Questions: Fatigued muscles signify lowered body temperature. decreased pH. oxygen recovery. too many metabolic reserves. accumulation of pyruvate.

The answer is the second one: decreased pH.

Explanation for each option:

1. Lowered body temperature: Fatigued muscles are not directly associated with a lowered body temperature. Muscle fatigue is more related to metabolic changes within the muscle cells rather than systemic temperature changes.

2. Decreased pH: This is correct. During intense exercise, muscles produce lactic acid, which lowers the pH within the muscle cells. This acidic environment can contribute to muscle fatigue.

3. Oxygen recovery: While oxygen recovery is important for muscle function, it is not a direct indicator of muscle fatigue. Muscle fatigue occurs when the muscle can no longer sustain its level of performance, often due to metabolic byproducts like lactic acid.

4. Too many metabolic reserves: This is incorrect. Muscle fatigue is typically due to the depletion of metabolic reserves (like glycogen) rather than an excess.

5. Accumulation of pyruvate: While pyruvate is a product of glycolysis, it is usually converted to lactic acid in the absence of sufficient oxygen. The accumulation of lactic acid, rather than pyruvate, is more closely associated with muscle fatigue.

Summary: Fatigued muscles signify decreased pH due to the accumulation of lactic acid during intense exercise.