Kinesiology Research & Publications
Permanent URI for this collection
Browse
Browsing Kinesiology Research & Publications by Department "Human Performance Laboratory"
Now showing 1 - 16 of 16
Results Per Page
Sort Options
Item Open Access Age-related Maintenance of Eccentric Strength: A Study of Temperature Dependence(University of Guelph, 2016-06) Herzog, Walter; Power, Geoffrey Alonzo; Dalton, Brian; Flaaten, NordanWith 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.Item Open Access Computing Average Passive Forces in Sarcomeres in Length-Ramp Simulations(PLOS Computational Biology, 2016-06) Herzog, Walter; Schnappacher-Tilp, Gudrun; Leonard, Timothy; Desch, GertrudPassive forces in sarcomeres are mainly related to the giant protein titin. Titin’s extensible region consists of spring-like elements acting in series. In skeletal muscles these elements are the PEVK segment, two distinct immunoglobulin (Ig) domain regions (proximal and distal), and a N2A portion. While distal Ig domains are thought to form inextensible end filaments in intact sarcomeres, proximal Ig domains unfold in a force- and time-dependent manner. In length-ramp experiments of single titin strands, sequential unfolding of Ig domains leads to a typical saw-tooth pattern in force-elongation curves which can be simulated by Monte Carlo simulations. In sarcomeres, where more than a thousand titin strands are arranged in parallel, numerous Monte Carlo simulations are required to estimate the resultant force of all titin filaments based on the non-uniform titin elongations. To simplify calculations, the stochastic model of passive forces is often replaced by linear or non-linear deterministic and phenomenological functions. However, new theories of muscle contraction are based on the hypothesized binding of titin to the actin filament upon activation, and thereby on a prominent role of the structural properties of titin. Therefore, these theories necessitate a detailed analysis of titin forces in ength-ramp experiments. In our study we present a simple and efficient alternative to Monte Carlo simulations. Based on a structural titin model, we calculate the exact probability distributions of unfolded Ig domains under length-ramp conditions needed for rigorous analysis of expected forces, distribution of unfolding forces, etc. Due to the generality of our model, the approach is applicable to a wide range of stochastic protein unfolding problems.Item Open Access A Cross-Bridge Based Model of Force Depression: Can a Single Modification Address both Transient and Steady-State Behaviours?(Elsevier, 2016-01) Herzog, Walter; Corr, David T.Force depression (FD), the reduction of isometric force following active shortening, is a phenomenon of skeletal muscle that has received significant attention in biomechanical and physiological literature, yet the mechanisms underlying FD remain unknown. Recent experiments identified a slower rate of force redevelopment with increasing amounts of steady-state FD, suggesting that FD may be caused, at least in part, by a decrease in cross-bridge binding rate (Corr and Herzog, 2005; Koppes et al., 2014). Herein, we develop a cross-bridge based model of FD in which the binding rate function, f, decreases with the mechanical work performed during shortening. This modification incorporates a direct relationship between steady-state FD and muscle mechanical work (Corr and Herzog, 2005; Herzog et al., 2000; Kosterina et al., 2008), and is consistent with a proposed mechanism attributing FD to stress-induced inhibition of cross-bridge attachments (Herzog, 1998; Maréchal and Plaghki, 1979). Thus, for an increase in mechanical work, the model should predict a slower force redevelopment (decreased attachment rate) to a more depressed steady-state force (fewer attached cross-bridges), and a reduction in contractile element stiffness (Ford et al., 1981). We hypothesized that since this modification affects the cross-bridge kinetics, a corresponding model would be able to account for both transient and steady-state FD behaviors. Comparisons to prior experiments (Corr and Herzog, 2005; Herzog et al., 2000; Kosterina et al., 2008) show that both steady-state and transient aspects of FD, as well as the relationship of FD with respect to speed and amplitude of shortening, are well captured by this model. Thus, this relatively simple cross-bridge based model of FD lends support to a mechanism involving the inhibition of cross-bridge binding, and indicates that cross-bridge kinetics may play a critical role in FD.Item Open Access The effect of compressive loading magnitude on in situ chondrocyte calcium signaling(Biomech Model Mechanobiol, 2014-05) Herzog, Walter; Madden, Ryan M.J.; Han, Sang-KuyChondrocyte metabolism is stimulated by deformation and is associated with structural changes in the cartilage extracellular matrix (ECM), suggesting that these cells are involved in maintaining tissue health and integrity. Calcium signaling is an initial step in chondrocyte mechanotransduction that has been linked tomany cellular processes. Previous studies using isolated chondrocytes proposed loading magnitude as an important factor regulating this response. However, calcium signaling in the intact cartilage differs compared to isolated cells. The purpose of this study was to investigate the effect of loading magnitude on chondrocyte calcium signaling in intact cartilage. We hypothesized that the percentage of cells exhibiting at least one calcium signal increases with increasing load. Fully intact rabbit femoral condyle and patellar bone/cartilage samples were incubated in calcium-sensitive dyes and imaged continuously under compressive loads of 10–40% strain. Calcium signaling was primarily associated with the dynamic loading phase and greatly increased beyond a threshold deformation of about 10%nominal tissue strain. There was a trend toward more cells exhibiting calcium signaling as loading magnitude increased (p =0.133). These results provide novel information toward identifying mechanisms underlying calcium-dependent signaling pathways related to cartilage homeostasis and possibly the onset and progression of osteoarthritis.Item Open Access High-Fat High-Sucrose Diet Leads to Dynamic Structural and Inflammatory Alterations in the Rat Vastus Lateralis Muscle(Journal of Orthopaedic Research, 2016) Herzog, Walter; Collins, Kelsey; Hart, David A.; Reimer, Raylene A.; Seerattan, Ruth A.; Banker, Christine W.; Sibole, Scott C.The influence of obesity on muscle integrity is not well understood. The purpose of this study 37 was to quantify structural and molecular changes in the rat vastus lateralis (VL) muscle as a 38 function of a 12-week obesity induction period and a subsequent adaptation period (additional 39 16-weeks). Male Sprague-Dawley rats consumed a high-fat, high-sucrose (DIO, n=40) diet or a 40 chow control-diet (n=14). At 12-weeks, DIO rats were grouped as prone (DIO-P, top 33% of 41 weight change) or resistant (DIO-R, bottom 33%). Animals were euthanized at 12-weeks or 28-42 weeks on the diet. At sacrifice, body composition was determined and VL muscles were 43 collected. Intramuscular fat, fibrosis, and CD68+ cells were quantified histologically and 44 relevant molecular markers were evaluated using RT-qPCR. At 12- and 28-weeks post obesity 45 induction, DIO-P rats had more mass and body fat than DIO-R and chow rats (p<0.05). DIO-P 46 and DIO-R rats had similar losses in muscle mass, which were greater than those in chow rats 47 (p<0.05). mRNA levels for MAFbx/atrogin1 were reduced in DIO-P and DIO-R rats at 12- and 48 28-weeks compared to chow rats (p<0.05), while expression of MURF was similar to chow 49 values. DIO-P rats demonstrated increased mRNA levels for pro-inflammatory mediators, 50 inflammatory cells, and fibrosis compared to DIO-R and chow animals, despite having similar 51 levels of intramuscular fat. The down-regulation of MAFbx/atrogin1 may suggest onset of 52 degenerative changes in VL muscle integrity of obese rats. DIO-R animals exhibited fewer 53 inflammatory changes compared to DIO-P animals, suggesting a protective effect of obesity 54 resistance on local inflammation.Item Open Access In vivo Sarcomere Lengths and Sarcomere Elongations Are Not Uniform across an Intact Muscle(Frontiers in Physiology, 2016-05) Herzog, Walter; Moo, Eng Kuan; Fortuna, Rafael; Sibole, Scott C.; Abusara, ZiadSarcomere lengths have been a crucial outcome measure for understanding and explaining basic muscle properties and muscle function. Sarcomere lengths for a given muscle are typically measured at a single spot, often in the mid-belly of the muscle, and at a given muscle length. It is then assumed implicitly that the sarcomere length measured at this single spot represents the sarcomere lengths at other locations within the muscle, and force-length, force-velocity, and power-velocity properties of muscles are often implied based on these single sarcomere length measurements. Although, intuitively appealing, this assumption is yet to be supported by systematic evidence. The objective of this study was to measure sarcomere lengths at defined locations along and across an intact muscle, at different muscle lengths. Using second harmonic generation (SHG) imaging technique, sarcomere patterns in passive mouse tibialis anterior (TA) were imaged in a non-contact manner at five selected locations (“proximal,” “distal,” “middle,” “medial,” and “lateral” TA sites) and at three different lengths encompassing the anatomical range of motion of the TA. We showed that sarcomere lengths varied substantially within small regions of the muscle and also for different sites across the entire TA. Also, sarcomere elongations with muscle lengthening were non-uniform across the muscle, with the highest sarcomere stretches occurring near the myotendinous junction. We conclude that muscle mechanics derived from sarcomere length measured from a small region of a muscle may not well-represent the sarcomere length and associated functional properties of the entire muscle.Item Open Access Letter to the editor regarding Cornachione et al. (2015)(American Journal of Physiology - Cell, 2016) Herzog, WalterIn their recent paper (Cornachione et al., 2015), Cornachione et al. draw three major conclusions: 1) that cardiac myofibrils do not show static tension or residual force enhancement; 2) that static tension/residual force enhancement is directly related to titin isoforms; and 3) that static tension/residual force enhancement is not associated with titin-actin interactions.Item Open Access Lower Limb Asymmetry in Mechanical Muscle Function: A Comparison Between Ski Racers With and Without ACL Reconstruction(Scandinavian Journal of Medicine and Science in Sports, 2016) Herzog, Walter; Jordan, Matthew; Aagaard, PerDue to a high incidence of anterior cruciate ligament (ACL) re-injury in alpine ski racers, the aim was to assess functional asymmetry in the countermovement jump (CMJ), squat jump (SJ) and leg muscle mass in elite ski racers with and without anterior cruciate ligament reconstruction (ACL-R). Elite alpine skiers with ACL-R (n=9; 26.2±11.8 months post-op) and uninjured skiers (n=9) participated in neuromuscular screening. Vertical ground reaction force during the CMJ and SJ was assessed using dual force plate methodology to obtain phase-specific bilateral asymmetry indices (AI) for kinetic impulse (CMJ and SJ phase-specific kinetic impulse AI). Dual X-Ray absorptiometry (DXA) scanning was used to assess asymmetry in lower body muscle mass. Compared to controls, ACL-R skiers had increased AI in muscle mass (P<0.001), kinetic impulse AI in the CMJ concentric phase (P<0.05) and the final phase of the SJ (P<0.05). Positive associations were observed between muscle mass and AI in the CMJ concentric phase (r=0.57, P<0.01) as well as in the late SJ phase (r=0.66, P<0.01). Future research is required to assess the role of the CMJ and SJ phase-specific kinetic impulse asymmetry index as a part of a multi-faceted approach for improving outcome following ACL-R in elite ski racers.Item Open Access A new paradigm for muscle contraction(Frontiers in Physiology, 2015-06-10) Herzog, Walter; Powers, Krysta; Johnston, Kaleena; Duvall, MikeMuscle contraction has fascinated lay people and scientists for centuries. However, a good understanding of how muscle contraction occurs seemed only possible once microscopy techniques had evolved to a level where basic structural features, such as the regular cross striation patterns of fibers, could be observed in the late 19th century. In the early 20th century, a stimulated muscle was simply considered a new elastic body (Gasser and Hill,1924). Shortening and work production took place with a fixed amount of energy tha twas stored in this body and evolved elastically through stimulation. However, this notion was proven false when Wallace Fenn demonstrated that muscle produced an increasing amount of total energy when increasing its mechanical work output; an observation that was in contradiction with Hill’s elastic body theory (Fenn, 1923,1924). Specifically, Fenn, who worked in the laboratory of Hill and measured heat and work production in frog muscles, found that a muscle allowed to shorten liberated more energy than a muscle held isometrically or a muscle that was stretched. This has become known as the Fenn effect in muscle physiology.Item Open Access Rapid Hamstring/Quadriceps Strength in ACL Reconstructed Elite Alpine Ski Racers(Medicine and science in sports and exercise, 2016) Herzog, Walter; Jordan, Matthew; Aagaard, PerDue to the importance of hamstrings (HAM) and quadriceps (QUAD) strength for anterior cruciate ligament (ACL) injury prevention, and the high incidence of ACL injury in ski racing, HAM and QUAD maximal and explosive strength was assessed in ski racers with and without ACL reconstruction (ACL-R).Item Open Access Relationship between inflammation, the gut microbiota, and metabolic osteoarthritis development: studies in a rat model(2016) Herzog, Walter; Collins, Kelsey H; Paul, Heather A; Reimer, Raylene A; Seerattan, Ruth A; Hart, David AWestern-type diets, high in fat and sugars, lead to obesity. Obesity in turn is associated with chronic inflammation, and thought to be a risk factor for the onset and increased rate of progression of metabolic osteoarthritis (OA) in joints. Emerging evidence suggests that intrinsic inflammatory mediators secreted by body fat, or adipose tissue, including cytokines, adipokines, and advanced glycation end products, may be sufficient to lead to onset and progression of OA. It appears that these obesity-associated, intrinsic inflammatory factors define a metabolic subtype of osteoarthritis. Characterizing the factors that comprise this unhealthy metabolic phenotype is critical to understanding the influence of obesity on OA. Furthermore, establishing the “indirect” role of the microbiota and the gut is required to fully understand the initiators and drivers of metabolic OA.Item Open Access Response to Diet-Induced Obesity Produces Time-dependent Induction and Progression of Metabolic Osteoarthritis in Rat Knees(Journal of Orthopaedic Research, 2016) Herzog, Walter; Collins, Kelsey; Hart, David A,; Reimer, Raylene A.; Seerattan, Ruth A.Obesity, and corresponding chronic-low grade inflammation, is associated with the onset and progression of knee OA. The origin of this inflammation is poorly understood. Here, the effect of high fat, high sucrose (HFS) diet induced obesity (DIO) on local (synovial fluid) and systemic (serum) inflammation is evaluated after a 12-week obesity induction and a further 16-week adaptation period. For 12-weeks of obesity induction, n=40 DIO male Sprague-Dawley rats consumed a HFS diet while the control group (n=14) remained on chow. DIO rats were allocated to prone (DIO-P, top 33% based on weight change) or resistant (DIO-R, bottom 33%) groups at 12-weeks. Animals were euthanized at 12- and after an additional 16-weeks on diet (28-weeks). At sacrifice, body composition and knee joints were collected and assessed. Synovial fluid and sera were profiled using cytokine array analysis. At 12-weeks, DIO-P animals demonstrated increased Modified Mankin Scores compared to DIO-R and Chow (p=0.026), and DIO-R had higher Mankin scores compared to Chow (p=0.049). While numerous systemic and limited synovial fluid inflammatory markers were increased at 12-weeks in DIO animals compared to Chow, by 28-weeks there were limited systemic differences but marked increases in local synovial fluid inflammatory marker concentrations. Metabolic OA may manifest from an initial systemic inflammatory disturbance. 12-weeks of obesity induction leads to a unique inflammatory profile and induction of metabolic OA which is altered after a further 16-weeks of obesity and HFS diet intake, suggesting that obesity is a dynamic, progressive process.Item Open Access A Return to Skiing Envelope of Function for Anterior Cruciate Ligament Reconstructed Elite Alpine Ski Racers(Science and Skiing VI, 2016) Herzog, Walter; Jordan, Matthew; Aagaard, PerElite alpine ski racing comprises bidirectional turning with forceful concentric but predominantly eccentric contractions that create large quadriceps muscle loading and hamstrings/quadriceps muscle co-contraction (4, 10). Ski racing also occurs in an unpredictable environment where skiers are at an increased risk for lower body injury, especially to the knee joint and the anterior cruciate ligament (ACL) (2, 3, 8, 15). Unlike field sports, there are no sex-differences in ACL injury rates due to the preclusion of sex-related risk factors resulting from the large forces and unique mechanisms of ACL injury (8, 15).Item Open Access The stretch-shortening cycle (SSC) revisited: residual force enhancement contributes to increased performance during fast SSCs of human m. adductor pollicis(Physiological Reports, 2015) Herzog, Walter; Seiberl, Wolfgang; Power, Geoffrey A.; Hahn, DanielThe stretch-shortening cycle (SSC) occurs in most everyday movements, and is thought to provoke a performance enhancement of the musculoskeletal system. However, mechanisms of this performance enhancement remain a matter of debate. One proposed mechanism is associated with a stretch-induced increase in steady-state force, referred to as residual force enhancement (RFE). As yet, direct evidence relating RFE to increased force/work during SSCs is missing. Therefore, forces of electrically stimulated m. adductor pollicis (n = 14 subjects) were measured during and after pure stretch, pure shortening, and stretch-shortening contractions with varying shortening amplitudes. Active stretch (30°, x = 161 6°s 1) caused significant RFE (16%, P < 0.01), whereas active shortening (10°, 20°, and 30°; x = 103 3°s 1, 152 5°s 1, and 170 5°s 1) resulted in significant force depression (9–15%, P < 0.01). In contrast, after SSCs (that is when active stretch preceded active shortening) no force depression was found. Indeed for our specific case in which the shortening amplitude was only 1/3 of the lengthening amplitude, there was a remnant RFE (10%, P < 0.01) following the active shortening. This result indicates that the RFE generated during lengthening affected force depression when active lengthening was followed by active shortening. As conventional explanations, such as the storage and release of elastic energy, cannot explain the enhanced steady-state force after SSCs, it appears that the stretch-induced RFE is not immediately abolished during shortening and contributes to the increased force and work during SSCs.Item Open Access Unfolding of membrane ruffles of in situ chondrocytes under compressive loads(Journal of Orthopaedic Research, 2016) Herzog, Walter; Moo, Eng KuanImpact loading results in chondrocyte death. Previous studies implicated high tensile strain rates in chondrocyte membranes as the cause of impact-induced cell deaths. However, this hypothesis relies on the untested assumption that chondrocyte membranes unfold in vivo during physiological tissue compression, but do not unfold during impact loading. Although membrane unfolding has been observed in isolated chondrocytes during osmotically induced swelling and mechanical compression, it is not known if membrane unfolding also occurs in chondrocytes embedded in their natural extracellular matrix. This study was aimed at quantifying changes in membrane morphology of in situ superficial zone chondrocytes during slow physiological cartilage compression.Item Open Access Vastus Lateralis Maximum Force-Generating Potential Occurs at Optimal Fascicle Length Regardless of Activation Level(2016) Herzog, Walter; de Brito Fontana, HeilianeDespite the fact that everyday movements are hardly ever performed with muscles contracting maximally, our understanding of the force-length relationship is mostly based on in vitro studies using maximal activation. In this study, the in vivo submaximal and maximal force-length relationships of vastus-lateralis were investigated. Force-length relationships were obtained based on maximal and submaximal levels of force and, also, onEMG activation.