Biomedical Engineering Reference
In-Depth Information
Knee Flexion (Males)
Knee Extension (Males)
120
250
100
200
80
150
60
100
40
20
50
0
0
100
100
50
90
100
50
80
80
70
60
200
150
60
200
150
50
40
40
Angle (deg)
20
250
Velocity (deg/s)
30
Angle (deg)
250
Velocity (deg/s)
20
0
300
10
300
Knee Flexion (Females)
Knee Extension (Females)
80
150
120
60
90
40
60
20
30
0
0
100
100
50
100
100
50
80
80
60
200
150
60
150
40
40
250
200
20
250
20
Angle (deg)
Velocity (deg/s)
Angle (deg)
Velocity (deg/s)
0
300
0
300
FIGURE 6.7
Mean 3D knee concentric strength surfaces for men (N
24) and women (N
21).
5
5
(
Khalaf and Parnianpour, 2001; Khalaf et al., 1997, 2000, 2001
). While both of
these approaches provide reasonable estimates of the peak strength surfaces,
they do not readily allow for significant interactions between joint angle and con-
traction velocity which are observed in experimental data (
Frey-Law et al.,
2012b
), and can result in non-physiologic torque predictions (i.e., values “crossing
zero”) when extrapolated to joint angles beyond those assessed for developing the
strength models.
We have found greater flexibility using logistic equations to best fit the
nonlinear experimental data. This approach maximizes the heuristic, nonlinear
representation of strength surfaces using only 7 to 8 parameters, thus is also
reasonably parsimonious. We chose to model the eccentric relationship as it is
challenging to train individuals to exert maximum eccentric strength and can
lead to DOMS or more severe muscle injury. Based on numerous previous
studies, we modeled peak eccentric strength as 120% of peak isometric
strength independent of eccentric contraction velocity. Using this assumption,
examples of the resulting 3D surfaces that model both concentric and eccentric
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