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Passive force characteristics of an architecturally complex muscle
T M G J van Eijden1, S J J Turkawski, L J van Ruijven
1Department of Functional Anatomy, Academic Center for Dentistry Amsterdam (ACTA), Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands. t.m.vaneijden@amc.uva.nl
Journal of Biomechanics
|August 7, 2002
Summary
Passive muscle force shifts position during jaw movement, increasing resistance. This anterior shift in the masseter muscle
Area of Science:
- Biomechanics
- Muscle physiology
- Anatomy
Background:
- Complex muscles exhibit regional length differences during movement.
- Passive forces generated by muscle regions vary accordingly.
- The resultant passive force vector's position may change dynamically.
Purpose of the Study:
- To test if the passive force vector's position is fixed in complex muscles.
- To investigate the dynamic behavior of passive force during jaw motion.
- To understand the contribution of passive force to jaw mechanics.
Main Methods:
- Used a three-component force transducer to measure masseter muscle passive force in rabbits.
- Recorded forces during stepwise jaw opening and closing cycles.
- Analyzed the magnitude, position, and orientation of the passive force vector.
Main Results:
- Masseter muscle showed force hysteresis (higher during opening than closing).
- Passive force magnitude increased exponentially with jaw gape.
- The passive force vector significantly shifted anteriorly during jaw opening.
- Moment arm length of passive force increased by approximately 100%.
Conclusions:
- The passive force vector's position is not fixed in architecturally complex muscles.
- Anterior shift of the passive force vector contributes to increased passive muscle moment during jaw opening.
- Increased passive resistance during lengthening involves both force magnitude and moment arm changes.