Last month’s North Country Trail 50K was a reversal in my usual race routine: I ran an ultra as a fun break in my regular training.

This year I’m working on getting faster, and frankly it’s been a struggle after three years of training to “go long” so I looked forward to this 50K as a diverting return to familiar territory. No pressure to put the hammer down; quite the opposite, in fact.

For this was the first race I ran entirely by heart rate instead of pace.

Why? To see how I would perform by staying “aerobic” which means maintaining a pace where the body is receiving enough oxygen to keep the muscles fueled. At a certain level of effort you go “anaerobic” where the body is using up oxygen faster than it comes in. This condition is standard for sprinters, but bad for distance runners if it happens too soon.

The key number to know is your Maximum Aerobic Heart Rate (MAHR). Go above that, and you’re running on borrowed time. It can be precisely determined in a medical lab, but there are ways to estimate it based on general assumptions on age and fitness level.

Using the popular “Maffetone method” I estimated my MAHR to be around 130 beats per minute (BPM). I decided I could go slightly over that for a 50K and set my target average heart rate for 135 BPM, slowing down if it hit 140 or more. After twenty miles I felt strong enough to step it up, so I ran the final 11 miles at a target BPM of 145.

The result was one of the smoothest 50K I have ever run. I felt good throughout, and by focusing on BPM I could ignore my competitive instincts when other runners passed me or I saw one up ahead. I’d hoped for a finish under six hours and somewhere in the top half of the field, but got a surprise: a time of 5:36 (near my best) and a top 10 finish, too!

One more smart move was staying hydrated, learning from my digestive issues at the Potawatomi Trail 50. As it was a cool day I drank “ahead of my thirst” to make sure I was getting enough, and had no problems.

Now in the spirit of balance, here’s something I screwed up.

The race was on a Sunday, and Monday is a Body Specs gym day. Naturally I gave myself the day off, right? Umm….not quite.

Okay, I’ll admit I was partly motivated by wanting to show off the humungous finisher’s medal. But I was also feeling good enough to go. A nice, light recovery workout would be great, right? And so it seemed to go, until my legs tightened up later, and for the next two days I had to press on my quads just to sit down. (At least it was good power hike training.)

So I suppose you could say my heart was in the right place, but the effort was in vein.