Modelling and Scaling Flashcards
(24 cards)
What is scaling?
increase or decrease in size of an object
What does the study of scaling allow for?
comparison of animals of different sizes
With regard to biomechanics, it allows
the anatomy, kinematics, kinetics and
other locomotory parameters of
different sized animals to be compared.
What is a constant?
Two systems are similar if any measurement
from one is equal to an equivalent
measurement from the other, multiplied by a
constant.
• This constant is called a scale factor.
What is geometric similarity or isometry?
if the measurements that are similar are distances, the 2 systems have geometric similarity or isometry
have different size but the same proportions
opposite of allometry
What is dynamic similarity?
if 2 systems have geometric, temporal and inertial similarity, they have dynamic similarity
Mammals of similar shape but different size,
running at an equivalent speed will use the
same gait, similar relative stride lengths and
apply a similar pattern of forces.
How is the change of speed different in small and large animals?
The transition from one gait to another occurs at lower speeds and higher frequencies in smaller animals
eg; Chihuahua gallop at great dans walk pace
What is a froude number?
Gives a dimensionless measure of speed. • Takes into account size. – ‘Equivalent speed.’ – ‘Normalised’. • What would be good measure to use? • Froude Number = Speed2/(Gravity x leg length)
What gait will mammals of a similar shape but different size use when running at equivalent speed?
same gait
What do mammals of different sizes, running with equal froude numbers tend to have?
dynamic similarity
therefore use the same gait at the same froude number
animals change gaits at roughly the same froude number
How can froude numbers be used to estimate speed on extent animals?
Animals moving at equal Froude number will
not necessarily move in a similar manner, but
they will move at comparably speeds,
according to their size
Why must form change with size?
all animals are made with the same materials so as size increases, structures become less able to support weight
eg;Gazelle, a graceful little creature with long thin
legs, is to become larger.
• It would break its bones unless it does one of
two things:
– legs short and thick, like the rhinoceros, so that every
pound of weight has still about the same area of
bone to support it.
– compress its body and stretch out its legs obliquely to
gain stability, like the giraffe
How do mammals compensate for decreased bone strength relative to size?
legs straighter with increasing size thicker bones increased limb mechanical advantage EMA restricted locomotion
What is EMA?
effective mechanical advantage
• The vertebrate musculoskeletal system is
composed of skeletal levers powered by
muscles.
• EMA is the leverage force, created from
individual muscles on bones and joints. It will
depend on the arrangement of muscles,
tendons and bones on each species.
EMA can be also defined as: the amount
of ground reaction force (GRF) generated at
the foot per unit muscle force, or
simply “overall leverage”
How are different sized animals EMA positioned?
small animals- crouched posture so have a low EMA
large animals- increased EMA by straightening limbs and therefore reducing GRF moment on arms (helps maintain bone stresses roughly constant across a wide range of animal sizes
How does increased EMA help large animals?
• Larger terrestrial mammals increase their
effective limb’s effective mechanical
advantage (EMA), reducing the magnitude of
muscle force transmitted to bone elements
and tendons.
• Modification of posture allows a muscle to
produce more output force for a given input,
and can result in safe muscle loads despite an
increase in body weight.
How does the limb EMA change with size?
– Allow different sized animals to maintain similar peak muscle and bone stresses. – Small animals: • Crouched posture • Low EMA – Large animals: • Upright posture • High EMA èTrade-off in manoeuvrability/balance.
Cost of transport vs size?
larger animals use less energy per kg body mass to travel a given distance compared to smaller animals.
What should all animals be able to jump the same height?
in theory jump height is independent to mass
• The height depends on how much muscle an
animal has, how efficient the muscles are, what
the animal’s shape is, gravity and capacity to
generate power.
• Therefore, a human-sized flea would not jump
higher than a normal-sized flea
Why do large animals have issues jumping?
cannot generate enough acceleration to get distance off the ground
Why do small animals not struggle jumping?
don’t feel the extent of gravity that large animals feel
What are the consequences of scaling?
surface area does not scale linearly with body mass
horses have more thermotolerant and sweat more
What are basic models?
Basic models;
– 3D motion.
– Motion of multiple body segments.
• Kinematics may vary between segments.
– Combinations of linear and angular movements.
- use basic models to generalise movement
What are computer based models?
Computer Based models; reduced need for real life studies – Whole body. – Single anatomical structure. – Joint models. – Simulation under different conditions
What are linked segment models?
• Simplified model consisting of body segments
linked at joints.
• Actions of muscles represented by moments.
