Resistance training and growth hormone (GH): effects on histology and typing of gastrocnemius muscle fibers

Purpose: The aim of this study was to investigate the effects of the application of GH and the realization of an RT protocol on the gastrocnemius muscle of Wistar rats using histological parameters. Methods: In total, 40 male animals Wistar rats (were used, 60 days old) were distributed into four groups: control (C) [n = 10], control and application of GH (GHC) [n = 10], training (T) [n = 10], and training and application of GH (GHT) [n = 10]. The training period consisted of 4 weeks. The amount of 0.2 IU per kilogram of body mass (0.2 IU/Kg) of “somatotropin” (GH) was administered. The RT was composed of four series of ten jumps, performed three times a week, on non-consecutive days. Histological analyses were performed with Hematoxylin–Eosin (HE) and Nicotinamide Adenine Dinucleotide Tetrazolium Reductase (NADH-TR). Results: A significant increase in body mass was verified in the animals in the GHT group after the first and second weeks of training (p < 0.05). An increase in the diameter of muscle fibers was observed in the GHC, T, and GHT groups of animals, especially in fast-twitch fibers (p < 0.05). Conclusion: In conclusion, both GHT and T groups demonstrated hypertrophy of muscle fibers, mainly in fast-twitch fibers.