High-intensity interval vs moderate-intensity continuous training in endurance runners: A systematic review of physiological, biochemical, physical, and biomechanical adaptations.

This systematic review examines the comparative chronic adaptations of High-Intensity Interval Training (HIIT) and Moderate-Intensity Continuous Training (MICT) specifically in endurance-trained runners across physical, physiological, biochemical, biomechanical, and perceptual domains. Analyzing eight studies with 160 participants, the review found that HIIT generally produces faster and larger improvements in aerobic capacity (e.g., maximal oxygen uptake), running performance (e.g., time-trial speed, pacing), metabolic regulation, and biomechanical efficiency (e.g., stride length, ground contact time) compared to MICT. Conversely, MICT supports more sustained cardiovascular and autonomic adaptations with lower perceived exertion, facilitating higher training volumes and long-term endurance sustainability. The findings suggest that integrating HIIT and MICT within periodized training programs can optimize both rapid performance gains and durable physiological adaptations in endurance runners.