Intended pacing strategy for Silverheels 100

The Silverheels 100 starting gun fires tomorrow morning at 4 AM, and I will be there. With a field of only about 40 and without an obvious ringer, this appears to be the lowest pressure and least competitive ultra that I have done. Furthermore, I’m no longer intimidated by the distance, the weather forecast is hardly ideal, and I only need a finish, since my ITRA ranking is greater than the 750-point minimum to be guaranteed entry into Ultra Trail du Mont Blanc (UTMB), which will likely be my A-priority ultra next year.

Given this low-risk context, Silverheels 100 seems like an excellent opportunity to experiment. For example, I intend to depend solely on aid stations and drop bags, not a crew, to help become more self-sufficient during ultra-sized efforts. (After her first week at a new job, Amanda will be back home recovering with Oden.) I also plan to be even more disciplined about my pace early in the race, to determine if I can run faster overall by running more evenly.


In every recent ultra, I feel like I have gone out too hard, despite normally placing well and finishing strong. For example, last year at Run Rabbit Run 100 my average pace for the final 60 miles was 65 seconds slower than for the first 40 miles, a falloff of 10 percent that cannot be explained by differences in the vertical change or technical footing. The race start was particularly intense: I allowed my heart rate to exceed 150 bpm for the first 40 minutes, peaking at 158 bpm. Thereafter, it dropped steadily due to intention (“Slow down, Skurka, it’s still early.”) and to muscle fatigue; overall, my average HR was just 127 bpm. For more in-depth analysis, view my Movescount data.

I’ve never heard any ultra runner regret starting their race “too easy.” After a multi-week taper, legs feel wonderfully fresh. The momentum of the psyched-up field is not easily defyed. And one’s “easy jog” pace is still often considerably faster than than what their average race pace will ultimately be.

For more discussion on ultra marathon pacing, read this, listen to this, and check out these charts.

Measure and data

In a mountain ultra, current pace (as measured in minutes per mile) is an unreliable indicator of effort. Instead, I use heart rate, which better accounts for the relative stress of running uphill, level, or downhill. With my Suunto Ambit GPS watch (long-term review) and Suunto Dual Comfort HR Belt (long-term review), I have on-board access to this data.

Based on past races, I believe that at Silverheels — which I expect to finish in about 22 hours — I should be able to maintain an average heart rate in the high-120’s. My history:

This is not a huge dataset, but the trend is clear: as the race duration gets longer, my average heart rate decreases, and fairly predictably. (At VUT, my HR would have been higher if not for having stopped nine times to empty volcanic sand from my shoes.) And since my current fitness has not changed dramatically since these races, I feel confident in extrapolating.

HR at Run Rabbit Run 100

HR at Run Rabbit Run 100. My HR steadily drops during the first 10 hours. Beyond that, it was steady to the finish.

HR at Vulcano Ultra Trail 100k. After about 2 hours, I settled into a good pace.

HR at Vulcano Ultra Trail 100k. After about 2 hours, I settled into a good pace.

HR at San Juan Solstice 50. My HR was fairly steady beyond 2 hours, once terrain is accounted for -- from about 4.5 through 7.5 hours, it's a long rolling descent.

HR at San Juan Solstice 50. My HR was fairly steady beyond 2 hours, once terrain is accounted for — from about 4.5 through 7.5 hours, it’s a long rolling descent.


My plan is to keep my average heart rate in the low-130’s for as long as I can. Even at the start and even on uphills, I will cap it at 140 bpm.

This may mean that I fall way off the lead, especially early in the race. But I think — and hope — that later I can make up the difference, and then some.

Posted in on August 5, 2016


  1. Kevin M on August 6, 2016 at 1:18 am

    Hope it goes well!

    Wise coach-figures have always said that most pacing mistakes happen in the first two hours of an ultra-anything, which is handy to repeat over and over in your head. (and over and over and over)

    For later data analysis, I’d be curious if your HR is actually dropping relative to pace. “Cardiac drift” is a well known phenomenon in cycling (and other sports?), where power (or pace on flat, windless courses) is held steady but heart rate drifts upward over time. If that holds true for ultra-running, your pace may be dropping faster than your HR, so your HR in previous efforts was actually drifting upwards relative to pace. Just curious – I’ve played the same game and “chill the hell out” pacing for the first few hours is definitely wise. Knowing cardiac drift just means you can start in the 130s and feel comfortable with your pacing if your HR drifts into the 150s late in the race – just you staying a steady pace.

    I hear run power meters are coming to market. If they work, they may make HR monitors largely irrelevant. Power won’t really change with the temperature, the amount of coffee you just chugged, or how nervous you are about a race.

    Good luck!

    • Andrew Skurka on August 9, 2016 at 8:08 am

      It’s difficult to imagine an ultra in which cardiac drift is experienced. You’d have to go out SUPER slow and you’d have to SUPER fit so that you can still run hard in the closing miles.

      The drift is pretty evident at the CO Marathon in May:

      But in every ultra, my HR and pace steadily drop off throughout the race, some worse than others. The basic issue is fatigue: even if you’re well trained, your legs will be zapped after 50 or 75 miles with 10k or 15k of climbing on them already. HR drifts down because (I think) the muscles no longer can generate the power to keep the heart revved at high rates.

Leave a Comment