DETERMINATION OF LACTATE THRESHOLD BY RESPIRATORY GAS-EXCHANGE MEASURES AND BLOOD LACTATE LEVELS DURING INCREMENTAL LOAD WORK

Objective: The purpose of this investigation was the determination of the lactate threshold (LT) by selected respiratory gas exchange measur es and venous blood lactate levels during incremental load work on a m echanically braked cycle ergometer. Design: Repeated measures design. Setting: Human Performance Laboratory. Participants: Eight healthy tra ined soccer players (mean age 21.9 +/- 3.0 yr, mean VO2max = 59.2 +/- 3.6 ml.kg.min-1). Outcome Measure: Subjects conducted two incremental load work tests. Incremental load work was increased by 1 kilopond (kp ) every third minute at 60 rpm until voluntary exhaustion. Blood sampl es from a forearm vein were collected during the second trial (T2) onl y and analyzed for lactic acid [LA-]. Results: One-way analysis of var iance (ANOVA) with repeated measures indicated no statistically signif icant difference between the two tests for maximal oxygen uptake (Vo2m ax), maximal carbon dioxide production (Vco2max), maximal heart rate ( HRmax), maximal pulmonary ventilation (V(E)BTPSmax) and lowest ventila tory equivalent of oxygen (V(E)/Vo2), respectively; however, there was a significant difference among the oxygen uptake (Vo2) values at the LT for the four determination methods. In our subjects, the measured ( mean +/- SD) V(E)/Vo2 in relation to Vo2 for the first trial (T1) of 2 2.9 +/- 1.9 occurred at Vo2 of 1.27 +/- 0.8 1.min-1. The lowest V(E)/V o2 and the onset of [LA-1 accumulation calculated from individual expo nential equations relating V(E) to Vo2 yielded Vo2 values of 1.77 +/- 0. 18 and 1.74 +/- 0.25 1. min-1 for the T2. Utilizing natural log for lactate In [LA-] to natural log for In (Vo2) equations, the LT for T2 occurred at Vo2 of 1.30 +/- 0.70 1. min-1. Conclusion: LT was best pr edicted by the measured lowest V(E)/Vo2 and the plot of the in [LA-] t o In Vo2 relationship. The methods used in this study provide a valid estimate of the LT and support the use of measured lowest V(E)/Vo2 as an indirect measure of the LT.