Determining Muscle Force

FIGURE 6.22 Comparison of the forward- and inverse-dynamics methods for determining muscle forces during movement. Top Body motions are the inputs and muscle forces are the outputs in inverse dynamics. Thus, measurements of body motions are used to calculate the net muscle torques exerted about the joints, from which muscle forces are determined using static optimization. Bottom Muscle excitations are the inputs and body motions are the outputs in forward dynamics. Muscle force (F ) is an intermediate product (i.e., output of the model for musculotendon dynamics). 

Hardt, D. E. (1978). Determining muscle forces in the leg during human walking An application and evaluation of optimization methods, Journal of Biomechancal Engineering, 100 72-78. 

The determination of forces and stresses acting at the cellular level in other ECMs is more complicated. In other ECMs, stresses and forces are transferred to cells through collagen, elastic fiber, and smooth muscle networks in a more complex fashion than occurs in tendon. In order to calculate the stresses and forces that occur at the cellular level we must gain new insight into how the components are connected and how the cells are attached. Until this is accomplished we can only guess at the cellular loads in each of these tissues. 

Zajac, EE. and Gordon, M.E., Determining muscles s force and action in multi-articular movement. In PandoffK. Ed.), Exercise Sport Science Review,Vol. 17. Williams and Wilkins, Baltimore, pp. 187-230,1989. 

The equations of motion are dynamic expressions relating kinematics with forces and moments. In a musculoskeletal biodynamic system, the forces and moments will consist of joint reactions internal forces, such as muscle, tendon, or ligament forces and/or externally applied loads. Consequently, the equations of motion can provide a critical understanding of the forces experienced by a joint and effectively model normal joint function and joint injury mechanics. They can yield estimates for forces that cannot be determined by direct measurement. For example, muscle forces, which are typically derived from other quantities such as external loads, center of mass locations, and empirical data including anatomical positioning and/or electromyography, can be estimated. 

The musculoskeletal geometry is required for the calculation of the muscle length. The musculoskeletal geometry consists of the three dimensional location of muscle attachment and the position relation of bones such as the pelvis, femur, tibias, and feet. There have been several attempts to develop a database for the lower extremities [10-12]. The model of Brand et al. [12] is used in this study because they provide a full database of the 43 muscles. The attachment points of each muscle are described based on the coordinates of the attached bone. The graphically reconstructed model of muscles and each coordinate of the bone are shown in Figure 2. Unlike the given coordinates in Brand et al., the coordinates for the femur are divided into the proximal and the distal in order to determine the fracture position. The coordinates of the force sensor are added to calculate the muscle forces and moments at the position of the force sensor, which will be compared to the force measured in real-time. 

R. Bogey, J. Perry, and A. Gitter, An emg-to-force processing approach for determining ankle muscle forces during normal human gait, Neural Syst. Rehabil. Eng., vol. 13, no. 3, pp. 302-310, September 2005. 

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