Abstract
IntroductionIn this study, we tested two assumptions that have been made in experimental studies on muscle mechanics: (i) that the torque-angle properties are similar among agonistic muscles crossing a joint, and (ii) that the sum of the torque capacity of individual muscles adds up to the torque capacity of the agonist group. MethodsMaximum isometric torque measurements were made using a specifically designed animal knee extension dynamometer for the intact rabbit quadriceps muscles (n = 10) for knee angles between 60 and 120°. The nerve branches of the vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) muscles were carefully dissected, and a custom made nerve cuff electrode was implanted on each branch. Knee extensor torques were measured for four maximal activation conditions at each knee angle: VL activation, VM activation, RF activation, and activation of all three muscles together. ResultsWith the exception of VL, the torque-angle relationships of the individual muscles did not have the shape of the torque-angle relationship obtained when all muscles were activated simultaneously. Furthermore, the maximum torque capacity obtained by adding the individual torque capacities of VL, VM and RF was approximately 20% higher than the torques produced when the three muscles were activated simultaneously. DiscussionThese results bring into question our understanding of in-vivo muscle contraction and challenge assumptions that are sometimes made in human and animal muscle force analyses.
Highlights
In this study, we tested two assumptions that have been made in experimental studies on muscle mechanics: (i) that the torque-angle properties are similar among agonistic muscles crossing a joint, and (ii) that the sum of the torque capacity of individual muscles adds up to the torque capacity of the agonist group
The sum of the maximum torque capacity for the isolated stimulation of vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) was approximately 20% higher than the maximum torque capacity for simultaneous stimulation of all muscles of the agonist group (p< 0.001) and for all joint angles (p = 0.997 for interaction between effects) (Figure 2)
We analyzed the mechanics of VL, VM and RF when activated individually and simultaneously in a rabbit model
Summary
We tested two assumptions that have been made in experimental studies on muscle mechanics: (i) that the torque-angle properties are similar among agonistic muscles crossing a joint, and (ii) that the sum of the torque capacity of individual muscles adds up to the torque capacity of the agonist group. Methods: Maximum isometric torque measurements were made using a designed animal knee extension dynamometer for the intact rabbit quadriceps muscles (n = 10) for knee angles between 60 and 120 degrees. Knee extensor torques were measured for four maximal activation conditions at each knee angle: VL activation, VM activation, RF activation, and activation of all three muscles together. Results: With the exception of VL, the torque-angle relationships of the individual muscles did not have the shape of the torqueangle relationship obtained when all muscles were activated simultaneously. The maximum torque capacity obtained by adding the individual torque capacities of VL, VM and RF was approximately 20% higher than the torques produced when the three muscles were activated simultaneously. Discussion: These results bring into question our understanding of in-vivo muscle contraction and challenge assumptions that are sometimes made in human and animal muscle force analyses
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