Lately, I have been trying get some exercise credits in my life by running around my neighborhood.  Listening to friends’ stories overheard at lunch, my pride determined that my goal was to improve my time running a mile as quickly as I could.  So, that was what I set out to do.

Pulling out my nerd skills, I hit the running path with a Garmin Edge 205 to log data on my heart rate, distance and speed.   My holy grail was to somehow get to below a 9 minute mile. However, everyday at the one mile mark I found myself absolutely winded, with a time of 10 minutes and 15 seconds.  Not a time to share with my friends over lunch.

Now Im thinking, “If I cant run a 10 minute mile without being absolutely consumed, how will I ever run 2 or even 3 miles?”  It simply does not make sense that one mile of running would shut  me down when I have logged 7 and 8 mile mountain biking rides with an average heart rate of 160 beats per minutes for 50 minutes.  

So, I start reviewing the data. I am noticing that my heart rate is getting up into the 160 and 170 beats per minute range during this short loop.  My first thought is “What’s the problem?  I can maintain this rate on my bike all day long (some exaggeration).” I decided it was time to call a friend, Dominic, who has logged 30 years of running. Maybe he could give me a tip or two.

When I get Dominic on the phone I explain the running dilemma. Very quickly he cuts to the chase and asked if I monitored heart  rate during the run. “Yessir, I do!” I answered, proud of my use of technology.  The next line of questions were about what average heart rate did I keep myself at during the trek.  Hoping to get some manly kudos for maintaining a high heart rate without dying, I shared the information.  This is where the voice of experience gave me an open hand slap.

Dominic quickly, but patiently, pointed out that I needed to establish my cardiac aerobic threshold for running. Simply put, this is the heart rate at which your body can no longer provide enough oxygen to your muscles when under a load.  Above this heart rate your body responds to this lack of oxygen by producing lactic acid. The lactic acid build-up in your muscles equals pain and eventually they simply say “no more”. In this situation, there is suspicion that I have been pushing above my aerobic threshold.

Now that Dominic has diagnosed the problem, he offers a solution. This is prefaced with the statement “There are many opinions about how to estimate your aerobic threshold, but this one has worked well for me over the years.”  And this is the wisdom he shared.

“Subtract your age from 180 and that should be your target heart rate to exercise aerobically. Run within 5 to 10 beats per minute of that and you can run longer distances with less pain.”

The next day I filled the prescription that Dominic offered me. I ran the math in my head to determine my target heart rate of 140 bpm. Once on the run I focused on a pace that kept my heart thumping close to this rate. I wrestled with the urges to manage my pace for time instead of heart rate.  And, to my surprise, I covered 2 miles with less pain than I had experienced on all my previous 1 mile runs.  I even felt like I might have had another mile in me.  The advice worked!

So, the answer to the question “What was the secret to Forrest’s epic run across America?” –  I believe it is that he paced himself to stay within his aerobic threshold.