Acute Hormonal Responses to Submaximal and Maximal Heavy Resistance and Explosive Exe

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doi: 10.1519/R-15404.1
The Journal of Strength and Conditioning Research: Vol. 19, No. 3, pp. 566–571.

Acute Hormonal Responses to Submaximal and Maximal Heavy Resistance and Explosive Exercises in Men and Women

Vesa Linnamo
Neuromuscular Research Center, Department of Biology of Physical Activity, University of Jyväskylä, Jyväskylä, Finland
Arto Pakarinen
Department of Clinical Chemistry, University of Oulu, Oulu, Finland
Paavo V. Komi
Neuromuscular Research Center, Department of Biology of Physical Activity, University of Jyväskylä, Jyväskylä, Finland
William J. Kraemer
Human Performance Laboratory, Department of Kinesiology, The University of Connecticut, Storrs, Connecticut 06269
Keijo Häkkinen
Neuromuscular Research Center, Department of Biology of Physical Activity, University of Jyväskylä, Jyväskylä, Finland


ABSTRACT
Linnamo, V., A. Pakarinen, P.V. Komi, W.J. Kraemer, and K. Häkkinen. Acute hormonal responses to submaximal and maximal heavy resistance and explosive exercises in men and women. J. Strength Cond. Res. 19(3):566–571. 2005.— The purpose of this study was to examine acute hormonal and neuromuscular responses in men and women to 3 heavy resistance but clearly different exercise protocols: (a) submaximal heavy resistance exercise (SME), (b) maximal heavy resistance exercise (HRE), and (c) maximal explosive resistance exercise (EE). HRE included 5 sets of 10 repetition maximum (10RM) sit-ups, bench press, and bilateral leg extensions (David 210 machine) with a 2-minute recovery between the sets. In SME, the load was 70%, and in EE, the load was 40% from that used in HRE. A significant increase (p < 0.05) in serum growth hormone (GH) was observed after HRE both in men and women, but the increase was greater (p < 0.05) in men than in women. Serum testosterone (T) increased significantly (p < 0.05) only during HRE in men. Since GH and T are anabolic hormones, the acute exercise-induced response during HRE may play an important role in the long-term anabolic adaptation processes related to muscle hypertrophy and maximal strength development.

Introduction
Growth hormone (GH) and testosterone (T) are anabolic hormones. Heavy resistance exercise is known to lead to acute increases in serum GH and T concentrations and is associated with acute decreases in neuromuscular function. The stress caused by heavy resistance exercise is believed to work as a major stimulus for muscle fiber hypertrophy (e.g., 5, 25, 31). The type of heavy resistance loading may, however, play an important role in the magnitude of the acute anabolic hormonal response. Increases in serum GH appear to be greatest during hypertrophic types of exercise when using rather high numbers of repetitions and sets (7, 18, 20). The load should be near the maximum (e.g., 70–80%), but each set should be performed until the 8– 12 repetition maximum (8–12RM).

The serum T level increases also during strength exercise if the exercise stimulus is sufficient (17, 33). The amount of serum anabolic hormone increases is dependent on the age of the subject, the resting periods during the exercise, the total amount of work, and the amount of activated muscle mass (2, 7, 10, 11, 14, 17, 19–21). In the case of serum T response, the high load exercise (100% 3–6RM) caused a more dramatic increase in serum T than did the moderate load (70%) training protocol (28). Although hormonal changes after heavy resistance exercise have also been observed in women, the acute responses, particularly for T, are generally greater in men than in women (11, 17, 34). Acute metabolic changes may be related to hormonal responses during heavy resistance exercise. Blood lactate has been shown to increase more when the number of repetitions is high with high loads than when loads are lower (1) or the number of repetitions is lower (10).

Women do not seem to be as able as men to aggressively activate the muscles rapidly, and it has been suggested that this is related to their lower T concentrations (9, 29). Indeed, in the explosive exercise, women seemed to be unable to exhaust themselves as men did (22). During heavy resistance exercise, the acute neuromuscular changes were greater than those caused by explosive exercise in men and especially in women (22). Since the hormonal responses appear to be related to the intensity of the exercise protocol, it is of interest to examine if the hormonal responses of an exercise protocol with low (40% of 10RM) loads but performed as explosively as possible are similar to those of moderate (70%) and high (100%) intensity exercises.

If the hormonal responses are related to the amount of muscle mass activated and to the metabolic changes, it is expected that the greatest responses will be observed after the 100% intensity exercise. In explosive situations, the muscles are also activated maximally but with a shorter duration of each repetition, accompanied by a lower metabolic response. It is not clear whether this type of stimulus is large enough to cause considerable hormonal changes. The purpose of this study was to examine acute hormonal responses in men and women to 3 heavy resistance but clearly different exercise protocols: (a) submaximal, (b) maximal heavy resistance, and (c) maximal explosive resistance exercises.

Methods

Experimental Approach to the Problem
Strength-training sessions can be performed with different intensities, depending on the goal of the session. With hypertrophic exercise, the load is typically rather high, and each repetition is performed with submaximal "steady" velocity, whereas in explosive exercise, the load is lower, but each repetition is performed with maximal action/movement velocity. Acute hormonal responses that are related to long-term muscle hypertrophy differ between different types of exercise session and also between the genders. The goal of the present study was to elucidate whether an exercise session performed either with the submaximal load of 70% of 10RM or with the submaximal load of 40% of 10RM but performed explosively would result in similar hormonal responses, as has been observed after the maximal load 10RM protocol. As the hormonal response may be related to the muscle mass used (e.g., 2, 15, 21, 26), large leg extensor muscles (leg press action) were chosen for the present experiment. To simulate a typical strength-training session, a series of sit-ups and bench press were performed in addition to the leg press actions.

Subjects
A total of 8 young adult men and 8 young adult women volunteered as subjects for the study. The mean (* SE) age, weight, height, and body fat were, for men, 27.1 * 0.7 years, 74.4 * 3.2 kg, 181.3 * 1.1 cm, and 13.8 * 1.1% and, for women, 23.3 * 0.5 years, 59.9 * 1.2 kg, 166.7 * 1.9 cm, and 28.5 * 2.0%, respectively. The subjects were physically fit and took an active part in various physical activities but had no background in regular strength training or competitive sports of any kind. The subjects were allowed to continue their normal physical activities throughout the experimental period but were instructed to have a full day of rest preceding the loadings. Complete advice about possible risks and discomfort was given to the subjects, and all of them gave their written informed consent to participate. The study was conducted according to the declaration of Helsinki and was approved by the Ethics Committee of the University of Jyväskylä.

This study was part of a larger research project. Some of the results regarding hormonal changes during maximal heavy resistance loading (11) and neuromuscular changes between maximal vs. explosive strength loading (22) have, in part, been published previously.

Experimental Design
The experimental design comprised 3 different loading sessions: (a) submaximal heavy resistance exercise (SME), (b) maximal heavy resistance exercise (HRE), and (c) maximal explosive resistance exercise (EE). The 3 loading protocols were performed separately, so that there was a recovery period for at least 2 weeks after each loading. HRE, which was administered first, included 5 sets of 10RM sit-ups, 5 sets of 10RM bench press (David 510 machine), and 5 sets of 10RM bilateral leg extensions on the David 210 machine (Figure 1 ).

A bilateral leg extension (leg press action in a sitting position) was chosen because it activates large muscle groups of the lower body. The subject was in a sitting position extending his/ her legs from 45 to 55° to full extension at his/her own speed and then resisting the load during the eccentric phase back to the starting angle. The loads used were always chosen so that the subject was just able to finish the required 10 repetitions of each set (5 × 10RM). The recovery period between the first 2 exercises, the sit-ups and the bench press, was 2 minutes, while a 12-minute recovery was allowed before the execution of the actual exercise for the leg extensors. The recovery time between the sets was always 2 minutes.

The same protocol but with less weights was then used in both SME and EE. In SME, the load was 70% (5 × 70% × 10RM), and in EE, the load was 40% (5 × 40% × 10RM) from that used in HRE. In EE, the subjects were instructed to extend their legs as explosively as possible, while in HRE and SME, submaximal "steady" velocities were used. A maximal voluntary bilateral isometric leg extension action (force-time curve) against a force plate was measured before and after each set and immediately after the exercise, as well as after a recovery period of 1 and 2 hours. Blood samples were drawn for the determination of serum GH, serum T, and blood lactate.

Measurements
The subjects became familiarized with the testing procedures during a separate pretesting day. In addition, appropriate loads for each exercise were tested for each subject to calculate his/her 10RM of the first set. During the actual testing day, maximal bilateral isometric force was determined by a specially designed dynamometer for the isometric testing, similar to that reported earlier by Komi (13). The subject was in a sitting position so that the knee and hip angles were at 107 and 110°, respectively. The subjects were instructed to exert their maximal bilateral force as fast as possible and release (relax) the force after a required 2.5- to 5-second contraction time. A maximal bilateral isometric extension test was administered before the actual loading, after each set (S), and after 1 and 2 hours after the loading. The force was recorded on magnetic tape (Racal 16, Racal Recorders Ltd., UK) and thereafter digitized and analyzed with a Codas TM computer system (Datag Instruments Inc.) to obtain the maximal peak force. Sampling frequency was 1,000 Hz.

Blood samples were drawn after 12 hours of fasting and about 8 hours of sleep in the mornings of the control day and the exercise day at 0800 hours from the antecubital vein of each subject. On the exercise day, the blood samples were also drawn before the exercise, during the exercise after the bench press, immediately after the exercise, and 1 and 2 hours after the exercise. On the control day, blood samples were repeatedly drawn at 1200, 1400, and 1600 hours, which corresponded to the time of the exercise (Table 1 ). The subjects were instructed to maintain their normal food intake during the experiment and to have their last light meal during the exercise day not later than 2 hours before 1200 hours.

Serum samples for the hormonal analyses were kept frozen at -20° C until assayed. The assays of serum cortisol and T were performed by radioimmunoassays (RIAs) using reagent kits from Farmos Diagnostica (Turku, Finland). Before the T RIA, unconjugated steroids were extracted from the samples with diethyl ether/ethyl acetate (9:1, vol/vol). Serum GH concentrations were measured using kits of Pharmacia Diagnostics (Uppsala, Sweden). The sensitivity of the cortical assay was 0.05 µmol·L-1, and the coefficient of intra-assay variation was 4.0%. The respective values were 0.36 nmol·L-1 and 6.5% for the T assay, and 0.2 µg·L-1 and 2.5–5.1% for the GH assay. All the assays were carried out according to the instructions of the manufacturers. All samples for each test subject were analyzed in the same assay for each hormone.

Blood lactate was analyzed (Boehringer, Mannheim, Germany) from the fingertip blood draw before the loading, after the bench press, and after the second, fourth, and fifth set of the leg extension exercise, as well as after a recovery period of 6 and 10 minutes.

Statistical Analyses
Conventional statistical methods were used for calculating means, standard errors, and coefficients of correlation. The data were then analyzed using multiple analysis of variance (MANOVA). When appropriate, comparisons of means were performed by the Student's paired t-test (within the group) and unpaired (between the genders). Significance was defined as p 0.05.

Results
Changes in serum GH and T as well as in blood lactate concentrations were observed after the bench press exercise. However, since the greatest values were observed after the entire exercise session, the values measured after the leg press exercise will be reported as the "after" values. A significant increase (p < 0.05) in serum GH concentrations was observed after HRE, both in men and women. In men, serum GH concentrations increased from 0.26 * 0.32 µg·L-1 to 18.95 * 17.96 µg·L-1, and in women, these concentrations increased from 2.84 * 3.63 µg·L-1 to 11.01 * 8.08 µg·L-1; the increase was greater (p < 0.05) in men than in women (Figure 2a,b ). In men, serum GH increased also after EE from 0.36 * 0.63 µg·L-1 to 4.18 * 4.32 µg·L-1 (p < 0.05), while in women, no significant changes were observed during either EE or SME. The only significant (p < 0.05) increase in serum T concentration was observed in men during HRE, with an increase from 27.07 * 8.52 nmol·L-1 to 29.38 * 9.85 nmol·L-1 (Figure 3a,b ). Table 1 shows the serum concentrations of the hormones during the control day.

Maximal force decreased significantly in all exercises (p < 0.05) in both genders, and the greatest decrease and the slowest recovery were observed during HRE in both groups. In men, the maximal force decreased by 16.9 + 4.8% in SME, by 23.7 + 16.3% in HRE, and by 11.0 + 8.2% in EE, while in women, the decreases were 16.2 + 7.1 in SME, 18.8 + 7.7% in HRE, and 12.2 + 6.8% in EE (Figure 4a,b ).
Blood lactate concentrations increased more in men than in women after HRE (p < 0.05) and after EE (p < 0.05), but the highest values were observed after HRE in both genders. For men, blood lactate levels increased by 5.6 + 2.5 mmol·L-1 in SME, by 11.5 + 3.7 mmol·L-1 (p < 0.01) in HRE, and by 4.2 + 2.3 mmol·L-1 (p < 0.05) in EE, while the respective increases for women were 3.0 + 0.8 in HRE, 6.6 + 1.7 mmol·L-1 (p < 0.01) in HRE, and 1.9 + 0.7 mmol·L-1 in EE (Figure 5 ).

Discussion
The greatest acute hormonal responses were expectedly observed after HRE in both men and women. Serum GH concentrations increased for both men and women in HRE. Also, EE led to an increase in the serum GH levels, but only in men, while no significant changes occurred in SME for either gender. Serum T concentrations increased also but only for men in HRE. As indicated by the greatest decrease and the slowest recovery of the isometric force as well as by the greatest increase in blood lactate concentration, the HRE proved to be the most fatiguing and stressful of the exercise protocols chosen for the present study.

Increased serum GH concentrations after HRE in both genders and after EE in men may be affected by several mechanisms. A decrease in blood pH resulting from the increased lactate production may be one of the mechanisms stimulating GH secretion during exercise (6). HRE resulted in the greatest increases in the blood lactate level as well as the greatest GH elevations for both men and women. The response for women was, however, smaller than for men, which may, in part, be related to a lower amount of muscle mass used in the exercise (15, 21, 26). The changes in the blood lactate and GH are well in line with previous reports regarding intensive heavy resistance exercise (1, 10, 12, 17, 19–21, 32). Kraemer et al. (17) showed that high-intensity 10RM exercise with 1-minute rest periods resulted in a greater acute response in GH than a 5RM exercise with 3-minute breaks. The present study further indicates that if the exercise protocol is otherwise kept the same but the load is lowered from 100% (HRE) to 70% (SME), it may not be stressful enough to lead to acute hormonal responses in either gender.
This would suggest that submaximal loading, which is often chosen, particularly for nonathletes, is not stressful enough to induce large acute responses associated with larger chronic adaptations leading to muscle hypertrophy.

Men, on the other hand, were able to exhaust themselves at 40% (EE) in which the exercise was performed with the maximal voluntary speed, as could be seen in the decreased force production. Although maximal force did not decrease as much as in HRE, dramatic decreases in the initial part of the isometric force-time curve as well as in EMG were observed (22). A significant increase in GH in men observed after EE but not after SME could thus be related to the amount of muscle activated. To achieve maximal speed, it is likely that a greater number of motor units will be activated than in the submaximal situation. The contraction time is, however, shorter, which may explain why blood lactate did not increase more. Substantial neuromuscular changes in men but not in women during EE indicate that men are more capable of performing rapid aggressive muscle actions than women. This difference in rapid activation has been suggested to be related to lower T concentrations in women (9, 29).

Serum T concentrations increased significantly only in men and only after HRE. This increase is in line with other studies with intensive heavy resistance protocols (10, 17, 20, 28). The exercise-induced changes of the serum T level are known to be related to the magnitude of the stress of the session (10, 17, 20, 28). The results of the present study support this, as marked increases in serum T concentrations were observed only during HRE. There is evidence that blood lactate would stimulate T secretion (23), so the higher blood lactate levels observed in HRE may partly explain the increases in serum T concentration. For women, however, the serum T levels did not increase above resting concentrations, which is also in line with previous studies (4, 15, 17, 34). Another explanation for the increased serum T may be related to increased adrenergic activity, which may increase as the intensity of the exercise increases (8). Although not measured in the present study, it is likely that catecholamines, which stimulate the secretion of T (3), had changed to a large extent in HRE. Pullinen et al. (27), however, could not demonstrate any significant correlations between plasma catecholamines and serum T during resistance exercises.

Possible changes in plasma volume may also have affected the results. Whether changes in the plasma volume are related to the intensity of the loading is not quite clear. Raastad et al. (28) reported a 6% change in plasma volume after the maximal (100%) exercise protocol, while no changes were observed in the submaximal (70%) exercise (28) or after 1 set of 80% 1RM exercise (16). On the other hand, changes in the plasma after 10RM (high force) and 15 repetitions (high power) were 10.4 and 7.5%, respectively, but the relative changes were not significantly different from each other (1). It has also been shown that correcting the GH values according to plasma volume change does not affect the results, although the response differed markedly between the 2 heavy resistance protocols (17). Since plasma volume was not measured in the present study, it is difficult to estimate its role in the reported results. However, if there had been an effect, it would most likely have been the greatest during HRE in which the highest blood lactate levels were observed. Accumulation of lactate and other metabolites increases intracellular osmolality in the active muscles, which may lead to fluid fluxes from interstitial to intracellular and from vascular to interstitial spaces, thus affecting the plasma volume (24, 30).

In conclusion, the serum GH and T responses during SME and EE were lower than during HRE in both genders. Hormonal changes may be related to metabolic responses, as the highest changes in blood lactate level were also observed in HRE. When the relative loading is kept the same for all subjects, it seems that heavy resistance exercise–induced GH and T responses are lower in women than in men. However, the specificity of the loading protocol regarding the effect of load and velocity to the neuromuscular system seems to be of great importance. While the EE-induced hormone responses were minor in men, the acute neuromuscular responses were larger in men than in women. Since women showed only minor neuromuscular changes in EE, which recovered fast, it is possible that they were unable to exhaust themselves in explosive exercise as men did. Since GH and T are anabolic hormones, it seems reasonable to suggest that acute exercise-induced responses during HRE play an important role in the long-term anabolic adaptation processes related to muscle hypertrophy and maximal strength development, especially during heavy resistance strength training.

Practical Applications
Given the results obtained in the present study, it can be suggested that in order for anabolic hormonal responses to take place, the exercise session should be performed with a heavy resistance hypertrophic-type of loading ]Hormonal changes appear to be related to the amount of muscle mass activated and to the metabolic response caused by the exercise. Thus, submaximal loading may not be strenuous enough in the long term for the hypertrophic effects to take place. This also seems to be true when the exercise is performed with maximal explosive effort. On the other hand, for neural control and achieving a higher rate of force development, explosive exercise, particularly in men, seems to be beneficial. For women, the responses after explosive exercise were not that clear, and it is suggested that, along with explosive training with lower loads, women include heavier loads in their training sets.

References

1. Bush, J., W. Kraemer, A. Mastro, T. Triplett-McBride, J. Volek, M. Putukian, W. Sebastianelli, and H. Knuttgen. Exercise and recovery responses of adrenal medullary neurohormones to heavy resistance exercise. Med. Sci. Sports Exerc. 31:554–559. 1999.

2. Craig, B., R. Brown, and J. Everhart. Effects of progressive resistance training on growth hormone and testosterone levels in young and elderly subjects. Mech. Aging Dev. 49:159–169. 198.

3. Eik-Nes, K. An effect of isoproterenol on rates of synthesis and secretion of testosterone. Am. J. Physiol. 217:1764–1770. 1969.

4. Fahey, T., R. Ralph, P. Moungnee, J. Nagel, and S. Mortara. Serum testosterone, body composition and strength of young adults. Med. Sci. Sports Exerc. 8:31–34. 1976.

5. Florini, J. Hormonal control of muscle cell growth. J. Anim. Sci. 61:21–37. 1985.

6. Gordon, S., W. Kraemer, N. Vos, J. Lynch, and H. Knuttgen. Effect of acid-base balance on the growth hormone response to acute high intensity cycle exercise. J. Appl. Physiol. 76:821–829. 1994.

7. Gotshalk, L., C. Loebel, B. Nindl, M. Putukian, W. Sebastianelli, R. Newton, K. Häkkinen, and W.J. Kraemer. Hormonal responses of multi-set versus single set heavy resistance exercise protocols. Can. J. Appl. Physiol. 22:244–255. 1997.

8. Guezennec, Y., L. Leger, F. Lhoste, M. Aymonod, and P. Pesquis. Hormone and metabolite response to weight-lifting training sessions. Int. J. Sports Med. 7:100–105. 1986.

9. Häkkinen, K. Neuromuscular fatigue and recovery in male and female athletes during strenuous heavy resistance exercise. Int. J. Sports Med. 14:53–59. 1993.

10. Häkkinen, K., and A. Pakarinen. Acute hormonal responses to two different fatiguing heavy resistance protocols in male athletes. J. Appl. Physiol. 74:882–887. 1993.

11. Häkkinen, K., and A. Pakarinen. Acute hormonal responses to heavy resistance exercise in men and women at different ages. Int. J. Sports Med. 16:507–513. 1995.

12. Häkkinen, K., A. Pakarinen, M. Alen, H. Kauhanen, and P.V. Komi. Neuromuscular and hormonal responses in elite athletes to two successive strength training sessions in one day. Eur. J. Appl. Physiol. Occup. Physiol. 57:133–139. 1988.

13. Komi, P.V. Relationship between muscle tension, EMG and velocity of contraction under concentric and eccentric work. In: New Developments in Electromyography and Clinical Neurophysiology. J.E. Desmedt, ed. Basel: Karger, 1973. pp. 596–606.

14. Kraemer, W.J. Endocrine responses to resistance exercise. Med. Sci. Sports Exerc. 20: (Suppl.). S152–S157. 1988.

15. Kraemer, W., S. Fleck, J. Dziados, E. Harman, L. Marchitelli, S. Gordon, R. Mello, P. Frykman, L. Koziris, and T. Triplett. Changes in hormonal concentrations after different heavy resistance exercise protocols in women. J. Appl. Physiol. 75:594–604. 1993.

16. Kraemer, W., S. Fleck, C. Maresh, N. Ratamess, S. Gordon, K. Goetz, E. Harman, P. Frykman, J. Volek, S. Mazzetti, A. Fry, L. Marchitelli, and J. Patton. Acute hormonal responses to a single bout of heavy resistance exercise in trained power lifters and untrained men. Can. J. Appl. Physiol. 24:524–537. 1999.

17. Kraemer, W., S. Gordon, S. Fleck, L. Marchitelli, R. Mello, J. Dziados, K. Friedli, E. Harman, C. Maresh, and A. Fry. Endogenous anabolic hormonal and growth factor responses to heavy resistance exercise in males and females. Int. J. Sports Med. 12:228–235. 1991.

18. Kraemer, W., and K. Häkkinen. eds. Strength Training for Sport,. 186 pages. The Handbook of Sports Medicine and Science. IOC Medical Commission Publication. Blackwell Science Ltd, Oxford. United Kingdom. 2002.

19. Kraemer, W.J., K. Häkkinen, R.U. Newton, M. McCormick, B.C. Nindl, J.S. Volek, L.A. Gotshalk, S.J. Fleck, W.W. Campbell, S.E. Gordon, P.A. Farrell, and W.J. Evans. Acute hormonal responses to heavy resistance exercise in younger and older men. Eur. J. Appl. Physiol. Occup. Physiol. 77:206–211. 1998.

20. Kraemer, W., L. Marchitelli, S. Gordon, E. Haman, J. Dziados, R. Mello, P. Frykman, D. McCurry, and S. Fleck. Hormonal and growth factor responses to heavy resistance exercise protocols. J. Appl. Physiol. 69:1442–1450. 1990.

21. Kraemer, W., R. Staron, F. Hagerman, R. Hikida, A. Fry, R. Gordon, B. Nindl, L. Gothshalk, J. Volek, and J. Marx. R. NEWTON, AND H&AUML;KKINEN. The effects of short-term resistance training on endocrine function in men and women. Eur. J. Appl. Physiol. 78:69–76. 1998.

22. Linnamo, V., K. Häkkinen, and P.V. Komi. Neuromuscular fatigue and recovery in maximal compared to explosive strength loading. Eur. J. Appl. Physiol. 77:176–181. 1998.

23. Lu, S., C. Lau, Y. Tung, S. Huang, Y. Chen, H. Shih, S. Tsai, C. Lu, S. Wang, and J. Chen. Lactate and the effect of exercise on testosterone secretion: Evidence for involvement of a cAMP-mediated mechanism. Med. Sci. Sports Exerc. 29:1048–1054. 1997.

24. Lundvall, J. Tissue hyperosmolality as a mediator of vasodilation and transcapillary fluid flux in exercising skeletal muscle. Acta Physiol. Scand. 379:S1–S142. 1972.

25. MacDougall, J., G. Ward, D. Sale, and J. Sutton. Biochemical adaptation of human skeletal muscle to heavy resistance training and immobilisation. J. Appl. Physiol. 42:700–703. 1977.

26. Nindl, B., W. Kraemer, L. Gotshalk, J. Marx, J. Volek, J. Bush, K. Häkkinen, R. Newton, and S. Fleck. Testosterone responses after resistance exercise in women: Influence of regional fat distribution. Int. J. Sport Nutr. Exerc. Metab. 11:451–465. 2001.

27. Pullinen, T., A. Mero, E. MacDonald, A. Pakarinen, and P.V. Komi. Plasma catecholamine and serum testosterone responses to four units of resistance exercise in young and adult male athletes. Eur. J. Appl. Physiol. 77:413–420. 1998.

28. Raastad, T., T. Bjoro, and J. Hallen. Hormonal responses to high- and moderate-intensity strength exercise. Eur. J. Appl. Physiol. 2000.

29. Ryushi, T., K. Häkkinen, H. Kauhanen, and P.V. Komi. Muscle fiber characteristics, muscle cross-sectional area and force production in strength athletes, physically active males and females. Scand. J. Sports Sci. 10:7–15. 1988.

30. Sjogaard, G., and B. Saltin. Extra- and intracellular water spaces in muscles of man at rest and with dynamic exercise. Am. J. Physiol. 243:R271–R280. 1982.

31. Staron, R., S. Hikida, F. Hagerman, G. Dudley, and R. Murray. Human skeletal muscle fiber type adaptability to various workloads. J. Histochem. Cytochem. 32:146–152. 1984.

32. Vanhelder, W., M. Radomsk, and R. Goode. Growth hormone responses during intermittent weight lifting exercise in men. Eur. J. Appl. Physiol. 53:31–34. 1984.

33. Viru, A. Plasma hormones and physical exercise [Review]. Int. J. Sports Med. 13:201–209. 1992.

34. Weiss, L., K. Cureton, and F. Thompson. Comparison of serum testosterone and androstenedione responses to weight lifting in men and women. Eur. J. Appl. Physiol. 50:413–419. 1983.


Tables

TABLE 1.Serum GH and testosterone concentrations (mean * SD) during the control day at 1200 and 1400 h.*



Figures

FIGURE 2.Mean (* SD) values for serum growth hormone (GH) concentrations before and after the exercises in (a) men and (b) women (* = p < 0.05)



FIGURE 3.Mean (* SD) values for serum testosterone concentrations before and after the exercises (* = p < 0.05)



FIGURE 4.Mean (* SD) changes in maximal force after the exercises in (a) men and (b) women



FIGURE 5. Mean (* SD) values in blood lactate concentrations after the exercises (* = p < 0.05, ** = p < 0.01)