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Research Papers

# The Influence of Modeling Separate Neuromuscular Compartments on the Force and Moment Generating Capacities of Muscles of the Feline Hindlimb

[+] Author and Article Information

Department of Bioengineering, University of Utah, Salt Lake City, UT 84112lisa.macfadden@utah.edu

Nicholas A. T. Brown

Department of Bioengineering, University of Utah, Salt Lake City, UT 84112; Biomechanics and Performance Analysis, Australian Institute of Sport, Leverrier Street, Bruce ACT 2617, Canberra, Australianick.brown@ausport.gov.au

J Biomech Eng 132(8), 081003 (Jun 15, 2010) (10 pages) doi:10.1115/1.4001680 History: Received July 23, 2009; Revised March 31, 2010; Posted April 28, 2010; Published June 15, 2010; Online June 15, 2010

## Abstract

Functional electrical stimulation (FES) has the capacity to regenerate motion for individuals with spinal cord injuries. However, it is not straightforward to determine the stimulation parameters to generate a coordinated movement. Musculoskeletal models can provide a noninvasive simulation environment to estimate muscle force and activation timing sequences for a variety of tasks. Therefore, the purpose of this study was to develop a musculoskeletal model of the feline hindlimb for simulations to determine stimulation parameters for intrafascicular multielectrode stimulation (a method of FES). Additionally, we aimed to explore the differences in modeling neuromuscular compartments compared with representing these muscles as a single line of action. When comparing the modeled neuromuscular compartments of biceps femoris, sartorius, and semimembranosus to representations of these muscles as a single line of action, we observed that modeling the neuromuscular compartments of these three muscles generated different force and moment generating capacities when compared with single muscle representations. Differences as large as $4 N m$ ($∼400%$ in biceps femoris) were computed between the summed moments of the neuromuscular compartments and the single muscle representations. Therefore, modeling neuromuscular compartments may be necessary to represent physiologically reasonable force and moment generating capacities of the feline hindlimb.

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Topics: Force , Modeling , Muscle , Knee , Motion

## Figures

Figure 1

Segments and joints of the feline hindlimb (lateral view of left hind limb). Joints are in bold font and segments are in italics. The metatarsalphalangeal joint is represented by the abbreviation MTP. The hip angle is defined as the anterior angle between the pelvis and thigh, the knee angle is the posterior angle between the thigh and shank, the ankle angle is the anterior angle between the shank and foot bones, and the MTP angle is defined on the plantar side of the paw and foot, from the plantar aspect of the foot to the plantar side of the digits.

Figure 2

Muscles of the feline hindlimb: (a) depicts the muscles from the lateral aspect of the left hindlimb and (b) shows the muscle from the medial aspect of the left hindlimb. Abbreviations are listed in Table 2.

Figure 3

Operating ranges of the biarticular muscles with neuromuscular compartments crossing the hip and knee (BF, SM, and SAR). Muscle force is normalized to peak muscle force (FoM) and fiber length is normalized to optimal fiber length. Note that a muscle at a length of LoM(LM/LoM=1) has a force of FoM. The compartments of sartorius operate on the same range of the force-length curve while the anterior compartment of semimembranosus operates at the beginning of the descending portion of the force-length curve and the posterior compartment operates on the plateau as well as the descending portion of the force-length curve. Finally, the compartments of biceps femoris operate over the same ranges; however, the medial and posterior compartments operate over extended ranges. Also depicted are the single muscle representations of these three muscles in bold.

Figure 4

Knee moment generating capacity for the sum of the compartmental model (solid lines) and single muscle model (dashed lines). Biceps femoris had the largest differences of up to 4 N m and the single muscle representation overestimated the moment generating capacity of the hamstrings. Semimembranosus has a smaller difference of up to 0.4 N m; however, the single muscle representation underestimated the net moment generation about the knee. Various hip angles are also shown; however, hip angle did not seem to have a large effect on the differences in moment generation.

Figure 5

Hip moment generating capacity for the sum of the compartmental model (solid lines) and single muscle model (dashed lines). Sartorius had negligible differences in hip flexion generation while both semimembranosus and biceps femoris had differences between the compartmental and single muscle representations. As opposed to Fig. 4, knee angle did have an effect on the differences between the two representations.

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