Energy and acidity threshold
In spite of it’s bad reputation, lactate is an important source of energy for aerobic activity. It is only when the muscle is too overload in lactate that fatigue and muscle cramps take over.
The MCT1 gene codes for a lactate transporter. Variants of this gene affect the rate of lactate flow into muscle cells. Fast rate MCT1 genetic setup is associated with both endurance and power performances.
Find out what your MCT1 adaptation holds for you. Understand how you can use it, in training and incompetition.
Lactate is a product of glucose metabolized in the muscle cell. Glucose, stored as glycogen in the myofibril, metabolizes into pyrovate, which is needed for energy production in the mitochondria. Used pyrovate turns to lactate, which is released to the blood.
Since lactate can be turned back into pyruvate to produce energy, lactate is transported from arterial blood back into muscle fibers when energy demand increases. However, lactate can be metabolized into pyrovate only in the presence of oxygen.
During high-intensity anaerobic exercise there is not enough oxygen around to turn lactate back to pyrovate, and so lactate accumulates. As lactate levels rise, the muscle cell content is getting more and more acidic, which results in fatigue and the sense of burning we feel when we exhaust ourselves.
Lactate is both an energy source and a fatigue-causing agent. It is useful for the athlete only when enough oxygen reaches the muscles, as in aerobic activity. On the other hand, anaerobic activity is always accompanied by lactate accumulation, and fatigue is quick to follow, sometimes resulting in cramps and even injury.
Gene: MONOCARBOXYLATE TRANSPORTER 1 (MCT1); SOLUTE CARRIER FAMILY 16 (MONOCARBOXYLIC ACID TRANSPORTER), MEMBER 1 (SLC16A1)
Genomic coordinates (GRCh38): 1:112,911,846-112,956,352
Lactate transport across the plasma membrane is mainly mediated by proton-linked monocarboxylate transporter 1 (MCT1, aka SLC16A1).
“Red muscles”, supporting long term enduring activities, express considerable amounts of MCT1. "White muscles" on the other hand are more suited to short, powerful bouts. They are fast twitching, able to withstand high intensity and produce more power per second, but they express very little MCT1 and tire quickly.
Variants of the MCT1 gene can alter the rate of lactate transport and were found to have significant impact on lactate concentrations inside muscle cells.
Homozygous AA carriers produce more lactate transporters. The increased lactate transport volume provides more lactate to be used as source of energy under oxygen-rich conditions, which is beneficial while performing aerobic activity. However, under low oxygen levels, the surplus lactate accumulates and increases muscle cell's acidity, leading to fatigue and risk of muscle injury. Studies have found that power athletes with the AA genotype exhibit significantly higher injury incidents compared to power athletes with the TT genotype.
Therfore, the AA genotype is advantageous for aerobic performance but disadvantageous for anaerobic activity.
These variants were statistically associated with endurance and power performances on epidemiological studies as well. The AA genotype was found common among endurance athletes, but relatively rare among power athletes. Homozygous TT carriers are more common than expected among power athletes, and less common among endurance athletes.
AA athletes are advised to reduce the intensity of power training. Stretching and warm-up before practice and cool-down afterwards is recommended to avoid injuries. To raise lactate threshold, AA individuals should follow aerobic interval practices, switching between low-intensity effort and high-intensity effort. Another approach to raise lactate threshold is performing high-intensity aerobic effort, followed by a short one minute rest, repeatedly.
TT athletes have lower lactate transport, on average. This is beneficial during high-intensity anaerobic activity, since low levels of lactate delays muscle fatigue and risk of muscle injury. However, this genetic set-up decreases lactate availability as energy source during aerobic effort, and so homozygous TT athletes have an edge in power sports, but are expected to have a disadvantage in endurance sports.