Biomechanics Flashcards
(42 cards)
Simply define biomechanics
Functional morphology
Effect of gravity
Define morphology
Basis of everything
Physical dimensions
Define energetics
Energetic equilibrium
Eg. Don’t starve
Define optimisation
Most efficient, energetic low cost solution for…
Morphology e.g. Musculoskeletal system
Function e.g. Contraction of muscles
Biological role e.g. Arm abduction to collect food
Define locomotor form
Morphology
= quadrupedal, bipedal, caudal
May change during an individual’s ontogenic development
e.g humans are originally quadrupedal before exclusively bipedal
Define locomotor type
Function
= walking, running, crawling, hopping, brachiating, leaping
Leaping can be bipedal (frogs) and quadrupedal (toads)
Usually decreases in number but increases in proficiency
Almost all animals use a variety - ‘trying them out’
Bipedal doesn’t conclude the type of moment
e.g walking/running/skipping
Cursorial animals are…
Animals that travel far, fast or easily on the ground
Quadrupedal cursors evolve from walkers
- predators or medium/large herbivores e.g sand lizard
Bipedal cursors balance body over the legs e.g ostrich
Saltatorial animals are…
Animals that jump or hop
Often, but not always, bipedal
Ricochet animals are…
Animals whose hindlimbs are used in unison for a succession of jumps e.g kangaroo
Characteristics relating to mammalian cursors are…
Flexion/extension of spine
Passage of hindlimbs outside forefeet
Varied position of shoulder
Tetrapod limbs
Forelimb and hindlimb
- stylopodium (proximal)
- zygopodium (middle)
- autopodium (distal)
Can be further subdivided, mainly in the autopodium
Autopodium
Distal
Most variety as it is in contact with the habitat
tree/ground fast/slow powerful/not
Gravity pull
Elongated tarus in specialised leapers
Shorter digits in powerful climber
Characteristics of bipedal leapers
(Relatively:)
Short forelimbs
Long hindlimbs, elongated feet
Grip:
- large palmar surface
- particularly large plantar surface area
- adduction of the hallux
Frogs adaptations to bipedal leaping…
Vertebral column is short (shorter than pelvis and ilium)
Composed of 9 vertebrae which are fused - urostyle
Short forelimbs, elongated hindlimbs (esp. autopodium)
Fibula and tibia are fused (zygopodium)
- reduced ability to rotate = increased stability
Amphibian and reptilian limb position
EG. salamander turtle lizards
Trunk is slung between limbs and frequently touches the ground
Limbs set at almost right angles to the body and digits point laterally
= not efficient
Radius/ulna tibia/fibula flexed at 90 degrees
Axes of all joints are directed parallel to the vertebral column
Mammalian limb position
ROTATION
= inline/parallel with body axis
Hindlimb - forward, forelimb - backward
More energy efficient
Limbs sagittal under or alongside trunk
POSTURE
-in late therapsids, limbs carried more under the body
=reflection of increased efficiency in locomotion
DIGIT ORIENTATION
Torsion of the humerus (rotated) and femur brought toes forward inline with the direction of travel
= efficient
SHOULDER GIRDLE
- limbs under the body so force is diverted more vertically (no need for interclavicular bone which supports sprawled postures)
PELVIC GIRDLE
rapid locomotion is common, so the orientation changes so that forward thrust of hindlimbs is more in alignment with the line of travel
= force transferred to vertebral column
How a cat skeleton relates to a human (limb position)
Forearm bones must cross to a pronated position so volar surfaces can rest on the ground
(No need in hindlimbs, thigh already rotated forward)
Essentially preserved in humans
Body size and limb design
- basic principles
Muscle force = linear dimensions (power of 2)
Mass is cubed
So… Small leapers can develop relatively more muscle
Limbs bear the mass of the body
Strength is proportional to their cross sectional area
Change in body size =
10 fold increase in diameter
1000 fold increase in mass
100 fold increase in cross-sectional area
This is why gravity has a greater impact on larger animals
Centre of mass - basic principles
“The single point at which the mass of the body can thought to be concentrated”
Security of stance is greater, the lower the position of the CoM is
Static equilibrium in vertebrates requires that the vertical from the CoM touches the ground within the area limits e.g forelimb - hindlimb
Primitive traits of Hadar Hominids (Lucy)
Long , curved proximal phalanges
Thorax funnel shaped
Scapula with cranially orientated glenoid
Midthoracic vertebrate with ventrally expanded centra
Iliac blades face posteriorly
Postcranial synapomorphies (=shared derived features) of the Hader Hominids and Homo Sapiens
Sacral retroflexion
Pelvis superinferiorly shortened and anteriorly rotated iliac blades
Long femoral neck
Distal femur has high bicondylar angle and elliptical lateral condyle
Calcenous has massive body
Strong transverse and longitudinal arch
Hallux is convergent and toes relatively short
Relatively small forelimbs
Difference is mass distribution within the hindlimb
Humans : 62% 29% 9%
Galgo : 67% 22% 11% - Saltorial
Femur ——Feet
More muscle mass proximally makes leaping more efficient
Feet relatively heavier and longer
= increases acceleration distance, grasping
Avatisms in the feet of horses
Modern horses are unguligrade (have only 1 enlarged and elongated digit on each foot)
Evolved from ancestors with 3 or 4 toes, ‘lost’ toes or remnants can rarely reappear
= evidence of presence of underlying ancestral developmental pattern
Changes in foot postures: Plantigrady - digitigrade - unguligrade
What does this mean for the animal?
Lengthens the limb and increases the length of stride
