Contractile Properties In Response Research Articles

Characteristics of Changes in Contractile Properties of Muscle after Anaerobic Exercise

Tensiomyography (TMG) has been described as an effective method for identifying differences in muscle response to athletic training stimuli. However, there is a lack of studies that evaluated changes in muscle contractile properties in response to anaerobic effort and related these changes to Wingate test parameters in more than one lower limb superficial muscle. The main contribution of this work is to evaluate changes in the contractile properties of muscles in response to anaerobic exercise. In a group of 20 physically active men, the body composition analysis was performed using a Tanita DC-360 device. The anaerobic effort was assessed by a Wingate test (30 s), and the contractile properties of muscles were measured using a TMG S2 device. The TMG parameters were measured in selected superficial muscles of the dominant lower limb. The study also calculated indices of the differences (d) and the size of the effect (r). An anaerobic effort in the form of the Wingate test resulted in greater stiffness (Dm) in the vastus lateralis muscle (p = 0.0365; r = 0.47) and a delayed response to stimulus (Td) in the vastus lateralis (p = 0.0239; r = 0.51) and vastus medialis (p = 0.0031; r = 0.66) muscles. The half relaxation time (Tr) (p = 0.0478; r = 0.44) and sustained contraction time (Ts) (p = 0.0276; r = 0.49) in the rectus femoris muscle were also increased. In contrast, a prolonged stimulus-response time (Td) with a decrease in sustained contraction time (Ts) was observed in the gastrocnemius lateralis (Td: p = 0.0054; r = 0.64 and Ts: p = 0.0012; r = 0.74) and gastrocnemius medialis (Td: p = 0.0229; r = 0.52 and Ts: p = 0.0054; r = 0.64) muscles. A significant decrease in contraction time (Tc) (p = 0.0051; r = 0.63) occurred only in the soleus muscle. In addition, significant correlations were shown between selected changes in contractile properties of muscle and parameters of the Wingate anaerobic test. Anaerobic exercise has a significant effect on changes in skeletal muscle contractility parameters. TMG is an effective method for identifying differences in muscle response to sports training stimuli.

Tensiomyography Derived Parameters Reflect Skeletal Muscle Architectural Adaptations Following 6-Weeks of Lower Body Resistance Training.

Measurement of muscle specific contractile properties in response to resistance training (RT) can provide practitioners valuable information regarding physiological status of individuals. Field based measurements of such contractile properties within specific muscle groups, could be beneficial when monitoring efficacy of training or rehabilitation interventions. Tensiomyography (TMG) quantifies contractile properties of individual muscles via an electrically stimulated twitch contraction and may serve as a viable option in the aforementioned applications. Thus, aims of this study were; (i) to investigate the potential use of TMG to quantify training adaptations and differences, in response to exercise specific lower limb RT; and (ii) investigate any associations between TMG parameters and accompanying muscle architectural measures. Non-resistance trained male participants (n = 33) were randomly assigned to 1 of 3 single-exercise intervention groups (n = 11 per group); back squat (BS), deadlift (DL), or hip thrust (HT). Participants completed a 6-week linearized training program (2× per week), where the assigned exercise was the sole method of lower body training. Pre- and post-intervention testing of maximal dynamic strength was assessed by one repetition maximum (1RM) of BS, DL, and HT. Radial muscle belly displacement (Dm) and contraction time (Tc) were obtained via TMG from the rectus femoris (RF) and vastus lateralis (VL) pre- and post-intervention, alongside muscle architectural measures (pennation angle and muscle thickness). All three groups displayed significant increases all 1RM strength tests (p < 0.001; pη2 = 0.677–0.753). Strength increases were accompanied by significant overall increases in RF muscle thickness (p < 0.001, pη2 = 0.969), and pennation angle (p = 0.007, pη2 = 0.220). Additionally, an overall reduction in RF Dm (p < 0.001, pη2 = 0.427) was observed. Significant negative relationships were observed between RF Dm and pennation angle (p = 0.003, r = −0.36), and with RF Dm and muscle thickness (p < 0.001, r = −0.50). These findings indicate that TMG is able to detect improved contractile properties, alongside improvements in muscle function within an untrained population. Furthermore, the observed associations between Dm and muscle architecture suggest that TMG contractile property assessments could be used to obtain information on muscle geometry.

3444 Development of human engineered cardiac tissue (hECT)-based screening assay to explore cardiac contractile properties in response to pharmacological challenge with proarrhythmic drugs

OBJECTIVES/SPECIFIC AIMS: The goals of this study were (1) to evaluate the effect of proarrhythmic drugs on calcium transient and (2) to use three-dimensional human engineered cardiac tissue (hECT) technology to evaluate cardiac contractile properties in response to pharmacological challenge with proarrhythmic drugs. METHODS/STUDY POPULATION: Calcium transient was measured in subject-specific iPSC-CMs by using the IonOptix system in Sotalol treated vs. untreated conditions. We fabricated human engineered cardiac tissues (hECT) in a custom designed bioreactor using low- and high-sentitive subject-specific iPSC-CMs. Contractile function of the hECT was evaluated at baseline and after Sotalol [300 µM] administration. The change in beat rate was recorded under spontaneous beating conditions; changes in other twitch parameters, including time to relaxation, were recorded under electrical stimulation. Time to relaxation served as an indicator of action potential duration (APD), which has a temporal correlation with the QT interval. RESULTS/ANTICIPATED RESULTS: The low-sensitive iPSC-CM showed a considerable drop in overall peak height of the calcium transient, in the presence of 100 µM Sotalol. The high-sensitive line, however, showed a more pronounced drop in peak height. Sotalol treatment also induced a more pronounced increase in the exponential decay time constant (tau) in the high-sensitive line compared to the low-sensitive line. The hECT fabricated with high sensitive hiPSC-CM showed a larger decrease in spontaneous beat rate in response to Sotalol (0.41 vs 0.23 fold decrease), with a higher increase in time to relaxation (1.8 vs 1.3 fold increase), compared to hECT from low sensitive hiPSC-CM. Moreover, while the low-sensitive hECT showed a positive correlation between time to relaxation and developed force, as expected after Sotalol stimulation; the high-sensitive hECT failed to show a positive inotropic response. DISCUSSION/SIGNIFICANCE OF IMPACT: Our findings suggest subject-specific iPSC-CMs and hECT, can be used to model functional abnormalities observed in diLQTS in response to Sotalol, and offer novel insights into human-based screening assays for toxic drug reactions. Success of this study may help identify key components underlying diLQT susceptibility to ultimately develop novel therapeutic agents.

Adaptation mechanisms of the knee extensors contractile properties in response to short-term stretch-shortening exercise training

Adaptation mechanisms of the knee extensors contractile properties in response to short-term stretch-shortening exercise training

Implications of exercise training and distribution of protein intake on molecular processes regulating skeletal muscle plasticity.

To optimize its function, skeletal muscle exhibits exceptional plasticity and possesses the fundamental capacity to adapt its metabolic and contractile properties in response to various external stimuli (e.g., external loading, nutrient availability, and humoral factors). The adaptability of skeletal muscle, along with its relatively large mass and high metabolic rate, makes this tissue an important contributor to whole body health and mobility. This adaptational process includes changes in the number, size, and structural/functional properties of the myofibers. The adaptations of skeletal muscle to exercise are highly interrelated with dietary intake, particularly dietary protein, which has been shown to further potentiate exercise training-induced adaptations. Understanding the molecular adaptation of skeletal muscle to exercise and protein consumption is vital to elicit maximum benefit from exercise training to improve human performance and health. In this review, we will provide an overview of the molecular pathways regulating skeletal muscle adaptation to exercise and protein, and discuss the role of subsequent timing of nutrient intake following exercise.

Finger flexor contractile properties and hemodynamics following a sustained submaximal contraction: A study using electrical stimulation and near-infrared spectroscopy

We examined the effect of a low-level sustained contraction on the muscle contractile properties, hemodynamics and oxygenation of the flexor digitorum superficialis muscle (FDS) of the finger. We tested the hypothesis that hemodynamics and oxygenation, reflecting the muscle metabolic characteristics, would recover more quickly than the muscle contractile properties. Eleven subjects (26 ± 4 years) were equipped with electrodes for electrical stimulation and a near-infrared spectroscopy (NIRS) probe on the forearm over the FDS. The experimental protocol consisted of three baselines measurements (−60, −30 min and pre-exercise), immediately after a sustained 15-min contraction of the FDS at 10% maximal voluntary contraction (post-exercise), and after 30, 60 and 120 min of recovery. For each time point, participants were subjected to a battery of test that included upper arm venous occlusion (at rest), a computer-mouse point and click task (standardized voluntary task), and electrical stimulation. For venous occlusion (50 mmHg, 1 min), slopes were calculated for NIRS-derived total hemoglobin (HbTslope) and deoxyhemoglobin (HHbslope) as estimates of blood flow and oxygen consumption, respectively. The computer-mouse task entailed using the mouse to point and click on targets presented on the screen during which NIRS signals were monitored for determination of change in total hemoglobin (ΔHbT) and oxygen saturation (ΔStO 2%). Electrical stimulation (2 Hz, 5 trains of 15 twitches) provided twitch force (Tw-force), contraction time (CT) and one-half relaxation time (½RT) data. Statistical analysis revealed significant changes over time for all contractile parameters as well as for HHbslope ( P < 0.05 for each). Post-hoc testing demonstrated significant decreases for Tw-force post-exercise and at 60 min; for CT at post-exercise, 30 and 60 min; and for ½RT at post-exercise and at 30 min. HHbslope was significantly higher post-exercise as compared to pre-exercise. During the computer-mouse point and click task, no significant differences were detected for ΔHbT, however, ΔStO 2% showed a tendency to decrease, albeit not significant ( P = 0.11). Further testing showed ΔStO 2% was significantly lower post-exercise and at 30 min as compared to pre-exercise. The present study shows that NIRS provides insight into muscle hemodynamics and oxygenation for low-level sustained activity to fatigue. The overall quick recovery of hemodynamic and oxygenation responses, and a more prolonged recovery of contractile responses confirms our hypothesis, and this may fit well with the classical definition of low-frequency fatigue. Relevance to industry Understanding changes in tissue hemodynamics, oxygenation and muscle contractile properties in response to sustained contractions may provide insight into mechanisms behind work-related musculoskeletal disorders. Detecting changes in the underlying physiology of the muscle before the onset and development of an injury, may lead to primary prevention methods to reduce the occurrence of such injuries.

Frequency-dependent power output and skeletal muscle design

Cyclically contracting muscles provide power for a variety of processes including locomotion, pumping blood, respiration, and sound production. In the current study, we apply a computational model derived from force–velocity relationships to explore how sustained power output is systematically affected by shortening velocity, operational frequency, and strain amplitude. Our results demonstrate that patterns of frequency dependent power output are based on a precise balance between a muscle's intrinsic shortening velocity and strain amplitude. We discuss the implications of this constraint for skeletal muscle design, and then explore implications for physiological processes based on cyclical muscle contraction. One such process is animal locomotion, where musculoskeletal systems make use of resonant properties to reduce the amount of metabolic energy used for running, swimming, or flying. We propose that skeletal muscle phenotype is tuned to this operational frequency, since each muscle has a limited range of frequencies at which power can be produced efficiently. This principle also has important implications for our understanding muscle plasticity, because skeletal muscles are capable of altering their active contractile properties in response to a number of different stimuli. We discuss the possibility that muscles are dynamically tuned to match the resonant properties of the entire musculoskeletal system.

Impact of α1-adrenoceptor expression on contractile properties of vascular smooth muscle cells

Low-frequency blood pressure oscillations (Mayer waves) are discussed as a marker for sympathetic modulation of vascular tone. However, the factors that determine the frequency response of the vasculature to sympathetic stimuli are not fully understood. Possible mechanisms include functions related to alpha(1)-adrenergic receptors (alpha(1)-AR) and postreceptor processes involved in the vascular contractile response. The purpose of the present study was to examine the hypothesis that expression levels of alpha(1)-AR and their subtype distribution determine velocity and magnitude of alpha(1)-AR-mediated vascular smooth muscle cell (VSMC) contraction. alpha(1A)-, alpha(1B)-, and alpha(1D)-AR subtypes were transfected into VSMCs from rat aorta and characterized immunocytochemically via confocal microscopy. Functional studies in isolated cells were performed using video microscopy. The alpha(1)-AR agonist phenylephrine produced dose-dependent contractions of VSMCs. All transfected groups were more sensitive to phenylephrine compared with controls. Maximal contraction velocity almost doubled in transfected cells. However, no differences in observed parameters were found between the three transfected groups. Contractile properties in response to membrane depolarization with KCl were similar in all groups. In conclusion, alpha(1)-AR density determines velocity and sensitivity of alpha(1)-AR-mediated contraction in VSMCs. alpha(1)-AR subtype distribution does not appear to influence vasoconstriction to sympathetic stimuli.

Changes in the human muscle force-velocity relationship in response to resistance training and subsequent detraining

Previous studies show that cessation of resistance training, commonly known as "detraining," is associated with strength loss, decreased neural drive, and muscular atrophy. Detraining may also increase the expression of fast muscle myosin heavy chain (MHC) isoforms. The present study examined the effect of detraining subsequent to resistance training on contractile performance during slow-to-medium velocity isokinetic muscle contraction vs. performance of maximal velocity "unloaded" limb movement (i.e., no external loading of the limb). Maximal knee extensor strength was measured in an isokinetic dynamometer at 30 and 240 degrees/s, and performance of maximal velocity limb movement was measured with a goniometer during maximal unloaded knee extension. Muscle cross-sectional area was determined with MRI. Electromyographic signals were measured in the quadriceps and hamstring muscles. Twitch contractions were evoked in the passive vastus lateralis muscle. MHC isoform composition was determined with SDS-PAGE. Isokinetic muscle strength increased 18% (P < 0.01) and 10% (P < 0.05) at slow and medium velocities, respectively, along with gains in muscle cross-sectional area and increased electromyogram in response to 3 mo of resistance training. After 3 mo of detraining these gains were lost, whereas in contrast maximal unloaded knee extension velocity and power increased 14% (P < 0.05) and 44% (P < 0.05), respectively. Additionally, faster muscle twitch contractile properties along with an increased and decreased amount of MHC type II and MHC type I isoforms, respectively, were observed. In conclusion, detraining subsequent to resistance training increases maximal unloaded movement speed and power in previously untrained subjects. A phenotypic shift toward faster muscle MHC isoforms (I --> IIA --> IIX) and faster electrically evoked muscle contractile properties in response to detraining may explain the present results.

Smooth, slow and smart muscle motors.

Smooth muscle is a slow and economical muscle with a large variability in contractile properties. This review describes results regarding the relation between expression of myosin isoforms and the contraction of smooth muscle. The focus of the review is on studies of the organised contractile system in the smooth muscle tissue. The role of the myosin heavy chain variants formed by alternative splicing in the myosin heavy chain tail (SM1, SM2 isoforms) and head (SM-A SM-B isoforms) regions, as well as the role of essential light chains (LC17a, LC17b isoforms) for the variability of contractile properties are discussed. Smooth muscle also has the ability to alter its contractile properties in response to altered functional demands in vivo, e.g. during hypertrophic growth of urinary bladder, intestine, uterus and vessels and in response to altered hormone levels. These alterations involve changes in myosin expression and altered contractile kinetics. Non-muscle myosin has been shown to have a contractile function in some smooth muscle tissues and recent data on the kinetic properties of non-muscle myosin filaments in smooth muscle tissue are described.

PAF-induced RANTES production by human airway smooth muscle cells requires both p38 MAP kinase and Erk.

Airway smooth muscle (ASM) cells, which have been regarded as having contractile properties in response to contractile inflammatory mediators, may also participate in airway inflammatory response by expressing various cytokines, including RANTES. However, the intracellular signal that regulates cytokine expression in ASM cells has not been determined. In the present study, we examined the role of p38 mitogen-activated protein (MAP) kinase and extracellular signal-regulated kinase (Erk) in RANTES production by ASM cells stimulated by platelet-activating factor (PAF) and tumor necrosis factor (TNF)-alpha. The results showed that PAF induced the threonine and tyrosine phosphorylation of p38 MAP kinase and Erk, and p38 MAP kinase and Erk activity. SB 203580 and PD 98059 almost completely inhibited p38 MAP kinase and Erk activity, respectively. SB 203580 and PD 98059 partially inhibited and acted additively to inhibit PAF-induced RANTES production. PAF also induced c-Jun-NH(2)-terminal kinase ( JNK) phosphorylation. TNF-alpha induced p38 MAP kinase and Erk phosphorylation, but neither SB 203580 nor PD 98059 inhibited RANTES production. These results indicate that both p38 MAP kinase and Erk involve RANTES production by ASM cells stimulated with PAF, but not TNF-alpha, and that the role of p38 MAP kinase and Erk in RANTES production by ASM cells appears to be stimulus-dependent.

Muscle fatigue during concentric and eccentric contractions.

We compared the contribution of central and peripheral processes to muscle fatigue induced in the ankle dorsiflexor muscles by tests performed during concentric (CON) and eccentric (ECC) conditions. Each fatigue test consisted of five sets of 30 maximum voluntary contractions at a constant speed of 50 degrees /s for a 30 degrees range of motion of the ankle joint. The torque produced by the dorsiflexors and the surface electromyogram (EMG) of the tibialis anterior muscle were recorded during the fatigue tests. Before, during, and after the tests, the compound muscle action potential (M wave) and the contractile properties in response to single and paired electrical stimuli, as well as the interpolated-twitch method and postactivation potentiation (PAP), were recorded during isometric conditions. Compared with ECC contractions, the CON ones resulted in a greater (P < 0.05) loss of force (-31.6% vs. -23.8%) and a decrease in EMG activity (-26.4% vs. -17.5%). This difference was most pronounced during the first four sets of contractions, but was reduced during the last set. Activation was not altered by the tests because neither the interpolated-twitch response nor the ratio of the voluntary EMG to the amplitude of the M wave was changed in the two fatigue tests. Although there was no significant difference in M-wave amplitude between the two tests, changes in the twitch parameters and in the PAP were found to be greater in the CON than ECC contractions. It is concluded that the greater alterations in the contractile properties observed during the CON contractions indicate that intracellular Ca(2+)-controlled excitation-contraction (E-C) coupling processes, possibly associated with a higher energy requirement, are affected to a much greater degree than during ECC contractions.

In vitro responses of cat skeletal muscle to halothane and caffeine.

Strips of soleus (100% type I) and gracilis (90% type II) muscle were obtained from anesthetized cats and mounted in organ baths filled with aerated Krebs-Ringer solution (37 degrees C). The contractile patterns in response to electrical stimulation (0.1 Hz, 25 V, 5 ms), caffeine, halothane, and caffeine in the presence of halothane were examined in the two fiber types. The ability of 25 microM dantrolene to alter the contractile patterns was also evaluated. In vitro contractile properties in response to electrical stimulation were similar to properties observed in situ, except that twitch tension in soleus muscle was significantly less in vitro than in situ. In the presence of halothane, type I soleus muscle developed a rapid contracture. The contracture was blocked by pretreatment with dantrolene and was reversed by addition of dantrolene at the peak of the response. Halothane-induced contractures were not observed at any time in type II gracilis. Type I soleus was also significantly more sensitive both to caffeine alone and to caffeine in the presence of halothane than was type II gracilis. In both fiber types, halothane increased the sensitivity of the muscles to caffeine. Dantrolene attenuated caffeine-induced contractures in both fiber types, but the attenuating effect was less in the presence of halothane. The findings of a halothane-induced contracture in the cat soleus and differential sensitivities of the two muscle fiber types to caffeine indicate that further studies in these two muscles may be useful for delineating the mechanisms inducing contracture in muscle from individuals susceptible to malignant hyperthermia.