Toward the finish of yesterday’s first stage of the Amgen Tour of California riders were dropping like flies while they melted in 100° temperatures around Escondido. Phil and Paul continued to bring attention to how hot weather was dragging down some of the strongest contenders in the stage. Reference was made to the cooler temperatures in Europe and the lack of riding in the heat for most of the peloton.

The topic of heat tolerance is an interesting one that I’ve written about previously, but today I wanted to take a closer look at a study that more closely examined the types of changes that take place when an athlete undergoes heat training in order to acclimate to high heat environments.

The Research

In a recent study examining heat acclimation and exercise performance, researchers examined the impact of 10 days of heat training on VO2max, time trial performance, power at lactate threshold, blood plasma volume, and maximal cardiac output [1]. Here is a basic breakdown outlining their methodology and results.

  1. 12 trained cyclists performed a VO2max test, time trial, and lactate threshold test in both cool (55.4°F) and hot (100.4°F) conditions before and after 10 days of heat training
  2. “Heat training” consisted of riding 10 times (in a controlled laboratory chamber) in 104° heat at 50% of a riders VO2max (approximately 185w).
  3. After heat training; VO2max, time trial performance, power at lactate threshold, blood plasma volume, and maximal cardiac output all increased significantly in both hot and cold conditions.
  4. Time trial performance was improved by 6% (measured by total work performed in kJ during a 60 minute TT) in cool conditions and 8% in hot conditions.

The Difference

In the context of this year’s Amgen Tour of California we’re looking at possible performance differences of 8% for riders that started yesterdays stage acclimated to riding in hot conditions. In the world of exercise physiology and human performance 8% is a huge number.

Although an admittedly imperfect translation, if you were talking about a rider climbing at 400w, an 8% difference in performance would translate to 32w. Those of you that have done sustained threshold intervals certainly recognize the magnitude of 32w.

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Hot And Cold

Perhaps an even more interesting finding from this study was the impact of heat training on cool weather performance. A 6% improvement in TT performance following 10 days of heat training could make the difference between winning and loosing even a short time trial.

  1. In the context of this study a few things jump out. First of all, being properly acclimated to a hot exercise environment can make a world (8% to be exact) of difference when it comes to performance.
  2. It seems reasonable to expect that during early season races taking place primarily in cool temperatures, a significant performance advantage could be achieved through integrating heat training into an overall training strategy. It wouldn’t surprise me if top athletes were already utilizing this strategy. Remember, we’re not talking about training with much intensity in the heat, just light exercise coupled with heat exposure for a potential payout of a 6% performance improvement: think riding on a trainer for 90 minutes, in 104° heat, watching a movie, humming along at roughly 200w, and 10 days later you might get some free watts to spend in a time trial or road race of your choosing.
  3. If you’re targeting a specific race, you should take into consideration the environmental factors impacting that race and adjust your training to acclimate toward the conditions you expect to encounter. Example: if you’re going to be racing in the afternoon heat, it doesn’t make a lot of sense to do all of your training in cooler morning temperatures.

Heat Matters

As we saw in yesterday’s ATOC first stage, heat matters: especially when an athlete is not acclimated to hot temperatures. Whether you’re using heat to gain an advantage in cool weather, or hoping to acclimate to current conditions, the potential for real improvements in performance exists.


1. Lorenzo, S., Halliwill, J. R., Sawka, M. N., & Minson, C. T. (2010). Heat acclimation improves exercise performance. Journal of Applied Physiology, 109(4), 1140-1147. doi: 10.1152/japplphysiol.00495.2010