Very Early Lactate Threshold in Healthy Young Men as Related to Oxygen Uptake Kinetics

摘要

We assessed the correspondence between the V-slope ventilatory threshold (VT) and the lactate threshold (LT) by using a distinctive slow submaximal ramp protocol to ensure that sufficient data points exist around the threshold. Twenty healthy young men participated. A submaximal test based on a prior maximal test (25 watt/min, medium ramp) was performed with an individual slow-ramp protocol (6-17 watt/min, slow ramp), in which the time to reach the VT workload was estimated to be 10minutes. The LT was determined visually by detecting a rise above the resting value, without or with log-log transformation (LT1, LT2). The point at which the blood lactate exceeded the minimal difference (LMD) of 2 resting values was also calculated.The VT appeared significantly earlier under the slow-ramp protocol compared to the medium-ramp protocol (from 19.33.9 to 15.0 +/- 4.0mL/kg/min VO2, P<0.001). The mean LT1 and LT2 values appeared even earlier than the VT (LT1, P=0.004; LT2, P=0.002) (LT1, 11.9; LT2, 13.4; LMD, 17.0; VT, 15.0mL/kg/min VO2). As the mean % of peak VO2, each occurred at 29.9%, 33.7%, 42.5%, and 37.8%. The VT correlated significantly with LT1, LT2, and LMD (r=0.61, 0.64, 0.80; P=0.004, 0.002, <0.001). Mean blood lactate showed a similar trend (1.30, 1.43, 1.81, 1.68mmol/L, respectively). Furthermore, the VO2/ work rate slope increased (from 10.8 +/- 0.9 to 11.5 +/- 0.9; P=0.01) with the slow ramp, and the lower LT was associated with the greater increase in slope (LT1, r=-0.47, P=0.03; LT2, r=-0.59, P=0.005), that is, the lower LT was an indication that on the faster medium ramp the slope would decrease. The LMD and VT did not show this relation.Under slow-ramp exercise testing in healthy young men, the VT appeared earlier than under medium-ramp exercise testing. In addition, the LT appeared even earlier (at approximately 30% of peak VO2) than the VT, although they correlated. This very early onset of LT was, however, associated with evidence of reduced oxygen uptake kinetics.