Early on the morning of April 19, 1924, doctors Samuel Levine, Burgess Gordon, and Clifford Derick reported to the finish line of the Boston Marathon. Their physician’s bags were packed with the usual assortment of bandages, stethoscopes, and salves they would use to tend to runners crossing the finish line later that day, but they also carried a set of syringes and vials for an ambitious scientific project.
Levine, Gordon, and Derick were scientists as well as physicians.[1] The previous year, they’d brought a cutting-edge machine to the finish line to conduct “roentgen-ray examinations”—chest X-rays—to study the heart structure of marathon finishers. This year, their aim was to study another frontier of medical science: blood sugar levels.
The existence of sugar in the blood was nothing new; doctors had known since 1776 that sugar circulates in the blood thanks to descriptions of type I diabetes. Research by French physiologist Claude Bernard in the mid-1800s had also shown that glycogen storage in the liver provided a steady supply of glucose to the bloodstream.
However, medical research on blood sugar was at a fever pitch in the early 1920s thanks to the discovery of a mysterious substance produced in the pancreas that was intimately linked to blood glucose levels.
In 1916, Romanian physician Nicolae Paulescu had shown that a crude extract from the pancreas of a healthy dog was able to normalize blood sugar levels in a diabetic dog, and in 1921, Canadian researchers Frederick Banting and Charles Best isolated a purified form of this substance—dubbed insulin—and used it to successfully treat a 14-year-old boy with type I diabetes.[2]
Two years later, Banting and Best were awarded the Nobel Prize, and three doctors in Boston began wondering whether blood sugar had any impact on performance in marathon runners.
The 1924 edition of the Boston Marathon served as the US Olympic Trials for the upcoming Paris Olympic Games, and as such, the race distance was increased from its usual 25 miles to the official Olympic distance of 26.2 miles.
Competitors from elsewhere on the east coast often had to travel for days to reach the starting line in Hopkinton, but Levine, Gordon, and Derick managed to track down five competitors before the race and measure their blood sugar and a few other key components of blood chemistry, including uric acid, nitrogen, and carbon dioxide levels in the blood. Their plan was to measure these same parameters in the finishers soon after they crossed the finish line.
On race day, their data collections started out well—they managed to take a blood draw from the race winner, Clarence DeMar, who was in excellent spirits after setting a world’s best of 2:29:40.[3]
Their attempts with subsequent runners were more of a mixed bag. Some of the runners were in very poor condition and were quite unhappy about having their blood drawn; others had broken away to have a snack after finishing the race, ruining the careful attempts to control for food intake.
One runner had dropped out at 15 miles and had a meal of meat, bread, and soda water—a combination that seemed perfectly designed to wreak havoc on measurements of nitrogen, glucose, and carbon dioxide. By far their biggest headache was a runner who was dragged into the medical tent completely unconscious![4]
When Levine, Gordon, and Derick returned to Peter Bent Brigham Hospital[5] and reviewed their data, they discovered a striking correlation between a runner’s post-race blood sugar level and their physical condition.
Clarence DeMar, who was upbeat and peppy after his win, had a blood sugar level of 89 mg/dL, while some of the other runners behind him who were pale, clammy, and irritable had blood sugar levels between 47 and 65 mg/dL—well below the usual range of 70–100 mg/dL.
Conversely, the runners who had slipped away for a post-race snack had much higher blood sugar levels: 123 mg/dL in one case, and 178 mg/dL in another.
Most remarkably, the lowest blood sugar measurement of all was in the runner who was dragged into the medical tent unconscious—he registered only 45 mg/dL.
Levine, Gordon, and Derick noted that the symptoms they observed in the exhausted runners at the finish line—pallor, clammy skin, agitation, signs of “shock” and “stupor”—were also classic symptoms of hypoglycemia: low blood sugar.
Armed with these findings, Levine, Gordon, and Derick wrote up their results and planned out a more ambitious project for the 1925 edition of the race: they would devise a nutritional intervention to maintain high blood sugar levels throughout the race, with the goal of improving performance and preventing the exhaustion they saw in the runners who stumbled across the finish line the previous year.
In the months leading up to the 1925 Boston Marathon, Levine and Gordon, alongside three other doctors, drew up a plan.
Runners who had struggled in the final miles of the race the previous year would undergo a scientifically designed nutrition program with two components: a pre-race diet for the 24 hours before the race that was designed to deliver a large amount of carbohydrates while posing a minimal risk of gastrointestinal problems, and a steady supply of sugar during the race in the form of glucose-containing candies prepared by Amelia Lautz, a dietician at Peter Bent Brigham Hospital.
On race day—April 20, 1925—their experiment was a resounding success: runners who had struggled badly the year before crossed the finish line in excellent condition, with many shaving five to ten minutes off their race times.
The pre-race “glycogen loading” and mid-race fueling with candy successfully maintained blood sugar levels too: runners who had finished in terrible condition with blood sugar levels measuring 49–65 mg/dL now finished feeling good with blood sugar levels of 81–114 mg/dL.
The runners themselves noticed a difference too: one runner stopped at an aid station 11 miles into the race, announcing his intention to drop out of the race. The medical team persuaded him to drink some sweetened tea and eat a few pieces of candy. He soon perked up and rejoined the race. Other runners made comments to a similar effect; one said, “if I didn't eat the candies, I couldn't have finished.”
After the race, the medical team again returned to Peter Bent Brigham Hospital to write up their findings, which they would later publish in the Journal of the American Medical Association.
Their report on their intervention at the 1925 Boston Marathon wasn’t a true randomized controlled trial—those wouldn’t be invented for another two decades—but it was nevertheless a landmark moment in the history of exercise physiology: the first evidence-based fueling plan for the marathon.
This year’s Boston Marathon marks the 100-year anniversary of this pioneering study. A century later, evidence-based fueling plans used by marathoners today have many of the same contours as the intervention designed by the 1925 team: a 24–48 hour period of increased carbohydrate intake, designed to increase muscle glycogen content while avoiding foods that cause gastrointestinal problems; plus a mid-race fueling plan aimed at sustaining a steady supply of sugar throughout the race.
There have, of course, been many novel developments in marathon fueling in the last 100 years, including the use of multi-carb fueling plans, major races providing individualized fueling and “bottle service” for elite runners, and true randomized experiments demonstrating the performance benefits associated with fueling.
Nevertheless, Samuel Levine, Burgess Gordon, and Clifford Derick would easily recognize and approve of the pre-race pasta dinners and mid-race energy gels used by runners today. Indeed, their 1925 paper closes with a recommendation well worth heeding by runners gearing up for this year’s race:
It seems, therefore, 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.
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Footnotes
[1] Dr. Samuel Levine would later become famous for being the doctor who correctly diagnosed future president Franklin D. Roosevelt with polio in 1921.
[2] The first treatment attempt resulted in a dangerous allergic reaction to the extract. At the time, diabetes was essentially a death sentence, so Banting and Best worked frantically for the next twelve days to develop an improved version of their insulin extract. The second treatment was a success: normalization of blood sugar and no allergic reaction.
[3] Alas, even in 1924, Boston’s course was not eligible for official world records. DeMar, though, would go on to win a bronze medal at the 1924 Paris Olympics.
[4] This level of exhaustion was nothing new for the medical team: in their previous paper on the 1923 marathon finishers, Gordon, Levine, and Milmaers noted that some runners were so exhausted they needed assistance just to stand upright during the chest X-ray!
[5] Peter Bent Brigham Hospital is now Brigham and Women's Hospital, the teaching hospital affiliated with Harvard University. Its cardiac intensive care unit is named after Dr. Levine.
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Thanks, that was a fascinating bit of history! I had no idea this kind of work had been pioneered so long ago.