Dogs don't swim, but run underwater

Dog-type paddle swimming, also known as "dog swimming", is one of the first basic swimming styles often taught to children. However, despite being an inspiration for the name of swimming and rapping with all four limbs, the researchers found that dogs do not swim in the water.

Instead, the dogs always perform a more complex cycle of movement in the water, to maximize their speed when traveling through water waves and reducing resistance.

Previous assumptions used to suggest that the movement of underwater dogs is almost like a treadmill. However, researchers from Pennsylvania, USA have shown for the first time that this movement is more like a dog running faster on the ground.

Professor Frank Fish of West Chester University (USA) used underwater cameras to film 8 individuals from 6 different breeds of dogs as they swim through a swimming pool. The video was recorded at 30 frames per second to make it easier for Professor Fish to analyze movements.

When a dog runs on the ground, its front legs will come up and down at the same time with a hind leg on the opposite side. For example, the front leg on the left will bring up and down at the same time with the hind legs on the right.

However, when a dog sprints on the ground, to accelerate, its legs move in a complicated cycle. The left foot on the left will land first, followed by the front, left, then the hind, right and the last, the right. The more the dog runs away, the more the legs will lift - up and down more smoothly, in the same style.

Professor Fish and colleagues found that the movements of underwater dogs were almost the same as how they ran quickly on land, except for one point: Although the front legs were still used to create thrust, but when Under the water, the hind legs are pulled close to close before stretching. This is to reduce the drag caused by the hind legs when the front leg creates thrust.

"By studying the characteristics of swimming dogs , they can learn more about how evolution has separated terrestrial and underwater mammals," the team said.