The potential role of selected body composition phenotypes in the interpretation of the exercise-induced components of the insulin-like growth factor systems

Introduction: Increased adiposity leads to impaired physiologic growth hormone secretion and low and high body mass index (BMI) values increase health risks. However, BMI only measures results in variations in fat-free mass (FFM), fat-free mass index (FFMI), normalized fat-free mass index (NFMI), and body fat mass (BFM). This study evaluated the insulin-like growth factor system responses to the given exercise and their interaction with the changes in BMI, FFM, FFMI, and NFFMI in healthy male participants. Material and methods: A randomized controlled trial with a parallel groups study design was used. Thirty healthy male participants (age: 21.33 ±1.24 years) were divided into three categories: high-intensity incremental (n = 12) and low-intensity constant (n = 12) cycling training groups and control group (n = 6). Training groups performed three times per week throughout eight weeks. VO2max, serum biomarkers, and neuromuscular performance were measured both during baseline and follow-up. Results: The changes in bioavailable IGF were not correlated with BMI (r = –.267), whereas they significantly positively correlated with BFM (r = .321), and inversely significantly correlated with FFM (r = –.472), FFMI (r = –.425), and NFFMI (r = –.379) after 8 weeks of exercise. For relative bioavailable IGF changes, FFM (r2 = 0.17), FFMI (r2 = 0.18), and NFFMI (r2 = 0.14) percent change explained nearly three times the variance as BMI percent change (r2 = 0.07). Conclusions: Increased bioavailable IGF-I suggests an increased anticatabolic effect and inverse interaction with body composition phenotypes following exercise. The partitioning of BMI into FFM, FFMI, and NFFMI rather than relying on sole measures of BMI seem to offer more precise results in the assessment of the interactions between the body composition, neuromuscular performance adjusted with body composition phenotypes, and training-induced changes in insulin-like growth factor system.