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Lactate and force production in skeletal muscle
Michael Kristensen1, Janni Albertsen, Maria Rentsch
1Copenhagen Muscle Research Centre, August Krogh Institute, Universitetsparken 13, DK-2100 Copenhagen, Denmark.
The Journal of Physiology
|November 20, 2004
Summary
Lactic acid may protect resting muscles but does not prevent fatigue in active muscles. Incubation with lactic acid improved force in K+-depressed muscles but had no effect or a negative effect on repetitively stimulated muscles.
Area of Science:
- Exercise Physiology
- Muscle Metabolism
- Biochemistry
Background:
- Muscle fatigue is often linked to lactic acid accumulation.
- Previous studies suggested lactic acid protects against fatigue in resting, K+-depressed muscles.
- However, the effect of lactic acid on active muscle fatigue remains unclear.
Purpose of the Study:
- To investigate whether lactic acid protects against fatigue in active muscle.
- To compare the effects of lactate/lactic acid on resting versus active muscle force.
- To understand the role of pH regulation and Na+-K+ pump activity in lactate's effects.
Main Methods:
- Rat soleus muscles were used in vitro.
- Muscles were either K+-depressed (resting) or stimulated to fatigue.
- Incubation solutions included Na-lactate and lactic acid to mimic different pH conditions.
Main Results:
- Lactate/lactic acid incubation improved force in K+-depressed resting muscles.
- This incubation also accelerated the Na+-K+ pump.
- However, none of the incubation solutions improved force development in repetitively stimulated muscles; Na-lactate had a negative effect.
Conclusions:
- Lactate/lactic acid incubation can restore force in resting, K+-depressed muscles.
- It does not provide protection against fatigue in active, repetitively stimulated muscles.
- The protective effect in resting muscle may be due to mitigating large depolarizations, unlike in active muscle.