I’ll start by answering directly a question asked of me recently: there is no such thing as an optimal heart rate for any running event. Heart rates do not relate to paces. There are many variations in heart rates (HR) due to both individual and environmental influences. See my previous entry on heart rates for more on this.
In fact, if you were to use heart rates to govern your marathon (or any other race for that matter) effort you would progressively run slower. The effect is known as cardiac drift. Despite an even effort, heart rates rise with the duration of the effort.
To illustrate this better let’s look at a real example. Let’s say your goal marathon time is 3:03 or about 7:00 per mile pace. The first question to answer is what heart rate is that? This of course is a question without an answer because of all the variables at work. It could be 145. It could be 135. It could be 155 or 165 depending on weather, nerves, medications, sleep status, training/overtraining/recovery status, etc.
The figures I am about to use are for illustration purposes to demonstrate this drift phenomenon. For argument sake let’s say you actually figure it out to be 145. You start out your marathon at that 145 and supposedly simultaneously you are at 7:00 per mile pace. By the time 10 miles passes your HR elevates to 150. Of course, to “stay on track” with your effort, you have to slow down slightly in order to keep your HR at 145. So now, you are at 7:05 per mile pace. By mile 20 your HR has elevated to 155 so you now back off to 7:15 per mile pace to get that pesky HR back to where you are supposed to have it – 145. And this of course is to be sure you don’t overdo it. In the end you can see that your goal of 3:03 will go by the wayside if you follow HR to govern your efforts.
The argument you will hear from HR training adherents is that they advocate “ranges of HR” not a specific HR so all those HR would fall within a zone and you wouldn’t slow yourself down. This may or may not be true depending on the individual. It may indeed cross zones. Furthermore, if your “zone” starts or ends (depending on how you look at it) at 153 and you hit 154 does that mean you have to slow down to get back under that threshold? How did that one beat per minute suddenly dictate that?
It is guess work. At what point is your HR too high? Too low?
Contrast that with 7:00 miles. It is specific. It is exact. It will lead you to your goal finish time. There is no guess work. And you will have trained at that “goal” pace so you will be able to handle it regardless of your HR.
By the way, at the end of the race when you want to kick it in do the HR advocates tell you to back off because your HR will go too high? No. Instead, it’s a matter of finishing as fast as possible. Isn’t it interesting when such an advocate wants results, they toss HR out the window?