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ABSTRACT: BACKGROUND: The rabbit knee is a frequently used model for experimental osteoarthritis (OA). Despite the acknowledged importance of joint loading in the onset and progression of OA, the load transfer in the three compartments of the intact rabbit knee remains unknown. Therefore, this study was aimed at determining load transfer in the three compartments for isometric, concentric, and eccentric knee extensor contractions. METHODS: Maximal and sub-maximal isometric, concentric, and eccentric knee extensor contractions were produced by electrical stimulation of the femoral nerve in 13 rabbits. Knee extensor forces were measured using a custom-built servomotor. Contact areas and pressure distributions were measured in the patello-femoral, and the medial and lateral tibio-femoral joints using Fuji Presensor film. FINDINGS: Contact areas and peak pressures increased with increasing quadriceps forces for all compartments. Maximal knee extensor forces, joint moments, and contact pressures reached values of 504N, 5.5Nm and 60MPa, respectively. Force transfer in the patello-femoral joint was about twice that observed in the individual tibio-femoral joints. During isometric contractions, force transfer was higher in the medial compared to the lateral tibio-femoral joint, while this trend was reversed for dynamic contractions. INTERPRETATION: The results of this study suggest that the increasing muscular forces are transferred through an increased contact area, thereby limiting the increase in average contact pressure. These results may be used as reference data for contact pressures in the intact rabbit knee and may form the foundation for studies using the lapine knee as an experimental model of osteoarthritis.
Clinical biomechanics (Bristol, Avon) 01/2013; · 1.76 Impact Factor
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ABSTRACT: OBJECTIVE: The primary objective of this study was to quantify the strains applied to the internal carotid artery (ICA) during neck spinal manipulative treatments and range of motion (ROM)/diagnostic testing of the head and neck. METHODS: Strains of the ICA (n = 12) were measured in 6 fresh, unembalmed cadaveric specimens using sonomicrometry. Peak and average strains of the ICA obtained during cervical spinal manipulations given by experienced doctors of chiropractic were compared with the corresponding strains obtained during ROM and diagnostic testing of the head and neck. RESULTS: Peak and average strains of the ICA for cervical spinal manipulative treatments were significantly smaller (P < .001) than the corresponding strains obtained for the ROM and diagnostic testing. All strains during ROM and treatment testing were dramatically smaller than the initial failure strains of the ICA. CONCLUSIONS: This study showed that maximal ICA strains imparted by cervical spinal manipulative treatments were well within the normal ROM. Chiropractic manipulation of the neck did not cause strains to the ICA in excess of those experienced during normal everyday movements. Therefore, cervical spinal manipulative therapy as performed by the trained clinicians in this study, did not appear to place undue strain on the ICA and thus does not seem to be a factor in ICA injuries.
Journal of manipulative and physiological therapeutics 11/2012; · 1.06 Impact Factor
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ABSTRACT: Ever since the 1950s, muscle force regulation has been associated with the cross-bridge interactions between the two contractile filaments, actin and myosin. This gave rise to what is referred to as the "two-filament sarcomere model". This model does not predict eccentric muscle contractions well, produces instability of myosin alignment and force production on the descending limb of the force-length relationship, and cannot account for the vastly decreased ATP requirements of actively stretched muscles. Over the past decade, we and others, identified that a third myofilament, titin, plays an important role in stabilizing the sarcomere and the myosin filament. Here, we demonstrate additionally how titin is an active participant in muscle force regulation by changing its stiffness in an activation/force dependent manner and by binding to actin, thereby adjusting its free spring length. Therefore, we propose that skeletal muscle force regulation is based on a three filament model that includes titin, rather than a two filament model consisting only of actin and myosin filaments.
Molecular & cellular biomechanics: MCB 09/2012; 9(3):175-91.
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ABSTRACT: We studied force-sharing behavior between the cat medial gastrocnemius (MG) and soleus (SOL) muscles by direct measurement of the muscle forces and electromyographic activities (EMGs), muscle lengths, speeds of contraction, joint kinematics and kinetics, for a variety of locomotor conditions. Previous studies suggested that the modulation of MG force and activation is associated with movement demands, while SOL force and activation remain nearly constant. However, no systematic, quantitative analysis has been done to evaluate the degree of (possible) modulation of SOL force and activation across a range of vastly different locomotor conditions. In the present study, we investigated the effects of speed and intensity of locomotion on the modulation of SOL force and EMG activity, based on quantitative, statistical analyses. We also investigated the hypothesis that MG forces are primarily associated with MG activation for changing movement demands, while SOL forces are primarily associated with the contractile conditions, rather than activation. Seven cats were trained to walk, trot and gallop at different speeds on a motor-driven treadmill, and to walk up and down different slopes on a walkway. Statistical analysis suggested that SOL activation (EMG activity) significantly increased with increasing speeds and intensities of locomotion, while SOL forces remained constant in these situations. MG forces and EMG activities, however, both increased with increasing speeds and intensities of locomotion. We conclude from these results that SOL is not maximally activated at slow walking, as suggested in the literature, and that its force remains nearly constant for a range of locomotor conditions despite changes in EMG activity. Therefore, SOL forces appear to be affected substantially by the changing contractile conditions associated with changing movement demands. In contrast, MG peak forces correlated well with EMG activities, suggesting that MG forces are primarily associated with activation while its contractile conditions play a minor role for the movement conditions tested here.
Journal of Experimental Biology 11/2003; 206(Pt 20):3645-55. · 3.00 Impact Factor
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ABSTRACT: Spinal manipulative therapy (SMT) has been established as a clinically effective modality for the management of several musculoskeletal disorders. One major issue with the use of SMT is its safety, especially with respect to neck manipulation and the risk of stroke in the vertebrobasilar system.
Our objectives were to quantify the strains and forces sustained by the vertebral artery (VA) in situ during SMT. Study Design: This was a cadaveric study.
Six VAs were obtained from 5 unembalmed postrigor cadavers. The cephalad/distal (C0-C1) and caudad/proximal (C6-subclavian artery) loops of the VA were carefully exposed and instrumented with a pair of piezoelectric ultrasonographic crystals. The strains between each crystal pair were recorded during range of motion testing and diagnostic tests and during a variety of SMT procedures. The VA was then dissected free and strained on a materials testing machine until mechanical failure occurred.
SMT performed on the contralateral side of the cervical spine resulted in an average strain of 6.2% +/- 1.3% to the distal (C0-C1) loop of the VA and a 2.1% +/- 0.4% strain to the proximal (C6) loop. These values were similar to or lower than the strains recorded during diagnostic and range of motion testing. Failure testing demonstrated that the VAs could be stretched to 139% to 162% of their resting length before mechanical failure occurred. Therefore the strains sustained by the VA during SMT represent approximately one ninth of the strain at mechanical failure.
SMT resulted in strains to the VA that were almost an order of magnitude lower than the strains required to mechanically disrupt it. We conclude that under normal circumstances, a single typical (high-velocity/low-amplitude) SMT thrust is very unlikely to mechanically disrupt the VA.
Journal of Manipulative and Physiological Therapeutics 11/2002; 25(8):504-10. · 1.36 Impact Factor
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ABSTRACT: In typical muscle models, it is often assumed that the contractile element (fascicle) length depends exclusively on the instantaneous muscle-tendon length and the instantaneous muscle force. In order to test whether the instantaneous fascicle length during dynamic contractions can be predicted from muscle-tendon length and force, fascicle lengths, muscle-tendon lengths, and muscle forces were directly measured in cat medial gastrocnemii during isometric and dynamic contractions. Two theoretical muscle models were developed: model A was based on force-time data obtained during the activation phase and model D on force-time data obtained during the deactivation phase of isometric contractions. To test the models, instantaneous fascicle lengths were predicted from muscle-tendon lengths and forces during dynamic contractions that simulated cat locomotion for speeds ranging from 0.4 to 1.6m/s. The theoretically predicted fascicle lengths were compared with the experimentally measured fascicle lengths. It was found that fascicle lengths were not uniquely associated with muscle-tendon lengths and forces; that is, for a given muscle-tendon length and force, fascicle lengths varied depending on the contractile history. Consequently, models A and D differed in fascicle length predictions; model D (maximum average error=8.5%) was considerably better than model A (maximum average error=22.3%). We conclude from this study that it is not possible to predict the exact fascicle lengths from muscle-tendon lengths and forces alone, however, adequate predictions seem possible based on such a model. The relationship between fascicle length and muscle force and muscle-tendon length is complex and highly non-linear, thus, it appears unlikely that accurate fascicle length predictions can be made without some reference contractions in which fascicle length, muscle-tendon length, and force are measured simultaneously.
Journal of Biomechanics 08/2002; 35(7):893-902. · 2.43 Impact Factor
