Coincidence of lactate threshold and HR-power output threshold under varied nutritional states

The purpose of this study was to cross-validate the method of Conconi et al. (5) that purports to determine "anaerobic threshold" based on a deflection point between heart rate (HR) vs power output. Eight males (22.6 +/- 1.6 y) were tested with maximal progressive cycle ergometry under normal (NG) and glycogen-depleted (GD) conditions. During the last min of each stage, HR was monitored via EKG and blood was sampled for lactate determination. Computerized data analysis was then conducted to determine the deflection points for lines respectively fit to each HR vs power output (heart rate threshold; HRT) and lactate vs power output (lactate threshold; LT) distribution. Under NG conditions, HRT and LT occurred at 200.4 +/- 33.3 and 211.4 +/- 46.5 watts, respectively (equivalent to VO2 = 2.455 +/- 0.368 and 2.618 +/- 0.507 l/min), with a correlation of r = 0.68 between HRT vs LT (S.E.E. for prediction of LT from HRT = 36.7 watts). However, under GD conditions, HRT = 182.9 +/- 43.3 watts and LT = 227.0 +/- 41.1 watts (equivalent to VO2 = 2.395 +/- 0.413 and 2.944 +/- 0.578 l/min) with HRT vs LT r = -0.04 and S.E.E. = 44.4 watts. Across the two conditions, < 4% of the variance in the change in LT was accounted for by the change in HRT. These data indicated that 1) under NG conditions the modest association between HRT and LT was not causally-linked and 2) HRT was not a stable predictor of LT across varying nutritional states such as those common to prolonged exercise.