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.