MuscleScience

Lactic acid cause the burn you feel under intense exercise. It is important to not say soreness because people mis-interpret this as causing long term soreness in the muscles.

I understand your point about acidosis and bicarbonate not being the only mechanism for regulating pH. I could talk about all the other methods such as respiratory blow off ect ect. But most of that stuff is beyond the scope of this writing and frankly the bicarbonate explanation is good enough to get the point across.

Lactate threshold (LT) in its most basic explanation is the point were lactate is being produced faster than the body is able to process it. There is another term used that has a slightly different definition termed the Onset of blood lactate accumulation (OBLA) this is similar to the LT in that it is a second onset of rapid lactate accumulation during intense exercise. In the lab exercise physiologist usually do not make a distinction between the two. Typically what is looked for is a blood lactate concentration of 4 mmol/L of blood.

With training the LT can be increased to have it moved at higher heart rates/exercise intensities. For endurance runners this is important because for them if they know at what heart rate the LT is reached they can train at intensities that bounce above and below that to help increase the LT. During a competition if they know that at for example their LT is reached at about 170 bpm they can run and pace themselves at that level as to not become to fatigued during the race. Because one thing that is known about the LT is that exercising durations are greatly reduced after the LT is reached. If a runner can avoid becoming overly fatigued before the final push to the end of the race. Those energy stores can be used for that final push to the finish line.

With training like sprinting the muscle cells become more efficient at producing energy from carbohydrates because of the increase in anaerobic enzymes in the muscle cells. They also shuttle lactate better to the blood for clearance. With endurance training lactate production is reduced because of increase in mitochondria in the cells and of course increased O2 carrying capacity of the blood. It is important to remember that even under aerobic conditions some lactate is produced by the muscle cells.