Comparison of mathematically determined blood lactate and heart rate “threshold” points and relationship with performance

Summary

The purpose of this study was to investigate the relationship between threshold points for heart rate (${\text{TH}}_{f_c }$) and blood lactate (Th_1a) as determined by two objective mathematical models. The models used were the mono-segmental exponential (EXP) model of Hughson et al. and the log-log (LOG) model of Beaver et al. Inter-correlations of these threshold points and correlations with performance were also studied. Seventeen elite runners (mean, SD = 27.5, 6.5 years; 1.73, 0.05 m; 63.8, 7.3 kg; and maximum oxygen consumption of 67.8, 3.7 ml · kg⁻¹ · min⁻¹) performed two maximal multistage running field tests on a 183.9-m indoor track with inclined turns. The initial speed of 9 km · h⁻¹ (2.5 m · s⁻¹) was increased by 0.5 km · h⁻¹ (0.14 m · s⁻¹) every lap for thef _c test and by 1 km · h⁻¹ (0.28 m · s⁻¹) every 4 min for the la test. After fitting the la or thef _c data to the two mathematical models, the threshold speed was assessed in the LOG model from the intersection of the two linear segments (LOG-1a; LOG-f _c) and in the EXP model from a tangent point (TI-1a; TI-f _c). Th_1a and${\text{TH}}_{f_c }$ speeds computed with the two models were significantly different (P<0.001) and poorly correlated (LOG-1a vs LOG-f _c:r=0.36, TI-1a vs TI-f _c:r=0.13). In general,${\text{TH}}_{f_c }$ were less well correlated with performance than Th_1a. With two different objective mathematical models, this study has shown significant differences and poor correlations between Th_1a and${\text{TH}}_{f_c }$. Thus thef _c inflection point with Conconi's protocol is a poor indicator of the la breakpoint with a conventional multistage protocol and a weaker indicator of running performance.