title: Caffeine attenuates acute growth hormone response to a single bout of resistance exercise.
abstract: The purpose of this study was to investigate the effects of caffeine consume on substrate metabolism and acute hormonal responses to a single bout of resistance exercise (RE). Ten resistance-trained men participated in this study. All subjects performed one repetition maximum (1RM) test and then performed two protocols: caffeine (CAF, 6 mg·kg(-1)) and control (CON) in counter balanced order. Subjects performed RE (8 exercises, 3 sets of 10 repetitions at 75% of 1RM) after caffeine or placebo ingestion one hour prior to RE. Blood samples collected prior to treatment ingestion (pre-60), immediately prior to RE (pre-exe), and 0, 15, 30 min post to RE (P0, P15, P30) for analysis of insulin, testosterone, cortisol, growth hormone, glucose, free fatty acid and lactic acid. Each experiment was separated by seven days. In this study, statistical analysis of a two-way analysis of variance (treatment by time) with repeated measures was applied. After ingesting caffeine, the concentrations of free fatty acid (pre- exe, P0, P15, P30) in CAF were significantly higher than CON (p < 0.05). Additionally, the responses of GH (P0, P15, P30) in CAF were significantly lower than CON (p < 0.05), whereas the concentrations of insulin, testosterone and cortisol were not different between CAF and CON (p < 0.05) after RE. The results of this study indicated that caffeine ingestion prior to RE might attenuate the response of GH. This effect might be caused by the elevation in blood FFA concentration at the beginning of RE. Key pointsCaffeine ingestion may attenuate the response of GH to a single bout of resistance exercise.The depression of GH response may be caused by the elevation in serum FFA concentration at the beginning of resistance exercise.Caffeine ingestion before resistance exercise may not alert the concentration of cortisol and testosterone.
authors.affiliation: Department of Sports & Recreation Management, Chang Jung Christian University , Tainan, Taiwan.
authors.forename: Bo-Han
authors.initials: BH
authors.lastname: Wu
authors.forename: Jung-Chang
authors.initials: JC
authors.lastname: Lin
keywords: Nutritional supplementation; ergogenic aids; free fatty acid; growth hormone