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Running in the Heat

Neil Feldman posing on a run


It’s that time of year again for runners (and walkers) where we switch our complaints from “too cold” to “too hot!”  As someone who HATES the cold, I actually prefer the hot days, though the extreme hot or cold is always tough.  The argument for the cold weather runners is that “you can always add more layers.”  While this is true, some of my winter runs end up requiring me to do the laundry after virtually every run as I have to wear so many layers!  The simplicity of socks, shorts and a shirt is really appealing.  Warm days are perfect for me.  Cool days are fine.  Hot days and humid days are the most challenging, and what this article is about.


Running is a thermodynamically active process.  In other words, as your muscles contract with movement, the muscles require blood flow which is powered by your heart, and that blood flow requires oxygen which is regulated by your lungs.  With muscle contraction, heat is generated.  This heat is then either used by the body to keep warm (on cooler days), released through evaporation if the body has enough heat already and expired through respiration.  If the body needs to release more heat, regardless of running, your blood flow to the skin and extremities increases to help release more heat.  If yet more heat needs to be released, then your heart rate will elevate to get even more blood to flow to the extremities along with increased respiration.  Humidity, which is the level of moisture saturation within the air, is even more troublesome as your body’s ability to evaporate fluid from the skin diminishes as humidity increases. Problems occur when you are generating more heat through activity than you can release and heat stroke occurs.


The following points are necessary to help both manage and develop better skills at running in the heat:

  1. Slow down!  The single best way for runners to mitigate the effects of heat is to SLOW DOWN!  The faster you move, the more heat you generate. Running at a faster pace requires a higher heart rate, and in the heat, your baseline is already set at a higher rate.  Those runners who are more aerobically fit (able to run faster at lower heart rates) tend to perform very well in the heat. Runners of smaller stature (yours truly) also tend to do better in the heat. Runners who generally run with higher heart rates (I will discuss this problem in later blogs) suffer most in the heat as your system is already running towards maximum capacity and can’t regulate further.  In these instances, the subconscious part of your brain will take over and start shutting down your muscles. This is a NORMAL safety mechanism which does not mean you are a poor runner! Take heart though, and be patient. Often, the body will be able to compensate quite well in the heat after an extended period of time, which of course differs for all of us. If your normal warm up period is 20 minutes (warm up period is defined as being what your body needs, not necessarily what you do!), then it may need to be extended to 30 minutes on really hot days to 40-60 minutes on the hottest of days.  If high humidity is thrown in, you may never be able to fully compensate. Not everyone runs for greater than 60 minutes, so understand that you just may have to stay slow.

  2. Hydrate.  While hydration is obvious, it’s not as important as slowing down. I generally will hydrate before runs of 30-60 minutes with about 20 ounces of sport drink.  I tend towards sugar free electrolyte sources such as Ucan Hydrate, but pre-hydrating is usually sufficient for this period of time. Beyond an hour, or on hotter (+/- humid) days, I will carry another bottle with me so as to offset the extra fluid depletion through sweat.  Understanding your sweat rate and salt replenishment needs becomes important the more serious you get with running and the longer the event. Under an hour, you probably don’t have too much to worry about. Also, understand your baseline fluid needs (on a perfect running weather day for you) and increase based on both temperature and effort.  If your needs outweigh your system capacity (if you require more fluids than your GI system can handle), then there is nothing you can do other than slow down or walk as you will otherwise become ill. You may also want to eat a little less as the amount of blood flow that helps the gut process food is significant and requires energy that produces more heat. Lessening the amount of work in the gut will help, but that doesn’t mean neglect food, it just means don’t overdo it.

  3. Clothing. In the non-clothing optional societies in which we live, there happens to be better options available.  Lightweight, coolmax synthetic blends do a very nice job of wicking moisture from the body. Avoid tight fitting shirts as it prevent/limits evaporative cooling off of the skin.  Stick with lighter colors as they absorb less heat. If you happen to have a very long run on a very hot day, perhaps even try and set up a way to change out of your shirts and/or shorts at some point as the sweaty, wet clothes add weight and keep the heat in.  Sock changes may be warranted as well, though I tend to train with the same socks so as to toughen up my feet (again, another future blog post).

  4. Hats and sleeves.  Believe it or not, sunscreen can limit your body’s ability to regulate temperature.  Given my melanoma history, blocking the Sun’s harmful rays is clearly a major priority for me, and one in which I would suggest for everyone! However, I try and limit my exposure to sunscreen by maximizing coverage with UV protective hats, sleeves and clothing.  I personally wear a sun hat with the flap that covers my neck along with arm AND often leg sleeves. The benefits of doing this in a race, especially long-distance racing, is that you can put ice in the hat and sleeves which will have the greatest cooling effect.  Ideal locations for ice would be in the neck, arms (outside upper arm and forearms) and the hat. On extremely hot days, ice in the hat, especially when directly against my bald head, can cause a feeling similar to an ice cream headache. It usually goes away after a minute, but this strategy helped immensely during my 2016 Javelina Jundred 100 mile run in the Scottsdale desert where temperatures reached 102 during the midafternoon sun (not to mention wearing 2 water bottles and carrying 2 water bottles) AND going slow during the hottest periods!  Additionally, soaking head buffs (like a head sleeve) in ice water as well as wearing an ice filled running bandana can make a major difference in keeping your core temperature cooler. I’ll even leave ice in a cooler in the back of my car when out for a long run away from my house or out in the woods somewhere.

  5. Practice! If you race, you can’t pick race day.  Hot and humid days become wonderful training days so that you can test out these strategies and see what works and what doesn’t.  If you stay inside on these weather days during training, yet your race is 90 and humid, you are really going to suffer.

 Links to some of my preferences, though there are other companies who make similar products: head buffs, ice bandana, Ucan Hydrate, sun hat, UV protection sleeves

Dr. Neil Feldman Dr. Neil Feldman is a Podiatrist at Central Massachusetts Podiatry, in Worcester and Westborough. As an ultramarathoner, runner and triathlete, he loves to help his patients remain consistent with their regular activities, assist in getting patients back to health and dedicates himself to patients achieving their goal events and races from walking the Camino de Santiago, to a first 5k run, to Ironman to a 250 mile run…and yes, that’s a thing!!

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