE and lower performers ( p > 0.05). At the age of 20, performance between ELITE and international level nonmedal winners reached significant difference (480.7 ± 20.9 W vs. 435.3 ± 33.9 W, respectively) and remained different onwards ( p ≤ 0.05). However, the average of the 10 best seasons cross-sectional performances of less successful rowers were significantly higher until age 18, compared with ELITE. ELITE rowers were able to improve their 2,000 erg performance to higher age; therefore, it is difficult to predict elite performers in junior rowers. Cross-sectional performances of less successful rowers may indicate temporary high-level performers, who might not be able to advance the elite level.

Effect of supervised sprint interval training on cardiorespiratory fitness and body composition in adolescent boys with obesity.

This study examined the effect of a supervised 12-week sprint interval training (SIT) on cardiorespiratory fitness (CRF) and body composition in adolescent boys with obesity. Twenty-eight adolescents with obesity were allocated to either an intervention group (SIT) (13.1 ± 0.3 yrs; body mass index [BMI]: 30.3 ± 0.9 kg.m-2) or a control group (CONT) (13.7 ± 0.4 yrs; BMI: 32.6 ± 1.6 kg.m-2). The SIT group performed 4-6 × 30s "all-out" cycling bouts, interspersed with 4 min of recovery 3 days a week for 12 weeks. CRF was measured by direct peak oxygen consumption (VO2peak) defined as VO2peak per kg of body mass (mL.min-1kg-1) or by VO2peak per kg of lean body mass (mL.min-1LBM-1) and body composition was assessed by dual-energy X-ray absorptiometry. SIT intervention led to a significant and large between-group difference in VO2peak (p = 0.004; η2 = 0.29). Although SIT group had a significant reduction in body fat percentage (BF%) (from 41.1 ± 1.3% to 39.2 ± 1.5%; p = 0.006), there were no between-group differences in the change of the pre- and post-measures in BF% (p = 0.067). In conclusion, 12-week SIT is effective in increasing CRF and decreasing BF% in adolescent boys with obesity.

Developing a comprehensive school-based physical activity program with flexible design - from pilot to national program.

This article focuses on the process of designing the vital, participatory school-based intervention program aiming to increase the physical activity in schools. The program analyzed is Estonian nationwide comprehensive physical activity program Schools in Motion (SiM) that recently received European Commission's #BeActive Education Award. The program has a good performance in terms of willingness of schools to participate in co-creation of program development, the high interest to join the program and zero dropouts, and strong partnership with ministries which enables to actively participate in policy making. Authors analyze the key elements of the planning, piloting, implementation, and scaling phases of the SiM program and share their lessons learnt in co-working with schools. The difficulties faced during the development process, the strengths and challenges associated with an interdisciplinary approach, and involvement of schools as experts have been addressed.

Vitamin D supplementation does not enhance resistance training-induced gains in muscle strength and lean body mass in vitamin D deficient young men.

PURPOSE: Vitamin D (Vit-D) supplementation has been shown to increased muscle strength in young adults. It remains unclear if Vit-D supplementation enhances the efficacy of resistance training (RT). This study tested the hypothesis that Vit-D supplementation would enhance the RT-induced increases in muscle strength and lean body mass (LBM) in Vit-D deficient young men. METHODS: Thirty-nine men (baseline serum 25(OH)D < 50 nmol L‒1) were quasi-randomly assigned to one of the two groups that performed a 12-week supervised RT program concomitant with either Vit-D (8000 IU daily; VD) or placebo (PLC) supplementation. RESULTS: During 12-week RT, energy and nutrient (except Vit-D) intake and training loads did not differ in the two groups. Serum 25(OH)D levels increased from 36.3 ± 9.2 to 142.4 ± 21.9 nmol L‒1 (P < 0.05) in VD group and remained unchanged between 36.3 ± 8.9 and 29.4 ± 6.6 nmol L‒1 (P > 0.05) in PLC group. Muscle strength (1-repetition maximum) increased (P < 0.05) to an equal extent in the two groups in 5 exercises performed on RT equipment, whereas strength gains in chest press and seated row were greater (P < 0.05) in PLC compared to VD group. Total and regional LBM (measured by DXA scan) increased (P < 0.05) equally in the two groups. Android fat mass decreased (P < 0.05) in VD group only. CONCLUSION: Vit-D supplementation does not enhance the efficacy of RT in terms of muscle strength and LBM gains in Vit-D deficient young healthy men.

Internal Load From Hard Training Sessions Is Related to Changes in Performance After a 10-Week Training Period in Adolescent Swimmers.

ABSTRACT: Pind, R, Mäestu, E, Purge, P, Jürgenson, J, Arend, M, and Mäestu, J. Internal load from hard training sessions is related to changes in performance after a 10-week training period in adolescent swimmers. J Strength Cond Res 35(10): 2846-2852, 2021-The purpose of this study was to investigate the association between session rating of perceived exertion (sRPE) and its categorization with the changes in swimming performance in adolescent swimmers. National level swimmers (age 16.4 ± 2.1 years, V̇o2max 50.0 ± 4.0 ml·min-1·kg-1) participated in a 10-week period preceding the National Winter Championships. Pre-training and post-training physiological parameters and swimming performance were measured. All training bouts with sRPE data were recorded. In addition, trainings were categorized as light, moderate, or hard. For calculating the corresponding internal training load (ITL), 2 fixed categorizations were applied based on earlier published sources and an individualized categorization based on ventilatory thresholds. During the 10-week training period, large to very large increases were found in aerobic (effect size [ES] = 1.58) and anaerobic threshold power output W·kg-1 (ES = 2.46), respectively, and smaller, but significant, improvement in 100-m swimming performance (ES = 0.36). Total ITL during the 10-week period was significantly related to changes in anaerobic threshold (r = 0.81). Fixed and individualized sRPE methods from hard sessions were associated with changes in V̇o2max (r = 0.77) and performance of only 100-m leg kicks (r = 0.76), respectively. Internal training load was related to changes in performance variables during the 10-week study period. Using individualized sRPE values, the accumulation of the ITL from hard training sessions was associated with changes in V̇o2max and swimming performance. The aforementioned categorization could help coaches in appropriate application of ITL for assessing the total training load in adolescent swimmers.

Changes in cardiorespiratory fitness through adolescence predict metabolic syndrome in young adults.

BACKGROUND AND AIMS: Higher cardiorespiratory fitness (CRF) has been suggested to reduce the risk of metabolic syndrome (MetS). We aimed to longitudinally examine the changes of CRF on MetS and its risk factors from adolescence to adulthood. METHODS AND RESULTS: At the age of 15 years, 1076 subjects were recruited from 2 cohorts. CRF was measured on a cycle ergometer. MetS was classified as having at least 3 of the following parameters above the threshold of risk factors: waist circumference, triglycerides, high-density lipoprotein cholesterol (HDL), high blood pressure (BP) and fasting glucose. In addition, insulin, total cholesterol and low-density lipoprotein cholesterol were measured and homeostasis model assessment of insulin resistance (HOMA-IR) was calculated. Persistently high, increasing, decreasing and persistently low CRF groups were formed according to change in CRF from adolescence to adulthood. Longitudinal increase in CRF was positively associated with change in HDL and negatively associated with change in insulin, HOMA-IR, triglycerides, BP and prevalence of MetS after adjustment for potential confounders. Subjects with persistently low CRF had 11.5- to 34.4-times higher risk of MetS at the age of 25 and 33 years compared to subjects with persistently high CRF and 14.6- to 15.9-times higher risk compared to the increasing CRF group. CONCLUSION: Higher CRF is strongly related to lower values of MetS risk factors. Increasing CRF from adolescence to adulthood reduces the risk to have MetS later in adulthood. High CRF in adolescence that decreases during adulthood has similar risks to MetS compared to individuals with persistently low CRF.

Association of FTO rs1421085 with obesity, diet, physical activity, and socioeconomic status: A longitudinal birth cohort study.

BACKGROUND AND AIMS: Fat mass and obesity-associated protein (FTO) variants are among genetic variants frequently associated with obesity. We analyzed the association between FTO rs1421085 polymorphism and obesity, dietary intake, cardiorespiratory fitness (CRF), physical activity, and socioeconomic status (SES) from the age of 9-25 years. METHODS AND RESULTS: The sample included both birth cohorts (originally n = 1176) of the Estonian Children Personality Behaviour and Health Study. The association between FTO rs1421085 and obesity, dietary intake, CRF, physical activity, and SES from the age of 15-25 years was assessed using linear mixed-effects regression models. Associations at ages 9 (younger cohort only), 15, 18, and 25 years were assessed by one-way ANOVA. Male C-allele carriers had significantly (p < 0.05) higher body mass index (BMI), sum of 5 skinfolds, body fat percentage, and hip circumference from the age of 15-25 years. Findings were similar at the age of 9 years. In female subjects, waist-to-hip ratio was significantly greater in CC homozygotes. Interestingly, female CC homozygotes had a greater decrease in the rate of change in daily energy intake and lipid intake per year and higher physical activity score at every fixed time point. Moreover, in females, an effect of FTO × SES interaction on measures of obesity was observed. CONCLUSION: The FTO rs1421085 polymorphism was associated with obesity and abdominal obesity from childhood to young adulthood in males, and with abdominal obesity from adolescence to young adulthood in females. This association is rather related to differences in adipocyte energy metabolism than lifestyle.

Maternal physical activity and sedentary behaviour before and during in vitro fertilization treatment: a longitudinal study exploring the associations with controlled ovarian stimulation and pregnancy outcomes.

PURPOSE: To evaluate the association of objectively measured physical activity (PA) and sedentary behaviour before and during in vitro fertilization (IVF) with controlled ovarian stimulation (COS) and pregnancy outcomes. METHODS: This longitudinal study involved 107 infertile women undergoing IVF treatment. PA and sedentary behaviour were measured for 14 consecutive days using accelerometry as follows: (1) before IVF treatment, (2) during IVF at the implantation time, immediately after embryo transfer, and (3) after positive pregnancy test. Total screen time was assessed by questionnaires. COS results were measured as the number of oocytes and embryos obtained, and the study outcomes included positive hCG, clinical pregnancy, and live birth. RESULTS: Compared with baseline activity levels, women significantly reduced their PA and increased sedentary behaviour during IVF (p ≤ 0.001). Higher average PA, light PA, and ratio between breaks in every ≥ 30-min blocks of sedentary time showed positive associations, while sedentary time, number, and time accumulated in blocks of ≥ 30 min of sedentary time associated negatively with oocyte and embryo counts (all p < 0.05). Women with high total screen time during non-work days (≥ 7 h) obtained 4.7 oocytes (p = 0.005) and 2.8 embryos (p = 0.008) less in COS. PA and sedentary behaviour before and during IVF did not affect the positive hCG, clinical pregnancy, and live birth outcomes. CONCLUSION: Our study results suggest that higher time spent in PA and lower time spent in sedentary behaviour before entering assisted reproduction is associated with better COS outcomes, while activity levels before and during IVF do not affect the implantation, pregnancy, and live birth outcomes.

Physical Activity in Puberty is Associated with Total Body and Femoral Neck Bone Mineral Characteristics in Males at 18 Years of Age.

Background and objectives: Studies indicate that genetic and lifestyle factors influence optimal bone development. Adaptations in bone mineral characteristics related to physical activity (PA) are most often observed in pre- and peri-puberty. Longitudinal associations between bone mineral accrual and objectively measured PA in puberty are poorly understood. The present study aims to investigate whether pubertal PA at different intensities is related to bone mineral characteristics in individuals at 18 years of age. Materials and Methods: Anthropometrics, pubertal stage, bone age and PA by accelerometer were measured in 88 boys at the mean age of 12.1 (T1), 13.1 (T2), 14.0 (T3) and 18.0 years (T4). Different bone mineral parameters were measured by dual-energy X-ray at T4. Stepwise multiple regression analysis was performed to determine the effect of bone age, body mass and PA characteristics on measured bone mineral parameters at 18 years of age. Results: Total PA in puberty together with mean pubertal body mass predicted 35.5% of total body (TB) bone mineral density (BMD), 43.0% of TB less head (LH) bone mineral content (BMC) and 48.1% of BMC/height in individuals at 18 years of age. Vigorous PA and body mass in puberty predicted 43.2% of femoral neck (FN) BMD; bone age at T1, vigorous PA and body mass in puberty predicted 47.3% of FN BMC at 18 years of age. No associations between pubertal PA levels and lumbar spine bone mineral characteristics in individuals at 18 years of age were found. Conclusions: Physical activity in puberty has a significant impact on bone mineral characteristics in individuals at 18 years of age, with total PA being a significant predictor of TB BMD and TB LH BMC as well as BMC/height, whereas vigorous PA is a significant predictor of FN BMD and FN BMC.

Rapid trabecular bone growth in puberty associated with stiffer arteries in adulthood - longitudinal study on healthy young males.

Longitudinal bone content data from puberty to adulthood was assessed in 102 healthy males and associations with arterial health in adulthood was analysed. Bone growth in puberty was related to arterial stiffening and final bone mineral content to decreased arterial stiffness. Relationships with arterial stiffness were dependent on the studied bone regions. INTRODUCTION: Our aim was to assess the relationships between arterial parameters in adulthood and bone parameters in several locations longitudinally from puberty to 18-years and cross-sectionally at 18-years. METHODS: 102 healthy male data from a 7-year follow-up study was used to analyse total body (TB), femoral neck (FN) and lumbar spine (LS) mineral content and density by DXA, carotid intima-media thickness (cIMT) by ultrasound, carotid-femoral pulse wave velocity (cfPWV) and heart rate adjusted augmentation index (AIxHR75) by applanation tonometry. RESULTS: Linear regression analysis revealed negative associations between LS bone mineral density (BMD) and cfPWV [ß=-1.861, CI -3.589, -0.132, p=0.035] which remained significant [ß=-2.679, CI -4.837, -0.522, p=0.016] after adjustment to smoking, lean mass, weight category, pubertal stage, physical fitness, and activity. For AIxHR75 similar results were present [ß=-0.286, CI -0.553, -0.020, p=0.035], but were dependent on confounders. Analysis on pubertal bone growth speed showed independent positive associations to AIxHR75 between Δ FN bone mineral apparent density (BMAD) [ß=672.50, CI 348.07, 996.93, p<0.001] and Δ LS BMAD [ß=700.40, CI 57.384, 1343.423, p=0.033]. Further analysis combining pubertal bone growth and adulthood BMC revealed that the relationships of AIxHR75 with LS BMC and ΔFN BMAD were independent of each other. CONCLUSION: Trabecular bone regions like lumbar spine and femoral neck, showed stronger relationships with arterial stiffness. Rapid bone growth in puberty is related to arterial stiffening, while final bone mineral content relates to decreased arterial stiffness. These results could indicate that bone metabolism is independently associated with arterial stiffness rather than bone and arteries just having common traits of growth and maturation.

School Children's Physical Activity and Preferred Activities during Outdoor Recess in Estonia: Using Accelerometers, Recess Observation, and Schoolyard Mapping.

Studies about recess have found that children have higher physical activity (PA) during outdoor recess compared to indoor recess, and well-constructed schoolyards play an important role in stimulating PA in children. This study aimed at investigating the affordances of schoolyards and outdoor recess PA in two urban and two rural primary schools in Estonia. Schoolyards were described with the geographical mapping method, children's activities during outdoor recess were registered by using observations, and PA levels were measured with accelerometers. Students from grades two to six (8-13-year-olds) were included in the study. All observed schoolyards had different spaces including various ball game areas, climbing facilities, and slacklines. The natural environment dominated in the rural schools, and artificial surfaces dominated in the urban schools. Boys in the study tended to enjoy more sport-related activities, whereas girls preferred more social and less active activities. Students participating in outdoor recess spent about twice as much time (20.4%) on moderate-to-vigorous PA (MVPA) compared to indoor recess (9.5%), although boys were more active than girls (22.9% vs. 17.3%). All schoolyards afforded more MVPA during outdoor recess compared to indoor recess, whereas schoolyards with more space per child and natural environment elements generated more varied PA and higher MVPA. These findings confirm the importance of schoolyard design and quality for the variety and intensity of students' PA during outdoor recess.

Results from Estonia's 2022 Report Card on Physical Activity for Children and Youth: Research Gaps and Five Key Messages and Actions to Follow.

The aim of this article is to summarize the results of the 2022 Estonian Physical Activity Report Card across 10 indicators based on available scientific data and national databases, and, additionally, to compare the current results with previous Report Card results. A national expert panel, consisting of research and policy experts, identified the available sources and synthesized as well as graded relevant data related to the physical activity (PA) of Estonian children and youth. Grade B was assigned to Organized Sports and Physical Activity (B-), Community and Environment (B+), and Government (B). Grade C was assigned to Overall Physical Activity (C+), Physical Fitness (C+), Family and Peers (C-), and School (C+). The lowest grade, D, was assigned to Active Play (D), Active Transportation (D+), and Sedentary Behaviors (D-). In Estonia, the participation rate in organized sport is relatively high, and government in addition to community support seem to be at a relatively good level. However, a relatively high number of children and youth did not meet the current PA guidelines, and the levels of sedentary behavior and screen time were very high. The PA of children and youth should be a cross-disciplinary priority, and focus should be put on developing schoolyards and outdoor breaks, varied and easily accessible organized sport, the use of active transportation, and the implementation of physical education that supports leisure time activities.

Serum Osteocalcin, Sclerostin and Lipocalin-2 Levels in Adolescent Boys with Obesity over a 12-Week Sprint Interval Training.

The aim of the study was to examine the effects of supervised cycling sprint interval training (SIT) on serum osteocalcin, lipocalin-2 and sclerostin levels, and bone mineral characteristics among obese adolescent boys. Untrained obese adolescent boys aged 13.4 ± 0.3 were assigned to either a 12-week SIT group (3 sessions/week), or a non-exercising control group who continued with their habitual everyday life. Serum osteocalcin, lipocalin-2 and sclerostin concentrations, and bone mineral values were assessed before and after intervention. After 12-week intervention, where 14 boys in both groups ended the study, there were no significant differences in serum osteokine levels between the groups after 12 weeks, while whole body bone mineral content and lower limb bone mineral density increased in the SIT group (p < 0.05). Change in body mass index was negatively correlated with the change in osteocalcin (r = -0.57; p = 0.034), and positively correlated with the change in lipocalin-2 levels (r = 0.57; p = 0.035) in the SIT group. Supervised 12-week SIT intervention improved bone mineral characteristics, but did not change osteocalcin, lipocalin-2 or sclerostin levels in adolescent boys with obesity.

The Effect of Different Periodization and Modes of Concurrent Strength and Endurance Training on Double Poling Performance and Body Composition in Adolescent Cross-Country Skiers.

The aim of the study was to compare the effects of different types and periodization of strength training on body composition and maximal aerobic performance in 10-week training period in adolescent XC skiers. Twenty-eight adolescent competitive cross-country skiers, including 10 females (age 17.9 ± 1.8 years; body mass 69.6 ± 9.7 kg; height 1.77 ± 0.1 m; training experience 8.6 ± 3.2 years) took part in this study. Pre-and post-intervention performance was measured with the incremental exercise test (Pmax) on a double poling ski ergometer. Changes in body composition were measured with DXA. In addition to regular endurance training, experimental group one (EXP1) performed maximal and explosive strength training two times per week, experimental group two (EXP2) performed maximal and explosive strength training 1-3 times per week, and the traditional (TRAD) group performed low intensity-high volume strength training 2 times per week. Increases in arm, trunk, and overall lean mass were found in TRAD (p < 0.05). Increases in arm lean-mass was found in EXP1 (p < 0.05), while no changes in body composition occurred in EXP2 (p ≥ 0.05). Pmax improved significantly in all groups (p < 0.05). Changes in body mass, overall and arm lean mass was related to changes in absolute performance (W; p < 0.05), while no relationships were found between changes in body composition parameters and relative performance (W/kg; p ≥ 0.05). In conclusion, different periodization of strength training led to similar improvements in double poling ergometer performance, but resulted in different changes in body composition (lean mass) in adolescent cross-country skiers.

Corrigendum: Increases in RPE Rating Predict Fatigue Accumulation Without Changes in Heart Rate Zone Distribution After 4-Week Low-Intensity High-Volume Training Period in High-Level Rowers.

[This corrects the article DOI: 10.3389/fphys.2021.735565.].

Leptin to adiponectin ratio in puberty is associated with bone mineral density in 18-year-old males.

INTRODUCTION: Inconsistent associations of leptin and adiponectin with bone mineral characteristics in puberty and adolescence have been reported. We aimed to examine the associations between leptin to adiponectin ratio (LAR) in puberty and bone mineral characteristics at the age of 18 years in healthy males. MATERIALS AND METHODS: 88 white Caucasian boys were investigated at T1 (mean age 12.1 years), T2 (14.0 years) and T3 (18.0 years). Serum leptin and adiponectin were measured and LAR was calculated at T1, T2 and T3, bone mineral density (BMD) and bone mineral apparent density (BMAD) for total body and lumbar spine (LS) at T1 and T3. Spearman correlation coefficient and partial correlation analyses were used to describe the associations between mean pubertal LAR and BMD at T3. RESULTS: Mean pubertal LAR was negatively correlated with both LS BMD (r = -0.23; P < 0.05) and LS BMAD at T3 (r = -0.33; P < 0.05). These associations remained significant also in partial correlation analysis after controlling for total body fat percentage, total testosterone, HOMA-IR and physical activity at T1 (r = -0.31; P < 0.05 and r = -0.41; P < 0.05 respectively). CONCLUSION: LAR in puberty is negatively associated with lumbar spine BMD and lumbar spine BMAD at the age of 18 years.