From Heat Stroke to Heat Aware

Collapse from heat stroke

“After 14,7 km I collapsed. I didn’t feel it coming, there were no warning signs, and I also don't know what happened but learned from some spectators that I fell on the ground, tried to continue running but that didn’t work. It turns out I was having a heat stroke, even though it was only 17° C [62° F] and I was wearing my cooling hat. My temperature quickly rose to above 40° C [104° F] and medics were trying to cool me with wet towels and ice. Eventually, the temperature went down and after 30–45 minutes I was released. But I couldn’t do anything other than sit on a bench with a golden blanket and wait for transport that didn’t come.”

This is how amateur athlete Daan Josephus Jitta described his collapse at the Amsterdam half marathon in October 2022.

Testing and more testing

Afterwards, he sought evaluation from a sports medical specialist. Daan was found to be very fit and healthy with no underlying health issues. The specialist believed that the heat stroke was triggered by a lingering fever/virus that he had in the week before the race.

Daan then did more testing, this time with a CORE sensor at the Thermo Clinics lab under the guidance of CORE Coach Joost Fonville. Again, the outcome was positive. Daan felt confident to resume training and started wearing a CORE sensor and monitoring his core temperature during his sporting activities.

Heat awareness

His next big race was the Valencia marathon in December 2022 (air temperature 17° C/62° F). Daan could monitor his core temperature only by opening the CORE app on the iPhone in his pocket, so he mostly relied on the heat awareness he had gained over the prior months. At 28km, he started getting tingling fingers and toes, his heart rate became erratic (suddenly going down from 165bpm to 130bpm and back up again), and his sweat rate greatly reduced. Even though his core temperature was below 39° C/102° F, he recognised these as warning signs. Coach Fonville says, “Sudden heartrate changes (up or down) seem to be an important indicator of an upcoming heatstroke.”

Daan slowed his pace, and then stopped at the next aid station to pour water over himself and walked for a couple of minutes. These measures brought his core temperature and Heat Strain Index down, and with a reduced pace he was able to finish the race. The plot of his core temperature, heart rate, and Heat Strain Index clearly illustrates this story.

The perfect race

In April 2023, Daan raced the Rotterdam marathon with even more heat awareness, a plan for cooling himself, and a Garmin watch that allowed him to easily monitor his core temperature in real time. Aided by air temperatures of 8° C/48 °F and pouring water over himself at each of the 9 aid stations, Daan kept his core temperature at a sustainable level and finished with a personal best 3:23 marathon. Contrast the core temp/heart rate/Heat Strain Index plot from this race against the one from Valencia, and it’s easy to see the results of everything he did right.

Next steps

Daan is aware that the cool weather conditions in Rotterdam played a big role in his staying cool and is considering his strategies for warmer weather races. But he believes that his newfound heat awareness – coupled with monitoring heart rate and core temperature – will help him greatly. We thank Daan and Joost for sharing this story. Daan says, “I am happy to contribute anything that helps in getting more understanding (and hopefully prevention and/or timely anticipation) of a heatstroke. Most athletes are ignorant relating to heat strokes. They do not happen only to people who are overweight and poorly trained – as I thought before I experienced it myself.” Coach Fonville added, “Heat stroke does occur to the unfit, but it especially occurs to young and highly trained runners who can perform at high power, generating a lot of heat.”