Walking In Quadrupeds

Question 1

Difference between kinematic and kinetics?

Answer 1

Kinematics = movement

Kinetics = force

Question 2

Gait progression in quadrupeds?

Answer 2

Animals select different gaits depending on their speed

Generally start at a walk, progressing to a trot, then galloping at their fastest speed

Question 3

How to calculate stride time and duty factor?

Answer 3

Stride= stance+ swing

Duty factor= stance/stride (time)

Duty factor typically changes with diff speeds.
Duty factor typically lower at faster speeds because stance time decreases.

Question 4

3 factors determining gait in quadrupeds?

Answer 4

Duty factor

Phase

Symmetry

Question 5

Phase?

Answer 5

The lag between the ‘foot on’ event of the fore- and hindfoot on the same side of the body, as a percentage of the stride

Phase = 50% Diagonal pairs in unison

Phase = 0% Lateral pairs in unison

Question 6

Typical characteristics of fast speed gaits?

Answer 6

Canter, gallop, bound
• Low duty factor (short stance time)
• Usually an aerial phase (a period where all feet are off the ground.
• Asymmetrical gait – hindfeet pair work independently of forefeet.
• Pairs may be in unison, or have leading limb.

Question 7

Direction of force and how to measure it?

Answer 7

Vertical, media lateral and horizontal

Force or weight (newtons)= mass (kg) x gravity acceleration(m/s2)

Question 8

What is ground reaction force?

Answer 8

For every action, there is an opposite and equal reaction – Newton’s third law

Peak GRF increases with speed because stance time is shorter.

All vertical forces must sum to body weight

Question 9

What is centre of mass is quadrupeds?

Answer 9

Weight shared between the fore- and hind- quarters.

Is this evenly shared? Usually not…

60% weight is usually taken by the forelimbs, 40% by the hind.

Primates buck this trend, take more weight on their hindquarters

Question 10

Calculation to compare locomotion in diff animals?

Answer 10

Froude number (Fr)=
Speed(squared)/gravity acceleration x leg length

At similar Froude, animals should have similar kinematics and kinetics

Froude number works fairly well for many animals!

Switch walk-run at Fr~0.4-0.6

Quadrupeds switch trot-canter at Fr~2-3
Why not at Fr 1 for walk-run? Why Fr 2-3 trot-canter?

Hypothesis 1: Mechanical stresses get too high near extreme Frs; animals switch gait to drop to lower stress
Hypothesis 2: Energetic costs of locomotion: is more optimal to change gait at an intermediate speed (costs less)

Question 11

Difference in animal shapes depending on size?

Answer 11

Smaller animals have more crouched postures; larger animals are more upright

Question 12

Moment calculation?

Answer 12

Moment = force * moment arm

a moment is the turning effect produced by a force. It is often synonymous with torque, which can be though of as the rotational analog to linear force (turning force), and is calculated by multiplying the perpendicular force by the distance from the pivot (or axis of rotation).

Question 13

Effective mechanical advantage (EMA)??

Answer 13

R = GRF moment arm
r = muscle moment arm

EMA = r/R

r/R happens to = 𝐦𝐮𝐬𝐜𝐥𝐞 𝐟𝐨𝐫𝐜𝐞/𝐆𝐑𝐅

So, animals with higher EMA need to produce less muscle force

EMA increases with body size.

Larger animals produce less muscle force to support their skeletons

However limit: Large animals>300kg produce relatively high muscle forces to resist gravity there the largest animals are not the fastest. Related to metabolic cost and peak skeletal stress.