Do you or a client have a bucket list of races or events you have been wanting (and needing?) to check off? These events often take place in exotic locales that present challenging environmental obstacles. Bucket lists can be a great motivational tool, but excitement and anticipation can quickly turn into fear and dread when you realize the performance decrement associated with racing in environmental extremes.

One example of such environmental extremes are races held at elevation (Western States 100, Leadville 100, UTMB, etc.). Indeed, endurance performance at altitude is compromised. This is due to several physiologic factors including decreases in oxygen saturation and plasma volume, and increased cardiovascular challenges. For this reason, best practice suggest at least 14 days of exposure to moderate altitude (5,000 to 8,000 feet) is necessary to acclimate to hypoxia¹. Outside of a fortunate few people, 14 days at altitude represents limitations as far as time (goodbye vacation days!), geography (anyone live near Whitney Portal?), or finances (who wants to cash in their Roth IRA?).

However, there are new lines of evidence that demonstrate exposure that culminates in adaptation to one environmental extreme can improve performance in a different environmental extreme. This phenomenon has been labeled cross-tolerance and is primarily attributed to changes at the cellular level. For example, a male cyclist improved 28 seconds over 16 km time trial at 14,271 feet after 10 days of heat acclimation compared to the time trial before the heat acclimation process². You see, the adaptations that are associated with exercise in the heat resulted in better performance at altitude (i.e., cross-tolerance). Similarly, heat acclimated subjects improved performance to a comparable degree as hypoxic-acclimated subjects during a 16 km cycling time trial at 14 percent fraction of inspired oxygen (similar to ~9,000 feet)³. Two important conclusions can be drawn from these data: 1) heat acclimation improves endurance performance in hypoxia and 2) endurance performance at elevation is improved after heat acclimation to the same degree as acclimation to hypoxia. This means that exercising in a hot environment could prepare you for exercising in hypoxia (and prepare you to a similar degree as training in hypoxia).

Heat acclimation is a relatively easy process that takes about 7 to 10 days. Each exercise session should be about 90 minutes in a hot environment. However, should you find yourself needing to become heat acclimated in the dead of winter, there's still hope. Simply conclude each exercise bout with a soak in hot water (~40°C). Researchers showed that training in 18°C followed by a 40-minute soak in hot water led to classic markers of heat acclimation (lower exercising core temperature, earlier onset of sweating, etc.)⁴. The best part, however, was that after 6 days of soaking after each training bout, 5 km run time improved almost 5 percent compared to the group that didn't sit in hot water (that's taking off almost one minute for a 19:00 5k!).

Heat acclimation will last as long as one is exposed to exercise in a hot environment (or hot water baths). Once this exposure ends there is about 1 week until acclimation starts to lessen, and after about 3 weeks, 75 percent of the benefits are lost5. With exercise in the heat it's important to use caution and monitor for signs of heat illness (headache, nausea, dizziness, etc.). Start exercising in the heat slowly and begin to add time as you feel more comfortable with this new stressor.

So quit putting off that dream race because of fears that racing at altitude will bring you to your knees. Don't stress that time, finances, or geography may limit your ability to acclimate to elevation. Rather, leverage the cross-tolerance phenomenon and get heat acclimated to perform better at elevation.

References
1. Schuler B, Thomsen JJ, Gassmann M, Lundby C. Timing the arrival at 2340 m altitude for aerobic performance. Scand J Med Sci Sports. 2007; 17(5): 588-94.
2. White AC, Salgado RM, Astorino TA, et al. The effect of 10 days of heat acclimation on exercise performance in acute hypobaric hypoxia (4350 m). Temperature. 2016; 3(1): 176-85.
3. Lee BJ, Miller A, James RS, Thake CD. Cross acclimation between heat and hypoxia: heat acclimation improves cellular tolerance and exercise performance in acute normobaric hypoxia. Front Physiol. 2016; 7: 78.
4. Zurawlew MJ, Walsh NP, Fortes MB, Potter C. Post-exercise hot water immersion induces heat acclimation and improves endurance exercise performance in the heat. Scand J Med Sci Sports. 2016; 26(7): 745-54.
5. Pandolf KB. Time course of heat acclimation and its decay. Int J Sports Med. 1998; 19: S157-S60.