A Primer On XC Course Differences

Times were a little slower at the Kokopelli 5K in November, but not because the course was measured with a wheel.

Back in November, as cross country season was beginning to wind down, I wrote the following in a meet coverage article:

And that brings us to the topic--one that should probably be explored further on these pages at some point--of the difference between a wheel-measured course and a GPS-measured course.

The short of it is that a GPS-measured course is invariably shorter than a wheel-measured course, though how much shorter depends a little on a few different factors, perhaps especially how many turns a course has.

Now, three months later, I need to level with you about that statement. It's bothered me ever since. It's been years since I tested that out, and GPS has advanced a step or two in the interim. I knew I needed to test it out. My opportunity to do that came last week.

There's a simple circuit in our neighborhood which I know is very close to one mile. The entire circuit is sidewalk, and the sidewalk is in good condition, so there would be no issues of what to do about serious dips along the way.

I got my trusty wheel, one I have tested for accuracy. I charged my Garmin 220 GPS watch. And, I devised a simple method to put the two to a test.

I strapped the watch to my right wrist and rolled the wheel with my right arm. I didn't want turns--though there are few along my circuit--to alter, even if only slightly, the results due to one device taking a wider turn radius than the other.

Running while trying to roll a wheel never was a good idea, so I walked.

Forgetting, for the moment, that I have my GPS watch set to beep at each mile, I figured I would roll the circuit until my wheel said 1609 meters (one mile). Then I would check that against what my GPS watch read.

I carefully watched the wheel as it passed 1600 meters. I slowed down, so I could stop the moment it hit 1609. Then, suddenly, at 1607 meters, my watch beeped.

"What was that?"

My watch was telling me I had just hit one mile. Two, maybe three, walking steps before my wheel would told me I had hit one mile. I made a mental note of where the watch and wheel told me one mile was on my circuit.

That was not the result I expected. I expected confirmation of what I'd written in November, but I didn't get it. It does us all good to find out now and then we've been wrong about something, even if the process is a little painful.

So, what do you do when you get an unexpected result? You go back, check to ensure you've done everything right, and do it again. The recheck wouldn't cost me any money, only time. And time is rarely an obstacle once my curiosity is piqued.

For my first do-over, I ditched the wheel. Instead, I picked up my phone and turned on a tracking app I use for hiking. I put the phone in my right hand and began again. Starting both my phone and my GPS watch together, I set out running this time.

"Possibly it makes a difference if I'm running!"

It makes no difference. Within one meter--it's hard to be more precise than that--of where my watch beeped the first time, it beeped again on the second circuit. Stopping as dead in my tracks as possible, I pulled up my phone and checked my app. It also reported 1.00 miles.

"Here's a bigger shovel. Keep digging." Two different GPS devices just yielded precisely the same result. So much for variability between devices.

Once more, for good measure, I went back into my house and retrieved the wheel. Watch on right wrist, wheel in right hand, I set out for one more trip around my circuit, this time a little wary of what the neighbors might think.

"Mabel, who's that strange old fella who keeps rolling a wheel down the sidewalk in front of our house?"

"I don't know, Wilferd, but don't you go poking yer nose into what's none of yer business!"

Would you believe I got the same results one more time?

So much for the idea that a wheel-measured course is meaningfully longer than a GPS-measured course! It may have been a different story 15 or 20 years ago, but it appears that a wheel and a GPS watch measure the same course as the same distance today. Which, by the way, makes a good wheel a lot less useful-at least for a cross country coach.

Now is as good of a time as any, though, to mention that my test course was mostly flat. I have not fully eliminated the possibility that wheel and GPS device could yield differing measures on a hilly course.

I am aware people have reported GPS watch distances of more than 3.10 miles for the Kokopelli/Harrison course. I also know two people--people whom I trust--have independently rolled the course to 5000 meters. Right now, I don't propose to be able to tell you what the resolution of that conflict is.

All this, then, takes us back to the original question raised in the article of why some courses run faster than others. A bit more humbly than before, I'm going to offer some suggestions, but this time the suggestions won't include the type of device by which the course was measured.

The first suggestions we'll consider are suggestions related to course conditions.

Course composition - Concrete is probably slightly faster than asphalt, which is faster than rolled crusher fine, which is faster than ordinary trail, which is faster than running where no trail exists. Concrete, asphalt, and, to a large degree, crusher fine tend to be very regular and even, which allows for faster running. When you have no doubts about the surface your foot is landing on, you put more effort into your speed.

Vegetation - On course composition, none of the options support much, if any, vegetation until we get to "running where no trail exists." But, "no trail" can take a lot of different forms.

One general type of option for no trail is what we could call "uneven." This might be rocky, rutted, or sloping. None of the three runs very fast. You have to pick your way and step gingerly in spots.

These conditions occur with some frequency in Colorado, but there is another, and more common, "no trail" condition. The norm is that there's something growing where no trail exists.

In a natural state, the something growing is likely uneven and a bit hummocky. That's not very fast. Hummocky is a lot like rutted, only with vegetation to obscure how uneven it really is. You have to pick your way around the worst of the bumps and let your ankles shift with the unevenness of the rest. Given enough practice, some people become adept at running on these surfaces, but still not as fast as they are on concrete or asphalt.

In a less natural state, you have grass. Grass is usually fairly even beneath and not especially slow, but some grasses are slower than others. In Colorado, most manicured grass is Kentucky bluegrass. At least when well-watered, this grass is a slower grass. It absorbs a lot of energy from runners passing over it. The ground beneath can also be somewhat spongy.

On the other hand, most cross country runners from Colorado have at least heard of a cross country course in Casa Grande, Arizona. The course is overwhelmingly on grass, yet it yields spectacular times. Assuming the course is accurately measured, what would account for famously fast times on grass?

A couple of things, actually, but the main thing is that it isn't Kentucky bluegrass. It's Bermuda grass.

About all that Bermuda grass has in common with Kentucky bluegrass is that both are green when not dormant. Whereas Kentucky bluegrass grows more or less straight up in single blades from the ground (and therefore takes a lot of water to continue thriving), Bermuda grass grows in flat bunches along the ground and takes much less water. So, the energy absorption of Bermuda grass is far, far less than that of Kentucky bluegrass. And, because Bermuda grass takes much less water, the ground beneath it is, typically, not nearly as spongy.

Taller grass, of course, is slower than grass that has been cut close to the ground. That's somewhat irrelevant with Bermuda grass (which is never tall), but it's a moderately big deal with Kentucky bluegrass.

Elevation profile - The main thing you need to know about elevation profile is that flat is fast and hilly is slower. How much slower depends on how hilly. Downhills never give you as much as uphills take away.

One additional advantage of flat is that you never have to change gears. Every time you change gears, you spend extra energy. It's more efficient to lock into the same pace and rhythm and stay there.

Another thing you might want to know about elevation profile is if the course is net uphill or net downhill. Most courses end approximately where they begin and are net neutral. A few, however, are not. Liberty Bell is a prime example of a course that is net downhill. Google Earth shows the Liberty Bell course is at least 50 feet net downhill, possibly as much as 75 feet.

Turns - Straight is fast. The fastest possible "cross country" course would likely be on concrete, slightly downhill, and would proceed 5000 meters without so much as a hint of a turn. Wide turns slow you down a little. Tight turns slow you down a lot and require a significant energy expenditure to get back up to speed. Many tight turns multiply the effect. The constant losing and regaining of speed wears runners down.

Elevation - Lower is better. Lower means better oxygen density. Oxygen density more typically comes up in discussions of meteorological conditions, but the altitude of a venue is fixed. All other things being equal, a lower venue will be faster than a higher venue because of more available oxygen for the competitors.

That more or less covers the relevant course conditions. But there are other differences between races. Courses differ permanently on account of conditions inherent to the courses in question. But runner experiences may differ dramatically from one race to the next on account of meteorological conditions. Meteorological conditions tend to vary much more than course conditions, though both are known to vary some.

Drop back by in two or three days and you will find Part II of this article. In Part II, I'll discuss how meteorological conditions impact courses and then spend some time revealing what makes Colorado's two fastest courses so fast.

Part II - What Makes Fast Courses So Fast?