Effects of a Ketogenic Diet Combined with Aerobic Exercise on Muscle Fiber Types and Exercise Capacity in Tail-Suspended Mice

Objective: To investigate the effects of an 8-week ketogenic diet combined with aero-bic exercise on muscle fiber composition and exercise capacity in mice subjected to simulated microgravity. Methods: Seven-week-old male C57BL/6J mice were randomly assigned to six groups: normal diet (NC), ketogenic diet (KC), normal diet + tail sus-pension (NH), ketogenic diet + tail suspension (KH), normal diet + tail suspension + exercise (NHE), and ketogenic diet + tail suspension + exercise (KHE). During the final two weeks of the intervention, a tail suspension model was employed to simulate mi-crogravity in the tail suspension groups, while the exercise groups performed moder-ate-intensity aerobic exercise. The exercise protocol involved running at 12 m/min for 60 minutes per day, 6 days per week, over the course of 8 weeks. Weekly measure-ments included body weight, blood ketones, and blood glucose concentrations. Respir-atory metabolic rates were assessed before and after tail suspension. Following the in-tervention, all mice underwent a forced exercise test. Blood was collected via the or-bital sinus immediately after the test, and the bilateral soleus muscles were quickly ex-cised. Biochemical analysis was performed to assess blood markers, and Western blot-ting and RT-PCR were used to examine changes in protein and gene expression in skeletal muscle. Additionally, Oil Red O and PAS staining were utilized to evaluate li-pid deposition and glycogen content in the muscles. Immunofluorescence staining was employed to analyze the distribution of MHC muscle fibers in skeletal muscle. Results: Mice in the tail suspension model exhibited weight loss, muscle atrophy, shifts in muscle fiber type, and decreased endurance. However, the combined intervention of a ketogenic diet and aerobic exercise significantly reduced markers of muscle atrophy, enhanced the expression of proteins and genes related to fat metabolism, increased the proportion of MHC-I muscle fibers in the soleus muscle, and decreased the proportion of MHC-IIb fibers. This combined intervention, which primarily utilizes ketone body metabolism, significantly enhanced fat metabolism, thereby improving exercise capac-ity in the mice. Conclusion: The combined intervention of a ketogenic diet and aerobic exercise effectively mitigated muscle atrophy in mice subjected to simulated micro-gravity, enhanced the expression of fat metabolism-related genes in skeletal muscles, and inhibited the transition from slow-twitch to fast-twitch muscle fibers, ultimately improving the exercise capacity of the mice.