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Conceptual Frameworks for Interpreting Motor Cortical Function: New Insights from a Planar Multiple-Joint Paradigm
Published in Alexa Riehle, Eilon Vaadia, Motor Cortex in Voluntary Movements, 2004
A key feature of both of these studies was that we could load the shoulder and elbow joints independently. It seems reasonable to assume that these single-joint loads would selectively influence the response of muscles that span that joint. We were mistaken. Many muscles that only spanned one of the two joints modified their activity for loads applied to the other joint. For example, brachioradialis, an elbow flexor muscle, increased its activity when the monkey generated either an elbow flexor or a shoulder extensor muscular torque (Figure 6.7). The greatest activity level was observed when the monkey generated an elbow flexor and a shoulder extensor torque simultaneously. At first, this seems paradoxical, but it simply reflects the action of biarticular muscles that span both joints. Changes in a biarticular muscle's activity for loads applied at one joint necessarily create torque at the other joint. As a result, the activity of muscles spanning this second joint must change to compensate for the change in activity of the biarticular muscles.7980
Scalable musculoskeletal model for dynamic simulations of upper body movement
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
Ali Nasr, Arash Hashemi, John McPhee
tact can have a value of for an adult subject (Thelen 2003) and tdeact is assumed to be equal to The excitation signal is in the range of for monoarticular muscles. However, even for monoarticular muscles, the antagonist and agonist muscles activate simultaneously. In addition, the biarticular muscle provides tension for two joints (Thelen et al. 2011; Nasr and McPhee 2022b). However, the MTG models assume a monoarticular joint. To overcome this assumption, the impact of the excitation signal of one joint on another joint should be investigated (Bell and McPhee 2022). Studying the excitation signal of joints is out of the scope of this article.