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Dong-Il Seo, Tae-Won Jun, Kae-Soon Park, Hyukki Chang, Wi-Young So and Wook Song

Background:

The purpose of this study was to examine the effects of combined exercise training on growth hormone (GH), insulin-like growth factor-1 (IGF-1), and metabolic-syndrome factors and determine whether the changes in GH and/or IGF-1 induced by exercise correlate to the metabolic-syndrome factors in healthy middle-aged women (50–65 years of age).

Methods:

The participants were randomly assigned into an aerobic-exercise training (walking + aerobics) group (AEG; n = 7), a combined-exercise training (walking + resistance training) group (CEG; n = 8), or a control group (CG; n = 7). Exercise sessions were performed 3 times per wk for 12 wk. The aerobic-exercise training consisted of walking and aerobics at 60–80% of heart-rate reserve, and the combined-exercise training consisted of walking and resistance exercise at 50–70% of 1-repetition maximum.

Results:

GH, percentage body fat, fasting glucose, systolic blood pressure, and waist circumference were significantly improved in CEG (p < .05). However, GH induced by exercise training showed no correlation with metabolic-syndrome factors. IGF-1 was not significantly increased in either AEG or CEG compared with CG.

Conclusion:

These results indicate that the combined-exercise training produced more enhancement of GH, body composition, and metabolic-syndrome factors than did aerobic-exercise training.

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Valerie J. Wirth and Joe Gieck

Growth hormone is one of the many dangerous and illegal ergogenic aids currently used by athletes. In those who suffer from a growth hormone deficiency, supplementation does produce positive results: Muscle volume increases while adipose tissue volume is significantly reduced. Growth hormone supplementation can also lead to strength increases in the deficient population (2, 6, 13) as well as in the elderly population (16, 18, 25). In healthy young men, growth hormone supplementation has been shown to increase fat-free mass and to decrease fat mass. However, these changes are not accompanied by strength gains (5, 7, 23, 24). This finding, coupled with the numerous side effects associated with the drug, presents a strong case for athletes to abandon its use as an ergogenic aid.

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Alon Eliakim and Dan Nemet

The diagnosis of Growth Hormone (GH) deficiency in children with short stature is complex, and in certain cases, might be very difficult. Most of the provocative tests used to evaluate GH deficiency use pharmacological agents. The artificial nature of the pharmacological tests and the possibility that these tests might not always reflect GH secretion under normal physiological conditions provides the impetus for a more physiologic test. Exercise is one of the important GH releasing physiological stimuli. This review will summarize the current knowledge on the methods for performing laboratory exercise provocation test for GH secretion in children. In addition to recommendations of more standardized exercise protocols and environmental considerations, we will also focus on GH responses to exercise in unique populations such as obese children.

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James A. Betts, Keith A. Stokes, Rebecca J. Toone and Clyde Williams

Endocrine responses to repeated exercise have barely been investigated, and no data are available regarding the mediating influence of nutrition. On 3 occasions, participants ran for 90 min at 70% VO2max (R1) before a second exhaustive treadmill run at the same intensity (R2; 91.6 ± 17.9 min). During the intervening 4-hr recovery, participants ingested either 0.8 g sucrose · kg−1 · hr−1 with 0.3 g · kg−1 · hr−1 whey-protein isolate (CHO-PRO), 0.8 g sucrose · kg−1 · hr−1 (CHO), or 1.1 g sucrose · kg−1 · hr−1 (CHO-CHO). The latter 2 solutions therefore matched the former for carbohydrate or for available energy, respectively. Serum growth-hormone concentrations increased from 2 ± 1 μg/L to 17 ± 8 μg/L during R1 considered across all treatments (M ± SD; p ≤ .01). Concentrations were similar immediately after R2 irrespective of whether CHO or CHO-CHO was ingested (19 ± 4 μg/L and 19 ± 5 μg/L, respectively), whereas ingestion of CHO-PRO produced an augmented response (31 ± 4 μg/L; p ≤ .05). Growth-hormone-binding protein concentrations were unaffected by R1 but increased similarly across all treatments during R2 (from 414 ± 202 pmol/L to 577 ± 167 pmol/L; p ≤ .01), as was the case for plasma total testosterone (from 9.3 ± 3.3 nmol/L to 14.7 ± 4.6 nmol/L; p ≤ .01). There was an overall treatment effect for serum cortisol (p ≤ .05), with no specific differences at any given time point but lower concentrations immediately after R2 with CHO-PRO (608 ± 133 nmol/L) than with CHO (796 ± 278 nmol/L) or CHO-CHO (838 ± 134 nmol/L). Ingesting carbohydrate with added whey-protein isolate during short-term recovery from 90 min of treadmill running increases the growth-hormone response to a second exhaustive exercise bout of similar duration.

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Scott C. Forbes, Vicki Harber and Gordon J. Bell

Acute resistance exercise and L-arginine have both been shown to independently elevate plasma growth hormone (GH) concentrations; however, their combined effect is controversial. The purpose was to investigate the combined effects of resistance exercise and L-arginine supplementation on plasma L-arginine, GH, GH secretagogues, and IGF-1 in strength trained participants. Fourteen strength trained males (age: 25 ± 4 y; body mass: 81.4 ± 9.0 kg; height: 179.4 ± 6.9 cm; and training experience: 6.3 ± 3.4 y) participated in a randomized double-blind crossover design (separated by ~7 days). Subjects reported to the laboratory at 08:00 in a fasted state, consumed L-arginine (ARG; 0.075 g·kg−1 body mass) or a placebo (PLA) before performing an acute bout of resistance exercise (3 sets of 8 exercises, 10 repetitions at ~75% 1RM). Blood samples were collected at rest, before exercise, and at 0, 15, 30, and 60 min of rest-recovery. The ARG condition significantly increased plasma L-arginine concentrations (~120%) while no change was detected in the PLA condition. There were no differences between conditions for GH, GH-releasing hormone, ghrelin, or IGF-1 at any time point. GH-inhibiting hormone was significantly lower in the ARG condition. However, integrated area under the curve for GH was blunted in the ARG condition (L-arginine = 288.4 ± 368.7 vs. placebo = 487.9 ± 482.0 min·ng·mL−1, p < .05). L-arginine ingested before resistance exercise significantly elevated plasma L-arginine concentration but attenuated plasma GH in strength trained individuals despite a lower GHIH. Furthermore our data shows that the GH suppression was not due to a GH or IGF-1 induced autonegative feedback loop.

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Michael I. Lambert, Janet A. Hefer, Robert P. Millar and Peter W. Macfarlane

Amino acids are commonly ingested as ergogenic aids in the belief that they enhance protein synthesis and stimulate growth hormone release. The aim of this study was to determine the acute effect that amino acid supplements have on serum growth hormone (GH) concentration. Seven male bodybuilders reported to the laboratory on four occasions after an 8-hr fast and ingested, in random order, either a placebo, a 2.4-g arginine/lysine supplement, a 1.85-g ornithine/tyrosine supplement, or a 20-g BovrilR drink. Blood was collected before each treatment and again every 30 minutes for 3 hours for the measurement of serum GH concentration. On a separate occasion, subjects had an intravenous infusion of 0.5 fig GH-releasing hormone-kg ' body weight to confirm that GH secretory response was normal. The main finding was that serum GH concentrations were not altered consistently in healthy young males following the ingestion of the amino acid supplements in the quantities recommended by the manufacturers.

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G. Mikael Fogelholm, Hannu K. Näveri, Kai T.K. Kiilavuori and Matti H.A. HärkÖnen

Using a double-blind, crossover protocol, we studied the possible effects of a 4-day combined L-arginine, L-ornithine, and L-lysine supplementation (each 2 g/day, divided into two daily doses) on 24-hr level of serum human growth hormone (hGH) and insulin in 11 competitive weightlifters, ages 19 to 35 yrs. Three similar daily hGH peaks, seemingly preceded by a decrease in serum insulin concentration, were found during both amino acid and placebo supplementation. Supplementation did not affect the physiological variation of serum hGH concentration (treatment and treatment × time interaction: p=0.43–0.55). Analogously, serum insulin levels were not higher after amino acid supplementation. Therefore the ergogenic value of lowdose oral amino acid supplementation in increasing hGH or insulin secretion seems questionable.

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Richard R. Suminski, Robert J. Robertson, Fredric L. Goss, Silva Arslanian, Jie Kang, Sergio DaSilva, Alan C. Utter and Kenneth F. Metz

Sixteen men completed four trials at random as follows: (Trial A) performance of a single bout of resistance exercise preceded by placebo ingestion (vitamin C); (Trial B) ingestion of 1,500 mg L-arginine and 1,500 mg L-lysine, immediately followed by exercise as in Trial A; (Trial C) ingestion of amino acids as in Trial B and no exercise; (Trial D) placebo ingestion and no exercise. Growth hormone (GH) concentrations were higher at 30,60, and 90 min during the exercise trials (A and B) compared with the resting trials (C and D) (p < .05). No differences were noted in [GH] between the exercise trials. [GH] was significantly elevated during resting conditions 60 min after amino acid ingestion compared with the placebo trial. It was concluded that ingestion of 1,500 mg arginine and 1,500 mg ly sine immediately before resistance exercise does not alter exercise-induced changes in [GH] in young men. However, when the same amino acid mixture is ingested under basal conditions, the acute secretion of GH is increased.

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Simon Walker, Fabrizio Santolamazza, William Kraemer and Keijo Häkkinen

The present study investigated changes in acute serum hormone responses to a resistance exercise bout following a prolonged period of hypertrophic resistance training in young (YM) and older men (OM). Subjects performed a 5 × 10RM leg press exercise protocol before and after 20 weeks of hypertrophic resistance training. In YM, the acute responses in growth hormone were greater compared with before training (p < .05), and cortisol concentration did not increase after training. Endocrine responses in OM were similar before and after training. Greater acute growth hormone responses after training were associated with larger gains in lean mass in the entire subject group (r = .596, p = .019). These findings suggest that, in general, YM demonstrate greater adaptability within the endocrine system compared with OM. However, adaptability in growth hormone response was associated with larger training-induced gains independent of age.

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James A. Betts, Milou Beelen, Keith A. Stokes, Wim H.M. Saris and Luc J.C. van Loon

Nocturnal endocrine responses to exercise performed in the evening and the potential role of nutrition are poorly understood. To gain novel insight, 10 healthy men ingested carbohydrate with (C+P) and without (C) protein in a randomized order and double-blind manner during 2 hr of interval cycling followed by resistancetype exercise and into early postexercise recovery. Blood samples were obtained hourly throughout 9 hr of postexercise overnight recovery for analysis of key hormones. Muscle samples were taken from the vastus lateralis before and after exercise and then again the next morning (7 a.m.) to calculate mixed-muscle protein fractional synthetic rate (FSR). Overnight plasma hormone concentrations were converted into overall responses (expressed as area under the concentration curve) and did not differ between treatments for either growth hormone (1,464 ± 257 vs. 1,432 ± 164 pg/ml · 540 min) or total testosterone (18.3 ± 1.2 vs. 17.9 ± 1.2 nmol/L · 540 min, C and C+P, respectively). In contrast, the overnight cortisol response was higher with C+P (102 ± 11 nmol/L · 540 min) than with C (81 ± 8 nmol/L · 540 min; p = .02). Mixed-muscle FSR did not differ between C and C+P during overnight recovery (0.062% ± 0.006% and 0.062% ± 0.009%/hr, respectively) and correlated significantly with the plasma total testosterone response (r = .7, p < .01). No correlations with FSR were apparent for the response of growth hormone (r = –.2, p = .4), cortisol (r = .1, p = .6), or the ratio of testosterone to cortisol (r = .2, p = .5). In conclusion, protein ingestion during and shortly after exercise does not modulate the endocrine response or muscle protein synthesis during overnight recovery.