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Alon Eliakim, Ita Litmanovitz and Dan Nemet

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.

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Alon Eliakim, Dan M. Cooper and Dan Nemet

The present study compares previous reports on the effect of “real-life” typical field individual (ie, cross-country running and wrestling—representing combat versus noncombat sports) and team sports (ie, volleyball and water polo—representing water and land team sports) training on GH and IGF-1, the main growth factors of the GH→IGF axis, in male and female late pubertal athletes. Cross-country running practice and volleyball practice in both males and females were associated with significant increases of circulating GH levels, while none of the practices led to a significant increase in IGF-I levels. The magnitude (percent change) of the GH response to the different practices was determined mainly by preexercise GH levels. There was no difference in the training-associated GH response between individual and team sports practices. The GH response to the different typical practices was not influenced by the practice-associated lactate change. Further studies are needed to better understand the effect of real-life typical training in prepubertal and adolescent athletes and their role in exercise adaptations.

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Oren Tirosh, Guy Orland, Alon Eliakim, Dan Nemet and Nili Steinberg

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 < .05) and lower transfer function of the acceleration values (−3.8 [1.9] and −1.2 [1.5], respectively, P < .05). Despite the nonsignificant differences between groups in tibia acceleration at foot–ground impact that was found in the current study, the shock absorption of overweight children was reduced compared with their healthy-weight counterparts.

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Eliahu Sadres, Alon Eliakim, Naama Constantini, Ronnie Lidor and Bareket Falk

The purpose of this study was to examine the effect of 2 school years (21 months) of a twice-weekly resistance training program on stature, muscle strength, and self-concept among prepubertal boys. The experimental group (E, n = 27) aged 9.2 ± 0.3 yrs, participated in progressive resistance training, while the control group (C, n = 22) aged 9.4 ± 0.3 yrs, participated in standard physical education classes (as advised by the Ministry of Education). Training sessions included 1–4 sets of 3–6 exercises, with 5–30 repetitions/set. The load ranged between 30% and 70% 1RM. No differences were observed in the gain in body height between groups. Muscle strength increased significantly more in E (e.g., knee extensors: 0.51 ± 0.13 to 0.77 ± 0.16 kg/kg body mass), compared with C (0.34 ± 0.12 to 0.54 ± 0.11 kg/kg body mass). One minor injury was reported throughout the study. Initial scores of self-concept were high in both groups, with no training effect. The results demonstrate that among prepubertal boys, a twice-weekly low-to-moderate-intensity resistance training program over a period of 2 school years (21 months) can result in enhancement in muscle strength with no detrimental effect on growth.

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Sigal Ben-Zaken, Yoav Meckel, Ronnie Lidor, Dan Nemet and Alon Eliakim

The aim of the study was to assess whether an aerobic-favoring genetic profile can predict the success of a shift from middle- to long-distance running. Thirteen elite middle-distance runners were divided into successful and nonsuccessful groups in their shift toward long-distance runs. All the runners began their training program at the age of 14–15, and after 6–7 years, changed focus and adjusted their training program to fit longer running distances. The participants’ personal records in the longer events were set at the age of 25–27, about 3–5 years after the training readjustment took place. The endurance genetic score based on 9 polymorphisms was computed as the endurance genetic distance score (EGDS9). The power genetic distance score (PGDS5) was computed based on 5 power-related genetic polymorphisms. The mean EGDS9 was significantly higher among the successful group than the nonsuccessful group (37.1 and 23.3, respectively, p < .005, effect size 0.75), while the mean PGDS5 was not statistically different between the 2 groups (p = .13). Our findings suggest the possible use of genetic profiles as an added tool for determining appropriate competitive transition and specialization in young athletes involved in early phases of talent development.

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Sigal Ben-Zaken, Yoav Meckel, Nitzan Dror, Dan Nemet and Alon Eliakim

In recent years several genetic polymorphisms related to the GH-IGF-I axis were suggested to promote athletic excellence in endurance and power sports. We studied the presence of the C-1245T SNP (rs35767), a nucleotide substitution in the promoter region of the IGF-I gene, and the presence of the 275124A > C SNP (rs1464430), a common nucleotide substitution in the intron region of the IGF-I receptor (IGF-IR) gene in elite long and short-distance swimmers compared with nonphysically active controls. The rare T/T IGF-I polymorphism was found only in 5.3% of the long-distance swimmers, and was not found at all in the short-distance swimmers or among the control group participants. The prevalence of the IGF-I receptor AA genotype was significantly lower in the swimming group as a whole (35%) compared with the control group (46%), in particularly due to reduced frequency of the AA genotype among short-distance swimmers (26%). In contrast to previous reports in elite endurance and power track and field athletes, single nucleotide polymorphisms of the IGF-I and the IGF-IR were not frequent among elite Israeli short- and long-distance swimmers emphasizing the importance of other factors for excellence in swimming. The results also suggest that despite seemingly similar metabolic characteristics different sports disciplines may have different genetic polymorphisms. Thus, combining different disciplines for sports genetic research purposes should be done with extreme caution.

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Alon Eliakim, Mark Y. Moromisato, David Y. Moromisato and Dan M. Cooper

In this study, the hypothesis that improvements in functional and structural measures could be detected in the young, female rat with only 5 days of moderate treadmill training was tested. Eight-week-old female Sprague-Dawley rats were divided randomly into control (n = 10) and training groups (n = 11). Over the 5-day period, running duration and treadmill speed increased progressively. Maximal running time and gas exchange were measured on Day 6. In trained compared with control rats, maximal running time was 54% greater (p < .005), right hindlimb muscle was 16% heavier (p < .01), and end-exercise respiratory exchange ratio (RER) was 17% lower (p < .05). Substantial metabolic and structural adaptations occurred in young female rats after only 5 days of treadmill training. This protocol may be useful in discovering the initiating mechanisms of the training response in the young organism.

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Baruch Wolach, Bareket Falk, Einat Kodesh, Judith Radnay, Hava Shapiro, Yonathan Yarom and Alon Eliakim

The purpose of the present study was to investigate the effect of anaerobic exercise on aspects of cellular immune function among 10–12-year-old highly trained female gymnasts (n = 7) compared with age- and maturity-matched untrained girls (n = 6). Blood samples were drawn before, immediately after, and 24 hr following exercise. Leukocyte number, particularly neutrophils and lymphocytes, increased following 30 s of supramaximal exercise and returned to baseline values following 24 hr in both groups. Total T-cell and B-cell concentrations, as well as T-helper (CD4) and T-suppressor (CD8) number increased immediately after exercise and decreased following 24 hr in both groups. The CD4:CD8 ratio was reduced following exercise mainly due to an increase in CD8. Natural killer cell count was elevated following exercise and continued to be elevated 24 hr following exercise in both groups. In summary, the exercise-induced changes in cellular immune function among both groups were similar to changes described in adults.

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Naama W. Constantini, Alon Eliakim, Levana Zigel, Michal Yaaron and Bareket Falk

Much attention has focused on the nutrition and hematological profile of female athletes, especially gymnasts. The few studies on iron status of male adolescent athletes found a low incidence of iron deficiency. The present study investigated the iron status of male and female gymnasts (G) and compared it with athletes of other sports. Subjects were 68 elite athletes (43 M, 25 F) ages 12-18, of four sports: gymnasts (11 M, 12 F), swimmers (11 M, 6 F), tennis players (10 M, 4 F), and table tennis players (11 M, 3 F). All lived in the national center for gifted athletes, trained over 25 hr a week, ate in the same dining room, and shared a similar lifestyle. Mean levels of hemoglobin (Hb), red blood cell indexes, serum ferritin, serum iron, and transferrin were measured in venous blood. There was no difference in mean Rb among gymnasts (G) and nongymnasts (NG). However, Hb was less than 14 g/dL in 45% of M G vs. only 25% in NG, and less than 13 g/dL in 25% of premenarcheal FG vs. 15% in NG. Low transferrin saturation (< 20%) was detected in 18% of M G and 25% of FG vs. 6% and 8% in male and female NG, respectively (p < .05). The percentage of males suffering from low ferritin level (< 20 ng/ml) was twice as high in G (36%) vs. NG (19%), and about 30% in all females. In summary, iron stores were consistently lower in M G vs. NG. Adolescent athletes of both genders, G in particular, are prone to nonanemic iron deficiency, which might compromise their health and athletic performance.

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Ben-El Berkovich, Alon Eliakim, Dan Nemet, Aliza Hannah Stark and Tali Sinai

Athletes competing in individual sports such as judo are categorized by weight. Before competitions, weight cutting is common. This cross-sectional study was designed to characterize and determine the prevalence of rapid weight loss (RWL) among adolescent judo competitors. Male athletes aged 12- to 17-years old (N = 108) were recruited from local judo teams. Each participant completed a validated questionnaire regarding RWL practices. Anthropometric measurements were also performed. Average age was 14.6 ± 1.6 years and all participants were of normal body mass index (BMI). RWL was practiced by 80% of the athletes before competition, beginning at an average age of 12.5 ± 2.2 years with the highest prevalence (~94%) in the oldest group of judoka (16–17.9 years). Precompetition weight loss duration was 8 ± 5.4 days, with an average weight reduction of 1.5 ± 1.1 kg. The number of weight loss efforts per athlete in the past season was 2.8 ± 2.2. RWL was achieved by increased physical activity (82.6%), skipped meals (56.3%), or fasting at least once (47%). Two-thirds of the athletes indicated that their coaches were the most influential figure in their decision to lose weight before competition. RWL is highly prevalent in adolescent judo competitors. The methods used by these athletes can potentially lead to significant health risks including compromised nutritional status, diminished physical performance and impaired growth and development. It is of great importance to insure that those who guide young adults in weight loss for competitive sports have the knowledge and understanding to make safe recommendations and appropriate decisions regarding achieving specific weight goals.