High-intensity interval training (HIIT) increases insulin-like growth factor-I (IGF-I) in sedentary aging men but not masters’ athletes: an observational study

Introduction: The aim of this investigation was to examine the impact high-intensity interval training (HIIT) on serum insulin-like growth factor-I (IGF-I) in active compared with sedentary aging men.

Methods: 22 lifetime sedentary (SED; 62?±?2 years) and 17 masters’ athletes (LEX; 60?±?5 years) were recruited to the study. As HIIT requires preconditioning exercise in sedentary cohorts, the study required three assessment phases; enrollment (phase A), following preconditioning exercise (phase B), and post-HIIT (phase C). Serum IGF-I was determined by electrochemiluminescent immunoassay.

Results: IGF-I was higher in LEX compared to SED at baseline (p?=?0.007, Cohen’s d?=?0.91), and phase B (p?=?0.083, Cohen’s d?=?0.59), with only a small difference at C (p?=?0.291, Cohen’s d?=?0.35). SED experienced a small increase in IGF-I following preconditioning from 13.1?±?4.7 to 14.2?±?6.0?μg·dl^?1 (p?=?0.376, Cohen’s d?=?0.22), followed by a larger increase post-HIIT (16.9?±?4.4?μg·dl^?1), which was significantly elevated compared with baseline (p?=?0.002, Cohen’s d?=?0.85), and post-preconditioning (p?=?0.005, Cohen’s d?=?0.51). LEX experienced a trivial changes in IGF-I from A to B (18.2?±?6.4 to 17.2?±?3.7?μg·dl^?1 p?=?0.538, Cohen’s d?=?0.19]), and a small change post-HIIT (18.4?±?4.1?μg·dl^?1 p?=?0.283, Cohen’s d?=?0.31]). Small increases were observed in fat-free mass in both groups following HIIT (p?d?=?0.32–0.45).

Conclusions: In conclusion, HIIT with preconditioning exercise abrogates the age associated difference in IGF-I between SED and LEX, and induces small improvements in fat-free mass in both SED and LEX.