Exercise such as sprinting or heavy lifting, done without relying primarily on oxygen for rapid energy production, is described as anaerobic. The word comes from Greek roots meaning “without air,” and in exercise science it refers to energy production that can meet intense demands faster than aerobic metabolism can.
Anaerobic efforts are usually short and powerful: a 100-metre sprint, a heavy deadlift, an explosive jump, or a brief burst of high-intensity interval training. Muscles draw on stored ATP and creatine phosphate first, then increasingly use anaerobic glycolysis, which breaks down glucose to make more ATP quickly.
A common mix-up is treating “anaerobic” as meaning the body stops using oxygen entirely. In real exercise, aerobic and anaerobic systems work simultaneously; the label identifies the dominant energy pathway. Lactate is produced during intense glycolysis and can be recycled as fuel, so it is not simply a waste product or the sole cause of next-day soreness.
Aerobic exercise, such as distance running or steady cycling, relies more heavily on oxygen and can generally be sustained longer. Anaerobic training is especially associated with power, speed, and muscular strength.