Threshold for muscle lactate accumulation during progressive exercise

The purpose of this study was to investigate the relationship between muscle and blood lactate concentrations during progressive exercise. Seven endurance-trained male college students performed three incremental bicycle ergometer exercise tests. The first two tests (tests I and II) were identical and consisted of 3-min stage durations with 2-min rest intervals and increased by 50-W increments until exhaustion. During these tests, blood was sampled from a hyperemized earlobe for lactate and pH measurement (and from an antecubital vein during test I), and the exercise intensities corresponding to the lactate threshold (LT), individual anaerobic threshold (IAT), and onset of blood lactate accumulation (OBLA) were determined. The test III was performed at predetermined work loads (50 W below OBLA, at OBLA, and 50 W above OBLA), with the same stage and rest interval durations of tests I and II. Muscle biopsies for lactate and pH determination were taken at rest and immediately after the completion of the three exercise intensities. Blood samples were drawn simultaneously with each biopsy. Muscle lactate concentrations increased abruptly at exercise intensities greater than the “below-OBLA” stage [50.5% maximal O2 uptake (VO2 max)] and resembled a threshold. An increase in blood lactate and [H+] also occurred at the below-OBLA stage; however, no significant change in muscle [H+] was observed. Muscle lactate concentrations were highly correlated to blood lactate (r = 0.91), and muscle-to-blood lactate ratios at below-OBLA, at-OBLA, and above-OBLA stages were 0.74, 0.63, 0.96, and 0.95, respectively