Effect of high-intensity intermittent training on lactate and H+ release from human skeletal muscle

The study investigated the effect of training on lactate and H+ release from human skeletal muscle during one-legged knee-extensor exercise. Six subjects were tested after 7-8 wk of training (fifteen 1-min bouts at similar to150% of thigh maximal O-2 uptake per day). Blood samples, blood flow, and muscle biopsies were obtained during and after a 30-W exercise bout and an incremental test to exhaustion of both trained (T) and untrained (UT) legs. Blood flow was 16% higher in the T than in the UT leg. In the 30-W test, venous lactate and lactate release were lower in the T compared with the UT leg. In the incremental test, time to fatigue was 10.6+/-0.7 and 8.2+/-0.7 min, respectively, in the T and UT legs (P<0.05). At exhaustion, venous blood lactate was 10.7±0.4 and 8.0±0.9 mmol/l in T and UT legs (P<0.05), respectively, and lactate release was 19.4+/-3.6 and 10.6+/-2.0 mmol/min (P<0.05). H+ release at exhaustion was higher in the T than in the UT leg. Muscle lactate content was 59.0±15.1 and 96.5±14.5 mmol/kg dry wt in the T and UT legs, and muscle pH was 6.82±0.05 and 6.69±0.04 in the T and UT legs (P=0.06). The membrane contents of the monocarboxylate transporters MCT1 and MCT4 and the Na+/H+ exchanger were 115±5 (P<0.05), 111+/-11, and 116+/-6% (P<0.05), respectively, in the T compared with the UT leg. The reason for the training-induced increase in peak lactate and H+ release during exercise is a combination of an increased density of the lactate and H+ transporting systems, an improved blood flow and blood flow distribution, and an increased systemic lactate and H+ clearance.