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Is Summer Over Yet? A Look at the Benefits of Hot Weather Training

Late summer is a time for many to curse the endless heat.  Paces get slower, easy workouts become a chore, and sometimes it seems impossible to stay ahead of hydration needs.  Let’s get some cool fall weather so we don’t sweat through our clothes five minutes into the workout! 

Many athletes secretly (or not so secretly) hope that we gain some benefit of suffering through heat.  Might heat training actually stimulate meaningful adaptations in fitness, and not just offer a moral badge of toughness?  According to the literature, there may be hope…

Most recently, Lorenzo (2010) studied twelve competitive cyclists to determine if heat acclimation would improve performance in cooler weather.  It is well established that training in heat will help one compete in hot weather, but does heat training confer any benefit that transfers into cooler temperatures?   

In this study, participants completed a battery of physiological and performance tests under both hot and cool conditions to set their baseline levels.  Then they were divided into two groups for the experiment: one group completed a training program in the heat for ten days in the lab; the control group completed the same training plan but in cooler conditions.

Both groups repeated their testing after the training cycle.  Results…

The heat acclimation group…

  • increased VO2max by 5% in cool and by 8% in hot
  • improved time-trial performance by 6% in cool and by 8% in hot 
  • increased power output at lactate threshold by 5% in cool and by 5% in hot 
  • increased plasma volume and maximal cardiac output in cool and hot 

The control group had no changes in VO2max, time-trial performance, lactate threshold, or any physiological parameters.

Sounds like we should all turn up the thermostat and just train hot all the time?  Not so fast.  First, it’s still uncertain whether runners would experience the same adaptations as cyclists.  Although runners and cyclists are governed by the same cardiovascular system, running has more complex neuromuscular demands than cycling.  Long term hot weather training at slower paces may impair coordination at faster paces greater than which can be compensated for by cardiovascular improvements.  Cycling might offer greater cooling than running due to higher velocities but that was not a factor in this study since it was entirely in the lab.  

Further, more study is required to ascertain optimal dosage.  These cyclists found an effective mix of training along with environmental conditions, but “overcooking” either variable may lead to excess fatigue.   Similarly, it is unclear how long the adaptations would persist even if you get the mix correct.   (“These heat acclimation benefits may be retained for 1 or 2 wk, and the rate of decay for heat acclimation will depend on many factors like fitness level of the subjects, environmental conditions where the subjects live, and intensity and duration of their training post-heat acclimation.”)

Despite these caveats, this study is not the first to explore the physiological adaptations possible with heat exposure. 

Previous studies have found:

  • heat acclimation lowers the aerobic metabolic rate and muscle and blood lactate accumulation during exercise in a cool as well as a hot environment (Young 1985)
  • increased ventricular compliance, chamber stiffness, and a decrease in the tension developed for each volume load (Horowitz 1986)
  • Increase in plasma volume (Senay 1976) which “enhances blood flow through the splanchnic circulation, enhancing lactate removal and thus delaying blood lactate accumulation.” (Lorenzo 2010)

Conclusion

Ultimately, this information does not conclusively prove that all forms of heat training will lead to positive adaptations, but it should offer encouragement for those of us who must deal with intense desert heat in the summer.  In appropriate doses, heat has the potential to make us fitter.  Authors also point out the potential value of heat acclimation as a substitute for altitude exposure, as altitude requires a much greater time commitment and logistics (along with flimsier support to justify its inclusion as a training strategy...).  Someone could include a heat protocol in a lab setting for ten days and remain consistent with the parameters of this study.  In contrast, after ten days of altitude exposure, most people are barely getting themselves back to their pre-altitude baseline.  

In sum...Just hang in there and fall will be here soon to reap the benefits of summer training!

References

Horowitz M, Shimoni Y, Parnes S, Gotsman MS, Hasin Y.  Heat acclimation: cardiac performance of isolated rat heart.  J Appl Physiol. 1986 Jan;60(1):9-13.

Senay LC, Mitchell D, Wyndham CH.  Acclimatization in a hot, humid environment: body fluid adjustments.  J Appl Physiol. 1976 May;40(5):786-96.

Lorenzo S, Halliwill JR, Sawka MN, Minson CT.  Heat acclimation improves exercise performance.  J Appl Physiol. 2010 Oct;109(4):1140-7. Epub 2010 Aug 19.

Young AJ, Sawka MN, Levine L, Cadarette BS, Pandolf KB.  Skeletal muscle metabolism during exercise is influenced by heat acclimation.  J Appl Physiol. 1985 Dec;59(6):1929-35.

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