In an active person, muscle burns fat.
In a sedentary person, fat damages muscle. That’s because adipose (fat) tissue doesn’t just sit there. It secretes inflammatory proteins called adipokines, which damage nearby muscle.
When muscle is damaged, its ability to burn fat declines, which accelerates the accumulation of fat. As the adipose cells fill up, they start to unload excess fat into adjacent muscle, which lowers the metabolic efficiency of muscle even further.