What are the nutrients that are stored in body cells and converted into the major fuel source for muscles called?

The nutrients stored in body cells and converted into the major fuel source for muscles are primarily carbohydrates, specifically glycogen, and fats. Glycogen is stored in the liver and muscle tissues, while fats are stored in adipose tissue. During physical activity, these nutrients are metabolized to provide energy, with glycogen being the preferred source for high-intensity exercise and fats being used more during prolonged, low-intensity activities.