Exercise modality influences lactate production and RPE: running vs. cycling, intervals vs. continuous

Introduction: Lactate has been redefined from a metabolic waste product to a key signaling molecule regulating energy metabolism, gene expression, and disease progression, making the precise regulation of exercise-induced lactate exposure critical for population-specific prescriptions (e.g., for the elderly or cancer patients). The aim of this study was to investigate the coupling between lactate accumulation and subjective fatigue by comparing whole-body (running) versus localized (cycling) exercise, as well as intermittent versus continuous modalities. Methods: Twelve healthy adults (six males and six females) participated in this study, completing combinations of three intensities and two modalities: Moderate-Intensity Interval Training (MIIT), Moderate-Intensity Continuous Training (MICT), and High-Intensity Interval Training (HIIT) via running and cycling ergometry. Blood lactate area-under-curve (AUC) was calculated, and Lactate Production Efficiency (LPE = AUC/RPE) was innovatively proposed to quantify lactate exposure per unit of Rating of Perceived Exertion (RPE). Results: Cycling induced 59% (MIIT, p < 0.01) and 67% (HIIT, p < 0.05) higher lactate AUC than running, irrespective of intensity or intermittency. Furthermore, HIIT cycling yielded a 52% higher LPE than running (20.48 vs. 13.47 mmol·min/L·scale, p < 0.01), indicating superior lactate stress per fatigue unit and optimizing lactate elevation, whereas running MIIT minimized lactate exposure. Males showed 36-43% higher running AUC than females (p < 0.05), suggesting heightened metabolic sensitivity. Interval efficacy was also confirmed, as HIIT increased lactate AUC by 44-87% versus MICT (p < 0.05). Discussion: The introduction of LPE effectively quantifies exercise-modality effects on fatigue-lactate decoupling. The findings demonstrate metabolic stress concentration in localized exercise (cycling) and male-specific lactate sensitivity during whole-body running, providing RPE-based strategies for precision exercise prescription and advancing personalized interventions in sports medicine.