We saw heart rate data illuminate Western States recently as it underlined how the great Kilian Jornet perfectly paced his race on the way to a podium place 14 years after his previous visit.
And it’s arguably even more enlightening when applied to John Kelly‘s recent attempt at the FKT (fastest known time) for the Appalachian Trail.
Tackling the 2,197.4-mile route had been a long-held ambition for the ultrarunning legend, who has three Barkley Marathon finishes to his name, and he was on course for 35 days before injury forced a halt.
94% of time in Zone 1
But a Coros deep dive into the data underlines just what an incredible toll it took on his body.
The 40-year-old data scientist left no stone unturned in his bid and one aim was to rarely allow his pulse to exceed 145 beats per minute despite averaging 56.4 miles per a day before the injury, while also climbing 14,000 feet or more
Kelly explained: “I set my watch to alert me if I ever went above 145 bpm. This kept me at an effort I knew I could manage.”
And sure enough no less than 94% of time was spent in Zone 1.
But while that minimised the effort, the elevation, terrain and especially the searing temperatures still pushed his body to the limits.
RHR and HRV flip-flop during attempt
And that is shown in no uncertain terms by his resting heart rate data and HRV (heart rate variability).
Let’s start with the first of those two metrics and Kelly explains: “On a normal day-to-day level my RHR is 40 +/- 5 and HRV sits between 120-200.”
Those figures are admittedly a world away from the averages for the wider population but what Kelly saw on his Appalachian adventure clearly stunned him.
For his resting heart rate climbed above 70, and heart rate variability plummeted below 40.
“I’ve never seen those numbers in my life,” he said – and you can see the transformation on the graphic below.
There are lots more insights, including the main learnings from the attempt and the incredible support he had along the way.
And in bigger picture terms, Kelly way exceeded his target as he raised $65,000 for communities affected by Hurricane Helene.
