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Jaak Jürimäe

For The Year that Was—2016, I have selected three papers in the area of growth, maturation, and exercise during youth. The year of 2016 was a successful year and it was not an easy task to highlight the most significant publications in this specific area of pediatric exercise science. The first paper has been chosen because it provides, for the first time, the growth and maturational status of elite junior tennis players belonging to the top eight players in the National rankings in various ages and compares against population norms. It appeared that individual differences in growth and maturation contribute towards the selection of elite junior tennis players in both sexes, with a bias towards these athletes who are comparatively tall and heavy for their age already in younger ages. The second paper is a methodological paper and was selected because it provides a unique perspective on the use of different tracking coefficients to investigate short-term tracking of cardiorespiratory and performance-related physical fitness among adolescents during growth and maturation. Specifically, three distinct statistical approaches were applied in this paper: auto-correlations, mulitilevel modeling corrected tracking values for time-varying covariates and Cohen`s Kappa in order to identify group and individual tracking as well as individuals whose trajectories are unstable across time. This methodological paper demonstrated the importance of the selection of the statistical approach to monitor and describe short-term tracking of cardiorespiratory and performance-related physical fitness variables in adolescents during growth and maturation. The third selected paper provided some evidence that the consequence of physical activity during childhood can be far reaching as physical activity might not only promote health benefits but also have positive effects on adulthood earnings.

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Jaak Jürimäe

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Jaak Jürimäe

For “The Year That Was 2017,” I have selected 3 papers in the area of growth, maturation, and exercise during youth. The first paper has been chosen because it provides for the first time the relative age, maturation, and anthropometric biases on position allocation in elite youth soccer players participating in talent identification programs in professional soccer league. Specific anthropometrical attributes characterized playing positions with a bias toward these athletes who are comparatively tall and heavy for their age already in younger ages, whereas position-specific physical attributes do not become apparent until the later stages of talent development. The second paper was selected because it provides a unique perspective on the contributions of different types of sport activities to the development of soccer performance. This paper demonstrated that early specialization and concentration on one sport only during growth is not beneficial in elite youth soccer. In contrast, variable early sporting experience, and not different physiological parameters, facilitates subsequent soccer performance development. The third paper provided some evidence that the consequence of physical activity during adolescence can be far reaching as physical activity might not only predict academic success during compulsory basic education but also boost educational outcomes in adulthood.

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Jaak Jürimäe

This study attempted to validate an anthropometric equation for predicting age at peak height velocity (APHV) in 193 Polish boys followed longitudinally 8-18 years (1961-1972). Actual APHV was derived with Preece-Baines Model 1. Predicted APHV was estimated at each observation using chronological age (CA), stature, mass, sitting height and estimated leg length. Mean predicted APHV increased from 8 to 18 years. Actual APHV was underestimated at younger ages and overestimated at older ages. Mean differences between predicted and actual APHV were reasonably stable between 13 and 15 years. Predicted APHV underestimated actual APHV 3 years before, was almost identical with actual age 2 years before, and then overestimated actual age through 3 years after PHV. Predicted APHV did not differ among boys of contrasting maturity status 8-11 years, but diverged among groups 12-15 years. In conclusion, predicted APHV is influenced by CA and by early and late timing of actual PHV. Predicted APHV has applicability among average maturing boys 12-16 years in contrast to late and early maturing boys. Dependence upon age and individual differences in actual APHV limits utility of predicted APHV in research with male youth athletes and in talent programs.

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Jaak Jürimäe

Physical exercise is known to regulate energy balance. Important to this regulatory system is the existence of several peptides that communicate the status of body energy stores to the brain and are related to the body fatness including leptin, adiponectin and ghrelin. These hormones assist in regulating energy balance as well as somatic and pubertal growth in children. It appears that rather few studies have investigated the responses of leptin, adiponectin and ghrelin to acute exercise and these studies have demonstrated no changes in these peptides as a result of exercise. Leptin levels are decreased and may remain unchanged advancing from prepuberty to pubertal maturation in young male and female athletes. A limited number of studies indicate that adiponectin levels are not different between prepubertal and pubertal athletes and untrained controls. However, in certain circumstances circulating adiponectin could be increased in young athletes after onset of puberty as a result of heavily increased energy expenditure. Ghrelin levels are elevated in young sportsmen. However, pubertal onset decreases ghrelin levels in boys and girls even in the presence of chronically elevated energy expenditure as seen in young athletes. Ghrelin may also be used as an indicator of energy imbalance across the menstrual cycle in adolescent athletes. There are no studies with high-molecular-weight adiponectin and only very few studies with acylated ghrelin responses to acute exercise and chronic training have been performed in young athletes. Since these forms of adiponectin and ghrelin have been thought to be bioactive forms, further studies with these specific forms of adiponectin and ghrelin are needed. In conclusion, further studies should be conducted to investigate the response of these hormones to acute and chronic negative energy balance to better understand their role in regulating energy balance during growth and maturation in young athletes.

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Jarek Mäestu, Jaak Jürimäe, Kairi Kreegipuu and Toivo Jürimäe

The aims were to assess (a) the usefulness of RESTQ-Sport in the process of training monitoring and (b) whether a change in psychological parameters is reflected by similar changes in specific biochemical parameters. The high volume training period, in general, caused increases in stress scales and decreases in recovery scales of the RESTQ-Sport, while during recovery period, stress levels declined. Cortisol was not changed during the study period, but significant increases in creatine kinase activity were found during the high training period compared to reference period. The results of the present study demonstrate that changes in training volume were reflected by changes in the RESTQ-Sport scales. A close relationship was found between cortisol and creatine kinase activity and subjective ratings of stress and recovery.

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Evelin Lätt, Jarek Mäestu and Jaak Jürimäe

Background: Little is known about the impact of sedentary and moderate-to-vigorous physical activity (MVPA) bouts on cardiometabolic health. The aim was to examine how the accumulation of bouts of sedentary time and MVPA associates to cardiometabolic health in children independently of total sedentary and MVPA time. Methods: In a cross-sectional study with 123 boys (10–13 y), sedentary and MVPA bouts were determined using 7-day accelerometry. Each bout was compared with cardiometabolic risk factors and with the risk score that was calculated using standardized values of body mass index, waist circumference, homeostasis model assessment for insulin resistance, triglycerides, and total cholesterol/high-density cholesterol ratio. Results: Time in 10- to 14-minute sedentary bouts was negatively associated with continuous cardiometabolic risk score in weekdays and weekend days and with triglycerides in a weekend (P < .05). Time accumulated in ≥30-minute sedentary bouts was associated with higher insulin and homeostasis model assessment for insulin resistance values in weekend (P < .05). Weekday total MVPA and time accumulated in ≥10-minute MVPA bouts were negatively associated with continuous cardiometabolic risk score and body mass index in weekdays (P < .05). No associations were found between total sedentary time and metabolic health. Conclusion: Significant associations between sedentary and MVPA bouts with cardiometabolic risk factors suggest the need of the more detailed analysis for sedentary behavior and its effects on health risks.

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Jaak Jürimäe, Kaja Haljaste, Antonio Cicchella, Evelin Lätt, Priit Purge, Aire Leppik and Toivo Jürimäe

The purpose of this study was to examine the influence of the energy cost of swimming, body composition, and technical parameters on swimming performance in young swimmers. Twenty-nine swimmers, 15 prepubertal (11.9 ± 0.3 years; Tanner Stages 1−2) and 14 pubertal (14.3 ± 1.4 years; Tanner Stages 3−4) boys participated in the study. The energy cost of swimming (Cs) and stroking parameters were assessed over maximal 400-m front-crawl swimming in a 25m swimming pool. The backward extrapolation technique was used to evaluate peak oxygen consumption (VO2peak). A stroke index (SI; m2 · s−1 · cycles−1) was calculated by multiplying the swimming speed by the stroke length. VO2peak results were compared with VO2peak test in the laboratory (bicycle, 2.86 ± 0.74 L/min, vs. in water, 2.53 ± 0.50 L/min; R2 = .713; p = .0001). Stepwise-regression analyses revealed that SI (R2 = .898), in-water VO2peak (R2 = .358), and arm span (R2 = .454) were the best predictors of swimming performance. The backward-extrapolation method could be used to assess VO2peak in young swimmers. SI, arm span, and VO2peak appear to be the major determinants of front-crawl swimming performance in young swimmers.

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Kristel Võsoberg, Vallo Tillmann, Anna-Liisa Tamm, Toivo Jürimäe, Meeli Saar, Katre Maasalu, Inga Neissaar, Evelin Lätt and Jaak Jürimäe

The aim of this study was to describe longitudinal changes in body composition, leptin, adiponectin, and ghrelin over a 36-month period in prepubertal rhythmic gymnasts (RG) and their age-matched untrained controls (UC) entering into puberty. Thirty-five RG (8.0 ± 0.6 yrs) and 33 UC (8.2 ± 0.6 yrs) were followed at 12-month intervals for the next 3 years. Height, weight, pubertal stage, body composition, leptin, adiponectin, and ghrelin were measured at each time points. The pubertal development over the next 36 months was slower in the RG compared with UC. Leptin was increased in UC and remained unchanged in RG over 3-year study period (3.7 ± 3.6 vs. 0.2 ± 1.1 ng/ml; p < .05). In RG, baseline leptin was negatively correlated with the change in body fat percentage over a 36-month period (r = −0.34; p < .05). The change in adiponectin over the study period was negatively correlated with the change in BMI (r = −0.43; p < .05). RG had relative leptin deficiency per body fat mass. In conclusion, relatively high leptin concentration at the beginning of puberty may predict those girls who do not increase their body fat percentage through coming years and therefore may have increased risk for delayed puberty.

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Anni Rava, Anu Pihlak, Jaan Ereline, Helena Gapeyeva, Tatjana Kums, Priit Purge, Jaak Jürimäe and Mati Pääsuke

The purpose of this study was to evaluate the differences in body composition, neuromuscular performance, and mobility in healthy, regularly exercising and inactive older women, and examine the relationship between skeletal muscle indices and mobility. Overall, 32 healthy older women participated. They were divided into groups according to their physical activity history as regularly exercising (n = 22) and inactive (n = 10) women. Body composition, hand grip strength, leg extensor muscle strength, rapid force development, power output, and mobility indices were assessed. Regularly exercising women had lower fat mass and higher values for leg extensor muscle strength and muscle quality, and also for mobility. Leg extensor muscle strength and power output during vertical jumping and appendicular lean mass per unit of body mass were associated with mobility in healthy older women. It was concluded that long-term regular exercising may have beneficial effects on body composition and physical function in older women.