Effect of Sprint Exercise on Serum Growth Hormone, Ghrelin, IGF-I, IGF-II and IGF-I Bioactivity

Abstract

PURPOSE: The aim of this study was to examine the growth hormone (GH), insulin-like growth factor (IGF) and ghrelin responses to sprint exercise and to identify whether the number of muscle actions performed during a sprint influences any of these responses. METHODS: Following ethics committee approval, seven physically active males (mean age (SD), 25.5 (2.9) years; body mass index, 24.9 (3.5) kg/m2) gave their informed consent to participate in this study and were familiarised before completing three trials in a random order. In two exercise trials, participants performed a single 30-s sprint on a cycle ergometer against a resistance equivalent to either 7% (FAST) or 9% (SLOW) of their body mass. In the other trial they rested in the laboratory (CON). Blood samples were taken pre-, immediately post-, 10 and 30 min post-exercise, and at equivalent times in the CON trial. These were centrifuged after clotting, stored at −20°C and later analysed for serum concentrations of GH, free and total IGF-I, total IGF-II, IGFBP-1, IGFBP-2 and IGFBP-1-bound IGF-I (binary complex), as well as a marker of IGF-I bioactivity (assessed using an IGF-I kinase receptor activation assay; KIRA). Plasma volume changes were used to correct for haemoconcentration following exercise apart from for free IGF-I and IGF-I KIRA signal. Data were analysed using repeated measures ANOVA and post hoc paired t-tests, with Bonferroni correction for multiple comparisons, where appropriate. RESULTS: The GH response was greater in the FAST than the SLOW trial, but this difference was not significant (maximum change from pre-exercise, 23.5 (24.0) vs. 13.2 (13.7) μg/L, P = 0.07; area under the curve, 520 (588) vs. 295 (353) μg/L/30 min, P = 0.11). Thirty minutes after the sprint in both trials, ghrelin concentrations were significantly lower than pre-exercise (pre-exercise vs. 30 min; FAST, 0.62 (0.19) vs. 0.49 (0.16) μg/L, P < 0.001; SLOW, 0.59 (0.15) vs. 0.47 (0.13) μg/L, P < 0.001) and were lower than at the corresponding time in the CON trial (0.61 (0.17) μg/L; vs. FAST, P = 0.003, n.s.; vs. SLOW, P = 0.001). There were no differences in the ghrelin responses between the two exercise trials. Serum concentrations of free IGF-I, total IGF-I, total IGF-II, IGFBP-1, IGFBP-2 and binary complex, and the IGF-I KIRA signal did not change in response to exercise. CONCLUSION: A single 30-s sprint did not elicit any significant changes in the IGF-related parameters measured in this study, but did result in increased GH and decreased ghrelin concentrations in both exercise trials. Pedal rate influenced the magnitude of changes in GH, but not ghrelin, following exercise.