Animal locomotion

lecture 4

How do land vertebrates move?

rolling

slithering

using legs

types of rolling

powered

unpowered (e.g. pangolins)

Slithering

used by snakes

sidewinding odd way of slithering

What can limbs do?

support, propel, recover from propulsive movement

often all going on at the same time

recovery often the most damaging

what phases can limbs undergo?

protraction, retraction

purpose of extensor muscles and why are they larger than flexors?

hold the animal upright

allow to recover from previous gait therefore larger than flexors in upper limbs

what happens to the flexor angle when the joint flexes?

decreases

‘shortened limb’

flexor angle can be reduced the most - at rest often sub 180^o

what happens to the flexor angle when the joint extends?

increases

‘lengthens limb’

quadrupedal gait

gait of animal that walks on 4 legs

3 main ways to diagrammatically represent gait

sequence (most likely to be examined)

roadkill

other ones too complicated

4 major equine gaits

walk

trot

canter

‘transverse’ gallop

walk

4 beat gait

LH, LF, RH, RF

at least one hoof on the floor at all times

trot

2 beat gait

very energy efficient - fastest endurance gait for most mammals

very symmetrical - used for lameness diagnosis

canter

3 beat gait

can be right or left lead and can switch between them

‘transverse’ gallop

4 beat gait

period during gallop when all 4 hooves are off the ground - meet in the middle of the horse

cannot jump at gallop

1-beat gaits

not propulsive gait in most species

bounding - lambs playing, frightened cats

demonstrate fitness to predators like lions (don’t even bother chasing me I can jump so high)

2-beat gaits

pace - can be trained in horses; certain horse breeds that pace instead of trot; natural gait for camels

bound - rare for larger mammals; used for jumping

3-beat gaits

only half bound practical, aside from canter

intermediate gait in lagomorphs

4-beat gait

rotating gallop - some dogs like greyhounds (2 suspended phases); not used by horses as more likely to clash limbs

Tölt - Icelandic horses use this; very smooth and no suspended phase

efficiency of cursorial specialisation

erect stance, rather than sprawling

limb movement restricted to sagittal plane by collateral ligaments and muscles

equine limb locking?

increasing stride length in cursorial specialisation

general lengthening of limbs

plantigrade → digitigrade → unguligrade

mobile scapula

suspended phase(s)

sagittal plane spinal flexion increases reach of limbs

examples of plantigrade, digitigrade and unguligrade

plantigrade - guinea pigs, humans

digitigrade - carnivores, rabbits

unguligrade - ungulates (walking around on hooves makes limbs longer)

How does a mobile scapula increase stride length?

freed from trunk, linked only by synsarcosis

lie in sagittal plane on either side of laterally flattened thorax

acts as limb bone protracting and retracting the shoulder joint

throws shoulder joint cranially and caudally - longer stride

increasing stride frequency for cursorial specialisation

not as effective and increasing stride length

very inefficient to increase movements above natural resonant frequency

loss of distal weight in limbs - allows foot to be swung more quickly in off the ground phase

Cats specialisation

least cursorially specialised domestic species

limb abduction

plantigrady (tail support)

digit abduction

supination