Initial Contraction Research Articles

TRANSVERSUS ABDOMINIS ACTIVATION AND TIMING IMPROVES FOLLOWING CORE STABILITY TRAINING: A RANDOMIZED TRIAL.

Patients with non-specific low back pain (LBP) often present with a decrease in transversus abdominis (TrA) muscle activation and delayed onset of contraction with extremity movements, potentially contributing to recurrent LBP. Core stability is required for extremity movement and if the timing of when the TrA contracts is not corrected patients may continue to experience LBP. The purpose of this study was to assess the effects of a four-week core stability rehabilitation program on TrA activation ratio and when the TrA initiates contraction during upper extremity movements in subjects with and without LBP. It was hypothesized that those with LBP would experience greater changes in TrA activation and onset of contraction by the TrA compared to the healthy group. Randomized Clinical Trial. Forty-two participants volunteered (21 healthy and 21 LBP). Ultrasound imaging measured the TrA activation ratio and time of initial contraction of the TrA during upper extremity movement into flexion. Half of the healthy and LBP participants were assigned to the exercise group. Participants reported twice a week to the athletic training facility to complete an exercise progression of three exercises. After four weeks, all participants returned to have TrA activation and timing measured again. Pertaining to demographics, there were no differences between the healthy and LBP participants. There was a group interaction for both TrA activation ratio (p=.049) and onset of initial contraction (p=.008). Those in the exercise group showed an increase in TrA activation ratio (1.85 ± 0.09) compared to the control group (1.79 ± 0.08), as well as an improvement in the onset of contraction (2.07 ± 0.08 seconds) compared to the control group (2.23 ± 0.09 seconds) after the four-week rehabilitation program. Strong effect sizes for TrA activation ratio (0.71 [0.06-1.35]) and initial onset of TrA contraction (-1.88 [-2.63 - -1.11]) were found indicating clinical differences related to the interventions. TrA activation and timing were altered following a four-week core stability program in people with and without LBP. Clinicians should consider incorporating these exercises for improving the function of the TrA. Therapy, level 2b.

The signaling of protease-activated receptor-2 activating peptide-induced contraction in cat esophageal smooth muscle cells.

Protease-activated receptors (PARs) are a family of G protein-coupled receptors with a unique activation mechanism involving proteolytic cleavage of the extracellular N-terminal domain of the receptor. PAR2 has a contractile effect on esophageal smooth muscle. We investigate the signaling pathways of the PAR2-activating peptide (PAR2-AP) induced contraction in cat esophageal smooth muscle cells. The length of freshly isolated smooth muscle cells and permeabilized cells from feline esophagus were measured by scanning micrometry, and by confirming molecular basis via western blot analysis. The responses to PAR2-AP were initial and sustained contractions, depending on time. The maximum contraction of the initial phase occurred at 60s. The PAR2-AP-induced contraction was mediated by Gαi1, Gαi3, and Gαq protein activation, leading to phospholipase-c (PLC) and myosin light chain kinase (MLCK) activation. 20kDa myosin light chain (MLC20) was phosphorylated by PAR2-AP. Rho kinase-2 (ROCK-2), an activator of 17kDa C-kinase potentiated Protein phosphatase-1 Inhibitor (CPI-17), was increased by PAR2 receptor activation. In conclusion, PAR2-AP produced an initial contraction mediated by Gαi1, Gαi3, and Gαq protein activation, resulting in PLC and MLCK activation. The sustained contraction by PAR2-AP was mediated by the Rho/Rho kinase-dependent pathway.

Retained Austenite Transformation during Heat Treatment of a 5 Wt Pct Cr Cold Work Tool Steel

Retained austenite transformation was studied for a 5 wt pct Cr cold work tool steel tempered at 798 K and 873 K (525 °C and 600 °C) followed by cooling to room temperature. Tempering cycles with variations in holding times were conducted to observe the mechanisms involved. Phase transformations were studied with dilatometry, and the resulting microstructures were characterized with X-ray diffraction and scanning electron microscopy. Tempering treatments at 798 K (525 °C) resulted in retained austenite transformation to martensite on cooling. The martensite start (Ms) and martensite finish (Mf) temperatures increased with longer holding times at tempering temperature. At the same time, the lattice parameter of retained austenite decreased. Calculations from the Ms temperatures and lattice parameters suggested that there was a decrease in carbon content of retained austenite as a result of precipitation of carbides prior to transformation. This was in agreement with the resulting microstructure and the contraction of the specimen during tempering, as observed by dilatometry. Tempering at 873 K (600 °C) resulted in precipitation of carbides in retained austenite followed by transformation to ferrite and carbides. This was further supported by the initial contraction and later expansion of the dilatometry specimen, the resulting microstructure, and the absence of any phase transformation on cooling from the tempering treatment. It was concluded that there are two mechanisms of retained austenite transformation occurring depending on tempering temperature and time. This was found useful in understanding the standard tempering treatment, and suggestions regarding alternative tempering treatments are discussed.

Shifts in the relationship between motor unit recruitment thresholds versus derecruitment thresholds during fatigue

Muscle fatigue is associated with diminished twitch force amplitude. We examined changes in the motor unit recruitment versus derecruitment threshold relationship during fatigue. Nine men (mean age = 26 years) performed repeated isometric contractions at 50% maximal voluntary contraction (MVC) knee extensor force until exhaustion. Surface electromyographic signals were detected from the vastus lateralis, and were decomposed into their constituent motor unit action potential trains. Motor unit recruitment and derecruitment thresholds and firing rates at recruitment and derecruitment were evaluated at the beginning, middle, and end of the protocol. On average, 15 motor units were studied per contraction. For the initial contraction, three subjects showed greater recruitment thresholds than derecruitment thresholds for all motor units. Five subjects showed greater recruitment thresholds than derecruitment thresholds for only low-threshold motor units at the beginning, with a mean cross-over of 31.6% MVC. As the muscle fatigued, many motor units were derecruited at progressively higher forces. In turn, decreased slopes and increased y-intercepts were observed. These shifts were complemented by increased firing rates at derecruitment relative to recruitment. As the vastus lateralis fatigued, the central nervous system's compensatory adjustments resulted in a shift of the regression line of the recruitment versus derecruitment threshold relationship.

Thermo-electro-radial coupling nonlinear instability of piezoelectric shear deformable nanoshells via nonlocal elasticity theory

In the present article, the size-dependent nonlinear thermo-electro-mechanical instability of piezoelectric nanoshells under a combined action of hydrostatic pressure, lateral electric field and uniform changes in temperature is examined in the presence of the geometric imperfection sensitivity. The non-classical formulations given herein are built upon the nonlocal continuum elasticity within the framework of the shear deformation shell theory incorporating von Karman nonlinearity due to large deflection. The nonlocal-based governing equations are constructed based on the minimum potential energy of the system and then they are deduced using boundary layer theory of shell buckling. By applying an efficient perturbation-based solution methodology, closed-form solutions including explicit expressions are extracted for nonlocal postbuckling equilibrium paths of thermo-electro-mechanical excited piezoelectric nanoshells. It is displayed that for the both local and nonlocal shell models, the lateral applied electric fields with positive and negative signs induce, respectively, initial contraction and expansion in the piezoelectric nanoshell which causes in order to increase and decrease the critical shortening relevant to the electro-radial instability of piezoelectric nanoshell.

Imaging sympathetic neurogenic Ca2+ signaling in blood vessels.

We review the information that has been provided by optical imaging experiments directed at understanding the role and effects of sympathetic nerve activity (SNA) in the functioning of blood vessels. Earlier studies utilized electric field stimulation of nerve terminals (EFS) in isolated arteries and vascular tissues (ex vivo) to elicit SNA, but more recently, imaging studies have been conducted in vivo, enabling the study of SNA in truly physiological conditions. Ex vivo: In vascular smooth muscle cells (VSMC) of isolated arteries, the three sympathetic neurotransmitters, norepinephrine (NE), ATP and neuropeptide Y (NPY), elicit or modulate distinct patterns of Ca2+ signaling, as revealed by confocal imaging of exogenous fluorescent Ca2+ indicators. Purinergic junctional Ca2+ transients (jCaTs) arise from Ca2+ influx during excitatory junction potentials (eJPs), and are associated with the initial neurogenic contraction. Adrenergic Ca2+ waves and oscillations cause contraction while SNA-induced endothelial Ca2+ 'pulsars' cause relaxation. In vivo: optical biosensor mice, which express genetically encoded Ca2+ indicators (GECI's) specifically in smooth muscle, combined with non-invasive imaging techniques has enabled imaging SNA-induced Ca2+ signaling and arterial diameter in vivo. SNA induces Ca2+ oscillations in intact arteries. [Ca2+] of arterial smooth muscle cells increased in hypertension, in association with increased SNA. High resolution imaging has revealed local sympathetic, neurogenic Ca2+ signaling within smooth muscle and endothelial cells of the vasculature. The ongoing development of in vivo imaging together with an expanding availability of different biosensor animals promises to enable the further assessment of SNA and its effects in the vasculature of living animals.

Chemical Physiology of Muscle Contraction

The mechanical response of an isolated muscle to an excitant is not accompanied by any oxygen consumption increase; the additional amount of oxygen is not consumed as long as contraction and relaxation have not occurred. Thus, there are two contraction phases, an anaerobic (anoxidative) phase and an aerobic (oxidative) or recovery phase, during which the muscle resumes its previous stage. When the muscle is repeatedly excited in a nitrogen atmosphere, it strongly contracts at the beginning, but it gets quickly exhausted, since between contractions it cannot get the necessary oxygen for its recovery. Lactic acid gathers in the muscle, which becomes stiff. If it gets oxygen at the beginning of its fatigue, the lactic acid disappears and the muscle recovers its initial contraction strength. The lactic acid concentration at which complete skeletal muscle fatigue sets in (i.e. the lactic acid peak) ranges between 0.3 and 06%. In order to release the energy it needs for its contraction, the muscle does not depend on immediate oxidative processes. It continues to contract for a certain amount of time even when it is completely deprived of oxygen.

Tissue-resident liver NK cell responses to MCMV infection

Abstract Natural Killer (NK) cells belong to the ILC1 subgroup, which contains conventional NK (cNK) cells, ILC1 and tissue-resident NK (trNK) cells. The murine liver is home to both cNK cells and trNK cells. In this organ, cNK cells and trNK cells can be distinguished based on the expression of the transcription factors Eomes and T-bet. cNK cells are double positive for Eomes and T-bet while trNK cells do not express Eomes. During viral infection, the fate of the activated cNK cell population is relatively well defined. However, the fate of the trNK cell population remains unexplored. Using the MCMV model of infection, we found that a contraction phase precedes a replenishment of the trNK cell subset, which inversely correlates with cNK cell kinetics. We sought to determine whether the trNK cell response was a direct result of MCMV infection or an indirect response to inflammatory milieu. In order to help distinguish between these two possibilities, mice were injected with the iNKT ligand a-galactosylceramide (a-GalCer). We found that treatment with a-GalCer lead to an initial contraction phase of liver trNK cells, indicating that the phenotype observed is independent of MCMV infection. Altogether, these data suggest that liver cNK and trNK cell subsets, which arise from distinct developmental pathways, perform different functions in this organ.

TCR signal strength and antigen affinity modulate CD8+ memory T Cell development

Abstract CD8+ T cells play a critical role in adaptive immunity by maintaining the ability to differentiate into CD8+ memory T cells. During an intracellular infection, CD8+ T cells pass through several characteristic phases before becoming mature memory cells. Initial antigen stimulation causes naïve CD8+ T cells to clonally expand and differentiate into short-lived effector cells (SLECs). Subsequently, SLECs undergo a contraction phase to give rise to memory precursor effector cells (MPECs); 5–10% of these MPECs survive the initial contraction phase from SLECs to further develop into CD8+ memory T cells. We have shown that the non-receptor tyrosine kinase Itk, which regulates TCR signal strength, can significantly suppress CD8+ memory T cell development. We hypothesize from that TCR signal strength may function synergistically with antigen affinity to regulate development of memory CD8+ T cells. We are testing this hypothesis using Itk deficient OT-1 TCR transgenic mice, in which CD8+ T cells are engineered to be specific for the Ovalbumin (Ova) protein but exhibit reduced TCR signaling, adoptive transfer of donor naïve CD8+ T cells into marked recipient mice, followed by an infection with recombinant Listeria monocytogenes expressing Ova peptide variant epitopes for CD8+ T cells. Using this model, we can quantitatively determine how TCR signal strength intersects with TCR affinity to control memory development. Our findings suggest that TCR signal strength and TCR affinity separately regulate CD8+ memory development. This data holds societal impact and promise for the advancement of rational vaccine development.

Decrease in RGS4 Expression via miR‐1 and Increase in CPI‐17 Expression via miR‐145 in Diabetes Lead to Augmentation of Ca2+‐Dependent Initial Contraction and Ca2+‐ Independent Sustained Contraction, Respectively, in Gastrointestinal Smooth Muscle

In gastrointestinal smooth muscle, contraction in response to G protein‐coupled receptor agonists is biphasic. Initial phase is mediated by Gaq/PLC‐β1/IP3/Ca2+ pathway involving Ca2+/calmodulin‐dependent activation of myosin light chain kinase (MLCK) and phosphorylation of MLC20. Sustained phase is mediated by RhoA‐dependent pathway involving Rho kinase‐mediated phosphorylation of MYPT1, a targeting subunit of myosin light chain phosphatase (MLCP), and PKC‐mediated phosphorylation of CPI‐17, an endogenous inhibitor of MLCP. Both lead to inhibition of MLCP activity and thus, an increase in MLC20 phosphorylation. Previous studies in gastrointestinal smooth muscle showed that the Gaq/PLC‐b1 signaling is rapidly terminated by the regulator of G protein signaling 4 (RGS4). Studies also showed that the expression of RhoA was increased and acetylcholine (ACh)‐induced contraction was augmented in gastric and colonic smooth muscle of diabetic mice. However, the effect of diabetes on the expression of RGS4 and CPI‐17 is unknown. Recent studies showed that microRNAs (miRs) play a key role in the pathogenesis of diabetes by regulating the expression of signaling molecules. RNA hybrid analysis showed binding sites for miR‐1 in the 3′ UTR of RGS4 mRNA and for miR‐145 in the 5′UTR of CPI‐17 mRNA.AimTo test the hypothesis that decrease in RGS4 expression via miR‐1 and increase in CPI‐17 expression via miR‐145 in diabetes leads to increase in Gaq/PLC‐b1/IP3/Ca2+/MLCK and CPI‐17/MLCP pathways and augmentation of both initial and sustained contraction.MethodsSmooth muscle of stomach and colon from control and diabetic (ob/ob and db/db) mice, and from diabetic patients were used to measure: i) expression of miR‐1, miR‐145, RGS4 and CPI‐17 by real‐time RT‐PCR; ii) PLC‐b1 activity by ion exchange chromatography; iii) cytosolic Ca2+ levels by image analysis in fura‐2 loaded cells; and iv) muscle contraction by organ bath experiments and scanning micrometry.ResultsExpression of miR‐1, miR‐145 and CPI‐17 was increased and RGS4 was decreased in gastric and colonic smooth muscle from diabetic mice, and from diabetic patients compared to control. Similar results were obtained in smooth muscle of stomach and colon from control mice treated with 30 mM glucose for 48h. Expression of RGS4 was decreased in cells transfected with pre‐miR‐1 and increased with antag‐miR‐1, suggesting that RGS4 expression is negatively regulated by miR‐1. ACh‐induced PLC‐b1 activity and Ca2+ release were increased in muscle cells treated with 30 mM glucose. ACh‐induced initial and sustained contraction were also augmented in gastric and colonic smooth muscle from diabetic mice.ConclusionIn smooth muscle, RGS4 expression is negatively regulated by miR‐1 and CPI‐17 expression is positively regulated by miR‐145. In diabetic smooth muscle, a decrease in RGS4 expression and an increase in CPI‐17 expression lead to upregulation of Gαq/PLC‐β1/IP3/Ca2+ and PKC/CPI‐17 pathways, respectively, and augmentation of MLCK‐dependent initial contraction and MLCP‐dependent sustained contraction.Support or Funding InformationR01DK28300

The mammalian skeletal muscle DHPR has larger Ca2+ conductance and is phylogenetically ancient to the early ray-finned fish sterlet (Acipenser ruthenus)

The L-type Ca2+ channel or dihydropyridine receptor (DHPR) in vertebrate skeletal muscle is responsible for sensing sarcolemmal depolarizations and transducing this signal to the sarcoplasmic Ca2+ release channel RyR1 via conformational coupling to initiate muscle contraction. During this excitation-contraction (EC) coupling process there is a slow Ca2+ current through the mammalian DHPR which is fully missing in euteleost fishes. In contrast to ancestral evolutionary stages where skeletal muscle EC coupling is still depended on Ca2+-induced Ca2+-release (CICR), it is possible that the DHPR Ca2+ conductivity during mammalian (conformational) EC coupling was retained as an evolutionary remnant (vestigiality). Here, we wanted to test the hypothesis that due to the lack of evolutionary pressure in post-CICR species skeletal muscle DHPR Ca2+ conductivity gradually reduced as evolution progressed. Interestingly, we identified that the DHPR of the early ray-finned fish sterlet (Acipenser ruthenus) is phylogenetically positioned above the mammalian rabbit DHPR which retained robust Ca2+ conductivity, but below the euteleost zebrafish DHPR which completely lost Ca2+ conductivity. Remarkably, our results revealed that sterlet DHPR still retained the Ca2+ conductivity but currents are significantly reduced compared to rabbit. This decrease is due to lower DHPR membrane expression similar to zebrafish, as well as due to reduced channel open probability (Po). In both these fish species the lower DHPR expression density is partially compensated by higher efficacy of DHPR-RyR1 coupling. The complete loss of Po in zebrafish and other euteleost species was presumably based on the teleost specific 3rd round of genome duplication (Ts3R). Ts3R headed into the appearance of two skeletal muscle DHPR isoforms which finally, together with the radiation of the euteleost clade, fully lost the Po.

Calcium handling precedes cardiac differentiation to initiate the first heartbeat.

The mammalian heartbeat is thought to begin just prior to the linear heart tube stage of development. How the initial contractions are established and the downstream consequences of the earliest contractile function on cardiac differentiation and morphogenesis have not been described. Using high-resolution live imaging of mouse embryos, we observed randomly distributed spontaneous asynchronous Ca2+-oscillations (SACOs) in the forming cardiac crescent (stage E7.75) prior to overt beating. Nascent contraction initiated at around E8.0 and was associated with sarcomeric assembly and rapid Ca2+ transients, underpinned by sequential expression of the Na+-Ca2+ exchanger (NCX1) and L-type Ca2+ channel (LTCC). Pharmacological inhibition of NCX1 and LTCC revealed rapid development of Ca2+ handling in the early heart and an essential early role for NCX1 in establishing SACOs through to the initiation of beating. NCX1 blockade impacted on CaMKII signalling to down-regulate cardiac gene expression, leading to impaired differentiation and failed crescent maturation.

Ca2+ activity during ATP‐induced tone changes in porcine retinal arterioles in vitro spreads along the processes of perivascular cells

PurposeRecently, a novel population of perivascular cells (PVC) located immediately external to the vascular smooth muscle cells of retinal arterioles has been identified. These cells display Ca2+ activity simultaneously with tone changes of retinal arterioles and have processes extending into the retina. This data suggests that PVCs could play a role in the neurovascular coupling in the retina. The aim of the study was to investigate Ca2+ signals in PVCs and their processes during successive contraction and relaxation of retinal arterioles induced by ATP.MethodsFirst order porcine retinal arterioles with preserved perivascular retinal tissue were mounted in a confocal myograph and loaded with the Ca2+‐sensitive fluorophore Oregon Green. The arterioles were preconstricted with 5*10‐8 – 10‐6 M U46619 and after the addition of ATP (10‐4 M) intracellular fluorescence from the PVC layer was recorded by a confocal microscope simultaneously with the vascular tone.ResultsATP induced a biphasic tone response in 19% (5 out of 26) of the studies arterioles. The tone response consisted of 15 ± 4% initial contraction followed by 30 ± 20% relaxation. ATP induced Ca2+ waves in 49 ± 16% PVCs and 46 ± 14% processes during the contraction and in 46 ± 16% PVCs and 46 ± 14% processes during the relaxation. There was no significant difference between the frequency of Ca2+ waves in PVCs and their processes during contraction and relaxation (p > 0.05), but the amplitude of Ca2+ waves was significantly higher (p < 0.01) during contraction than during relaxation in the two structures.ConclusionsPVC Ca2+ waves associated with contraction and relaxation of porcine retinal arterioles spread along cellular processes. The amplitude of Ca2+ waves in PVCs and their processes can be used to differentiate contracting and relaxing responses of retinal arterioles.

Nitrergic Pathway Is the Main Contributing Mechanism in the Human Gastric Fundus Relaxation: An In Vitro Study.

BackgroundHuman gastric fundus relaxation is mediated by intrinsic inhibitory pathway. We investigated the roles of nitrergic and purinergic pathways, two known inhibitory factors in gastric motility, on spontaneous and nerve-evoked contractions in human gastric fundus muscles.MethodsGastric fundus muscle strips (12 circular and 13 longitudinal) were obtained from patients without previous gastrointestinal motility disorder who underwent gastrectomy for stomach cancer. Using these specimens, we examined basal tone, peak, amplitude, and frequency of spontaneous contractions, and peak and nadir values under electrical field stimulation (EFS, 150 V, 0.3 ms, 10 Hz, 20 s). To examine responses to purinergic and nitrergic inhibition without cholinergic innervation, atropine (muscarinic antagonist, 1 μM), MRS2500 (a purinergic P2Y1 receptor antagonist, 1 μM), and N-nitro-L-arginine (L-NNA, a nitric oxide synthase inhibitor, 100 μM) were added sequentially for spontaneous and electrically-stimulated contractions. Tetrodotoxin was used to confirm any neuronal involvement.ResultsIn spontaneous contraction, L-NNA increased basal tone and peak in both muscle layers, while amplitude and frequency were unaffected. EFS (up to 10 Hz) uniformly induced initial contraction and subsequent relaxation in a frequency-dependent manner. Atropine abolished initial on-contraction and induced only relaxation during EFS. While MRS2500 showed no additional influence, L-NNA reversed relaxation (p = 0.012 in circular muscle, and p = 0.006 in longitudinal muscle). Tetrodotoxin abolished any EFS-induced motor response.ConclusionsThe relaxation of human gastric fundus muscle is reduced by nitrergic inhibition. Hence, nitrergic pathway appears to be the main mechanism for the human gastric fundus relaxation.

Hypoxia-induced contraction of chicken embryo mesenteric arteries: mechanisms and developmental changes.

The fetal cardiovascular responses to acute hypoxia include a redistribution of the cardiac output toward the heart and the brain at the expense of other organs, such as the intestine. We hypothesized that hypoxia exerts a direct effect on the mesenteric artery (MA) that may contribute to this response. Using wire myography, we investigated the response to hypoxia (Po2 ~2.5 kPa for 20 min) of isolated MAs from 15- to 21-day chicken embryos (E15, E19, E21), and 1- to 45-day-old chickens (P1, P3, P14, P45). Agonist-induced pretone or an intact endothelium were not required to obtain a consistent and reproducible response to hypoxia, which showed a pattern of initial rapid phasic contraction followed by a sustained tonic contraction. Phasic contraction was reduced by elimination of extracellular Ca2+ or by presence of the neurotoxin tetrodotoxin, the α1-adrenoceptor antagonist prazosin, or inhibitors of L-type voltage-gated Ca2+ channels (nifedipine), mitochondrial electron transport chain (rotenone and antimycin A), and NADPH oxidase (VAS2870). The Rho-kinase inhibitor Y27632 impaired both phasic and tonic contraction and, when combined with elimination of extracellular Ca2+, hypoxia-induced contraction was virtually abolished. Hypoxic MA contraction was absent at E15 but present from E19 and increased toward the first days posthatching. It then decreased during the first weeks of life and P45 MAs were unable to sustain hypoxia-induced contraction over time. In conclusion, the results of the present study demonstrate that hypoxic vasoconstriction is an intrinsic feature of chicken MA vascular smooth muscle cells during late embryogenesis and the perinatal period.

Regression analysis for bivariate gap time with missing first gap time data.

We consider ordered bivariate gap time while data on the first gap time are unobservable. This study is motivated by the HIV infection and AIDS study, where the initial HIV contracting time is unavailable, but the diagnosis times for HIV and AIDS are available. We are interested in studying the risk factors for the gap time between initial HIV contraction and HIV diagnosis, and gap time between HIV and AIDS diagnoses. Besides, the association between the two gap times is also of interest. Accordingly, in the data analysis we are faced with two-fold complexity, namely data on the first gap time is completely missing, and the second gap time is subject to induced informative censoring due to dependence between the two gap times. We propose a modeling framework for regression analysis of bivariate gap time under the complexity of the data. The estimating equations for the covariate effects on, as well as the association between, the two gap times are derived through maximum likelihood and suitable counting processes. Large sample properties of the resulting estimators are developed by martingale theory. Simulations are performed to examine the performance of the proposed analysis procedure. An application of data from the HIV and AIDS study mentioned above is reported for illustration.

Effect of Hip Adduction Position on the Vastus Medialis Oblique and Vastus Lateralis During Closed Kinetic Chain Exercise in Sitting Posture

Background: Several studies have discussed diverse exercise methods considered to be useful for the selective contraction of the vastus medialis oblique (VMO) muscle for the treatment of patellofemoral pain syndrome. Some studies have reported that exercise methods, including hip adduction, in closed kinetic chain exercises are more effective in terms of the muscle activation of the VMO and the timing of the muscle’s initial contraction. We focused on isometric contraction during a closed kinetic chain exercise with hip adduction. Objects: The purpose of this study was to examine muscle activation in the VMO and the vastus lateralis (VL) and the onset time difference between their initial contractions via closed kinetic chain isometric quadriceps femoris exercises including hip adduction. Methods: In total, 36 healthy subjects adopted two hip positions during isometric contraction of the quadriceps femoris in a closed kinetic chain exercise (hip neutral and hip adduction position). Statistical analyses were conducted using a paired t-test (α=.05). Results: Isometric contraction of the quadriceps femoris in a closed kinetic chain exercise caused a greater increase in VMO muscle activity in the hip adduction position [52.68±22.21 percentage of maximal voluntary isometric contraction (%MVIC)]than the hip neutral position (43.43±19.85 %MVIC). The onset time difference (VL-VMO) decreased more in the hip adduction position (-82.14±34.2 ㎳) than the hip neutral position (73.94±2.94 ㎳). Conclusion: We recommend this exercise as a clinically useful therapeutic method for patients with patellofemoral pain syndrome due to weakening of the VMO muscle and lateral inclination of the patella.

EMG Changes In Fatigue

INTRODUCTION: Instrumental musicians frequently undergo similar levels of physical strain to sport athletes, yet the physical demands of musicianship are rarely considered during practices/rehearsals. PURPOSE: To develop a quantitative model of fatigue in violin performance and provide a basis for smarter practice/rehearsal programming. METHODS: This study was conducted in three distinct phases: (1) MEDLINE, PubMed, Web of Science, SportDISCUS, and Cochrane Library were searched for articles reporting changes in electromyographic (EMG) amplitude and/or frequency data during constant force isometric, intermittent isometric, or dynamic contraction protocols ≥20 seconds. Meta-analysis was conducted using general regression models to model the relations between initial EMG levels and both the rate of change in EMG and time to failure. (2) Professional/university violinists (n=55; ≥10 years experience) performed 5 randomly ordered 45-second music excerpts designed to elicit 5 typical right arm movements. Surface EMG data were obtained for 16 relevant muscles of the core, shoulders, chest, and right arm during excerpt performances. (3) Models from the meta-analysis were applied to the EMG data during violin performance. RESULTS: Database searches identified 7273 articles; after removal of duplicates, 5079 articles were screened and 82 articles were included in the meta-analysis. Meta-analysis revealed that a higher initial EMG contraction intensity was associated with a greater rate of change of EMG amplitude (%MVC/min) and a shorter time to task failure (min). During violin performance, average EMG amplitude ≤12.5% MVC for investigated core, shoulder, and upper arm muscles across all excerpt performances; wrist flexors and extensors ranged from 11.8% MVC (excerpt #5) to 55.8% MVC (excerpt #4). Applying the results of the meta-analysis, the rate of EMG amplitude increase and time to task failure were estimated to range from 0 - 38.9 %MVC/min and .88 - 42.4 min, respectively, during violin performance. CONCLUSION: The physical demands of instrumental music performance vary widely with repertoire and must be considered during practice/rehearsal programming to minimize fatigue and injury risk. **Research supported by the Australian-American Fulbright Commission and Australian Research Council**

Is hygrothermal recovery of tension wood temperature-dependent?

When a green wood specimen is hygrothermally treated, it often shows dimensional changes in the longitudinal and transversal directions, which is called hygrothermal recovery of wood. Hygrothermal recovery of tension wood is assumed to be behind the unusual contraction of gelatinous layer along the longitudinal axis. This study investigated whether hygrothermal recovery of tension wood was temperature-dependent. Hygrothermal treatment at 80, 100 and 120 °C was given to green Quercus serrata tension wood, and longitudinal and tangential dimensions were recorded. In the longitudinal direction, the trend line obtained after 10 times of 10-min hygrothermal treatments at respective temperatures unraveled that it was comprised of initial recovery and continuum contraction at 100 and 120 °C, but no initial recovery was recognized at 80 °C. In the tangential direction, both the initial and the continuum deformations were expansive, and initial recovery was smaller at 80 °C. The results of multiple comparison test revealed that the parameters characterizing the trend line differed significantly among three temperature sets. Further, the result highlighted the existence of breakage of hygrothermal recovery mechanism at temperature between 80 and 100 °C.

Physicochemical Properties of the (LiF + CaF2)eut + LaF3 System: Phase Equilibria, Volume Properties, Electrical Conductivity, and Surface Tension

The physicochemical behavior of the molten system (LiF (1) + CaF2 (2))eut + LaF3 (3) has been studied and the phase equilibria, density and volume properties, electrical conductivity, and surface tension have been selected for investigation. Well-established methods for determination of these physicochemical properties of molten salts have been used, such as thermal analysis, the Archimedean method of hydrostatic weighing, and the phase shift and maximum bubble pressure methods. A significant change in all investigated properties was detected in the region of x3 = 0.04–0.06. In regard to phase equilibria, this region is close to and may contain the eutectic point; in volumetric properties, the initial volume contraction (on increasing mol %) starts to reverse. A sharp change of electrical conductivity reflects the changes in ionic composition, and surface tension also shows different behavior below and above this region.