# Eccentric treadmill training and skeletal muscle immunometabolic responses in HFD-induced insulin resistance

## TL;DR

Eccentric treadmill training improves insulin resistance in mice, possibly by reducing inflammation through AKT signaling.

## Contribution

This study reveals that eccentric treadmill training reduces insulin resistance via AKT-mediated anti-inflammatory effects in skeletal muscle.

## Key findings

- Eccentric treadmill training reversed HFD-induced insulin resistance and inflammation in skeletal muscle.
- AKT activation suppressed M1 macrophage polarization and increased anti-inflammatory markers in vitro.
- Phospho-AKT levels correlated with reduced pro-inflammatory cytokines and improved glucose metabolism.

## Abstract

In recent years, repeated eccentric exercise has gained increasing attention as a potentially superior intervention for ameliorating insulin resistance (IR). However, the underlying mechanisms responsible for these effects remain incompletely understood. This study aims to investigate the effects and underlying mechanisms of moderate-intensity eccentric treadmill training on skeletal muscle IR.

A mouse model of IR was established using a high-fat diet (HFD) for 12 weeks, followed by an 8-week eccentric treadmill training. In vitro, RAW264.7 macrophages under high-glucose conditions were treated with the AKT agonist SC79 or inhibitor MK2206. Comprehensive assessments included protein localization and expression (immunofluorescence, Western blot), macrophage polarization status (flow cytometry), inflammatory infiltration (H&E staining), cytokine profiles (ELISA), and cellular viability (CCK-8).

HFD-induced IR led to elevated pro-inflammatory factors and reduced GLUT4, F4/80 & phospho-AKT (Ser473) co-localization, IL-10, and Arg-1 levels, all of which were significantly reversed by eccentric training. In vitro, high glucose reduced the phospho-AKT (Ser473)/AKT ratio, while SC79 suppressed an M1-like pro- inflammatory phenotype, as indicated by decreased iNOS and F4/80&CD86 double-positive rates and increased Arg-1 and F4/80&CD206 double-positive rates. These effects were abolished by MK2206.

Moderate-intensity eccentric treadmill training ameliorates HFD-induced skeletal muscle IR, likely driven by AKT-mediated reduction in pro-inflammatory M1 macrophage polarization.