by Dick Vincent, USATF/I.A.A.F. Level 3/5 Coach
With the heat and humidity upon us we are all waging the battle against the elements. Running in this weather is a war you will not win, rather it is a treaty you must negotiate. Regardless what some distance runners will tell you, no long distance runner performs to their potential in extreme conditions. By understanding what is happening to your body you will better know how to approach your hot runs and how to adjust your expectations. Without getting too technical (for fear of embarrassing myself), here is an overview of that happens. As our body warms up, we begin to sweat. The evaporation of that sweat is what cools us. Our body sends blood to the skin surface so that evaporation can dissipate the heat from our blood, hence: cooling our core. Simultaneously, as we run faster, our muscles are calling for more blood to the working muscles. That is when the overheating begins. The faster we run, the hotter we get, causing more blood going to the skin surface, resulting in less blood to carry oxygen to the working muscles. As you dehydrate your cardiac output decreases, blood volume drops, your blood pressure begins to drop, and your heart rate must increase to maintain adequate pressure. The chain of failure has begun. You begin to slow, gasp, and the muscles begin to lose power. Your head begins to swim, you may cramp, and in extreme cases you can lose consciousness and even die.
It is imperative to minimize overheating.
There are tables to predict pace slow down at different temperatures, but these are rough estimates. Fitness, body weight, running economy will affect that formula as well as some previous heat adaptation.
When temperature rises over 60 degrees, one formula predicts it will affect your pace 2-3%. An 8 minute pace slows to 8:10- 8:15. By the time the mercury hits 80 degrees that same effort will slow to well over 9 minute miles. Keep in mind this is not taking humidity into account. It would be best to look at real feel rather than actual temperature, because as the humidity rises evaporation rate on your skin slows down, which is why you are drenched in sweat. If you are running in the sun as opposed to the shade that too will cause you to produce more heat. The temperature on the road or track might be well into the triple digits, so even if the air temperature is 80, the temperature 3 feet off the ground is what you are dealing with. Also keep in mind that this formula is applied to running a marathon. If you are running a shorter race the effort will be greater and more heat will be produced.
It doesn't matter if you are running a race or a speed workout, you must take into consideration the heat/humidity and adjust your pace. Failing to do so is a path to failure.
If you are going to maintain or build fitness for the fall racing season, you will have to train in the summer. Keep an eye on the weather and be sure to adjust your pace/effort on those hot days. Be sure to drink fluids and maintain your electrolytes. Start conservatively; better to be overly cautious than overly zealous. It is what you do in the second half of your run that will determine success.
Racing in Hot Weather: Temperature Calculator
Impact of Heat of Marathon Performance
Temperature + Dew Point For Pace Adjustments