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Force Production (force + production)
Selected AbstractsEffects of supra-physiological changes in human ovarian hormone levels on maximum force production of the first dorsal interosseus muscleEXPERIMENTAL PHYSIOLOGY, Issue 2 2005Kirsty Jayne Elliott The purpose of this study was to investigate the effects of supra-physiological changes in ovarian hormone levels on maximum force production in two conditions, one physiological (pregnancy) and one pseudo-physiological (in vitro fertilization (IVF) treatment). Forty IVF patients were tested at four distinct stages of treatment and 35 women were tested during each trimester of pregnancy and following parturition. Maximum voluntary isometric force per unit cross-sectional area of the first dorsal interosseus muscle was measured. Plasma concentrations of total and bioavailable oestradiol and testosterone were measured, in addition to the total concentrations of progesterone and human chorionic gonadotropin. Despite significant changes in the concentrations of total progesterone, 17,-oestradiol, bioavailable oestradiol and testosterone between phases, strength did not change significantly throughout IVF treatment (1.30 ± 0.29, 1.16 ± 0.38, 1.20 ± 0.29 and 1.26 ± 0.34 N mm,2, respectively, in the 4 phases of IVF treatment). Force production was significantly higher during the second trimester of pregnancy than following childbirth (1.33 ± 0.20 N mm,2 at week 12 of pregnancy, 1.51 ± 0.42 N mm,2 at week 20, 1.15 ± 0.26 N mm,2 at week 36 and 0.94 ± 0.31 N mm,2 at week 6 postnatal) but was not significantly correlated with any of the hormones measured. These data suggest that extreme changes in the concentrations of reproductive hormones do not affect the maximum force-generating capacity of young women. [source] The decrease in electrically evoked force production is delayed by a previous bout of stretch,shortening cycle exerciseACTA PHYSIOLOGICA, Issue 1 2010S. Kamandulis Abstract Aim:, Unaccustomed physical exercise with a large eccentric component is accompanied by muscle damage and impaired contractile function, especially at low stimulation frequencies. A repeated bout of eccentric exercise results in less damage and improved recovery of contractile function. Here we test the hypotheses that (1) a prior stretch,shortening cycle (SSC) exercise protects against impaired muscle function during a subsequent bout of SSC exercise and (2) the protection during exercise is transient and becomes less effective as the exercise progresses. Methods:, Healthy untrained men (n = 7) performed SSC exercise consisting of 100 maximal drop jumps at 30 s intervals. The same exercise was repeated 4 weeks later. Peak quadriceps muscle force evoked by electrical stimulation at 15 (P15) and 50 (P50) Hz was measured before exercise, after 10, 25, 50 and 100 jumps as well as 1 and 24 h after exercise. Results:, P15 and P50 were higher during the initial phase of the repeated bout compared with the first exercise bout, but there was no difference between the bouts at the end of the exercise periods. P15 and P50 were again larger 24 h after the repeated bout. The P15/P50 ratio during exercise was not different between the two bouts, but it was higher after the repeated bout. Conclusion:, A prior bout of SSC exercise temporarily protects against impaired contractile function during a repeated exercise bout. The protection can again be seen after exercise, but the underlying mechanism then seems to be different. [source] The effect of number of lengthening contractions on rat isometric force production at different frequencies of nerve stimulationACTA PHYSIOLOGICA, Issue 3 2009M. E. T. Willems Abstract Aim:, To test the effect of 3, 10, 60 and 240 lengthening contractions (LC) on maximal isometric force of rat plantar flexor muscles at different stimulation frequencies. Methods:, Using a dynamometer and electrical nerve stimulation, maximally active skeletal muscles were stretched by ankle rotation to produce LC of the plantar flexor muscles in intact female rats. After the lengthening contraction protocols, maximal isometric force was measured at different frequencies of nerve activation to obtain frequency-dependent force deficits (weakness). Results:, The magnitude of the force deficit, measured 1 h after the protocols at 80 Hz, increased as a function of repetition number (three LC, 33.3 ± 1.7%; 10 LC, 37.2 ± 2.3%; 60 LC, 67.6 ± 1.5%; 240 LC, 77.7 ± 1.2%). Force deficits were also measured at each stimulation frequency tested (5:120 Hz). Using a ratio of isometric force at 20:100 Hz stimulation, the relative depression of force at low frequency was determined. The relative depression of isometric force at low frequency was most prominent during the early repetitions. Conclusion:, As low-frequency force depression appears to result primarily from excitation,contraction (E,C) coupling failure, the early LC in a series of repeated contractions probably contribute most to damage of the cellular components involved in E,C coupling. [source] Androgen replacement therapy improves function in male rat muscles independently of hypertrophy and activation of the Akt/mTOR pathwayACTA PHYSIOLOGICA, Issue 4 2009C. Hourdé Abstract Aim:, We analysed the effect of physiological doses of androgens following orchidectomy on skeletal muscle and bone of male rats, as well as the relationships between muscle performance, hypertrophy and the Akt/mammalian target of rapamycin (mTOR) signalling pathway involved in the control of anabolic and catabolic muscle metabolism. Methods:, We studied the soleus muscle and tibia from intact rats (SHAM), orchidectomized rats treated for 3 months with vehicle (ORX), nandrolone decanoate (NAN) or dihydrotestosterone (DHT). Results:, Orchidectomy had very little effect on the soleus muscle. However, maximal force production by soleus muscle (+69%) and fatigue resistance (+35%) in NAN rats were both increased when compared with ORX rats. In contrast, DHT treatment did not improve muscle function. The relative number of muscle fibres expressing slow myosin heavy chain and citrate synthase activity were not different in NAN and ORX rats. Moreover, NAN and DHT treatments did not modify muscle weights and cross-sectional area of muscle fibres. Furthermore, phosphorylation levels of downstream targets of the Akt/mTOR signalling pathway, Akt, ribosomal protein S6 and eukaryotic initiation factor 4E-binding protein 1 were similar in muscles of NAN, DHT and ORX rats. In addition, trabecular tibia from NAN and DHT rats displayed higher bone mineral density and bone volume when compared with ORX rats. Only in NAN rats was this associated with increased bone resistance to fracture. Conclusion:, Physiological doses of androgens are beneficial to muscle performance in orchidectomized rats without relationship to muscle and fibre hypertrophy and activation of the Akt/mTOR signalling pathway. Taken together our data clearly indicate that the activity of androgens on muscle and bone could participate in the global improvement of musculoskeletal status in the context of androgen deprivation induced by ageing. [source] Metabolic cost of lengthening, isometric and shortening contractions in maximally stimulated rat skeletal muscleACTA PHYSIOLOGICA, Issue 2 2004J. G. M. Beltman Abstract Aim:, The present study investigated the energy cost of lengthening, isometric and shortening contractions in rat muscle (n = 19). Methods:, With electrical stimulation the rat medial gastrocnemius muscle was maximally stimulated to perform 10 lengthening, isometric and shortening contractions (velocity 25 mm s,1) under experimental conditions (e.g. temperature, movement velocity) that resemble conditions in human movement. Results:, Mean ± SD force,time-integral of the first contraction was significantly different between the three protocols, 2.4 ± 0.2, 1.7 ± 0.2 and 1.0 ± 0.2 N s, respectively (P < 0.05). High-energy phosphate consumption was not significantly different between the three modes of exercise but a trend could be observed from lengthening (7.7 ± 2.7 ,mol , P muscle,1) to isometric (8.9 ± 2.2 ,mol , P muscle,1) to shortening contractions (10.4 ± 1.6 ,mol , P muscle,1). The ratio of high-energy phosphate consumption to force,time-integral was significantly lower for lengthening [0.3 ± 0.1 ,mol , P (N s),1] and isometric [0.6 ± 0.2 ,mol , P (N s),1] contractions compared with shortening [1.2 ± 0.2 ,mol , P (N s),1] contractions (P < 0.05). Conclusion:, The present results of maximally stimulated muscles are comparable with data in the literature for voluntary human exercise showing that the energy cost of force production during lengthening exercise is ,30% of that in shortening exercise. The present study suggests that this finding in humans probably does reflect intrinsic muscle properties rather than effects of differential recruitment and/or coactivation. [source] Versatile fluorescent probes for actin filaments based on the actin-binding domain of utrophinCYTOSKELETON, Issue 11 2007Brian M. Burkel Abstract Actin filaments (F-actin) are protein polymers that undergo rapid assembly and disassembly and control an enormous variety of cellular processes ranging from force production to regulation of signal transduction. Consequently, imaging of F-actin has become an increasingly important goal for biologists seeking to understand how cells and tissues function. However, most of the available means for imaging F-actin in living cells suffer from one or more biological or experimental shortcomings. Here we describe fluorescent F-actin probes based on the calponin homology domain of utrophin (Utr-CH), which binds F-actin without stabilizing it in vitro. We show that these probes faithfully report the distribution of F-actin in living and fixed cells, distinguish between stable and dynamic F-actin, and have no obvious effects on processes that depend critically on the balance of actin assembly and disassembly. Cell Motil. Cytoskeleton 2007. © 2007 Wiley-Liss, Inc. [source] The ultrastructural distribution of prestin in outer hair cells: a post-embedding immunogold investigation of low-frequency and high-frequency regions of the rat cochleaEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2010Shanthini Mahendrasingam Abstract Outer hair cells (OHCs) of the mammalian cochlea besides being sensory receptors also generate force to amplify sound-induced displacements of the basilar membrane thus enhancing auditory sensitivity and frequency selectivity. This force generation is attributable to the voltage-dependent contractility of the OHCs underpinned by the motile protein, prestin. Prestin is located in the basolateral wall of OHCs and is thought to alter its conformation in response to changes in membrane potential. The precise ultrastructural distribution of prestin was determined using post-embedding immunogold labelling and the density of the labelling was compared in low-frequency and high-frequency regions of the cochlea. The labelling was confined to the basolateral plasma membrane in hearing rats but declined towards the base of the cells below the nucleus. In pre-hearing animals, prestin labelling was lower in the membrane and also occurred in the cytoplasm, presumably reflecting its production during development. The densities of labelling in low-frequency and high-frequency regions of the cochlea were similar. Non-linear capacitance, thought to reflect charge movements during conformational changes in prestin, was measured in OHCs in isolated cochlear coils of hearing animals. The OHC non-linear capacitance in the same regions assayed in the immunolabelling was also similar in both the apex and base, with charge densities of 10 000/,m2 expressed relative to the lateral membrane area. The results suggest that prestin density, and by implication force production, is similar in low-frequency and high-frequency OHCs. [source] Effect of anti-inflammatory and antioxidant drugs on the long-term repair of severely injured mouse skeletal muscleEXPERIMENTAL PHYSIOLOGY, Issue 4 2005A. Vignaud Non-steroidal anti-inflammatory drugs are frequently prescribed after skeletal muscle injury. It is not known whether this type of medication can interfere with muscle repair, although inflammatory response is thought to play an important role in this process. Tibialis anterior muscles of mice were injured by myotoxic agent (snake venom) or crushed. Then, animals were treated daily for 10,14 days with different types of non-steroidal anti-inflammatory and antioxidant drugs. The long-term repair was studied 10,42 days after injury by analysing the recovery of in situ muscle force production, size of regenerating muscle cells and expression of myosin heavy chain. Our results show that diclofenac, diferuloylmethane (curcumin), dimethylthiourea or pyrrolidine dithiocarbamate treatment did not significantly affect muscle recovery after myotoxic injury (P > 0.05). Similarly, diferuloylmethane, dimethyl sulphoxide or indomethacin administration did not markedly change muscle repair after crush injury. However, we noted that high doses (> 2 mg kg,1) of diferuloylmethane or indomethacin increased lethality and reduced muscle repair after crush injury. In conclusion, non-steroidal anti-inflammatory and antioxidant drugs did not exhibit long-term detrimental effects on muscle recovery after injury, except at lethal doses. [source] Effects of supra-physiological changes in human ovarian hormone levels on maximum force production of the first dorsal interosseus muscleEXPERIMENTAL PHYSIOLOGY, Issue 2 2005Kirsty Jayne Elliott The purpose of this study was to investigate the effects of supra-physiological changes in ovarian hormone levels on maximum force production in two conditions, one physiological (pregnancy) and one pseudo-physiological (in vitro fertilization (IVF) treatment). Forty IVF patients were tested at four distinct stages of treatment and 35 women were tested during each trimester of pregnancy and following parturition. Maximum voluntary isometric force per unit cross-sectional area of the first dorsal interosseus muscle was measured. Plasma concentrations of total and bioavailable oestradiol and testosterone were measured, in addition to the total concentrations of progesterone and human chorionic gonadotropin. Despite significant changes in the concentrations of total progesterone, 17,-oestradiol, bioavailable oestradiol and testosterone between phases, strength did not change significantly throughout IVF treatment (1.30 ± 0.29, 1.16 ± 0.38, 1.20 ± 0.29 and 1.26 ± 0.34 N mm,2, respectively, in the 4 phases of IVF treatment). Force production was significantly higher during the second trimester of pregnancy than following childbirth (1.33 ± 0.20 N mm,2 at week 12 of pregnancy, 1.51 ± 0.42 N mm,2 at week 20, 1.15 ± 0.26 N mm,2 at week 36 and 0.94 ± 0.31 N mm,2 at week 6 postnatal) but was not significantly correlated with any of the hormones measured. These data suggest that extreme changes in the concentrations of reproductive hormones do not affect the maximum force-generating capacity of young women. [source] Trimetazidine Reduces Basal Cytosolic Ca2+ Concentration During Hypoxia in Single Xenopus Skeletal MyocytesEXPERIMENTAL PHYSIOLOGY, Issue 3 2003C. M. Stary We tested the hypotheses that: (1) Ca2+ handling and force production would be irreversibly altered in skeletal muscle during steady-state contractions when subjected to severe, prolonged hypoxia and subsequent reoxygenation; and (2) application of the cardio-protective drug trimetazidine would attenuate these alterations. Single, living skeletal muscle fibres from Xenopus laevis were injected with the Ca2+ indicator fura 2, and incubated for 1 h prior to stimulation in 100 ,M TMZ-Ringer solution (TMZ; n = 6) or standard Ringer solution (CON; n = 6). Force and relative free cytosolic Ca2+ concentration ([Ca2+]c) were measured during continuous tetanic contractions produced every 5 s as fibres were sequentially perfused in the following manner: 3 min high extracellular PO2 (159 mmHg), 15 min hypoxic perfusion (3-5 mmHg) then 3 min high PO2. Hypoxia caused a decrease in force and peak [Ca2+]c in both the TMZ and CON fibres, with no significant (P < 0.05) difference between groups. However, basal [Ca2+]c was significantly lower during hypoxia in the TMZ group vs. the CON group. While reoxygenation generated only modest recovery of relative force and peak [Ca2+]c in both groups, basal [Ca2+]c remained significantly less in the TMZ group. These results demonstrated that in contracting, single skeletal muscle fibres, TMZ prevented increases in basal [Ca2+]c generated during a severe hypoxic insult and subsequent reoxygenation, yet failed to protect the cell from the deleterious effects of prolonged hypoxia followed by reoxygenation. [source] Numerical simulation of flapping-wing insect hovering flight at unsteady flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2007Decan Zuo Abstract A computational fluid dynamics (CFD) analysis was conducted to study the unsteady aerodynamics of a virtual flying bumblebee during hovering flight. The integrated geometry of bumblebee was established to define the shape of a three-dimensional virtual bumblebee model with beating its wings, accurately mimicking the three-dimensional movements of wings during hovering flight. The kinematics data of wings documented from the measurement to the bumblebee in normal hovering flight aided by the high-speed video. The Navier,Stokes equations are solved numerically. The solution provides the flow and pressure fields, from which the aerodynamic forces and vorticity wake structure are obtained. Insights into the unsteady aerodynamic force generation process are gained from the force and flow-structure information. The CFD analysis has established an overall understanding of the viscous and unsteady flow around the virtual flying bumblebee and of the time course of instantaneous force production, which reveals that hovering flight is dominated by the unsteady aerodynamics of both the instantaneous dynamics and also the past history of the wing. A coherent leading-edge vortex with axial flow and the attached wingtip vortex and trailing edge vortex were detected. The leading edge vortex, wing tip vortex and trailing edge vortex, which caused by the pressure difference between the upper and the lower surface of wings. The axial flow, which include the spanwise flow and chordwise flow, is derived from the spanwise pressure gradient and chordwise pressure gradient, will stabilize the vortex and gives it a characteristic spiral conical shape. Copyright © 2006 John Wiley & Sons, Ltd. [source] Myometrial mechanoadaptation during pregnancy: implications for smooth muscle plasticity and remodellingJOURNAL OF CELLULAR AND MOLECULAR MEDICINE, Issue 4 2008X. Wu Abstract The smooth muscle of the uterus during pregnancy presents a unique circumstance of physiological mechanotransduction as the tissue remodels in response to stretches imposed by the growing foetus(es), yet the nature of the molecular and functional adaptations remain unresolved. We studied, in myometrium isolated from non-pregnant (NP) and pregnant mice, the active and passive length,tension curves by myography and the expression and activation by immunoblotting of focal adhesion-related proteins known in other systems to participate in mechanosensing and mechanotransduction. In situ uterine mass correlated with pup number and weight throughout pregnancy. In vitro myometrial active, and passive, length-tension curves shifted significantly to the right during pregnancy indicative of altered mechanosensitivity; at term, maximum active tension was generated following 3.94 ± 0.33-fold stretch beyond slack length compared to 1.91 ± 0.12-fold for NP mice. Moreover, mechanotransduction was altered during pregnancy as evidenced by the progressive increase in absolute force production at each optimal stretch. Pregnancy was concomitantly associated with an increased expression of the dense plaque-associated proteins FAK and paxillin, and elevated activation of FAK, paxillin, c-Src and extracellular signal-regulated kinase (ERK1/2) which reversed 1 day post-partum. Electron microscopy revealed close appositioning of neighbouring myometrial cells across a narrow extracellular cleft adjoining plasmalemmal dense plaques. Collectively, these results suggest a physiological basis of myometrial length adaptation, long known to be a property of many smooth muscles, whereupon plasmalemmal dense plaque proteins serve as molecular signalling and structural platforms contributing to functional (contractile) remodelling in response to chronic stretch. [source] Mitochondrial function and apoptotic susceptibility in aging skeletal muscleAGING CELL, Issue 1 2008Béatrice Chabi Summary During aging, skeletal muscle undergoes sarcopenia, a condition characterized by a loss of muscle cell mass and alterations in contractile function. The origin of these decrements is unknown, but evidence suggests that they can be partly attributed to mitochondrial dysfunction. To characterize the nature of this dysfunction, we investigated skeletal muscle contractile properties, subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondrial biogenesis and function, as well as apoptotic susceptibility in young (6 months old) and senescent (36 months old) Fischer 344 Brown Norway rats. Muscle mass and maximal force production were significantly lower in the 36-month group, which is indicative of a sarcopenic phenotype. Furthermore, contractile activity in situ revealed greater fatigability in the 36-month compared to the 6-month animals. This decrement could be partially accounted for by a 30% lower mitochondrial content in fast-twitch muscle from 36-month animals, as well as lower protein levels of the transcriptional coactivator peroxisome proliferator-activated receptor , coactivator-1,. Enzyme activities and glutamate-induced oxygen consumption rates in isolated SS and IMF mitochondria were similar between age groups. However, mitochondrial reactive oxygen species (ROS) production during state 3 respiration was ~1.7-fold greater in mitochondria isolated from 36-month compared to 6-month animals, and was accompanied by a 1.8-fold increase in the DNA repair enzyme 8-oxoguanine glycosylase 1 in fast-twitch muscle. Basal rates of release of cytochrome c and endonuclease G in SS mitochondria were 3.5- to 7-fold higher from senescent animals. These data suggest that the age-related sarcopenia and muscle fatigability are associated with enhanced ROS production, increased mitochondrial apoptotic susceptibility and reduced transcriptional drive for mitochondrial biogenesis. [source] Comparative analysis of masseter fiber architecture in tree-gouging (Callithrix jacchus) and nongouging (Saguinus oedipus) callitrichidsJOURNAL OF MORPHOLOGY, Issue 3 2004Andrea B. Taylor Abstract Common marmosets (Callithrix jacchus) and cotton-top tamarins (Saguinus oedipus) (Callitrichidae, Primates) share a broadly similar diet of fruits, insects, and tree exudates. Common marmosets, however, differ from tamarins by actively gouging trees with their anterior teeth to elicit tree exudate flow. During tree gouging, marmosets produce relatively large jaw gapes, but do not necessarily produce relatively large bite forces at the anterior teeth. We compared the fiber architecture of the masseter muscle in tree-gouging Callithrix jacchus (n = 10) to nongouging Saguinus oedipus (n = 8) to determine whether the marmoset masseter facilitates producing these large gapes during tree gouging. We predict that the marmoset masseter has relatively longer fibers and, hence, greater potential muscle excursion (i.e., a greater range of motion through increased muscle stretch). Conversely, because of the expected trade-off between excursion and force production in muscle architecture, we predict that the cotton-top tamarin masseter has more pinnate fibers and increased physiological cross-sectional area (PCSA) as compared to common marmosets. Likewise, the S. oedipus masseter is predicted to have a greater proportion of tendon relative to muscle fiber as compared to the common marmoset masseter. Common marmosets have absolutely and relatively longer masseter fibers than cotton-top tamarins. Given that fiber length is directly proportional to muscle excursion and by extension contraction velocity, this result suggests that marmosets have masseters designed for relatively greater stretching and, hence, larger gapes. Conversely, the cotton-top tamarin masseter has a greater angle of pinnation (but not significantly so), larger PCSA, and higher proportion of tendon. The significantly larger PCSA in the tamarin masseter suggests that their masseter has relatively greater force production capabilities as compared to marmosets. Collectively, these results suggest that the fiber architecture of the common marmoset masseter is part of a suite of features of the masticatory apparatus that facilitates the production of relatively large gapes during tree gouging. J. Morphol. 261:276,285, 2004. © 2004 Wiley-Liss, Inc. [source] Functional properties and regional differences of human masseter motor units related to three-dimensional bite forceJOURNAL OF ORAL REHABILITATION, Issue 10 2006T. OGAWA summary, The aim of this study was to estimate numerically the properties of masseter motor units (MUs) in relation to bite force magnitude and direction three-dimensionally and to confirm the hypothesis that the properties differ between different parts of the muscle by means of simultaneous recording of MU activity along with the MU location and three-dimensional (3D) bite force. The MU activity of the right masseter of four healthy men was recorded using a monopolar needle electrode in combination with a surface reference electrode. The location of the needle electrode was estimated stereotactically with the aid of magnetic resonance images and a reference plate. The magnitude and direction of the bite force was recorded with a custom-made 3D bite force transducer. The recorded bite force was displayed on a signal processor, which enabled the participant to adjust the direction and magnitude of the force. The activities of 65 masseter MUs were recorded. Each MU had specific ranges of bite force magnitude and direction (firing range: FR) and an optimum direction for recruitment (minimum firing threshold: MFT). There was a significant negative correlation between MFT and FR width. There were functional differences in MU properties between the superficial and deep masseter and between the superficial layer and deep layer in the superficial masseter. These results indicate that the contribution of human masseter motor units to bite force production is heterogeneous within the muscle. [source] Evaluation of a novel biomaterial for intrasubstance muscle laceration repairJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 3 2007Bradley D. Crow Abstract The authors compare the effects of small intestinal submucosa (SIS) treatment to suture repair with respect to histologic and functional outcomes for complete muscle lacerations in a rabbit model. The authors hypothesized that SIS treatment of full-thickness muscle belly lacerations would significantly improve muscle function, strength, and regeneration compared to the current standard-of-care treatment. Muscle belly lacerations were created in the extensor digitorum longus (EDL) of both hind limbs of each rabbit. After randomization, lacerations were left unrepaired (n,=,48) or repaired using a 4-0 Prolene modified Kessler stitch (n,=,48). A flap of SIS graft was sutured into half (n,=,24 each) of the repaired and unrepaired muscles forming four study groups. Suture repair with SIS augmentation of complete muscle lacerations resulted in healed tissue that most closely resembled normal muscle in terms of morphology and function when compared to current standard-of-care treatments. Active force production in this group reached 79% of uninjured controls 12 weeks after surgery. SIS may have important clinical advantages over suture repair alone and warrants further clinical study. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 2007 [source] Action monitoring in motor control: ERPs following selection and execution errors in a force production taskPSYCHOPHYSIOLOGY, Issue 5 2003Ellen R. A. De Bruijn Abstract Action monitoring has been studied in many tasks by means of measuring the error-related negativity (Ne/ERN), but never in a motor control task requiring precise force production. Errors in discrete choice reaction tasks are the result of incorrect selections, but errors in force production can also arise from incorrect executions. ERPs were obtained while participants produced low or high isometric forces with their left or right hand. As expected, incorrect choices of hand elicited an Ne/ERN. Interestingly, Ne/ERNs were also present in the less discrete selection error of an incorrect choice of force, but only when erroneously a low instead of a high force was chosen. In both force ranges, no Ne/ERNs were found after errors in execution. These errors showed a large positivity in feedback ERPs and, similar to correct responses, a prolonged negativity in response ERPs. We propose that, compared to selection errors, the time uncertainty aspects of execution errors and the resulting changing response representations prohibit error detection by the internal monitoring system responsible for generating the Ne/ERN. [source] Functional Correlates of Fiber Architecture of the Lateral Caudal Musculature in Prehensile and Nonprehensile Tails of the Platyrrhini (Primates) and Procyonidae (Carnivora)THE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 6 2009Jason M. Organ Abstract Prehensile-tailed platyrrhines (atelines and Cebus) and procyonids (Potos) display bony tail features that have been functionally and adaptively linked to their prehensile behaviors, particularly the need to resist relatively greater bending and torsional stresses associated with supporting their body weight during suspensory postures. We compared fiber architecture of the mm. intertransversarii caudae (ITC), the prime tail lateral flexors/rotators, in 40 individuals distributed across 8 platyrrhine and 2 procyonid genera, divided into one of two groups: prehensile or nonprehensile. We tested the hypothesis that prehensile-tailed taxa exhibit relatively greater physiologic cross-sectional areas (PCSAs) to maintain tail suspensory postures for extended periods. As an architectural trade-off of maximizing force, we also predicted prehensile-tailed taxa would exhibit relatively shorter, more pinnate fibers, and a lower mass to tetanic tension ratio (Mass/PO). Prehensile-tailed taxa have relatively higher PCSAs in all tail regions, indicating their capacity to generate relatively greater maximum muscle forces compared to nonprehensile-tailed taxa. Contrary to our predictions, there are no group differences in pinnation angles, fiber lengths or M/PO ratios. Therefore, the relatively greater prehensile PCSAs are driven largely by relative increase in muscle mass. These findings suggest that relatively greater ITC PCSAs can be functionally linked to the need for prehensile-tailed taxa to suspend and support their body weight during arboreal behaviors. Moreover, maximizing ITC force production may not come at the expense of muscle excursion/contraction velocity. One advantage of this architectural configuration is it facilitates suspension of the body while simultaneously maximizing tail contact with the substrate. Anat Rec, 292:827,841, 2009. © 2009 Wiley-Liss, Inc. [source] Dihydrotestosterone activates the MAPK pathway and modulates maximum isometric force through the EGF receptor in isolated intact mouse skeletal muscle fibresTHE JOURNAL OF PHYSIOLOGY, Issue 3 2010M. M. Hamdi It is generally believed that steroid hormones have both genomic and non-genomic (rapid) actions. Although the latter form an important component of the physiological response of these hormones, little is known about the cellular signalling pathway(s) mediating these effects and their physiological functions in adult mammalian skeletal muscle fibres. Therefore, the primary aim of this study was to investigate the non-genomic actions of dihydrotestosterone (DHT) and their physiological role in isolated intact mammalian skeletal muscle fibre bundles. Our results show that treating the fibre bundles with physiological concentrations of DHT increases both twitch and tetanic contractions in fast twitch fibres. However, it decreases them in slow twitch fibres. These changes in force are accompanied by an increase in the phosphorylation of MAPK/ERK1/2 in both fibre types and that of regulatory myosin light chains in fast twitch fibres. Both effects were insensitive to inhibitors of Src kinase, androgen receptor, insulin-like growth factor 1 receptor and platelet-derived growth factor receptor. However, they were abolished by the MAPK/ERK1/2 kinase inhibitor PD98059 and the epidermal growth factor (EGF) receptor inhibitor tyrphostin AG 1478. In contrast, testosterone had no effect on force and increased the phosphorylation of ERK1/2 in slow twitch fibres only. From these results we conclude that sex steroids have non-genomic actions in isolated intact mammalian skeletal muscle fibres. These are mediated through the EGF receptor and one of their main physiological functions is the enhancement of force production in fast twitch skeletal muscle fibres. [source] Mechanisms of stretch-induced muscle damage in normal and dystrophic muscle: role of ionic changesTHE JOURNAL OF PHYSIOLOGY, Issue 3 2005D. G. Allen Muscle damage, characterized by prolonged weakness and delayed onset of stiffness and soreness, is common following contractions in which the muscles are stretched. Stretch-induced damage of this sort is more pronounced in the muscular dystrophies and the profound muscle damage observed in these conditions may involve similar pathways. It has been known for many years that damaged muscles accumulate calcium and that elevating calcium in normal muscles simulates many aspects of muscle damage. The changes in intracellular calcium, sodium and pH following stretched contractions are reviewed and the various pathways which have been proposed to allow ion entry are discussed. One possibility is that TRPC1 (transient receptor potential, canonical), a protein which seems to form both a stretch-activated channel and a store-operated channel, is the main source of Ca2+ entry. The mechanisms by which the changes in intracellular ions contribute to reduced force production, to increased protein breakdown and to increased membrane permeability are considered. A hypothetical scheme for muscle damage which incorporates these ideas is presented. [source] Central command and the cutaneous vascular response to isometric exercise in heated humansTHE JOURNAL OF PHYSIOLOGY, Issue 2 2005Manabu Shibasaki Cutaneous vascular conductance (CVC) decreases during isometric handgrip exercise in heat stressed individuals, and we hypothesized that central command is involved in this response. Seven subjects performed 2 min of isometric handgrip exercise (35% of maximal voluntary contraction) followed by postexercise ischaemia in normothermia and during heat stress (increase in internal temperature ,1°C). To augment the contribution of central command independent of force generation, on a separate day the protocol was repeated following partial neuromuscular blockade (PNB; i.v. cisatracurium). Forearm skin blood flow was measured by laser-Doppler flowmetry, and CVC was the ratio of skin blood flow to mean arterial pressure. The PNB attenuated force production despite encouragement to attain the same workload. During the heat stress trials, isometric exercise decreased CVC by ,12% for both conditions, but did not change CVC in either of the normothermic trials. During isometric exercise in the heat, the increase in mean arterial pressure (MAP) was greater during the control trial relative to the PNB trial (31.0 ± 9.8 versus 18.6 ± 6.4 mmHg, P < 0.01), while the elevation of heart rate tended to be lower (19.4 ± 10.4 versus 27.4 ± 8.1 b.p.m., P= 0.15). During postexercise ischaemia, CVC and MAP returned to pre-exercise levels in the PNB trial but remained reduced in the control trial. These findings suggest that central command, as well as muscle metabo-sensitive afferent stimulation, contributes to forearm cutaneous vascular responses in heat stressed humans. [source] Disruption of excitation,contraction coupling and titin by endogenous Ca2+ -activated proteases in toad muscle fibresTHE JOURNAL OF PHYSIOLOGY, Issue 3 2005Esther Verburg This study investigated the effects of elevated, physiological levels of intracellular free [Ca2+] on depolarization-induced force responses, and on passive and active force production by the contractile apparatus in mechanically skinned fibres of toad iliofibularis muscle. Excitation,contraction (EC) coupling was retained after skinning and force responses could be elicited by depolarization of the transverse-tubular (T-) system. Raising the cytoplasmic [Ca2+] to ,1 ,m or above for 3 min caused an irreversible reduction in the depolarization-induced force response by interrupting the coupling between the voltage sensors in the T-system and the Ca2+ release channels in the sarcoplasmic reticulum. This uncoupling showed a steep [Ca2+] dependency, with 50% uncoupling at ,1.9 ,m Ca2+. The uncoupling occurring with 2 ,m Ca2+ was largely prevented by the calpain inhibitor leupeptin (1 mm). Raising the cytoplasmic [Ca2+] above 1 ,m also caused an irreversible decline in passive force production in stretched skinned fibres in a manner graded by [Ca2+], though at a much slower relative rate than loss of coupling. The progressive loss of passive force could be rapidly stopped by lowering [Ca2+] to 10 nm, and was almost completely inhibited by 1 mm leupeptin but not by 10 ,m calpastatin. Muscle homogenates preactivated by Ca2+ exposure also evidently contained a diffusible factor that caused damage to passive force production in a Ca2+ -dependent manner. Western blotting showed that: (a) calpain-3 was present in the skinned fibres and was activated by the Ca2+exposure, and (b) the Ca2+ exposure in stretched skinned fibres resulted in proteolysis of titin. We conclude that the disruption of EC coupling occurring at elevated levels of [Ca2+] is likely to be caused at least in part by Ca2+ -activated proteases, most likely by calpain-3, though a role of calpain-1 is not excluded. [source] Reversible changes in Ca2+ -activation properties of rat skeletal muscle exposed to elevated physiological temperaturesTHE JOURNAL OF PHYSIOLOGY, Issue 3 2002Chris van der Poel Exposure of relaxed rat extensor digitorum longus (EDL; predominantly fast-twitch) muscle to temperatures in the upper physiological range for mammalian skeletal muscle (43-46 °C) led to reversible alterations of the contractile activation properties. These properties were studied using the mechanically skinned fibre preparation activated in Ca2+ -buffered solutions. The maximum Ca2+ -activated force (maximum force per cross-sectional area) and the steepness of force-pCa (-log10[Ca2+]) curves as measured by the Hill coefficient (nH) reversibly decreased by factors of 8 and 2.5, respectively, when the EDL muscle was treated at 43 °C for 30 min and 5 and 2.8, respectively, with treatment at 46 °C for 5 min. Treatment at 47 °C for 5 min produced an even more marked depression in maximum specific force, which fully recovered after treatment, and in the Hill coefficient, which did not recover after treatment. After all temperature treatments there was no change in the level of [Ca2+] at which 50 % maximum force was generated. The temperature-induced depression in force production and steepness of the force-pCa curves were shown to be associated with superoxide (O2,) production in muscle (apparent rate of O2, production at room temperature, 0.055 ± 0.008 nmol min,1 (g wet weight),1; and following treatment to 46 °C for 5 min, 1.8 ± 0.2 nmol min,1 (g wet weight),1) because 20 mm Tiron, a membrane-permeant O2, scavenger, was able to markedly suppress the net rate of O2, production and prevent any temperature-induced depression of contractile parameters. The temperature-induced depression in force production of the contractile apparatus could be reversed either by allowing the intact muscle to recover for 3-4 h at room temperature or by treatment of the skinned fibre preparation with dithiothreitol (a potent reducing agent) in the relaxing solution. These results demonstrate that mammalian skeletal muscle has the ability to uncouple force production reversibly from the activator Ca2+ as the temperature increases in the upper physiological range through an increase in O2, production. [source] Impaired myofibrillar function in the soleus muscle of mice with collagen-induced arthritisARTHRITIS & RHEUMATISM, Issue 11 2009Takashi Yamada Objective Progressive muscle weakness is a common feature in patients with rheumatoid arthritis (RA). However, little is known about whether the intrinsic contractile properties of muscle fibers are affected in RA. This study was undertaken to investigate muscle contractility and the myoplasmic free Ca2+ concentration ([Ca2+]i) in the soleus, a major postural muscle, in mice with collagen-induced arthritis (CIA). Methods Muscle contractility and [Ca2+]i were assessed in whole muscle and intact single-fiber preparations, respectively. The underlying mechanisms of contractile dysfunction were assessed by investigating redox modifications using Western blotting and antibodies against nitric oxide synthase (NOS), superoxide dismutase (SOD), 3-nitrotyrosine (3-NT), carbonyl, malondialdehyde (MDA), and S-nitrosocysteine (SNO-Cys). Results The tetanic force per cross-sectional area was markedly decreased in the soleus muscle of mice with CIA, and the change was not due to a decrease in the amplitude of [Ca2+]i transients. The reduction in force production was accompanied by slowing of the twitch contraction and relaxation and a decrease in the maximum shortening velocity. Immunoblot analyses showed a marked increase in neuronal NOS expression but not in inducible or endothelial NOS expression, which, together with the observed decrease in SOD2 expression, favors peroxynitrite formation. These changes were accompanied by increased 3-NT, carbonyl, and MDA adducts content in myofibrillar proteins from the muscles of mice with CIA. Moreover, there was a significant increase in SNO-Cys content in myosin heavy-chain and troponin I myofibrillar proteins from the soleus muscle of mice with CIA. Conclusion These findings show impaired contractile function in the soleus muscle of mice with CIA and suggest that this abnormality is due to peroxynitrite-induced modifications in myofibrillar proteins. [source] Model study of time-dependent muscle response to pulsed electrical stimulationBIOELECTROMAGNETICS, Issue 5 2010Ravindra P. Joshi Abstract A systems-level model analysis of neuromuscular response to external electrical stimulation is presented. Action potential (AP) generation, dynamics of voltage-based calcium release at the motor endplates controlled by the arrival of APs, and muscle force production are all comprehensively included. Numerical predictions exhibit trends that are qualitatively similar to measurements of muscle response in rats from a burst of cortical stimulation and a nanosecond impulse. Modulation of neural membrane conductances (including possible electroporation) that alters the neural impulse generation frequency is hypothesized as a possible mechanism leading to observed changes in muscle force production. Other possibilities such as calcium release at nerve end endings also exist. It is also proposed that multipulsing strategies and changing the electric field direction by using multielectrode systems would be useful. Bioelectromagnetics 31:361,370, 2010. © 2010 Wiley-Liss, Inc. [source] Endurance training adaptations modulate the redox,force relationship of rat isolated slow-twitch skeletal musclesCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 1-2 2003David R Plant Summary 1.,Studies have shown that, in isolated skeletal muscles, maximum isometric force production (Po) is dependent on muscle redox state. Endurance training increases the anti-oxidant capacity of skeletal muscles, a factor that could impact on the force-producing capacity following exogenous exposure to an oxidant. We tested the hypothesis that 12 weeks treadmill training would increase anti-oxidant capacity in rat skeletal muscles and alter their response to exogenous oxidant exposure. 2.,At the conclusion of the 12 week endurance-training programme, soleus (slow-twitch) muscles from trained rats had greater citrate synthase (CS) and catalase (CAT) activity compared with soleus muscles from untrained rats (P < 0.05). In contrast, CAT activity of extensor digitorum longus (EDL; fast-twitch) muscles from trained rats was not different to EDL muscles of untrained rats. The CS activity was lower in EDL muscles from trained compared with untrained rats (P < 0.05). 3.,Equilibration with exogenous hydrogen peroxide (H2O2, 5 mmol/L) increased the Po of soleus muscles from untrained rats for the duration of treatment (30 min), whereas the Po of EDL muscles was affected biphasically, with a small increase initially (after 5 min), followed by a more marked decrease in Po (after 30 min). The H2O2 -induced increase in Po of soleus muscles from trained rats was less than that in untrained rats (P < 0.05), but no differences were observed in the Po of EDL muscles following training. 4.,The results indicate that 12 weeks endurance running training conferred adaptations in soleus but not EDL muscles. These adaptations were associated with an attenuation of the oxidant-induced increase in Po of soleus muscles from trained compared with untrained rats. We conclude that endurance training-adapted soleus muscles have a slightly altered redox,force relationship. [source] Influence of chronic hypoxemia on peripheral muscle function and oxidative stress in humansCLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 2 2004Marion Faucher Summary Transient re-oxygenation of humans suffering from chronic obstructive pulmonary disease (COPD) allows the assessment of the consequences of chronic hypoxemia on peripheral muscle and metabolism apart from the effects of de-conditioning. The subjects performed maximal voluntary contractions (MVC) of flexor digitorum and vastus lateralis muscles and sustained infra-maximal contractions. COPD patients repeated the whole challenge during a 50-min oxygen breathing period and after recovery to baseline hypoxemia. We measured the compound evoked muscle mass action potential (M-wave) and the medium frequency (MF) of surface electromyography (EMG) power spectrum. Blood lactate (LA) and potassium (K+), erythrocyte-reduced glutathione (GSH), and plasma thiobarbituric acid reactive substances (TBARS) were also measured. Compared with a control group, COPD patients had lower MVCs, an attenuated decrease in MF during exercise, lower resting level of GSH, no posthandgrip TBARS increase and no GSH consumption. Reoxygenation (1) increased MVCs, (2) accentuated the MF decline and (3) elicited a posthandgrip TBARS increase and GSH consumption. Thus, we conclude that chronic hypoxemia exerts specific muscular effects: a reduced force production, an attenuated ,muscle wisdom', and the suppression of the exercise oxidative stress. [source] | ||||||||||||||||