Acute Resistance Exercise on Bioactive and Immunoreactive Growth Hormone in Women.

Abstract

PURPOSE: The purpose was to determine the differences between trained and untrained women for concentrations of BGH and IGH in response to acute resistance exercise. METHODS: Untrained recreationally active women (UT) (N= 12), mean ± SD: 24 ± 2.4 yr, 167 ± 6.3 cm, 68.8 ± 7.3 kg, 27.3 ± 4.0% body fat, and trained women (TW) (N= 12), 25 ± 3.4 yr, 168 ± 7.3 cm, 69.8 ± 6.3 kg, 19.3 ± 2.7% body fat gave informed consent. Trained status was determined by participation in aerobic/resistance training programs for at least 1 year. The women were tested for 1 repetition maximum strength (1 RM) in the squat and were familiarized with the squat test protocol that consisted of 6 sets of 10 repetitions at 75% of their 1 RM with 2 minutes rest between sets. Testing was performed during the early follicular phase between 0630 and 1100 after an 8- to 12-h fast. Pre-exercise blood samples were obtained via standard venipuncture 15 min before the test and post-exercise samples were obtained immediately after the resistance training test protocol. Plasma was collected and assayed for IGH using polyclonal and monoclonal assays. Total BGH was assayed using the rat tibial line in vivo bioassay. A two-way analysis of variance (2 X 2) for group and time were used to analyze the data, with p ≤ 0.05 defined as significance. RESULTS: The TW were significantly stronger than the UT in the squat. Both groups significantly increased their IGH concentrations post-exercise, with the monoclonal assay showing significantly higher values than polyclonal assays and TW showing greater post-exercise values than UT [Monoclonal: (TW: 5 ± 2 to 19 ± 3 μg/L-1, UT: 4.9 ± 2 to 10.2 ± 3.0 μg/L-1)]. BGH did not increase pre to post exercise in either group, yet TW had significantly higher pre-exercise and post-exercise BGH (3900 ± 233 to 4100 ± 323 μg/L-1) than UT women (2500 ± 333 to 2100 ± 223 μg/L-1). BGH was significantly higher than IGH assays at all time points. CONCLUSIONS: Resistance training impacts both the BGH and IGH secretion patterns from the anterior pituitary gland. IGH is acutely increased in response to resistance training in women, with an even higher response in trained women. BGH is chronically higher in trained women than untrained, but shows no response with acute resistance training. These findings may be more responsible for GH’s role in chronic resistance training adaptations.