Train with CORE: Identifying Threshold Core Temps

Picture this: You’ve done your heat training, practiced pre-race cooling, and dialled in your race-day cooling strategies. On race day, the weather is hot, but everything is going to plan late in the race. You have a shot a personal best, and maybe even a podium. Should you drop the hammer and go for it? Or pace conservatively and avoid a meltdown?

Some athletes are very familiar with negative splits or surging toward the end of a race. They know they can hold an elevated power/pace for the final 10, 20, or 30 minutes. Similarly, they may pace themselves early based on a target heart rate, but then allow that heart rate to climb at the end of the race, knowing they can sustain. Is the same possible for those who are heat pacing (ie. not exceeding a given core temp)? Can they exceed that planned core temp for the last 10, 20 or 30 minutes of a race?

Elite athletes know their limits very well. It’s not uncommon for them to finish a race with a core temp of 40.0°C/104.0°F with no medical attention needed. That does NOT, however, mean that it’s a wise decision for other athletes – we’ve all seen athletes (even professionals) run themselves into the med tent, or even collapse before the finish line. Both are dangerous situations that can threaten the athlete’s health.

Unlike determining maximum power or maximum heart rate, experimenting with maximum core temp is dangerous and should NOT be done. So how can you know what your maximum core temp should be on race day?

Another heat ramp test

Early in your usage of CORE, you likely did a heat ramp test to identify your heat training zone. If it’s been more than four weeks since you’ve done that heat ramp test, it’s time for another. If you’ve done heat training, it’s likely that your heat training zone is now higher.

When you do the heat ramp test this time, consider starting the test at planned race power or heart rate if your race will be longer than an hour. (If your race is shorter than an hour, race-day intensity may be too high for a heat ramp test.) Other than that, conduct the heat ramp test as normal, keeping heart rate steady and stopping when power or pace declines 20%. Note your maximum core temperature.

Field testing the results

The heat ramp test identifies the core temp at which your performance starts to decline – your power/pace worsens at your race-pace heart rate. This is likely the lower end of your heat training zone, and is possibly your planned race-day core temp threshold – exceeding it will cause a performance drop.

This means that to maintain or increase power/pace once you’re above that core temp, your heart rate would need to rise. But we know that it’s sometimes possible and desirable to have such a heart rate and core temp rise toward the end of a race.

This is a scenario you can cautiously test.

Workout 1

  1. Warmup, gradually building to planned race pace and heart rate. Adjust clothing so that your core temp is at planned race-day core temp (which is likely below your heat training zone).
  2. Next, simulate a finishing surge. For 15 minutes, increase your power/pace to the extent you think may be feasible at the end of the race. Carefully monitor your heart rate and core temp. Both will likely rise. Do not allow your core temp to exceed the highest part of your heat training zone. And, if at any time you feel weak or dizzy, stop the workout and cool down.
  3. At the end of the 15 minutes, note your heart rate, core temp, and Heat Stress Index. Also note your perceived effort.
  4. The results of this field test will not be definitive – there are too many variables on race day to know exactly how your body will respond to a surge in pace or a rise in core temp. However, this test should give you an idea of what to expect. And if your heart rate or core temp climbs too quickly, it is unlikely you’ll be able to maintain such a surge on race day. But if it feels sustainable, it may give you information needed to make strategic decisions during the closing kilometres of the race.


Core temperature up to 41.5ºC during UCI Road Cycling World Championship in the heat