June 30, 2020 – Heat Acclimatization

Hi Everyone!


I’m not sure if everyone has experienced runs in the the real heat yet, but if you’ve somehow managed to dodge around the hottest days so far, you will get a taste of it over the next couple of months for sure. I had some toughies this weekend and it reminded me some important things about running in the heat which I thought I’d share with you.


First up, a quick lesson on what happens to your body when you exercise in the heat. As your body temperature starts to rise, your body immediately goes into action to cool it off to maintain a safe core temperature. Your blood vessels expand and blood is diverted to the skin and surface areas where cooling takes place through sweating and evaporation. This diversion of blood means there is less available to deliver oxygen to your working muscles. It also adds a strain to your heart as it tries to pump blood to all the areas asking for it at once. This makes running at any pace feel harder than it normally would. On top of this, our cooling system relies on sweating, and in the process we can lose a lot of fluid and start to become dehydrated which further stresses our system and perceived effort.


So the first thing I want you all to understand is that running in the heat really IS harder on your body, and your performance WILL suffer. It’s not in your head. There are real physiological changes which are making it feel like you’re running underwater or at high altitude with less oxygen. Your muscles are getting less than they normally do! So don’t look at your pace, assess your effort, and decide you’re out of shape or “having a bad one” and call it quits. It is supposed to feel this way if your body is doing what it’s supposed to be doing.


The second important point is that as humans, we are actually well adapted to running in the heat, and our bodies respond to the stress by making physiological adaptations. First, we start to produce more plasma, so that our blood can circulate more efficiently to our skin (for cooling), our hearts (for pumping) and our muscles (for fuel and oxygen consumption). Second, our core temperatures at rest and during exercise become lower, so we are able to take on more heat without danger. And finally, we become more efficient sweaters: we sweat earlier, to start our cooling process quickly, and our sweat itself changes in composition so we don’t lose as many precious electrolytes, but more expendable water.


The awesome news is that these adaptations make us more fit and better runners at all temperatures. Many athletes train in the heat specifically for the performance adaptations. So once you’re acclimatized your runs will feel soooo much better and when you run in the cooler fall temps you’ll have a superpower!


The not so great news: it takes about 1-2 weeks to get there. Meanwhile, your runs will feel harder than usual. What you need to do in this phase is remember that just getting out the door is training. Let go of pacing goals and go solely by effort. Cut your runs shorter if you have to, and slow down. It’s all fine, you’re getting the added boost of heat training (no, it’s not a metric for your log, but it IS real!)


Also a quick word on recovery. After a harder run or workout in the heat your body has to spend more energy on cooling itself down so there is less to spend on delivering nutrients to damaged muscles for repair. This doesn’t mean you won’t recover, it just means it will take more time. So respect that. If you’re feeling rough day after day, you may need to be adding a bit more recovery to your routine.


That is all – also enjoy it while we can – remember those absolutely horrible freezing cold runs? Let’s absorb as much heat into our bodies now because winter will come again!


Workouts for this week:


  1. 4×3 min with 1:30 rest @20 sec per K faster than tempo pace. 4 min easy. 5-6×1:30 with 1 rest at 30 sec per K faster than tempo (adjust paces according to heat)
  2. 6-10×3 min with 1:30 rest at 20 sec per K faster than tempo
  3. 2 x 600 w 1:30 rest; 2 x 800 w 1:30 rest, 2 x 600 w 1:30 rest, option of 1 last 800 to finish.
  4. Short Riverdale hills with 10 x squats at top, 10 x push-ups at bottom – SUCH a good one! Option to finish with 3-4 good flat strides.
  5. Tempo: 3 x 6 min tempo w 2 min easy jog, 4 min easy, 6 x 1 min tempo (a bit faster) with 1 min rest


Have a good one!