Endurance

Dogs are built to go the extra mile

Most dogs, it seems, are born to run. They can run for long periods of time and over long distances. What makes them so well adapted for running? Lots of things!

A body built for breathing...

As a dog runs, its body works like a bellows. Like other four-legged animals, a galloping dog takes one breath with each stride (the distance between successive footfalls of the same foot). When its back extends, it's easy for the lungs to expand and the dog inhales. When its back flexes, the lungs are compressed, squeezing out air, and the dog exhales.

The long, lean legs of many dogs make running a breeze because it takes relatively little energy to pump them back and forth. Dogs with the longest legs relative to their body size are usually the fastest runners because they take the longest strides. Dogs with shorter, squat legs are usually not very fast runners.

...a hard working heart...

Hard-working muscles need lots of oxygen. Without that extra oxygen, muscles tire and begin to ache, causing both dogs and us to slow down. When dogs run, their heart rate skyrockets, pumping oxygen-rich blood to the muscles. In fact, a snoozing dog has a heart rate about the same as a resting human, 80 beats per minute. A working dog's heart rate can reach 274 beats a minute, almost double the rate of a healthy, active human. No wonder dogs can keep going after most people are exhausted!

...and a super spleen!

Red blood cells, made in the spleen, carry oxygen throughout the body. An exercising dog dumps extra red blood cells into its bloodstream, increasing the amount of oxygen in its blood. This helps prevent muscle fatigue.

When dogs rev up, they pant to cool down

Like all mammals, dogs can overheat when they exercise. Because too much heat damages body systems, mammals need a way to get rid of excess heat. Humans sweat. Dogs pant.

Hot dogs...

A small dog panting in a field of flowers

Have you ever held your hand in front of a panting dog's mouth? Whew -- dog breath is hot! What you feel is excess heat leaving the dog's body.

An overheated dog breathes in and out through its mouth. With each pant, dogs inhale cool air. As the cool air moves into the lungs, it absorbs heat and moisture. When dogs exhale hot breath across a wet tongue, water evaporates, cooling their bodies. To maximize heat loss, panting dogs direct warm blood to their tongue to be cooled. The hot, moist air the dog exhales is some 10°F warmer than if it exited the nose, helping to rapidly dump body heat. But just like sweating, panting cools by evaporation, and a panting dog needs access to plenty of drinking water.

...and cool dogs...

Unless it's a really hot day, a resting dog doesn't generate excess body heat. A resting dog breathes normally, in and out through its nose. Inhaled air is warmed and moistened by passing through the nose on its way to the lungs. On the reverse trip, exhaled air returns some of its warmth and water to the body as it flows through the previously cooled nose. Breathing in and out through the nose preserves body fluids and heat, keeping the dog hydrated and warm.

...and somewhere in between.

Dogs that are only slightly hot will breathe in the nose and out the mouth. This helps reduce water loss. To breathe in one way and out another, dogs use their tongues to direct air-flow. The rhythmic movement of a panting dog's tongue matches its breathing. When the tongue moves backwards, it keeps air from traveling between the mouth and lungs and the dog inhales through the nose. As it moves forward, it allows air to move out through the mouth. With the tongue back the dog will inhale, with the tongue forward the dog will exhale -- all of this happening at least 5 times a second!

In the wild

Wild dogs run to avoid predators and to catch prey. Some wild canines like wolves and African wild dogs will chase prey over long distances, tiring their prey out before moving in for the kill.

Here at home: sled dogs

Many domestic dogs rely on this incredible endurance to work as racers, herders, and hunting companions. Sled dogs are famous for their ability to run over long distances, pulling the weight of their human handler and sled behind them. In fact, the main factor limiting a racing sled dog is the number of calories it needs and how fast it can gobble these up!