The importance of carbohydrate for endurance athletes dates back almost
100 years when marathoners were shown to have low blood glucose levels
at the end of the 1924 Boston marathon.
The following year carbohydrate
feeding was shown to prevent the decline in blood glucose and improve
performance. Subsequent research led to the understanding of the
importance of muscle glycogen, the storage form of carbohydrate in
muscles, as a fuel for active muscle during prolonged exercise and made
the connection between glycogen depletion and fatigue. Researchers
discovered that manipulating an athlete's training combined with a high
carbohydrate diet several days prior to exercise (
carbohydrate loading)
significantly increased muscle glycogen levels and delayed fatigue.
Subsequent work throughout the 1970s and 80s continued to show that
carbohydrate feeding could enhance endurance performance. Whether or
not protein is important for endurance athletes remains less clear, but
recent evidence shows it may be important. Researchers examined whether
a carbohydrate beverage with added protein (carb-protein) would have
any performance benefit compared to a matched carbohydrate beverage
(carb), a matched carbohydrate beverage with additional carbs to match
the calories provided by
protein (
carb-carb),
and a placebo (water). Trained cyclists performed four exercise tests
where they were asked to ride to exhaustion using one of the 4
beverages. They cycled the longest with the carb-protein beverage, with
the next best performance in the carb-carb trial followed by the carb
and water trials. Interestingly, the carb-protein trial also had lower
levels of muscle damage after exercise and increased muscle strength 24
hours after exercise. These findings support the idea that adding
protein to carbohydrate is important for endurance athletes to increase
performance and enhance recovery.
Valentine
RJ, Saunders MJ, Todd MK, St Laurent TG. Influence of
carbohydrate-protein beverage on cycling endurance and indices of
muscle disruption. Int J Sport Nutr Exerc Metab. 2008 Aug;18(4):363-78.
