Neuroscience 2005 Abstract
| Presentation Number: | 868.8 |
|---|---|
| Abstract Title: | Influence of limb biomechanics on the force constraint strategy for postural control. |
| Authors: |
McKay, J.*1
; Ting, L. H.2
1Electrical Engineering, Georgia Inst. of Technology, Atlanta, GA 2GA, Box 336773 eorgia Tech Station, 30332, |
| Primary Theme and Topics |
Sensory and Motor Systems - Kinematics and EMG -- Posture |
| Secondary Theme and Topics | Techniques in Neuroscience<br />- Computation and Simulation |
| Session: |
868. Posture: Animal and Clinical Studies Poster |
| Presentation Time: | Wednesday, November 16, 2005 11:00 AM-12:00 PM |
| Location: | Washington Convention Center - Hall A-C, Board # BB20 |
| Keywords: | CAT, MODEL, MUSCLE |
During postural responses to perturbation, the directions of forces at the ground change at different stance distances in cats (Macpherson and Fung 1994). When the fore- and hindlimbs are closer together, a wider range of ground reaction force directions are used; at longer stance distances, forces are constrained to act along a single diagonal axis. We hypothesize that the set of feasible forces the hindlimb can produce is more elongated in long stance due to changes in biomechanics rather than neural control strategy. To investigate the force producing capacities of the leg we used a 3D musculoskeletal model to compute the feasible force set (FFS) and physiological force set (PFS) of the hindlimb over a range of postures. Based on a model of the hindlimb that includes the hip, knee, ankle, and 13 muscles (Korkmaz et al, 2004 SfN abstract), we generated equations describing the Jacobian transformation from muscle force to endpoint force. We generated a set of joint angle combinations which spans the physiological range of stance distances and postures. For each combination, the maximum feasible forces (FFS) and maximum projected feasible forces (PFS) in 260 directions distributed on the unit sphere were calculated with a linear optimization solver. Because the dorsal projection of each FFS and PFS was roughly elliptical along the axis of the leg, we quantified the skew as the ratio of major to minor axes. At short limb lengths, the FFS and PFS dorsal projections were comparably skewed. At longer limb lengths, the skew increased (FFS: 35%, PFS: 250%), consistent with the force constraint strategy observed at long stances. The greater increase in the PFS at long stances showed that maximum off-axis forces were generated by exerting forces along the axis of the leg, while at short stances there was no significant benefit. From these results we conclude the force constraint strategy reflects biomechanical limitations on force production at long stances.
Supported by NICHD 46922
Sample Citation:
[Authors]. [Abstract Title]. Program No. XXX.XX. 2005 Neuroscience Meeting Planner. Washington, DC: Society for Neuroscience, 2005. Online.
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