Friday, January 25, 2013

Diet, Blood Sugar and the 1925 Boston Marathon

The Science of Soccer Online was established to translate “cutting-edge” research into practical applications for the coach. For the most part, I have focused on newly published research and how it relates to performance on the pitch. However, it is worthwhile to look back at our roots, to reflect on early research that set the foundation for what we understand about exercise, training, nutrition and performance. Early studies were simple in design and focused more on observations and less on statistical analyses. Also, these early studies allowed researchers more leeway in the interpretation and application of their results. This post describes two studies from the mid-1920s. Researchers from the Peter Bent Brigham Hospital and Harvard Medical School took one of the earliest looks at blood glucose, diet and performance during the Boston Marathon. What they conclude still holds true for today’s athlete.

The first study was conducted at the 1924 Boston Marathon. Blood samples were taken from several runners before and after the race. They were then analyzed for several constituents, primarily blood glucose (or blood sugar). In 1924, this was not easy task. Today’s ability to draw bold into storage vials, place them on ice or freeze them for later analysis was not available then. The biochemical analysis was also rather complex and time consuming. Thus, at the time, this study was a rather difficult undertaking.

The investigators were quite amazed with the level of post-race hypoglycemia in some runners (low blood sugar). Four of the 12 runners had blood glucose levels at or below 40 mg/dl (2.8 mol/L). This group and others with low blood glucose showed post-race physical conditions that were described as “poor”, “pale” and “stuporous”. In fact, the runner with the lowest blood glucose was “…unconscious ad brought in by the police, perfectly limp.”

At the other end of the spectrum, the winner of the 1924 race did not experience hypoglycemia (he also broke the world record). He, along with others who maintained their blood glucose, had a “good” physical condition at the finish.

What impressed the researchers was how their data related to an earlier study performed on dogs. Dogs with blood glucose levels of 60 mg/dl became weak, those who reached 50 mg/dl became flaccid and those whose blood glucose dropped below 40 mg/dl died. Levine et al. point out that low blood glucose levels in the marathoners (40-50 mg/dl) are rarely seen except in cases of insulin shock.

The significance of the study is that for the first time, researchers showed that during “…such a prolonged and violent effort as a marathon race…” the reserve supply of blood sugar is insufficient. The authors conclude that this condition of hypoglycemia could be avoided by taking in carbohydrates before and during the race. And, eating carbohydrates could help performance. This was a somewhat novel concept since most athletes in the 1920’s ate diets that were high in protein (beef, chicken and eggs) rather than carbohydrates.

In the second study, carried during the 1925 race was designed to test their hypothesis. The runners in the 1924 study were encouraged to eat a high carbohydrate meal the day before competition and to eat candies along the route. Blood samples were again collected before and after the race.

Those runners, who experienced hypoglycemia in 1924 but ate well before and during the second race, maintained their blood glucose and reported “good” or “very good” physical conditions at the finish line. Many also improved their race time (although the distance may have been slightly longer – see comment below).

Comments made about one runner emphasize their findings. “One runner who developed symptoms of exhaustion between the tenth and twelfth mile arrived at the first station in very poor condition and wished to retire from the race. He was persuaded to take some tea and candies and continued running. He made only one other stop for candy between this station and the finish line. When asked after the race how he felt while running, he said that he felt "fine except for weakness and starving" and "felt better after eating the candy." On the other hand, another runner was, “…advised, so he stated, not to eat sugar or much potato during his training. He apparently started the race in good condition, but was noticed by observers to be running poorly and, as he passed the second station, it seemed as if he would collapse.”

In the end, the researchers confirmed their hypothesis and concluded that, “…the picture of exhaustion, weakness, shock and other symptoms of hypoglycemia following prolonged effort may be prevented by the adequate and timely ingestion of carbohydrate.” This is exactly what sports nutritionists recommend for today’s endurance athlete – carbohydrates play a major role in performance.

What is unique about these early studies is the description of the athletes during and after the race. The eloquent characterization of individual cases of success and failures paints a vivid picture of how diet affects performance.

The idea that carbohydrates eaten before and during endurance exercise can improve performance is not novel. Subsequent research studies conducted over the past 90 years have confirmed that 1) blood glucose can drop during prolonged exercise leading to hypoglycemia, 2) hypoglycemia can impair performance and 3) a high carbohydrate diet can help avoid this situation.

Unfortunately far too few young players heed this advice. Despite nearly 100 years of evidence, many players eat a diet that contains too many fats and too few carbohydrates. Thus, today’s goal is to educate these players on why carbohydrates are important as well as how improve their performance through the diet. By doing this, players can capitalize on nearly 100 years of research, that began with the 1924 Boston Marathon.

References

Levine SA, Gordon B, Derik CL (1924) Some changes in the chemical constituents of the blood following a marathon race. Journal of the American Medical Association, 82: 1778-1779.

Gordon B, Kohn LA, Levine SA, Matton M, Scriver WM, Whiting WB (1925) Sugar content of the blood in runners following a marathon race, Journal of the American Medical Association, 85: 508-509.

Notes

A few side notes about these editions of the Boston Marathon (or the American Marathon as it was called then). In 1924, the race was lengthened from 24.5 miles to 26 miles, 385 yards, in order to comply with the Olympic standard. Clarence DeMar (shown in the photo) won in what was noted in the JAMA article as a world record time of 2:29:40. However, it was later found that the distance was 197 yards short of the standard distance, negating the world record. In 1925, Chuck Mellor defeated DeMar. According the Boston Athletic Association’s website, Mellor ran with “…a wad of tobacco tucked inside his cheek and the morning edition of the Boston Globe placed inside the front of his shirt to serve as a windbreaker.”

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Read more at www.soccerteamdiet.com