If you’re like most people you have been told time and time again that lactate/lactic acid is the cause of muscle fatigue, “burning” and tying up. You may even have bought supplements for your horse based on claims that they could reduce lactic acid, or changed your horses diet based on similar claims. Truth is, blaming lactic acid for poor performance, fatigue or muscle damage is like looking at the pile of ashes after a building has burned down and assuming that ashes caused the damage.
Muscles produce lactate continuously. It’s generated during the breakdown of glucose as an energy source. If the horse is at rest, or moving very slowly, most of the lactate is further broken down to pyruvate and goes into aerobic (use oxygen) energy pathways in the mitochondria. However, as the horse moves faster and needs to produce energy very quickly to keep up with the demands, the aerobic pathways are too slow and more energy is generated anaerobically, producing lactate.
Lactic acid isn’t a “waste” product or a toxin; it’s actually beneficial. Lactic acid is a buffer – a way that muscle cells can carry harmful acidity (H+ ions) out of the cells. This is because the lactic acid binds the acidifying hydrogen ions and carries them into the circulation – lactic acid + hydrogen ion = lactate. The lactate is then further broken down as a fuel by other cells, or converted back to glucose in the liver.
People who have been used to thinking of lactate as harmful have trouble accepting this concept, but the evidence is impossible to ignore:
- Sodium bicarbonate is an alkalinizing (anti-acidity) substance that is used to improve performance in racehorses, although now prohibited in most areas. Kesl and Engen from the Veterinary School at Iowa State found that when sodium bicarbonate supplements are used blood is less acid, and muscle recovers from exercise induced acidity quicker, but lactate levels actually are higher
- Horses that are sugar/starch sensitive and tie up show lower levels of muscle enzyme release, an indicator of muscle damage, when put on lower starch diets but the level of lactate produced is identical with high fat vs high starch feeding. Also, starch sensitive horses exercised on high grain diets show more muscle damage, but their lactate levels are the same as normal horses.
- Many studies have failed to find any relationship between lactate levels after exercise and poor performance. In fact, it is often found that the superior performing horses are those with the highest lactate levels after exercise.
A similar association between high lactate production and superior performance has long been recognized in human athletes (e.g. Reilly, 1999).
What this all boils down to is that blood lactate after exercise is nothing more than an indicator of how hard/fast the horse worked. It’s not connected in any way to tying up or muscle damage. Instead of being harmful, lactate is actually a source of energy and reduces the acidity inside hard working cells by carrying the hydrogen ions out of the cell. High blood lactate is associated with superior performance, not fatigue. Next time you see advertising for a supplement or grain that claims to make your horse work harder or longer by lowering lactate, pass it up.
Eleanor Kellon, VMD