Influence of lactate on the active force produced in skinned psoas and soleus muscle fibers from female rabbits.

Lactate has been recognized as an energy source, suggesting its potential use as an ergogenic supplement. However, its effect on muscle contraction remains unclear. This study examined the effect of lactate on muscle active force using skinned fibers. Rabbit psoas (N = 8) and soleus (N = 5) fibers were activated using three activating solutions as follows: (1) activating solution, pH 7.0 (Normal); (2) activating solution with lactate, pH 6.0 (Lactate pH 6.0); (3) activating solution with lactate, pH 7.0 (Lactate pH 7.0). Under these conditions, the fibers were isometrically activated at an average sarcomere length of 2.4 μm, and their length was subsequently shortened by 20%. Statistical test revealed that although the muscle active force (both isometric and concentric force) in Lactate pH 6.0 was smaller than in Normal and Lactate pH 7.0, no significant difference in muscle force was observed between Normal and Lactate pH 7.0. These patterns were consistent in both psoas and soleus fibers. These findings indicate that lactate ions do not affect muscle active force whereas a low-pH environment (acidosis) induces significant muscle force depression.