Effect of lactate infusion on M-wave characteristics and force in the rat plantaris muscle during repeated stimulation in situ.

Abstract

It is unclear whether accumulation of lactate in skeletal muscle during exercise contributes to muscle fatigue. The purpose of the present study was to examine the effect of lactate infusion on muscle fatigue during prolonged indirect stimulation in situ. For this purpose, the plantaris muscle was electrically stimulated (50 Hz, for 200 ms, every 2.7 s, 5 V) in situ through the sciatic nerve to perform concentric contractions for 60 min while either saline or lactate was infused intravenously (8 rats/group). Lactate infusion (lactate concentration approximately 12 mM) attenuated the reduction in submaximal dynamic force (-49 vs. -68% in rats infused with saline; P < 0.05). Maximum dynamic and isometric forces at the end of the period of stimulation were also higher (P < 0.05) in rats infused with lactate (3.8 +/- 0.3 and 4.4 +/- 0.3 N) compared with saline (3.1 +/- 0.2 and 3.6 +/- 0.2 N). The beneficial effect of lactate infusion on muscle force during prolonged stimulation was associated with a better maintenance of M-wave characteristics compared with control. In contrast, lactate infusion was not associated with any reduction in muscle glycogen utilization or with any reduction of fatigue at the neuromuscular junction (as assessed through maximal direct muscle stimulation: 200 Hz, 200 ms, 150 V).