A METHOD FOR DETERMINING THE MAXIMAL STEADY-STATE OF BLOOD LACTATE CONCENTRATION FROM 2 LEVELS OF SUBMAXIMAL EXERCISE

The aim of this study was to estimate the characteristic exercise inte nsity (W-CL) which produces the maximal steady state of blood lactate concentration (MLSS) from submaximal intensities of 20 min carried out on the same day and separated by 40 min. Ten fit male adults I:maxima l oxygen uptake (VO2max) 62 (SD 7) ml.min(-1) kg(-1)] exercised for tw o 30-min periods on a cycle ergometer at 67% (test 1.1) and 82% of VO2 max (test 1.2) separated by 40 min. They exercised 4 days later for 30 min at 82% of VO2max without prior exercise (test 2). Blood lactate w as collected for determination of lactic acid concentration every 5 mi n and heart rate and O-2 uptake (VO2) were measured every 30 s. There were no significant differences at the 5th, 10th, 15th, 20th, 25th, or 30th min between VO2 lactacidaemia, and heart rate during tests 1.2 a nd 2. Moreover, we compared the exercise intensities (W-CL) which prod uced the MLSS obtained during tests 1.1 and 1.2 or during tests 1.1 an d 2 calculated from differential values of lactic acid blood concentra tion ([la(-)](b)) between the 30th and the 5th min or between the 20th and the 5th min. There was no significant difference between the diff erent values of W-CL [68 (SD 9), 71 (SD 7), 73 (SD 6), 71 (SD 11)% of VO2max] (ANOVA test, P<0.05). Four subjects ran for 60 min at their W- CL determined from periods performed on the same day (test 1.1 and 1.2 ) and the difference between the [la(-)](b) at 5 min and at 20 min (De lta([la(-)](b))) was computed. The [la(-)](b) remained constant during exercise and ranged from 2.2 to 6.7 mmol.l(-1) [mean value equal to 3 .9 (SD 1) mmol.l(-1)]. These data suggest that the W-CL protocol did n ot overestimate the exercise intensity corresponding to the maximal fr actional utilization of VO2max at MLSS. For half of the subjects the W -CL was very close to the higher stage (82% of VO2max) where an accumu lation of lactate in the blood with time was observed. It can be hypot hesized that W-CL was very close to the real MLSS considering the leve l of accuracy of [la(-)](b) measurement. This study showed that exerci se at only two intensities, performed at 65% and 80% of VO2max and sep arated by 40 min of complete rest, can be used to determine the intens ity yielding a steady state of [la-lb near the real MLSS workload valu e.