DOHA, Qatar — The stopwatch is only one way to measure the gains athletes are making at the world championships this year.

About 200 runners volunteered to swallow red-and-white capsules that contain data transmitters. It is part of an International Association of Athletics Federations research project on the effects of heat and body-core temperatures.

They could not have picked a better time or place — in Doha, where the temperatures reach 100 degrees every day, and less than a year removed from the Olympics in Tokyo, where conditions are expected to be every bit as stifling.

Most of the volunteers for this study come from endurance events such as the marathon, 10,000 meters and race walks. The marathon and race walks have been held outside the air-conditioned stadium. Temperatures have been about 90 degrees with humidity above 70% each night. About 25% to 40% of the athletes dropped out of the women’s marathon and 50k race walks. About 20 runners took part in the study for the men’s marathon Saturday.

“We’re learning a lot from these elite athletes with this technology,” said Paolo Emilio Adami, the health and science department medical manager for the track federation.

This is how it works: About two hours before they start, runners in the study are asked to swallow a capsule that contains a transmitter and battery. The capsule works its way into the intestines by race time and the medical staff takes it from there, with equipment set up to sync with the transmitter after an athlete finishes the race. The transmitters record body-core temperatures.

In addition, thermal cameras are set along the course that calculate heat emission through high-definition pictures. And the participating athletes are weighed before and after the race to assist in gauging hydration levels.

American marathoner Roberta Groner, of Montclair, New Jersey, raised her hand to take part in the project. No surprise, given that her background is in nursing.

“I’ll do anything for research,” Groner said.

Shortly after finishing the midnight women’s marathon on Day 1 of worlds, Groner was escorted to a station, where the medical staff hung a transmitter around her neck to download the information.

“It’s good data for the sport and for myself to find out how I did throughout the competition,” Groner said.

She is eager to see what the results yield after her sixth-place finish. It could offer useful training tips going forward and with the Olympics on the horizon.

For the project, IAAF partnered with Aspetar, an orthopedic and sports medicine clinic in Doha. It is similar to the heat research cycling conducted during its 2016 world championships in Doha.

Adami stresses that the data is being conducted only for research purposes and cannot be used to affect an athlete during the competition.

The IAAF medical team focuses on body core temperature. If that number runs too high, it could be an indication of such things as heat stroke.

“Our body is the most perfect machine that exists,” Adami said. “We are learning with this technology device and interpreting the messages that we normally feel and that we would not be paying enough attention to.”

All athletes competing at worlds have been urged to fill out a survey in which the researchers asked questions involving hydration and acclimation plans to brace for the Doha heat.

Distance runners can use all the information they can get with Tokyo less than a year away. They will be running in extreme heat, as well as sunshine.

“That will be a massive difference,” Adami said.

Some of the teams that reached out to participate in the project include Germany, Italy, Spain, Japan, China, Australia and Kenya. Individual athletes from France, Britain and the U.S. have wanted in on the research, too.

“Based on this data, ideally, they should be able to tailor the needs to each athlete,” Adami said.

As for how the device is dispelled — well, nature simply runs its course.