The Biomechanics of Terrestrial Locomotion

John Merck

Walking an running animals encompass terrific diversity and, in contrast to swimming:

Thus, we can only deal with walking superficially. In this lecture, we will address two broad themes:

Common requirements:

Support: The limbs must physically bear the load of the animal's weight. For this, they must be scaled and shaped appropriately.

Stability: The limbs that touch the ground form a base of support (right) that encompasses the animal's center of mass when it is standing or walking.

Propulsion: Animals don't just stand there. The limb must be able to exert lateral force against the ground, causing the animal to move in reaction.

Maneuverability: The animal must be able to vary the size and direction of the locomotor force it exerts in order to accelerate, turn, and stop without excessively sacrificing stability. Note: A running animal is essentially always falling and catching itself. It is deliberately sacrificing support for speed and maneuverability.

Sources of difference:

Posture: Major issues:

Ecology: Regardless of gait, we can divide all terrestrial locomotion into:

These factors, together, give us.

Gait. Depending on the foregoing factors and the specific demands of the moment, animals choose between distinct gaits, repeated patterns of footfalls, including:

Otherwise similar animals under similar conditions will choose different gaits if their body proportions are different. Under conditions where a horse will trot, a camel will pace, to avoid interference of its very long fore and hind limbs.

A running specialist may choose gaits that a non-runner would avoid.

large animals operate under stricter biomechanical limitations than small ones.

Scaling effects: We have previously discussed the responses of organisms to the demands of increasing size:

Energy storage:

Many terrestrial animals conserve energy by storing it in some way. Two significant strategies:

Torso flexion:

Of course, not all locomotor power comes from the limbs. We've seen how axial flexion aids locomotion in sprawlers. Even cursorial upright walkers often use flexion of the torso in the sagittal plane to assist locomotion.







Additional reading: