Lecture 15 - Locomotion Flashcards
What are three environmental medias?
Air, water, and land
What does the high density of water cause?
Drag is a challenge but gravity is not
What is the biggest challenge of land and air?
resisting gravity is a problem but drag is not
What is newtons first law?
Every object in motion will stay in motion unless external force is applied
What is newtons second law?
F = ma, accleration and force are vectors
What is newtons thirds law?
Every action has an equal and opposite reaction
What is GRF?
Ground force reaction
What id ground force reaction?
when the limb contacts the ground it is the force that it experiences
What the components of GRF?
Vertical, horizontal, and medio-lateral
What does the vertical component do?
support the animals weight
What does G(h) and G (ml) allow for?
acceleration/deceleration, maneuvering, and balancing
What must occur over a series of strides with the average vertical force?
Must equal the animals weight
At rest, what must the force on a limb equal?
weight/n (n= # of limbs)
What is a gait?
Pattern of locomotion
What are the phases of a gait?
support and swing phase
What is a stride?
one full cycle of support and swing phases
What is a duty cycle?
relative fraction of stride period represented by limb’s support phase
What is required to maintain equilibrium?
Increase in maximum forces exerted against ground (Gv = W)
How does locomotion proceed?
By repetitively throwing CG forward and then catching it
What are cursorial quadrupeds built for?
Forward locomotion
Where is the normal center of gravity in located where in cursorial quadrupeds?
Just caudal to thoracic limbs
What direction is the center of gravity shifted when head and neck are lowered?
Forward
What direction is the center of gravity shifted when head and neck are raising?
Backward
What direction is the center of gravity shifted when head and neck are turned to the side?
Laterally
What does the tail do?
Contributes to longitudinal and lateral shifts in GC
What features decided whether a tail has any effect on GC?
mass and length
What are two groups of gaits?
Asymmetric and symmetric
What is a symmetric gait?
Movement of limbs on one side repeat motions on other side with intervals between foot falls being evenly spaced
What is an asymmetric gait?
Limb movements on one side do not repeat those on other side and foot falls are unevenly space
What is a symmetric gait?
Walking
What is an asymmetric gait?
Galloping
What is forward motion normally started by?
One of the hind limbs, shifts CG forward toward contralateral limb
What happens at a slow gait with oscillation?
CG rhythmically oscillates left and right trunks. Tail, head, and trunk swing side to side
What happens with rapid gaits with oscillation?
forward momentum and inertia are increased, less lateral oscillation
What happens to foot placement with increasing speed?
Fewer limbs provide simultaneous support, placement becomes more medial to maintain balance
What is EMA?
Effective limb mechanical advantage
What does EMA show?
Ratio of muscles moment arm (r) to moment arm of GRF (R)
What is limb mechanical advantage?
Ground reaction force acting on limb relative to limb’s posture during support
What does limb mechanical advantage determine?
moments, or torques, developed at the joints of the limb
What can cause EMA to increase?
Increasing size of animal
What is the posture of larger cursorial mammals when they run?
More upright
What do larger animals run more upright?
Align joints with GRF, increase mechanical advantage, and reduce magnitude of forces against bones and muscles
What is mechanical work?
Physical work of the animal to maintain oscillations in PE and KE
What is PE?
Potential energy, energy supplied by muscles to raise and lower body’s center of mass
What is KE?
Kinetic energy, energy needed to reaccelerate center of mass and limbs
What is the affect of the out of phase nature of PE to KE energy during walking?
PE is converted to KE then back, 70% energy exchange which reduces metabolic costs
What is the spring mechanism?
Elastic storage of PE and KE in muscles and tendons as the limb lands on ground, is restored back to limb as it is propelled off the ground
What occurs with elastic rebound in regards to metabolic cost?
Galloping gaits are metabolically cheaper then trot gait at high speeds
What does it mean for something to be metabolically cheaper?
Less oxygen needed
What was the pelvic limb adapted for?
Propulsion
What was the thoracic limb adapted for?
Support
How do thoracic limbs differ from pelvic limbs?
Shorter, straighter, and connect to trunk via fibro-muscular attachments
What are the characteristics of the pelvic limbs?
Long, angular, heavily muscled, connected directly to the vertebral column
What muscle group assists to elevate CG?
Epaxial muscles
Why is the elevation of CG needed?
to extend duration of forward motion which is limited due to the pull of gravity
What do the pelvic limbs do to the CG?
Move it forward and upward
What do the thoracic limbs provide?
Upward propulsion and directional stability
