Marathon factors

NYTimes

November 3, 2006
New York City Marathon
Everything You Know About Marathons Is Wrong
By GINA KOLATA

Most runners have heard the marathon lore: Your time will be best if the weather on race day is about 55 degrees and overcast, or even drizzly. And avoid dehydration at all costs, because it will cause your muscles to cramp and you could collapse at the finish line.

But none of that is true, researchers said at a recent marathon medicine and science conference in Chicago.

The weather theory “needs adjusting,” said Scott J. Montain, a research physiologist at the United States Army Research Institute of Environmental Medicine in Natick, Mass.

“Most of what we know comes from the lay literature,” he said.

Thousands of runners are no doubt monitoring the weather forecast for Sunday, when the New York City Marathon makes its annual tour of the five boroughs. (As of yesterday, it looked promising, with temperatures expected to be in the upper 40’s and partially cloudy skies.) But the weather nostrums for marathoning that are cited so authoritatively in journal articles and textbooks are not always borne out in legitimate science. Montain and his colleagues set out to conduct a proper study.

They gathered data from 28 years of the New York City Marathon, 35 years of the Boston Marathon and 23 years of the marathons in Hartford, Vancouver, Duluth, Minn., and Richmond, Va. The routes for those marathons have barely changed over the years, and each had a large field — more than 10,000 runners. The investigators looked at the average times for the top three men and women, and at the times for the runners who placed 25th, 50th, 100th and 300th.

Elite runners ran fastest in the coldest conditions — 41 to 50 degrees. But the slowing effect with heat was not as great as had been previously reported. For every five-degree increase in temperature, times slowed by 0.4 percent.

Warmer weather had a greater effect on slower runners. On a 77-degree day, an elite runner would be about 5 percent slower than on a 41-degree day. But a runner who finished in three hours on a 41-degree day would be slowed by about 12 percent on a 77-degree day, finishing in 3 hours 21 minutes.

One reason, Montain said, could be that slower runners spend more time on the course, and the temperature generally rises through the day. Or it could be because slower runners tend to run with a larger pack. A tightly clustered group of runners generates heat and blocks it from dissipating.

Montain and his colleagues also looked at whether marathon times were better under sunny or overcast skies. Only 13 percent of records were set on cool and cloudy days.

“It is more likely that a record will be set when it is sunny or when there are scattered clouds,” Montain said. He is not sure why that is; perhaps sunny conditions put runners in a better mood, he suggested.

Then there is the issue of cramping, that often excruciating, spasmodic, involuntary contraction of muscles that can occur during or, more often, just after a marathon. It almost always involves the muscles that were used to run — the hamstrings or calf muscles, for example. And it can last a minute or two — or much longer.

Conventional wisdom says cramps are caused by dehydration and that the solution is to consume salt and drink more fluids. Not true, says Martin P. Schwellnus, a professor of sports medicine at the University of Cape Town in South Africa.

At the conference in Chicago last month, he reported that he could find no relationship between dehydration and cramping. He has studied cyclists, marathoners and triathletes, measuring levels of electrolytes and body-weight changes, both of which are indicators of dehydration. Those who cramped were no different from those who did not.

Two other studies looked at how much weight ultramarathon runners and triathletes lost during races — a measure of fluid loss and a direct indicator of dehydration. Those who cramped lost no more weight than those who did not. If anything, Schwellnus said, those who did not have cramps were slightly more dehydrated.

The cause of cramps, Schwellnus believes, is an alteration in the electrical signals going to exhausted muscles so that the balance between those signals activating muscles and those inhibiting them is distorted. One way to protect yourself is with proper marathon training and proper pacing. “Racing at too high of an intensity is one of the single most important risk factors,” Schwellnus said.

When muscles cramp, there is a simple and effective treatment: stop running and stretch that muscle. And, Schwellnus said, realize that the cramping will soon stop.

“Almost no matter what you do, if you stop the activity, the muscle will come back to normal,” he said.

Beyond the finish line of every marathon are runners who feel dizzy, and some of them collapse. It is not as common as muscle cramps, but the condition can afflict up to about 5 percent of marathon runners, said Michael N. Sawka, head of the thermal and mountain medicine division at the United States Army Research Institute of Environmental Medicine. He wondered whether the cause could be dehydration, a commonly evoked mechanism.

Sawka looked at published studies. One compared 45 athletes who collapsed after an ultramarathon to 65 who completed the race and did not collapse. There were no obvious differences between the two groups: their body temperatures were the same (dehydration makes the temperature rise), as were their electrolyte levels. But those who collapsed were pushing themselves as hard as they could, were at or close to their personal records, or were medal winners in the race. Perhaps, Sawka said, “that final effort might contribute to collapse.”

The actual cause, though, does not appear to be dehydration, Sawka said. Instead, it is a pooling of blood in the lower legs and feet when vigorous exercise suddenly stops and the heart rate slows markedly.

Timothy Noakes, a professor of exercise and sports science at the University of Cape Town, said he had stopped giving intravenous fluids to collapsed runners.

“We completely changed the way we treat patients,” Noakes said. “All we do is have them lie down and put their feet higher than their head.”

Postmarathon collapse, Noakes added, “is a benign condition.”

“Just lift their legs and you will help the majority of patients,” he said. “That’s all you need to do to make most people recover very, very quickly. You can infuse as much fluid as you want, and you will not get the same response.”