The Conconi test in not valid for estimation of the lactate turnpoint in runners

Conconi et al. (1982) reported that an observed deviation from linearity in the heart rate-running velocity relationship determined during a field test in runners coincided with the 'lactate threshold'. The aim of this study was to assess the validity of the original Conconi test using conventional incremental and constant-load laboratory protocols. Fourteen trained male distance runners (mean +/-s: age 22.6 +/- 3.4 years; body mass 67.6 +/- 4.8 kg; peak VO2 66.3 +/- 4.7 ml kg-1 min-1) performed a standard multi-stage test for determination of lactate turnpoint and a Conconi test on a motorized treadmill. A deviation from linearity in heart rate was observed in nine subjects. Significant differences were found to exist between running velocity at the lactate turnpoint (4.39 +/- 0.20 m s-1) and at deviation from linear heart rate (5.08 +/- 0.25 m s-1) (P < 0.01), and between heart rate at the lactate turnpoint (172 +/- 10 beats min-1) and at deviation from linearity (186 +/- 9 beats min-1) (P < 0.01). When deviation of heart rate from linearity was evident, it occurred at a systematically higher intensity than the lactate turnpoint and at approximately 95% of maximum heart rate. These results were confirmed by the physiological responses of seven subjects, who performed two constant-velocity treadmill runs at 0.14 m s-1 below the running velocity at the lactate turnpoint and that at which the heart rate deviated from linearity. For the lactate turnpoint trial, the prescribed 30 min exercise period was completed by all runners (terminal blood lactate concentration of 2.4 +/- 0.5 mM), while the duration attained in the trial for which heart rate deviated from linearity was 15.9 +/- 6.7 min (terminal blood lactate concentration of 8.1 +/- 1.8 mM). We concluded that the Conconi test is invalid for the non-invasive determination of the lactate turnpoint and that the deviation of heart rate from linearity represents the start of the plateau at maximal heart rate, the expression of which is dependent upon the specifics of the Conconi test protocol.