Dehydration linked to muscle cramps in IRONMAN triathletes

Contrary to previous research, a Washington State University-led study of three decades of the IRONMAN's top competition found a connection between dehydration and exercise-induced muscle cramps.

Based on medical data of more than 10,500 triathletes, the study, published in the Clinical Journal of Sport Medicine, found a strong link between dehydration and participants seeking treatment for muscle cramps during the competition. While many popular theories hold that unbalanced electrolytes or potassium and salt levels contribute to cramps, this study did not find evidence to support that, which is consistent with other recent research.

"We pretty much know that electrolyte imbalance is likely not related. Muscle cramps are complex but may be due to altered neuromuscular function issues, and now we think that more severe dehydration might be playing into that for ultra-endurance triathletes," said Chris Connolly, a WSU physiologist and the study's corresponding author. "It's important to point out that athletes are sometimes a little dehydrated before the race and some of them are very, very dehydrated by the end of it."

Exhaustion, low blood pressure, abdominal pains and headaches were also associated with muscle cramps, the researchers found. The strongest prediction of being treated for muscle cramps was having one earlier in the race. In other words, many of those who suffered from muscle cramps did so more than once in the competition of swimming, cycling and running that takes most participants all day to complete.

Muscle cramps are among the most common medical complaints in triathlons affecting as many as 63% of athletes, according to previous research that relied on self-reports. This study focused only on participants who sought treatment for muscle cramps, which usually involves intravenous fluids. These represented 6% of competitors across 30 years.

Notably, the athletes who were treated for cramps tended to have overall finish times that were slightly better than those who had not.

"It probably has to do with the intensity of the activity, so people that are finishing faster, relatively speaking, are probably working at a faster rate and higher intensity," said Connolly.

That intensity might be leading to more muscle cramping, but that connection would need further investigation, he added.

On average, incidence in the muscle cramping has been going down at the IRONMAN championships over time, a decrease of about 0.4% a year, which the researchers hoped was a sign of improved prevention and treatment at the races.

As the official curators of World Triathlon and IRONMAN data housed at WSU, Connolly and collaborator Dr. Douglas Hiller, a WSU clinical medical professor and an IRONMAN Hall of Fame inductee, hope to continue that improvement and overall safety of the sport through continued research.

They will also be on-hand at the medical tents in Hawaii during this year's race: Hiller directly helping patients and Connolly collecting data.

This is the second year the competition has been split into a men's and women's competitions with the women competing in Nice, France this past September. The split is a sign of the growing numbers of triathletes.

With that surge in participation comes increased dangers, Connolly said. Other medical issues experienced during ultra-endurance triathlons include heat injury, severe nausea and hyponatremia, a potentially serious condition where body sodium levels drop well below normal. Though uncommon, deaths have also occurred during these rigorous events.

"Ultra-endurance triathlons have had a meteoric rise in popularity across the world. It's gotten huge. Anytime something that is this physiologically demanding grows that quickly, I think it takes a while for safety procedures and plans to catch up," he said.

In addition to Connolly and Hiller, co-authors on this study include first author Paal Nilssen and second author Dr. Kasey Johnson both recent graduates of WSU's Elson S. Floyd College of Medicine as well as Dr. Thomas Miller of Virginia Tech.