Biomedical Engineering Reference
In-Depth Information
Left Foot
60%
40%
40%
60%
Right Foot
Swing
Stance
Fig. 1
Gait cycle division according to [
47
]
1.1
Characterization of Plantar Forces
Since gait is a common movement for all humans, gait analysis is an area of study
transversal to several fields of study in the area of Biomechanics. Gait kinetics [
42
]
and kinematics [
41
] have been extensively studied [
37
,
46
]. Physical quantities like,
acceleration, velocity, cadence, gait period, step and stride length, single stance and
swing phase durations can be experimentally measured for a kinematical description
of the movement. Others, like flexion and dorsiflexion angles, segment angular
velocity, plantar pressures and reaction forces provide a more specific characteri-
zation related to the way the subject performs the movement. Therefore, temporal
and spatial knowledge are two combined aspects of plantar forces characterization
describing a certain movement.
A detailed description of the gait cycle can be found in both Winter et al. and
Vaughan et al., who are cited extensively and their division of the gait cycle has
been widely adopted as a reference. Both consider gait cycle divided in two phases:
stance and swing phases as illustrated in Fig.
1
. The differences between these two
authors are quite small, since Winter considers a division of 60/40 [
47
] and Vaughan
establishes a 62/38 gait phases division [
46
].
Considering standing position, for a normal foot, forefoot, rear foot (or heel) and
lateral area are those in contact with the ground. Due to inter-subject variability,
one can find a large variety of foot geometries being common in the forefoot to
observe quite different contact areas under the toes. Nevertheless, the intensities of
their pressures are very similar exhibiting peak values corresponding to a vertical
force of 1.1-1.2 times Body Weight (BW).
During gait, the heel is the first body part to support body weight right after
initial contact (IC). This phase occurs during the period of single stance starting
with loading response with a maximum peak force occurring at around 25% of the
gait cycle, at which the whole foot is in contact to the ground (midstance).
In kinematic terms, during initial contact the center of pressure accelerates until
single stance, decreasing afterwards and regaining acceleration after heel rise (HR),
corresponding to the terminal stance phase, which determines the beginning of
the second double support phase. The period elapsed between these instants, i.e.,
between IC and HR, is around 50% of the gait cycle. This acceleration evolution
is related to the magnitude of the horizontal anterior-posterior component of the
ground reaction force (GRF). This description is generally accepted as a typical gait
profile, in spite of substantial differences found between every individual pattern, as
seen in literature.
