Growth Hormone Responses to Stress

The following is an exclusive excerpt from the book Essentials of Strength Training and Conditioning-4th Edition With Web Resource, published by Human Kinetics. All text and images provided by Human Kinetics.

Pituitary hormones (e.g., proopiomelanocortin [POMC], GHs, and prolactin) respond to a variety of exercise stressors, including resistance exercise (26, 29, 56, 60, 113, 116, 132, 134). Growth hormone (22 kDa) concentrations increase in response to breath holding and hyperventilation alone (33), as well as to hypoxia (177). It appears that a substantial stimulus for 22 kDa GH release is increased hydrogen ion (drop in pH) and lactate concentrations (64). Not all resistance exercise protocols demonstrate increased serum GH concentration. Vanhelder and colleagues (184) observed that when a light load (28% of 7RM) was used with a high number of repetitions in each set, no changes in the serum concentration of the 22 kDa GH occurred. It appears that an intensity threshold must be reached in order to elicit a significant 22 kDa GH response to resistance exercise, especially when longer rest periods (>3 minutes) are used (113). This may be due to the metabolic connection with glycolytic metabolism (at least for the 22 kDa variant).

Depending on the load, rest, exercise volume, and exercise selection of a resistance exercise protocol, different 22 kDa GH responses occur (5, 43, 44, 139, 143, 166, 167, 174). In a study designed to determine the different variables related to GH increases, Kraemer and colleagues (113) found that serum increases in the 22 kDa GH are differentially sensitive to the volume of exercise, the amount of rest between sets (less rest, higher 22 kDa GH), and the resistance used (10RM produces higher lactate values and higher 22 kDa GH responses). When the intensity used was 10RM (heavy resistance) with three sets of each exercise (high total work, approximately 60,000 J) and short (1-minute) rest periods, large increases were observed in serum 22 kDa GH concentrations. The most dramatic increases occurred in response to a 1-minute rest period when the duration of exercise was longer (10RM vs. 5RM). Because such differences are related to the configuration of the exercise session (e.g., rest period length), it appears that greater attention needs to be given to program design variables when physiological adaptations to resistance training are being evaluated.

Growth hormone release is affected by the type of resistance training protocol used including the duration of rest period. Short rest period types of workouts result in greater serum concentrations compared to long rest protocols of similar total work; however, at present it is not clear how the various molecular forms (e.g., aggregates and splice variants) or types of GH are affected by rest period duration.

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