A089: The Relationship Between LTHR and the HRDP Based on TheDmax

<bold>Introduction:</bold> Blood lactate serves as a physiological biomarker, offering insights into an individual's health and training status. Lactate threshold (LT) is commonly used to determine training zones and intensity for endurance athletes. The Dmax method and its modified version, Dmaxmod, are currently prevalent for LT determination. The heart rate deflection point (HRDP) is a specific point on the heart-velocity curve used to assess the transition between aerobic and anaerobic. The purpose of this study was to explore the relationship between LT determined by Dmax and Dmaxmod, as well as the relationship between the HRDP determined using the Dmax (HRDP-Dmax) and the lactate threshold heart rate (LTHR). <bold>Methods:</bold> Twenty amateur runners underwent treadmill maximal incremental load tests. Prior to testing, a 5-15-minute warm-up was conducted. The formal test began with the treadmill at an initial speed of 4 km/h, with each load level lasting 3 minutes, followed by the collection of 10 μL of fingertip blood. The speed then increased incrementally by 1.2 km·h⁻¹, repeating the process until the participant reached exhaustion. Participants were required to wear a Polar H10 heart rate monitor to record heart rate during the test. Post-experiment, blood lactate concentrations were analyzed using the EKF blood lactate analyzer. LT was determined using the Dmax and Dmaxmod methods with third-order polynomial interpolation. Additionally, the HRDP was determined using the Dmax method, based on the heart rate and speed. <bold>Results:</bold> After confirming normal distribution of the data, repeated measures ANOVA tests were used to verify potential differences among different thresholds determined in the maximal incremental running test. In addition to intraclass correlation coefficient (ICC), Cohen's d (d), and Pearson’s (r), Bland-Altman plots provided a visual analysis of dataset bias. (1) The LT were calculated using both the Dmax and Dmaxmod methods, they were 3.10 ± 0.82 and 4.22 ± 1.19 mmol·L⁻¹ respectively, r = 0.544 (p &lt; 0.05), with d = 1.10, bias ± LoA = -1.12 ± 1.02 mmol·L⁻¹ (95% CI, -3.112 - 0.869), and ICC = 0.672 (p &lt; 0.05). (2) LTHR was 175 ± 11 bpm, and HRDP-Dmax was 175 ± 12 bpm, p = 0.29, r = 0.58 (p &lt; 0.05), d = 0.85, bias ± LoA = -8.45 ± 9.93 bpm (95% CI, -27.91 -11.01), and ICC = 0.722 (p &lt; 0.05). <bold>Conclusion:</bold> The Dmax and Dmaxmod methods for determining LT demonstrate good consistency; HRDP-Dmax showed consistent results with the LTHR. This indicates that the HRDP by the Dmax method exhibited favorable reliability and practical utility in predicting LTHR during incremental running.