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Acute Increases in Exercise GH Increase Post-exercise Fat Utilization |
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Written by Robbie Durand
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Friday, 02 January 2009 |
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Page 1 of 4  Growth hormone is an important anabolic agent. Besides its
growth-promoting effects, it has important effects on substrate
metabolism. The effects of GH on metabolism are increased protein
synthesis, reduced protein breakdown and mobilization of fats from
adipose tissue.
"You've got to say, I think that if I keep working at this and want it badly enough I can have it. It's called perseverance." -Lee Iacocca
Growth hormone is an important anabolic agent. Besides its growth-promoting effects, it has important effects on substrate metabolism. The effects of GH on metabolism are increased protein synthesis, reduced protein breakdown and mobilization of fats from adipose tissue. At rest, GH secretion is characterized by episodic bursts over a 24-hour period and is influenced by age, gender, nutrition, sleep, body composition, regional distribution of body fat, stress, fitness level, sex hormones (testosterone and estrogen), insulin and IGF-1 levels. Of the factors listed that influence GH secretion, if you had to choose the two most important predictors of your 24-hour GH release, what would they be? Researchers examined the 10 physiological factors regulating GH secretion in men at rest and found that the two with the greatest impact on resting GH secretion are abdominal (visceral) fat and fasting insulin levels. In the study, abdominal fat was the strongest predictor of 24-hour GH release among the 10 variables studied, followed closely by fasting insulin levels. An inverse relationship between abdominal fat and 24-hour GH release (the bigger your stomach, the lower GH secretion you have) was demonstrated in both young and old men. It's interesting that although with age there's a reduction in GH secretion, having a big gut suppresses GH greater than getting older. Having a big gut not only suppresses GH secretion, but also serum IGF-1 concentrations, which is a powerful muscle builder. 22,23,24. GH seems to just strip the fat off your body, particularly the stomach. A study by Gravholt et al., found that acute GH administration has the greatest effect on fat mobilization from two specific sites: the stomach and gluteals (buttocks) adipose tissue.27 So, if you want to increase your resting GH levels, losing your stomach and adhering to a reduced-carbohydrate diet that controls insulin are sure ways to increase your resting GH concentrations. So, what's the best way to lose abdominal fat? Vigorous exercise training has been reported to decrease abdominal fat and improve fasting insulin levels in men.25,26
High-intensity Exercise: A Potent Non-pharmacological Stimulator of GH!
The most powerful, non-pharmacological stimuli for GH secretion are sleep and high-intensity exercise. In relation to exercise, the GH response is dependent on muscle mass exercised, rest duration and of course, exercise intensity. It's been emphasized repeatedly in each issue of MD that high-intensity exercise is a potent stimulator of GH response. One of the leading pioneers in GH and exercise research- Arthur Weltman- has reported a direct relationship between how much GH you secrete during exercise and the degree of lactic acid production (exercise intensity). If you feel like your legs are on fire during squats, chances are you have significant GH secretion occurring during exercise! In his study, Weltman et al.8 reported a dose-dependent response between lactate and GH levels to low- and high-intensity running protocols. In that study, five treadmill-running intensities were studied at various percentages of the subjects' lactate threshold (0.25 LT, 0.75 LT, LT, 1.25 LT, and 1.75 LT). Lactate threshold is the exercise intensity at which lactate (lactic acid) starts to accumulate in the bloodstream. GH responses were the lowest with low lactates being produced, while GH responses were the highest with increasing production of lactate being produced. Choosing exercises that build large muscle mass (squats, deadlifts, bench press, jump squats, etc.) with minimal rest periods is a sure way to increase GH during exercise. Large increases in lactic acid production are a must for a good GH response during exercise, and long rest periods won't cause large increases in GH. For example, a study by Gordon et al.33 reported that even if one exercises at high thresholds, without large increases in lactate production, GH responses are blunted. In this interesting study, researchers administered sodium bicarbonate (sodium bicarbonate reduces lactate accumulation in the blood, increases the pH in the blood and makes the blood pH less acidic) to athletes and had them perform a cycle exercise test to exhaustion. Ingestion of sodium bicarbonate resulted in lowered lactic acid levels in addition to a blunted GH secretion in response to exercise. Moderate-volume training programs, which have reduced rest periods (less than 1 minute) and produce high lactate levels during exercise, result in greater GH responses than those with high volume and protracted rest periods (greater than 5 minutes).
Although GH increases produced during exercise are associated with increasing lean muscle mass, GH is a powerful fat-loss hormone. GH is important in facilitating mobilization of stored fat at rest, but also particularly following exercise. For example, Gibney et al.13 had GH-deficient men, who were either receiving GH or who had been withdrawn from GH, go through exhaustive exercise. After GH withdrawal, markers of fat oxidation were significantly depressed at rest and in response to exercise, compared to subjects who were GH-treated. So, if you want to shed the fat off your stomach, high-intensity exercise that stimulates GH will increase fat utilization, particularly post-exercise.
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Research and Review 
