Trail racing is a sport with extreme variations in terrain and weather. And athletes must be prepared for the accompanying extreme variations in core temperature. Tobias Schmid did just that while training for the 31km race in the Zugspitz Ultratrail, one of Germany’s largest trail races. His heat training helped propel this talented amateur to a 13^th place finish in a field of 750.

Tobias kindly shared his race data and heat training protocols with us.

Up and down core temperature

The race started at 14:00 in a hot sun, with air temperature close to 30° C/86° F. After a fast and flat 2km, the trail climbed 1000 meters in 8 km of distance. We see his core temperature also climb – peaking at 39.4° C/102.9° F.

One hour into the climb the runners were soaked by a strong thunderstorm with high winds. Tobias said, “Up there at 1700 metres it was really windy and I got immediately cold from my wet clothes. We continued to climb but I struggled to keep a high heart rate.” We can see his core temperature start to drop, and it continued to fall through the subsequent technical downhill.

After 21km (16:07) a long nontechnical gravel-road descent started, where Tobias could again push the pace. Combined with the reappearance of the sun and the warmer air temperature of lower elevation, his core temp again climbed, reaching 39° C/102.2° F at the finish.

Heat training protocol

Tobias reported feeling comfortable with his high core temperatures – likely due to the heat training he had done before the race. He had completed a 10 consecutive days of heat training that ended 10 days before the race. These heat sessions were done on an indoor bike trainer while wearing a CORE heat training suit. In each session he would spend at least 60 minutes in his heat training zone.

Take-away lessons

In comparing the chart of his race with the chart of a heat training session, several things stand out. First, his core temperature during heat training was lower than the peaks of the race. This is typical – an extremely high core temp in training is not necessary to cause physiological adaptions.

Second, his Heat Strain Index in training was higher than anything experienced on race day. Higher numbers are caused when skin temperature (as well as core temp) is very elevated. The Heat Strain Index is strongly correlated with thermal discomfort. Being acclimated to a higher Heat Strain Index tends to make athletes more comfortable with temperature extremes on race day.

Lastly, Tobias’ Heat Strain Score during the race was 1014. During the heat training session shown, it was 810. Heat Strain Score is the total amount of heat stress accumulated during a day. It seems likely that athletes benefit by having training sessions where they accumulate a Heat Strain Score similar to what they will experience on race day.

Tobias’ conclusion was that “I for sure think the heat training helped me to tolerate the heat in the early and late stages of the race!”