Q.Muscle fatigue is due to accumulation of ........

During strenuous or prolonged activity, a muscle's oxygen supply can become insufficient for oxidative phosphorylation, so the muscle shifts to anaerobic glycolysis, producing lactic acid. Lactic acid yields far less ATP than aerobic respiration and is toxic, causing tiredness, pain and cramps — this build-up is the direct cause of muscle fatigue. During recovery, the muscle consumes extra oxygen, well above its resting requirement, to oxidise the accumulated lactic acid and restore depleted creatine phosphate and ATP; this extra oxygen consumption is the oxygen debt.

How quickly a muscle fatigues also depends on its fibre type. Red (slow-twitch) muscle fibres are richly supplied with myoglobin, mitochondria and blood vessels, favouring sustained aerobic respiration, so they can work for a prolonged period without much lactic-acid build-up. White (fast-twitch) fibres have less myoglobin and fewer mitochondria, rely more heavily on anaerobic glycolysis for quick, powerful bursts of contraction, and therefore accumulate lactic acid and fatigue sooner.