My last blog post looked at a study of elite Kenyan runners. This post continues the theme with a look at an even more exceptional group of endurance athletes: dogs.
Dogs, you say? That’s right: Dogs are “among nature’s most elite endurance athletes,” as the authors of Should Your Doctor Check Your VO2 Max in the Journal of Experimental Biology write. The University of California, Santa Cruz study compares the running prowess of retrievers, hounds, and northern breeds, with some impressive results.
What’s the big deal with dogs? They’ve demonstrated the “highest sustained metabolic rates on record,” burning about 4,400 kilojoules of energy (just over 1,000 calories) per kilogram (to the power of 0.75) of bodyweight per day while racing over 300 miles in three days at temperatures of -4 Fahrenheit (-20 Celsius). For comparison, Tour de France riders managed to sustain about 1,400 kJ/kg^0.75/day.
(Technical aside: the reason the bodyweight is raised to the power of 0.75 is to account for how total muscle mass scales with changing body size, a technique known as allometric scaling. It enables fair comparisons between, say, dogs and humans. If you just do a pound-for-pound comparison with body mass, dogs appear even more impressive, sustaining roughly four times the maximum metabolic rate of Tour de France cyclists.)
To deliver this kind of endurance performance, the authors write, “dogs possess structural and functional adaptations at each step in the pathway for oxygen, including in the muscle mitochondria, muscle microvasculature, heart, and lungs.”
Another measure of their remarkable endurance capacity is their “aerobic scope,” which is the ratio of their maximal oxygen capacity (VO2max) to their oxygen use at rest. Dogs have a ratio of 20 to 30, compared to about 10 for goats of equal body mass. The result of this wide aerobic scope is “the ability to run for extended periods at sustained speeds without becoming anaerobic”—which, of course, is exactly what sled dogs (and their wolf ancestor/relatives) have to do.
The paper doesn’t mention the aerobic scope of humans, but if you take a typical resting metabolic rate of 3.5 ml/kg/min and multiply it by 20 to 30, you get a VO2max of 70 to 105 ml/kg/min. A typical value for elite (human) endurance athletes is about 80 ml/kg/min, which suggests that exceptional humans can compete with mediocre dogs on a pound-for-pound basis.
So what does this new paper add to the picture? By looking at three breeds of similarly sized large dogs, the researchers wanted to get a sense of how domestication has altered some of the key physiological traits that originated with wolves.
All dogs are descended from wolves, having been domesticated in the last 15,000 to 30,000 years. But selective breeding has created some very different (and funny-looking, if you ask me) breeds.
Retrievers, hounds, and “northern breeds” (sled dogs like Siberian Huskies and Alaskan Malamutes), which are similar in some respects, have all been bred for different purposes. Sled dogs are the oldest and most wolf-like; hounds are good trackers, which requires an excellent nose but only moderate endurance; retrievers are supposed to retrieve killed or injured hunting game, which requires short bursts of strength and speed but not so much stamina.
The researchers recruited 23 dogs and ran them through a series of tests, consisting of walking, trotting, and galloping over open ground while their gaits were videotaped for analysis, then doing the same thing in a metabolic chamber on a treadmill so their energy use could be measured.
The results? As expected, the sled dogs were by far the most efficient at covering ground, particularly at the trot used for long-distance travel. Here’s a look at the overall energy cost of locomotion in the three breeds, compared to the “maintenance” cost of their resting metabolic rates:
While it’s not clear exactly which changes have made the hounds and retrievers less wolf-like in their traveling efficiency, the researchers suggest two of the key differences may be the angle of the head (lower and more streamlined in wolves and sled dogs), and the angle of the rear leg (more upright in the wolves and sled dogs, which may assist in storing and re-using energy in spring-like tendons from stride to stride).
So what training advice can we take from dogs? Get outside at least three times a day no matter how cold it is, pull your share of the load, and chase every frisbee in sight, and you’ll be an exceptional endurance athlete in no time.
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