From Incremental Test to Continuous Running at Fixed Lactate Thresholds: Individual Responses on %VO_2max, %HR_max, Lactate Accumulation, and RPE

With Norway's successes in middle and long-distance running, lactate-guided threshold training has regained importance in recent years. Therefore, the aim of the present study was to investigate the individual responses on common monitoring parameters based on a lactate-guided conventional training method. In total, 15 trained runners (10 males, 5 females; 18.6 ± 3.3 years; VO_2max: 59.3 ± 5.9 mL kg^-1 min^-1) completed a 40-min continuous running session at a fixed lactate threshold load of 2 mmol L^-1. Lactate (La), oxygen uptake (VO₂), heart rate (HR), and rating of perceived exertion (RPE) were recorded. The chosen workload led to lactate values of 2.85 ± 0.56 mmol L^-1 (range: 1.90-3.80), a percentage of VO_2max utilization (%VO_2max) of 79.2 ± 2.5% (range: 74.9-83.8), a percentage of HR_max utilization (%HR_max) of 92.2 ± 2.5% (range: 88.1-95.3), and an RPE of 6.1 ± 1.9 (range: 3-10) at the end of the running session. Thereby, the individual responses differed considerably. These results indicate that a conventional continuous training method based on a fixed lactate threshold can lead to different individual responses, potentially resulting in various physiological impacts. Moreover, correlation analyses suggest that athletes with higher lactate threshold performance levels must choose their intensity in continuous training methods more conservatively (lower percentage intensity based on a fixed threshold) to avoid eliciting excessively strong metabolic responses.