The What-Why-How of Hot Weather Training

As endurance athletes, we look forward to summer. Summers means more outdoor training, no need for toe covers or gloves, and icecream as post-workout rewards. It generally also means race season, but I won’t poke that particular sore spot. One element of summer that is not universally loved is the heat. The Scandanavians have a saying: ‘there’s no bad weather, just bad clothing’, but I don’t think it applies all that well on 40C humidex days.

So given that hot weather is unavoidable during Ontario summer, it makes sense for athletes to do what we can to not only deal with it, but also profit from the experience. Here then is my synopsis of the physiological effects of training in the heat, the adaptations that result from this stimulus, and how best to cope with this less-than-pleasant fact of training life.

  1. The effects of hot-weather training on the body

Working muscles generate heat. The harder those muscles work – the more power they produce – the more heat is generated. The human body is remarkably adept at shedding this excess heat. This is a very good thing, since our bodies are designed to operate within a fairly narrow band of internal temperatures. Anything from around 37.0C to 38.5C is considered optimal during exercise. Exceed 38.5C, and performance begins to decline.

There is a range of reasons for this decline including

  • Dehydration caused by excessive sweating
  • Increased cooling load on the cardiovascular system
  • Psychological or ‘central governor’ constraints on power generation

These factors combine to reduce our ability to perform in the heat and make the process decidedly less comfortable.

  1. Physiological adaptations to training in the heat

There is good news however. The process of training in the heat has some very real, positive outcomes. Here’s what we can expect after 7-14 days worth spending some time at or above that critical 38.5C core temperature.

  • Earlier sweat response leading to improved cooling and lower core temperature
  • Increase in blood plasma leading to improvement in aerobic performance
  • Reduced HR when training in the heat
  • Improved thirst response: earlier desire to drink
  • Better psychological tolerance for training or racing in the heat

Sadly, these truly tangible performance benefits tend to fade almost as quickly as they are developed. Remove the heat stimulus, and we lose this tolerance within a couple of weeks.

  1. Best practices for successful training in hot weather

So now that you know what heat does to your body and your mind, as well as some of the benefits that may be reaped from exposing yourself to this stimulus, let’s talk about optimizing the experience. That is, some steps for making training – and especially racing – in hot conditions both more bearable and more effective. It’s important to note, however, that some of these interventions MAY blunt the magnitude of the heat training stimulus. So we may not get that same bang for our sweaty buck. Still, it is this coach’s opinion, that taking measures to make sure that the training objectives like frequency, duration, and intensity are accomplished is worth the potential risk of a somewhat decreased heat training effect!

Here then are some strategies to mitigate the impact of that thermal stress:

  • Pre-cool. Before you head out for that midday run or toe the line in that hot race, drop your core temperature as much as you can by consuming ice drinks / slushies, wearing ice vests, and even taking a pre-event ice bath.
  • Cool yourself during activity. Again, those cold drinks – and especially ice slurry drinks – are the most effective way to do this.
  • Limit sun exposure by running in the shade. Not only does the sun feel hot, it adds a non-trivial thermal load. Avoiding it is the way to go.
  • Slow down! If the goal of the workout is aerobic endurance and the intensity is meant to be low, make sure you reduce your pace or power target for the session. Given how much extra strain hot-weather training adds to the cardiovascular system, reducing the mechanical load will help keep your intensity on target. Keeping tabs on heart rate is one way to ensure that you don’t overcook the effort.
  • Avoid high intensity training in the heat. Unless there is a very real, very near-term, race-specific reason why you are doing high intensity training in the heat, try to avoid it. Schedule workouts that are near or above threshold intensity in cooler parts of the day or reshuffle your week to shift those workouts to days where the forecast calls for lower temperatures. Even if you CAN hit your performance targets in the heat, you are more than likely exceeding the desired intensity, compromising recovery and future workouts.

There you have it! The ‘what, why, and how’ of training in the heat. If you have questions, I may have answers. And if I do not, I know many smart people who I can ask!

About the author.

Michael is a mechanical-engineer-turned-triathlon-coach and founder of X3 Training. He has competed in all the common distances of triathlon and run everything from track to 50k. When he’s not coaching or playing with his kiddies, he co-hosts the Endurance Innovation Podcast.