Resistance exercise is the most effective way for achieving acute increase in the concentration of anabolic hormones, which in turn stimulates strength and muscle hypertrophy (4,42). High-intensity hypertrophic REs when performed in multiple sets (3-5 sets for each exercise), with short rest intervals (60-120 seconds) and high repetition (8-12 repetition) lead to acute hormonal responses (17,26,27). The amount or time of acute hormonal responses after RE may be related to gain of muscle strength and hypertrophy (1,24). The role of acute hormonal responses is very important because anabolic hormones such as TS (10) and GH (12) will increase protein synthesis in muscle cells. Therefore, instigation of endocrine gland through exercise activity may be a stimulant for the compatibility process of skeletal muscle cells and leads to an increase of contractile proteins. There has been a more acute increase of GH and TS in a multiple-set resistance training program (3 sets per training) than in a single-set RE program (15). Also, an RE protocol with average intensity (with 10RM load), high volume (3 sets of 10RM for each exercise), and with a short rest interval (1 minute) between the sets caused an increase in GH and cortisol concentration (31).
It is inferred from the previous research that acute hormonal response related to RE is dependent on the kind of RE protocol that is affected by variables such as number of repetitions and sets, rest period between sets, load or intensity, frequency, and muscle volume involved. In present research, the young athletes have performed a 3-RE protocol (4 set × 85% of 1RM) to failure (maximum repetition per sets) with different rest intervals of 60, 90, and 120 seconds between the sets. Therefore, the difference in programs was in the different rest intervals between sets, and because of using resistance training sets to failure (RE to failure), we expected a different training volume related to the rest intervals. Also, different metabolic needs, which these 3 RE protocols have, are expected to cause different acute hormonal responses. The findings of the present study showed that total training volume in the RE programs with rest intervals of 90 and 120 seconds between sets increased 20 and 15% more than that of the protocol with rest intervals of 60 seconds between sets. Although, these differences were not statistically significant, they cannot be neglected because these differences might affect measured physiological responses.
Although the relative share of adjusting mechanisms for the increases in serum GH concentrations during heavy RE with very short rest period is unknown, it may be affected by glycolytic metabolism increase and acid-base changes (13,14,27). Previous research suggests that factors related to anaerobic metabolism are involved adjusting control GH and that these factors may respond much to an intense resistance training program with short rest intervals between sets. Häkkinen and Pakarinen (17) observed a significant correlation between individual changes in lactate accumulation and GH response when 2 different strength exercises were combined. We did not measure changes in blood pH, but changes in blood-lactate concentration could explain differences in GH responses during 3 protocols. Also, previous research with restriction of blood flow during exercise has shown that local accumulation of metabolic intermediaries such as lactate and hydrogen ion stimulate the increase of GH (45). Corroborating this hypothesis, Gordon et al. (13) showed that alkalosis stimulated by sodium bicarbonate ingestion has decreased GH response during resistance training. Although the real mechanism through which the acid-base changes stimulates GH secretion is not known correctly, it has been suggested that the hypothalamic-hypophysial axis is activated by muscle metabolic receptors signals (13,43). In line with the findings for GH, blood-lactate concentrations increased during all 3 kinds of RE to failure protocols with greater responses observed in protocol with 60-second rest between sets than in 120-second rest between sets.
Growth hormones are actually a ‘family of hormones’ because >100 different variant forms exist in circulation (46). The specific biological activity of each GH variant awaits complete elucidation; however, acute RE dramatically affects concentrations of these GH variants (20,36). Additionally, Kraemer et al. (29) recently demonstrated that long-term training increases the biological activity of circulating GH molecular weight variants. Although our results showed that RE with a very short rest period instigates 20-kD GH monomer levels (the most frequently studied form), they are not solely responsible for adaptations to RE. In addition, GH exerts its function by eliciting IGF-1 production from the liver and/or muscle, which stimulate muscle hypertrophy via PI3K and Akt-mTOR signaling. Additionally, IGF-1 stimulates the proliferation and differentiation of satellite cells (42).
The results presented here indicate several conclusions concerning the number of repetitions possible in an exercise session and consecutive sets of the same exercise to failure when rest periods between sets are 60, 90, or 120 seconds in length. A rest period of 60 seconds results in less total training volume than a rest period of 120 seconds because of a greater decrease in the number of repetitions to failure in consecutive sets with a 60-second rest period. This decrease in training volume in the 60-second rest periods is probably related to insufficient time to replenish anaerobic energy sources and neural drive and higher blood-lactate concentrations, all of which result in fatigue (34).
According to the results, the TS concentration was higher immediately after protocols with 120- and 90-second rest than after a protocol with 60-second rest between sets, but 30 minutes postexercise, no meaningful difference was observed in TS concentrations among the protocols. In addition, meaningful differences in TS concentration during RE protocols with 90- and 120-second rest periods between sets were not observed. These findings are in accordance with those of Kraemer et al. (27,28) who showed that high-intensity RE (5RM) with large muscle groups and with 3-minute rest between sets elevates TS concentrations.
Although circulating hormone concentration is one of the symptoms of hormone function, they are not solely responsible for adaptations to RE, and there are factors such as number of receptors and affinity of receptors that affect hormone function and subsequent adaptations in body tissues. Testosterone exerts its influence on skeletal muscle protein synthesis via androgen receptors (ARs). Testosterone binds to and converts AR to a transcription factor capable of translocating to the nucleus and associating with DNA to regulate androgen-specific gene expression. Previous studies reported that training influences the number of androgen binding sites in skeletal muscles. The increase in ARs would lead to an enhancement of the sensitivity of muscles to circulating androgens. A significant increase in the number of ARs has been shown to occur after endurance and strength training and electrical stimulation in animal studies (46). Because the subjects were male resistance trained athletes, and they prevalently trained with submaximal load, high repetitions, and short rest period between sets, upregulation of ARs may have occurred in fast-twitch fibers, and this led to low TS concentration in a very short rest protocol. Additionally, like IGF-1, TS exerts some influence on muscle growth via satellite cells. Supraphysiological doses of TS increase satellite cell number in a dose-dependent manner (41) and stimulate satellite cell proliferation and differentiation (19).
Unfortunately, studies focusing on the effects of different rest periods between sets on TS concentration, in resistance trained men, are lacking, making it difficult to compare our results. However, in terms of RE intensity, Raastad et al. (38) showed that the acute responses of TS was greater during the high-intensity protocol as compared to the moderate-intensity protocol, and no meaningful difference was observed in luteinizing hormone (LH), follicle stimulating hormone, and GHs (38). Linnamo et al. (32) examined acute hormonal responses to maximal heavy RE, submaximal heavy RE, and explosive RE. They observed greater increase in GH and TS concentrations in maximal heavy RE compared with submaximal and explosive RE.
Our findings showed that the RE protocol with a long rest period between sets and greater training volume elicited an increase in TS concentration, but the possible mechanisms responsible for these changes were not measured in this study. However, previous studies suggest that exercise-induced elevations in TS are caused by mechanisms other than the normal LH stimulation of Leydig cells (38,44). Stress related to RE (32,38), reduced clearance (44), adrenergic-stimulated secretion (8,16,22) and lactate-stimulated secretion (33) and hemoconcentration have been suggested as other mechanisms for exercise-induced increases in TS concentration.
Lactate stimulates TS secretion in Leydig cells from rats in vitro, and lactate infusions, resulting in similar elevations in plasma TS concentrations as seen during exercise, have been shown to elevate TS concentrations in rats in vivo (33). In the present study, significant differences were observed in mean blood lactate from pre to postexercise within protocols but not between each protocol. Also, there was no correlation between individual changes in lactate and TS concentrations for either protocol. Therefore, this hypothesis that lactate-stimulated secretion of TS was not confirmed by the results of the present study because the greater lactate accumulation observed during the 60-second protocol which has the least TS concentrations as compared to the 120-second protocol. The possible role of lactate in stimulating TS secretion during exercise in men requires further investigation.
In summary, the results of this investigation indicate that serum GH and TS concentrations were dependent on the length of the rest interval between sets in heavy RE protocols to failure. The primary finding of this study was that the patterns of GH and TS responses were dramatically different from the length of rest interval between sets in heavy RE (4 sets of squat and bench press to failure using 85% of 1RM). An RE protocol with a short rest interval between sets elicited greater increase in serum GH concentration compared to a long rest period, but acute TS responses were greater in the protocol with a long rest period and high training volume.
There are few limitations of this study that warrant discussion. First, manipulation of the acute RE program variables (i.e., exercise choice, load, volume, rest periods, and exercise order) dramatically influences the signaling responses and subsequent adaptations to RE (42). The direct influence of rest periods on mediating RE-induced muscle signaling responses is largely unexplored. Therefore, it is recommended that future studies evaluate the effect of different rest periods on signaling response. Second, these findings are related to few numbers of anabolic hormones. Further investigations are necessary to determine more anabolic hormones and growth factor. Third, these findings are specific to the RE protocol that was performed to failure. Further investigations are necessary to determine if these findings are generalizable to the RE protocol not to failure. Fourth, our findings are specific to the RE protocol performed at 85% of 1RM. It is unknown whether similar findings exist during RE protocols performed at different intensities. Additionally, our findings are specific to healthy resistance trained men. Further investigations are necessary to determine if these findings are generalizable to other populations.
In this study, we demonstrated that the rest interval between sets affects GH and TS responses and so could influence hypertrophy gains over time. During an RE session, a rest period of 60 seconds results in greater serum GH levels and less total training volume than a rest period of 90 and 120 seconds, but the TS response was greater in the RE sessions with long rest periods (90-120 seconds) and higher training volume. Short rest periods are typically recommended for RE protocols designed to maximize muscle hypertrophy because short rest periods augment the GH response when compared with long rest periods (40). However, short rest periods impair physical performance during subsequent sets (39,40) and, over several weeks, attenuate strength increase when compared with long rest periods (42). Of particular importance to the RE practitioner is that specific combinations of RE variables must be used to optimize the desired functional outcome (muscle strength, muscle power, muscle size, or muscle endurance). Therefore, it is recommended that short rest periods can be used to stimulate hypertrophy and that long rest periods are used to maximize strength gains.
The authors are grateful to the subjects who participated in this study. The authors also would like to acknowledge Dr. D. Sheikholeslami Vatani for feedback on a related proposal of the study. They also thank Dr. F. Jian at the Laboratory of Endocrinology for technical assistance with the immunoassay procedures. Funding was provided by Azad University Branch of Mahabad, Vice Chancellor for Research.
1. Ahtiainen, JP, Pakarinen, A, Alen, M, Kraemer, WJ, and Häkkinen, K. Acute hormonal and neuromuscular responses and recovery to forced vs. maximum repetitions multiple resistance exercises. Int J Sports Med
24: 410-418, 2003.
2. Ahtiainen, JP, Pakarinen, A, Alen, M, Kraemer, WJ, and Häkkinen, K. Short vs. long rest period between the sets in hypertrophic resistance training: Influence on muscle strength, size, and hormonal adaptations in trained men. J Strength Cond Res
19: 572-582, 2005.
3. Baechle, TR and Earle, RW. Essentials of Strength Training and Conditioning
. Champaign, IL: Human Kinetics, 2000.
4. Boroujerdi, SS and Rahimi, R. Acute GH and IGF-I responses to short vs. long rest period between sets during forced repetitions resistance training system. South African J Res Sport, Phy Ed Rec
30: 31-38, 2008.
5. Bottaro, M, Martinsb, B, Gentila, P, and Wagnerc, D. Effects of rest duration between sets of resistance training on acute hormonal responses in trained women. J Sci Med Sport
12: 73-78, 2009.
6. Bush, JA, Kimball, SR, O'Connor, PM, Suryawan, A, Orellana, RA, Nguyen HV, Jefferson, LS, and Davis, TA. Translational control of protein synthesis in muscle and liver of growth hormone
-treated pigs. Endocrinology
144: 1273-1283, 2003.
7. Craig, B and Kang, H-Y. Growth hormone
release following single versus multiple sets of back squats: total work versus power. J Strength Cond Res
8: 270-275, 1994.
8. Eik-Nes, KB, An effect of isoproterenol on rates of synthesis and secretion of testosterone
. Am J Physiol
217: 1764-1770, 1969.
9. Feigenbaum, MS and Pollock, ML. Prescription of resistance training for health and disease. Med Sci Sports Exerc
31: 38-45, 1999.
10. Ferrando, AA, Tipton, KD, Dolye, D, Phillips, SM, Cortiella, J, and Wolfe, RR. Testosterone
injection stimulates net protein synthesis but not tissue amion acid transport. Am J Physiol
275: E2864-E2871, 1998.
11. Fleck, SJ. Cardiovascular adaptations to resistance training. Med Sci Sports Exerc
20: S146-S151, 1988.
12. Fryburg, DA and Barrett, EJ. Growth hormone
acutely stimulates skeletal muscle but not whole-body protein synthesis in humans. Metabolism
42: 1223-1227, 1993.
13. Gordon, SE, Kraemer, WJ, Vos, NH, Lynch, JM, and Knuttgen, HG. Effect of acid-base balance on the growth hormone
response to acute high-intensity cycle exercise. J Appl Physiol
76: 821-829, 1994.
14. Gosselink, KL, Grindeland, RE, Roy, RR, Zhong, H, Bigbee, AJ, and Grossman, EJ. Growth hormone
in the rate pituitary. J Appl Physiol
15. Gotshalk, LA, Loebel, CC, Nlndl, BC, Plitukian, M, Sebastianelli, WJ, Newton, RU, Hakkinen, K, and Kraemer, WJ. Hormonal response of multiset versus single-set heavy-resistance exercise protocols. Can J Appl Physiol
22: 244-255, 1997.
16. Guezennec, Y, Leger, L, Lhoste, F, Aymonod, M, and Pesquis, PC. Hormone and metabolite response to weight-lifting training sessions. Int J Sports Med
7: 100-105, 1986.
17. Häkkinen, K and Pakarinen, A. Acute hormonal responses to two different fatiguing heavy resistance exercise protocols in male strength athletes. J Appl Physiol
74: 882-887, 1993.
18. Hansen, S, Kvorning, T, Kjaer, M, and Sjogaard, G. The effect of short term strength training on human skeletal muscle: The importance of physiologically elevated hormone levels. Scand J Med Sci Sports
11: 347-354, 2001.
19. Herbst, KL and Bhasin, S. Testosterone
action on skeletal muscle. Curr Opin Clin Nutr Metab Care
7: 271-277, 2004.
20. Hymer, WC, Kraemer, WJ, Nindl, BC, Marx, JO, Benson, DE, Welsch, JR, Mazzetti, SA, Volek JS, and Deaver, DR. Characteristics of circulating growth hormone
in women after acute heavy resistance exercise. Am J Physiol Endocrinol Metab
281: E878-E887, 2001.
21. Izquierdo, M, Javier, I, Jose, J, Glez-Badillo, Häkkinen, K, Ratamess, NA, Kraemer, WJ, French, DN, Eslava, J, Altadill, A, Asiain, X, and Gorostiaga, EM.X, and Gorostiaga, EM. Differential effects of strength training leading to failure versus not to failure on hormonal responses, strength, and muscle power gains. J Appl Physiol
100: 1647-1656, 2006.
22. Jezovaa, D and Vigas, M. Testosterone
response to exercise during blockade and stimulation of adrenergic receptors in man. Horm Res
15: 141-147, 1981.
23. Kraemer, WJ. Exercise prescription in weight training: Manipulating program variables. Nat Strength Cond Nat Strength Cond Assoc J
5: 58-59, 1983.
24. Kraemer, WJ. Endocrine responses and adaptations to strength training. In: Strength and Power in Sport
. Komi, PV, ed. Oxford; Boston: Blackwell Scientific Publications, 1992. pp. 191-304.
25. Kraemer, WJ. A series of studies: The physiological basis for strength training in American football: Fact over philosophy. J Strength Cond Res
11: 131-142, 1997.
26. Kraemer, WJ, Fleck, SJ, Dziados, JE, Harman, EA, Marchitelli, LJ, Gordon, SE, Mello, R, Frykman, PN, Koziris, LP, and Triplett, NT. Changes in hormonal concentrations after different heavy resistance exercise protocols in women. J Appl Physiol
75: 594-604, 1993.
27. Kraemer, WJ, Gopdon, SE, Fleck, SJ, Marchitelli, LJ, Mello, R, Dziados, JE, Friedl, K, Harman, E, Maresh, C, and Fry, AC. Endogenous anabolic hormonal and growth factor responses to heavy-resistance exercise males and females. Int J Sports Med
12: 228-235, 1991.
28. Kraemer, WJ, Marchitelli, L, Gordon, SE, Harman, E, Dziados, JE, Mello, R, Frykman, P, McCurry, D, and Fleck, SJ. Hormonal and growth factor responses to heavy-resistance exercise protocols. J Appl Physiol
69: 1442-1450, 1990.
29. Kraemer, WJ, Nindl, BC, Marx, JO, Gotshalk, LA, Bush, JA, Welsch, JR, Volek, JS, Spiering, BA, Maresh, CM, Mastro, AM, and Hymer, WC. Chronic resistance training in women potentiates growth hormone
in vivo bioactivity: Characterization of molecular mass variants. Am J Physiol Endocrinol Metab
291: El 177-187, 2006.
30. Kraemer, WJ, Noble, BJ, Clark, MJ, and Culver, BW. Physiologic responses to heavy-resistance exercise with very short rest periods. Int J Sports Med
8: 247-252, 1987.
31. Kraemer, WJ, Hakkinen, K, Newton, RU, Nindl, BC, Volek, JS, McCormick, M, Gotshalk, LA, Gordon, SE, Fleck, SJ, Campbell, WW, Putukian, M, and Evans, WJ. Effects of heavy-resistance training on hormonal response patterns in younger vs. older men. J Appl Physiol
87: 982-992, 1999.
32. Linnamo, V, Pakarinen, A, Komi, PV, Kraemer, WG and Häkkinen, K. Acute hormonal responses to heavy resistance and explosive exercise in men and women. J Strength Cond Res
19: 566-571, 2005.
33. Lu, S-S, Lau, CP, Tung, Y-F, Huang, S-W, Chen, Y-H, Shih, H-C, Tsai, S-C, Lu, C-C, Wang, S-W, Chen, J-J, Chein, EJ, Chein, CH, and Wang, PS. Lactate and the effect of exercise on testosterone
secretion: Evidence for the involvement of a cAMP-mediated mechanism. Med Sci Sports Exerc
29: 1048-1054, 1997.
34. Miranda, H, Fleck, SJ, Simao, R, Barreto, AC, Dantas, EHM, and Novaes, J. Effect of two different rest period lengths on the number of repetitions performed during resistance training. J Strength Cond Res
21: 1032-1036, 2007.
35. Mulligan, SE, Fleck, SJ, Gordon, SE, Koziris, LP, Triplett, NT, and Kraemer, WJ. Influence of resistance exercise volume on serum growth hormone
and cortisol concentrations in women. J Strength Cond Res
10: 256-262, 1996.
36. Nindl, BC. Exercise modulation of growth hormone
isoforms: Current knowledge and future directions for the exercise endocrinologist. Br J Sports Med
41: 346-348, 2007.
37. Pollock, ML, Gaesser, GA, Butcher, JD, Despres, JD, Dish-man, RK, Franklin, BA, and Garber, CE. The recommended quantity and quality of exercise for developing and maintaining cardiorespiratory and muscular fitness, and flexibility in healthy adults. Med Sci Sports Exerc
30: 975-991, 1998.
38. Raastad, T, Bjoro, T, and Hallen, J. Hormonal responses to high-and moderate-intensity strength exercise. Eur J Appl Physiol
82: 121-128, 2000.
39. Rahimi, R. Effect of different rest intervals on the exercise volume completed during squat bouts. J Sports Sci Med
4: 361-366, 2005.
40. Rahimi, R, Boroujerdi, SS, Ghaeeni, S, and Noori, SR. The effect of different rest intervals between sets on the training volume of male athletes. Facta Univ Phys Educ Sport
5: 37-46, 2007.
41. Sinha-Hikim, I, Roth, SM, Lee, MI, and Bhasin, S. Testosterone
-induced muscle hypertrophy is associated with an increase in satellite cell number in healthy, young men. Am J Physiol Endocrinol Metab
285: E197-E205, 2003.
42. Spiering, BA, Kraemer, WJ, Anderson, JM, Armstrong, LE, Nindl, BC, Volek, JS, and Maresh, CM. Resistance exercise biology, manipulation of resistance exercise program variables determines the responses of cellular and molecular signaling pathways. Sports Med
38: 527-540, 2008.
43. Takarada, Y and Ishii, N. Effects of low-intensity resistance exercise with short interset rest period on muscular function in middle-aged women. J Strength Cond Res
16: 123-128, 2002.
44. Terjung, R. Endocrine response to exercise. Exerc Sport Sci Rev
7: 153-180, 1979.
45. Vanhelder, WP, Radomski, MW, and Goode, RC. Growth hormone
responses during intermittent weight lifting exercise in men. Eur J Appl Physiol Occup Physiol
53: 31-34, 1984.
46. Viru, A and Viru, M. Resistance exercise and testosterone
. In: The endocrine System in Sport and Exercise
. Kraemer, WJ, and Rogol, AD, eds. Malden, MA: Blackwell Publishing Ltd, 2005. pp. 319-323.
47. Willardson, JM and Burkett, LN. A comparison of 3 different rest intervals on the exercise volume completed during a workout. J Strength Cond Res
19: 23-26, 2005.