Journal of Applied Physiology

Last Word on Viewpoint: Are there valid concerns for completing a marathon at 39 weeks of pregnancy?

Gerald S. Zavorsky, Lawrence D. Longo


amber miller completed the 2011 Chicago marathon at 39 weeks of pregnancy and received some widespread media attention for doing so (4). Some media said that her completion of the full 26.2-mile distance at near term was a great feat, and some said it was reckless with potentially harmful effects on the fetus. On the basis of our view, we think that was that it was neither a great feat nor was it potentially harmful to the fetus (5). Rather, we believe that her completion of a marathon in over 6 h was not a great accomplishment, physiologically speaking, as she finished the race as one of the slowest 5% of all women finishers. Her average pace was equivalent to a brisk walk and therefore not overly physiologically taxing.

Humans are well built for endurance exercise (1) because they are well adapted to exercise in heat. Studies have shown that even in extreme heat, body core temperature is not drastically altered if fluid is consumed ad libitum (3). Amber consumed fluids regularly (5) in an external environment not exceeding 26°C (39% relative humidity); thus hyperthermia was likely not an issue. Individuals usually terminate exercise at a body core temperature of ∼40°C (104°F) (2). Thus, given that Amber was able to complete the full marathon, drank fluids, and ate food at her own desire and did not prematurely drop out of the race, it can be assumed that she did not have exertional hyperthermia (core temperature >40°C) postfinish, nor did she become hypoglycemic.

Amber Miller did have Braxton Hicks contractions (false labor) during the marathon. They were irregular and painless. She also experienced these same contractions during her training. Amber said that her real contractions began ∼30 min after the race was completed. Thus labor ensued shortly after completion of her marathon, with birth occurring 8 h postfinish.

As marathon runners ourselves, we appreciate that from a personal and psychological standpoint, completing a marathon is meaningful. However, from a physiological standpoint of the mother and fetus, we affirm that walking at a brisk pace to complete a marathon in over 6 h in temperatures that ranged between 14 to 26°C, while keeping adequately hydrated and nourished, was, in our opinion, “not that big a deal.”


No conflicts of interest, financial or otherwise, are declared by the authors.


Author contributions: G.S.Z. and L.D.L. drafted manuscript; G.S.Z. and L.D.L. edited and revised manuscript; G.S.Z. and L.D.L. approved final version of manuscript.


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