Musculoskeletal system muscle force

Muscles provide the forces needed to make movement possible they transmit their forces to tendons, whose forces in turn cause rotation of the bones about the joints. Muscles, however, are not simple force generators the force developed by a muscle depends not only on the level of neural excitation provided by the central nervous system (CNS), but also on the length and speed at which the muscle is contracting. Thus, muscles are the interface between the neuromuscular and musculoskeletal systems, and knowledge of their force-producing properties is crucial for understanding how these two systems interact to produce coordinated movement. 

Equations (6.1) and (6.7) can be combined to form a model of the musculoskeletal system in which the inputs are the muscle activation histories (a) and the outputs are the body motions (q, 4, q) (Fig. 6.22). Measurements of muscle EMG and body motions can be used to calculate the time histories of the musculotendinous forces during movement (Hof et al., 1987 Buchanan et al., 1993). Alternatively, the goal of the motor task can be modeled and used, together with dynamic optimization theory, to calculate the pattern of muscle activations needed for optimal performance of the task (Hatze, 1976 Pandy et al., 1990 Raasch et al., 1997 Pandy, 2001). Thus, one reason why the forward-dynamics method is potentially more powerful for evaluating musculotendinous forces than... 

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. 

Li G, Pierce JE, Herndon JH. A global optimization method for prediction of muscle forces of human musculoskeletal system. JBiomech 2006 39(3) 522-9. 

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