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D. I. Stoia et al.
The elements of the inertia tensor (4) were computed using the radius of gyration
in concordance to the axis of rotation. The gyration radii were computed using the
Dempster’s percentages for every axis (frontal, sagittal and longitudinal) applied to
the total length of each segment [13].
The mass of each segment and its center were determined using the same approach
(Dempster), as percentages of body mass and segment length. The length of each
segment was determined form measurements, using the joint coordinates.
The position vectors were determined using the joint and CoM coordinates, while
the linear velocity was computed as numerical derivative of those.
The angular displacements were provided by the system, while the angular
velocity was computed as numerical derivative.
3 Results and Discussions
In Fig. 2, one kinematic (flexion-extension angle) and two kinetic parameters (spin
and orbital angular momentum) of shank are presented. The representations were
drawn in a gait cycle by normalizing the time series. In this way, representation of
one parameter measured or computed for three or more velocities is possible without
showing large frequency differences.
In every graphic (Fig. 2a–d), the series vel-1 represents the lowest velocity of
movement, the vel-3 represents the largest velocity and vel-2 the middle velocity.
As expected, larger amplitudes in both kinematic and kinetic parameters are
recorded when the velocity of movement increases. The orbital angular momentum,
computed in respect to the body center of mass, is four times larger than the spin
angular momentum due to the segmental mass position according to the two rotation axes. Lower values of spin angular momentum are associated with low angular
velocity of the segment and vice versa. The orbital component shows a dramatic
decreasing when the limb passes through the midstance position.
By adding the series of orbital component by the series of spin component, the
variation of total (segmental) angular momentum was determined. It represents the
kinetic characteristic of a body segment that is varying along the gait cycle due to
the muscular actions. It displays the highest peaks during the segment acceleration
periods.
In the same manner, the thigh parameters are presented in the Fig. 3. Larger
amplitudes are also associated with larger velocities. Due to the proximity of this
segment to the B CoM , the orbital angular momentum is less large comparing to shank
case. Also, less evident tendency is recorded. The spin component is as for the shank,
proportional to the angular velocity. The total (segmental) angular momentum is
highly influenced by the orbital component, and therefore, their variations look very
similar (Fig. 3c, d).
D. I. Stoia et al.
The elements of the inertia tensor (4) were computed using the radius of gyration
in concordance to the axis of rotation. The gyration radii were computed using the
Dempster’s percentages for every axis (frontal, sagittal and longitudinal) applied to
the total length of each segment [13].
The mass of each segment and its center were determined using the same approach
(Dempster), as percentages of body mass and segment length. The length of each
segment was determined form measurements, using the joint coordinates.
The position vectors were determined using the joint and CoM coordinates, while
the linear velocity was computed as numerical derivative of those.
The angular displacements were provided by the system, while the angular
velocity was computed as numerical derivative.
3 Results and Discussions
In Fig. 2, one kinematic (flexion-extension angle) and two kinetic parameters (spin
and orbital angular momentum) of shank are presented. The representations were
drawn in a gait cycle by normalizing the time series. In this way, representation of
one parameter measured or computed for three or more velocities is possible without
showing large frequency differences.
In every graphic (Fig. 2a–d), the series vel-1 represents the lowest velocity of
movement, the vel-3 represents the largest velocity and vel-2 the middle velocity.
As expected, larger amplitudes in both kinematic and kinetic parameters are
recorded when the velocity of movement increases. The orbital angular momentum,
computed in respect to the body center of mass, is four times larger than the spin
angular momentum due to the segmental mass position according to the two rotation axes. Lower values of spin angular momentum are associated with low angular
velocity of the segment and vice versa. The orbital component shows a dramatic
decreasing when the limb passes through the midstance position.
By adding the series of orbital component by the series of spin component, the
variation of total (segmental) angular momentum was determined. It represents the
kinetic characteristic of a body segment that is varying along the gait cycle due to
the muscular actions. It displays the highest peaks during the segment acceleration
periods.
In the same manner, the thigh parameters are presented in the Fig. 3. Larger
amplitudes are also associated with larger velocities. Due to the proximity of this
segment to the B CoM , the orbital angular momentum is less large comparing to shank
case. Also, less evident tendency is recorded. The spin component is as for the shank,
proportional to the angular velocity. The total (segmental) angular momentum is
highly influenced by the orbital component, and therefore, their variations look very
similar (Fig. 3c, d).