K Karelson

University of Tartu, Dorpat, Tartu County, Estonia

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Publications (23)35.04 Total impact

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    ABSTRACT: Evaluate hormonal responses to incremental-stage exercise (EX) test to exhaustion in adolescents. Adolescents were tested at 16 years of age in Tanner Stage 4 (TS4) and at 17 years of age in Tanner Stage 5 (TS5) (n = 6). Adults were tested at 21 ± 1 y. (X ± SD) (n = 4) and served as controls. Blood samples were taken at rest, at the end of each EX stage. Main effects for EX in cortisol (p < 0.01, increasing with each EX stage) and for subject group for testosterone (T) occurred (p < 0.01; TS4 < TS5, adults). Interaction effect of group by EX stage occurred for GH (p < 0.05). GH increased in response to EX in all groups, however, the magnitude of increase was significantly less for TS5 and adults than TS4. Differences in T and GH responses for TS4 than those for TS5 and adults reflect the differing maturation levels of the endocrine system between Tanner Stages. TS5 adolescents are more similar to young adults in hormonal responses to EX than are TS4 adolescents.
    Arquivos brasileiros de endocrinologia e metabologia 04/2011; 55(3):213-8. · 0.68 Impact Factor
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    ABSTRACT: The purpose of this study was to determine if the ingestion of sodium citrate (CIT) alters blood levels of fluid and electrolyte regulatory hormones at rest and during exercise. Using a randomized, double-blinded, crossover design, 13 young, male well-trained runners performed continuous incremental running tests to volitional exhaustion on a treadmill 2 h after ingestion of 0.5 g.kg-1 body mass of CIT or placebo (PLC) in 1000 mL of solution. These trials were separated by 2 weeks. Baseline (before ingestion) aldosterone concentration did not differ between the 2 trials; however, it was 36.5% (p = 0.003) lower in the CIT trial compared with the PLC trial before the running test (i.e., after ingestion). The extent of the running-induced increase in aldosterone was 33% (p = 0.009) smaller in the CIT trial. There were no between-trial differences in the levels of adrenocorticotropic hormone, N-terminal pro-B-type natriuretic peptide, or renin activity at any stage of the study. However, a greater relative increase in plasma volume (mean +/- SD, 6.41% +/- 3.78% vs. 4.08% +/- 3.33%; p = 0.042) was observed after administering the CIT compared with the PLC drink. Serum Na+ concentration increased (by 3.1 +/- 1.2 mmol.L-1; p < 0.0001) after ingestion of the CIT but not the PLC drink. A higher Na+ level was observed in the CIT trial than in the PLC trial (142.4 +/- 1.6 vs. 139.3 +/- 1.4 mmol.L-1, p = 0.00001) after completion of the run. In conclusion, pre-exercise ingestion of CIT induces a decrease in serum aldosterone concentration in the resting condition and a blunting of the aldosterone response during incremental running exercise to volitional exhaustion. The observed effect of CIT on the serum aldosterone level may be mediated by an acute increase in plasma volume and serum Na+ concentration alterations.
    Applied Physiology Nutrition and Metabolism 06/2010; 35(3):278-85. · 2.01 Impact Factor
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    ABSTRACT: The purpose of this study was to explore the mechanisms for increased exercise performance in conditions of competition. Endurance trained subjects (n=14) performed incremental treadmill running to exhaustion in control laboratory conditions (non-competition) and in conditions of simulated competition to assess performance (running duration). Heart rate and respiration gases were monitored continuously through each exercise condition. Blood lactate, cortisol, growth hormone and testosterone concentrations were also determined at pre- (rest) and postexercise in each condition. Results indicated competition exercise performance was significantly increased 4.2% (+49 sec; p<0.05) as was peak VO2 response 4.4% (+2.5 ml O2 x kg(-1) x min(-1); p<0.05) versus non-competition. No significant differences were found in peak measurements of minute ventilation, respiratory exchange ratio, ventilation threshold, post-exercise lactate, heart rate, or the ventilation equivalent for O 2 between the exercise conditions. In both conditions growth hormone and testosterone concentrations increased significantly in response to exercise (p<0.001), whereas cortisol responses post-exercise were significantly elevated in the competition (p<0.05) but not in the control condition (p>0.05). These findings support that in competitive situations the affective state (motivation) experienced by athletes can enhance performance in exercise events, and lead to an increased peak oxygen uptake. The magnitude of the improvement is of a substantial nature and of a level seen with some training programs. Competitive conditions also augment the cortisol response to exercise, suggesting that enhanced sympatho-adrenal system activation occur in such situations which may be one of the key "driving forces" to performance improvement.
    Acta Physiologica Hungarica 03/2010; 97(1):22-30. · 0.88 Impact Factor
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    ABSTRACT: The purpose of this cross-sectional study was to determine the physiological reaction to the different intensity Nordic Walking exercise in young females with different aerobic capacity values. Twenty-eight 19-24-year-old female university students participated in the study. Their peak O2 consumption (VO2 peak kg(-1)) and individual ventilatory threshold (IVT) were measured using a continuous incremental protocol until volitional exhaustion on treadmill. The subjects were analysed as a whole group (n = 28) and were also divided into three groups based on the measured VO2 peak kg(-1) (Difference between groups is 1 SD) as follows: 1. >46 ml min(-1) kg(-1) (n = 8), 2. 41-46 ml min(-1) kg(-1) (n = 12) and 3. <41 ml min(-1) kg(-1) (n = 8). The second test consisted of four times 1 km Nordic Walking with increasing speed on the 200 m indoor track, performed as a continuous study (Step 1 - slow walking, Step 2 - usual speed walking, Step 3 - faster speed walking and Step 4 - maximal speed walking). During the walking test expired gas was sampled breath-by-breath and heart rate (HR) was recorded continuously. Ratings of perceived exertion (RPE) were asked using the Borg RPE scale separately for every 1 km of the walking test. No significant differences emerged between groups in HR of IVT (172.4 +/- 10.3-176.4 +/- 4.9 beats min(-1)) or maximal HR (190.1 +/- 7.3-191.6 +/- 7.8 beats min(-1)) during the treadmill test. During maximal speed walking the speed (7.4 +/- 0.4-7.5 +/- 0.6 km h(-1)) and O2 consumption (30.4 +/- 3.9-34.0 +/- 4.5 ml min(-1) kg(-1)) were relatively similar between groups (P > 0.05). However, during maximal speed walking, the O2 consumption in the second and third groups was similar with the IVT (94.9 +/- 17.5% and 99.4 +/- 15.5%, respectively) but in the first group it was only 75.5 +/- 8.0% from IVT. Mean HR during the maximal speed walking was in the first group 151.6 +/- 12.5 beats min(-1), in the second (169.7 +/- 10.3 beats min(-1)) and the third (173.1 +/- 15.8 beats min(-1)) groups it was comparable with the calculated IVT level. The Borg RPE was very low in every group (11.9 +/- 2.0-14.4 +/- 2.3) and the relationship with VO2and HR was not significant during maximal speed Nordic Walking. In summary, the present study indicated that walking is an acceptable exercise for young females independent of their initial VO2 peak level. However, females with low initial VO2 peak can be recommended to exercise with the subjective 'faster speed walking'. In contrast, females with high initial VO2 peak should exercise with maximal speed.
    Clinical Physiology and Functional Imaging 05/2009; 29(5):330-4. · 1.33 Impact Factor
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    ABSTRACT: This study examined the cortisol response to incremental exercise; specifically to see if there was an increase in blood cortisol levels at low intensity exercise (i.e., < 60% VO2 intensity threshold) and determine whether a linear relationship existed between the blood cortisol responses and exercise of increasing workloads (i.e., intensity). Healthy, physically active young men (n = 11) completed exercise tests involving progressive workload stages (3 min) to determine peak oxygen uptake responses (VO2). Blood specimens were collected at rest and at the end of each stage and analyzed for cortisol. Results showed cortisol was significantly increased from resting levels at the end of the first exercise stage (80 W; 41.9 +/- 5.4% peak VO2) and remained significantly elevated from rest until the exercise ended. Interestingly, however, the cortisol concentrations observed at 80 W through 200 W did not significantly differ from one another. Thereafter, during the final two stages of exercise the cortisol concentrations increased further (p < 0.01). The subjects exceeded their individual lactate thresholds over these last two stages of exercise. Regression modeling to characterize the cortisol response resulted in significant regression coefficients (r = 0.415 [linear] and r = 0.655 [3rd order polynominal], respectively; p < 0.05). Comparative testing (Hotelling test) between the two regression coefficents revealed the polynominal model (sigmoidal curve) was the significantly stronger of the two (p = 0.05). In conclusion, the present findings refute the concept that low intensity exercise will not provoke a significant change in blood cortisol levels and suggest the response to incremental exercise involving increasing exercise workloads (i.e., intensities) are not entirely linear in nature. Specifically, a sigmoid curve more highly accurately characterizes the cortisol response to such exercise.
    Acta Physiologica Hungarica 06/2008; 95(2):219-27. · 0.88 Impact Factor
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    ABSTRACT: The aim of this study was to investigate the response of N-terminal propeptide of type I procollagen, crosslinked telopeptide of type I collagen and the growth hormone/insulin-like growth factor-I axis to acute aerobic exercise in boys at different pubertal stages The subjects were 60 healthy boys (group I - Tanner stage 1, N=20; group II - Tanner stages 2 and 3, N=20; group III - Tanner stages 4 and 5, N=20) who exercised 30 minutes at constant load on cycle ergometer at the level of ~95% of their individual ventilatory threshold. Venous blood samples were obtained before, immediately after and after 30 minutes of recovery for the measurement of serum testosterone, growth hormone (GH), insulin-like-growth factor-I, insulin-like-growth factor binding protein-3, N-terminal propeptide of type I procollagen (PINP) and crosslinked telopeptide of type I collagen. Acute exercise did not affect significantly serum testosterone, insulin-like-growth factor-I, insulin-like-growth factor binding protein-3 or bone turnover markers concentrations in any of study groups. The rise in growth hormone concentration during exercise was highest in group III (62.3+/-41.7 mU/L vs 15.5+/-11.4 in group I and 41.8+/-20.0 in group II). The increment in serum growth hormone level during exercise was positively correlated (r=0.64; P<0.001) to basal serum testosterone concentration. It can be concluded that growth hormone response to exercise was directly dependent on serum testosterone concentration. Acute exercise did not affect serum testosterone, insulin-like-growth factor-I, insulin-like-growth factor binding protein-3 or bone markers levels.
    The Journal of sports medicine and physical fitness 06/2008; 48(2):266-71. · 0.73 Impact Factor
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    ABSTRACT: The purpose of the study was to assess the effects of sodium citrate ingestion on the metabolic response to exercise and performance in a 1500-m competitive run in trained female middle-distance runners in field conditions. Seventeen athletes (mean (± SD) aged 18.6 ± 2.5 years, VO2max 55.2 ± 7.6 ml·kg(-1)·min(-1)) competed in two 1500-m races following ingestion of 0.4 g·kg(-1) body mass of sodium citrate (CIT) and placebo (PLC - 1.0% solution of NaCl). The two substances, CIT and PLC were administered in 800 ml of solution in a randomly assigned double-blind crossover manner. Capillary blood samples were analysed for lactate, glucose, haemoglobin and haematocrit before administering the solutions (baseline) as well as before and after both 1500-m races. The athletes' times for trials CIT and PLC were 321.4 ± 26.4 and 317.4 ± 22.5 s, respectively (p > 0.05). A greater relative increase in plasma volume after administering the experimental solution, an increased body mass (by 0.4 kg; p = 0.006) immediately before the race and a restrained increase in blood glucose concentration (by 2.5 ± 1.2 mmol·l(-1) vs 3.4 ± 0.8 mmol·l(-1); p = 0.002) during the race were observed in the CIT trial compared to the PLC. A significant relationship was observed between body mass of the subjects immediately before the race and performance time (r = 0.374; p = 0.029). There were no between-treatment differences in heart rate in any stage of the run or in blood lactate accumulation during the race (final concentration of lactate was 14.4 ± 3.0 mmol·l(-1) and 13.4 ± 2.5 mmol·l(-1) (p > 0.05) in the CIT and PLC trials, respectively). The results suggest that sodium citrate induces an increase in water retention before exercise and may modify carbohydrate metabolism in high intensity running, but does not improve performance in 1500-m competitive run in female middle-distance runners. Key pointsPrevious studies have found that sodium bicarbonate administration may enhance performance in male athletes in running distances of 400-1500 m.The use of sodium bicarbonate in competitive sports is limited because it induces gastrointestinal distress in many subjects.The limited data on the effects of sodium citrate ingestion on the metabolic response to exercise and performance suggest that it may have all the benefits of sodium bicarbonate without the associated negative side effects.We assessed the effects of sodium citrate ingestion on the metabolic response to exercise and performance in a 1500-m competitive run in trained young female middle-distance runners.The results suggest that sodium citrate induces an increase in water retention before exercise and may modify carbohydrate metabolism in high intensity running, but does not improve performance in 1500-m competitive run in female middle-distance runners.
    Journal of sports science & medicine 01/2008; 7(1):125-31. · 0.89 Impact Factor
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    ABSTRACT: This study evaluated the influence of adrenergic factors on the cortisol response to maximal exercise in endurance-trained men. This was achieved by testing healthy young men during exercise while varying both the condition of beta-adrenergic blockage and the presence of a well-controlled simulated competitive environment to simulate activity of the sympatho-adrenal systems. Subjects (n = 10) performed maximal exercise (running) to exhaustion on a treadmill during four conditions: (1) placebo non-competitive [PNon] (2) after administration of 80 mg propranolol non-competitive [betaNon] (3) in a simulated competition after a placebo intake [PCom], and (4) in a simulated competition after propranolol intake [betaCom]. Blood samples were obtained before (pre-) and 3 min after (post-) exercise and assayed for cortisol (C). The data were analyzed with a multi-factorial repeated measures ANCOVA procedure. Statistical analysis revealed a significant three-way interaction for the drug versus competition versus sampling time effects (P < 0.05). Post-hoc tests revealed that the pre-exercise cortisol values did not differ significantly among the conditions. Cortisol did increase from pre- to post-exercise in all experimental conditions (P < 0.01), and the magnitudes of increase in the PCom, betaNon and betaCom conditions were greater than that of the PNon condition. Furthermore, the cortisol increases for both beta-blockage conditions post-exercise (betaNon, betaCom) did not differ from one another (P > 0.05). The findings suggest beta-adrenergic blockage and competitive conditions enhance the exercise cortisol response. In combination, however, these conditions do not act in an additive fashion. This suggests that perhaps there may be two separate influences or mechanisms (i.e., excitatory, inhibitory) on the adrenergic control of adrenocortical function, or a sympathetic compensation for beta-blockage during exhaustive maximal exercise. Furthermore, the data suggests a possible "ceiling" on the hypothalamic-pituitary-adrenal axis response to exercise in endurance-trained men.
    Arbeitsphysiologie 05/2007; 100(2):241-5. · 2.66 Impact Factor
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    ABSTRACT: The aim of this study was to investigate the changes in serum ghrelin and leptin concentrations during acute aerobic cycle ergometer test in 60 boys at different pubertal stages. Boys were divided according to their pubertal status as group I (Tanner stage 1, n=20), group II (Tanner stages 2 and 3, n=20) and group 3 (Tanner stages 4 and 5, n=20). Maximal oxygen consumption and individual ventilatory threshold of the subjects were measured directly using stepwise increasing loads on cycle ergometer. Second exercise test consisted of a 30 minute constant load exercise on the same ergometer at the level of approximately 95% of the individual ventilatory threshold. Venous blood samples were obtained before, immediately after and after 30 minutes of recovery for the measurement of serum ghrelin, leptin, testosterone and insulin. At baseline, prepubertal children had significantly higher values for serum ghrelin compared to the groups II and III. Acute exercise altered significantly only insulin concentration. In all the groups, the maximal oxygen consumption/kg correlated positively with basal levels of testosterone (r=0.60, p<0.001) and insulin (r=0.34), and negatively to ghrelin (r=-0.35) and leptin (r=-0.32) (p<0.05). We conclude that moderate acute aerobic exercise does not change serum ghrelin or leptin level in boys at different pubertal stages.
    Hormone and Metabolic Research 11/2006; 38(11):752-7. · 2.15 Impact Factor
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    Medicine and Science in Sports and Exercise - MED SCI SPORT EXERCISE. 01/2006; 38.
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    ABSTRACT: The purpose of the study was to (a) assess the effects of sodium citrate ingestion on metabolism and performance capacity in a 5-km competitive outdoor stadium run in trained male runners, and (b) elucidate the potential relationship between citrate-induced changes in plasma volume, body mass, and performance. Ten subjects (age 22.1 +/- 2.5 yrs, body mass 74.1 +/- 6.1 kg, height 180.1 +/- 5.7 cm, (.)VO(2)max 60.8 +/- 5.5 ml x kg(-1) x min(-1)) participated in the study. There was no effect of treatment on 5-km running time: 1100.0 +/- 79.1 and 1082.7 +/- 62.0 s in citrate (CIT) and in placebo (PLC) trials, respectively, p = 0.09. Blood pH increased from 7.34 +/- 0.07 to 7.49 +/- 0.07 (p = 0.002) as a result of administering sodium citrate in the amount of 0.5 g x kg(-1) body mass in 1.5 litres of solution but remained stable while the equal volume of placebo drink was consumed: 7.40 +/- 0.04 and 7.44 +/- 0.09. The relative change in plasma volume after administering the drink was -1.99 +/- 3.49% in the PLC and 9.75 +/- 6.51% in the CIT trial (p = 0.001). Body mass did not differ before drinking; however, before the start the subjects were heavier in the CIT trial (74.2 +/- 6.1 kg) vs. the PLC trial (73.4 +/- 6.2 kg, p = 0.048). The shifts in plasma volume and body mass were not related to changes in performance. The results suggest that ingestion of sodium citrate induces an increase in water retention, plasma volume, and blood pH before exercise but does not improve performance in a 5-km competitive run in field conditions in trained male runners.
    Canadian journal of applied physiology = Revue canadienne de physiologie appliquée 01/2005; 29(6):691-703. · 1.30 Impact Factor
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    ABSTRACT: To test the hypothesis that sodium citrate administered two hours before exercise improves performance in a 5 km running time trial. A total of 17 male well trained college runners (mean (SD) O(2)MAX 61.3 (4.9) ml/kg/min) performed a 5 km treadmill run with and without sodium citrate ingestion in a random, double blind, crossover design. In the citrate trial, subjects consumed 1 litre of solution containing 0.5 g of sodium citrate/kg body mass two hours before the run. In the placebo trial, the same amount of flavoured mineral water was consumed. The time required to complete the run was faster in the citrate trial than the placebo trial (1153.2 (74.1) and 1183.8 (91.4) seconds respectively; p = 0.01). Lower packed cell volume and haemoglobin levels were found in venous blood samples taken before and after the run in the citrate compared with the placebo trial. Lactate concentration in the blood sample taken after the run was higher in the citrate than the placebo trial (11.9 (3.0) v 9.8 (2.8) mmol/l; p<0.001), and glucose concentration was lower (8.3 (1.9) v 8.8 (1.7) mmol/l; p = 0.02). The ingestion of 0.5 g of sodium citrate/kg body mass shortly before a 5 km running time trial improves performance in well trained college runners.
    British Journal of Sports Medicine 01/2004; 37(6):485-9. · 3.67 Impact Factor
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    ABSTRACT: Previous studies have failed to demonstrate that aerobic exercises increase the adrenocortical activity in prepubescent boys. The purpose of the present study was to check this fact using a longitudinal approach. Two cohorts of boys participated in a one-year follow-up. The first cohort consisted of 14 boys at sexual maturation stage 1 (age 10 to 11 years) and the second cohort of 5 boys at stage 2 (age 12 years) at the onset of the observation. Boys performed 20-min aerobic exercise on a cycle ergometer at the beginning and end of the year of observation. Before and 5 min after the exercise, blood cortisol and testosterone were determined by radioimmunoassays. Before the onset of puberty (stage 1) cortisol increase during exercise was found in only 25% of boys. Exercise induced significant increase of cortisol level after achieving sexual maturation stage 2. Testosterone response was insignificant at the first three stages of sexual maturation.
    Research in Sports Medicine - RES SPORTS MED. 01/2004; 12(3):201-207.
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    ABSTRACT: This study examined the possibility that fatigue may modify the hormone responses to exercise. A group of 12 endurance trained athletes ran for 2 h (blood lactate concentrations of approximately 2 mmol x l(-1)) in order to induce fatigue. The subjects exercised for 10 min at 70% maximal oxygen uptake before (1st test) and after (2nd test) the 2 h run to assess hormone responsiveness. A 1 min anaerobic power test was performed to assess muscle power. Cortisol, growth hormone, testosterone and insulin concentrations were determined before and after the 1st and 2nd tests. The 1st test resulted in increases in concentrations (P < 0.05) of cortisol and growth hormone, a decrease in insulin concentration (P<0.01) and no change in testosterone concentration. The 2 h run caused decreases of insulin, increases of growth hormone concentration and variable responses in the concentrations of cortisol and testosterone. The 2nd test decreased insulin concentration further (P < 0.05), but responses of the concentrations of testosterone, growth hormone and cortisol were variable. In 6 subjects (group A) cortisol displayed an increase [mean (SD)] from baseline concentrations [+ 304.0 (60.0) nmol x l(-1)], while in the other 6 subjects (group B) a decrease or no change was seen [+ 3.1 (5.3) nmol x l(-1), between groups, P<0.05]. Growth hormone concentration was substantially higher in group A [+ 14.7 (4.8) ng x ml(-1)] than group B [+ 6.0 (2.9) ng x ml(-1)] following the 2nd test. In group A anaerobic muscle power was higher, while in group B it was lower, after the 2 h run than before the 2 h run (P < 0.05). The findings suggest that fatigue from prolonged endurance activity may introduce a resetting in the pituitary-adrenocortical component of the endocrine system, expressed either by intensified or by suppressed endocrine functions.
    Arbeitsphysiologie 10/2001; 85(6):578-85. · 2.66 Impact Factor
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    ABSTRACT: Blunted response of growth hormone secretion to several pharmacological challenges is present in depression, but much less is known about the relationship of depression and secretion of growth hormone elicited by physiological stimuli. Furthermore, it is not known whether blunted growth hormone response occurs in depressiveness as measured with psychometric scales. A total of 82 healthy male volunteers (age 18-26 years) exercised on a bicycle ergometer with incremental load to achieve their maximal performance. Before exercise, subjects filled in approbated versions of Beck Depression Inventory (BDI), Spielberger's State-Trait Anxiety Scale, Cohens Perceived Stress Scale, and Schwartzers Self-Efficacy Scale. Blood samples were collected before and after exercise, and growth hormone, cortisol, and testosterone were measured by chemiluminescence immunoassay. Median perceived stress score of the subjects was identical to our population-based database median value, but the subjects had higher self-efficacy and lower depressiveness as shown by median values. In the majority of subjects, physical exercise induced remarkable increases in blood levels of the hormones. Cortisol and testosterone levels were not associated with the scores of psychometric scales. However, growth hormone response was virtually absent in high scorers (above median population score, n = 24) in BDI total score and the negative attitude subcomponent. Hence, this study demonstrates that growth hormone response to physiological stimuli is reduced in psychometrically measured depressiveness.
    Psychoneuroendocrinology 08/1999; 24(5):505-17. · 5.14 Impact Factor
  • L Laaneots, K Karelson, T Smirnova, A Viru
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    ABSTRACT: The dependence of hormonal responses to exercise on sexual maturation was tested in three-year longitudinal experiment on 34 girls (11-12 years old at the beginning of the study). Sexual maturation of the girls was evaluated using Tanner scale. Girls were divided into three groups: maturation stages 1-2, 2-4 and 4-5. Children performed a 20-min cycle exercise at 60% of maximal oxygen uptake (VO max) once a year. Cortisol, insulin, somatotropin, beta-estradiol, progesterone and testosterone were determined in venous blood by RIA procedures. High basal levels of beta-estradiol and somatotropin appeared in stages 2-4 (387 +/- 92 pmol.l-1) and 12.9 +/- 2.85 ng.ml-1, respectively) and 4-5 (358 +/- 54 pmol.l-1) and 14.3 +/- 1.53 ng.ml-1, respectively). The basal progesterone level increased with maturation, testosterone appeared in the blood in stages 2-4 and 4-5. The exercise resulted in increased levels of cortisol and somatotropin, and a drop in insulin in all girls. The cortisol response was most pronounced in stage 1-2. Postexercise insulin concentration was the highest in stage 4-5. beta-estradiol level increased by 23% in stages 1-2 and 4-5, while the response was insignificant in stages 2-4. Exercise-induced progesterone increase was significant in stage 4-5. In conclusion, sexual maturation associates with several quantitative changes in exercise-induced hormonal responses.
    Journal of physiology and pharmacology: an official journal of the Polish Physiological Society 04/1998; 49(1):121-33. · 2.48 Impact Factor
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    ABSTRACT: The dependence of exercise-induced hormone responses on sexual maturation was tested in a 3-year longitudinal experiment on 34 girls (aged 11–12 years at the beginning). Sexual maturation was evaluated by Tanners five-stage scale. Children cycled for 20-min at 60% maximal oxygen uptake once a year. Cortisol, insulin, growth hormone, β-oestradiol, progesterone and testosterone concentrations in venous blood were determined by radioimmunoassay procedures. Basal concentrations of growth hormone increased and of cortisol decreased when breast stage III was reached. Reaching breast stage IV was associated with an increase in basal concentrations of β-oestradiol, progesterone and testosterone. The exercise induced significant increases in concentrations of cortisol, growth hormone and β-oestradiol and a decrease in insulin concentration. At breast stage III the increase in cortisol concentration was to a lower level [467 (SEM 42) vs 567 (SEM 46)nmol · l−1] and growth hormone concentration to a higher level [29.4 (SEM 0.5) vs 12.8 (SEM 0.4)ng · ml−1], while the fall in insulin concentration was less pronounced [postexercise level 10.6 (SEM 0.9) vs 7.8 (SEM 0.8)mU · l−1] than in stage II. The magnitude of the cortisol response was reduced in the last stage of breast development (+42.1% vs +55.5% at stage II, +66.2% at stage III, and +50.0% at stage IV). The magnitude of β-oestradiol response was the lowest in breast stage IV (+15.8%) and the highest at stage V (+41.1%). The progesterone response became significant at stage IV and testosterone response at stage V. In conclusion, we found that reaching breast stage III was associated with altered responses of cortisol, insulin and growth hormone concentrations while the responses of the sex hormone concentrations became pronounced in the last stages of sexual maturation.
    European Journal of Applied Physiology and Occupational Physiology 04/1998; 77(5):401-408.
  • Biological Psychiatry - BIOL PSYCHIAT. 01/1997; 42(1).
  • European Neuropsychopharmacology 01/1996; 6. · 4.60 Impact Factor
  • A. Viru, K. Karelson, T. Smirnova, J. Ereline
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    ABSTRACT: To compare individual peculiarities in hormone responses and glucose pattern during prolonged exercise, 34 untrained persons and 27 endurance athletes performed a 2‐hour exercise test on a bicycle with an ergometer at the level of 60% maximal oxygen uptake (VO2max). Serial blood samples were taken through a venous catheter before exercise, at 10, 26, 30, 60, and 120 minutes of exercise and 1,6, and 24 hours after the cessation of exercise. Serum glucose, corticotropin, cortisol, somatotropin, and insulin concentrations were determined. In 79% of cases a slight initial decrease of 0.7 ± 0.23 mM in untrained and of 0.6 ± 0.31 mM in trained subjects was observed in the blood glucose concentration. In half of these subjects an increase over the initial concentration followed after 30 to 60 minutes of exercise. Despite the stable euglycemic level of the mean concentration during the succeeding stages of exercise, individual analysis indicated the existence of five variant glucose patterns: (1) an initial decrease followed by a slight elevation (in 12% of untrained persons and 41% of athletes); (2) a steady level below the initial value throughout exercise (in 50% of untrained persons and 30% of athletes); (3) an initial increase followed by a slight decrease (in 12% of untrained persons and 7% of athletes); (4) a steady level slightly above the initial value throughout exercise (in 12% of untrained persons and 11% of athletes); and (5) an initial decrease followed by a slight elevation and then by a decline (in 11% of untrained persons and 14% of athletes). The distribution of persons between these variants did not depend on the fitness level. In the case of an initial increase in glucose concentration, a substantial rise in blood somatotropin level was observed during the first 30 minutes of exercise. A lag period in the rise of somatotropin level was common for some of the cases with an initial decrease in glucose concentration. When the initial increase was followed by a decrease in glucose concentration, a diminution in somatotropin concentration began during the second half of the first hour (in other cases it occurred within the second hour of exercise) and was more pronounced than in persons with a different glucose pattern. The highest somatotropin concentration was observed in the case of a steady glucose concentration being maintained initially and throughout exercise. Insulin dynamics were similar in all variants of the blood glucose pattern. During the postexercise recovery period, an elevated insulin concentration was detected in conjunction with a maintained euglycemia. When the postexercise increase of insulin concentration was not found, an augmented glucose level was shown either at the 6th or at the 24th hour after the cessation of exercise.
    Research in Sports Medicine - RES SPORTS MED. 01/1995; 6(2):127-137.