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How does flexibility of the vertebral column affect a running animal’s stride?

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Least tern, Sternula antillarum, flying with wings raised and its yellow-tipped black bill pointed forward. — Locomotion These birds largely reside in coastal areas of North America, although some populations live in the continent's interior along large rivers.

In running animals, the flexibility of the vertebral column plays a significant role in determining the efficiency and length of a stride.

In many land vertebrates, the evolution of efficient running is associated with the development of dorsoventral (up-and-down) flexibility in the spine, which allows the body to bend and extend during movement. This flexibility enables the animal to increase the distance between successive footfalls, effectively lengthening the stride. Conversely, if the vertebral column remains rigid, the distance between footfalls is reduced.1

While flexibility is advantageous for stride length, the vertebral column also functions as a structural support. In some large or heavy animals, such as rhinoceroses, the column acts as a firm girder to bear weight, with specialized structures like high dorsal spines providing stability. Additionally, intervertebral disks between the vertebrae help cushion shock during locomotion. Ultimately, the degree of spinal mobility is a balance between the need for stability to support body weight and the need for flexibility to maximize the reach and speed of the limbs.231