If you run all out for 10 kilometers in 30 minutes, does that mean that you can run all out for 20 kilometers in 60 minutes?
No. But many people like to think so.
As the distance increases, the maximum sustainable speed will decrease. If the speed decreases, then the time-to-distance ratio will increase. As the ratio increases, so does the proportionate time. So if 10 kilometers takes 30 minutes, then 20 kilometers may take...70 minutes?
"Trees don't grow to the sky" as they say.
Despite that fact, many are tempted to think that they can wish themselves to a smashing performance the first time they try. I prefer to reason myself into a respectable performance.
The tricky part is that mountain sports are too variable to allow for performance calculators that are common in other sports. However, there is a way to fudge an estimate.
How to estimate a goal time
First, look at the time, distance, and elevation gain from a previous objective that was successfully completed. Imagine a skimo race of 15 kilometers and 1,500m in elevation gain. If you finished that in 2.5 hours, then you have a concrete "base case" to use to estimate future events.
Second, estimate your way to a goal time. Figure out a fudgy formula to describe your previous performance. This will become your "personal rule of thumb" for similar events.
To do so, randomly select divisors for the distance and gain until the total time equals your finishing time. Take the distance and divide it by X. Take the gain and divide it by Y. Add the two together. Success? Great. No? Try again.
(There's no secret to this. You need to find your own rule of thumb. Just plug in some numbers and see what happens.)
For example, in the 2.5-hour skimo race:
- Let's try divisors of 10 kph and 1,000 m/h:
(15 km / 10 kph) + (1,500 m / 1,000 m/h) = 1.5h + 1.5h = 3h.
The formula doesn't reflect the finishing time; the duration is too long. So try again using bigger divisors.
- (15 km / 12 kph) + (1,500 m / 1,200 m/h) = 1.25h + 1.25h = 2.5h. Voila!
Note that there is always more than one "right" answer. In the above example, 15 kph and 1,000 m/h would work just as well. Or 10 kph and 1,500 m/h, etc.
Third, apply the fudgy formula to your next goal event. What if your next event is The Grand Traverse (with 64 km with 2,100 meters of gain)? Well, your handy formula suggests:
- (64 km / 12 kph) + (2,100 m / 1,200 m/h) = 5.3h + 1.8h = 7.1h
Fourth, remember: trees don't grow to the sky. As the distance increases, the sustainable speed of an all-out effort must decrease. So not only does the absolute duration increase, but the proportionate duration does too. For example, if the distance doubles, the duration will more than double.
Again, it's a guess, but in the above example, a goal time between 7-8 hours seems realistic. (The Grand Traverse is a relatively flat course, so for anyone but the front runners that might have to break trail, a good skin strategy and a glidey nordic stride could be a big help.)
Now you have an estimate of your performance.
Fifth, as your fitness improves between events, you'll need to adjust your divisors. As this method suggests, estimating goal times in mountain sports is tricky. There are too many variables for any method to be 100% repeatable. Constructing something like the Daniels' VDOT calculator is impossible.
That also makes it difficult to compare performances across events. But once you start outperforming your personal rules of thumb and have to adjust them, you'll know that you're improving.
But do personal rules of thumb really work?
You won't win a Nobel prize in statistics, but yes, personal rules of thumb work well enough.
In a recreational context, mountain guides often use similar rules of thumb when estimating the duration of an objective with a new client. In that context, 5 kph and 300 m/hr is a common formula. So the first skimo race described above would take eight hours at "client pace."
Or try the Smart-Like-Tractor approach
Of course, what is much, much more common is to go as hard as possible out of the gates and gradually get slower and slower and slower over the course of the event. It makes for shitty race times but it provides a lot of emotional support via misplaced gratification.
With a sudden, naive burst in speed, the tractor's muscles are flooded with lactate. The aerobic system (which was probably not warmed up properly) is immediately overwhelmed. That makes for a slower average pace for the rest of the event. That "strategy" always results in the same thing: a good story for your buddies to laugh at. And a sub-optimal performance.
But ignorance is bliss, as they say. Especially for tractors.