You would have repeatedly heard the phrase “Lactate threshold” from coaches, athletes, fans & sportspeople. Lactate threshold is an intrinsic to endurance sports & training & plays a vital role in exercise performance.
To understand the Lactate Threshold, let us discuss Lactate first. Lactate is a molecule that is produced & consumed by the body during exercise. It forms as a by-product in the muscle cells when glycogen is produced via a process called glycolysis to produce ATP-a high energy molecule which is used for muscle contraction. While blood lactate concentration increases with longer & more intense exercise, it leads to fatigue. However, please remember that fatigue is not caused by elevated lactate levels.
When the end product of glycolysis, pyruvic acid, is converted to lactic acid, it quickly dissociates itself by releasing Hydrogen ion & forming lactate. These hydrogen ions are allowed to accumulate which can cause an acidic environment within muscle cells. This may in turn impair muscle contraction.
Lactate can be cleared to stop its accumulation and increase acidity in muscle cells thereby delaying fatigue. The clearance of lactate from muscle fibre to mitochondria (powerhouse of cell for producing energy) is empowered by specific transporter proteins. Once lactate enters mitochondria, it is recycled back to pyruvate, which through a series of complex molecular cycles is able to produce more ATP which further helps in more muscle contraction.
When we workout, the rate of lactate production increases since more glucose is utilised by contracting muscles. If the rate of lactate production exceeds the rate of clearance, it starts accumulating hydrogen ions inhibiting muscle contraction in a number of ways & thereby causing muscles to fatigue.
The lactate threshold is commonly defined as a point at which lactate formation exceeds lactate clearance for fuel/ATP production. Beyond this point, blood lactate levels inhibit muscle contraction. So do we have a way to improve this lactate threshold? If we can delay the point at which lactate accumulates & begin to fatigue then we can exercise for longer & burn more calories.
People with high lactate thresholds would be able to climb hills (trekkers & adventure folks generally have high lactate thresholds) and power through sprints.
Both genetic & environmental factors help in determining your lactate threshold levels. Let us explore these:
- MCT-1 & PGCA1 are two genes that help in determining your lactate threshold. Both are discussed below
- Your MCT genes encode lactate transporter proteins referred to as monocarboxylate transporters. As discussed above, these transporter proteins transport lactate into mitochondria & facilitate production of more ATP. Out of MCT(s), MCT-1 & MCT-4 transporters are particularly abundant in slow twitch & fast twitch muscle fibres respectively. “A” allele of MCT-1 gene is associated with a high level of MCT-1 transporter protein. If you have “AA” genotype, you have a genetic advantage. In such a case you will be able to delay the muscle fatigue as compared to individuals who have “TT” genotype. If you have “TT” genotype, you have slow lactate clearing potential (rate at which lactate is transported to mitochondria). However this does not mean that you will have to face long workout muscle fatigue. There are distinctive types of workout such as HIIT, MRT & resistance training that can help you elevate your muscular MCT. Such increase in MCT expression in muscle will accentuate increase in acidity & delay fatigue.
- PGC-1a is encoded by the PGCA1 gene and plays an important role in mitochondrial biogenesis (formation of new mitochondria). As mentioned above, lactate is cleared when transported to mitochondria & used to produce more ATP & other molecules needed for better metabolism. A higher number & more dense mitochondria will help in greater & quicker lactate clearing thereby increasing lactate threshold. GG genotypes of PGCA1 gene have higher levels of genes that code for PGC-1a protein & therefore have higher mitochondria density & improved lactate clearing capacity. However if you have AG or AA genotype, you have a lower level of PGC-1a. However, this gap can be minimised through workout. Aerobic exercise can improve production of PGC-1a gene by 30 to 40X & to trigger formation of a new mitochondria. Hence having cardio workout in your workout schedule can help you improve production of lactate clearing mitochondria.
- Given that oxygen is necessary for lactate clearance in mitochondria, factors that impact VO2 max (ability to use oxygen during workout) also affects lactate threshold. These factors include age, gender, fat mass, fat free mass, environmental temperature & workout. Although lactate threshold declines as you age, it is attributed to age related decline in VO2 max.
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