Gait

Question 1

Describe the kinetics and kinematics of fore and hind limbs during the stride cycle.

Answer 1

Forces (kinetics) occurring during locomotion include-
- Ground reaction force (GRF)
- Muscle forces
- Joint contact forces

Ground reaction forces - support animal bodyweight and propulses the force in the direction of movement

Peak vertical GRF increases with speed and vice versa
Forelimb supports a greater load in comparison to the hindlimb, therefore one more susceptible to damage

Forelimb peak vertical forces decrease uphill whereas hindlimb peak vertical forces increase uphill
- When the animal is inclined, the weight distribuition is inverted, therefore hindlimbs bear the majority of the weight (same for the reverse)

Lack of symmetry between left and right limbs is a typical indicator of lameness
The amount of unloading in the lame limb will increase with severity of lameness - GRF increases on the compensating leg(s) when the animal is lame

Question 2

Compare the basic differences between gaits based on (i) footfall patterns and (ii) biomechanical principles.

Answer 2

• Stride = the whole cycle of an animals footfall pattern (1 full cycle) - contains 2 phases-
• Stance = part of the stride when a single foot is on the ground
• Swing = part of the stride when foot is swinging through the air

Stance phase:
Limb experiences high GRFs
Muscles need to-
- Withstand GRF
- Stabilise joints
- Resist over-extension of distal joints
- Provide propulsion (hindlimb)
High speed locomotion may cause the joint (elastic structures) to hyperextend - (eg: when a horse is running, their fetlock joint is almost touching the ground when the horse’s pressure is placed onto the leg)

Swing phase:
Demands on the musculoskeletal system during swing phase is lower than the stance phase
No GRFs
Muscles need to-
- Protract the limb
- Clear the foot away from the ground
- Prepare limb position for stance

Relationship between kinetics and kinematics at the fetlock:
Linear relationship between the force experience by the limb and the and the angle of the joint - behaves like a spring (greater force applied = greater hyperextension)
Implications for-
- Amount of energy stored in tendons
- Likelihood of injury

Defining gaits:
Based on footfall patterns
Based on biomechanical principles - either inverted pendulum or spring biomechanics

Inverted pendulum:
- PE = potential energy / KE = kinetic energy
- Energy efficient - energy is transferred between forms, hence is conserved (70%)
- A pendulum works by converting one form of energy into another
- COM drops when taking the step and increases when pushing off
- Energy can be produced without muscle contraction

Trotting
- Uses storage and release of elastic energy for energy saving
- Moving quickly allows the long tendons to store energy which can be used to increase efficiency

Galloping spreads the footfall of the animal as far as possible - the more contact points and the more spread out they are allows for more fluid movement at high speed

Question 3

Explain why animals might choose to use particular gaits.

Answer 3

Locomotion - method of travel or movement:
Gaits might include-
- Terrestrial-
—Walking
—Running - includes trotting and pacing (quadrupeds)
—Skipping - includes cantering and galloping (quadrupeds)
Jumping
Flying
Swimming
Climbing
These specific ways of travelling can be termed ‘modes’ of locomotion
Gaits = the specific ways of travelling and mechanics involved in terrestrial locomotion forms

Why choose a particular gait?
- Energetic efficiency
Minimise GRFs-
- Reduce fatigue (eg: from muscle damping)
- Reduce impact on musculoskeletal tissues

When gait goes weird - lameness:
How can I tell an animal is lame?
- Disruption to normal gait (eg: pacing instead of walking)
- Disruption to normal rhythm of gait
- Shortened steps/swing phase
- Non-weight bearing
- Head motions (forelimb) - moving the head upwards and backwards shifts the body weight distribution backwards meaning less weight is being beared on the painful forelimb
- Hip motions (hindlimb) - symmetry - hips rise and fall the same amount on each side - increased movement on one side of the hip unloads the body weight off the painful hindlimb

Gait analysis:
A way to analyse an animal’s gait for abnormalities and to track improvement/deterioration
Quantitative rather than subjective