Pubertal stage differences in hormonal and hematological responses to maximal exercise in males THOMAS D. FAHEY, ANTONIO DEL VALLE-ZURIS, GEORGE OEHLSEN, MARTIN TRIEB, AND JOYCE SEYMOUR 95014 Human Physiology Laboratory, De Anza College, Cupertino, California
FAHEY, THOMAS D., ANTONIODEL VALLE-ZURIS, GEORGE OEHLSEN,MARTIN TRIEB, AND JOYCE SEYMOUR.PubertaZ stage differences in hormonal and hematobgid responses to maximal exercise in males. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 46(4): 823-827, 19’79.-Concentrations of serum testosterone (ST), growth hormone (SGH), and insulin (SI) at rest and following maximal exercise were compared in 27 males in different stages of pubertal development. Oxygen consumption and heart rate were measured while subjects performed a continuous-incremental work capacity test to voluntary cessation on a cycle ergometer. Pre- and postexercise blood samples were analyzed for hemoglobin (Hb) and hematocrit (Hct) by Coulter Counter, and for ST, SGH, and SI by radioimmunoassay. ST at rest increased with pubertal stage and was related to the increase in body weight and work capacity seen with increasing development during adolescence. There were no differences between pubertal stages in changes in hormone concentrations following exercise or in Hct or Hb before or after exercise. Our results do not support the hypothesis of a critical pubertal stage that exhibits enhanced response to exercise. testosterone; growth physical activity
hormone;
insulin;
plasma volume; growth;
FROM CHILDHOOD toadulthoodinvolves profound changes in physical stature, maturation, work capacity, and many other physiological characteristics. The improvement in work capacity observed during adolescence seemsto be related more to physical and sexual maturation than to chronological age (3, 6). Presumably, the increase in testosterone secretion that occurs with sexual maturation in males is related to the advancing work capacity seen in puberty. Females, who do not experience increases in testosterone at puberty, do not exhibit the same degree of rapid increase in exercise capacity or muscle mass during adolescence (6). In the adult, testosterone, insulin, growth hormone, and plasma volume are affected by maximal exercise. Typically, levels of testosterone (25) and growth hormone (9,13) increase as insulin (9) and plasma volume decrease (30). At rest, testosterone is known to increase levels of growth hormone (16), stimulate erythropoiesis (17), and perhaps indirectly influence insulin by its effect on growth hormone (20). Serum testosterone has been shown to be highly correlated to pubertal stage (31). Ekblom (4) has shown that physical training during puberty results in greater growth than would be expected
THETRANSITION
OlSl-7567/79/oooO-oooO$O1.25
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0 1979 the American
Physiological
in the untrained subject. This implies the existence of a period during puberty when subjects may experience enhanced hormonal activity during exercise. The purpose of this study was to determine if differences exist in the levels of serum testosterone, insulin, growth hormone, and selected hematological variables at rest and following maximal exercise in male children who are in different stages of pubertal development. METHODS
AND PROCEDURES
Subjects. Twenty-seven males ranging in age from 5 to 18 yr volunteered as subjects. The nature of the study.
was explained and informed consent was obtained from the subjects and their parents. Twenty-two of the subjects were of Latin American extraction with the remainder of Northern European descent. Pubertal staging by examination of pubic hair and penile and testicular development was performed according to the criteria of Tanner (28). Subjects were healthy and free of any diagnosed endocrine disorders. No subject was taking any medication, such as anabolic steroids or insulin, that might affect the results of the experiment. Subjects were instructed not to eat or exercise for a minimum of 2 h before the experiment and to rest quietly for 10 min prior to the preexercise blood sampling. All tests were administered at approximately the same time in late afternoon to minimize the effects of diurnal variations. Exercise protocol. Subjects performed a continuous incremental work task on a Monark cycle ergometer to voluntary cessation. Subjects in pubertal stages 1 and 2 began the test at a work rate of 360 kg l m. min-‘; subjects in pubertal stages 3-5 began at 720 kg l m*min-‘. Work rates were increased 180 kg. rn. min-’ every 2 min for all subjects. Pedaling speed, paced by a metronome, was 60 rpm. Pedaling rate was measured with a trigger and microswitch attached to the sprocket and frame of the ergometer. Minute-by-minute oxygen consumptions were obtained by an open-circuit method. Pulmonary ventilation was measured with a Godart-Statham pneumotachometer regularly calibrated against a Collins l20liter Tissot gasometer. Samples of expired air, drawn through Drierite, were immediately analyzed for percent oxygen with an Applied Electrochemistry model S-3A 02 analyzer, and for CO2 with a Godart capnograph. The 02 and CO2 analyzers were regularly calibrated with gas samples of known concentration verified with a ScholanSociety
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ET
AL.
der apparatus. VO 2 maxwas identified as the highest iJ02 TABLE 1. Description subjects -.-____of-__~--~. value reached during a 1-min period. Pubertal Sage Heart rates were determined from the ECG obtained Tu ke yL;rnparfor 15 s at I-min intervals from a Gilson recorder using (n2 6) (*P; 3) (2 7) (2 6) (2 5, Beckman surface electrodes (CM5 lead). Maximal heart 9.6 10.7 12.9 15.4 15.1 P&5 > PI-2; rate was identified as the highest value recorded during Age9yr ztl.0 *0.3 *0.5 ztO.8 a.5 P3 > P2 the test. 50.0 59.8 58.7 30.0 41.2 P3-5 > PI; w kg *2.5 *3.7 *6.8 k7.2 *3.4 P‘&5 > P2 Analytical methods. Blood samples were taken from 150.7 164.2 168.1 134.0 146.1 P5 > R-2; an antecubital vein without stasis immediately before Ht, cm *5.9 *2.9 *3.0 *5.1 *3.4 P.4 > PI and immediately after the exercise with subjects seated Body surface 1.05 1.28 1.42 1.63 1.66 P3-3 > P,; on the ergometer. Blood samples were collected in Vacarea, m2 *0.07 *0.06 *0.09 *0.11 *0.07 P4 > PP utainers, which were plain or contained EDTA. Blood in Hemoglobin, 12.9 13.6 13.6 14.1 14.3 NS kO.5 a.0 dzo.4 *0.5 *to.5 g/1(@ ml the plain Vacutainers was allowed to clot and the serum 37.6 39.6 39.4 42.6 42.2 NS separated by centrifugation. Hematocrit (Hct) and he- Hematocrit, a.4 d.2 a.0 k2.7 k2.6 % moglobin (Hb) using EDTA-treated blood were deterValues are means * SE. NS, not signifhnt. mined with a Coulter Counter (model S). All samples were refrigerated and analyzed for Hct and Hb within 3 TABLE 2. Performance characteristics __.--- _-h of being drawn. The change in plasma volume (APV) ___-- --- ____- ~______-------was determined by the method of Van Beaumont (29). Pubertal Stage Tu key CompiriSerum testosterone (ST), serum insulin (SI), and serum P:, PI P5 sons (n = 7) Cn2 6) in = 6) (n =3) growth hormone (SGH) were determined by radioim1.56 1.60 2.00 2.98 2.66 P4e5 > munoassays: ST by the method of Ismail et al. (II), SI vo 2 max9 1. *o. 14 min-‘, *o. 15 *0.20 to.38 *0.43 P 1-2; by the method of Morgan and Lazarow (19), and SGH STPD PA > by the method of Morgan (18). Radioimmunoassays P3 (RIA) were performed with materials and by procedures VO 2 max9 52.0 39.4 41.3 48.4 45.2 NS ml* *3.5 k2.9 *3.7 obtained from ICN Pharmaceuticals. Activity of 3H for k3.1 ~~6.5 kg-’ the determination of ST was detected with a Packard Tri-Carb liquid scintillation spectrometer. Activity of 1251 min-‘, STPD for the determination of SGH and SI was measured with HRmax, 201 200 198 190 192 NS a Hershaw sodium iodide crystal and Ortec counter. beats/ *4 k4 *2 -+6 k6 mm Serum was frozen at -2OOC and analyzed within 3 wk of 51.7 67.9 80.2 90.9 P4a5 > 1. 57.1 the venipuncture. Quality control was assured by per- VI3 mam . -1 *3.5 k6.1 k6.1 *5.7 k 15.8 P l-2 forming the RIA procedures on serum containing known :+PG hormone concentrations. For each hormone, the samples Max work 797 886 1,044 1,413 1,495 P&5 > kperne 260 ~56 *96 k82 k172 P l-3 were analyzed in one assay with intra-assay variance less . -1 than 5%. When sample variation exceeded 5%, the assay -6.1 -8.7 -6.8 -2.6 -10.4 NS was repeated. Postexercise hormone values were adjusted *Py% a.7 k2.3 ~~2.5 k2.6 k4.6 for the changes in plasma volume. Values are means * SE. STPD, standard temperature and pressure One- and two-way analysis of variance (ANOVA) and dry. APV; change in plasma volume. NS, not significant. the Tukey procedure were used to determine if significant differences existed between compared groups. The level in pubertal stage 1 (PI). Work capacity also tended to of significance was chosen at P < 0.05. increase with pubertal stage, but again there were not always differences among all groups. There were no RESULTS significant differences in APV between groups. The physical characteristics-age, weight, height, and Significant differences existed in serum testosterone body surface area-(Table 1) tended to increase with between all pubertal stages at rest and following exercise advancing sexual development, although this was not (Fig. 1). However, pre-postexercise differences in ST were always the case. Some overlapping between pubertal nonsignificant, both within and between groups. stages was evident for each of the characteristics. There Because of the high correlation between testosterone were no significant differences between pubertal stages and pubertal stage (r = 0.94, Spearman’s rank order in resting values of hematocrit or hemoglobin. correlation), ST levels at rest were used as a means of . vo 2m8X(Table 2) tended to rise with increased pubertal examining the relationship between pubertal stage and development, although again there was overlapping be- the other variables examined in this study. This was done tween stages. There was, however, no difference in because it is inappropriate to use ordinal data (pubertal . vo 2 maxbetween groups when oxygen consumption was stages) in a Pearson’s product moment correlation (7). In expressed as ml kg-’ min. The increased \j02 max (1 addition to the use of linear regression ( Y = a + bx), ST min-‘) was attributed to an increase in body mass rather and AST were correlated to each of the 12 variables with than actual increases in metabolic capacity. Comparisons power (Y = aebX) and exponential equations ( Y = axb). The type of regression equation rendering the highest Of VE maxrevealed a trend similar to VOW max(lemin-‘). There were no differences in maximal heart rate, despite correlation for each comparison is shown in Table 3. HR maxvalues in excess of 210 beats/min in two subjects Resting ST was related to maturational variables age, l
l
l
l
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RESPONSES
600
TO
EXERCISE
-’
B I
IN
825
PUBERTY
POST EXERCISE PRE EXERCISE
= I-
POST EXERCISE PRE EXERCISE
18-
Lm
z
PI
R
N=7
N=6
PS N=6
PUBERTAL FIG. 1. Serum 2 SE; postexercise
R
R
N=5
N=3
PI
STAGE
testosterone (ST) before and after exercise; means values corrected for changes in plasma volume.
3. Correlation between testosterone and change in testosterone, with physical, hormonal, and performance variables TABLE
Variables
Ht
Wt ASGH AS1
-0.09
Work,,,,
lmin-’ pmax, ml* kg-’
2 max,
emin-’
Hb APV Correlations from equation Number of subj is 27. ST, terone. * P < 0.05.
-0 .40*
R
N=7
N=6
I?
p3 N=6
N=5
R N=3
PUBERTAL STAGE FIG.
means volume.
2. Serum growth t SE; postexercise
hormone values
(SGH) before corrected for
and after exercise; changes in plasma
FZZI POST EXERCISE I PRE EXERCISE
AST
0.07 0.31 (2) 0.20 (2)
(2)
0.06 (1) -0.36 0.60* 0.76* 0.60*
HRmax hll,X VO VO
ST
0.70* 0.74* 0.77* (1)
Age
6-
iz LLl m
(2)
-0.23
(2)
-0.62* -0.35 0.33 0.28 -0.25
(1) (2) (2) (1)
-0.16
(1)
.38* (1) 0.22 (2) .06 -0.37 (1) Y = a + bx; (I), Y = aebx; (2), Y = ax'. testosterone;
AST,
change
in
-
testos-
PI
R
N=7
weight, and height. In addition, there were significant correlations between resting ST and performance variables VE max,maximum (max) work, and VO, max(ml kg-‘. min-‘). AST was not significantly related to any variable with the exception of ASI. To separate the relative contribution of age from the relationship between resting ST and physical and performance characteristics, partial correlations were used. Holding age constant, resting ST was only correlated with body weight and maximal work capacity (r = 0.49 and 0.51, respectively). Correlations of ST were reduced to 0.34 with height, 0.09 with Tj02 max (1l rein-‘), and -0.02 with Hb. Growth hormone (Fig. 2) increased as a result of exercise in PI, Pp, and Pd, but the changes were not significantly different between groups. There were no differences between the groups in SGH either before or after exercise. At rest there were no significant differences between groups in serum insulin (Fig. 3). There was a significant decrease in SI with exercise only in Pg subjects. There were no differences between iFUPS in pre-postchanges in SI or in the postexercise levels of the hormone. l
N=6
R
N=6
R
N=5
R
N=3
PUBERTAL STAGE 3. Serum insulin (SI) before and after exercise; means postexercise values corrected for changes in plasma volume. FIG.
in SE;
DISCUSSION
The results of our study indicate that hormonal and hematological changes occurring with maximal exercise are similar during different pubertal stages. Development patterns were evident for body weight, height, age, work capacity, ir02 (1 min-l), hemoglobin, and VE max. max When the effect of age was held statistically constant, testosterone was only significantly related to body weight and work capacity. Body weight and work capacity on a cycle ergometer are partially dependent on the relative development of skeletal muscle. Because of the importance of testosterone in muscle development and hypertrophy, it is not surprising that ST should be related to these factors independent of age. We were unable to identify pubertal stages with enhanced hormonal or hematological response to exercise. Our data, therefore, cannot serve as an explanation for l
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826
FAHEY
the findings of Ekblom (4), who found an apparent acceleration in growth by subjects involved in exercise training during puberty. Klissouras et al. (14, 15) studied the relative potency of training at different developmen tal stages. They were unable to identify a period during adolescence when heavy training would result in increased performance. They hypothesized that during the accele rated growth phase of adolescence, ho rmonal activity is optimum and additional stimuli such as training cannot override its influence. Our study failed to identify a pubertal stage that responded differently to a single bout of exercise; so it is unlikely that aP articular stage would respond differently to the repea ted exercise stimulation of training. Hormone metabolic effects cannot be assessed by serum levels alone; metabolic clearance and production rates must be considered as well. We failed to find changes in ST with exercise, which agrees with the findings of Lamb (16), but not with the findings of Sutton et al. (27). Sutton et al. (24) have found testosterone clearance rates decrease during exercise in adult males, whereas production rates do not change. Testosterone metabolism in the adolescent, occurring during a period of rapid growth, cannot be compared to ST metabolism in the adult. Studies by August et al. (1) and Spona and Lunglmayr (23) indicate that the sensitivity of the hypothalamic-pituitary-gonadal axis is greatest during the middle-pubertal years. Different patterns of ST production and clearance may exist in the developing adolescent male. Because we measured only serum concentrations, our findings do not rule out possible pubertal stage differences in ST production and clearance rates during exercise. There were no significant differences between groups in growth hormone concentrations. Changes in SGH with exercise are probably more related to intensity and duration of exercise and fitness of the subjects than to maturational factors (26). In addition, because we obtained our samples immediately after exercise, we may have missed the peak in growth hormone concentration that may occur up to 15 min after the exercise stimulus (26). Serial samples were not taken because of reluctance on the part of the subjects. Kaplan et al. (12) have found fasting levels of growth hormone higher in young children less tha .n 4 yr old but found no apparent correlation with age in pubertal children. Age differences in the disposal rate for growth hormone with a more rapid turnover in growing children could lead to lower concentrations of hormone and obscure a change in serum concentration that might otherwise reveal a significant relationship in our subjects. Several pubertal groups may have failed to increase in SGH significantly because of high initial values seen in several subjects. This may have been caused by emotional distress induced by the experiment or by possible nonbasal conditions in these subjects. Kaplan et al. (12) have noted that growth hormone responses to various stimuli are blunted when subjects already have high levels due to stress. Sutton and Lazarus (26) have indi-
ET
AL.
cated the desirability of collecting two or three basal samples for SGH determination prior to any stimulus, exercise or other, . being applied. Insulin decreased in Pg but remained unch .anged in the other gro ups. Hartley, et al. (9) have found that insulin levels decrease in response to exercise, but this has not been found by others (5, 27) . There was a significant relationship between AST and AS1 (r = -0.62) that was moderately reduced to r = -0.53 when APV was held constant with partial correlation. This may be due to individual differences in the relative intensity of the exercise. Pruett (21) has found that insulin changes during exercise are dependent upon th .e perce nt of VoZ reached during work. The relative intensity of work may also act ount for the different findings reported in the literature for ST levels with exercise. Performance on a cycle ergometer, used in the present investigation, is partly dependent on such factors as body size, leg strength, motivation, and familiarity with cycling. These, as well as other, factors may have resulted in differences in the relative work intensity of our subjects. Hemoglobin, like resting ST, increases during growth. Garn and Smith (8) have found that children who have hemoglobin levels that are low for their age, sex, and race tend to be smaller and lean, whereas children with higher levels of Hb tended to be taller, heavier, and fatter. These data are consistent with our findings. Moderately high linear correlations were found between resting levels of Hb and height (r = 0.58) and weight (r = 0.56). There was no significant difference between groups in hemoglobin and hematocrit levels. However, these measurements tended to be lower in earlier pubertal stages as evidenced by their significant correlation with serum testosterone (used as a measure of pubertal stage). VOZ max(ml. kg-’ min-‘) was the same in all groups and did not appear to be influenced by the hematological variabIes. Blood lower in hematocrit and hemoglobin has a lower viscosity and a decreased resistance to flow (2, 22). This phenomenon may partially act to create a parity in 02 delivery capacity between subjects with different hematological characteristics (10) . Hematological changes with exercise were similar in all pubertal groups. Differences in hemoconcentration during exercise does not seem to be the mechanism that allows children with lower Hb concentrations to maintain an equal oxygen transport capacity relative to body weight. Additionally, because oxygen consumption is related to muscle respiratory capacity, small differences in hematocrit and hemoglobin may not result in significant differences in the To2 maxof children. In summary, the developmental differences existing in physical and performance characteristics between males in different stages of pubertal development are probably partially hormone related. However, we were unable to identify a particular pubertal stage that exhibited higher concentrations of ST, SI, or SGH following maximal exercise. l
Received
30 January
1978; accepted
in final
form
19 December
1978.
REFERENCES AND S. KAPLAN. 1. AUGUST, F. M., GRUMBACH, puberty . III. Correlation of plasma testosterone,
Hormonal changes in LF, FSH, testicular
size, and bone age with pubertal Metab. 34: 319-326, 1972.
development.
J. Clin. EndocrinoZ.
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PUBERTY
2. CHIEN, S., S. USAMI, H. M. TAYLOR, J. L. LUNDBERG, AND M. GREGERSEN. Effects of hematocrit and plasma proteins on human blood rehalogy at low shear rates. J. Appl. Physiol. 21: 81-87, 1966. 3. CLARKE, H., AND J. HARRISON. Differences in physical and motor traits between boys of advanced, normal, and retarded maturity. Res. Q. Am. Assoc. Health Phys. Educ. Retreat. 32: 449-460, 1961. 4. EKBLOM, B. Effects of physical training in adolescent boys. J. Appl. Physiol. 27: 350-355, 1969. 5. ERIKSSON, B., B. PERSSON, AND J. THORELL. The effects of repeated prolonged exercise on plasma growth hormone, insulin, glucose, free fatty acids, glycerol, lactate and P-hydroxybutyric acid in 13-year old boys and in adults. Acta Paediatr. Stand. Suppl. 217. 6. ESPENSCHADE, A. Motor performance in adolescence including the study of relationships with measures of physical growth and maturity. Monogr. Sot. Res. ChiZd Dev. 5: 1-126, 1940. 7. FERGUSON, G. StatisticaL Analysis in Psychology and Education. New York: McGraw, 1966, p. 106. 8. GARN, S., AND N. SMITH. More on hemoglobin levels relation to growth performance. J. Pediatr. 81: 346, 1973. 9. HARTLEY, L., J. MASON, R. HOGAN, L. JONES, T. KOTCHEN, E. MOUGLY, F. WHERRY, L. PENNINGTON, AND P. RICKETTS. Multiple hormonal responses to gradual exercise in relation to physical training. J. AppZ. Physiol. 33: 602-606, 1972. 10. HORSTMAN, D., M. GLESER, D. WOLFE, T. TRYON, AND J. DELEHUNT. Effects of hemoglobin reduction on v02 m8X and related hemodynamics in exercising dogs. J. AppZ. Physiol. 37: 97-102, 1974. 11. ISMAIL, A., G. NISWENDER, AND A. MIDGLEY. Radioimmunoassay of testosterone without chromatography. J. CZin. Endocrinol. Me-
tab. 34: 177-184, 1972. 12. KAPLAN, S., C. ABRAMS, J. BELL, F. CONTE, AND M. GRUMBACH. Growth and growth hormone. Pediatr. Res. 2: 43-63, 1968. 13. KEENAN, B., L. KILLMER, AND J. SODE. Growth hormone response to exercise. Pediatrics 50: 760-764, 1972. 14. KLISSOURAS, V. Prediction of athletic performance: genetic consideration. Can. J. AppZ. Sport Sci. 1: 195-200, 1976. 15. KLISSOURAS, V., F. PIRNAY, AND J. M. PETIT. Adaptation to maximal effort: genetics and age. J. AppZ. PhysioZ. 35: 288-293, 1973. 16. LAMB, D. Androgens and exercise. Med. Sci. Sports 7: l-5, 1975. 1% MIRAND, E., A. GORDON, AND J. WENIG. Mechanism of testosterone
827 action in erythropoiesis. Nature London 206: 270-272, 1965. 18. MORGAN, C. R. Human growth hormone immunoassay: two-antibody method using I-125 tracer. Proc. Sot. Exp. BioZ. Med. 121: 62-64, 1966. 19. MORGAN, C. R., AND A. LAZAROW. Immunoassay of insulin using a two-antibody system. Proc. Sot. Exp. BioZ. Med. 110: 29-32, 1962. 20. O’MALLEY, B. Hormonal regulation of nucleic acid and protein synthesis. Trans. NY Acad. Sci. 31: 478-484, 1969. 21. PRUETT, E. Plasma insulin levels during prolonged exercise. In: Muscle Metabolism during Exercise. New York: Plenum, 1971, p. 165-175. 22. SCHRIER, R., K. MCDONALD, R. WELLS, AND D. LANLER. Influence of hematocrit and cohoid on whole blood viscosity during volume expansion. Am. J. PhysioZ. 218: 346-352, 1970. 23. SPONA, J., AND G. LUNGLMAYR. Physiologil des Hypophysartestikularen Regulationssystems des Mannes; Radioimmunologische Hormonuntersuchungen. Wien. KZin. Wochenschr. 86: 311-315, 1974. 24. SUTTON, J., M. COLEMAN, AND J. CASEY. Testosterone production rate during exercise. Proc. Int. Symp. Biochem. 3rd Quebec City p. 72, 1976. 25. SUTTON, J., M. COLEMAN, J. GASEY, AND I. LAZARUS. Androgen response during physical exercise. Br. Med. J. 1: 520-522, 1973. 26. SUTTON, J., AND L. LAZARUS. Growth hormone in exercise: comparison of physiological and pharmacological stimuli. J. AppZ. PhysioZ. 41: 523-527, 1976. 27. SUTTON, J., J. YOUNG, L. LAZARUS, J. HICKIE, AND J. MAKSVYTIS. The hormonal response to physical exercise. AustraZas. Ann. Med. 18: 84-90, 1969. 28. TANNER, J. Physique and body composition. In: Fitness, Health and Work Capacity, edited by L. Larson. New York: Macmillan, 1974, p. 516-517. 29. VAN BEAUMONT, W. Evaluation of hemoconcentration from hematocrit measurement. J. AppZ. PhysioZ. 31: 712-713, 1972. 30. VAN BEAUMONT, W., J. GREENLEAF, AND L. JUHOS. Disproportional changes in hematocrit, plasma volume, and proteins during exercise and bed rest. J. AppZ. Physiol. 33: 55-61, 1972. 31. VERMEULEN, A. Leydig ceII secretion in (pre) pubertal boys in delayed puberty. In: The Endocrine Function of the Human Testes, edited by V. James, M. Serio, and L. Martini. New York: Academic, 1974, vol. II, p. 145-160.
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FAHEY, THOMAS D., ANTONIODEL VALLE-ZURIS, GEORGE OEHLSEN,MARTIN TRIEB, AND JOYCE SEYMOUR.PubertaZ stage differences in hormonal and hematobgid responses to maximal exercise in males. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 46(4): 823-827, 19’79.-Concentrations of serum testosterone (ST), growth hormone (SGH), and insulin (SI) at rest and following maximal exercise were compared in 27 males in different stages of pubertal development. Oxygen consumption and heart rate were measured while subjects performed a continuous-incremental work capacity test to voluntary cessation on a cycle ergometer. Pre- and postexercise blood samples were analyzed for hemoglobin (Hb) and hematocrit (Hct) by Coulter Counter, and for ST, SGH, and SI by radioimmunoassay. ST at rest increased with pubertal stage and was related to the increase in body weight and work capacity seen with increasing development during adolescence. There were no differences between pubertal stages in changes in hormone concentrations following exercise or in Hct or Hb before or after exercise. Our results do not support the hypothesis of a critical pubertal stage that exhibits enhanced response to exercise. testosterone; growth physical activity
hormone;
insulin;
plasma volume; growth;
FROM CHILDHOOD toadulthoodinvolves profound changes in physical stature, maturation, work capacity, and many other physiological characteristics. The improvement in work capacity observed during adolescence seemsto be related more to physical and sexual maturation than to chronological age (3, 6). Presumably, the increase in testosterone secretion that occurs with sexual maturation in males is related to the advancing work capacity seen in puberty. Females, who do not experience increases in testosterone at puberty, do not exhibit the same degree of rapid increase in exercise capacity or muscle mass during adolescence (6). In the adult, testosterone, insulin, growth hormone, and plasma volume are affected by maximal exercise. Typically, levels of testosterone (25) and growth hormone (9,13) increase as insulin (9) and plasma volume decrease (30). At rest, testosterone is known to increase levels of growth hormone (16), stimulate erythropoiesis (17), and perhaps indirectly influence insulin by its effect on growth hormone (20). Serum testosterone has been shown to be highly correlated to pubertal stage (31). Ekblom (4) has shown that physical training during puberty results in greater growth than would be expected
THETRANSITION
OlSl-7567/79/oooO-oooO$O1.25
Copyright
0 1979 the American
Physiological
in the untrained subject. This implies the existence of a period during puberty when subjects may experience enhanced hormonal activity during exercise. The purpose of this study was to determine if differences exist in the levels of serum testosterone, insulin, growth hormone, and selected hematological variables at rest and following maximal exercise in male children who are in different stages of pubertal development. METHODS
AND PROCEDURES
Subjects. Twenty-seven males ranging in age from 5 to 18 yr volunteered as subjects. The nature of the study.
was explained and informed consent was obtained from the subjects and their parents. Twenty-two of the subjects were of Latin American extraction with the remainder of Northern European descent. Pubertal staging by examination of pubic hair and penile and testicular development was performed according to the criteria of Tanner (28). Subjects were healthy and free of any diagnosed endocrine disorders. No subject was taking any medication, such as anabolic steroids or insulin, that might affect the results of the experiment. Subjects were instructed not to eat or exercise for a minimum of 2 h before the experiment and to rest quietly for 10 min prior to the preexercise blood sampling. All tests were administered at approximately the same time in late afternoon to minimize the effects of diurnal variations. Exercise protocol. Subjects performed a continuous incremental work task on a Monark cycle ergometer to voluntary cessation. Subjects in pubertal stages 1 and 2 began the test at a work rate of 360 kg l m. min-‘; subjects in pubertal stages 3-5 began at 720 kg l m*min-‘. Work rates were increased 180 kg. rn. min-’ every 2 min for all subjects. Pedaling speed, paced by a metronome, was 60 rpm. Pedaling rate was measured with a trigger and microswitch attached to the sprocket and frame of the ergometer. Minute-by-minute oxygen consumptions were obtained by an open-circuit method. Pulmonary ventilation was measured with a Godart-Statham pneumotachometer regularly calibrated against a Collins l20liter Tissot gasometer. Samples of expired air, drawn through Drierite, were immediately analyzed for percent oxygen with an Applied Electrochemistry model S-3A 02 analyzer, and for CO2 with a Godart capnograph. The 02 and CO2 analyzers were regularly calibrated with gas samples of known concentration verified with a ScholanSociety
823
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824
FAHEY
ET
AL.
der apparatus. VO 2 maxwas identified as the highest iJ02 TABLE 1. Description subjects -.-____of-__~--~. value reached during a 1-min period. Pubertal Sage Heart rates were determined from the ECG obtained Tu ke yL;rnparfor 15 s at I-min intervals from a Gilson recorder using (n2 6) (*P; 3) (2 7) (2 6) (2 5, Beckman surface electrodes (CM5 lead). Maximal heart 9.6 10.7 12.9 15.4 15.1 P&5 > PI-2; rate was identified as the highest value recorded during Age9yr ztl.0 *0.3 *0.5 ztO.8 a.5 P3 > P2 the test. 50.0 59.8 58.7 30.0 41.2 P3-5 > PI; w kg *2.5 *3.7 *6.8 k7.2 *3.4 P‘&5 > P2 Analytical methods. Blood samples were taken from 150.7 164.2 168.1 134.0 146.1 P5 > R-2; an antecubital vein without stasis immediately before Ht, cm *5.9 *2.9 *3.0 *5.1 *3.4 P.4 > PI and immediately after the exercise with subjects seated Body surface 1.05 1.28 1.42 1.63 1.66 P3-3 > P,; on the ergometer. Blood samples were collected in Vacarea, m2 *0.07 *0.06 *0.09 *0.11 *0.07 P4 > PP utainers, which were plain or contained EDTA. Blood in Hemoglobin, 12.9 13.6 13.6 14.1 14.3 NS kO.5 a.0 dzo.4 *0.5 *to.5 g/1(@ ml the plain Vacutainers was allowed to clot and the serum 37.6 39.6 39.4 42.6 42.2 NS separated by centrifugation. Hematocrit (Hct) and he- Hematocrit, a.4 d.2 a.0 k2.7 k2.6 % moglobin (Hb) using EDTA-treated blood were deterValues are means * SE. NS, not signifhnt. mined with a Coulter Counter (model S). All samples were refrigerated and analyzed for Hct and Hb within 3 TABLE 2. Performance characteristics __.--- _-h of being drawn. The change in plasma volume (APV) ___-- --- ____- ~______-------was determined by the method of Van Beaumont (29). Pubertal Stage Tu key CompiriSerum testosterone (ST), serum insulin (SI), and serum P:, PI P5 sons (n = 7) Cn2 6) in = 6) (n =3) growth hormone (SGH) were determined by radioim1.56 1.60 2.00 2.98 2.66 P4e5 > munoassays: ST by the method of Ismail et al. (II), SI vo 2 max9 1. *o. 14 min-‘, *o. 15 *0.20 to.38 *0.43 P 1-2; by the method of Morgan and Lazarow (19), and SGH STPD PA > by the method of Morgan (18). Radioimmunoassays P3 (RIA) were performed with materials and by procedures VO 2 max9 52.0 39.4 41.3 48.4 45.2 NS ml* *3.5 k2.9 *3.7 obtained from ICN Pharmaceuticals. Activity of 3H for k3.1 ~~6.5 kg-’ the determination of ST was detected with a Packard Tri-Carb liquid scintillation spectrometer. Activity of 1251 min-‘, STPD for the determination of SGH and SI was measured with HRmax, 201 200 198 190 192 NS a Hershaw sodium iodide crystal and Ortec counter. beats/ *4 k4 *2 -+6 k6 mm Serum was frozen at -2OOC and analyzed within 3 wk of 51.7 67.9 80.2 90.9 P4a5 > 1. 57.1 the venipuncture. Quality control was assured by per- VI3 mam . -1 *3.5 k6.1 k6.1 *5.7 k 15.8 P l-2 forming the RIA procedures on serum containing known :+PG hormone concentrations. For each hormone, the samples Max work 797 886 1,044 1,413 1,495 P&5 > kperne 260 ~56 *96 k82 k172 P l-3 were analyzed in one assay with intra-assay variance less . -1 than 5%. When sample variation exceeded 5%, the assay -6.1 -8.7 -6.8 -2.6 -10.4 NS was repeated. Postexercise hormone values were adjusted *Py% a.7 k2.3 ~~2.5 k2.6 k4.6 for the changes in plasma volume. Values are means * SE. STPD, standard temperature and pressure One- and two-way analysis of variance (ANOVA) and dry. APV; change in plasma volume. NS, not significant. the Tukey procedure were used to determine if significant differences existed between compared groups. The level in pubertal stage 1 (PI). Work capacity also tended to of significance was chosen at P < 0.05. increase with pubertal stage, but again there were not always differences among all groups. There were no RESULTS significant differences in APV between groups. The physical characteristics-age, weight, height, and Significant differences existed in serum testosterone body surface area-(Table 1) tended to increase with between all pubertal stages at rest and following exercise advancing sexual development, although this was not (Fig. 1). However, pre-postexercise differences in ST were always the case. Some overlapping between pubertal nonsignificant, both within and between groups. stages was evident for each of the characteristics. There Because of the high correlation between testosterone were no significant differences between pubertal stages and pubertal stage (r = 0.94, Spearman’s rank order in resting values of hematocrit or hemoglobin. correlation), ST levels at rest were used as a means of . vo 2m8X(Table 2) tended to rise with increased pubertal examining the relationship between pubertal stage and development, although again there was overlapping be- the other variables examined in this study. This was done tween stages. There was, however, no difference in because it is inappropriate to use ordinal data (pubertal . vo 2 maxbetween groups when oxygen consumption was stages) in a Pearson’s product moment correlation (7). In expressed as ml kg-’ min. The increased \j02 max (1 addition to the use of linear regression ( Y = a + bx), ST min-‘) was attributed to an increase in body mass rather and AST were correlated to each of the 12 variables with than actual increases in metabolic capacity. Comparisons power (Y = aebX) and exponential equations ( Y = axb). The type of regression equation rendering the highest Of VE maxrevealed a trend similar to VOW max(lemin-‘). There were no differences in maximal heart rate, despite correlation for each comparison is shown in Table 3. HR maxvalues in excess of 210 beats/min in two subjects Resting ST was related to maturational variables age, l
l
l
l
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RESPONSES
600
TO
EXERCISE
-’
B I
IN
825
PUBERTY
POST EXERCISE PRE EXERCISE
= I-
POST EXERCISE PRE EXERCISE
18-
Lm
z
PI
R
N=7
N=6
PS N=6
PUBERTAL FIG. 1. Serum 2 SE; postexercise
R
R
N=5
N=3
PI
STAGE
testosterone (ST) before and after exercise; means values corrected for changes in plasma volume.
3. Correlation between testosterone and change in testosterone, with physical, hormonal, and performance variables TABLE
Variables
Ht
Wt ASGH AS1
-0.09
Work,,,,
lmin-’ pmax, ml* kg-’
2 max,
emin-’
Hb APV Correlations from equation Number of subj is 27. ST, terone. * P < 0.05.
-0 .40*
R
N=7
N=6
I?
p3 N=6
N=5
R N=3
PUBERTAL STAGE FIG.
means volume.
2. Serum growth t SE; postexercise
hormone values
(SGH) before corrected for
and after exercise; changes in plasma
FZZI POST EXERCISE I PRE EXERCISE
AST
0.07 0.31 (2) 0.20 (2)
(2)
0.06 (1) -0.36 0.60* 0.76* 0.60*
HRmax hll,X VO VO
ST
0.70* 0.74* 0.77* (1)
Age
6-
iz LLl m
(2)
-0.23
(2)
-0.62* -0.35 0.33 0.28 -0.25
(1) (2) (2) (1)
-0.16
(1)
.38* (1) 0.22 (2) .06 -0.37 (1) Y = a + bx; (I), Y = aebx; (2), Y = ax'. testosterone;
AST,
change
in
-
testos-
PI
R
N=7
weight, and height. In addition, there were significant correlations between resting ST and performance variables VE max,maximum (max) work, and VO, max(ml kg-‘. min-‘). AST was not significantly related to any variable with the exception of ASI. To separate the relative contribution of age from the relationship between resting ST and physical and performance characteristics, partial correlations were used. Holding age constant, resting ST was only correlated with body weight and maximal work capacity (r = 0.49 and 0.51, respectively). Correlations of ST were reduced to 0.34 with height, 0.09 with Tj02 max (1l rein-‘), and -0.02 with Hb. Growth hormone (Fig. 2) increased as a result of exercise in PI, Pp, and Pd, but the changes were not significantly different between groups. There were no differences between the groups in SGH either before or after exercise. At rest there were no significant differences between groups in serum insulin (Fig. 3). There was a significant decrease in SI with exercise only in Pg subjects. There were no differences between iFUPS in pre-postchanges in SI or in the postexercise levels of the hormone. l
N=6
R
N=6
R
N=5
R
N=3
PUBERTAL STAGE 3. Serum insulin (SI) before and after exercise; means postexercise values corrected for changes in plasma volume. FIG.
in SE;
DISCUSSION
The results of our study indicate that hormonal and hematological changes occurring with maximal exercise are similar during different pubertal stages. Development patterns were evident for body weight, height, age, work capacity, ir02 (1 min-l), hemoglobin, and VE max. max When the effect of age was held statistically constant, testosterone was only significantly related to body weight and work capacity. Body weight and work capacity on a cycle ergometer are partially dependent on the relative development of skeletal muscle. Because of the importance of testosterone in muscle development and hypertrophy, it is not surprising that ST should be related to these factors independent of age. We were unable to identify pubertal stages with enhanced hormonal or hematological response to exercise. Our data, therefore, cannot serve as an explanation for l
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826
FAHEY
the findings of Ekblom (4), who found an apparent acceleration in growth by subjects involved in exercise training during puberty. Klissouras et al. (14, 15) studied the relative potency of training at different developmen tal stages. They were unable to identify a period during adolescence when heavy training would result in increased performance. They hypothesized that during the accele rated growth phase of adolescence, ho rmonal activity is optimum and additional stimuli such as training cannot override its influence. Our study failed to identify a pubertal stage that responded differently to a single bout of exercise; so it is unlikely that aP articular stage would respond differently to the repea ted exercise stimulation of training. Hormone metabolic effects cannot be assessed by serum levels alone; metabolic clearance and production rates must be considered as well. We failed to find changes in ST with exercise, which agrees with the findings of Lamb (16), but not with the findings of Sutton et al. (27). Sutton et al. (24) have found testosterone clearance rates decrease during exercise in adult males, whereas production rates do not change. Testosterone metabolism in the adolescent, occurring during a period of rapid growth, cannot be compared to ST metabolism in the adult. Studies by August et al. (1) and Spona and Lunglmayr (23) indicate that the sensitivity of the hypothalamic-pituitary-gonadal axis is greatest during the middle-pubertal years. Different patterns of ST production and clearance may exist in the developing adolescent male. Because we measured only serum concentrations, our findings do not rule out possible pubertal stage differences in ST production and clearance rates during exercise. There were no significant differences between groups in growth hormone concentrations. Changes in SGH with exercise are probably more related to intensity and duration of exercise and fitness of the subjects than to maturational factors (26). In addition, because we obtained our samples immediately after exercise, we may have missed the peak in growth hormone concentration that may occur up to 15 min after the exercise stimulus (26). Serial samples were not taken because of reluctance on the part of the subjects. Kaplan et al. (12) have found fasting levels of growth hormone higher in young children less tha .n 4 yr old but found no apparent correlation with age in pubertal children. Age differences in the disposal rate for growth hormone with a more rapid turnover in growing children could lead to lower concentrations of hormone and obscure a change in serum concentration that might otherwise reveal a significant relationship in our subjects. Several pubertal groups may have failed to increase in SGH significantly because of high initial values seen in several subjects. This may have been caused by emotional distress induced by the experiment or by possible nonbasal conditions in these subjects. Kaplan et al. (12) have noted that growth hormone responses to various stimuli are blunted when subjects already have high levels due to stress. Sutton and Lazarus (26) have indi-
ET
AL.
cated the desirability of collecting two or three basal samples for SGH determination prior to any stimulus, exercise or other, . being applied. Insulin decreased in Pg but remained unch .anged in the other gro ups. Hartley, et al. (9) have found that insulin levels decrease in response to exercise, but this has not been found by others (5, 27) . There was a significant relationship between AST and AS1 (r = -0.62) that was moderately reduced to r = -0.53 when APV was held constant with partial correlation. This may be due to individual differences in the relative intensity of the exercise. Pruett (21) has found that insulin changes during exercise are dependent upon th .e perce nt of VoZ reached during work. The relative intensity of work may also act ount for the different findings reported in the literature for ST levels with exercise. Performance on a cycle ergometer, used in the present investigation, is partly dependent on such factors as body size, leg strength, motivation, and familiarity with cycling. These, as well as other, factors may have resulted in differences in the relative work intensity of our subjects. Hemoglobin, like resting ST, increases during growth. Garn and Smith (8) have found that children who have hemoglobin levels that are low for their age, sex, and race tend to be smaller and lean, whereas children with higher levels of Hb tended to be taller, heavier, and fatter. These data are consistent with our findings. Moderately high linear correlations were found between resting levels of Hb and height (r = 0.58) and weight (r = 0.56). There was no significant difference between groups in hemoglobin and hematocrit levels. However, these measurements tended to be lower in earlier pubertal stages as evidenced by their significant correlation with serum testosterone (used as a measure of pubertal stage). VOZ max(ml. kg-’ min-‘) was the same in all groups and did not appear to be influenced by the hematological variabIes. Blood lower in hematocrit and hemoglobin has a lower viscosity and a decreased resistance to flow (2, 22). This phenomenon may partially act to create a parity in 02 delivery capacity between subjects with different hematological characteristics (10) . Hematological changes with exercise were similar in all pubertal groups. Differences in hemoconcentration during exercise does not seem to be the mechanism that allows children with lower Hb concentrations to maintain an equal oxygen transport capacity relative to body weight. Additionally, because oxygen consumption is related to muscle respiratory capacity, small differences in hematocrit and hemoglobin may not result in significant differences in the To2 maxof children. In summary, the developmental differences existing in physical and performance characteristics between males in different stages of pubertal development are probably partially hormone related. However, we were unable to identify a particular pubertal stage that exhibited higher concentrations of ST, SI, or SGH following maximal exercise. l
Received
30 January
1978; accepted
in final
form
19 December
1978.
REFERENCES AND S. KAPLAN. 1. AUGUST, F. M., GRUMBACH, puberty . III. Correlation of plasma testosterone,
Hormonal changes in LF, FSH, testicular
size, and bone age with pubertal Metab. 34: 319-326, 1972.
development.
J. Clin. EndocrinoZ.
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IN
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2. CHIEN, S., S. USAMI, H. M. TAYLOR, J. L. LUNDBERG, AND M. GREGERSEN. Effects of hematocrit and plasma proteins on human blood rehalogy at low shear rates. J. Appl. Physiol. 21: 81-87, 1966. 3. CLARKE, H., AND J. HARRISON. Differences in physical and motor traits between boys of advanced, normal, and retarded maturity. Res. Q. Am. Assoc. Health Phys. Educ. Retreat. 32: 449-460, 1961. 4. EKBLOM, B. Effects of physical training in adolescent boys. J. Appl. Physiol. 27: 350-355, 1969. 5. ERIKSSON, B., B. PERSSON, AND J. THORELL. The effects of repeated prolonged exercise on plasma growth hormone, insulin, glucose, free fatty acids, glycerol, lactate and P-hydroxybutyric acid in 13-year old boys and in adults. Acta Paediatr. Stand. Suppl. 217. 6. ESPENSCHADE, A. Motor performance in adolescence including the study of relationships with measures of physical growth and maturity. Monogr. Sot. Res. ChiZd Dev. 5: 1-126, 1940. 7. FERGUSON, G. StatisticaL Analysis in Psychology and Education. New York: McGraw, 1966, p. 106. 8. GARN, S., AND N. SMITH. More on hemoglobin levels relation to growth performance. J. Pediatr. 81: 346, 1973. 9. HARTLEY, L., J. MASON, R. HOGAN, L. JONES, T. KOTCHEN, E. MOUGLY, F. WHERRY, L. PENNINGTON, AND P. RICKETTS. Multiple hormonal responses to gradual exercise in relation to physical training. J. AppZ. Physiol. 33: 602-606, 1972. 10. HORSTMAN, D., M. GLESER, D. WOLFE, T. TRYON, AND J. DELEHUNT. Effects of hemoglobin reduction on v02 m8X and related hemodynamics in exercising dogs. J. AppZ. Physiol. 37: 97-102, 1974. 11. ISMAIL, A., G. NISWENDER, AND A. MIDGLEY. Radioimmunoassay of testosterone without chromatography. J. CZin. Endocrinol. Me-
tab. 34: 177-184, 1972. 12. KAPLAN, S., C. ABRAMS, J. BELL, F. CONTE, AND M. GRUMBACH. Growth and growth hormone. Pediatr. Res. 2: 43-63, 1968. 13. KEENAN, B., L. KILLMER, AND J. SODE. Growth hormone response to exercise. Pediatrics 50: 760-764, 1972. 14. KLISSOURAS, V. Prediction of athletic performance: genetic consideration. Can. J. AppZ. Sport Sci. 1: 195-200, 1976. 15. KLISSOURAS, V., F. PIRNAY, AND J. M. PETIT. Adaptation to maximal effort: genetics and age. J. AppZ. PhysioZ. 35: 288-293, 1973. 16. LAMB, D. Androgens and exercise. Med. Sci. Sports 7: l-5, 1975. 1% MIRAND, E., A. GORDON, AND J. WENIG. Mechanism of testosterone
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