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Terrestrial Locomotion Part 2
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Covers terrestrial locomotion following on from part 1 of the lectures.
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Comparative Anatomy and Physiology of AnimalsLecture 22 Terrestrial locomotion 2 13/01/21
Legged locomotion
- Needs legs.
- Needs to have a hard skeleton.
- Legs allow the animal to move in all directions.
Basic mechanics
- Stride: one full cycle of leg movement.
- Two phases in one stride: swing phase (leg moves up and forwards) and a stance phase (leg
planted on the ground and provides thrust).
Leg movement
- Leg movement is achieved by a set of muscles that connect inside of the thorax to the coxa
od the leg.
- Leg flexing and extension controlled by muscles in the femur.
- Muscles attack to the inside surface of the skeleton.
- Muscles can only produce force when shortening, so different sets of extension and flexing
muscles are needed.
- One set of muscles will contract during the swing phase, the other during the stance phase.
Leg posture
- Horizontal sprawled leg postures allow some insects to take advantage of gravity for leg
movement.
- Vertical sprawled leg postures can decouple weight loading from movement muscles.
Gaits
- Pattern of limb movement over a hard surface.
- Defined by several different descriptors: leg position, stepping pattern, stride period, stride
length, stride cycle, speed (= stride length x stride frequency), duty factor (fraction of time
one leg supports load), phase (fraction of cycle one leg leads or lags another), etc.
- Not extensive list but provides general idea.
- Walking and running are just two different types of gaits.
- Although it is possible to categorise gaits, the animal world is much more complex, as they
use a continuous range of gaits.
, - These are dependent on morphological constraints, the nature of the terrain, ecological
context, and energy requirements among other things.
- A higher work potential comes at the cost of motility in vertebrate limbs.
- Gaits become a more relevant consideration in vertebrate motility.
Insect gaits
-
Sprawled gait
- Sprawled vertebrates increase speed by moving legs faster and exaggerating sideways
movement to increase step distance; energetically costly.
- Some lizards can run in two legs; however, this is also costly.
-
Upright posture
- Strong upwards thrust.
- Enables more energy efficient gaits for higher speeds.
- Although intermediate gaits exist, walking and running constitute quite different gaits, with
distinct mechanics and energetics.
Bipedal gaits
Walking
- For walking to occur, potential energy must be converted to kinetic energy.
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