In short, through the process of photosynthesis, plants grow, animals eat plants. The football player eats food that comes from the plants and/or animals. The food becomes the athlete's energy, sometimes stored as fat, but also stored in our livers and muscles, most often as carbohydrate energy. These carbohydrates came from the plant and animal materials and are stored as glycogen which gets converted into glucose for use by the athletes muscles. Energy that originated from the sun, but is now energy used by the football player in the game.
