by Leaddog » Tue Jan 25, 2011 5:40 am
Hi Eric. I know you want a simple answer, but I'm afraid I don't have one, and I'm pretty sure you can guess why - not all trails are the same. The key to sled dog racing is sustainable exercise, meaning that you are providing the nutrients as fast as you are burning them, and you are getting rid of waste as quickly as you are producing it. So if you say that the dog's energy reserves are "off-limits", at least from a planning standpoint, then you need to stop and refuel when you've burned the calories you put in the tank since the last stop. The rule of thumb for a reasonably flat, groomed trail is 60 calories/mile, so if you fed 2 meals at the beginning and end of the last break, and the meals totalled roughly 3000 calories, then you've got 50 miles in the tank. From a calorie-burn standpoint, there is actually little difference between a walk, trot, or lope with respect to calories/mile (again, assuming a uniformly flat, groomed trail), provided the dog is capable of selecting whichever gait they chose. They will chose the most energy-efficient one for that speed. The difference is whether internally, they can supply the nutrients and get rid of the heat fast enough. If you assume that all dogs have a uniform-sized stomach that holds 3000 calories (indulge me here for the sake of illustration), a dog that internally can only supply nutrients to support 6 mph will need to stop after 8.5 hrs, but a dog that can supply nutrients to support 12 mph will need to stop after a bit more than 4 hrs - both after having traveled 50 miles. Obviously, the equation starts to shift if it is not a nice, flat groomed trail - if you are going up mountains or breaking trail in soft snow, calories/mile will be higher and you will be stopping sooner.
We've done a bit of study on rest periods, and to a large extent, the rest period is dictated by how far off that ideal "didn't use reserves" the previous run actually was. Early on in a race, before the dogs have really adapted, their rest periods probably need to be a bit longer to fully recharge and restore the balance. However, later in the race when they've adapted, the rest periods probably don't need to be as long - provided the run speeds and intensity have remained the same. If the run speed or difficulty increases, then the rest period may need to increase because even in the face of that wonderful adaptation, you still tapped in to the reserves.To illustrate - we did a study on the Denali Highway (nice smooth groomed trail) running 6 hr on, 6 hr off, with the runs covering 50 miles. During the first 2 days, the dogs weren't completely recovered metabolically from the run at the end of the 6 hr rest. They were good to go, but they weren't quite back to baseline. During the latter 3 days, the 6 hr rest was more than enough to get them back to baseline for the same run.
I think one of the critical "mistakes" mushers make in planning their races is planning per day, and treating the run times and the rest times as somehow needing to fit a specific ratio (whatever that ratio is). That produces the unavoidable temptation of having everything add up to an even 24 hrs. That 24 hrs makes the math more manageable, but it is an arbitrary endpoint that doesn't necessarily fit what the dogs are doing. The goals and demands of the run period and rest period are different and only partially related to each other, so tightly linking them inevitably makes one or the other an imperfect fit.