Active fibre force in a muscle with no activation
Posted: Wed Mar 02, 2016 11:49 am
Hi all,
I've been running forward dynamic simulations to investigate the action of two muscles acting as synergists but I've come across a problem that makes little sense to me.
I firstly obtain the controls and initial states of one muscle through CMC. I use these results to active one muscle. Then I include a second muscle which I leave inactive but will have identical fibre lengths and velocity as the activated muscle. The passive properties of the second muscle are set to be negligible. Assuming the second muscle is inactive and has negligible passive properties, it should not produce any force or compute to a spanned joint moment.
When I obtain the results of the forward simulations, the activated muscle contributes to the joint moments as predicted. However, for some reason, the second muscle produces active fibre force causing the total joint moment to be overestimated. I double checked the passive fibre force, resultant controls and states files and all show that the second muscle was inactive and had negligible passive force. I also made sure that the fibres were still operating in the F-L force producing regions.
Has anyone come across this situation and found a way to rectify the problem? I've tried a few different combinations and nothing has worked so far.
UPDATE: I noticed the active fibre force in the inactive muscle correlates to normalised fibre velocity. Is this possible?
Thanks in advance!
Adrian
I've been running forward dynamic simulations to investigate the action of two muscles acting as synergists but I've come across a problem that makes little sense to me.
I firstly obtain the controls and initial states of one muscle through CMC. I use these results to active one muscle. Then I include a second muscle which I leave inactive but will have identical fibre lengths and velocity as the activated muscle. The passive properties of the second muscle are set to be negligible. Assuming the second muscle is inactive and has negligible passive properties, it should not produce any force or compute to a spanned joint moment.
When I obtain the results of the forward simulations, the activated muscle contributes to the joint moments as predicted. However, for some reason, the second muscle produces active fibre force causing the total joint moment to be overestimated. I double checked the passive fibre force, resultant controls and states files and all show that the second muscle was inactive and had negligible passive force. I also made sure that the fibres were still operating in the F-L force producing regions.
Has anyone come across this situation and found a way to rectify the problem? I've tried a few different combinations and nothing has worked so far.
UPDATE: I noticed the active fibre force in the inactive muscle correlates to normalised fibre velocity. Is this possible?
Thanks in advance!
Adrian