Individuality of Heat Zones

CORE's Heat Zones are designed to help athletes understand the impact of heat stress on their body, guiding them during racing and training. It is important, however, to realize that thermoregulation is highly individual. Therefore, the thresholds of the Heat Zones may vary from athlete to athlete.

For example, one may already experience considerable negative effects of heat at a HSI of 2.5, while another may only be affected at a HSI of 4.5. Similarly, the optimal heat training range may be at HSI of 2.5–3.5 for one, but 5.0–6.0 for another.

With a bit of curiosity and patience, you can find the range of HSI where your performance is affected, and where your heat training will be optimal. For most people, this will be at a HSI between 3.0 and 6.9, ie. Heat Zone 3. Follow the guidance below to find out where on the spectrum you are.

Try a Heat Session

First, try a heat session as described in the article How to do a Heat Session. Try to get your HSI into Heat Zone 3 (3.0–6.9) and keep it there for a while.

• Are you sweating profusely?
• Does your power/pace decrease as you keep heart rate steady?
• Is the session hard, but not extremely so?

If your answers to these questions are “Yes”: Great! Like most people, you have all or most of Heat Zone 3 to do your heat training in. Even though the general guidelines are right for you – make sure to always listen to your body. One day you may be more tolerant to heat stress than the other!

If your answers to one or more of these questions are “No”: continue reading.

Troubleshooting

The heat session was too hard

• Did you struggle to get your HSI above 3.0?
• Were you sweating profusely when HSI was less than 2.0?
• Did you see a substantial increase in heart rate at a HSI below 3.0?
• Did you feel like a HSI of 3.0 or 4.0 was causing extreme heat discomfort?

If any of these apply, you may have a ‘lower thermostat’, and perhaps lower heat tolerance compared to others. Read below how you can determine your individual Heat Zone 3 thresholds.

The heat session was too easy

• Did you breeze through HSI values of 3.0 and even 4.0 without feeling much discomfort from the heat?
• Did your heart rate remain constant at a steady power/pace at the lower range of Heat Zone 3?

If so, you have a ‘higher thermostat’, and perhaps higher heat tolerance compared to others. Read below how you can determine your individual Heat Zone 3 thresholds.

Determine your individual Heat Zone 3 thresholds

If you believe the generalized thresholds of Heat Zone 3 do not work for you, try these two workouts (~40–60minutes per workout).

Workout 1: No heat strain (control)

1. Do the workout on an indoor treadmill or bike trainer. Keep the room relatively cool, wear light clothing, and use a fan or two to create airflow. Your HSI should stay in Heat Zone 1 (HSI 0.0-0.9) for this entire workout.
2. Work at an easy power/pace (perhaps 55–65% of FTP for cyclists, or an ‘all-day’ endurance pace for runners).
3. Watch your heart rate climb for 10–15 minutes, after which it should stabilise. Hold the same power/pace for at least another 30 minutes. As you are not under heat strain, your heart rate should stay constant. Note both your power/pace and the heart rate during this steady-state exercise. These two numbers should stay ‘coupled’ any time you have good cooling and are not otherwise fatigued (day-to-day heart rate variation of a few percentage points is normal).

Workout 2: High heat strain

1. On a different day, do a heat session – overdress or exercise in a hot environment (see How to do a Heat Session).
2. Start exercising at the same power/pace you did for Workout 1. Unlike Workout 1, you will now start to heat up. Monitor your HSI and heart rate.
3. When heart rate has risen 10% higher than your steady-state heart rate from Workout 1, note your HSI. At this HSI value, the heat strain is starting to considerably affect your exercise performance. This is also the HSI value you want to target for heat training.
4. Keep a steady heart rate for another 15 minutes. HSI will likely increase.
5. The range of HSI values you experience between steps 3 and 4 are likely your target for heat training.

Example

1. In Workout 1, a cyclist with a low thermostat maintains 170 watts with a heart rate of 140 bpm. HSI is 0.0.
2. In Workout 2, the cyclist overdresses and maintains 170 watts after a brief warmup.
3. Heart rate climbs as HSI climbs. When heart rate reaches 154 bpm (10% higher than 140 bpm), HSI is observed to be 3.5.
4. For the rest of the heat session, power is reduced to maintain a hr of ~154. HSI will likely increase, but not extremely so.
5. A good heat training range for this athlete is likely 3.5–4.5

Questions?

If you do the above workouts and still struggle to identify a suitable heat training zone, please contact us a info@corebodytemp.com. You can chat with a coach who will guide you in finding your ideal Heat Zone 3.