Anaerobic and Aerobic Energy System Contribution During Maximal Exercise: A Systematic Review

BACKGROUND: The capacity to generate energy during exercise is dependent on the bioenergetic pathways within muscle cells. These pathways include the phosphagen, glycolytic, and oxidative phosphorylation systems, which work together to resynthesize adenosine triphosphate (ATP) and meet the energy demands of exercise. Understanding the relative contributions of these systems during maximal exercise has theoretical and practical importance for optimizing athletic performance and training. OBJECTIVE: This study aimed to systematically review literature on the relative contributions of anaerobic and aerobic energy systems during single bouts of maximal exercise across various durations. The goal was to consolidate evidence from multiple methodologies to provide a more precise understanding of energy system interactions and inform both theoretical knowledge and practical applications in sports performance and training. METHODS: A systematic search was conducted across seven electronic databases, including CINAHL, Cochrane, Embase, MEDLINE/PubMed, Scopus, SPORTDiscus, and Web of Science, covering studies from 1984 to January 2020. Eligible studies included peer-reviewed, English-language research that examined energy system contributions during maximal exercise in adults (≥ 18 years). Data extraction focused on participant details, exercise trial specifics, assessment methods, and relative energy system contributions. Studies were categorized on the basis of their assessment approach. Nonlinear regression modeling was used to estimate anaerobic and aerobic contributions across different exercise durations. RESULTS: A total of 102 studies were included, providing 311 individual data points (mean results from studies comprising 78% male, 12% female, 11% mixed adult samples). The oxygen deficit (OD) method was used in 66 studies, mixed methods (MM) in 33 studies, and theoretical models (TM) in 7 studies. The data reviewed indicated that the anaerobic system predominates in short-duration maximal exercise, up until approximately 75-80 s. The maximal exercise duration that derived equal contributions from both the anaerobic and aerobic energy systems was 78.6 s (95% confidence interval [95% CI] ± 1.1 s), with longer durations contributing an increasingly greater proportion of aerobic energy to the total energy supply. Comparison of regression curves showed no differences between running and cycling or training status but revealed small significant effects of measurement method and pacing strategy. CONCLUSIONS: This review refines previous estimates of energy system contributions during maximal exercise, reaffirming the dynamic interplay between anaerobic and aerobic metabolism. The findings emphasize the importance of considering both energy systems in training strategies and highlight the need for more precise measurement techniques. Athletes and coaches can optimize performance by tailoring high-intensity training, work-rest ratios, and pacing strategies to improve anaerobic capacity, oxygen uptake efficiency, and short-term recovery.