TY - JOUR T1 - Metabolic Factors Limiting Performance in Marathon Runners A1 - Rapoport, Benjamin I. Y1 - 2010/10/21 N2 - Author Summary Marathon running, historically perceived as testing the physiologic limits of human endurance, has become increasingly popular even among recreational runners. Of those runners who test their endurance by racing the marathon distance, however, more than two in five report ‘hitting the wall,’ the rapid onset of severe fatigue and inability to maintain a high-intensity pace, resulting from the near-complete depletion of carbohydrate stores in the leg muscles and liver. An apparent paradox of long-distance running is that even the leanest athletes store enough fat to power back-to-back marathons, yet small carbohydrate reservoirs can nevertheless catastrophically limit performance in endurance exercise. In this study I develop and validate a mathematical model that facilitates computation of personalized estimates of the distances at which runners will exhaust their carbohydrate stores while running at selected paces. In addition, I provide a systematic approach to estimating personalized maximum speeds at which runners can safely complete a marathon, based on accessible physiologic parameters such as heart rate and running speed. This analysis provides a quantitative basis for improving the safety and optimizing the performance of endurance runners, evaluating midrace fueling requirements, and estimating limits of performance in human endurance running, for elite and recreational runners alike. JF - PLOS Computational Biology JA - PLOS Computational Biology VL - 6 IS - 10 UR - https://doi.org/10.1371/journal.pcbi.1000960 SP - e1000960 EP - PB - Public Library of Science M3 - doi:10.1371/journal.pcbi.1000960 ER -