Here's why:
* Glycolysis: This is the first stage of cellular respiration, where glucose is broken down into pyruvate. It occurs in both aerobic and anaerobic conditions.
* Anaerobic Conditions: Without oxygen, the pyruvate produced in glycolysis cannot enter the Krebs cycle and electron transport chain, which are the primary ways cells produce ATP in aerobic respiration.
* Lactic Acid Fermentation: To continue generating a small amount of ATP, cells resort to a process called lactic acid fermentation. Pyruvate is converted into lactate, using NADH as an electron donor. This regenerates NAD+ which is needed for glycolysis to continue.
Key Point: While lactic acid fermentation allows some ATP production, it's far less efficient than aerobic respiration. Lactic acid buildup can also lead to muscle fatigue and soreness.
