Train with CORE: Simple Heat Training for Triathletes

Once you have done a heat ramp test, identified your ideal temperature zones, and gained some heat awareness, you are ready to start heat training. Heat training is a simple technique that has been proven to boost VO2max, power at lactate threshold, and time trial performance by 5–8% in both hot and cool conditions. The physiological changes mostly involve creating more blood plasma and red blood cells, allowing greater delivery of oxygen to muscles. The gains from season-long heat training allow you to train at a higher intensity, which further boosts your race performance.

Basics of heat training

The article Heat Training for Sporting Performance gives details on heat training. But the basics involve doing 2–3 heat sessions per week, with each session having 45–75 minutes in your heat training zone. This amount of time accumulated in the heat training zone is known as thermal load, and it is easily tracked in the CORE mobile app.

Accumulating this amount of thermal load is easy with a typical triathlete’s training plan. The required thermal load should be reached each week; missing 2–3 weeks of heat training will greatly diminish the extra blood plasma you have created.

Note that while some people will choose to do a heat training block (2–4 weeks of 6 days/week of heat training), to get their plasma gains immediately, most find it more convenient to accumulate those gains more gradually with something like the schedule below. If you do choose a heat training block, the below schedule can be used for season-long maintenance.

Sample heat training schedule















Easy bike

Bike intervals



Easy bike (optional 45–75 minute heat session)

Long ride (include
45–75 minute heat session)



Easy run

Easy run
(45–75 minute heat session)

Run intervals


Transition run

Long run (include 45–75 minute heat session)


Details of the heat sessions

Wednesday, easy run

Most athletes find it easy to elevate their core temp into the heat training zone while running, even during easy efforts. Simply wearing an extra layer or two, even during winter weather, should be enough. If your run isn’t long enough to give you 45–75 minutes in the heat training zone, sitting in a hot bath or sauna after you run can extend your heat session and give you the total thermal load you desire.

Friday, easy bike (optional)

As an alternative to (or in addition to) the easy run, you can accumulate thermal load on the indoor trainer, even during an easy session. An extra layer of clothes, or turning off a fan, is likely all that is needed. Reaching the heat training zone on the bike during an easy outdoor ride may require a lot of extra clothing, depending on the air temperature.

Saturday, long ride

Even though your long ride duration might total 2–6 hours, be sure to accumulate no more than 75 minutes in the heat training zone. More than that may cause excess fatigue. This means you’ll need to add and subtract layers during the ride to regulate your core temp. Arm/leg warmers, a beanie, and a light jacket may be enough to get you into the heat training zone during mild weather. Colder outdoor temperatures will require more layers and more planning.

Note: If you’re doing a transition run after the ride, you may find that run challenging if you end the ride with your core temp in the heat training zone.

Sunday, long run

Similar to the long ride, you should accumulate no more than 75 minutes in the heat training zone, even if your total run duration is longer than that. Adding or subtracting layers will help you keep your core temperature where you want it. Depending on air temperature/humidity, it may be difficult to lower your core temp once it’s in the heat training zone.

Tracking thermal load

The CORE mobile app makes it easy to track your thermal load. You can see how many heat training sessions you’ve done in a week or month, and also the cumulative time you’ve accumulated in that zone. Remember that athletes can also easily share their CORE mobile app data with their coach – it will be synced to the coach’s app as soon as the athlete uploads it to the CORE app (or if using a Garmin device, as soon as the workout syncs with the Garmin app).

Next steps

Once you’ve become accustomed to heat training, the next step in using CORE is learning how to pre-cool before a race or intense workout.