Muscle behaviors when changing the dimensions
Posted: Fri May 09, 2014 2:57 am
Hi everybody,
I have a basic question, I have to success in explaining the problem. When trying to run two similar simulations with different muscle sizes, each is made by one segment that rotate about z axis and two muscles (agonist and antagonist muscles), in both the tendon slack to optimal fiber length ratio =3. In the first simulation, the muscle-tendon length is 3cm (Lm_opt=3*1/4cm and Lt_slack=3*3/4cm). In the second simulation, the muscle-tendon length is 35 cm (Lm_opt=35*1/4cm and Lt_slack=35*3/4cm). In both simulations, the initial muscle length = optimal fiber length and muscle-tendon length Lmt=Lm_opt+Lt_slack. After 0.5 sec, I apply an external force to angularly shift the segment.
What I obtain is similar muscle behaviors in terms of force development before applying the external force, and completely two different muscle behaviors at and after applying the external force. In the first case, the muscle generating force opposite to the external force tries to compensate it by slowing increasing the force and therefore the moment applied on the segment, instead the other muscle decreases everything. This is very fine....in the second case, the muscle forces rapidly vary and the outcome is that the segment rotates.
I don't see why the muscle behaviors are different in the two case just because I increases the muscle tendon length from 3 to 35 cm keeping the tendon slack to fiber length ratio the same as well as the other muscle parameters (i.g. isometric force, pennation angle, max contraction velocity)
What is the reason?
Thanks
Ali
I have a basic question, I have to success in explaining the problem. When trying to run two similar simulations with different muscle sizes, each is made by one segment that rotate about z axis and two muscles (agonist and antagonist muscles), in both the tendon slack to optimal fiber length ratio =3. In the first simulation, the muscle-tendon length is 3cm (Lm_opt=3*1/4cm and Lt_slack=3*3/4cm). In the second simulation, the muscle-tendon length is 35 cm (Lm_opt=35*1/4cm and Lt_slack=35*3/4cm). In both simulations, the initial muscle length = optimal fiber length and muscle-tendon length Lmt=Lm_opt+Lt_slack. After 0.5 sec, I apply an external force to angularly shift the segment.
What I obtain is similar muscle behaviors in terms of force development before applying the external force, and completely two different muscle behaviors at and after applying the external force. In the first case, the muscle generating force opposite to the external force tries to compensate it by slowing increasing the force and therefore the moment applied on the segment, instead the other muscle decreases everything. This is very fine....in the second case, the muscle forces rapidly vary and the outcome is that the segment rotates.
I don't see why the muscle behaviors are different in the two case just because I increases the muscle tendon length from 3 to 35 cm keeping the tendon slack to fiber length ratio the same as well as the other muscle parameters (i.g. isometric force, pennation angle, max contraction velocity)
What is the reason?
Thanks
Ali