In endurance running there has been much study and debate into the role of lactate. For years, lactate was seen as a waste product that caused fatigue and muscle soreness, the ‘lactic fatigue’ theory. However in following years research has shed light on the crucial role lactate plays in providing energy to the muscles through mechanisms such as the lactate shuttle and in regulating many physical processes such as hunger.
First of all, what exactly is lactate? Lactate is a simple carbohydrate molecule, that is, it contains carbon, hydrogen and oxygen. Lactate is not a waste product; it is a valuable fuel source for the body. Lactate is produced when glucose undergoes glycolysis, a process that occurs in the muscles during intense exercise when oxygen availability is limited. As glycolysis proceeds, lactate accumulates in the muscle cells, leading to the familiar “burn” sensation experienced during strenuous activities.
Rather than being a hindrance, lactate serves as an essential energy source during endurance running. In fact, lactate can be utilized by both muscles and other organs as fuel. Muscles can use lactate to generate additional energy, taking in the lactate through a mechanism known as the lactate shuttle. This mechanism allows muscles to sustain prolonged exercise by utilizing lactate as a valuable source of fuel.
But how can we train our bodies to use lactate more effectively given it is a fuel source? This is where two things come into play you can use in your training.
The first is a large amount of Zone 1 and Zone 2 training which has been proven to increase performance [1]. Using heart rate zones as a guide, the use of zone 1 and 2 training in a has been shown to increase the activity of the lactate shuttle and the ability for your slow twitch muscle fibres to utilise lactate as a source of fuel. Zone 2 training also promotes your Type 2a muscle fibres to take on more characteristics of Type 1 muscle fibres which is higher fatigue resistance and fat-burning adaptation [2]. Beyond that, low-intensity training also increases the amount of blood capillaries (capillarization) reaching muscle and the number of mitochondria present inside the muscle, building more of these essential power plants of the muscle.
The second part is training your body to be able to withstand higher amounts of lactate. Normally the lactate accumulates in the bloodstream along with a hydrogen ion, it’s the hydrogen ion that makes the process build up acid in the muscles and bloodstream leading to a range of things within the body that occur to keep this acid buildup from getting worse. In simple terms there is two points of exercise intensity where big changes occur when it comes to lactate concentration (and therefore the acid buildup). The first is what is known as the lactate steady state, or LT1. This is the point where intensity matches the amount of lactate the body can use up, and the other is LT2 or the lactate threshold. At LT1 if you have to describe your exertion at this point it won’t be that hard, maybe a 6 out of 10. LT2 is fairly uncomfortable. By the way, when you watch gives you a threshold heart rate, this is usually LT2.
Knowing this, we can then focus efforts on training between LT1 and LT2 or just above it, to increase the body’s tolerance of that buildup and kick off a bunch of metabolic adaptations to be able to deal with it better next time around.
Now onto the role of the lactate shuttle The lactate shuttle refers to the transport of lactate from the muscle fibres where it is produced to other tissues and organs, such as the heart, liver, and even other muscles, where it is utilised as an energy source.
The lactate shuttle operates through a series of complex mechanisms involving lactate transporters, enzymes, and specific receptors. These components work together to regulate the movement of lactate between cells and facilitate its uptake and oxidation in various tissues. The lactate shuttle system ensures that lactate produced in one area of the body is efficiently distributed to other regions where it can be utilised, promoting energy production and overall endurance.
The lactate shuttle plays a vital role in optimizing energy production during endurance running. By efficiently transporting lactate to other organs and muscles, it helps to:
- Spare glycogen: By utilizing lactate as a fuel source, muscles can preserve their glycogen stores, which are crucial for sustaining prolonged exercise. This preservation of glycogen allows runners to maintain a steady pace and delay the onset of fatigue.
- Enhance aerobic capacity: The lactate shuttle system aids in the oxidative capacity of the muscles by providing an additional energy source. This enables endurance runners to enhance their aerobic capacity, allowing them to endure longer periods of exercise.
- Promote muscle recovery: Contrary to the misconception that lactate causes muscle soreness, the lactate shuttle actually assists in muscle recovery. Lactate produced during exercise can be taken up by neighbouring muscle fibres, reducing muscle damage and promoting repair and adaptation.
More recent research has also highlighted the role of lactate in other exercise physiology. A compound known as Lac-Phe which is formed from lactate production during exercise has been found to lower hunger levels in humans, providing a very interesting topic for further research [3]. Personally knowing after a hard effort how I don’t always feel hungry I can see how this might be the case! It has also been found to have a significant range of effects including increased mitochondria in muscle, activation of genes, providing a fuel source for the heart and many other effects [4].
In conclusion, lactate plays a crucial role in endurance running. It is not merely a waste product but a valuable energy source that can be utilized by various organs and muscles. The lactate shuttle system ensures the efficient transport and utilisation of lactate, optimising energy production and promoting endurance. By understanding the role of lactate in endurance running, athletes can better utilise this valuable resource to enhance performance and achieve their running goals.
References:
- Muñoz, I., Seiler, S., Bautista, J., España, J., Larumbe, E., & Esteve-Lanao, J. (2014). Does polarized training improve performance in recreational runners?. International journal of sports physiology and performance, 9(2), 265-272. https://www.researchgate.net/profile/Jonathan-Esteve/publication/237096628_Does_Polarized_Training_Improve_Performance_in_Recreational_Runners/links/0a85e530cba391399a000000/Does-Polarized-Training-Improve-Performance-in-Recreational-Runners.pdf
- Pette D, Staron RS. Mammalian skeletal muscle fiber type transitions. Int Rev Cytol. 1997;170:143-223. doi: 10.1016/s0074-7696(08)61622-8. PMID: 9002237. https://pubmed.ncbi.nlm.nih.gov/9002237/
- Li, V. L., He, Y., Contrepois, K., Liu, H., Kim, J. T., Wiggenhorn, A. L., … & Long, J. Z. (2022). An exercise-inducible metabolite that suppresses feeding and obesity. Nature, 606(7915), 785-790. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9767481/
- Brooks, G. A., Osmond, A. D., Arevalo, J. A., Curl, C. C., Duong, J. J., Horning, M. A., … & Leija, R. G. (2022). Lactate as a major myokine and exerkine. https://escholarship.org/content/qt2sx1s48h/qt2sx1s48h.pdf