Commentaries on Viewpoint: The two-hour marathon: Who and when?

TO THE EDITOR: It was with great interest that we read the Journal of Applied Physiology Viewpoint on the 2-h marathon barrier (3). We would argue that, alongside having a superlative V̇O2max, lactate threshold, and running economy, it will be required for this athlete to have an individualized and aggressive fueling strategy coupled with a predisposition for high exogenous CHO oxidation (CHOexog), without a history of GI distress. It is clear that supplemented carbohydrate (CHO) improves prolonged endurance performance ( 90 min) compared with water (2). Furthermore, recent evidence has demonstrated a positive dose-response relationship between supplemented CHO, CHOexog, and endurance performance; where 60 g CHO/h outperformed either 15 or 30 g CHO/h (5). The maximal CHOexog with single CHO sources appears to be 1 g/min due to limitations of the intestinal transporters (1). However, despite any individual differences in CHOexog or history of GI distress (4), CHOexog is not dependent on body weight (BW), as a recent analysis has shown no relationship between BW and CHOexog (1). Accordingly, a 56-kg runner is able to oxidize 20% more per kg BW compared with a 70-kg runner with a given CHOexog rate of 1 g/min (1.07 vs.0.86 g CHO·h ·kg BW ). Therefore, there appears to be a distinct CHOexog advantage for lighter marathon runners compared with heavier. Thus the future 2-h marathon runner will feature a low BW, both for improved thermoregulation, but also optimal CHOexog per kg BW. All of these elements will need to be possessed by the first athlete to break the 2-h marathon barrier.