Q2. What is the main characteristic of skeletal muscle?
The variation in maximum muscle force with the rate of change of muscle length is a fundamental characteristic of skeletal muscle.
Q3. What was the common torque model developed?
A torque model was developed using a four parameter function to express maximum joint torque at full activation as a function of joint angular velocity.
Q4. What is the effect of the eccentric phase on the tetanic muscle force?
In the concentric phase tetanic muscle force decreases hyperbolically with increasing speed of shortening to approach zero at maximum shortening velocity (Hill, 1938).
Q5. What is the effect of eccentric muscle force on the knee?
In the eccentric phase maximum muscle force increases rapidly to around 1.5 times the isometric value with increasing speed of lengthening and then plateaus for higher velocities (Harry et al., 1990).
Q6. What is the focus of the present paper?
The accuracy of such simulations is dependent upon realistic torques being generated by the muscle representations and this is the focus of the present paper.
Q7. What would be the way to offset the lack of high velocity concentric torque data?
Establishing appropriate lower and upper bounds for ωmax would offset the lack of high velocity concentric torque data to some extent.
Q8. What is the effect of eccentric loading on EMG?
They found that EMG activity was lower under eccentric loading than concentric loading and did not appear to change across eccentric velocities, while EMG increased with increasing concentric velocities.
Q9. What were the free parameters for the torque / angular velocity relationship?
There were only two free parameters as T0 was set equal to the average of the torques corresponding to crank velocities of ± 50os-1 and again Tmax was fixed at 1.5 times the value of T0 .
Q10. What was the simplest hyperbola for the concentric phase?
The hyperbola representing the concentric phase was a rotational equivalent of the classic hyperbola of Hill (1938) and an inverted rectangular hyperbola was used to represent the eccentric phase.
Q11. What is the activation level of Subject 2 at a joint velocity of zero?
Consequently at a joint angular velocity of zero the activation level of Subject 2 was 0.90 compared to a level of 0.78 for Subject 1.
Q12. What was the result of the regressive torque values?
This resulted in a set of 18 “maximal” joint torques and joint angular velocities that were less noisy than the original maximum torque values and were independent of joint angle.
Q13. What is the effect of the seven parameter function on the activation level of Subject 2?
As a consequence the seven parameter function of Subject 1 shows a pronounced plateau for low concentric velocities whereas that of Subject 2 is closer to a hyperbola with concave curvature for all concentric velocities (Figures 3a, 4a).
Q14. What was the maximum torque at each angular velocity?
In order to estimate the likely error in each parameter the torque deviations from the seven parameter fit were calculated by subtracting the fitted torque value from the maximal torque at each angular velocity.
Q15. What is the way to generate a relative activation profile?
Thus the seven parameter function may be used for both maximal and submaximal activities so long as there is a basis for generating an appropriate relative activation profile.
Q16. What were the deviations used to generate the torque data?
These deviations were then added to the fitted torque values at the corresponding angular velocities to generate eight new maximal torque / angular velocity data sets which were used to produce eight new seven parameter fits.
Q17. What is the difference between the three data points corresponding to high concentric velocities?
The three data points corresponding to high concentric velocities in Figure 3a suggest that a higher value for ωmax might be more appropriate and that setting a higher lower bound in the optimisation procedure might reduce this problem.
Q18. What is the relationship between the eccentric and the concentric functions?
In the eccentric phase the relationship between T and ω was given by the rectangular hyperbola:max eT )( ET + ω−ω = (if ω ≤ 0) (3)where: )( . kT)TT(cmaxcmax00max e ω+ωωω− =ω , e0max )TT(E ω−−= and k = ratio of the slopes of theeccentric and concentric functions at ω =
Q19. What is the maximum activation level of a squat jump?
For movements which require primarily concentric muscle action such as squat jumps (van Soest et al., 1993) there will be maximal activation only for higher concentric velocities and the Hill relationship may be adequate providing appropriate muscle parameters are used.