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Lactate and Performance

Lactate is the byproduct of glucose utilization by muscle cells. The higher the glucose flux into the cell, the higher the lactate production—independently of oxygen availability. During high intensity exercise, Type II-Fast Twitch muscle fibers are fully recruited, due to high contractile demands by skeletal muscle to produce energy (ATP). Type II muscle fibers are highly glycolytic (they use lots of glucose) which results in the production of high amounts of lactate. This production is a natural by-product of glucose utilization by skeletal muscle cells.

During intense exercise, lactate production is many times higher than that of resting levels. The release of hydrogen ions (H+) associated with lactate can cause an important reduction of contractile muscle pH, resulting in acidosis. This excessive accumulation of H+, not only from lactate, but also from ATP breakdown for muscle contraction (ATP hydrolysis), may interfere with muscle contraction at different sites.

For example, it may compete with Calcium (Ca++) for Troponin C binding site (a protein involved in muscle contraction regulation). H+ may also inhibit calcium release and re-uptake from sarcoplasmic reticulum. Both processes are involved in muscle contraction. All this can result in a decrease muscle contraction capacity which can cause an important decrease in peak twitch force, a decrease in maximum muscle shortening velocity and performance.

We know very well that the better the competitive and training level of an athlete is, the less blood lactate accumulation that is observed. In table-1 we can observe blood lactate levels of different cycling categories at different exercise intensities (watts/kg) that I have collected over the years during physiological tests. We can clearly see that the higher the competitive level of a cyclist, the lower the blood lactate and the higher the power output and performance.

Table 1. Differences in Blood Lactate levels (mmol/L)between competitive cyclists of different levels. Table Modified from San Millán et al, 2009

This lower blood lactate levels observed in the top athletes is due to an enhanced lactate clearance capacity. Lactate can be exported to the blood for clearance and energy purposes in pretty much every organ in the body. However, this process takes time (minutes) while lactate is produced continuously during exercise.

Well trained athletes are very efficient and export less lactate to the blood as they clear it in higher amounts right in the lactate producing muscle which takes seconds or milliseconds. This is very advantageous as it allows contractile muscles a faster H+ removal as well as a faster lactate “recycling” for extra energy (ATP).

During exercise, lactate is mainly produced in fast twitch muscle fibers, which use lots of glucose for energy. It is cleared mainly by slow twitch muscle fibers. This is a complex process involving different lactate-specific transporters and enzymes. Fast twitch fibers have a high content of one transporter called MCT-4 (Monocarboxylate-4) which transports lactate away from these fibers. Slow twitch fibers possess a transporter called MCT-1 which takes lactate inside these fibers. That lactate is then converted to pyruvate in the mitochondria by an enzyme called mLDH (mitochondrial lactate dehydrogenase), to then finally synthesize ATP (energy).

Endurance training (Zone 2) has the purpose of improving lactate clearance capacity by increasing the number of mitochondria to clear lactate mainly in slow twitch muscle fibers as well as by increasing the number of MCT-1 and mLDH. Both high intensity and endurance training increases the number of MCT-4 to increase lactate transport away from fast twitch fibers.

As shown in table-1 lactate is probably the parameter that discriminates the most between different levels of athletic performance. Lactate analysis can give us a lot of information on muscle metabolism during exercise, where we can indirectly assess mitochondria density, oxidative and substrate utilization status or muscle fiber recruitment patterns.

Lactate testing is probably the best way to assess muscle metabolic stress and performance, especially in endurance athletes. It is also probably the best method that we have to predict performance in endurance events as well as an excellent parameter to prescribe individual exercise training zones for athletes. Among those training zones “lactate threshold” is that special training zone we all want to train and improve. The only way though to directly measure lactate threshold is by doing lactate testing.

In conjunction with the INSCYD performance analysis software, we take into account, and connect to one another, the most important metrics for training purposes:

VO2max – maximum aerobic capacity

VLamax – maximum glycolytic (anaerobic) capacity

Anaerobic threshold and how it is composed

Accumulation of Lactate and how quick you can recover from it

Fat combustion rate and FatMax

Carbohydrate combustion during training & racing

Economy – how much energy you need at a given speed.

Each of the above metrics is measured by INSCYD and is critical for your performance. Remember: each sport performance is predictable and can be broken down into these fundamental elements. Get in touch today and book your consultation and test session.

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