Browsing by Author "Herzog, Walter"

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    A Proposed Mechanism for Enhanced Titin-Based Force during Ca2+-activation
    (2017) Powers, Krysta; Herzog, Walter; Pollack, Gerald; Schmidt, Tannin; Syme, Douglas; Nishikawa, Kiisa; Shemanko, Carrie; Federico, Salvatore
    When an active skeletal muscle sarcomere is stretched, it generates more force after the stretch is completed when compared to a contraction at the same corresponding length. This mechanical property of skeletal muscle defies explanation by any conventional mechanism of contraction. Surmounting evidence indicates that the explanation for enhanced force following active stretch may be provided by the titin protein in the sarcomere, which becomes stiffer during Ca2+-activation. This thesis explores the mechanisms by which titin force is enhanced in actively stretched sarcomeres. Known to stiffen in the presence of Ca2+, the first study quantifies the contribution of Ca2+ to enhanced titin force, showing that an alternative mechanism accounts for the majority of titin force enhancement. The mechanism is further investigated using chemical inhibition of cross-bridges which shows that titin force enhancement is initiated with the development of contractile force. The next set of studies increase support for an interdependence of titin force enhancement and contractile force, showing that titin force enhancement is essentially eliminated and contractile force is decreased in sarcomeres with muscular dystrophy with myositis (mdm), a genetic mutation affecting the titin protein. The final study seeks to determine whether mechanical deficiencies in titin force enhancement are observed in a less reduced, single fiber preparation. Mutant fibers generated comparable contractile force and total force following active stretch beyond filament overlap as control fibers. Titin force enhancement was abolished in some mutant fibers and measured in other mutant fibers suggesting that the mdm mutation differentially affects fibers (and titin) in skeletal muscle. Passive force was increased in mutant fibers, showing that alternative structural components in a fiber can re-establish enhanced active stiffness in the absence of titin force enhancement. Collectively, the findings from this thesis show that titin-based force enhancement is an inherent property of skeletal muscle. The mechanism of titin force enhancement is crucial to sarcomere mechanics; as in its absence, sarcomeres generate less force and alternative structures to titin establish a comparable increase in active stiffness.
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    A Prospective Study Evaluating the Effects of Manual Therapy on the Treatment of Patellofemoral Pain
    (2014-05-16) Tang, Conrad; Herzog, Walter
    Objective: To determine whether manual therapy, specifically myofascial release technique (MRT) and Trigger Point Therapy (TPT) of the quadriceps, directly affects knee-extensor voluntary activation (VA) in patients with patellofemoral pain (PFP). Methods: This study was a randomized controlled trial (RCT). Thirty patients with PFP were recruited and randomized into group 1, who received MRT; group 2, who received TPT; and group 3, who received a sham ultrasound treatment (control group). Main outcomes: Voluntary activation, subjective knee pain scores (Visual Analogue Scale), subjective functional knee scores (Anterior Knee Pain Score - AKPS), knee-extensor torque (Biodex machine), and quadriceps electromyography (EMG) were measured over a six week experimental period. Results: Pain decreased in all three groups over the six week experimental period and there was a significant increase in % VA for the TPT group at 2 weeks post-baseline (9% increase) and 6 weeks post-baseline (10% increase). Conclusion: The TPT increased % VA, whereas MRT intervention and the control condition did not. Pain decreased in all groups to a similar degree, suggesting that a placebo effect may have produced a decrease in symptoms in this chronic PFP patient group.
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    A Review of the Combination of Experimental Measurements and Fibril-Reinforced Modeling for Investigation of Articular Cartilage and Chondrocyte Response to Loading
    (2013-04-08) Julkunen, Petro; Wilson, Wouter; Isaksson, Hanna; Jurvelin, Jukka S.; Herzog, Walter; Korhonen, Rami K.
    The function of articular cartilage depends on its structure and composition, sensitively impaired in disease (e.g. osteoarthritis, OA). Responses of chondrocytes to tissue loading are modulated by the structure. Altered cell responses as an effect of OA may regulate cartilage mechanotransduction and cell biosynthesis. To be able to evaluate cell responses and factors affecting the onset and progression of OA, local tissue and cell stresses and strains in cartilage need to be characterized. This is extremely challenging with the presently available experimental techniques and therefore computational modeling is required. Modern models of articular cartilage are inhomogeneous and anisotropic, and they include many aspects of the real tissue structure and composition. In this paper, we provide an overview of the computational applications that have been developed for modeling the mechanics of articular cartilage at the tissue and cellular level. We concentrate on the use of fibril-reinforced models of cartilage. Furthermore, we introduce practical considerations for modeling applications, including also experimental tests that can be combined with the modeling approach. At the end, we discuss the prospects for patient-specific models when aiming to use finite element modeling analysis and evaluation of articular cartilage function, cellular responses, failure points, OA progression, and rehabilitation.
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    Acute and Chronic Effects of Botulinum Toxin Type-A on the structure and Function of the Quadriceps Femoris Muscles of New Zealand White Rabbits
    (2015-10-01) Fortuna, Rafael; Herzog, Walter
    Botulinum toxin type-A (BTX-A) injections have become a common treatment modality for a variety of neuromuscular disorders with the primary aim to relax spastic muscles, for example, in children with cerebral palsy, or following a stroke. Once injected, BTX-A prevents acetylcholine release at the motor nerve endings, thereby producing a dose-dependent muscle paralysis. Despite an exponential growth of patients receiving BTX-A treatment, there has been no systematic evaluation of the effects of the toxin on target and non-target muscles. Therefore, the general purpose of this PhD project was to evaluate muscle mass, strength, and contractile material in injected and contralateral non-injected quadriceps muscles of New Zealand White (NZW) rabbits following single and repeated BTX-A injections. Muscle mass was assessed as the wet weight of muscles following sacrifice, strength was assessed by stimulating the knee extensor muscles via femoral nerve stimulation and quantifying the knee extensor force, the amount of contractile material was quantified histologically. We found that six-monthly BTX-A injections into the quadriceps caused substantial muscle weakness, atrophy, and contractile material loss in the injected and the contralateral non-injected muscles. Adding direct electrical muscle stimulation during the BTX-A injection help to alleviate muscle mass, strength and contractile material loss and the injected and contralateralnon injected muscles, and finally, BTX-A injections had long lasting effects that were not fully recovered at six months following the end of the injection protocol. We concluded from the results of this series of studies that BTX-A treatment resulted in adverse effects on the injected and contralateral non-injected musculature up to six months following the iii injection protocol. Future studies should be aimed at identifying strategies that minimize/prevent adverse effects of BTX-A injections on target and non-target muscles.
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    Additional in-series compliance does not affect the length dependence of activation in rat medial gastrocnemius
    (2020-03-30) MacDougall, Keenan Barry; MacIntosh, Brian R.; Herzog, Walter; Syme, Douglas A.
    Background: The force-length relationship describes the amount of force a muscle can produce as a function of its length, typically during maximal isometric contractions. When activation is submaximal, it has been shown that the length at which force production is highest (the optimum length) is shifted towards longer lengths. The usual explanation for this shift is a length-dependent increase in calcium sensitivity due to an increased proximity of the myofilaments with increases in length, which has been dubbed the “length dependence of activation” (LDA). Some recent research has suggested that shortening-induced force depression, (a phenomenon which describes the relative reduction in muscle force when a muscle is actively shortening to a given length compared to contracting isometrically at that same length) has the potential to alter a muscle’s optimum length in an activation-dependent way, thereby affecting any activation dependent shifts in optimum length. Purpose: The purpose of this study was to determine whether shortening-induced force depression would impact the relative shift in optimum length that occurs with submaximal activation. Methods: Rat medial gastrocnemius muscle was isolated and stimulated at 200 Hz triplet pulses and single pulse stimulation over a range of lengths, both with and without additional in-series compliance provided by a small piece of silicon tubing in series with the muscle tendon unit. Peak force and optimum length were calculated by curve-fitting of the force-length data, and these data were compared between low- and high-compliance conditions as well as with maximal and submaximal activation. Results: Additional in-series compliance led to a significant decrease in force at both maximal and submaximal activation, but did not impact the optimum length for either condition. Therefore, in our model, shortening-induced force depression did not impact the length dependence of activation. Conclusion: The additional in-series compliance allowed greater muscle shortening upon activation, which was accompanied by a reduction in force, however the post-shortening length at which the muscle produced the most force was unchanged. The best explanation for the length dependence of activation in skeletal muscle remains a length dependent increase in calcium sensitivity.
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    Age-related Maintenance of Eccentric Strength: A Study of Temperature Dependence
    (University of Guelph, 2016-06) Herzog, Walter; Power, Geoffrey Alonzo; Dalton, Brian; Flaaten, Nordan
    With adult aging, eccentric strength is maintained better than isometric strength leading to a higher ratio of eccentric:isometric force production (ECC:ISO) in older than younger adults. The purpose was to investigate the ECC:ISO during electrical activation of the adductor pollicis during lengthening (20-320°∙s-1) contractions in 24 young (n=12, ~24 years) and old (n=12, ~72 years) males across muscle temperatures (Cold; ~19oC, Normal; ~30oC, Warm; ~35oC). For isometric force, the old were 20-30% weaker in the normal and cold conditions (P<0.05) with no difference for the warm condition compared to young (P>0.05). Half-relaxation time (HRT) did not differ across age for the normal and warm temperatures (P>0.05), but slowed significantly for old in the cold condition compared with young (~15%; P<0.05), as well, there was a 20 and 40% increase in muscle stiffness for the young and old, respectively. ECC:ISO was 50-60% greater for the cold condition than the normal and warm conditions. There was no age-difference in ECC:ISO across age for the normal and warm conditions (P>0.05), but for the cold, the old exhibited a 20-35% higher ECC:ISO than young for velocities above 60°∙s-1 (P<0.05). A contributing factor to the elevated ECC:ISO is an increased proportion of weakly- compared to strongly-bound cross-bridges. These findings highlight the relationship (r=0.70) between intrinsic muscle contractile speed (HRT) and eccentric strength in old age.
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    Alteration of Strain Distribution in Distal Tibia After Triple Arthrodesis: Experimental and Finite Element Investigations
    (Journal of Medical and Biological Engineering, 2018-06-01) Chitsazan, Ahmad; Herzog, Walter; Rouhi, Gholamreza A.; Abbasi, Mostafa
    Arthrodesis, or fusion of subtalar joints (STJs), is a well-accepted and a routine treatment in the end stage of ankle injuries or disorder, such as arthritis or fractures. Arthrodesis can restore daily life function quickly at the expense of limiting joint motion. A triple arthrodesis (TA) consists of the surgical fusion of the talocalcaneal (TC), talonavicular (TN), and calcaneocuboid (CC) joints in the foot. This study aimed at investigating the effects of TA on strain distribution around tibia near the ankle joint. A finite element (FE) model, generated using computed tomography (CT) images of the human ankle, was then used to estimate stress distribution on the ankle joint surface. Axial load was applied to a human cadaveric ankle before and after TA, and load patterns were determined in various anatomical positions by measuring strain distribution around the tibia. Therefore, the effects of fusion were investigated by comparing strain distribution obtained from experiment and from FE model before and following to fusion. A good agreement between the experiment and FE, for the mean value of experimentally measured strains per the strains determined by FEM was observed (1.4±0.32 before TA, and 1.51±0.49 after TA). Moreover, a wellaccepted point-by-point comparison between FE results and experimentally measured strains was observed with a good correlation coefficient (r=0.94). Results of this study showed that: (1) there was a significant difference in strain magnitude and strain distribution around the tibia before and after TA; (2) the strain and stress were more uniformly distributed after fusion; and (3) the peak strain and stress values were shifted to the lateral and anterolateral portion of the tibia after the fusion. Results of this investigation showed that STJs fusion reduces the average values of strains around the cortical bone through changing the pattern of load transmission at the ankle joint.
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    Alterations in structural macromolecules and chondrocyte deformations in lapine retropatellar cartilage 9 weeks after anterior cruciate ligament transection
    (Wiley-Blackwell, 2018-01) Han, Sang Kuy; Ronkainen, Ari P.; Saarakkala, Simo J.; Rieppo, Lassi; Herzog, Walter; Korhonen, Rami K.
    The structural integrity and mechanical environment of the articular cartilage matrix directly affect chondrocyte deformations. Rabbit models of early osteoarthritis at 9 weeks following anterior cruciate ligament transection (ACLT) have been shown to alter the deformation behavior of superficial zone chondrocytes in mechanically loaded articular cartilage. However, it is not fully understood whether these changes in cell mechanics are caused by changes in structural macromolecules in the extracellular matrix. Therefore, the purpose of this study was to characterize the proteoglycan content, collagen content, and collagen orientation at 9 weeks post ACLT using microscopic techniques, and relate these changes to the altered cell mechanics observed upon mechanical loading of cartilage. At 9 weeks following ACLT, collagen orientation was significantly (p < 0.05) altered and proteoglycan content was significantly (p < 0.05) reduced in the superficial zone cartilage matrix. These structural changes either in the extracellular or pericellular matrix (ECM and PCM) were also correlated significantly (p < 0.05) with chondrocyte width and height changes, thereby suggesting that chondrocyte deformation response to mechanical compression in early OA changes primarily because of alterations in matrix structure. However, compared to the normal group, proteoglycan content in the PCM from the ACLT group decreased less than that in the surrounding ECM. Therefore, PCM could play a key role to protect excessive chondrocyte deformations in the ACLT group. 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:342350, 2018.
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    Altered mechanical properties of titin immunoglobulin domain 27 in the presence of calcium
    (European Biophysics Journal, 2013-04) DuVall, Michael M.; Gifford, Jessica L.; Amrein, Matthias W.; Herzog, Walter
    Titin (connectin) based passive force regulation has been an important physiological mechanism to adjust to varying muscle stretch conditions. Upon stretch, titin behaves as a spring capable of modulating its elastic response in accordance with changes in muscle biochemistry. One such mechanism has been the calcium-dependent stiffening of titin domains that renders the spring inherently more resistant to stretch. This transient titin-calcium interaction may serve a protective function in muscle, which could preclude costly unfolding of select domains when muscles elongate to great lengths. To test this idea, fluorescence spectroscopy was performed revealing a change in the microenvironment of the investigated immunoglobulin domain 27 (I27) of titin with calcium. Additionally, an atomic force microscope was used to evaluate the calcium-dependent regulation of passive force by stretching eight linked titin I27 domains until they unfolded. When stretching in the presence of calcium, the I27 homopolymer chain became stabilized, displaying three novel properties: (1) higher stretching forces were needed to unfold the domains, (2) the stiffness, measured as a persistence length (PL), increased and (3) the peak-to-peak distance between adjacent I27 domains increased. Furthermore, a peak order dependence became apparent for both force and PL, reflecting the importance of characterizing the dynamic unfolding history of a polymer with this approach. Together, this novel titin Ig-calcium interaction may serve to stabilize the I27 domain permitting titin to tune passive force within stretched muscle in a calcium-dependent manner.
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    An Examination of Sarcomere Length Non-uniformities in Actively Stretched Muscle Myofibrils
    (2015-04-30) Johnston, Kaleena; Herzog, Walter
    Residual force enhancement (RFE) is a characteristic of skeletal muscle describing the increase in isometric steady-state force following an active stretch, compared to the force of an isometric contraction at the same final length. It has been argued that RFE is a result of unstable sarcomeres on the descending limb of the force-length relationship, causing long, weak sarcomeres to lengthen more than short, strong sarcomeres when a myofibril is actively stretched, as described by the Sarcomere Length Non-uniformity Theory (SLNT). While the SLNT is currently the most popular explanation for RFE, its primary predictions have never been experimentally tested. In this research we performed experiments on rabbit psoas muscle myofibrils, comparing isometric contractions to isometric contractions following active stretch in order to examine the predictions of the SLNT. The results suggest that, while sarcomere length non-uniformities may play a role, the SLNT does not fully capture the mechanism of RFE.
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    Analyses of muscle force predictions based on optimization
    (2002) Jinha, Azim; Herzog, Walter
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    Anterior cruciate ligament transection alters the n-3/n-6 fatty acid balance in the lapine infrapatellar fat pad
    (2019-03-18) Mustonen, Anne-Mari; Käkelä, Reijo; Finnilä, Mikko A J; Sawatsky, Andrew; Korhonen, Rami K; Saarakkala, Simo; Herzog, Walter; Paakkonen, Tommi; Nieminen, Petteri
    Abstract Background The infrapatellar fat pad (IFP) of the knee joint has received lots of attention recently due to its emerging role in the pathogenesis of osteoarthritis (OA), where it displays an inflammatory phenotype. The aim of the present study was to examine the infrapatellar fatty acid (FA) composition in a rabbit (Oryctolagus cuniculus) model of early OA created by anterior cruciate ligament transection (ACLT). Methods OA was induced randomly in the left or right knee joint of skeletally mature New Zealand White rabbits by ACLT, while the contralateral knee was left intact. A separate group of unoperated rabbits served as controls. The IFP of the ACLT, contralateral, and control knees were harvested following euthanasia 2 or 8 weeks post-ACLT and their FA composition was determined with gas chromatography–mass spectrometry. Results The n-3/n-6 polyunsaturated FA (PUFA) ratio shifted in a pro-inflammatory direction after ACLT, already observed 2 weeks after the operation (0.20 ± 0.008 vs. 0.18 ± 0.009). At 8 weeks, the FA profile of the ACLT group was characterized with increased percentages of 20:4n-6 (0.44 ± 0.064 vs. 0.98 ± 0.339 mol-%) and 22:6n-3 (0.03 ± 0.014 vs. 0.07 ± 0.015 mol-%) and with decreased monounsaturated FA (MUFA) sums (37.19 ± 1.586 vs. 33.20 ± 1.068 mol-%) and n-3/n-6 PUFA ratios (0.20 ± 0.008 vs. 0.17 ± 0.008). The FA signature of the contralateral knees resembled that of the unoperated controls in most aspects, but had increased proportions of total n-3 PUFA and reduced MUFA sums. Conclusions These findings provide novel information on the effects of early OA on the infrapatellar FA profile in the rabbit ACLT model. The reduction in the n-3/n-6 PUFA ratio of the IFP is in concordance with the inflammation and cartilage degradation in early OA and could contribute to disease pathogenesis.
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    Are titin properties reflected in single myofibrils?
    (Journal of Biomechanics, 2012-07-26) Herzog, Jens A.; Leonard, Timothy R.; Jinha, Azim; Herzog, Walter
    Titin is a structural protein in muscle that spans the half sarcomere from Z-band to M-line. Although there are selected studies on titin's mechanical properties from tests on isolated molecules or titin fragments, little is known about its behavior within the structural confines of a sarcomere. Here, we tested the hypothesis that titin properties might be reflected well in single myofibrils. Single myofibrils from rabbit psoas were prepared for measurement of passive stretch-shortening cycles at lengths where passive titin forces occur. Three repeat stretch-shortening cycles with magnitudes between 1.0 and 3.0μm/sarcomere were performed at a speed of 0.1μm/s·sarcomere and repeated after a ten minute rest at zero force. These tests were performed in a relaxation solution (passive) and an activation solution (active) where cross-bridge attachment was inhibited with 2,3 butanedionemonoxime. Myofibrils behaved viscoelastically producing an increased efficiency with repeat stretch-shortening cycles, but a decreased efficiency with increasing stretch magnitudes. Furthermore, we observed a first distinct inflection point in the force-elongation curve at an average sarcomere length of 3.5μm that was associated with an average force of 68±5nN/mm. This inflection point was thought to reflect the onset of Ig domain unfolding and was missing after a ten minute rest at zero force, suggesting a lack of spontaneous Ig domain refolding. These passive myofibrillar properties observed here are consistent with those observed in isolated titin molecules, suggesting that the mechanics of titin are well preserved in isolated myofibrils, and thus, can be studied readily in myofibrils, rather than in the extremely difficult and labile single titin preparations.
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    Association of Metabolic Markers with self-reported osteoarthritis among middle-aged BMI-defined non-obese individuals: a cross-sectional study
    (2018-09-03) Collins, Kelsey H; Sharif, Behnam; Reimer, Raylene A; Sanmartin, Claudia; Herzog, Walter; Chin, Rick; Marshall, Deborah A
    Abstract Background Osteoarthritis (OA) is a chronic degenerative joint disease. While it is well-established that obesity affects OA through increased axial loading on the joint cartilage, the indirect effect of obesity through metabolic processes among the body mass index (BMI)-defined non-obese population, i.e., BMI < 30 kg/m2, is less known. Our goal was to evaluate the association of metabolic markers including body fat percentage (BF%), waist circumference, maximum weight gain during adulthood and serum creatinine with self-reported OA to establish if such measures offer additional information over BMI among the non-obese population between 40 and 65 years of age. Methods Cross-sectional data from two cycles of the Canadian Health Measures Survey (CHMS) in 2007–2009 and 2009–2011 were analyzed. Sex-specific logistic regression models were developed to evaluate the association of self-reported OA with metabolic markers. Models were separately adjusted for age, BMI categories and serum creatinine, and a stratified analysis across BM categories was performed. In a secondary analysis, we evaluated the association of self-reported OA, cardiovascular diseases and hypertension across BF% categories. Results Of 2462 individuals, 217 (8.8%) self-reported OA. After adjusting for age and BMI, those within BF%-defined overweight/obese category had 2.67 (95% CI: 1.32–3.51) and 2.11(95% CI: 1.38–3.21) times higher odds of reporting self-reported OA compared to those within BF%-defined athletic/acceptable category for females and males, respectively. BF% was also significantly associated with self-reported OA after adjusting for age and serum creatinine only among females (OR: 1.47, 95%CI: 1.12–1.84). Furthermore, among the BMI-defined overweight group, the age-adjusted odds of self-reported OA was significantly higher for overweight/obese BF% compared to athletic/acceptable BF% in both females and males. In a secondary analysis, we showed that the association of self-reported OA and hypertension/cardiovascular diseases is significantly higher among BF% overweight/obese (OR: 1.37, 95%CI: 1.19–3.09) compared to BF% athletic/acceptable (OR: 1.13, 95%CI: 0.87–2.82). Conclusion Our results provide corroborating evidence for a relationship between body fat and OA in a population-based study, while no significant independent correlates were found between other metabolic markers and OA prevalence. Future investigation on the longitudinal relationship between BF and OA among this sub-population may inform targeted prevention opportunities.
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    Botulinum toxin and a new animal model of muscle weakness
    (2003) Longino, Peter David; Herzog, Walter
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    Calcium sensitivity of residual force enhancement in rabbit skinned fibers
    (American Journal of Physiology, 2014-08-15) Joumaa, Venus; Herzog, Walter
    Isometric force after active stretch of muscles is higher than the purely isometric force at the corresponding length. This property is termed residual force enhancement. Active force in skeletal muscle depends on calcium attachment characteristics to the regulatory proteins. Passive force has been shown to influence calcium attachment characteristics, specifically the sarcomere length dependence of calcium sensitivity. Since one of the mechanisms proposed to explain residual force enhancement is the increase in passive force that results from engagement of titin upon activation and stretch, our aim was to test if calcium sensitivity of residual force enhancement was different from that of its corresponding purely isometric contraction and if such a difference was related to the molecular spring titin. Force-pCa curves were established in rabbit psoas skinned fibers for reference and residual force-enhanced states at a sarcomere length of 3.0 μm 1) in a titin-intact condition, 2) after treatment with trypsin to partially eliminate titin, and 3) after treatment with trypsin and osmotic compression with dextran T-500 to decrease the lattice spacing in the absence of titin. The force-pCa curves of residual force enhancement were shifted to the left compared with their corresponding controls in titin-intact fibers, indicating increased calcium sensitivity. No difference in calcium sensitivity was observed between reference and residual force-enhanced contractions in trypsin-treated and osmotically compressed trypsin-treated fibers. Furthermore, calcium sensitivity after osmotic compression was lower than that observed for residual force enhancement in titin-intact skinned fibers. These results suggest that titin-based passive force regulates the increase in calcium sensitivity of residual force enhancement by a mechanism other than reduction of the myofilament lattice spacing.
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    Cartilage and chondrocyte response to extreme muscular loading and impact loading: Can in vivo pre-load decrease impact-induced cell death?
    (Elsevier, 2015-07) Bourne, Douglas A.; Moo, Engkuan; Herzog, Walter
    Impact loading causes cartilage damage and cell death. Pre-loading prior to impact loading may protect cartilage and chondrocytes. However, there is no systematic evidence and understanding of the effects of pre-load strategies on cartilage damage and chondrocyte death. This study aimed at determining the effects of the pre-load history on impact-induced chondrocyte death in an intact joint.
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