Some researchers model passive joint moments (elastic by double exponential equations which account for the influence of the adjacent joint angles and passive viscous joint moments by linear damping functions) while other researchers don't model these properties. Could someone explain to me how passive joint moments (elastic and viscous) are important in controlling FES assisted movement in paraplegic patients? Also, how can they affect the performance of the total joint moments?
Rufaida,
There are a few reasons for including passive moments in a biomechanical model. Inertial effects of the segments can produce apparent moments at the joints. Tensile elastic forces of the passive structures and muscles can produce moments, even if muscles aren't activated. Joint coupling can produce moments if muscles cross multiple joints, and even if they aren't active.
Whether or not you do include them likely depends on the question you are answering. For example, during maximal active contraction of the stance leg during running, the active moments of the model will greatly exceed any passive moments. Depending on how accurate we want to be with our model, we may assume that any resultant joint moments that we calculate are 100% active, although this is probably not the case. During the swing phase, however, the active/passive breakdown is very different.
This paper shows a nice breakdown of moments during sprinting:
Lingyan Huang, Yu Liu, Shutao Wei, Li Li, Weijie Fu, Yuliang Sun, Yi Feng
Segment-interaction and its relevance to the control of movement during sprinting
Journal of Biomechanics, Volume 46, Issue 12, 9 August 2013, Pages 2018–2023
I am not 100% sure how this applies to your specific question, but I would assume that an assisted movement device would need to account for inertial effects of the segments, as well as passive elastic and coupling effects at the joints. Hence the need for passive moments as potential inputs to a controller.
Hope that helps.
To add to Sean Osis answer, the passive elastic and damping moments could be exacerbated by spasticity and joint contractures after spinal cord injury. Also, the only way to generate active joint moments after SCI is by functional electrical stimulation of the otherwise paralyzed muscles. It is common knowledge that this method does not generate as much moment as the intact muscles (30-50%). Thus the impact of passive moments could be more prominent in the model. You can find the quantitative details of these moments in the paper: Amankwah, K., R. Triolo, et al. (2006). "A model-based study of passive joint properties on muscle effort during static stance." J Biomech 39(12): 2253-2263. Also, you can get information on the relative amount of active moments generated by FES in: Kobetic, R., Marsolais, E.B. and Miller, P.C. (1994). "Function and Strength of Electrically Stimulated Hip Flexor Muscles in Paraplegia." IEEE Transactions on Rehabilitation Engineering, 2(1): 11-17. I hope this helps.
Thank you for your helps
I couldn't find the paper that Sir Osis that he suggest. But I found that Mr. Audu suggests.
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