A method for determining the maximal steady state of blood lactate concentration from two levels of submaximal exercise

Abstract

The aim of this study was to estimate the characteristic exercise intensity$\dot W$ _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 [maximal oxygen uptake$\dot V{\text{O}}_{\text{2}}$ _max 62 (SD 7) ml · min⁻¹ · kg⁻¹] exercisOed for two 30-min periods on a cycle ergometer at 67% (test 1.1) and 82% of$\dot V{\text{O}}_{\text{2}}$ _max (test 1.2) separated by 40 min. They exercised 4 days later for 30 min at 82% of$\dot V{\text{O}}_{\text{2}}$ _max without prior exercise (test 2). Blood lactate was collected for determination of lactic acid concentration every 5 min and heart rate and O₂ uptake$\dot V{\text{O}}_{\text{2}}$ were measured every 30 s. There were no significant differences at the 5th, 10th, 15th, 20th, 25th, or 30th min between$\dot V{\text{O}}_{\text{2}}$, lactacidaemia, and heart rate during tests 1.2 and 2. Moreover, we compared the exercise intensities$\dot W$ _CL which produced the MLSS obtained during tests 1.1 and 1.2 or during tests 1.1 and 2 calculated from differential values of lactic acid blood concentration ([1a⁻]_b) between the 30th and the 5th min or between the 20th and the 5th min. There was no significant difference between the different values of$\dot W$ _CL [68 (SD 9), 71 (SD 7), 73 (SD 6),71 (SD 11) % of$\dot V{\text{O}}_{\text{2}}$ _max (ANOVA test,P<0.05). Four subjects ran for 60 min at their$\dot W$ _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 (Δ ([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$\dot W$ _CL protocol did not overestimate the exercise intensity corresponding to the maximal fractional utilization of$\dot V{\text{O}}_{\text{2}}$ _max at MLSS. For half of the subjects the$\dot W$ _CL was very close to the higher stage (82% of$\dot V{\text{O}}_{\text{2}}$ _max where an accumulation of lactate in the blood with time was observed. It can be hypothesized that$\dot W$ _CL was very close to the real MLSS considering the level of accuracy of [la⁻]_b measurement. This study showed that exercise at only two intensities, performed at 65% and 80% of$\dot V{\text{O}}_{\text{2}}$ _max and separated by 40 min of complete rest, can be used to determine the intensity yielding a steady state of [la⁻¹]_b near the real MLSS workload value.