Background Little is known about the concurrent change in physical activity (PA), sedentary behavior (SB) and sport participation (SP) during adolescence. The main purpose of this prospective and partly objective study was to simultaneously investigate PA, SBs and SP changes between the 1st and 2nd grades of high school in urban adolescents. Methods In this 1-year follow-up study, the participants were 81 secondary-school students (28 boys and 53 girls) aged 15.5 years at the baseline. PA was assessed with the SenseWear Armband multi-sensor activity monitor, while SBs were assessed by using School Health Action, Planning and Evaluation System (SHAPES) PA questionnaire. The SHAPES questionnaire was supplemented with two questions inquiring about SP in organized sports in school and outside of school. Results PA decreased markedly in both genders between the 1st and 2nd grades of high school. Total energy expenditure (TEE) was reduced by 13 kcal/kg/day on average in boys and by 10 kcal/kg/day in girls (p for both <0.001), while mean daily active energy expenditure (AEE) decreased by 7 kcal/kg/day (p < 0.001) and 3 kcal/kg/day (p = 0.04) in boys and girls, respectively. Similarly, the amount of moderate PA declined by 49 min/day in boys and 21 min/day in girls (p for both <0.001). At the same time vigorous PA was cut by 14 min/day (p < 0.001) and 3 min/day (p = 0.003) in boys and girls, respectively. Conversely, time spent in SBs did not show any change. Conclusion In conclusion, a decline in PA between the 1st and 2nd grades of high school was marked but was not accompanied with an increase in SBs. Policies aimed at increasing PA should be targeting the period of entering secondary school to offset the observed drop in PA.

The main aims of this study were: (1) to determine the objectively assessed physical activity (PA) patterns in urban 15-year-old male and female adolescents according to school type and (2) to assess the differences in PA between school days and weekend days. In this cross-sectional study, participants were 187 secondary-school male and female adolescents (61.4% females) attending grammar and vocational schools. Patterns of PA were objectively evaluated using a multi-sensor body monitor for 5 consecutive days. Confounders assessed included biological age, socio-economic status, sum of 4 skinfolds, maximal temperature and the amount of rainfall. Males and females from grammar schools achieved higher total daily energy expenditure (TEE) and active energy expenditure (AEE) compared to their peers from vocational schools (TEE: 50 ± 12 kcal/kg/day vs. 47 ± 12 kcal/kg/day, p = 0.02; AEE: 23 ± 5 kcal/kg/day vs. vocational = 21 ± 6 kcal/kg/day, p = 0.04). No differences in time spent in light (LPA), moderate (MPA) or vigorous (VPA) physical activity were noted between the two groups (p = 0.16–0.43). Next, a significant decline in TEE and MPA between school days and weekends was observed (p< 0.001 and p = 0.02, respectively), while VPA remained the same throughout the week (p = 0.76). Weekly patterns of PA did not show differences by school type or gender (p for interactions = 0.21–0.50). In addition, significantly lower amount of MPA was accumulated during weekends compared to school days, resulting in lower TEE, regardless of school type or gender. Policies and strategies on PA in adolescents should focus vocational schools and weekend days.

Background: The aim of the present study was to investigate the extent of tracking of physical activity (PA), sports participation (SP), and sedentary behaviors (SB) over four years of high school education among the Croatian Physical Activity in Adolescence Longitudinal Study (CRO-PALS) cohort. Methods: In this investigation, participants were 844 high school students (15.6 years at baseline; 49% girls). The SHAPES questionnaire was used to assess PA, SP, and SB at ages 15, 16, 17, and 18 and tracking was assessed using generalized estimating equations. Results: Tracking coefficients for PA were similar in both sexes, ranged from 0.49 to 0.61, and indicated moderate tracking, while the tracking of SB tended to be somewhat higher over the four years of follow-up (β = 0.60–0.72). Youth that participated in sports at baseline had a 16 to 28 times higher odds of continued participation at follow-up, depending on the type of sport and gender. Finally, both low physical activity and high screen time showed strong tracking in both genders. Conclusion: PA and SB tracked moderately between ages 15 and 18. Moreover, the strong tracking of low PA and high screen time indicates that the detection of these risk factors at the beginning of high school should be advocated.

During a soccer match players perform a substantial number of explosive activities such as jumps, duels, shots and dribblings, accelerations, decelerations, changes of direction and sprints. Precisely such repetitive eccentric contractions are related to muscle damage (exercise-induced muscle damage) that is, two or three days after the match, clinically presented as muscle soreness. The aim of this research was to identify the changes in muscle damage indicators in young players after playing a soccer game. The sample of examinees was composed of 43 soccer players (16.8±1.06 years) who were divided into two groups according to their age (22 cadets aged 15.86±0.35 years and 21 U19 players aged 17.76±0.54 years). Each group played one soccer game lasting 90 minutes each. Right before and immediately after the soccer match, examinees venous blood samples were taken in order to determine the markers of muscle damage. All statistical analyses were conducted by the SPSS software. The examinees demonstrated significantly higher values of myoglobin, creatine kinase, lactate dehydrogenase, aminotransferase, alkaline phosphatase and gamma-glutamyl-transferase after the game, as well as total number of leukocytes and concentration of C-reactive protein as indicators of inflammation. The results of this research showed that, as the muscle protein concentration was increased and an inflammatory reaction also occurred, soccer matches caused muscle damage in young players.