The Science Behind Lactate Accumulation
As the intensity of exercise increases, the body reaches a point where the level of oxygen within the cell’s mitochondria becomes insufficient to meet the energy demands. This oxygen deficit limits the ability to fully oxidize pyruvate, a key intermediate in cellular respiration. To compensate for the reduced aerobic capacity, the body relies more heavily on anaerobic glycolysis, a process that generates ATP more rapidly but less efficiently.
Lactate Threshold
The lactate threshold (LT) is a physiological point during exercise where the rate of lactate production exceeds the rate of lactate clearance. This leads to a significant increase in blood lactate concentration. The LT is influenced by various factors, including training status, genetics, and environmental conditions.
Lactate Threshold Vs Anaerobic Threshold
For glycolysis to continue to produce ATP, certain compounds that were “used up” (i.e. reduced) in glycolysis must be regenerated (i.e. oxidized) so that the process can continue. For this to happen the excess pyruvate is reduced to lactate. Lactate production begins to occur at a rapidly increasing rate (due to maintaining a high level of intensity for either seconds or minutes, depending on conditioning). This point is known as the Lactate Threshold (LT). Note: this is also often referred to as the Anaerobic Threshold (AT). The only essential difference between the lactate and anaerobic threshold is that the lactate threshold is measured through blood concentrations of lactate and the anaerobic threshold is measured by a ventilatory (gas exchange) test.
What is Blood Lactate Accumulation?
Lactate accumulation in the blood is signal that there is not enough oxygen getting to the working muscles (i.e. “going anaerobic”). During energy production, there are several reactions that cause the release of a hydrogen ion (H+). This causes a decrease in blood pH (i.e. making the blood more acidic). Without going into detailed biochemistry, when the body is “aerobic” it uses buffering capabilities so that the pH of the blood does not go down. However, when there is not enough oxygen being supplied to the working muscles, muscle acidosis can begin.
Why do The “burning” sensation in muscles is attributed to this muscle acidosis and correlates to the accumulation of lactate. The point where so much lactate accumulates that exercise intensity is forcibly decreased (due to muscle acidosis induced fatigue) is known as the Onset of Blood Lactate Accumulation (OBLA).
Why is this important? These values (LT, AT, OBLA) attempt to find the point where an athlete will “redline”. The athlete who can delay acidosis the longest typically wins the race. High lactate values increase injury risk due to the disturbance of coordination capacity because the affected muscle(s) is (are) unable to sufficiently contract.
At rest, it takes about 25 minutes to remove 50% of the accumulated lactate and muscle acid, and about 75 minutes to remove 95% of the buildup. Lactate will either be converted back to glucose in the liver at rest (gluconeogenesis), excreted in urine or metabolized for fuel by other organs (brain, heart or other muscles).
If sufficient rest/recovery between intense workouts is not achieved there may be severe damage to muscle cells. This damage may take days or weeks for full repair, which results in lost performance and training time.
Key Points:
- Oxygen Limitation: Insufficient oxygen supply to the muscles triggers a shift towards anaerobic metabolism.
- Pyruvate Buildup: The accumulation of pyruvate leads to its conversion into lactate via the enzyme lactate dehydrogenase.
- Lactate Clearance: The body continuously removes lactate from the blood through various mechanisms, including oxidation in the heart and other tissues, and conversion to glucose via the Cori cycle.
- Training Adaptations: Regular endurance training can increase the lactate threshold and delay the onset of blood lactate accumulation, allowing athletes to sustain higher exercise intensities for longer periods.
Implications for Exercise Performance
Understanding the lactate threshold and OBLA is crucial for optimizing training and performance. By training at intensities that challenge the lactate threshold, athletes can improve their aerobic capacity and delay fatigue. Additionally, monitoring blood lactate levels can provide valuable insights into training response and recovery.
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