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Muscle wobbling mass dynamics: eigenfrequency dependencies on activity, impact strength, and ground material
Kasper B Christensen1, Michael Günther2,3, Syn Schmitt2,4
1Motion and Exercise Science, University of Stuttgart, Stuttgart, Germany. kasper.christensen@inspo.uni-stuttgart.de.
Scientific Reports
|November 10, 2023
Summary
Muscle oscillations during locomotion are affected by impacts. Active rat muscles (GAS) showed higher dominant eigenfrequencies than passive ones, with differences attributed to myosin-actin attachments.
Area of Science:
- Biomechanics
- Muscle Physiology
- Locomotion Dynamics
Background:
- Muscles in legged locomotion experience damped oscillations upon ground impact.
- The nature of muscle oscillation is influenced by impact conditions.
Purpose of the Study:
- To investigate the impact of activation state on muscle eigenfrequencies during simulated ground contact.
- To determine the influence of impact parameters (height, surface) on muscle oscillation.
- To model muscle stiffness and relate it to observed eigenfrequencies.
Main Methods:
- Isolated rat gastrocnemius (GAS) muscles were subjected to impact using a custom-built apparatus.
- Muscles were tested in both active (fully activated) and passive states.
- Impacts were performed from varying heights onto different ground materials.
- A 3 Degrees of Freedom (3DoF) model was developed to estimate muscle stiffness.
Main Results:
- Active GAS muscles exhibited significantly higher dominant eigenfrequencies (163 Hz, 265 Hz, 399 Hz) compared to passive GAS muscles (139 Hz, 215 Hz, 286 Hz).
- Neither falling height nor ground material significantly altered eigenfrequencies in active or passive GAS.
- The 3DoF model accurately predicted experimental eigenfrequencies, with small deviations for both active and passive states.
Conclusions:
- Muscle activation state significantly alters dominant eigenfrequencies during impact.
- The primary cause for differences in active versus passive muscle eigenfrequencies is myosin head-actin attachment.
- Impact parameters like height and surface material have minimal effect on GAS muscle eigenfrequencies in this model.
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