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Summary BBS2052 - All cases
All cases, including notes from the lectures
[Meer zien]Voorbeeld 4 van de 69 pagina's
Voorbeeld 4 van de 69 pagina's
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Voorbeeld van de inhoud
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The Gait Cycle
Locomotion is the controlled act of moving the body from one place to another, and is guided by the
organism, but not powered by it. When locomotion is self-propelled, three components of control
can be distinguished:
1. Control of the limb and body movements that generate propulsive force
2. Control of direction where you are heading, including control of speed
3. Control of posture and orientation.
A bipedal gait cycle is the sequence of events that are performed during locomotion and depends on
the propulsion of the centre of gravity in the direction of motion. Each gait cycle can be subdivided
into two large stages, namely the Stance Phase, during which the foot touches the ground until it
breaks this contact, and the Swing Phase, during which the foot is not in contact with the ground
until it makes contact again.
● The Stance phase is also known as the Power Stroke or Propulsive Phase: the phase during
which the propulsive force if produced that propels the organism ‘forward’.
● The Swing Phase is also known as the Return Stroke: a phase that returns the limb to a position
suitable for beginning another power-stroke.
Both phases can be further divided into smaller sequential steps, that are constantly repeated during
movement:
At the beginning of the Stance Phase, the leg starts supporting the weight of the body, but a nihil
amount of propulsive force is produced, this primarily occurs during the later phase, in which the
foot pushes against the ground.
A. During the Initial Contact Phase, also called the Heel-Strike, the heel encounters the ground. In
this phase, both feet touch the ground.
B. In the Loading Response Phase, or Foot-Flat Phase, the foot sits flat on the ground and the
weight is transferred onto the foot in question, which is important for weight-bearing,
shock-absorption and forward progression.
C. The Midstance involves the alignment and balancing of body weight on said foot. During this
phase the body begins to move from force absorption at impact, to force propulsion forward.
D. In the Terminal Stance the heel rises from the ground, however, the toes are still in contact
with the ground. During this Heel-Off phase, the bodyweight is divided over the metatarsal
heads.
E. During the Toe-Off Phase, also known as Pre-Swing, the toes also swing into the air and the
contact with the ground is lost.
During the Swing Phase, the foot is transferred from one point on the ground to another, to repeat
the Stance Phase which produces the propulsive force. An entire cycle of stance and swing is called a
stride.
F. The Initial Swing + Mid Swing
G. During the Terminal Swing
1
,Walking:
● Speed is 0.5-2 m/s
● Step length is 0.5-1 meter
● 110-120 step/min
● The Stance phase is 60% of the gait cycle, and the Swing phase takes the remaining 40%.
● One step is created between the time difference of a Left Heel-Strike and a Right Heel-Strike,
whereas an entire stride is composed out of two steps.
○ If one step does not take 50% of a stride (Symmetrical walking pattern), there is a
sine of injury or neurological disorder
● The legs are always in antiphase with one another: one leg is in the stance whilst the other is
in the swing and vice-versa.
● The double support phase refers to the moment when both legs touch the ground →
contains the overlap between the slightly longer 60% Stance phase in comparison to the
swing phase.
However, all these steps compromise only a single step during the locomotive movement, during the
primary period this will form a Rhythmic Stage, during which the velocity of the movement is
constant. To reach this constant velocity human and animal locomotion first starts off with the
Development Stage, in which the resting human starts walking and increasing speed until it starts
reaching its equal velocity, the aforementioned Rhythmic Phase, but eventually also comprises the
Decay Stage, in which the organism starts slowing down and will go back into a rest mode.
During jogging and running
The stance phases form a less integral
part of the stride period, hence at a
certain speed, the feet will never touch
the ground at the same point in time
anymore: the flight periods. Walking
and jogging are normally Plantegrade
forms of locomotion, in which the
entire foot sole (calcaneus up until
distal phalanges and digits) will touch
the ground during the stance phases,
whereas Sprinting is Digitigrade, during
2
,which only the Digits touch the ground to propel the body forwards.
Movement/ propulsive force is created through the Ground Reaction Force
The propulsive force is provided by the reaction
force from the ground (Ground reaction Force):
● Ground Reaction Force starts at the Initial
Contact of the gait cycle. At this point, the
bodyweight is rapidly transferred onto one leg,
where the foot and leg function as a shock
absorber. The GRF stops at the end of the
stance phase, as a response to the leg pushing
against the ground.
From the Ground Reaction Forces, an inverted
pendulum is created, which is composed of a
vertical (reaction of body weight load to the ground)
and a horizontal force (reaction of foot pushing
against the ground, which is the case during the
deceleration process in the early phase of the
stance, and the acceleration during the later stance
phases). When standing still, there is no horizontal
force, creating the relative minimal dip between the
two maximal peaks during the stance phase. These horizontal forces can only be produced due to
friction between the foot and the ground, as such muscular activity is needed to generate the
backward push against the ground.
● The Gastrocnemius; the knee extension muscle, and the ankle plantar flexors create the main
bulk of the horizontal propulsive force. The medial gastrocnemius is nearly inactive in the early
stance but becomes much more active during the midstance and peaks shortly before toe-off.
When walking uphill the knee and hip extensors become more prominent as well. The
dorsiflexion of the ankle are mainly active during the swing phase, to prevent the foot from
scraping over the ground, but are relatively inactive during the stance phase.
The magnitude of the GRF under each foot depends on whether the limb is in Double Support, Single
Support, or Swing Phase. During the double support, the vertical GRF rapidly increases in magnitude
as the external load is transferred from one leg to another. During the first phase of single support,
upward movement coincides with a GRF bigger than the body weight, reaching its highest elevation
at approximately 30% of the gait cycle.
● The vertical deceleration upwards occurs, being caused by the GRF that is smaller than the
bodyweight and giving rise to the relative minimum value in between the peaks, reflecting a
downward acceleration that is now decreasing.
● The second rise in the vertical GRF above the bodyweight, later in the single support,
coincides with a second upward acceleration that slows and controls the downward
movement of the body.
● Finally, during the second double support, the body weight is transferred upon the second
leg, and hence the vertical GRF decrease, creating an Inverted Pendulum.
3
, The Gait cycle works with two types of Energy
During the gait cycle/movement the smooth and continuous passage and alteration of the Common
Centre of Mass are essential for walking. During the early limb forward deceleration, in which the
person starts standing on a single limb, the Centre of Mass becomes elevated and reaches its highest
point when fully standing. When the centre of mass reaches its greatest height, about 30% of the
gait cycle, the Potential Energy is maximal, whereas the Kinetic Energy is on its lowest. During
double limb support periods, the opposite is true, the Centre of Mass reaches its lowest point, and
hence the Potential Energy, which is purely based on the distance between the point of gravity and
floor, is minimal, however, the kinetic energy is maximal. During both periods of time, the total
energy is presumably equal and simply differ between kinetic and potential counterparts.
The major subdivisions of the gait cycle describe the transitions that must occur while the body’s
centre of mass passes over the oscillating limbs.
Muscles involved in the Gait Cycle (in the pattern)
1. During the Heel-Strike Phase, the ankle becomes slightly more plantar-flexed, due to the
eccentric contraction of the Tibialis Anterior, whereas the knee extends by the contraction of
the quadriceps, and hip flexion is caused by contraction of the Rectus Femoris.
2. During the Loading Response, the shock
is absorbed by the foot rolling into
pronation. The hip slowly starts to
extend, caused by contraction of the
Adductor Magnus and Gluteus
Maximus, whilst the knee flexes and the
ankle further plantar flexes.
3. In the midstance, the flexed hip further
extends due to the Rectus Femoris. The
knee reaches maximal flexion and starts
to extend, at the same as the ankle
4
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