A comparison of two lactate threshold protocols

During a progressive multi-stage running test, heart rate (HR) increases linearly with running speed. However, the HR eventually reaches a speed where it begins to level off. Conconi et al. call the velocity at HR deflection (V_d) and they repot a close agreement (r = 0.99) between V_d and the lactate threshold or LT_discont (using a test of there own design). Other researchers have compared V_d to continuous LT protocols (LT_cont), and have found that V_d overestimates LT_cont. In an effort to determine if the discrepancy results from the different LT protocols used, this study compared LT_cont to LT_discont protocols. Additionally, this study compared V_d to LT on continuous and discontinuous tests. Seven trained runners completed four tests each: 1.) a V O₂ max test, 2.) a Concom HR test conducted on a 400 m outdoor track with speeds increasing ~ 0.5 km/h every 200 m, 3.) an LT_discont conducted on a 400 m outdoor track with six runs at predetermined speeds (3 above and 3 below) V_d and 4.) an LT_cont protocol with 3-min stages on a treadmill. There were significant differences (P < 0004) between LT_discont (16.84 ± 1.72 km/h) and LTcont (13 56 ± 2.29 km/h) The correlation between V_d and LT_cont was r = 0.86, while a correlation of r = 0.94 was found between V_d and LT_discont. In conclusion, Conconi’s LT_discont significantly over-estimates LT as determined by a conventional LT protocol (LT_cont). Therefore, the validity of the Conconi test must be questioned and V_d should not be used as an estimate of LT.