Final answer:
Blood lactate levels begin to raise when exercise intensity is above the lactate threshold, marking the point where lactate accumulates faster than it can be cleared, typically signaling the onset of fatigue.Option B is the correct answer.
Step-by-step explanation:
Blood lactate will begin to raise when exercise is performed at a rate that is above the lactate threshold. The lactate threshold is the exercise intensity at which lactate begins to accumulate in the blood at a faster rate than it can be removed. This is often coinciding with the onset of fatigue, due to factors such as the exhaustion of energy reserves and the accumulation of lactate in the muscle leading to an increased acidity and decreased pH of the blood.
Lactate production is the result of anaerobic glycolysis, where the body breaks down glucose for energy without the presence of oxygen, forming ATP and lactate as a result. Normally, pyruvate, a product of glycolysis, enters the TCA cycle in the mitochondria for further energy production. However, during high-intensity exercise, when the rate of glycolysis exceeds the rate of the TCA cycle, the pyruvate is converted into lactate. This process is a natural response to the increased energy demand during intense exercise, and over time, training can improve the body's ability to deal with the elevated lactate levels.