Reliability and validity of a continuous incremental treadmill protocol for the determination of lactate threshold, fixed blood lactate concentrations, and V̇O₂max

Fifteen male runners were tested on two occasions to determine the reliability of a continuous incremental level running treadmill protocol (C), with 3-min stages, for lactate threshold (LT) and fixed blood lactate concentration (FBLC) (2.0 mM, 2.5 mM, 4.0 mM) assessment. Test-retest (T-RT) reliability coefficients for velocity at LT, 2.0 mM, 2.5 mM, and 4.0 mM were r = 0.89, 0.91, 0.95, and 0.95, respectively (velocity ranged from 215.3 m/min at LT to 273.6 m/min at 4.0 mM). Mean differences in T-RT velocity values ranged from 0.7 m/min (at LT) to 6.0 m/min (at 2.5 mM; 252.3 m/min vs 258.3 m/min; NS) and the standard errors of measurement were less than ±10.0 m/min. Similar results were observed for V̇O₂, with T-RT r values ranging from r = 0.82 (at LT) to r = 0.88 (at 2.0 mM) (V̇O₂ ranged from 47.2 ml/kg·min^-1 at LT to 60.9 ml/kg·min^-1 at 4.0 mM; V̇O₂ peak = 65.6 ml/kg·min^-1). Mean differences in T-RT V̇O₂ values were less than 1.4 ml/kg·min^-1 (NS) and the standard errors of measurement were less than ± 2.95 ml/kg·min^-1. Interinvestigator and intrainvestigator reliability coefficients were high and ranged from r = 0.91 to r = 0.99. Validity of C was assessed in an additional 16 male runners who completed C and a criterion discontinuous (D) protocol (using a series of 10-min stages) for LT and FBLC assessment. Results indicated that C and D resulted in similar V̇O₂ and velocity values at LT and FBLC. For V̇O₂ correlations ranged from r = 0.75 (V̇O₂LT) to r = 0.90 (V̇O₂ 2.5 mM and V̇O₂ 4.0 mM) with SEE ranging from ±1.99 to ±3.58 ml/kg·min^-1. For velocity, correlations ranged from r = 0.87 to r = 0.97 with SEE ranging from ±6.5 m/min to ±13.1 m/min. It was concluded that a continuous horizontal treadmill protocol using 3-min stages results in reliable and valid measurement of velocity and V̇O₂ at LT and FBLC of 2.0 mM, 2.5 mM, and 4.0 mM.