Locomotion Flashcards
What is gait
Movements that produces locomotion for humans:
- walking,
– running,
– swimming,
– cycling,
Characteristics of gait:
- energy-economical, particularly walking
– Robust systems, flexibility to cope with different speeds,
terrains, injuries etc.
– sophisticated control mechanisms (bipedal gait inherently
unstable)
Stride:
a complete gait cycle, measured from one heel strike to next heel strike of the same foot
Step (=pace)
interval from heel strike of one foot to
subsequent heel strike of the other foot
how many steps equal 1 stride?
1 stride = 2 steps
The terms “stride” and “step/pace” may refer to any of
the following properties of the relevant movement:
- time duration
- distance covered
- number
Cadence
steps taken per minute
Cycle time (=stride time)
stride duration in seconds
For young adult males:
Cadence = 90-135
Cycle Time (s) = 0.9-1.3
Stride length (m) = 1.2-1.8
Speed (m s^ -1) = 1.1-1.8
Note:
* Natural walking speeds, and stride lengths, are close to the optimum for energy efficiency
* Walking speeds higher in towns than in rural environments
The principal forces are:
– body weight (BW)
– ground reaction force (GRF)
– muscle force (MF)
Which forces are external forces? What does this mean regarding the movement of the centre of mass?
BW and GRF are external forces; so the movement of the centre of mass (CoM) can be predicted from them alone.
MF must be examined however if we wish to consider either of the following:
– movements of individual limbs or body segments,
– why GRF changes in magnitude and direction during the gait cycle.
Vitally important point:
Muscle forces can only influence
the movement of the body as a
whole indirectly, by their effects
on the GRF
The gait mechanism: an overview
- Walking is a precise, co-ordinated set of movements involving multiple joints and body segments
- It comprises a pattern of alternating action of the two lower limbs
- Pendulum-like movements of the limbs give rise to two distinct phases: swing and support (or stance)
- In walking, but not running, the support phases of the two legs overlap
Walking as a controlled fall: forces involved
- When starting to move, we lean forward (MF)
- As the body starts to fall (BW), a leg is extended forwards and halts the fall (MF; GRF)
- At the same time, the other leg “kicks off, upwards and forwards” (MF; GRF) in order to keep the body moving forwards.
- This forward momentum carries the body forward into the next forward fall, i.e. the start of the next step
Body weight
- Always acts vertically downwards from the C of M
- If its line of action does not pass through a joint, it will produce a torque about that joint
- The torque will cause rotation at the joint unless it is opposed by another force (e.g. muscle, or ligament)
- BW contributes to GRF
Ground reaction force: Action Force
- Push exerted on ground by foot
Ground reaction force: Reaction Force
- Push exerted by ground on foot, as a consequence of Newton’s
3rd Law (Equal magnitude, opposite direction, same point of application
as action force) - If line of the reaction force does not pass through a joint, it will
produce a torque about that joint
In gait, as in all human movement, muscle activation generates:
internal joint moments (torques) that:
– Contribute to ground reaction force
– Ensure balance
– Increase energy economy
– Allow flexible gait patterns
– Slow down and/or prevent limb movements
Much muscle activity during gait is _________ or __________, rather than __________
Much muscle activity during gait is eccentric or isometric, rather than concentric
It’s obvious, from the previous slide, that GRF varies, through the stance phase, in terms of all three aspects namely:
– Magnitude
– Direction
– Point of action (= centre of pressure)
* We can understand GRF more readily if we resolve it into components that act vertically and horizontally
Both the horizontal and vertical components of the GRF vary during the _______ phase
stance
The direction of the horizontal component (i.e. forwards or backwards) tells us:
whether the body is accelerating or decelerating in its forwards movement at that moment of time
The magnitude of the vertical component (and specifically whether it is greater or less than body weight) tells us:
what is happening to the vertical
movement of the body
GRF during the contact phase
- Initially GRF acts diagonally backwards and upwards, from the heel. The horizontal component acts backwards, and the vertical component is greater than that of body weight. GRF at this moment therefore:
– stops the “controlled downwards fall” of the body
– exerts a braking, or slowing, effect on forward movement - During the middle of the stance phase the GRF:
– remains > body weight and therefore the CoM is lifted up slightly in
midstance.
– point of action moves forward from the heel.
– line of action becomes more nearly vertical and therefore the braking/slowing effect disappears - After the midpoint of the stance phase the vertical component of GRF
falls (< body weight) as the leg passes the vertical position and the CoM moves downwards. - At the end of the stance phase, the GRF increases in magnitude again,
acting forwards and upwards. This gives the necessary propulsive force to stop downwards movement of the CoM, and to to keep the body moving forwards.
