Hello,
Does anybody know of a way to increase the max isometric force of the muscles without affecting the passive forces values ?
Because when I just increased the isometric value then when I did a muscle analysis I found passive muscle forces impossibly high. I don't know why these passive forces are so high.
The same goes for activation, normally it would range from 0 to 1 however due to the Static optimisation process, it would be necessary to increase it and to make it go from 0 to 10 however when I look at the forces afterwards, they are also really high.
If anyone has had the same problem and found a solution, I'll be glad to hear it.
Thanks
Frederic
anormally high passive forces
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Emil Walczak
- Posts: 50
- Joined: Fri Feb 06, 2015 6:45 am
Re: anormally high passive forces
Hello once again!
Passive force is related to the maximum isometric force so if you want to increase maximal active force that muscle can generate and in the same time don't change the passive forces you need to change the passive force shape factor value.
You can also change optimal fibre lengths in muscles since the occurance and value of passive force in the muscle is strongly related to normalized fibre length. But increasing optimal fibre length will provoke lower value of forces that muscles can produce(for lengths smaller than optimal fibre length) and it is possible that it wont really help.
Passive force is related to the maximum isometric force so if you want to increase maximal active force that muscle can generate and in the same time don't change the passive forces you need to change the passive force shape factor value.
You can also change optimal fibre lengths in muscles since the occurance and value of passive force in the muscle is strongly related to normalized fibre length. But increasing optimal fibre length will provoke lower value of forces that muscles can produce(for lengths smaller than optimal fibre length) and it is possible that it wont really help.
Last edited by Emil Walczak on Wed Jun 24, 2015 8:51 am, edited 1 time in total.
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Emil Walczak
- Posts: 50
- Joined: Fri Feb 06, 2015 6:45 am
Re: anormally high passive forces
Btw. Passive forces are not included into muscles during Static Optimization simulations.
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Frédéric Lamon
- Posts: 27
- Joined: Wed May 06, 2015 1:01 pm
Re: anormally high passive forces
Hello Emil,
thanks again for answering. I am not sure however of what you suggest concerning the k shape factor that should be increased in order to lower the passive force. I really tried to understand how this passive shape factor is working and I reach 2 conclusions:
1) no matter the value of K, at (1+epsilon0) normalized fiber length, the value of the passive force will always be equal to the max isometric force. In my case epsilon0 (passive strain) = 0.6 so at 1.6 lm, the passive force equal fmax iso. So if I increase fmax iso by 3 times, the passive force will also increase by 3 times.
2) if I increase the K value as you suggested, for low activation level (meaning as long as I have not crossed the active force curve with the passive curve intersection point) the passive forces will indeed be reduced, however for high activation level (meaning when normalized fiber length is big (>1.6)) the passive forces will dramatically increase...
I don't know what do you think about it ? Am I mistaken or do you also agree with that ?
Cheers,
Fred
thanks again for answering. I am not sure however of what you suggest concerning the k shape factor that should be increased in order to lower the passive force. I really tried to understand how this passive shape factor is working and I reach 2 conclusions:
1) no matter the value of K, at (1+epsilon0) normalized fiber length, the value of the passive force will always be equal to the max isometric force. In my case epsilon0 (passive strain) = 0.6 so at 1.6 lm, the passive force equal fmax iso. So if I increase fmax iso by 3 times, the passive force will also increase by 3 times.
2) if I increase the K value as you suggested, for low activation level (meaning as long as I have not crossed the active force curve with the passive curve intersection point) the passive forces will indeed be reduced, however for high activation level (meaning when normalized fiber length is big (>1.6)) the passive forces will dramatically increase...
I don't know what do you think about it ? Am I mistaken or do you also agree with that ?
Cheers,
Fred