Pre-race dietary carbohydrate intake can independently influence sub-elite marathon running performance


Journal Title (Medline/Pubmed accepted abbreviation): Int. J. Sports Med.
Year: 2011
Volume: 32
Pages: 611-617
doi: 10.1055/s-0031-1273739

Summary of background and research design:

Background: The interest in marathons is becoming much more popular and, consequently, so are studies regarding the physiological and nutritional parameters that can optimize running endurance. 

Research question: Can correlations be seen between selected body measurements and/or nutritional factors and marathon race performance in a selected marathon?

Subjects: In total, 400 marathon runners were recruited and 257 completed the study.  The average age was 39 ± 8 y and the average finish time was 273.8 ± 59.5 min.

Experimental design: cross-sectional (no intervention)
 

Protocol: Runners were recruited from the participants of the 2009 Flora London marathon.  Participants were requested to complete on-line questionnaires about themselves (age, height, weight, training history), and their endurance training for 5 wks before the race.  Their diet the day before the race and the day of the race was also requested.  Race times were provided by the race coordinators.  The runners’ perceived exertion, pleasure/displeasure, and activation/arousal were inquired about at 5 km and 40 km during the 42.2 km marathon.

Summary of research findings:
  • There were 6 factors identified that correlated with running speed:
    • Gender: Males were typically faster than females (15%, on average).
    • Race speed was inversely correlated with body mass index.
    • Those who trained more (specifically the longest training distance and the net training distance during the 5th and 2nd wk before the race) tended to run faster.
    • Carbohydrates the day before the race directly correlated with race speed.
  • After a secondary analysis, it was found that runners who consumed greater than 7 g carbohydrates/kg body weight typically ran faster than those who consumed less.  Moreover, these runners tended to keep up pace better.
  • None of the other data collected were statistically significant.

Key practice applications:

Eat a high carbohydrate diet (greater than 7 g/kg body weight) at least the day before the race.  Although this notion has been shown in controlled studies of carbohydrate intake and performance, this study also suggests that it is true in an actual event.  Interestingly, the nutritional composition the day before the race seemed to have a larger impact than the runners’ nutrition the day of the race (though the diets of the runners the day of the race were probably more similar to one another).  These data also suggest that the total running distance performed in the weeks before training is more important than distance at any one training session.


Limitations:

The nutritional intake of these participants was not assessed on the days prior to the day before the marathon.  It is unknown whether a habitual high carbohydrate diet (that carried over to the day before the marathon) contributed to the noted benefits, or if just a single day of high carbohydrates is sufficient.

 

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