Exercise Modality Influences Lactate Production and RPE: Running vs. Cycling, Intervals vs. Continuous

PURPOSE: Lactate has been redefined from a metabolic waste product to a key signaling molecule regulating energy metabolism, gene expression, and disease progression. While it confers benefits like mitochondrial biogenesis and cognitive enhancement, it poses risks such as tumor microenvironment exacerbation. Precise regulation of exercise-induced lactate exposure is thus critical for population-specific prescriptions (e.g., elderly, cancer patients). This study investigated the coupling between lactate accumulation and subjective fatigue by comparing whole-body (running) vs. localized (cycling) and intermittent vs. continuous modalities, using blood lactate area-under-curve (AUC) and Rating of Perceived Exertion (RPE). Methods: Twelve healthy adults (6M/6F) completed 3 intensities×2 modalities (MIIT/MICT/HIIT×running/cycling ergometry). Lactate AUC was calculated via trapezoidal rule. We innovatively proposed Lactate Production Efficiency (LPE = AUC/RPE) to quantify lactate exposure per unit RPE. Results: 1.Cycling induced 59% (MIIT, P<0.01) and 67% (HIIT, P<0.05) higher lactate AUC than running, irrespective of intensity/intermittency. HIIT cycling yielded 52% higher LPE than running (20.48 vs. 13.47 mmol·min/L·scale, P<0.01), indicating superior lactate stress per fatigue unit. 2.Males showed 36-43% higher running AUC than females (P<0.05), suggesting heightened metabolic sensitivity. HIIT increased lactate AUC by 44-87% versus MICT (P<0.05), confirming interval efficacy. 3.Cycling HIIT/MIIT optimized lactate elevation; running MIIT minimized lactate exposure. Conclusion: We introduce LPE as the first metric quantifying exercise-modality effects on fatigue-lactate decoupling. Key findings include: (1) metabolic stress concentration in localized exercise (cycling), (2) male-specific lactate sensitivity during whole-body running, and (3) RPE-based strategies for precision exercise prescription. This advances personalized interventions in sports medicine.