Heat Acclimatization To Improve Running Performance

Heat acclimatization is a crucial aspect of training that is often overlooked by many runners. Yet, adapting to hot conditions leads to substantial physiological gains and boosts race performance. Here is a closer look at what heat acclimatization means, its potential benefits, and how to incorporate it into training.

What is heat acclimatization?

Heat acclimatization is the process of training our bodies to adapt to high temperatures through repeated exposure. In case of running, it involves getting more mileage during the hotter parts of the day, or simulating such conditions artificially.

Though there is no one size fits all approach to this, about 10 days of consecutive exposure is a good starting point, beyond which runners can customize and build their own plans. [1]

Why should you acclimatise?

Adding heat acclimatization to your training program offers multiple advantages.

• Heart efficiency
  A reduction in resting and exercising heart rate is observed due to the increased efficiency in blood circulation. The heart’s stroke volume also increases due to the expansion of the plasma volume in the blood - allowing more blood to flow into both muscles and the skin and hence improving running performance.

• Better handling of hydration levels
  Due to the increased efficiency of losing heat via the skin, heat acclimatization results in a reduction in the sweat rate - preserving the body’s hydration levels and electrolytes.

• Increased Cardiovascular Stamina
  As a direct consequence of improved heart efficiency and hydration levels, cardiovascular markers such as Time to Exhaustion (TTE), VO2 Max and Lactate Threshold improve as well.

A study conducted by Tyler Et al. [2] measured a 6% increase in VO2 max and 23% improvement in TTE after a two week acclimatization program, which are extremely impressive gains.

• Better preparedness for races Races can often be unpredictable, a lot of people struggle post sunrise mid-race due to the increased heat. Even missing a single hydration point can distort a race. Benefits of training in the heat can significantly reduce the effect of such uncertainties during a race.

How to acclimatise?

The best time for heat acclimatization is immediately prior to a target race. However, exposure to heat over a long period of time (> 2 weeks) leads to the body “remembering” this adaptation for longer times.

To acclimatize to heat, start by gradually exposing yourself to warmer conditions, such as running short distances during hotter parts of the day or in a humid environment. Begin with shorter, low-intensity easy runs and increase duration over 7-14 days, allowing your body to adapt. We suggest not running intervals and other forms of speed workouts. Stay well-hydrated, monitor your effort, and listen to your body to avoid overheating.

A few tips for effective and safe heat acclimatisation are -

• Frequency - Best results are seen if a heat training block consists of daily runs in the heat, with the duration of the runs gradually increasing. However, if you are not recovering well, with signs such as unusually high resting heart rate, headache or nausea, it is important to take a break and re-attempt in slightly lesser temperatures after a short break.
• Pacing - When starting out, completely forget about your pace and only pay attention to your perceived effort and heart rate. It is tempting to compare paces with efforts done in cooler conditions, but running in the heat is a different game altogether. Try to not exceed Zone 3, and focus on running longer than faster.
• Hydration - Ensure that you are well hydrated throughout the day and before the run. This will help during longer efforts in the heat. Even during the run, ideally a hydration break should be taken before you actually feel thirsty. However, it is difficult to gauge this and it is wise to drink water/electrolytes upon the first feeling of thirst. Make sure to consume a good amount of fluid post running. A good indicator of optimal hydration levels is extremely mild yellow urine.
• Humidity - Humidity needs to be taken into account as well along with the temperature, which is why it is prudent to look at the wet bulb temperature instead. If this temperature exceeds a certain value (usually anything over 40 degrees Celsius is considered outright dangerous) then it is best to wait for a cooler time of the day. However, with practice it is possible for this personal threshold to shift higher.
• Diet - Even though we could not find any direct studies on this, in our experience it is best to avoid spicy food and dehydrating beverages like tea and coffee during heat training blocks, as they can cause heart rate spikes.
• Sleep - Make sure to get enough sleep to completely recover from the day’s workout. The exact amount will vary depending on your lifestyle. Piling on the physical stress from the heat on a daily basis is counter productive.
• Clothing - It is best to wear light colored fast wicking clothes which absorb sweat and dry faster. During long runs and in humid conditions, it is recommended to keep a change of clothes handy mid run. Some people prefer wearing a cap/headband to deal with the sweat.
• Sunscreen - Depending on your skin type, you might benefit from wearing a good sports sunscreen if running during the day.

Alternate methods

In case your local climate never gets this hot, you can simulate such conditions by wearing extra layers while running. However, it is difficult to quantify tolerance thresholds in this case and should be done cautiously based on perceived effort and heart rate.

References

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC6422510/
2. https://link.springer.com/article/10.1007/s40279-016-0538-5

Sanchit is a software engineer who started running as a hobby and got addicted. If he’s not running, he’s probably thinking about his next run or surfing Strava. He can be reached out on Twitter @sanchit3008 or on Strava at this URL.