The Impact of K-1 Kickboxing Tournament Fights on Growth Hormone, IGF-1, and Insulin Levels: Preliminary Findings from a Pilot Study in Elite Athletes

Abstract

Background: Evidence on acute endocrine responses to K-1 kickboxing is limited. This pilot study assessed pre-to-post changes in GH, IGF-1 and insulin after a single K-1 bout and explored relationships with training experience (TE), final heart rate (HRFINAL) and perceived exertion (RPE). Methods: Elite male K-1 athletes (n = 10) completed an interclub, referee-supervised three-round bout (3 × 2 min). Venous blood was sampled pre-fight and +2 min. GH, IGF-1 and insulin were assayed (ELISA). Paired t-tests and Pearson’s r quantified changes and associations. Results: GH rose from 1.20 ± 2.05 to 11.27 ± 8.82 ng/mL (p = 0.007; d = 1.85), and insulin from 5.95 ± 1.56 to 12.95 ± 5.95 µU/mL (p = 0.002; d = 1.86); IGF-1 showed no change (200.90 ± 55.89 to 203.00 ± 54.10 ng/mL; p = 0.497). ΔGH and Δinsulin correlated positively with HRFINAL (rp = 0.89 and 0.88, both p < 0.001) and RPE (rp = 0.70 and 0.68; p = 0.024 and 0.031), and negatively with TE (rp = −0.72 and −0.68; p = 0.019 and 0.031). Conclusions: A single K-1 fight elicited large acute increases in GH and insulin but not IGF-1 at +2 min. HRFINAL and RPE tracked response magnitude, while more experienced athletes showed smaller deltas. Findings are preliminary and limited by a small sample, elite-only cohort, in an interclub setting, with immediate sampling and absence of a control group.