At slower walking speeds, double-limb support times
are greater. Conversely, with increasing walking
speeds, double-limb support time intervals decrease.
Walking becomes running when there is no longer an
interval of time in which both feet are in contact with
the ground.KINEMATICS
- The kinematics (motion) of an individual while walk-
ing or running can be effectively assessed by model-
ing the individual’s body as a multibody system. A
multibody system is composed of links (body seg-
ments) and joints between the links. The kinematics
of the system is completely known when orientation
and position of each of its segments is known. Joint
angles are obtained from the kinematics of both joint
distal and proximal segments. Joint angular velocities
are obtained from the joint angles and refer to the
rapidity of variation of such angles. Joint accelera-
tions are similarly obtained from joint velocities. - Each segment possesses a center of mass(CoM). A
whole body CoM can also be defined as the point at
the center of the body mass distribution. As segments
move, the whole body CoM moves. Its position in
time is important for both balance and energy related
issues (Birrer et al, 2001).
•With quantitative 3D gait analysis, joint angles
throughout the gait cycle are described with respect to
flexion/extension, ab/adduction and internal/external
rotation. CoM position in time is expressed in vertical,
anterior–posterior and mediolateral time histories. - Both joint and CoM kinematics are obtained from the
instantaneous 3D position of markers attached on the
individual’s body segments. - Joint kinematics patterns during running differ some-
what from the patterns during walking. Hip
flexion/extension and ab/adduction ranges are wider in
running (about 60°and 15°, respectively) than in walk-
ing (about 40°and 10°, respectively) (Novacheck, 1998;
Perry, 1992). Hip and knee full extension is reached
only during walking. Maximum knee flexion is higher
in running (about 90°) than walking (about 60°). Ankle
joint angle ranges are greater in running (about 50°)
than in walking (about 30°).- During walking the CoM trajectory reaches its highest
point in stance when its speed is minimum. During
running the CoM trajectory reaches its maximum
height during the double floating phase at which time
its velocity is maximum.
KINETICS- Kinetics is defined as the study of forces and moments
that cause movement. - Ground reaction forces refer to the forces exerted on the
foot during foot contact. They are measured with force
platforms embedded in the ground, over which the indi-
vidual walks or runs. The center of the distribution of
these forces is called center of pressure. Knowing seg-
ment kinematics and ground reaction forces, in addition
to some segment characteristics such as mass and CoM
location, it is possible to estimate joint kinetics (joint
forces andmoments). Joint moments refer to forces
applied at a distance from a joint and are expressed as
either external (due to the ground reaction force, gravity,
and inertia) or internal due to internal structures includ-
ing muscle, ligamentous, and bony structures. Joint
powersindicate the rate of work operated by the joint
muscles, and are obtained by multiplying the joint
moment by the joint angular velocity.
•To measure ground reaction forces and center of pres-
sure trajectory, one force platform per foot contact is
sufficient. To measure joint kinetics, a combination of
measurements synchronously obtained from force
platforms and a motion analysis system is necessary. - The vertical ground reaction force typically demon-
strates an initial peak at the very first contact of the
heel, and then a force absorption and a force genera-
tion phase. During walking, in addition to a peak at
initial contact at the heel, the pattern of the vertical
reaction force shows two maxima—one during the
force absorption phase and another during the force
generation phase. During running, a single maximum
is present which divides absorption from generation.
In running, maximum and minimum values are
dependent on the speed of the runner. The amplitude
of the pattern during running can be threefold the
amplitude during walking (Novacheck, 1998). - Sagittal ankle joint moment (flexion/extension
moment) patterns in running and walking are similar. In
running the joint moment activity is faster (shorter
stance phase) and more intense (greater maximum
amplitude). Knee sagittal moment in running demon-
strates higher amplitude after initial contact than during
walking. Hip sagittal moments patterns are similar
128 SECTION 2 • EVALUATION OF THE INJURED ATHLETE
TABLE 21-1 Typical Values of Some Temporal and Spatial
Walking Gait Variables
TEMPORAL/SPATIAL VARIABLE AVERAGE VALUE
Velocity (m/min) ~80
Cadence (steps/min) 113
Stride length (m) 1.41
Stance (percent of gait cycle) ~60
Swing (percent of gait cycle) ~40
Double support (percent per leg per gait cycle) ~10