Locomotion- Walking and Running LECTURE 6

Features of walking

1. No aerial phase

2. 1 or 2 feet on the ground

3. slow

Features of Running

1. Aerial phase

2. 0 to 1 foot on the ground

3. Fast

IN both→ the energy

• Move up and down

• accelerates and decesrates

  → Kinetic and potential energy oscillate in a regular way

Potential vs Kinetic energy in walking

Out of phase

• Kinetic highest when Potential is the lowest

→ Model: inverted pendulum

Potential vs Kinetic energy in running

In phase

• Kinetic highest when potential the highest

  • .eg the highest when in the air

→ Not like the pendulum

• decelerates at the lowest postion→ all energy into the ground

  → how get this back?→ Elastic energy stores it:

  • Model: bouncing ball

  • elastic energy is re-coverted to kinetic energy

Walking speed limit

Only feasible whilse body weight> centripetal force

mg> m v²/l

Around 3m/s

How to racewalkers achieve higher walking speeds?

• sticking the pelvis out

• increasing he radius of the arc l

  → higher speeds are possible

Types of gaits in quadrupeds

1. Walking

2. Running

3. Gallop→ 2 forlimbs move in phase, followed by two hind limbs

Advantage of using a gallop?

• Larger stride lengths

How do cheetahs increase their stride length even more?

• Elastic flexion and extension of the spinal column

• Also have two areial phases

Why can’t horses do this?

• Must have a stiff back

• needed for backbone support

At what speeds do animals change gaits?

• Upper limit of walking speed can be generalised to predict running speeds at which animals change gait

Re-written as v²/gl< 1→ Froude Number (Fr)

• Twice the ratio of kinetic to potential energy!

How do gaits differ?

• in the type of exchange between kinetic and potential energy

  9 e.g walking is pendulum but running is a spring)

What does it mean for two movements to have the same Froude number

• Dynamically similar

e.g a small and large pendulum winging through the same angle

Different sized animals can change gaits at the same Froude numbers

• e.g walk-trot transition at Fr=0.5

• trop-gallop transtion at Fr= 2.5