In Greek, the prefix a- or an- means "not" or "without", and bios means "life". Anaerobic sports and exercise, such as gymnastics, weight lifting, and sprinting, are of high intensity but short duration, so they don't involve much oxygen intake. Anaerobic exercise triggers a different type of cell activity from aerobic exercise. As a result, it doesn't do much for your heart and lungs and it doesn't burn off fat; what it does do is build muscle. Anaerobic bacteria are bacteria that live without oxygen. They're responsible for several nasty conditions, including tetanus, gangrene, botulism, and food poisoning. They often live in deep wounds, so a bad dog bite—or, even worse, a human bite—can be dangerous, since the mouth is full of anaerobic bacteria. But most anaerobic bacteria are harmless, and many are essential to our lives.