Effects of moderate- and high-intensity interval training on muscle remodeling and insulin sensitivity in Wistar rats

Abstract

Exercise-induced modulation of myokines is a key mechanism linking skeletal muscle remodelling to metabolic regulation; however, the extent to which interval-training intensity governs anabolic–catabolic signalling and its metabolic correlates remains unclear. Fifteen healthy male Wistar rats were randomised to control, moderateintensity interval training (MIIT; 70% maximal aerobic speed, MAS), or high-intensity interval training (HIIT; 90% MAS) (n = 5/group). Animals trained three times weekly for six weeks. Gastrocnemius expression of myostatin (MSTN), follistatin (FST), and atrogin-1 (FBXO32) was quantified via RT-qPCR. Metabolic status was assessed using fasting insulin, HOMA-IR, QUICKI, and TyG index. Data were analysed using mixed ANOVA with post hoc comparisons. Both training protocols significantly downregulated MSTN and atrogin-1 and upregulated FST versus control (P < 0.05), indicating a shift toward an anabolic and anti-atrophic transcriptional profile. HIIT elicited greater increases in FST and the FST/MSTN ratio, alongside a more pronounced suppression of MSTN. Metabolically, both protocols improved insulin sensitivity (↓HOMA-IR, ↑QUICKI), with larger effects observed in HIIT. Importantly, insulin resistance indices were inversely associated with MSTN and atrogin-1 expression and positively associated with FST-related indices, supporting a coordinated molecular–metabolic adaptation. Interval training induces integrated anabolic and metabolic remodelling in healthy skeletal muscle, with high-intensity loading amplifying these adaptations. The observed coupling between myokine regulation and insulin sensitivity highlights exercise intensity as a critical determinant of muscle–metabolic crosstalk.