Correct Option (D)
The sensation of fatigue in muscles after prolonged strenuous physical activity is primarily attributed to the accumulation of lactic acid. During intense exercise, when oxygen supply to muscle cells becomes insufficient to meet energy demands, anaerobic respiration occurs. This process breaks down glucose into lactic acid, producing a small amount of ATP. The buildup of lactic acid lowers the pH within muscle cells, inhibiting enzyme activity and interfering with muscle contraction, leading to the sensation of fatigue and muscle soreness.
Incorrect Options:
Option A: While a decrease in oxygen supply (hypoxia) does trigger anaerobic respiration and subsequent lactic acid production, it is the accumulation of lactic acid itself, rather than merely the reduced oxygen supply, that directly causes the fatigue sensation.
Option B: Minor wear and tear of muscle fibres can occur during strenuous exercise, contributing to muscle soreness and damage. However, this is a distinct physiological process from the immediate sensation of fatigue experienced during or immediately after the activity, which is more directly linked to metabolic byproducts.
Option C: Depletion of glucose (muscle glycogen) is a factor in prolonged endurance activities, leading to exhaustion. However, the immediate sensation of fatigue during strenuous work is more closely associated with the metabolic consequences of anaerobic respiration, specifically lactic acid accumulation, rather than the complete absence of glucose.