I saw what you posted Chaz, and thought It would be intresting to have a little look on pubmed to see what I could find:
J Strength Cond Res.
2009 Jan;23(1):62-71
The effect of resistive exercise rest interval on hormonal response, strength, and hypertrophy with training.
Buresh R, Berg K, French J.
The purpose of this study was to compare the effects of different between-set rest periods (1 and 2.5 minutes) on changes in hormone response, strength, arm cross-sectional area (CSA), thigh muscular cross-sectional area (MCSA), and body composition during a 10-week training period. Twelve untrained males (24.8 +/- 5.9 years) engaged in resistance training using either 1 minute (short rest [SR], n = 6) or 2.5 minutes (long rest [LR], n = 6) of rest between sets, with a load that elicited failure on the third set of each exercise. Body composition, thigh MCSA, arm CSA, and five-repetition maximum (RM) squat and bench press were assessed before and after training. Blood samples were collected after exercise in weeks 1, 5, and 10. In week 1, postexercise plasma testosterone levels were greater in SR (0.41 +/- 0.17 mmolxL) than in LR (0.24 +/- 0.06 mmol x L, p < 0.05), and postexercise cortisol levels were greater in SR (963 +/- 313 mmol x L) than in LR (629 +/- 127 mmol x L, p < 0.05). Week 1 postexercise GH levels were not different (p = 0.28). The differences between hormone levels in weeks 5 and 10 were not significant. Arm CSA increased more with LR (12.3 +/- 7.2%) than with SR (5.1 +/- 2.9%, p < 0.05). There were no differences in strength increases.
These results show that in healthy, recently untrained males, strength training with 1 minute of rest between sets elicits a greater hormonal response than 2.5-minute rest intervals in the first week of training, but these differences diminish by week 5 and disappear by week 10 of training. Furthermore, the hormonal response is highly variable and may not necessarily be predictive of strength and lean tissue gains in a 10-week training program.
Strength Cond Res. 2005 Aug;19(3):572-82.
Short vs. long rest period between the sets in hypertrophic resistance training: influence on muscle strength, size, and hormonal adaptations in trained men.
Ahtiainen JP, Pakarinen A, Alen M, Kraemer WJ, H?kkinen K.
Acute and long-term hormonal and neuromuscular adaptations to hypertrophic strength training were studied in 13 recreationally strength-trained men. The experimental design comprised a 6-month hypertrophic strength-training period including 2 separate 3-month training periods with the crossover design, a training protocol of short rest (SR, 2 minutes) as compared with long rest (LR, 5 minutes) between the sets. Basal hormonal concentrations of serum total testosterone (T), free testosterone (FT), and cortisol (C), maximal isometric strength of the leg extensors, right leg 1 repetition maximum (1RM), dietary analysis, and muscle cross-sectional area (CSA) of the quadriceps femoris by magnetic resonance imaging (MRI) were measured at months 0, 3, and 6. The 2 hypertrophic training protocols used in training for the leg extensors (leg presses and squats with 10RM sets) were also examined in the laboratory conditions at months 0, 3, and 6. The exercise protocols were similar with regard to the total volume of work (loads x sets x reps), but differed with regard to the intensity and the length of rest between the sets (higher intensity and longer rest of 5 minutes vs. somewhat lower intensity but shorter rest of 2 minutes). Before and immediately after the protocols, maximal isometric force and electromyographic (EMG) activity of the leg extensors were measured and blood samples were drawn for determination of serum T, FT, C, and growth hormone (GH) concentrations and blood lactate. Both protocols before the experimental training period (month 0) led to large acute increases (p < 0.05-0.001) in serum T, FT, C , and GH concentrations, as well as to large acute decreases (p < 0.05-0.001) in maximal isometric force and EMG activity. However, no significant differences were observed between the protocols. Significant increases of 7% in maximal isometric force, 16% in the right leg 1RM, and 4% in the muscle CSA of the quadriceps femoris were observed during the 6-month strength-training period. However, both 3-month training periods performed with either the longer or the shorter rest periods between the sets resulted in similar gains in muscle mass and strength. No statistically significant changes were observed in basal hormone concentrations or in the profiles of acute hormonal responses during the entire 6-month experimental training period.
The present study indicated that, within typical hypertrophic strength-training protocols used in the present study, the length of the recovery times between the sets (2 vs. 5 minutes) did not have an influence on the magnitude of acute hormonal and neuromuscular responses or long-term training adaptations in muscle strength and mass in previously strength-trained men.
J Sci Med Sport. 2007 Dec 17.
Effects of rest duration between sets of resistance training on acute hormonal responses in trained women.
Bottaro M, Martins B, Gentil P, Wagner D.
This study investigated the acute hormonal response to three different rest periods between sets of a traditional lower body resistance training session in young women. Twelve healthy trained females (26.83+/-3.93 years) participated in the study. On three separate sessions of a lower body resistance exercise protocol, subjects were assigned in a random order a rest interval of 30s (P30), 60s (P60) or 120s (P120) between sets. The resistance exercise session consisted of four lower body exercises with three sets performed until contractile failure using 10-repetition maximum (RM) load. Blood samples were drawn for determination of serum growth hormone (GH) and cortisol concentrations before exercise (T0), immediately after each training session (T1), and after 5min (T5), 15min (T15), and 30min (T30) of recovery. Statistical evaluation of the area under the time-concentration relationship for GH (GHauc) and for cortisol (Cauc) were analyzed using a one-way ANOVA There were no differences among protocols (P30, P60 and P120) in the serum GH and cortisol concentrations at baseline (T0). However, as compared to T0, all protocols led to acute increases (p<0.05) in serum GH concentrations after each training session. The GHauc was greater for P30 than for both P60 and P120, however, there were no differences between P60 and P120. The Cauc were not different among protocols.
Thus, the magnitude of acute GH responses in previously strength-trained women appears greater with a 30-s rest interval between sets compared to longer rest periods of 60- or 120-s.
I found something interesting while I was looking around on pubmed, which I have noticed alot of experienced lifters on these forums do:
J Sports Med Phys Fitness. 2003 Jun;43(2):243-9.
A single set of low intensity resistance exercise immediately following high intensity resistance exercise stimulates growth hormone secretion in men.
Goto K, Sato K, Takamatsu K.
AIM: The purpose of the present study was to examine the effects of an additional set immediately following high intensity resistance exercise on growth hormone (GH) response. METHODS: Subjects (n=8) performed 4 resistance exercise protocols (bilateral knee extension exercise) on separate days. The protocols were categorized into 2 types of protocol, namely "Strength-up type (S-type)" and "Combination type (Combi-type)". The S-type was resistance exercise which consisted of 5 sets at 90% of 1 repetition maximum (RM) with 3-min rest periods between sets, whereas the Combi-type is a training protocol which adds an additional set (either 50% of 1 RM [C50-type], 70% of 1 RM [C70-type] or 90% of 1 RM [C90-type]) to the S-type. Serum GH concentration and blood lactate concentration were determined pre-exercise and at 0-60 min postexercise. Relative changes in thigh girth and maximal unilateral isometric strength were determined pre-exercise and immediately postexercise. RESULTS: The increasing values of GH concentration (DGH) in the S-type was the lowest of all protocols. On the other hand, DGH in the C50-type showed a significantly (p<0.05) higher increase than in the S-type and C90-type, and a relatively higher increase than in the C70-type. CONCLUSION:
These results suggests that a high intensity, low volume training protocol to induce neural adaptation resulted in little GH response, but GH secretion was increased by performing a single set of low intensity resistance exercise at the end of a series of high intensity resistance sets.
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