Running in the heat

[shipo]

For much of the northern hemisphere, summer has already taken hold with high temperatures and humidity, however, here in New England the heat and humidity thing really got going in the last week.  Yesterday my planned run was 12-miles, "was" being the operative word here.  During my run in temperatures in the 90°F range I found myself reflecting on runs I'd made a few years ago, runs which were done in worse conditions (very humid and in the low 100s) and were up in the 16 to 18-mile range.  From there my brain wandered back to research I'd done a few years ago, possibly at the same time, which discussed how the human body adapts to intense aerobic exercise in adverse heat and humidity.  Here are a few paraphrased bullet points from that research:

• Heat acclimatization (or acclimation) confers biological adaptations that reduce physiological strain (e.g., heart rate and body temperature), improve comfort, improve exercise capacity and reduce the risks of serious heat illness during exposure to heat stress.
• The biological adaptations include integrated thermoregulatory, cardiovascular, fluid-electrolyte, metabolic and molecular responses.
• Heat acclimatization occurs when repeated exercise-heat exposures are sufficiently stressful to invoke profuse sweating and elevate whole-body temperatures.
• Generally, about 1-2 wk of ~90 min daily heat exposures are required; but highly aerobic fit athletes can heat acclimatize in less time.
• Heat acclimatization is specific to the climatic heat stress (desert or tropic) and physical exercise intensities the athletes are exposed to, which should simulate the expected competitive environment.

The above bullet points are pulled from a Gatorade Sports Science Institute dissertation titled "Heat Acclimatization to Improve Athletic Performance in Warm-Hot Environments"

• https://www.gssiweb.org/sports-science-exchange/article/sse-153-heat-acclimatization-to-improve-athl....

A few additional nuggets pulled from the dissertation (once again, paraphrased):

• The benefits of heat acclimatization are achieved by improved sweating and skin blood flow responses, improved cardiovascular stability (ability to sustain blood pressure and cardiac output), better fluid-electrolyte balance and a lowered metabolic rate.
• The effect of heat acclimatization on aerobic exercise can be dramatic, test subjects were able to complete workouts in the heat after only two weeks which were impossible when initially exposed to the new environment.
• The benefits of heat acclimatization during exercise spills over into non-rigorous activities, allowing the acclimatized individuals to be more comfortable in high heat and humidity then they would have been before training in the heat.

As for my run yesterday?  I was on an "out and back" rail trail, by the time I was 4-miles out I knew 12-miles was probably not going to happen, and by the time I hit the 5-mile mark and was faced with either running either 5 or 7 more miles, I turned around and headed for my car.  By the time I finished I knew it was a good decision, I was pretty much out of gas, two more miles could well have gotten too close to the edge to have been safe.

So, for those of y'all who will be doing out of doors training in high heat and humidity this summer, hang in there, take it slow, adjust your workouts accordingly, and before you know it, you'll be shrugging off the heat without a second thought.

[Odyssey13]

Good advice @shipo and it's also good for those who walk. I tend to move slower in the heat, but still keep moving. Heat can really sneak up on a person. Glad you decided to end the run and head back to your car. Staying safe is always the best decision.

[shipo]

Thanks @Odyssey13, yeah, one of the things old age has taught me is, "Discretion is definitely the better part of valor".  

[Heybales · Accepted solution]

Excellent info for new ones, and reminders for us all.

Had my 1st hot ride of the year, and the heat elevated HR for cooling was evident. On a run Sat, a good 10 bpm higher on easy sections, probably 15-20 on hills.

Both showed up as the HR-based calorie burn was badly inflated compared to the more accurate power meter calc for bike, distance calc for run, whereas when cool they almost match up decently.

That's a good one for people to keep in mind depending on how long a workout in the heat, and if attempting a diet to lose fat.

While you want to eat enough to power a good workout, sometimes logging a Workout Record with distance and time and letting Fitbit calculate calorie burn can be more accurate during summer.