A Comparison Of The Intensity Of Exercise At Different Definitions Of The “Lactate Threshold”

Abstract

Endurance athletes use information about their “lactate threshold” to design an effective training program, to monitor training progress, and to estimate a race pace. Various definitions of the “lactate threshold” are available in the literature. PURPOSE: The purpose of this study was to compare the intensities of exercise at which the “lactate threshold” occurs based on common definitions. METHODS: Six well-trained men, 18-39 years of age with VO2max values ranging between 56 and 65 mL/kg/min volunteered to participate in this study. Each participant completed an exercise test to determine VO2max and lactate threshold. Intravenous blood samples were taken during the last 30 s of each 3 min stage. Blood lactate levels were measured using the YSI analyzer and corrected for changes in hemoglobin and hematocrit. The “lactate threshold” was identified in each subject using each of the following methods: (1) visual detection of the inflection point of the lactate response curve, (2) a blood lactate level of 1 mmol/L greater than the previous value, (3) a blood lactate level of 1 mmol/L above a baseline value, (4) a fixed blood lactate of 4 mmol/L, and (5) the ventilatory threshold. RESULTS: An ANOVA indicated that the VO2 (mL/kg/min), HR (bpm), running speed, RER, and plasma blood lactate levels were not significantly different between four definitions of the “lactate threshold”: visual detection of the inflection point of the lactate response curve, ventilatory threshold, and 1 mmol/L above the previous lactate value and above the baseline value. The fixed blood lactate value of 4 mmol/L resulted in VO2 and HR values that were not significantly different from maximal values, and an RER value significantly greater than RER values at all other definitions. CONCLUSIONS: Although there were no significant differences in VO2. HR, RER, running speed, and blood lactate between four of the definitions of “lactate threshold”, there were practical differences that could influence training and performance.