How to execute "active" heat training

It's June and, as expected, heat training is the buzz. If you're training for a specific event or an event where it will likely be hot and/or humid, there are some things you should think about when preparing, whether or not you live somewhere warm.

Heat acclimatization

If you live in a warm climate, chances are you've already begun the acclimatization process to heat. Here are some things that can help as you adjust and prepare.

Time of Day

If you are doing an aerobic or sub-threshold type of session, you can start in the warmer part of the day. However, for VO2max type workouts, you're probably better off riding early in the morning while temperatures are still cooler.

Clothing

During training, wear your usual kit, similar to what you plan to race in.

Hydration

Have plenty of fluids before and during the session. If you normally drink 500 ml per hour, plan on taking in at least 700 ml per hour or more, depending on how long/hot the ride is and your thirst. Drink enough to avoid losing more than ~3% of your body weight in a session that lasts up to 4 hours.

Intensity/Effort 

When you first start out riding in the warm temperatures, you'll likely want to keep the effort easier in your aerobic zone. After a week or two of acclimatization at aerobic intensities, you can begin to increase intensity as needed for your training.

Adaptations and Time Frame

When you acclimatize to the heat, your body adapts to the thermal stress via increased core temperature and sweating through repeated exposure to the conditions.

The resulting physiological adaptations include increased plasma volume, improved electrolyte retention, increased sweat efficiency, and decreased core temperature at given intensities. You should also observe decreased heart rate, decreased perception of effort and thermal sensation, and increased thirst sensation. It takes approximately three to five days to experience decreased heart rate and perception of effort, whereas the benefits of increased sweat rate and decreased sodium loss in sweat take up to ten days to attain.

Indoor heat acclimation

For athletes living in cooler climates who need to prepare for an event where it might be hot, indoor active heat training protocols and passive heat acclimation protocols like hot water baths or sauna may also be used post-training.

Indoor Environment

As much as possible, simulate the indoor environment to the heat and humidity of race day when you have aerobic sub-threshold sessions planned. At least for the first week, keep the intensity controlled and complete any VO2max-type sessions in cooler conditions. 

Duration

Start with 60+ minute active heat training sessions and gradually increase, up to about 3-4 hours as needed. 

Clothing

If you can't get your indoor environment warm enough, you can use additional clothing to increase thermal strain, such as long sleeves, pants, hats, and gloves.

Hydration

As with riding outdoors in the heat, have plenty of fluids before and during the session. Drink enough to avoid losing more than ~3% of your body weight in a session.

Post-Exercise Protocol

Rehydrate slowly by drinking 125-150% of the fluids lost from sweating using a higher sodium electrolyte drink. If you are also doing post-training sauna or hot-water immersion, go directly into hot water (104 deg F) or sauna (150-180 deg F) for 15-35 minutes as tolerated. Avoid drinking during the heat exposure, but slowly rehydrate with fluids containing sodium once you're out of the bath or sauna. ***Note: When exiting the bath or sauna, rise and move slowly and carefully. It's best if another person is present. I highly recommend starting with only 15 minutes and being very conservative with the protocol when starting out.

Adaptations and Time Frame

Because the adaptations can take up to ten days to achieve and they decay quickly, it is best to start the heat acclimation process around three weeks prior to your event in order to be able to recover adequately in the five to seven days prior to the event. 

Weighing the pros and cons

Finally, remember that thermal stress adds a significant overall strain to your body and can be highly fatiguing. Athletes undergoing heat training may need to decrease training volume and/or intensity, and they typically require additional recovery time. Be patient with the process, especially during the first week of exposure. Adjust intensity down as required and weigh the pros and cons of indoor heat training versus simply completing your training program as normal. Always make sure to adequately hydrate during these sessions and afterward. 

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