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Ben-Zaken, S, Meckel, Y, Nemet, D, and Eliakim, A. Insulin-like growth factor axis genetic score and sports excellence. J Strength Cond Res 35(9): 2421-2426, 2021-It has been suggested that IGF1 polymorphisms associated with circulating IGF1 levels may be linked to elite short-distance running performance. This study assessed genetic score based on 6 polymorphisms related to the Insulin-like growth factor axis (rs7136446, rs35767, rs6220, rs680, rs2854744, and rs1805086) among elite Israeli runners and swimmers. One hundred sixty-one track and field athletes (123 men and 38 women, age 17-50 years) and 94 swimmers (61 men and 33 women, age 16-49 years) participated in the study. Athletes were divided into short-distance runners (SDRs, major event: 100-200-m sprints and jumps, n = 63) and long-distance runners (LDRs, major event: 5,000 m and marathon, n = 98). Swimmers were divided into short-distance swimmers (SDSs, major event: 50-100 m, n = 44) and long-distance swimmers (LDSs, major event: 400-1,500 m, n = 50). Groups were subdivided into top-level and national-level athletes. We calculated the IGF genetic score (IGF-GS) of all the subjects on a 0-100 scale. Top-level SDRs' mean IGF-GS (30.8 ± 11.7) was significantly higher (p0.006) compared with national-level SDRs' (20.5 ± 11.3) and top-level SDSs' (19.9 ± 8.5). Subjects with IGF-GS25 had an increased odds ratio (OR) of being elite-level SDRs (OR: 4.2; 95% confidence interval: 0.68-26.09; p0.001). In summary, a combined assessment of 6 single-nucleotide polymorphisms, all known to modulate circulation IGF1 levels, was associated with a higher genetic score among SDRs, emphasizing the importance of the IGF system to land speed sports events but not to swimming events. Whether the IGF-GS may be used for selection of elite-level sprinters in early stages of their athletic career needs to be further investigated.

Purpose: To examine the effect of growth hormone (GH) treatment on physical performance in children with idiopathic short stature and normal GH secretion. Materials and Methods: A total of 24 children participated in the study (13 GH-treated, 11 non-treated, aged 8–13 y, 11 males and 13 females, Tanner stage 1–2). Participants performed a battery of motor skill performance tests (Eurofit), as well as the Wingate anaerobic test. Results: No statistically significant differences in any of the Eurofit physical fitness test results (eg, 20-m shuttle run 33.0 [15.1] vs 25.1 [21.0] laps in treated and nontreated participants, respectively, P = .25) or the Wingate anaerobic test were found between the groups (eg, peak power 5.0 [2.9] vs 3.9 [2.6] watts/kg in treated and nontreated participants, respectively, P = .2). Conclusions: Therapeutic usage of exogenous GH for pre and early pubertal children with idiopathic short stature and normal GH secretion was not associated with beneficial effects on physical performance indices. This suggests that the use of GH as a potential performance enhancing agent, in this age group, at least at commonly used doses, is not advantageous.

The effects of childhood obesity on tendon structure and its relation to physical activity are barely known. We aimed to investigate the influence of a 6-month multidisciplinary childhood obesity management program (which included dietary intervention and an exercise program) on Achilles tendon structure in overweight/obese children. Twenty-five overweight/obese children (overweight group) who participated in a 6-month multidisciplinary childhood obesity program, and 27 normal-weight controls were examined for anthropometric measurements and for Achilles tendon structure (using ultrasound tissue characterization to capture a three-dimensional structure of four echo type fibers and the cross-sectional area) at baseline, 3, and 6 months. The BMI of the overweight group significantly decreased from the pre- to the post-intervention period, (p = .002, η2 = .229), yet among the control group, the BMI significantly increased (p = .002, η2 = .222). Interactions (pre-post × group) showed a significant decrease in the prevalence of echo type I and in echo type III fibers and a significant increase in the prevalence of echo type II fibers and in the cross-sectional area along the intervention. No significant changes in echo type fibers were found in the control group along the 6 months. Conclusion: At pre-intervention, the overweight group had significantly “worse” tendon structure, with a lower prevalence of echo type II fiber and a higher prevalence of echo type III fibers compared with the control group. Following the 6-month intervention, the tendon structure of the overweight group was “positively” changed, with reduced echo type III fibers and increased echo type II fibers.

The aim of the study was to examine the effect of Newcomb ball (also known by the name of catchball) training on the physical fitness of women at midlife. One hundred and eighteen women, aged 29 - 45 yrs, were assigned to an experimental group (EG) or a control group (CG), and completed two similar sets of tests before and after seven months of training. The EG performed two Newcomb ball training sessions per week that included technical and tactical drills with and without the ball, small sided games and full games at different variations. The CG remained non-active throughout the seven months. Leg power, arm power, agility, speed, and aerobic scores were significantly higher for the EG compared to the CG at baseline (p p p < 0.05), were found for the CG in any of the other fitness variables. The findings indicate that amateur Newcomb ball training can be used as an efficient and enjoyable tool for fitness development among midlife women.

Aim: To investigate differences in Achilles tendon structure between children with overweight/obesity and children with normal weight.Methods: Twenty-two children with obesity, 10 children with overweight, and 44 children with normal weight participated in the study. BMI% was calculated. The Achilles tendon was examined using ultrasound tissue characterization (UTC) imaging to capture a three-dimensional structure of four echo-type fibers and a cross-sectional area.Results: A significantly higher percentile of echo-types II, a lower percentile of echo-types III and IV, and a lower cross-sectional area were found for children with normal weight compared with children with overweight/obesity (p < .05). Following a piecewise linear regression model according to tendon structure, a BMI percentile of 75% was found to be the most accurate cutoff point of the children into the "unaffected" (BMI%

Aim The aim of the study was to examine the effect of information placebo on fitness test results in normal weight, overweight and obese children. Methods Twenty-four pre-pubertal children with overweight or obesity and 24 age and maturity-matched normal weight children performed a progressive treadmill exercise test twice. Different types of information were randomly provided regarding a water drink consumed prior to testing; standard (water) vs deliberate positive (presumed energy drink, placebo) information. Results Following the placebo drink, both groups demonstrated significantly higher peak heart rate (overweight 165.8 ± 16.7 vs 174.2 ± 14.8 bpm and normal weight 177.9 ± 13.6 vs 189.8 ± 12.2 bpm) and longer time to exhaustion (overweight 396.9 ± 161.9 vs 521.5 ± 182.5 seconds; normal weight: 700.1 ± 155.2 vs 893.3 ± 150.1 seconds). Despite longer exercise duration and higher peak heart rate, average and peak rate of perceived exertion were significantly lower after the placebo drink (overweight 14.1 ± 2.5 vs 12.5 ± 2.5; normal weight 12.1 ± 1.4 vs 10.7 ± 1.5), with significantly shorter recovery time (overweight 132.2 ± 28.5 vs 118.4 ± 31.6; normal weight: 106.7 ± 18.6 vs 96.7 ± 17.8 seconds). Conclusion Our results demonstrate a significant effect of information placebo on fitness test results that is unrelated to body weight. Children with obesity may enhance their physical activity levels and energy expenditure if properly encouraged.

Ben-Zaken, S, Eliakim, A, Nemet, D, and Meckel, Y. Genetic variability among power athletes: the stronger vs. the faster. J Strength Cond Res XX(X): 000-000, 2019-Athletic events can be divided into "aerobic-type events" or "anaerobic-type events" based on energy usage. Power, speed, and strength are also used to specify sports subtypes. Weightlifters (WLs), sprinters, and jumpers feature high-intensity efforts lasting a few seconds. However, their performance requires different proportions of power, speed, and strength. The aim of the current study was to examine genetic differences between subtypes of anaerobic athletes in 3 genetic variants: ACTN3 R577X, which is associated with muscle contractions; AGT Met235Thr which is associated with muscle growth; and PPARD T/C, which is associated with aerobic capacity. Seventy-one sprinters and jumpers (S/J), 54 WLs, and 86 controls participated in the study. Genomic DNA was extracted from peripheral blood using a standard protocol. Genotypes were determined using a TaqMan allelic discrimination assay. The ACTN3 RR genotype frequency was significantly higher among S/J (39.4%) compared with WLs (22.2%) and controls (18.6%). The AGT Thr-Thr genotype frequency was significantly higher among WLs (25.9%) compared with S/J (4.2%) and controls (12.8%). PPARD T294C genotype frequencies did not differ between groups. The results suggest that there may be a specific genetic makeup enabling an athlete to excel in speed-oriented events (sprints), rather than in strength-oriented events (weightlifting).

BackgroundA structured transition process for young adults with chronic medical conditions from pediatric to adult clinics is strongly promoted. However, the most appropriate transition model has not yet been determined. This study evaluated the effect of a “combined team” Endocrinology Transition Clinic model, including a joint meeting with the patient and pediatric and adult endocrinologists, regarding medical treatment, adherence to follow-up and patient satisfaction with the process.MethodsClinical and demographic data of patients admitted to the Endocrinology Transition Clinic were collected. The clinical impact of the transition meeting was evaluated based on treatment modifications and patient adherence to follow-up. Patient satisfaction was evaluated using a questionnaire.ResultsFrom September 2014 through November 2018, 107 patients attended the Endocrinology Transition Clinic, 85.0% were females, mean age 19.7 ± 2.2 years (range 16–29), 97.2% were unmarried. The most common endocrine disorders were obesity (41.1%), Hashimoto’s thyroiditis (41.1%) and ovarian hyperandrogenism (38.3%). The Transition Clinic visit modified treatment and/or evaluation for 48 (44.8%) patients. Adherence to follow-up in the adult clinic was 82.9% and was not associated with gender (p = 0.366), ethnicity (p = 0.725), age at transition (p = 0.479) or obesity (p = 0.375). Overall satisfaction reported by 65/85 patients was high (86.8%), although higher among patients who were adherent to follow-up (89.4% vs. 65.6%, p = 0.006).ConclusionsThe “combined team” transition model in endocrinology requires relatively few resources and has considerable clinical impact, high adherence to follow-up and high patient satisfaction rate. Implementing this model at the interface of pediatric and adult endocrinology units, and possibly in other medical fields, is feasible and efficient.

Hejla, D, Dror, N, Pantanowitz, M, Nemet, D, and Eliakim, A. Reduced growth hormone response to anaerobic exercise among children with overweight and obesity. J Strength Cond Res 36(8): 2194-2197, 2022-The aim of the present study was to examine the effect of an anaerobic exercise test on growth hormone (GH) secretion in children with overweight and obesity compared with children with normal weight. Fifteen children with overweight (body mass index percentile [BMI%ile] ≥8595) and obesity (BMI%ile ≥95) and 10 children with normal weight (BMI%ile585) participated in the study. Subjects performed a modification of the Wingate anaerobic test (WAnT), with 10 bouts of 15-second cycling separated by 1 minute of rest. Blood samples for GH and lactate were collected before and 15, 30, 45, and 60 minutes after the beginning of the exercise test. There was a significant increase in GH levels following the modified repeated WAnT in both groups, but the increase in GH levels was significantly greater among the normal weight children compared with those with overweight and obesity ( p0.003). Seven of the 10 subjects with normal weight had GH increase above the threshold for GH sufficiency compared with only 2 subjects with overweight and obesity. Growth hormone response to the modified repeated WAnT was significantly reduced among children with overweight and obesity compared with those with normal weight. Anaerobic interval-type training may not be a sufficient exercise alternative to stimulate appropriate GH levels among children with obesity.

Background The aim of the study was to examine the influence of the placebo effect on the endurance capacity results in normal weight children. Methods Twenty-four pre-pubertal normal-weight children aged 6–13 years participated in the study. Subjects underwent anthropometric measurements (weight, height, BMI percentile, and fat percentage), a progressive treadmill exercise test to evaluate endurance capacity, and filled habitual activity questionnaire. The participants were examined twice, in a random order, with each child being compared to him/herself. Different types of information were provided regarding a water drink consumed prior to testing- standard information (water) vs. deliberate positive information (presumed energy drink, placebo). Results Following the placebo drink, children demonstrated significantly higher peak pulse (177.9 ± 13.6 vs. 189.8 ± 12.2 bpm), higher stage achieved and longer time of exercise to exhaustion (700.1 ± 155.2 vs. 893.3 ± 150.1 s). Although the exercise duration was longer, stage and heart rate achieved were higher, the reported average, and peak rate of perceived exertion (RPE) were significantly lower for the placebo (18.3 ± 1.4 vs 16.2 ± 1.5). Although the effort was higher while drinking placebo (longer run, higher exercise phase, higher heart rate), recovery time was significantly shorter. The reported differences were not associated with order of tests, age, gender or child activity level. Conclusion Our results demonstrate a significant information placebo effect on children’s endurance capacity test results. This highlights the possible role of positive information (placebo) in trying to encourage physical activity in children. Whether this effect could be applied to longer-term interventions has yet to be tested. Trial registration ClinicalTrial.gov identifier: NCT03165604, Registered May 24, 2017.

Objectives To determine the between-visit reliability of an accelerometer as a measure of lower-extremity impact acceleration at a variety of gait speeds in children. Design Absolute reliability assessment. Methods Ten children with no known gait pathology attended two testing sessions, three weeks apart. A tri-axial accelerometer was fixed to the child’s distal tibia to measure peak positive acceleration responses while walking and running on the treadmill at three different speeds (comfortable walking, threshold walking, and jogging). Reliability of the average and standard deviation Peak Positive Acceleration (avgPPA and sdPPA, respectively) was calculated by intra-class correlation coefficients (ICC) and Minimum Detectable Change (MDC). Results Excellent reliability was indicated with ICC values for avgPPA of 0.90, 0.95, and 0.81 for comfortable walking, threshold walking, and jogging, respectively. Moderate reliability was found for the sdPPA measures. MDC values were calculated to be 18%, 26%, and 23% for comfortable walking, threshold walking, and jogging, respectively, indicating the amount by which an avgPPA value would need to change to ensure that the change is greater than a measurement error. Conclusions An accelerometer attached to the distal tibia is practical for use in a clinical environment to collect lower extremity acceleration data in children. Clinicians can utilise this technique for assessing a change following an intervention, such as biofeedback gait retraining.

Physical education teachers should be able to evaluate exercise intensity objectively as well as subjectively in order to implement the appropriate load during activity sessions. Whereas measuring oxygen uptake or blood lactate level during exercise may be a complicated task in field conditions, monitoring heart rate (HR) values can be a relatively simple procedure when performed outdoors. The aim of this study was to examine the subjective estimation accuracy of HR in different exercises among physical education students. Pre-exercise estimations of HR were collected from 180 students prior to a multi-task activity session. The estimated HR values were then compared with true HR values, which were monitored throughout the session using a portable HR monitor system. A mean significant difference of 13.4% was found between the estimated and actual HRs for all activities. A majority of the students (70%) estimated HR values to be lower than the true values. The most accurate HR estimations were found in extremely easy or in extremely difficult activities, whereas the least accurate estimations were found in moderate-level activities. No significant differences were found in HR estimation accuracy between males and females or between individuals with higher and with lower aerobic fitness. The results indicated that physical education students can estimate their HR responses to a reasonable degree of accuracy, but with most underestimating them compared to the actual values.

Purpose: To assess the effect of 1 week of consuming a placebo “energy drink” compared with a week of drinking regular water on daily physical activity in obese children participating in a weight reduction multidisciplinary program. Methods: Seventeen prepubertal (age = 128.7 [26.6] m) overweight and obese children (7 females and 10 males) participated in the study. Participants received 7 bottles of mineral water per week for 2 weeks. Different types of information were randomly provided regarding the drink consumed in each week: standard (water) versus deliberate positive information (presumed energy drink and placebo). Daily step count was measured using pedometers and compared using paired t test. Results: After consuming the placebo drink, children demonstrated a significantly higher average daily step number (10,452 [4107]) compared with the days they drank water (8168 [2928], P Conclusion: The use of placebo in the form of deliberate positive information was associated with a significant increase in real-life physical activity in overweight and obese children, especially in boys. Positive information may be used to encourage children with obesity to enhance daily physical activity and energy expenditure.

The aim of the present study was to assess prospectively the effect of pre-season fitness on injury rate during the competitive season among professional soccer players. Thirty-one players participated in the study during two consecutive competitive seasons (2015–16 and 2016–17; a squad of 22 players in each season). During the 6-week pre-season training period (8 training sessions and a friendly match every week, 14–18 training hours/week) there was a significant improvement in VO2 max, a significant increase in ideal and total sprint time and no change in vertical jump, flexibility and repeated sprint-test performance decrement. During the two consecutive seasons, 28 injuries were recorded. Ten injuries were classified as mild (missing 3–7 days of practice/match), 8 as moderate (missing 8–28 days) and 10 as severe (missing >28 days). The rate of match injuries was higher (9.4 per 1000 match hours) compared to practice injuries (4.7 per 1000 training hours). Most injuries were overuse injuries (72%) of the lower limbs (71%). Most of match injuries occurred during the last 15 min of each half. There were no differences in fitness characteristics in the beginning of pre-season training between injured and non-injured players. However, improvements in VO2 max during the pre-season training period were significantly lower among injured players (0.9±5.5%) compared to non-injured players (10.4±6.5%, p

The Pediatric Exercise Science “Year That Was” section aims to highlight the most important (to the author’s opinion) manuscripts that were published in 2017 in the field of endocrinology and pediatric exercise science. This year’s selection includes studies showing that 1) in pubertal swimmers, there is a decrease in insulin-like growth factor-1 (IGF-I) and IGF-binding protein-3 (IGFBP-3) during intense training (a catabolic-type hormonal response) with an anabolic “rebound” characterized by a significant increase of these growth factors during training tapering down. Moreover, it was shown that changes of IGF-I and IGFBP-3 paralleled changes in peak and average force but not with endurance properties, showing decreases during intense training and increases during tapering; 2) a meta-analysis showing that growth hormone administration elicits significant changes in body composition and possible limited effect on anaerobic performance but does not increase either muscle strength or aerobic exercise capacity in healthy, young subjects; and 3) short-term exercise intervention can prevent the development of polycystic ovary syndrome in a dose-dependent manner in letrozole-induced polycystic ovary syndrome rat model with high-intensity exercise being most effective. The implication of these studies to the pediatric population, their importance, and the new research avenues that were opened by these studies is emphasized.

Previous studies have shown that the IGF1 polymorphism is associated with greater muscle mass and improved power athletic ability, but very little is known about the IGF2 polymorphism and athletic performance.The aim of the present study was to assess the frequency distribution of the IGF2 rs680 polymorphism among Israeli athletes.185 short- (n=72) and long-distance (n=113) runners, 94 short- (n=44) and long-distance (n=50) swimmers, 54 weight lifters and 111 controls participated in the study. Genomic DNA was extracted from peripheral EDTA treated anti-coagulated blood using a standard protocol. Genotyping of the IGF2 A/G polymorphism (rs680) was performed using allelic discrimination assay.The frequency of IGF2 (rs680) G allele carriers was significantly greater among top compared to national-level track and field sprinters and jumpers (p0.05). The IGF2 (rs680) GG genotype frequency was significantly greater among track and field sprinters and jumpers compared to weight lifters p0.02), and among top-level sprinters and jumpers compared to top-level weight lifters p0.01). There were no statistically significant differences in the IGF2 (rs680) GG genotype frequency among endurance athletes and between the swimmers and the other sports disciplines and the controls.While a single polymorphism cannot determine athletic success or failure, the findings of the present study suggest a potential importance of the IGF2 polymorphism, mainly regarding speed sport performance.

To investigate the influence of a weight-reduction program with locomotion-emphasis on improving biomechanical characteristics of children who are obese (OW).Ten children who are OW participated in a 6-month multidisciplinary childhood obesity management program (GRP1); another 10 children who are OW participated in the same multidisciplinary childhood obesity management program with additional locomotion-emphasis exercises for improving biomechanical characteristics (GRP2); and 10 control children who are OW with no intervention program. Outcomes were anthropometric measurements and temporal and foot pressure parameters.GRP2 had significantly improved foot pressure in the different walking/running speeds compared with GRP1. In the temporal parameters, pretests by speed by group interactions were significantly improved for GRP2 compared with GRP1.We found evidence to support beneficial effects of combined dietary and physical activity/locomotion-emphasis exercises on the movement characteristics of children who are OW.

Tibial stress fractures are associated with increased lower extremity loading at initial foot-ground contact, reflected in high peak positive acceleration (>8 g) of the tibia in adults. There is no reported data on peak positive acceleration of the tibia in children during walking and running. The aim of this study was to establish tibial peak positive acceleration responses in children across a range of age and gait speeds. Twenty-four children aged 8.5 ± 1.4 years with no known gait pathology comprised two age groups; Young (7–9 year, n = 12) and Older (10–12 years, n = 12). Wireless Inertial Measurement Unit comprising a tri-axial accelerometer was securely taped to the anteromedial aspect of the distal tibia to measure peak positive acceleration responses while walking and running on the treadmill at 3 different speeds (20% below baseline, baseline, and 20% above baseline). Results showed significant increase in peak positive acceleration with increased gait speed and greater variability in young children compared to older children. The study suggests that ground impact in walking, but not running, is mature by age 7 years. Future studies should explore strategies using peak positive acceleration responses to monitor ground impact during sport activities and its application in gait retraining.

The characterization of activity patterns of overweight and obese (OW) children and adolescents is essential, and should be carried out before they join an exercise training programme and increase their physical activity in order to maintain or reduce body weight.The purpose of this study is to verify whether the biomechanical parameters characterizing frequently used walking and running speeds vary between OW and normal-weight (NW) children. Thirty-one prepubescent OW children (9.9 y ± 1.3) and 10 prepubescent NW children (9.9 y ± 1.2) participated in this study. All participants were evaluated for temporal parameters (e.g. cycle length, cycle time, stance phase time, double support phase time, etc.) and for foot pressure parameters (e.g. contact area, duration of contact, peak pressure, etc.) in six different foot areas, at three walking velocities, and two running velocities. A group effect (p < .05) was found for the peak pressure, duration of contact percentile, maximum force, foot pressure–time inte...

The IL-6 -174G/C single nucleotide polymorphism (SNP) functionally affects IL-6 activity, with the G-allele associated with increased IL-6 levels. The C-allele was found to be associated with exercise-induced skeletal muscle damage. The aim of the present study was to examine the association between the IL-6 -174G/C polymorphism and athletic performance among elite swimmers and runners. The study sample included 180 track and field athletes and 80 swimmers. Track and field athletes were assigned to three sub-groups: long-distance runners, middle-distance runners and short-distance runners. Swimmers were assigned to two subgroups: long-distance swimmers and short-distance swimmers. The control group consisted of 123 non-athletic healthy individuals. Genomic DNA was extracted from peripheral blood following a standard protocol. Genotyping was performed using polymerase chain reaction (PCR). The CC genotype and C-allele frequency were significantly higher in the long-distance swimmers (18 and 43%, respectively) compared to the long-distance runners (3 and 14%, respectively, p < 0.001); middle-distance runners (4 and 22%, respectively, p < 0.001); and controls (5 and 19%, respectively, p < 0.001). In addition, the CC genotype and C-allele frequency were significantly higher (p < 0.001) in long-distance swimmers compared to short-distance swimmers (18 versus 5% and 43 versus 29% for the CC genotype and C-allele frequency, respectively). The higher frequency of the C-allele and CC genotype among long-distance swimmers suggests that the rarity of exercise-associated rhabdomyolysis among swimmers is probably related to other sports-specific or water-related protective mechanisms. It is possible that swimming selection in talented endurance athletes who are C-allele carriers represents an example of genetically-dependent sports selection.

The Pediatric Exercise Science Year That Was section aims to highlight the most important (to the author’s opinion) manuscripts that were published in 2016 in the field of endocrinology and pediatric exercise science. This year’s selection includes studies showing that 1) Induction of T4 to T3 conversion by type 2 deiodinase following aerobic exercise in skeletal muscles was associated with concomitant increase in peroxisome proliferatoractivated receptor-γ coactivator-1α, and mitochondrial oxidative capacity and therefore plays an important mechanistic role in the muscle adaptation to exercise training. 2) Hypothyroidism in fetal and early postnatal life was associated with impaired spatial learning and memory and with reduced hippocampal brain-derived neurotrophic factor in male and female rat pups. Forced (treadmill) and voluntary (wheel) exercise alleviated all these biochemical and neuro-cognitive deficits. 3) The relationship between different exercise intensities and carbohydrate requirements to maintain euglycemia at basal insulin levels among adolescent and young adults with Type 1 diabetes are nonlinear but rather inverted- U with no exogenous glucose required to maintain stable glucose level at high-intensity exercise (80%). The implication of these studies to the pediatric population, their importance and the new research avenues that were opened by these studies is emphasized.

The effectiveness of exercise training depends on the training load and on the individual ability to tolerate it, and an imbalance between the two may lead to under- or overtraining. Therefore, efforts have been made to find objective parameters to quantify the balance between training load and the athlete’s tolerance.

The aim of the study was to estimate the current incidence and the distribution of etiologies of primary ovarian insufficiency (POI) in a nationwide study. The prevalence of POI in young adult women has recently increased, but the data cited for adolescents are more than three decades old.Data regarding females aged21 years diagnosed with POI during the years 2000-2016 were collected from all the pediatric endocrinology units in Israel. POI was defined by at least 4 months of amenorrhea in association with menopausal levels of follicle-stimulating hormone. Iatrogenic cases were excluded.For the 130 females aged21 years included in the study, the distribution of POI etiologies was Turner syndrome/mosaicism in 56 (43%), idiopathic in 35 (27%), and other (developmental, genetic, metabolic, adrenal, and autoimmune) in 39 (30%) females. During the years 2009-2016, compared with 2000-2008, the incidence rate of new POI diagnoses per 100,000 person-years doubled (4.5 vs. 2.0; p value.0001), and incidence rates of idiopathic and other etiologies increased by 2.6 (p value = .008) and 3.0 (p value = .002), respectively. In contrast, the incidence of Turner syndrome was constant (p value = .2). In the age group of 15-21 years, the current incidence of non-Turner POI in adolescents is one per 100,000 person-years.In this nationwide study, the incidence rate of POI in youth aged21 years was one tenth of the rate that is commonly cited. A significant increase in the rate of POI in non-Turner females was observed over the last decade. Contributions of environmental and epigenetic factors should be studied.

BACKGROUND The aim of the study was to examine the placebo effect on fitness test results in trained and untrained overweight and obese children. METHODS Twenty pre-pubertal overweight children performed two pairs of progressive treadmill exercise tests before and 12 weeks into a multidisciplinary program for the treatment of childhood obesity. In each test pair, at random order, participants received different types of information regarding a water drink consumed prior to testing-standard information (water) vs deliberate positive information (presumed energy drink, placebo). RESULTS The intervention led to a significant change (P

Previous studies have demonstrated that compared to runners, swimmers carry a higher prevalence of the IL-6 -174C polymorphism and lower single nucleotide polymorphism frequencies of the IGF system.The aim of the present study was to assess the combined frequency of the IL-6 -174G/C and IGFBP3 -202A/C polymorphisms among track and field athletes and swimmers.Track and field athletes were divided into long-distance runners (major event 5000 m-marathon, n = 63) and power athletes (major event 100-200 m sprints and long jump, n = 67). Swimmers were divided into long-distance swimmers (major event: 400-1500 m, n = 50), and short-distance swimmers (major event: 50-100 m, n = 43). All participants had achieved results that ranked them among the top all-time Israeli athletes in their event, and competed at national and/or international level on a regular basis.Carrying both IL-6C and IGFBP3C mutations was significantly greater among long-distance swimmers (LDS - 44%) compared to long distance runners (LDR - 21%, p .01), and among short distance swimmers (SDS - 49%) compared to sprinters and jumpers (S/J - 28%, p .05). Among runners, the prevalence of those not carrying either of the two mutations was significantly higher among LDR (25%) compared to S/J (10%, p .03).The prevalence of carrying both IL-6C and IGFBP3C mutations was significantly higher among the swimmers compared to runners. It is possible that carrying the IGFBP3C polymorphism is required to compensate for the potential genetically non-beneficial effects of a higher IL-6C genotype and an attenuated IGF system among the swimmers.

This study aimed to identify differences in ground impact shock attenuation between overweight and healthy-weight children during running. Twenty overweight children aged 8.4 (1.1) years and 12 healthy-weight children aged 10.7 (1.3) years ran on a treadmill (120% of baseline speed) while wearing 2 inertial sensors located on their distal tibia and lower back (L3). Peak acceleration attenuation coefficient at foot contact and transfer function of the acceleration were calculated. Peak positive acceleration values were not significantly different between the overweight children and healthy-weight children (3.98 [1.17] g and 3.71 [0.84] g, respectively, P = .49). Children with healthy weight demonstrated significant greater attenuation as evident by greater peak acceleration attenuation coefficient (35.4 [19.3] and 11.9 [27.3], respectively, P P

This commentary highlights 23 noteworthy publications from 2018, selected by leading scientists in pediatric exercise science. These publications have been deemed as significant or exciting in the field as they (a) reveal a new mechanism, (b) highlight a new measurement tool, (c) discuss a new concept or interpretation/application of an existing concept, or (d) describe a new therapeutic approach or clinical tool in youth. In some cases, findings in adults are highlighted, as they may have important implications in youth. The selected publications span the field of pediatric exercise science, specifically focusing on: aerobic exercise and training; neuromuscular physiology, exercise, and training; endocrinology and exercise; resistance training; physical activity and bone strength; growth, maturation, and exercise; physical activity and cognition; childhood obesity, physical activity, and exercise; pulmonary physiology or diseases, exercise, and training; immunology and exercise; cardiovascular physiology and disease; and physical activity, inactivity, and health.

exercise stimulates growth hormone (GH) secretion and may serve as a promising physiological test for the diagnosis of GH deficiency. However, exercise standardization for a feasible GH test is still lacking. The aim of the present study was to examine the GH secretion to high intensity interval exercise.Seventeen children (12.4 ± 2.6 years) with impaired growth rate performed high-intensity interval exercise test (HIIE) that included 10 intervals of 15 s all out pedaling against resistance determined by age, sex and weight on a cycle ergometer with 1-min active rest between each interval. Power output measurements were collected during the test. Blood samples were collected before, immediately after, 30, 45, and 60min after the beginning of the exercise test. GH response was compered to pharmacological provocation test (clonidine or glucagon).HIIE led to a significant increase in GH levels (p 0.001), with high correlation to GH response following pharmacological stimulation (r = 0.82, r = 0.80 for clonidine and glucagon respectively, p 0.001) A significant correlation was found between mean peak power to body weight and the GH response (r = 0.50, p = 0.04). 83% of the participants who reached peak power 10 watts/kg had normal GH secretion.HIIE is a brief and individualized exercise protocol that may be used as a physiological provocation test for GH secretion. There might be a minimum of anaerobic power needed to induce adequate GH response during HIIE.

We aimed to assess whether a twice daily assisted exercise interventional program will have a greater effect on bone strength compared to a once daily intervention or no intervention in very low birth weight (VLBW) preterm infants. Thirty-four very VLBW preterm infants (mean BW 1217 ± 55 g and mean gestational age 28.6 ± 1.1 weeks) were randomly assigned into one of three study groups: twice daily interventions (n = 13), a once daily intervention (n = 11), and no intervention (control, n = 10). The intervention was initiated at a mean of 8 ± 2.4 days of life and continued for 4 weeks. It included passive extension and flexion range-of-motion exercise of the upper and lower extremities. Bone strength was measured at enrollment and after 2 and 4 weeks using quantitative ultrasound of tibial bone speed of sound (SOS, Sunlight Omnisense™). At enrollment, the mean bone SOS was comparable between the twice daily interventions, once daily intervention and control groups (2918 ± 78, 2943 ± 119, and 2910 ± 48 m/s, respectively). As expected, the bone SOS declined in all groups during the study period (-23.6 ± 24, -68.8 ± 28, and -115.8 ± 30 m/s, respectively, p

In recent years there has been a remarkable enhancement in the knowledge and understanding of endocrine responses to exercise and exercise training in children and adolescents who participate in sports. This includes, for example, exercise-associated changes in growth factors that regulate muscle adaptations to exercise training, the use of hormonal changes to assess training intensity, as well as deleterious effects of competitive sports, in particularly if associated with inadequate nutrition, on growth and the reproductive system. However, major scientific gaps still exist in our understanding of the application and translation of this knowledge to the everyday use of young athletes and their coaches. These gaps include the translation of laboratory research to “real-life” training setting to optimize training efficiency, mainly due to the lack of “real-life” exercise studies; and the use of genetic endocrinology for sports selection, the prediction of excellence in sports and to improve training.

Context Congenital adrenal hyperplasia (CAH) was among the first genetic disorders included in newborn screening (NBS) programs worldwide, based on 17α-hydroxyprogesterone (17-OHP) levels in dried blood spots. However, the success of NBS for CAH is hampered by high false positive (FP) rates, especially in preterm and low-birthweight infants. Objective To establish a set of cutoff values adjusting for both gestational age (GA) and birthweight (BW), with the aim of reducing FP rates. Design This cross-sectional, population-based study summarizes 10 years of experience of the Israeli NBS program for diagnosis of CAH. Multitiered 17-OHP cutoff values were stratified according to both BW and GA. Participants A total of 1,378,132 newborns born between 2008 and 2017 were included in the NBS program. Results Eighty-eight newborns were ultimately diagnosed with CAH; in 84 of these, CAH was detected upon NBS. The combined parameters-adjusted approach significantly reduced the recall FP rate (0.03%) and increased the positive predictive value (PPV) (16.5%). Sensitivity among those referred for immediate attention increased significantly (94%). There were four false negative cases (sensitivity, 95.4%), all ultimately diagnosed as simple-virilizing. Sensitivity and specificity were 95.4% and 99.9%, respectively, and the percentage of true-positive cases from all newborns referred for evaluation following a positive NBS result was 96%. Conclusions The use of cutoff values adjusted for both GA and BW significantly reduced FP rates (0.03%) and increased overall PPV (16.5%). Based on our 10 years of experience, we recommend the implementation of this two parameter-adjusted approach for NBS of classic CAH in NBS programs worldwide.

Being overweight may increase the risk for developing stress fracture, as overweight adults and children were reported to have greater pressure peaks and rates under the heel during walking when compared with their normal-weight counterparts. Biofeedback gait retraining was shown to reduce ground impact magnitude in adults but not yet in children.The study examined whether overweight children have greater tibia peak positive acceleration (PPA) at ground impact during fast walking and running compared to healthy weight children, and whether visual feedback gait retraining program can be used to reduce PPA in overweight children.Twenty five overweight and 12 healthy weight children participated in the study. Overweight children were randomly assigned into either feedback group or control no-feedback group of 8 sessions training program over 2-weeks. Tibia PPA at ground impact output from a wearable inertial sensor attached to the tibia was the feedback displayed on a monitor placed in front of the treadmill during walking and running.Compared to healthy weight children, overweight participants showed significant greater PPA values in running (p 0.05), but not in fast walking. Feedback group significantly reduced PPA by 16% (p 0.01), and these changes persisted at the 1-month follow-up.Tibia PPA may be used in evaluating overweight children as a risk assessment to potential injuries due to high ground impact during running. Gait retraining using real-time feedback of tibia PPA may be useful in rehabilitation programs to reduce ground impact in overweight children.

Objective The purpose of the present study was to compare the physiological and perceived exertion responses of two different interval-training protocols – decreasing- and increasing-distance, matched for total distance, throughout a six-week training period. Methods Forty male physical education students (23 ± 1.3 years) were randomly assigned to either the increasing- or decreasing-distance interval-training group (ITG and DTG). The ITG performed increasing-distance interval training (100–200–300–400–500 m) and the DTG performed decreasing-distance interval training (500–400–300–200–100 m), twice a week for each. Heart rate (HR) and rate of perceived exertion (RPE) responses were monitored in each of the six-week training program sessions. Results Mean HR values were significantly higher (p = .00) in the DTG (181 ± 2.8 bpm) compared with the ITG (163 ± 10.4 bpm). Mean RPE values were significantly higher (p = .00) in the ITG (7.5 ± 0.3 a.u.) compared with the DTG (5.8 ± 0. 6 a.u.). The percent change in RPE responses throughout the six-week training program was significantly greater (p = .00) in the DTG (50% ± 0.7) compared with the ITG (25% ± 0.7). Conclusions The findings demonstrated that physiological responses may not necessarily match the participant's perceived exertion, and that in addition to training physical load, a sensation of relief from the achievement is probably a significant factor to be considered during training.

General fatigue can cause aggravation of postural balance, with increased risk for injuries. The present longitudinal study aimed to evaluate the postural balance of young athletes following field aerobic tests throughout 1 year of training. Thirty children from a sports center in Nazareth, participating in a 3 times/week training program (specific to basketball, soccer, or athletic training), were assessed. Postural balance parameters were taken before, immediately after, and 10 min after a 20 m shuttle-run aerobic test, at 3 time points during 1 training year (Start/Y, Mid/Y, and End/Y). Fitness improved at the Mid/Y and End/Y compared to Start/Y. Postural balance significantly deteriorated immediately after the aerobic test and improved significantly in the 10-min testing in all 3 time points, with significant deterioration in the End/Y compared with the Start/Y. In conclusions, postural balance deteriorates immediately after aerobic exercises, and at the end of the year. To better practice drills related to postural balance and possibly to prevent injuries, it is best for young athletes to properly rest immediately following aerobic exercises and to practice postural balance mainly at the beginning and at the middle of the training year.

Obesity is the most common chronic pediatric disease in westernized, especially low socioeconomic societies. We previously demonstrated the beneficial effects of a kindergarten dietary-physical activity intervention applied by the kindergarten teachers, on nutrition and physical activity knowledge and preferences, fitness, and BMI (Body Mass Index) percentile, even one year after the end of intervention. The current article demonstrates the Kindergarten teachers’ feedback and perspectives on the intervention, a feedback that is important when planning such programs. Quantitative and descriptive feedback questionnaires were distributed to all kindergarten teachers twice, upon completion of the intervention program and one year after. Training kindergarten teachers on the importance of health promotion should be an integral part of their training curriculum. We believe that in our efforts to prevent and treat childhood obesity, a kindergarten dietary-physical activity health promotion intervention applied by kindergarten teachers may play an important role.

To examine the prevalence of the Insulin-Like Growth Factor-I receptor (IGF-IR) 275124AC polymorphism, known to be associated with exercise-related cardiac hypertrophy, among elite endurance and power athletes.One hundred and fifty-nine athletes (118 men and 41 women, age: 35.9±12.2 yrs) participated in the study.We hypothesized that presence of the A allele will be significantly more common among endurance athletes (n=77) compared to power athletes (n=82) and non-physically active controls (n=68). Athletes within each group were further divided according to their individual best performance into elite athletes (those who had represented the country in international track-and-field or triathlon competitions or in the Olympic Games) and national-level athletes.The prevalence of the AA genotype was significantly higher (p0.05) in the endurance athletes group (49%) compared to the power athletes group (33%), but did not differ from the control group (46%). There was no significant difference in the prevalence of the AA genotype between elite and national level endurance athletes (44% versus 52%, respectively). In contrast, among power athletes, the prevalence of the AA genotype was significantly lower in the elite compared to national level athletes (17% versus 42%, respectively; p0.05).The results of the present study may suggest that the IGF-IR AA polymorphism is beneficial for endurance-type sports, but is not associated with elite endurance performance. In contrast, the presence of the AA genotype may be a disadvantage in power sports. All together the results of the present study suggest that IGF-IR polymorphism may differentiate between the two edges of the endurance-power athletic performance spectrum.

The present study was designed to compare the effects of high-intensity intermittent training (HIIT) and small-sided games (SSGs) training on fitness variables of elite handball players. Eighteen highly trained players (mean age ± SD: 25.6 ± 0.5 years) were assigned to either HIIT or SSGs group training protocols twice per week for 8 weeks. The HIIT consisted of 12-24 × 15 seconds of high-intensity runs interspersed by 15 seconds of recovery. The SSGs training consisted of 3 against 3 small-sided handball games. Both training methods were matched for exercise duration and recovery at each training session. Before and after 8-week training, the following fitness variables were assessed-speed: 10- and 20-m sprint time, agility: handball agility specific test (HAST), upper arm strength: 1 repetition maximum (1RM) bench press test, lower limb power: counter-movement jump tests with (CMJarm) and without (CMJ) arm movement, and aerobic fitness (yo-yo intermittent recovery test level 1 [YYIRTL1]). Significant improvement was found in the YYIRTL1 (23.3 and 26.3%, respectively), 10-m sprint (2.3 and 4.1%, respectively) and 20-m sprint (2.1 and 4%, respectively), HAST (1.1 and 2.2%, respectively), 1RM bench press (6.8 and 12.3%, respectively), CMJ (7.4 and 10.8%, respectively), and CMJarm (6.4 and 8.9%, respectively) following training in both groups (p ≤ 0.05 for all). There was a significantly greater improvement in 10- and 20-m sprint, HAST, 1RM, CMJ, and CMJarm following the SSGs training compared with the HIIT (p ≤ 0.05 for all). These results indicated that both HIIT and SSGs are effective training methods for fitness development among elite adult handball players. However, SSGs training may be considered as the preferred training regimen for improving handball-specific fitness variables during the in-season period.

Introduction:Competitive female athletes restrict energy intake and increase exercise energy expenditure frequently resulting in ovarian suppression. The purpose of this study was to determine the impact of ovarian suppression and energy deficit on swimming performance (400-m swim velocity).Methods:Menstrual status was determined by circulating estradiol (E2) and progesterone (P4) in ten junior elite female swimmers (15-17 yr). The athletes were categorized as cyclic (CYC) or ovarian-suppressed (OVS). They were evaluated every 2 weeks for metabolic hormones, bioenergetic parameters, and sport performance during the 12-week season.Results:CYC and OVS athletes were similar (p > .05) in age (CYC = 16.2 ± 1.8 yr, OVS = 17 ± 1.7 yr), body mass index (CYC = 21 ± 0.4 kg·m, OVS = 25 ± 0.8 kg·m), and gynecological age (CYC = 2.6 ± 1.1 yr, OVS = 2.8 ± 1.5 yr). OVS had suppressed P4 (p < .001) and E2 (p = .002) across the season. Total triiodothyronine (TT3) and insulin-like growth factor (IGF-1) were lower in OVS (TT3: CYC = 1.6 ± 0.2 nmol·L, OVS = 1.4 ± 0.1 nmol·L, p < .001; IGF-1: CYC = 243 ± 1 μg·mL, OVS = 214 μg·mL p < .001) than CYC at week 12. Energy intake (p < .001) and energy availability (p < .001) were significantly lower in OVS versus CYC. OVS exhibited a 9.8% decline in Δ400-m swim velocity compared with an 8.2% improvement in CYC at week 12.Conclusions:Ovarian steroids (P4 and E2), metabolic hormones (TT3 and IGF-1), and energy status markers (EA and EI) were highly correlated with sport performance. This study illustrates that when exercise training occurs in the presence of ovarian suppression with evidence for energy conservation (i.e., reduced TT3), it is associated with poor sport performance. These data from junior elite female athletes support the need for dietary periodization to help optimize energy intake for appropriate training adaptation and maximal sport performance

The aim of the present study was to compare the effect of an increasing-distance interval-training program with a decreasing-distance interval-training program, matched for total distance and recovery times, on blood free radicals and total anti-oxidative capacity (TAC) at rest and following intense exercise. Forty physical education students were randomly assigned to either the increasing- or decreasing-distance interval-training group (ITG and DTG), and completed two similar relevant sets of tests before and after a six-week twicea- week training program. One training program consisted of increasing-distance interval training (100-200- 300-400-500 m) and the other decreasing-distance interval training (500-400-300-200-100 m). Following training, free radical resting levels were significantly higher in the ITG compared to the DTG (7.94 ± 4.76 vs. 3.84 ± 1.49 μmole, respectively, p

The aim of the present study was to compare the effect of an increasing-distance, interval-training programme and a decreasing-distance, interval-training programme, matched for total distance, on aerobic and anaerobic physiological indices. Forty physical education students were randomly assigned to either the increasing- or decreasing-distance, interval-training group (ITG and DTG), and completed two similar relevant sets of tests before and after six weeks of training. One training programme consisted of increasing-distance interval-training (100–200–300–400–500 m) and the other decreasing-distance interval training (500–400–300–200–100 m). While both training programmes led to a significant improvement in VO2 max (ES = 0.83–1.25), the improvement in the DTG was significantly greater than in the ITG (14.5 ± 3.6 vs. 7.8 ± 3.2%, p

Premature infants have an increased risk of osteopenia due to limited bone mass accretion in utero and a greater need for bone nutrients. Until recently, most efforts to prevent osteopenia of prematurity focused on nutritional changes. Recent studies indicate that passive range-of-motion exercise of the extremities may lead to beneficial effects on body weight, increased bone mineralization, increased bone formation markers and leptin levels, and attenuation of the natural postnatal decline in bone speed of sound. These results suggest that exercise may play an important role in the prevention and treatment of osteopenia of prematurity. This review summarizes our current knowledge on the role of exercise in the prevention and treatment of osteopenia of prematurity.

Exercise-associated effects on the growth hormone-insulin-like growth factor-I (GH-IGF-I) axis were studied, mainly after aerobic exercise. We determined the gender effect on the GH-IGF-I axis response to a standard all-out Wingate anaerobic test (WAnT) in healthy active young adult men and women (men = 12 and women = 16; age range: 24-34 years). Blood samples for GH and IGF-I, key elements of the GH-IGF-I axis, were collected before and 20, 30, 40, and 60 minutes after the beginning of exercise. In addition, we collected postexercise blood lactate levels. Postexercise lactate levels were higher among men; however, this difference did not reach statistical significance (13.8 +/- 1.3 vs. 11.1 +/- 1.0 mmol[middle dot]L-1, respectively; p = 0.1). The WAnT was associated with a significant increase in GH in both genders. However, GH peak was greater among women (10.8 +/- 1.8 vs. 5.6 +/- 1.4 ng[middle dot]ml-1, in women and men, respectively; p < 0.01). In addition, postexercise GH peak occurred significantly earlier in female (20 minutes) compared with male participants (40 minutes). Exercise was associated with a significant increase in IGF only among men (from 166.8 +/- 8.4 to 186.9 +/- 9.3; p < 0.02); however, no significant between-gender effect was found. In summary, supramaximal anaerobic exercise was associated with a greater and earlier postexercise GH peak in women compared with men. All together, the results suggest anaerobic exercise-related anabolic-type hormonal response.

Athletic excelling capability in a specific sport results from the combined influence of hundreds of genetic polymorphisms. The aim of the current study was to characterize athletes' polygenetic scores. We developed two polygenetic scores: (a) Power Genetic Distance Score based on two polymorphisms (PGDS2; ACE(I/D), ACTN3(C/T)) or five polymorphisms (PGDS5; ACTN3(C/T), ACE(I/D), IL6(-174G/C), NOS3(T/C), AGT(MET235THR)); and (b) Endurance Genetic Distance Score based on two polymorphisms (EGDS2; ACEI / D , ACTN3C / T ) or five polymorphisms (EGDS5; PPARGC1(AGly482Ser), PPAR(Aintron7G/C), PPARD(T294C), NRF2(A/C), HIF(C/T)). Eighty-two power-speed athletes, 87 endurance athletes, and 119 nonathletic controls participated in the study. Genomic DNA was extracted from peripheral blood. Power-speed athletes' mean PGDS2 (46.1) and PGDS5 (29.4) were significantly higher compared with their mean EGDS2 (36.4) and EGDS5 (23.1; P

We examined the effect of training on hormonal and inflammatory response to a single volleyball practice in elite adolescent players. Thirteen female, national team level, Israeli volleyball players (age 16.0 ± 1.4 years, Tanner stage 4-5) participated in the study. Blood samples were collected before and immediately after a typical 60 minutes of volleyball practice, before and after 7 weeks of training during the initial phase of the season. Training involved tactic and technical drills (20% of time), power and speed drills (25% of time), interval sessions (25% of time), endurance-type training (15% of time), and resistance training (15% of time). To achieve greater training responses, the study was performed during the early phase (first 7 weeks) of the volleyball season. Hormonal measurements included the anabolic hormones growth hormone (GH), insulin-like growth factor-I (IGF-I) and IGF-binding protein-3, the catabolic hormone cortisol, the proinflammatory marker interleukin-6 (IL-6), and the anti-inflammatory marker IL-1 receptor antagonist. Training led to a significant improvement of vertical jump, anaerobic properties (peak and mean power by the Wingate Anaerobic Test), and predicted VO2max (by the 20-m shuttle run). Volleyball practice, both before and after the training intervention, was associated with a significant increase of serum lactate, GH, and IL-6. Training resulted in a significantly reduced cortisol response ([INCREMENT]cortisol: 4.2 ± 13.7 vs. -4.4 ± 12.3 ng · ml, before and after training, respectively; p < 0.02), and IL-6 response ([INCREMENT]IL-6: 1.3 ± 1.0 vs. 0.3 ± 0.4 pg · ml, before and after training, respectively; p < 0.01) to the same relative intensity volleyball practice. The results suggest that along with the improvement of power and anaerobic and aerobic characteristics, training reduces the catabolic and inflammatory response to exercise.

The manuscript “Plasma Somatomedin-C in 8- to 10-Year-Old Swimmers” by Denison and Ben-Ezra published in the first issue of Pediatric Exercise Science in 1989 was among the first to address the relationship between growth, the growth hormone (GH)/insulin like growth factor-1 (IGF-1) axis, and exercise. Since their pioneering article, this topic has become of great interest to pediatricians and pediatric exercise researchers, and today our understanding of the effects of exercise training on the growth axis during childhood and puberty, on differences between systemic and local (i.e., muscle) responses to exercise, and our ability to use these responses to assist the adolescent competitive athlete in the evaluation of the training load have markedly improved. The aim of the present review is to summarize our current knowledge on this topic.

Objective Insulin-like growth factor-I (IGF-I) plays a key role in exercise-associated muscle growth and development. The regulatory region of the promoter of the IGF-I gene is labile, but changes in this region were studied mostly in the elderly and in relation to pathological states. C-1245T (rs35767) is a genetic variation in the promoter region of the IGF-I gene. The minor allele T was found to be associated with higher circulating IGF-I levels, and possibly with increased muscle mass. The aim of the current study was to analyze the frequency distribution of C-1245T SNP in athletic and nonathletic Israeli populations. Design One hundred and sixty-five athletes (78 endurance-type athletes, and 87 power-type athletes) and 159 nonathletic healthy individuals participated in the current study. Genomic DNA was extracted from peripheral EDTA treated anti-coagulated blood using a standard protocol. Genotyping of the IGF1 C-1245T polymorphism was performed using polymerase chain reaction (PCR). Results We found that the endurance and power athletes' allele and genotype frequencies were significantly different from those of the control group. Only 4.8% of the athletes were TT carriers, but none of the controls carried this genotype. The T allele was found to be more frequent in the top-level power athletes (international and Olympic level) compared to national level athletes, but such a difference was not found in endurance athletes. Conclusion Our findings suggest a possible contribution for the relatively rare IGF-I TT genotype to endurance performance, and in particular to power sport excellence in Israeli athletes.

The aim of the study was to compare the effect of an increasing-distance interval-training program and a decreasing-distance interval-training program, matched for total distance, on aerobic and anaerobic performance capabilities. Forty physical education students were randomly assigned to either increasing- or decreasing-distance interval-training group (ITG and DTG), and completed two similar sets of tests before and after six weeks of training. One training program consisted of 100 – 200 – 300 – 400 – 500m running intervals, and the other 500 – 400 – 300 – 200 - 100m. While both training programs led to a significant improvement in 2000m run (ES = 0.02-0.68), the improvement in the DTG was significantly greater than in the ITG (18.3 ± 3.6 vs. 12.2 ± 3.2 %, p< 0.05). In addition, while both training programs led to a significant improvement in 300m run (ES = 0.25-0.73), the improvement in the DTG was significantly greater than in the ITG (21.1 ± 1.8 vs. 15.4 ± 1.1 %, p< 0.05). The findings indicate that beyond the significant positive effects of both training programs, the DTG showed significant superiority over the ITG in improving aerobic and anaerobic performance capabilities. Athletes should acknowledge that, in spite of identical total work, interval-training program might induce different physiological impacts if order of intervals is different.