What is blood lactate and why is it important for exercise?

Lactate — once incorrectly viewed as a cause of muscle fatigue during exercise — is actually a fatigue biomarker that also plays a role in energy production and metabolic regulation in your body and brain.

Lactate was once thought of as a bad actor. This substance was said to be a metabolic poison that was responsible for the soreness we experience in our muscles after strenuous exercise. But scientists now have a very different view of lactate, seeing it as a valuable form of energy for the brain, heart and skeletal muscles. In fact, your body benefits from lactate production not only during exercise, but also at rest. But what is blood lactate, what’s the difference between lactate and lactic acid, and how do athletes use lactate to their advantage? We will explore this and other issues. 

Lactate vs. lactic acid — what’s the difference?

Before we go into further detail, let’s clarify some terminology. You might hear people talk about lactic acid instead of lactate. What is the difference? Lactate is the conjugate base of lactic acid — which simply means that lactic acid has one more hydrogen ion than lactate. Although the two terms are often used interchangeably, it is lactate — and not lactic acid — that is being produced by your body.

For many decades, it was assumed that glycogen and glucose were degraded in cells to form permanent pools of pyruvate, a lactate precursor. This pyruvate would then be converted to lactate during periods of intense exercise when your body needs to temporarily move into an anaerobic mode. However, this thinking turned out to be incorrect — as pyruvate is continuously converted to lactate, even at rest.

Furthermore, lactate is neither a metabolic poison nor a waste product. On the contrary, the compound is a key energy source. Once lactate forms, it is quickly burned in the mitochondrial reticulum (a network of mitochondria) to produce the energy molecule ATP.

A 2014 review noted that lactate is increasingly being viewed as a biomarker of fatigue — and not the direct cause. The review pointed out many of the crucial roles that lactate plays:

  • Lactate is a key energy substrate in skeletal muscle fibers, providing us with sufficient energy during exercise.

  • Lactate increases the number of mitochondria (the energy powerhouses of cells) in muscle cells.

  • Lactate plays a key role in supplying energy for cognitive functioning during exercise. One way it does this is by optimizing the function of gamma-aminobutyric acid (GABA) receptors, ensuring that your body responds properly to decreases in cell pH during exercise.

The 2014 review also pointed out that lactate can neutralize certain harmful components in the body:

  • Lactate accumulation is believed to counteract the negative effects of undesirable metabolites like inorganic phosphate and potassium.

  • Lactate is known to remove muscular protons and act synergistically with catecholamines to reduce fatigue. Catecholamines — which include dopamine, norepinephrine and epinephrine (adrenaline) — are released into the body in response to physical and emotional stress.

Interestingly, the physiological cause of exercise fatigue is increasingly being attributed to these other metabolites as opposed to lactate.

In 2018, another key review written by physiologist and lactate expert George Brooks further set the record straight about lactate and its benefits. Brooks coined the term “lactate shuttle” to describe the various feedback loops in which lactate acts as an intermediary to support cells in tissues and organs throughout the body. In addition to reiterating the role of lactate as a major source of energy, Brooks characterized lactate’s other roles as:

  • A precursor for making more glucose in the liver (a process called gluconeogenesis), which helps to reduce blood sugar levels

  • A signaling molecule that communicates with different tissues as it circulates through the body and blood, which affects the expression of genes responsible for managing stress

What science says about the importance of lactate

Now that we have debunked these myths about lactate as a harmful substance, we can focus on what the latest science is telling us about the physiological roles that this crucial fuel source plays:

  • Muscle cell regeneration: A 2020 review demonstrated that lactate appears to play a key role in muscle regeneration via satellite cells (cells that proliferate in response to injury and turn on skeletal muscle cells). However, the precise mechanisms by which lactate influences satellite cells remain unknown.

  • Hunger suppression: Another 2020 review explored the role that lactate may play in controlling energy intake. High blood lactate accumulation is associated with the suppression of the hunger hormone, ghrelin, which sends a signal to your brain to make you feel hungry.

  • Formation of “the anti-hunger molecule: Related to appetite, there appears to be a link between lactate levels and a newly discovered molecule called Lac-Phe (N-lactoyl-phenylalanine), known as the anti-hunger molecule. A 2022 study demonstrated how the spike in lactate that occurs during exercise triggers the formation of Lac-Phe. This, in turn, reduces hunger and leads to weight loss in rats.

  • Disease marker: A 2022 paper argued that, while elevated lactate levels during exercise are necessary for healthy cells, chronic exposure to lactate may cause cellular disruption. This disruption may lead to cancer, heart failure, and type 2 diabetes. The authors exposed heart muscle cells in rats to various concentrations of lactate for up to 48 hours. This long-term exposure led to several negative outcomes.

  • Association with post-COVID-19 syndrome: Intriguingly, another 2022 study noted that increased blood lactate accumulation during exercise is also associated with what is called “post-COVID-19 syndrome” or post-acute sequelae of SARS-CoV-2 — a syndrome called PASC for short. The underlying pathogenesis of PASC is not well understood, and there is an urgent need for treatments.

  • Antidepressant action: A 2021 study reported that lactate reverses the effects of corticosterone on depressive behavior in rats. They also found that lactate promotes the survival and proliferation of new neurons in the hippocampus.

  • Association with bipolar disorder: A 2018 review concluded that people with bipolar disorder may have elevated cerebrospinal lactate levels. However, this is still unclear, and more research is necessary. 

What athletes need to know about lactate

At rest, your muscles release lactate into the blood at a slow rate, but during high-intensity exercise, your muscles produce lactate rapidly — so quickly, in fact, that lactate starts building up in your blood. At some point, you will hit a “lactate threshold” at which point your body can no longer flush lactate faster than the rate of accumulation. This will force you to slow down. Otherwise, you will simply not be able to go on anymore.

But what happens to your lactate when you are taking a slow walk for an hour? Once again, the muscles will initially push lactate into the blood. However, over time, the situation may reverse, and your muscles may start taking up lactate again. This “shuttling” of lactate between muscles and blood is still not fully understood.

Conditioning in sports is all about using lactate optimally. When lactate is taken up efficiently, the mitochondrial reticulum in your cells grows larger and provides your body with more energy. So, what kinds of exercise are best if you want to optimize your lactate profile?

  • An older study from 2000 suggested that endurance training improves muscle capacity for lactate utilization. But are the optimal conditions only met under both high-volume and high-intensity training? The authors were unsure.

  • High-intensity interval training (HIIT) has been shown to result in cognitive benefits through a mechanism that is thought to be driven by lactate. HIIT (also called sprint interval training) is a cardiovascular exercise strategy that alternates short periods of intense anaerobic exercise with less intense recovery periods. This goes on until you are too exhausted to continue. However, it is still not understood which specific HIIT conditions (work interval durations, session volumes, and work-to-rest ratios) are optimal for lactate uptake. A future literature review is investigating this question.  

Taking supplements to enhance lactate

Now that we understand the benefits of lactate, are there any supplements you can take to temporarily increase your lactate levels? Here are some possibilities:

Key takeaways

Lactate is a hot research area right now. Once seen as a toxic metabolite, lactate is now being appreciated for its protective effects. Among other attributes, lactate (often interchangeably referred to as lactic acid) is recognized as a major energy source, a precursor for glucose formation, and an important signaling molecule. Since 2020, new evidence has been published that supports the role of lactate in muscle cell regeneration, hunger suppression, as a disease biomarker and as an antidepressant. Conditioning the body to use lactate more efficiently is a major goal in fitness training. While early studies suggest that certain supplements, such as caffeine, could improve lactate use and athletic performance, more studies are needed before we fully understand how to maximize the function of a molecule that until recently was viewed as an enemy. 

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