My particular take on the issue goes a little something like this.
Based on my experience with higher temperatures three things happen. First, my heart jumps up to handle the extra stress of the heat. More blood will flow near the skin to help cool my body which means less going to muscles to reoxygenate them. Less oxygen means means my muscles will tirer quicker. Third, I will begin to sweat which is my body's way of attempting to cool off but depending on the weather, this can mean water running off me rather than evaporating.
What does all this mean? Well, we have to have to accept that either our distance needs to be shortened or our pace needs to slow. The only way to maintain both is to do the obvious – get in better shape. However, this easier said than done during the summer.
So which is better running less distance but at the same pace or running slower but the same distance? Sometimes, I like to answer a question with a question. What are your goals? What races are on your upcoming schedule?
If you are running nothing but 5k and 10ks, then running a shorter distance but at the same pace or a little better is most likely the way to go. However, if say you are looking for a Labor Day Boston Qualifier, you are going to be pounding out the miles, the choice of running slower but going the distance makes the most sense.
I’ll throw out other request to you. Make sure you are seeing your family doctor regularly. Running in general puts a great deal of stress on your body and your heart. The summer time heat surely elevates this stress. As the commercial says, you should always think “Safety, safety, safety” first.
The Cool Down Runner