This question is about exercise. During vigorous exercise, anaerobic respiration occurs in a person's body. Explain two effects of anaerobic respiration on the person's body.

During vigorous exercise, the cardiovascular system cannot supply oxygen to the muscles fast enough for aerobic respiration to meet the energy demand. Therefore, the muscle cells also respire anaerobically. 1. **Lactic Acid Build-up:** Anaerobic respiration in animals breaks down glucose into lactic acid (glucose → lactic acid). This lactic acid accumulates in the muscle tissue. The build-up of lactic acid lowers the pH in the muscle cells, which inhibits enzyme activity and leads to muscle fatigue, pain, and cramp. This is why you feel a "burn" and your muscles get tired during intense exercise. 2. **Oxygen Debt:** Lactic acid is toxic and must be removed. After exercise stops, the person continues to breathe heavily. The extra oxygen taken in is used to break down the accumulated lactic acid (by oxidising it back to carbon dioxide and water, or converting it to glucose in the liver). This requirement for extra oxygen after exercise is known as an oxygen debt.