Figure 1.
Illustration of method used to estimate Subject-Specific Tendon-Aponeurosis.
(A) Geometric model of the muscle-tendon-aponeurosis complex that includes fascicle, tendon, and aponeurosis adapted from Fukashiro et al. [23]. The aponeurosis length is: . Hill-type muscle model with the tendon and the aponeurosis in series (B) and a resulting Tendon-Aponeurosis element representing the tendon and aponeurosis in series (C).
Figure 2.
Illustration of method used to estimate the fascicle length and pennation angle.
The proximal and distal ends of the superficial aponeurosis, deep aponeurosis, and muscle fascicle were tracked automatically at each frame. The missing part was estimated by linear interpolation.
Figure 3.
Estimation of Tendon-Aponeurosis force-strain relationship from tendon and aponeurosis individual force-strain relationship.
At the same force level, the tendon and aponeurosis strain were estimated and combined with an experimentally-derived ratio to compute the Tendon-Aponeurosis strain (see eq. 5 in text).
Figure 4.
Description of EMG-driven model (A) Calibration and (B) Prediction process of the EMG-driven model.
(1) represents the Anatomical Model used to estimate muscle-tendon lengths and moment arms, (2) an EMG-to-Activation Model to represent muscle activation dynamics, (3) a Hill-type Model to characterize muscle-tendon contraction dynamics and estimate the forces in the muscle-tendon complex, (4) a calibration process to tune model parameters based on ankle net joint moment computed by Inverse Dynamic, and (5) a prediction process to predict joint moment by using adjusted model parameters.
Table 1.
Summary of muscle-tendon geometric parameters estimated by US in rest position or from Maganaris et al. [6] and used to estimate the muscle specific tendon-aponeurosis force-strain relationships.
Figure 5.
Example of input and output data of an EMG-driven model.
Example of input data (Normalized EMG, muscle-tendon lengths and moment-arms) and output data (muscle forces and net ankle joint moment) for one subject during the contact phase of a hopping trial. The output data were obtained for both SEE definitions: the SS T-A and the generic.
Figure 6.
Force-strain relationships estimated by ultrasonography and used in Hill-type muscle model.
Group averaged subject-specific tendon and aponeurosis force-strain relationships of the GM and subject-specific Tendon-Aponeurosis force-strain relationships for each muscle. The generic tendon force-strain relationship described by Zajac [5] and used for the generic calibration and prediction processes is also presented for comparison.
Figure 7.
Comparison of maximal muscle force: SS T-A vs. Generic.
Mean maximal force estimated by the EMG-driven model according to the condition, SS T-A and Generic for the GL (A), GM (B), SOL (C) and the Triceps Surae group (i.e., sum of GL, GM, and Sol muscles) (D). * indicates a significant difference between the conditions (SS T-A vs. Generic).
Table 2.
Summary of the behaviour of the muscle fibre and the tendon-aponeurosis unit in terms of variation of length and velocity.
Figure 8.
Normalized fibre length and velocity with corresponding muscle forces for the soleus.
Trajectory of normalized fibre length and velocity for one subject corresponding to the soleus. The colours of the curve represent the different part of the force-length and force-velocity relationships cover by the normalized fibre length and velocity according to the SEE definition. The figure at the bottom represents the muscle forces according to the SEE definition.
Figure 9.
Decoupling behaviour between muscle fibre and muscle-tendon unit.
Comparison of the velocity of the muscle fibre, the tendon-aponeurosis unit and the muscle-tendon unit from one subject on running tasks for the (A) generic and (B) SS T-A conditions and from (C) a previous experimentation with the muscle fibre velocity measured using ultrasonography. Note that the SS T-A condition leads to physiologically sound behaviour of the muscle fibre while the generic condition simply shared the muscle-tendon stretch over both the fibre and the SEE complex. Reprinted with permission.