Biomedical Engineering Reference
In-Depth Information
FIGURE 10-11
Illustration of the gait
cycle. (a) Definition
of gait cycle stages.
(b) Normalised load
response on the
active leg. [Adapted
from (Perry 1992;
Dehghani 2010).]
Initial swing:
The limb is advanced by hip flexion, with increased knee flexion and a slight
lifting of the foot. The objective of this phase is to provide foot clearance to avoid tripping
or stubbing. The gracilis and sartorius muscles control the three-dimensional (3-D) path of
the limb and induce knee flexion as they act at the hip. The popliteus and the short head of
the biceps provide direct knee flexion up to 40
◦
, and the pretibila muscles perform toe lift.
Mid-swing:
Knee flexion reaches 60
◦
at an angular velocity of about 350
◦
/s. Hip activity
is reduced with the advancement of the limb being a continuation of the action of the
initial swing. The popliteus and the short head of the biceps continue to provide direct
knee flexion, and at the ankle there is continuing dorsi-flexion.
Terminal swing:
This is the final preparation in the transition from swing to stance.
Muscle activity prepares the advancing limb for load acceptance. The hamstring muscles
start to decelerate. Some muscles also produce a slight hyperextension of the knee, whereas
others maintain a slight degree of flexion with the final knee angle being about 5
◦
of flexion
in preparation for initial contact.
Initial contact and loading response:
At initial contact, the knee flexes from 5
◦
to a
maximum of 18
◦
to absorb shock. The quadriceps functions eccentrically to restrain the
degree of flexion to allow for stable weight bearing.
10.6
KINEMATICS OF LIMB MOVEMENT
10.6.1 Center of Mass and Moment of Inertia of a Limb Segment
Each segment of a limb can be described by its total mass, the center of mass, and the
moment of inertia around that point. The mass can be determined by dividing the segment
