There are two main types of muscle fibers: slow-twitch and fast-twitch. Slow-twitch fibers sustain repeated contractions but generate less power, while fast-twitch fibers contract quickly and powerfully but fatigue easily. Slow fibers use aerobic cellular respiration to break down glucose, producing more ATP than fast fibers, which can operate anaerobically. Cellular respiration yields carbon dioxide, water, and ATP to power cellular functions, while photosynthesis and respiration provide energy for life through the production and consumption of glucose and oxygen.