Debunking the Myth: The Real Correlation Between Lactic Acid and Muscle Fatigue

There are many long-held beliefs pertaining to the origin, cause, and effects of lactic acid. Challenging these assumptions, two recent studies from major research universities (Aarhus in Denmark and University of North Carolina) provide evidence that lactic acid is often harmless and at other times beneficial, depending on its state.

When athletes fail in endurance events, it is often attributed to excessive buildup of lactic acid in muscles. In a blog post for, Matt Fitzgerald enumerates some of the traditional beliefs relating to lactic acid:

  • Lactic acid is the byproduct of anaerobic muscle metabolism, produced when working out at high intensities
  • It causes muscle fatigue by a buildup of acid in muscles
  • It cannot be used as muscles as fuel
  • It causes muscle soreness after exercise

On the contrary, the new studies provide evidence for the following characteristics of lactic acid:

  • Muscles do not produce lactic acid at all but rather its close cousin, lactate
  • Lactate is not a byproduct of the anaerobic metabolism but an intermediate product of the aerobic metabolism
  • Around 75 percent of lactate produced by muscles is used as fuel aerobically
  • Buildup of lactate does not cause muscle fatigue but in fact prevents it
  • There is no relationship between lactic acid and muscle soreness
  • Scientists now know that leaky calcium channels, not lactic acid, causes muscle fatigue.

Lactic Acid for Energy

Fitzgerald goes on to describe lactic acid as a key substance in providing energy to the body, disposing of dietary carbohydrate, producing blood glucose and liver glycogen, and assisting in survival in stressful situations.

Once the body has received sufficient oxygen, the lactic acid is used for energy or reconverted back into glucose. This is happening even during rest situations, not only intense exercise. Further studies have shown that lactate production works in correlation to metabolic rates. The concentration of lactate is by far the highest at the point known as the lactate (anaerobic) threshold that occurs usually at 50 to 80 percent of the maximal oxygen consumption, or VO2max in other words. This is the point where production is greater than removal.

Contractile and metabolic functions are hindered when acidity levels are too high. Many athletes choose to use active recovery to help diminish these levels but this may also decrease necessary glycogen levels. For this reason, a combination of active and passive recovery techniques is recommended. This can be achieved by warming down until the breathing has returned to normal, followed by eating a high- carbohydrate meal after the workout to replace glycogen.

The Bottom Line

The above evidence paints a very different picture from traditional beliefs about lactic acid. When training at the lactate threshold, lactic acid buildup can play a small factor in muscle fatigue but this can be overcome by responsible training and diet. In normal situations and during workouts not at the anaerobic threshold, lactic acid is an important source of energy.

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