Protective effects of lactic acid on force production in rat skeletal muscle

J Physiol. 2001 Oct 1;536(Pt 1):161-6. doi: 10.1111/j.1469-7793.2001.t01-1-00161.x.


1. During strenuous exercise lactic acid accumulates producing a reduction in muscle pH. In addition, exercise causes a loss of muscle K(+) leading to an increased concentration of extracellular K(+) ([K(+)](o)). Individually, reduced pH and increased [K(+)](o) have both been suggested to contribute to muscle fatigue. 2. To study the combined effect of these changes on muscle function, isolated rat soleus muscles were incubated at a [K(+)](o) of 11 mM, which reduced tetanic force by 75 %. Subsequent addition of 20 mM lactic acid led, however, to an almost complete force recovery. A similar recovery was observed if pH was reduced by adding propionic acid or increasing the CO(2) tension. 3. The recovery of force was associated with a recovery of muscle excitability as assessed from compound action potentials. In contrast, acidification had no effect on the membrane potential or the Ca(2+) handling of the muscles. 4. It is concluded that acidification counteracts the depressing effects of elevated [K(+)](o) on muscle excitability and force. Since intense exercise is associated with increased [K(+)](o), this indicates that, in contrast to the often suggested role for acidosis as a cause of muscle fatigue, acidosis may protect against fatigue. Moreover, it suggests that elevated [K(+)](o) is of less importance for fatigue than indicated by previous studies on isolated muscles.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / metabolism
  • Isometric Contraction / drug effects
  • Isometric Contraction / physiology*
  • Lactic Acid / pharmacology*
  • Muscle Fatigue / drug effects
  • Muscle Fatigue / physiology
  • Muscle, Skeletal / drug effects
  • Muscle, Skeletal / physiology*
  • Potassium / pharmacology
  • Rats
  • Rats, Wistar
  • Sodium-Potassium-Exchanging ATPase / metabolism


  • Lactic Acid
  • Sodium-Potassium-Exchanging ATPase
  • Potassium
  • Calcium