How do four-legged animals walk and run?

Quadrupedal locomotion, the way four-legged animals walk and run, is a marvel of biomechanics. It involves a complex interplay of muscles, bones, and joints to achieve coordinated and efficient movement. While there are variations among different species, here's a general overview of how four-legged animals walk and run:

Walking:

1. Limb Movement: Quadrupeds have two pairs of limbs - the forelimbs (front legs) and hindlimbs (back legs). During a walk, the limbs move in a diagonal sequence. As one front leg moves forward, the opposite hind leg moves forward as well, creating diagonal pairs.

2. Stance Phase: When a foot is on the ground, it's in the stance phase. During this phase, the animal distributes its weight onto the foot and uses muscles to provide support and forward propulsion.

3. Swing Phase: When a foot is lifted off the ground and moves through the air, it's in the swing phase. The animal's muscles help swing the leg forward in preparation for the next stance phase.

4. Weight Distribution: As an animal walks, it continuously shifts its weight from one foot to another. This weight distribution ensures balance, stability, and smooth locomotion.

Running:

1. Increased Speed: Running is essentially an accelerated form of walking. As the animal increases its speed, the diagonal sequence of limb movement remains, but the strides become longer, and the feet spend less time on the ground.

2. Aerial Phase: During running, the animal's feet may completely leave the ground, creating an aerial phase where all feet are in the air simultaneously. This occurs when the animal's body is propelled forward by the force of its limbs pushing off the ground.

3. Spring-Like Movement: The elastic properties of tendons, ligaments, and muscles contribute to a spring-like recoil during running. This elasticity helps animals conserve energy and achieve efficient forward propulsion.

4. Increased Flexibility: Running requires greater flexibility in the spine and limbs compared to walking. This allows for more extensive limb movements and increased stride length.

It's important to note that the specific gait or running style can vary among different species of four-legged animals. Some, such as horses, have a pronounced aerial phase during galloping, while others, like dogs, have a more continuous bounding gait when running. These differences are influenced by factors such as the animal's body structure, limb proportions, and habitat requirements.