Scand J Med Sci Sports 1994: 4: 113-118 Printed in Denmark All rights rererved

Copyright 0 Munksgaard 1994

Scandinavian Journal of MEDICINE & SCIENCE

IN SPORTS ISSN 0905-7188

Physical training, growth hormone and testosterone levels and blood pressure in prepubertal, pubertal and adolescent boys

Zakas A, Mandroukas K, Kararnouzis M, Panagiotopoulou G. Physical training, growth hormone and testosterone levels and blood pressure in prepubertal, pubertal and adolescent boys. Scand J Med Sci Sports 1994: 4: 113-118. 0 Munksgaard, 1994

The purpose of this study was to determine the resting values of growth hormone (GH) and testosterone (T) within prepubertal, pubertal and ado- lescence ages and to compare the effects of physical training in each age,

~ in 2 groups. The exercise group (A) consisted of 10 ten-year-old boys, 10 thirteen-year-old boys and 9 sixteen-year-old boys. The control group (B) consisted of approximately the same number of subjects of the same ages. Group A, in addition to the school activity, trained with intervals (3 months, 50 midday, 3 daydweek). at high intensity (80-85% of max) and at light intensity (3040% of max). Group B participated only in the school physical education program 2-3 timedweek. Venous blood samples were taken at rest by intravenous catheter before and after training. Levels of GH and T in blood serum was determined by radioimmunoassay. Before training, the levels of T differed between the 3 ages, but there were no significant differences in GH (group A and B). After training, the levels of GH and T in group A were sigmficantly higher in the 13-year-old boys and in the 16-year-old boys, but were unchanged in the 10-year-old boys. In group B the levels of GH and T were unchanged in all 3 ages. The conclusion is that neither high nor mild intensity training can change the levels of GH and T in prepubertal boys. However, high intensity training can be a stimulus for increasing GH and T levels in puberty and adoles-

Growth hormone is essential for normal growth. Its effects are both direct and indirect. Direct effects re- flect the metabolic role on carbohydrate and fat me- tabolism, and indirect effects on somatic growth are mediated by somatomedin (1).

Testosterone is a steroid hormone that has a con- siderable anabolic effect on muscle tissue. It has been suggested that it is related to both muscular strength (2, 3) and aerobic capacity (4). In regard to growth hormone levels during prepuberty, puberty and ado- lescence, Tanner (5 ) did not find differences between the 3 ages. However, Malina & Bouchard (1) sug- gested that mean concentrations of growth hormone from childhood to adolescence increase and reach a peak that is almost coincident with the time of peak height velocity. There is, of course, variation in the frequency and amplitude of growth hormone pulses. Both vary with age, and there is an increase in the frequency and amplitude of bursts as the individual

A. Zakas, K. Mandroukas, M. Karamouzis, 6. Panagiotopoulou Ergophysiology Laboratory, Department of Physical Education and Sports Science, University of Thessaloniki, Greece

Key words: Orowth hormone; testosterone; blood pressure; prepubertal boy; pubertal boy: adolescent boy; training

Konstantinos Mandroukas PhD., Department of Physical Education and Sports Science, University of Thessaloniki, Thessaloniki 540 06, Greece

Accepted for publication August 4, 1993

passes from childhood to adolescence. With regard to testosterone levels, it has been shown that prepub- ertal children have the lowest concentrations and pu- bertal children the highest ones (5) .

Generally, in men, physical exercise is known to affect plasma levels of hormones. Although the short-term response to exercise of different inten- sities and durations has been established (6-9), few studies have determined the long-term effects (10). Many articles have been published regarding the ef- fects of physical exercise on plasma growth hormone and testosterone levels, but the results reported to date have been conflicting. In men, conflicting results were found for testosterone by several groups: some authors observed an increase with short-term intense exercise (9, 11-14), others observed a decrease with sub-maximal exercise of longer duration (6, 15) and still others observed unchanged hormone levels (1 6). The interactions between exercise and growth hor-

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mone have been extensively studied in men, and the results have been reported previously (17). The effect of short-term physical exercise on growth hormone during puberty have been studied. Oseid & Herm- ansen (18) have found that the levels of growth hor- mone increase in prepuberty, and Wirth et al. (19) suggest that this increase is more evident in puberty than in prepuberty. Nevertheless, no information exists about the adaptation of long-term physical training during prepuberty, puberty and adolescence associated with the initial levels of growth hormone and testosterone. There are no studies that examine the alterations that may occur in plasma levels of growth hormone and testosterone in children after some months of physical training.

Thus, the purpose of the present study was to de- termine the rest values of growth hormone and tes- tosterone in prepuberty, puberty and adolescence and to compare the effects of physical training in each age, in 2 groups.

Material and methods Subjects Fifty-five (55) boys aged 10, 13 and 16 years old par- ticipated in this study. The subjects were separated in two groups. Both training group A and the con- trol group B consisted of the same number of sub- jects (A=29; B=26). Each group included 3 ages (10, 13 and 16). All subjects and their parents were in- formed of the nature, purpose and possible risks in- volved in the study before giving their voluntary written consent for participation. The subjects were born in the first 6 months of the year (January-June), and none of these boys were involved in an organ- ized sports program during the last year. Pubertal staging, by examination of pubic hair and penile and testicular development, was performed according to the criteria of Tanner (20). So, the classification for the sexual maturity of the 10-year-old boys was in Tanner stage 1, the 13-year-old boys in stages 2-4 and the 16-year-old boys in stage 5. Subjects were healthy and free of any diagnosed endocrine dis- orders. No subject was taking any medication prior to or during the study that might affect the results of the experiment. All subjects attended the laboratory early in the morning after an overnight fast from 2100 the previous evening. Subjects were instructed to avoid smoking and strenuous exercise the pre- vious day and to rest on the bed quietly for 30 min prior to the blood sampling.

Maximal exercise test Before training, each subject of both groups per- formed one maximal test on a mechanically braked cycle ergometer (Monark-Sweden). In order to deter-

mine heart rate during the submaximal and maximal exercise test, the initial workloads for pubertal stage 1 (10 years) was 50 W, subjects in pubertal stages 2 and 4 (13 years) was 100 W and subjects in pubertal stage 5 (16 years) was 125 W. These workloads were previously determined by means of a work test on a bicycle ergometer. In the first workload they cycled for 6 min. The pedaling rate was 50 rpm. After that the workload was stepwise increased every minute by 25 W until exhaustion. During the testing, heart rate was monitored continuously by an electrocardio- graph. Before and after 3 months of training, blood pressure (systolic) was taken with a mercury man- ometer after 30 min of rest in the supine position. Two skinfold measurements were taken at each site, triceps and subscapula. If they differed by more than 5% a third trial was undertaken. The average of all trials was used. Percentage fat was estimated from the sum of the two skinfolds (triceps and subscapu- lar) according to Boileau et al. (21).

Physical training program During the training period, the exercise group A par- ticipated both in the school physical education pro- gram and in the organized training program for 3 months. Group A was trained for 3 months (Jan- uary-April), 3 times a week. The duration of the training session was 50 min, starting with 10-15 min of warm-up exercises including walking, jogging and calisthenics of light intensity, including exercise with all parts of the body. The program then continued with alternating heavy and light periods, Heavy in- tervals (a total of 3) were performed on a cycle erg- ometer and lasted for 4 min. The intensity was chosen individually, based on the maximal workload performance at the test before the training. The workload during each heavy interval was standard- ized for each subject, so that he was performing at 80-85% of his maximal heart rate. Light intervals lasted 8-10 min (3040% of maximal heart rate) and consisted of walking and calisthenics, affecting mainly other muscle groups than those utilized dur- ing heavy intervals. For several training sessions tel- emetry was used on all subjects to record heart rate during cycle exercise and to adjust the workloads gradually during training. After 3-4 weeks of train- ing, the workload was gradually increased. The in- tensity of the training in group A was estimated in each subject by telemetry (Sport Tester, Finland).

Control group B participated only in the normal school physical education program of 2-3 40-min sessions per week (mainly ballgames and some calis- thenics). The intensity of this program was estimated by telemetry (Sport Tester). Both the duration and the intensity of training in group B were much less than the specific training program for exercise group

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Physical training, growth hormone and testosterone levels

mone and testosterone. It is noted that these corre- lations increase as age increases.

After 3 months of physical training, there were changes in body weight and height in both groups. The height increased (P<O.OOl) in training group A and control group B (Table 1). The significant in- crease in body weight was observed only in group B (10 and 13 years. P<O.OOl; 16 years, P<O.Ol). For group A, the significant increase was shown only in the 13-year-old boys (P<O.OOl). Changes in systolic blood pressure were observed only in group A (10 years, KO.01; 13 years, ZWO.001; 16 years, PC0.05) (Table 1). No changes in systolic blood pressure were found in group B. It should be pointed out that, dur- ing the training period of 3 months, no changes were observed in the sexual maturity in both groups. The percentage of subcutaneous fat decrease was signifi- cant in group A (10 and 13 years, P<O.OOl; 16 years, PC0.05). In group B, there was a significant increase in ages 10 years and 13 years (P<O.OOl) (Table 1).

The effects of physical training in growth hormone (Fig. 1) and testosterone (Fig. 2) were observed only in group A. However, this increase is shown only in the 13- and 16-year-old boys (P<0.05; P<O.Ol). No changes were found in the prepubertal ages in the same group A (10 years). In group B the resting levels of growth hormone and testosterone were un- changed in all 3 ages.

A. During the period of physical training, the sub- jects in both groups were instructed to follow only their programmed physical activities and to maintain their usual food intake.

Blood samples Venous blood samples were taken (5 ml) by intra- venous catheter before and after training. Blood was taken at rest during standardized fasting conditions at 0800, to get baseline hemodynamic and hormonal values. The blood samples were centrifuged (1 500Xg for 15 min) and the serum was stored at -20°C until analyzed. The levels of growth hormone and testos- terone in the blood serum were determined by radio- immunoassay according to Mollinatti et al. (22), and to Abraham (23) respectively, by using kits from SO- RIN Biomedical Company (Italy). All assays were carried out in duplicate.

The method used contained antiserum with speci- fic antibodies of growth hormone or testosterone. The minimum quantifiable serum levels were 0.15 ngl ml for growth hormone and 4 ng/100 ml for testos- terone. The intra- and interassay coefficient of vari- ation (CV%) for growth hormone were 3.9% and 5.5% respectively. The analogous values for testos- terone were 6.8% and 9.5% respectively.

Statistics The significance of differences between means was determined by one-way analysis of variance (ANOVA), and the comparison between the means, before and after training, was done by a paired t-test (two-tailed test). Pearson product-moment correlation coefficient was also determined. Statisti- cal significance was at P<0.05.

Results Before training, it was observed that, in both groups (n=55), the levels of growth hormone did not differ within the 3 ages. However, there were daerences in testosterone and systolic blood press- ure (P<O.OOl). The highest values were shown in adolescence (16 years) and the lowest in the prepu- bertal ages (10 years) (one-way ANOVA). The in- crease in height was related to parallel increases in body weight (10, 13 and 16 years, P<O.OOl) and the increase in body weight correlated with percen- tage subcutaneous fat (10 and 13 years, P<O.OOl; 16 years, P<O.Ol). The increase in height correlated with percentage subcutaneous fat (10 and 13 years, R0.05). No sigmficant correlations were found be- tween the other variables. However, there was a tendency for height to be related with testosterone and body weight to be related with growth hor-

Discussion The purpose of this study was to determine serum growth hormone and testosterone concentrations in subjects of 3 different ages at rest and to compare the effects of training in 2 groups.

The results clearly showed that, after 3 months of training, secreted growth hormone and testosterone in prepubertal subjects (10 years) did not change. In puberty (1 3 years) and adolescence (1 6 years) growth hormone secretory pattern and testosterone undergoes a remarkable change.

It has been reported by Oseid & Hermansen (18) and Wirth et al. (19) that short-term exercise in- creased the levels of growth hormone in prepubertal boys. However, in the above studies they did not in- clude a control group and did not regard biological maturity, fitness level of the subjects or the time of the day that the blood samples were taken. Thus, it is impossible to separate the changes related to growth and maturation from those induced by training.

Fahey et al. (24) observed that short-term exercise can not change the levels of testosterone in prepuber- tal children. Our results are in agreement with the above study. Also, it seems that the testosterone levels cannot be changed during either short- or long-term physical exercise. No available infor-

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Table 1. Physiological characteristics for training and control groups before and after training. The measurements of blood pressure were done at rest. Values of k 0 . 0 5 were considered significant. The values are expressed as mean2SD.

Training group 10 years before (n= 10) after 13 years before (n= 10) after 16 years before (n=9) after

Heigh (cm)

141.226.3 142.926.3" * 159.757.1 162.127.1"' 175424.9 176.3~5.0"'

Weight Systolic blood pressure (kg) (mmHe)

38.628.2 109.727.9 39.028.4 NS 105.529.7" 51.729.1 115.228.8 53.02 9.0' 72.421 3.3 120.527.8 71.4211.8 NS 11 6.957.5'

I I 0.226.9'

Subcutaneous far %

22.528.9 19.929.1"' 22.026.3 19.225.9"' 22.556.7 20.727.5'

Control group 10 years before 138.326.6 35.726.0 102.627.6 18.956.7 (n=8) after 139.9?6.7**' 37.026.7" 102.225.3 NS 20.9+-6.7"* 13 years before 157.824.9 48.826.4 114.656.1 20.526.8 (n=9) after 160.225.4*" 51.426.9"* 115.826.3 NS 22.726.7"' 16 years before 173.0t7.8 67.621 2.0 120.724.7 20.657.1 (n=9) after 173.727.9* 68.7212.0** 120.725.5 NS 21.425.8 NS

NS: not significant; k 0 . 0 5 ; * * FkO.01; * * * kO.001. a % fat was estimated from sum of two skinfolds (triceps and subscapular).

Qnnrth hormone (uU/rnl)

T 4

S

2

1

a 19' . 1 6 . . . . . . . . 10 10 13 16 age

Tralnlng group Control group

Fig. 1. Growth hormone levels for training group and control group before and after training. The values are expressed as mean2SEM. P<0.05; ** P<O.Ol.

26 J 20

16

10

0 . . . . . 10 13 16 10 13 16 age

Training group Control group

Fig. 2. Testosterone levels for training group and control group before and after training. The values are expressed as mean2 SEM. Pc0.05; ** P<O.Ol.

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mation exists among the effects of long-term physical training in children. Therefore, it is difficult to com- pare our results with previous investigations. The mechanics that are involved during exercise and their effects on growth hormone and testosterone in children are unknown.

In adults the responses of growth hormone and testosterone during acute exercise have been re- ported (25-27). The influence of physical exercise on the increase of growth hormone levels depends on several factors. In adults the main factors are the type of training (25), intensity and duration of train- ing (26, 27), age of the subjects (19) and the muscle mass involved in exercise (28).

The interactions between exercise and growth hor- mone have been extensively studied (17, 29).

In adults, it is generally accepted that short-term maximal exercise elevates the circulating testosterone levels (9, 1 1 , 12, 30). Vigorous endurance and strength training causes a decrease in testosterone levels, but data about the effects of training should be under careful observation. The lower levels of tes- tosterone at rest, which have been shown in endur- ance athletes (31) and power athletes (32), may indi- cate an overtraining situation (33). In fact, several reports have suggested the use of diminished resting serum testosterone-to-cortisol ratios as indicators of overtraining (32, 34).

In this study, neither high- nor moderate-intensity training in prepurbertal boys changed the levels of growth hormone and testosterone. However, train- ing in puberty can be a stimulus for increased growth hormone and testosterone levels. It must be empha- sized that this increase can only be observed in pu- berty (1 3 years) and adolescence (1 6 years).

Physical training, growth hormone and testosterone levels

Our results suggest that the effects of training in children are strongly influenced by such factors as selection of the subjects and the exact description of training. So, it seems that intensity and duration of training are important factors to consider for the evaluation of growth hormone and testosterone re- sponse to exercise, but only in puberty (1 3 years) and adolescence (1 6 years). The previous factors affect the increase of growth hormone and testosterone in adults; the same seems to exist for the children also.

Before training, the correlations of testosterone and growth hormone to the other variables in both groups were very low. After training, no changes were observed in these correlations. It seems also that the variables are independent of these two hor- mones and that the training has limited effects.

Physical training has several beneficial cardio- vascular and metabolic effects. As a result of train- ing, systolic blood pressure and subcutaneous fat de- creased significantly only in training group A, which shows that exercise is an important factor for the regulation of body weight. The significant increase of body weight in 13-year-old boys in the training group could be attributed to the growth spurt and increase of height that is observed in this age.

In summary, the results suggest that training elev- ates serum growth hormone and testosterone con- centrations in puberty and adolescence, when there is a stimulus such as a high intensity and duration in exercise. On the other hand, independently of the intensity and duration of exercise, there are no ef- fects in these hormone levels in prepuberty (10 years).

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