Lactate and fatigue?

One of the biggest myths athletes have picked up is that lactate is our enemy and that it causes fatigue — but that’s not true at all.

Lactate is a marker of what can cause fatigue, but lactate itself does not cause fatigue, and it isn’t even a "waste product" — it’s FUEL!

Lactate and acidity

Lactate itself is not harmful to the body, but producing large amounts of it leads to a drop in pH. This acidic environment has a negative effect on performance and on the recovery processes after exercise. That’s exactly why we measure lactate — to find the balance where we can do more and go harder, but without the strong negative consequences that would impair recovery and further progression.

Lactate as an energy source

As exercise intensity rises, athletes start using more carbohydrates as an energy source. As a result, more lactate is produced. About 30% of all the glucose we use during exercise comes from "recycling" lactate back into glucose.

At high exercise intensities the lactate concentration is high and athletes get tired — this is one of the reasons people have grown used to thinking that lactate is a by-product that causes fatigue. However, there is no cause-and-effect relationship between lactate and fatigue. During intense exercise, lactate production is many times higher than at rest.

The role of glycolysis and ATP

Since more and more ATP (adenosine triphosphate — the body’s energy currency) is required to meet the demands of an increasing workload, the contribution of the glycolytic anaerobic system also increases. The end product of the glycolytic anaerobic system is pyruvate, which is either oxidized in the mitochondria or converted into lactate.

The higher the flow of glucose into the cell, the higher the lactate production, regardless of the presence of oxygen. During high-intensity exercise, type II muscle fibers are fully recruited because of the high contractile demands placed on skeletal muscle to produce energy (ATP). Type II muscle fibers preferentially use glucose, which leads to the production of large amounts of lactate.

Hydrogen ions and muscle fatigue

The release of hydrogen ions (H⁺) associated with lactate can lead to a significant drop in the pH of contracting muscle, resulting in acidosis. This excessive accumulation of H⁺ — not only from lactate, but also from the breakdown of ATP for muscle contraction — can interfere with muscle contraction in several places.

For example, H⁺ can compete with calcium (Ca²⁺) for the binding site on troponin C, a protein involved in the regulation of muscle contraction.

H⁺ can also inhibit the release of calcium. Both processes are involved in muscle contraction. All of this can lead to a significant reduction in muscle performance.