Gaits - Pattern of Steps for Legged Animals

Gaits - pattern of steps for legged animals

Controllable Rhythms - particularly common and particularly interesting in locomotion

                        - kick in when necessary and adapt those rhythms to immediate needs.

High Speed Photography

(Before high speed photography it was virtually impossible to find out exactly how an animal's legs moved as it ran or galloped)

The photographic technique grew out of a bet on a horse

1870s

Rail- road tycoon Leland Stanford bet twenty-five thousand dollars that at some times a trotting horse has all four feet completely.

A photographer who was born as Edward Muggeridge to Eadweard Muybridge

- Photographed the different phases of the gait of the horse, by placing a line of cameras with tripwires for the horse to trot past.

- Pioneered the scientific study of gaits

- Adapted a mechanical device known as the zoetrope to display them as "moving pictures

Gaits

Some animals have only one gait, which means they only have one rhythmic default pattern for moving their limbs.

Elephants for example can only walk and amble, but amble is just a fast walk.

Milton Hildebrand - American Zoologist who pioneerrd the contemporary scientific analysis and classification of gaits. Noticed that most gaits posses a degree of symmetry.

When an animal bounds this gait preserves the animal’s bilateral symmetry

7 Types of Gaits

1. Pace         - is a lateral two-beat gait

                 - where two legs from the same side of animal move forward or backward together

2. Bound         - is a leaping movement upward

                    - both front legs move together, both back legs move together

3. Walk         - to move at a regular & fairly slow pace by lifting and setting down each foot in                  turn never having all feet off the ground once

4. Trot                 - a moderately fast gait of a quadruped in which legs move in diagonal pairs

                - front left and back right then front right and back left

5. Rotary Gallop - also preserves the bilateral symmetry

                   - is the fastest of all gaits

                   - a four beat double suspension

                   - it’s pattern is right back then left back, suspension, then right front,                  

                     suspension

6. Transverse Gallop - is similar to rotary gallop only, the sequence is reversed & it only has one                          suspension

                          - it starts with left back then right back, left front then right front

7. Canter         - is a three-beat gait that includes a period of suspension at fast speeds.

                - first front left then back right, then the other two legs simultaneously

Pronk - an uncommon gait in which all four legs simultaneously push off the ground at once

Bipeds - the two gaits are the ones most commonly observed in bipeds since the network representing the CPG (Central Pattern Generator) of a biped requires only two identical oscillators (one for each leg)

Quadrupeds - simplest model is a system of four coupled oscillators (one for each leg), the most symmetric gait is the pronk since it corresponds to all four oscillators, synchronized.

SIx-legged Creatures - the typical gait of most insects is the tripod in which the middle leg on one side moves in phase with the front and back legs of the other side.

This is one of the natural patterns for six oscillators connected in a ring.

1. OSCILLATOR

 -The organizing principle behind many biological cycles, such as gaits, is the mathematical concept of oscillators. In other words, it is possible for animals to create different types of gaits because of oscillators. It is a unit whose natural dynamic causes to repeat the same cycle of behavior over and over again. Biology hooks together huge "circuits" of oscillators, called

"COUPLED OSCILLATOR NETWORKS"

-These circuits interact with each other to create complex patterns of behavior.

2. PERIODIC OSCILLATION

  -series of motions that works, and

repeat over and over again.

  -It breaks time-translation symmetry in order for periodic oscillation to happen.

Ex.

-The repeated pacing of a tiger inside a cage.

-The vibration of a violin string.

Why do systems oscillate?

The answer is that this is the simplest thing you can do if you don't want, or are not allowed, to remain still.

Why does a caged tiger pace up and down? Its motion results from a combination of two constraints. First, it feels restless and does not wish to sit still. Second, it is confined within the cage and cannot simply disappear over the nearest hill. The simplest thing you can do when you have to move but can't escape altogether is to oscillate. Of course, there is nothing that forces the oscillation to repeat a regular rhythm. Oscillations arise out of steady states. The tiger is free to follow an irregular path around the cage.