Physical inactivity, adiposity, and metabolic dysfunction exhibit a bidirectional and dynamic relationship across the life course, where physical inactivity contributes to metabolic dysfunction and metabolic dysfunction reduces physical activity, with the strength and direction of these influences varying by developmental stage.

When a person moves less, their muscles don't contract as often, which makes it harder for the body to use sugar and fat for energy. This causes fat to build up in the wrong places like the liver and muscles, and fat tissue becomes inflamed. The body then becomes less able to respond to insulin, leading to high blood sugar and energy imbalance. This metabolic damage makes the person feel more tired and less motivated to move, creating a cycle where inactivity and metabolic problems reinforce each other.