The growth hormone response to repeated bouts of sprint exercise with and without suppression of lipolysis in men

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Abstract
A single 30-s sprint is a potent physiological stimulus for growth hormone (GH) release. However, repeated bouts of sprinting attenuate the GH response, possibly due to negative feedback via elevated systemic free fatty acids (FFA). The aim of the study was to use nicotinic acid (NA) to suppress lipolysis to investigate whether serum FFA can modulate the GH response to exercise. Seven nonobese, healthy men performed two trials, consisting of two maximal 30-s cycle ergometer sprints separated by 4 h of recovery. In one trial (NA), participants ingested NA (1 g 60 min before, and 0.5 g 60 and 180 min after sprint 1); the other was a control (Con) trial. Serum FFA was not significantly different between trials before sprint 1 but was significantly lower in the NA trial immediately before sprint 2 [NA vs. Con: mean (SD); 0.08 (0.05) vs. 0.75 (0.34) mmol/l, P < 0.05]. Peak and integrated GH were significantly greater following sprint 2 compared with sprint 1 in the NA trial [peak GH: 23.3 (7.0) vs. 7.7 (11.9) μg/l, P < 0.05; integrated GH: 1,076 (350) vs. 316 (527) μg·l−1·60 min−1, P < 0.05] and compared with sprint 2 in the Con trial [peak GH: 23.3 (7.0) vs. 5.2 (2.3) μg/l, P < 0.05; integrated GH: 1,076 (350) vs. 206 (118) μg·l−1·60 min−1, P < 0.05]. In conclusion, suppressing lipolysis resulted in a significantly greater GH response to the second of two sprints, suggesting a potential role for serum FFA in negative feedback control of the GH response to repeated exercise.