Determination of the Heart Rate Zone Corresponding to the Lactate Threshold in Colombian Paso Horses

Colombian Paso Horses (CPH) excel in gait competitions due to their endurance, speed, and precision, which demand a high level of cardiorespiratory fitness. However, their training often lacks scientific support, and few studies have linked physiological pa-rameters to optimal training zones. This study aimed to estimate the aerobic lactate threshold (LTaer) using non-invasive methods and to correlate it with heart rate (HR) zones. Eighteen CPH were evaluated and classified into trained (GT) and untrained (GD) groups. All animals underwent a field-based incremental exercise test (IET) with con-tinuous HR monitoring and serial blood sampling for lactate, creatinine, urea, AST, and CK analysis. LTaer was estimated using three methods: visual inspection, fixed thresholds at 2 mmol/L (ZL2), and 4 mmol/L (ZL4). HR zones corresponding to each threshold were then calculated based on a maximum estimated HR of 220 bpm. The visual method placed LTaer in zone 2 for both groups. ZL2 located the threshold in zone 2 for GT and in zone 3 for GD, whereas ZL4 placed the threshold in zone 4 for both groups. Although no intergroup differences in lactate or HR were observed, intragroup differences emerged above 75% of HRmax, indicating exponential lactate accumulation. Biomarker analysis revealed significant pre- to post-exercise changes, but no differences between groups, suggesting a standardized workload. This is the first study to propose field-based pre-diction of LTaer in CPH using HR derived from wearable technologies and a standardized exercise test. Correlating HR zones with lactate thresholds facilitates workload analysis in the field when blood biomarkers are not available. Future studies should investigate the maximal lactate steady state (MLSS) in this breed.