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

Denen Studien nevner at laktat og CO2 var en bedre beskyttelse for utslitte muskler enn glukose. Kan virkelig en mild acidifisering av blodet være bedre restitusjon enn karbohydratpåfyll??

Det kan se ut som at det er opphopning av K+ utenfor muskelcellene som styrer utmattelse, og dermed vil en økning av CO2 som gir acifdifisering virke restituerende. Men dette må jeg undersøke nærmere.

  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 CO2 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 Ca2+ 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.

More importantly, this study also shows that in muscles where force and excitability are depressed by high [K+]o, lactic acid produces a pronounced recovery of force. A recovery of force could also be obtained by acidifying the muscle fibres using CO2 or propionic acid. In contrast, 20 mm glucose failed to induce a recovery of force. These findings indicate that the effect of lactic acid was related to the acidification of the muscles rather than to a possible metabolic effect (Van Hall, 2000). The pH of the muscles in the presence of 20 mm lactic acid was similar to the values for muscle pH observed after intensive exercise (Sjøgaard et al. 1985).

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