Isotonic Test Research Articles

ACUTE EFFECT OF BLOOD FLOW RESTRICTED RESISTANCE EXERCISE ON IRISIN AND SEX HORMONES

Purpose: The relationship between exercise and irisin and sex hormone release is unclear and is of interest to current research. This study aimed to investigate the acute effect of blood flow restricted (BFR) resistance exercise on irisin and sex hormones.
 Material and Methods: The study included healthy males over 18 years of age. Participants' physical activity levels were determined using International Physical Activity Questionnaire (IPAQ). Participants underwent body composition analysis and isotonic muscle strength measurement and were randomly divided into 3 groups: low-intensity (20% of 1-RM) resistance exercise with BFR, high-intensity (70% of 1-RM) resistance exercise without BFR, and a control group. Blood samples were obtained 15 minutes post-exercise to assess acute irisin, testosterone, and estrogen responses.
 Results: The study included 17 healthy males. The average age was 26.1±2.9 years, mean physical activity was 1259.2±1003.1 MET/week, and mean 1-RM max (as measured with isotonic muscle strength test) was 41.1±7.5 kg. The descriptive characteristics of the three groups were statistically similar (p>0.05). The acute post-intervention irisin and sex hormone levels were not statistically different between the groups (p>0.05).
 Conclusion: Acute changes in irisin and sex hormone levels were not statistically different for low-intensity BFR and high-intensity non-BFR exercise.

Development of a Novel Technique for the Measurement of Neuromuscular Junction Functionality in Isotonic Conditions

IntroductionThe neuromuscular junction (NMJ) is a chemical synapse responsible for converting electrical pulses generated by the motor neuron into electrical activity in muscle fibers, and is severely impaired in various diseases, such as Amyotrophic Lateral Sclerosis (ALS). Here, we proposed a novel technique to measure, for the first time, NMJ functionality in isotonic conditions, which better reflect muscle physiological activity.MethodsWe employed the in-situ testing technique, studied a proper placing of two pairs of wire electrodes for nerve and muscle stimulation, developed an extensive testing protocol, and proposed a novel parameter, the Isotonic Neurotransmission Failure (INF), to properly capture the impairments in neurotransmission during isotonic fatigue. We employed wild-type mice to assess the feasibility of the proposed technique, and the ALS model SOD1G93A mice to demonstrate the validity of the INF.ResultsResults confirmed the measurement accuracy in term of average value and coefficient of variation of the parameters measured through nerve stimulation in comparison with the corresponding values obtained for membrane stimulation. The INF values computed for the SOD1G93A tibialis anterior muscles pointed out an impairment of ALS mice during the isotonic fatigue test, whereas, as expected, their resistance to fatigue was higher.ConclusionsIn this work we devised a novel technique and a new parameter for a deep assessment of NMJ functionality in isotonic conditions, including fatigue, which is the most crucial condition for the neuronal signal transmission. This technique may be applied to other animal models, to unravel the mechanisms behind muscle-nerve impairments in other neurodegenerative pathologies.

Retentive capacity of power output and linear versus non-linear mapping of power loss in the isotonic muscular endurance test

The limit of dynamic endurance during repetitive contractions has been referred to as the point of muscle fatigue, which can be measured by mechanical and electrophysiological parameters combined with subjective estimates of load tolerance for revealing the human real-world capacity required to work continuously. In this study, an isotonic muscular endurance (IME) testing protocol under a psychophysiological fatigue criterion was developed for measuring the retentive capacity of the power output of lower limb muscles. Additionally, to guide the development of electrophysiological evaluation methods, linear and non-linear techniques for creating surface electromyography (sEMG) models were compared in terms of their ability to estimate muscle fatigue. Forty healthy college-aged males performed three trials of an isometric peak torque test and one trial of an IME test for the plantar flexors and knee and hip extensors. Meanwhile, sEMG activity was recorded from the medial gastrocnemius, lateral gastrocnemius, vastus medialis, rectus femoris, vastus lateralis, gluteus maximus, and biceps femoris of the right leg muscles. Linear techniques (amplitude-based parameters, spectral parameters, and instantaneous frequency parameters) and non-linear techniques (a multi-layer perception neural network) were used to predict the time-dependent power output during dynamic contractions. Two mechanical manifestations of muscle fatigue were observed in the IME tests, including power output reduction between the beginning and end of the test and time-dependent progressive power loss. Compared with linear mapping (linear regression) alone or a combination of sEMG variables, non-linear mapping of power loss during dynamic contractions showed significantly higher signal-to-noise ratios and correlation coefficients between the actual and estimated power output. Muscular endurance required in real-world activities can be measured by considering the amount of work produced or the activity duration via the recommended IME testing protocol under a psychophysiological termination criterion. Non-linear mapping techniques provide more powerful mapping of power loss compared with linear mapping in the IME testing protocol.

The Influence of Active Hamstring Stiffness on Markers of Isotonic Muscle Performance.

Background: Previous research demonstrates hamstring muscle-tendon stiffness (HMTS) influences isometric strength, landing biomechanics and architectural tissue properties. However, the influence on kinetics & kinematics during other modes of strength testing (isotonic dynamometry) has yet to be established. Purpose: Investigate how HMTS influences kinetics and kinematics during a novel isotonic muscle performance test which has never been done for the hamstrings. Previous work using dynamometry has been limited to isometric or isokinetic contractions, so the novelty arises from our custom isotonic protocol which allows quantitative assessment of the stretch-shortening cycle. Methods: Twenty-six recreationally active individuals (15 males, 11 females, 23.8 ± 2.5 years) completed baseline testing for anthropometry and maximum isometric hamstring strength (MVIC). At least 48 h later, subjects completed a measure of HMTS (damped oscillation technique) followed by an isotonic knee flexion test (eccentric velocity 180°/s; concentric torque 25% of MVIC). Separate linear regression models with examination of residuals were conducted between HMTS and each muscle performance variable. Standardized coefficients determined the magnitude of the relationships. Results: Significance was found for all outcome variables tested. HMTS and rate of torque development demonstrated the strongest relationship followed by isotonic concentric peak torque. The weakest relationship observed was with isometric peak torque. Conclusions: These findings build off previous work quantifying HMTS by showing HMTS more strongly relates to dynamic versus static muscle testing and identifies the potential clinical utility of isotonic dynamometry.

Rehabilitation physical training after anterior cruciate nanofibrous ligament reconstruction of sports knee joint

The anterior cruciate ligament (ACL) is an important stable structure of the knee joint. It has the physiological function of maintaining the stability of the knee joint at rest and during exercise. When the knee anterior cruciate ligament is damaged, due to the mechanical structure and proprioception of the knee joint Damage, resulting in decreased knee stability. This article studies rehabilitation physical fitness training after sports knee anterior cruciate nanofibrous ligament reconstruction. In this study, the isotonic muscle strength test system was first used to test the isokinetic strength of patients after anterior cruciate nanofibrous ligament reconstruction, and statistical analysis was used to study the recovery time and lower extremity muscle strength of patients after anterior cruciate nanofibrous ligament reconstruction. Relationship, and further study the true situation of muscle strength loss after anterior cruciate nanofibrous ligament reconstruction. The degree of recovery of muscle strength and motor function of patients in each period is clarified, so that a rehabilitation plan is formulated according to the degree of recovery, and the recovery of muscle strength and motor function around the knee joint of patients after anterior cruciate nanofiber ligament reconstruction is promoted. In this study, the drainage volume on the first postoperative day was (142.8 ± 61.5) ml, and the drainage volume on the second day was (45.13 ± 39.7) ml. Experimental data show that rehabilitation physical training after anterior cruciate nanofibrous ligament reconstruction has a repairing effect on ligament injury.

A new hand rehabilitation system based on the cable-driven mechanism and dielectric elastomer actuator

Abstract. The increasing number of patients with hand disabilities after strokes or peripheral nerve injuries necessitates the continuous development of rehabilitation system devices to accelerate muscle recovery and to help patients regain the motor functions of their hands. This paper introduces the design of a hand rehabilitation system for patients who have a solitary impairment of their hand extension. The system was designed to be portable, simple, and cheap. Using a system based on a cable-driven mechanism instead of traditional rigid links reduces the degrees of freedom of the finger to one. The dielectric elastomer actuator was designed and fabricated as a smart actuator for the system, which supports the low cost of the system. A kinematic analysis of the cable-driven mechanism has been done. Parameters of the actuator were optimized to reach the required output. In order to characterize the performance of the actuator, a uniaxial tension test, isotonic test, and isometric test have been implemented.

The Influence Of Hamstring Muscle-tendon Stiffness On Isolated And Dynamic Velocity Based Parameters

Previous research has demonstrated sex differences in active hamstring muscle-tendon stiffness as well as associations between stiffness and landing biomechanics and architectural tissue properties. Little is known whether active stiffness relates to other measures of muscle function (i.e., maximum voluntary isometric contraction [MVIC], isotonic dynamometry) and performance (i.e., sprinting). PURPOSE: To conduct a pilot study examining the relationship between active hamstring muscle-tendon stiffness and isometric torque production, isotonic velocity development, and sprint velocity. A secondary research interest was to examine the relationship between the isotonic velocity parameters and sprint performance. METHODS: Nine recreationally active and healthy subjects (7 males, 2 females) (24 ± 3 years) completed an MVIC for the hamstrings (30° knee flexion) followed by three 40m sprint trials using an infrared timing gate system (Brower, Draper, UT). At least 48 hours later, subjects completed a measure of hamstring muscle-tendon stiffness (damped oscillatory technique) and an isotonic knee flexion test on a fixed dynamometer (Biodex, Shirley, NY). The isotonic test began at 90° of knee flexion and was eccentric/concentric through a 90° arc of motion with subjects lying prone. Eccentric velocity was set at 180°/s and concentric torque was set at 25% of MVIC. Bivariate correlations were conducted between stiffness, MVIC (normalized to body mass), sprint times, time to peak velocity, rate of velocity development (RVD, 0-100ms), and rebound time (-50°/s to +50°/s). RESULTS: Stiffness (24.3 ± 11.7 Nm/kg) was only significantly related (r= .681, P= .043) to MVIC (1.48 ± 0.23 Nm/kg). Stiffness was not significantly related to rebound time (0.076 ± 0.026s) (r= -.354, P= .350), time to peak velocity (0.214 ± 0.034s) (r= -.285, P= .457), RVD0-100 (1314.64 ± 222.30°/s2) (r= -.336, P= .377), or sprint velocities (5.90 ± 0.56 m/s) (r= .248, P= .521). Rebound time (r= -.535, P= .138) and RVD0-100 (r= -.436, P= .241) were not significantly related to sprint times. CONCLUSIONS: Although only the association between stiffness and normalized MVIC reached statistical significance, the magnitude of the other observed relationships provides impetus for further study with a larger sample size.

Reliability Of Muscle Power And Functional Performance In Healthy, Older Women

Functional performance measures in older adults are commonly used in studies investigating age-related declines in mobility. Surprisingly, there is a lack of literature on the clinimetric properties associated with these tests, especially in healthy, older adults. In addition, reliability of tests is commonly measured over 1-2 weeks, and does not address the question of longer-term reliability that might be more relevant for a typical training study. PURPOSE: The purpose of this study was to assess the longer-term reliability (over 9 weeks and 15 weeks) of an isotonic muscle power test (using an isokinetic dynamometer) and commonly-used functional measures (Short Physical Performance Battery, maximal gait, 30s chair stand test, stair climbing, and the 400-meter walk) in healthy, older women. METHODS: Participants were older women (n = 18) who were healthy and untrained (Age = 73.3 ± 3.4 years, Height = 159.6 ± 7.7 cm, Weight = 69.5 ± 12.7 kg, BMI = 27.3 ± 4.8). Test-retest measures (muscle power and function) took place at baseline, week 9, and week 15. Intraclass correlation coefficients (ICC) and the coefficient of variation of the typical error (CV) are reported for all time point comparisons. RESULTS: ICCs ranged from 0.83-0.97 for muscle power, and 0.64-0.93 for functional performance, indicating moderate to excellent reliability. CVs for upper-leg muscle power ranged from 5.7 - 10.5%, and lower-leg muscle power ranged from 9.9 - 20.0%, while CVs for functional tests ranged from 1.9 - 14.9%. For function, the stair-climb power test demonstrated the greatest reliability from baseline to week 15, with the CV = 8.94% and ICC = 0.94 (CI = 0.82-0.98). There were no changes in mean values for tests over time, with the exception of the chair stands which improved significantly from baseline to week 15 (p < 0.05). Although the chair stands were significantly different, these changes were smaller than what has previously been identified as clinically meaningful (eg. < 3.3 chair stands for the 30s chair stand test). CONCLUSIONS: Muscle power and functional tests demonstrated consistency over durations typically used in exercise studies. Conducting these tests under standardized conditions should enable researchers to confidently describe the impact of exercise interventions on muscle power and function in this population.

RETRACTED: Clinical and functional impairment after nonoperative treatment of distal biceps ruptures

Clinical and functional impairment after nonoperative treatment of distal biceps ruptures is not well understood. The goal of this study was to measure patients' perceived disability, kinematic adjustment, and forearm supination power after nonoperative treatment of distal biceps ruptures. Fourteen individuals after nonoperative treatment of distal biceps ruptures were matched to a control group of 18 uninjured volunteers. Both groups prospectively completed the Disabilities of the Arm, Shoulder and Hand (DASH), Single Assessment Numerical Evaluation (SANE), and Biceps Disability Questionnaire. Both performed a new timed isotonic supination test that was designed to simulate activities of daily life. The isotonic torque dynamometer measures the supination arc, center of supination arc, torque, angular velocity, and power. Motion analysis quantifies forearm and shoulder contributions to the arc of supination. The nonoperative treated group's DASH (23.2 ± 10.3) and SANE (59.6 ± 16.2) scores demonstrated a clinical meaningful impairment. The control group showed no significant differences in kinematic values between dominant and nondominant arms (P = .854). The nonoperative biceps ruptured arms, compared with their uninjured arms, changed supination motion by decreasing the supination arc (P ≤ .036), shifting the center of supination arc to a more pronated position (P ≤ .030), and increasing the shoulder contribution to rotation (P ≤ .001); despite this adaptation, their average corrected power of supination decreased by 47% (P = .001). Patients should understand that nonoperative treatment for distal biceps ruptures will result in varying degrees of functional loss as measured by the DASH, SANE, and Biceps Disability Questionnaire, change their supination kinematics during repetitive tasks, and that they will lose 47% of their supination power.

Comparative performance of isometric and isotonic quadriceps strength testing in total knee arthroplasty

BackgroundEarly quadriceps muscle strength assessment after a total knee arthroplasty (TKA) provides timely information on progress, but little is known about the pain profile and predictive validity associated with common clinical muscle strength tests. This study aimed to, in patients with a recent TKA, examine the associations of isometric and isotonic quadriceps strength with gait speed, accounting for knee pain experienced during testing. MethodsA sample of 76 patients (mean age 68 years; 46 women) with a recent TKA (median, 1.5 months) participated. Quadriceps strength was measured on both limbs using a knee extension machine. Isotonic strength was assessed with a one-repetition maximum test. Isometric strength was measured at 40° and 70° of knee flexion using a custom-built load cell. To allow for valid comparisons between the tests, quadriceps strength symmetry ratios were calculated. Knee pain during testing was measured using an 11-point pain scale. Fast gait speed was measured using the 10-m walk test. ResultsCompared with isotonic test, quadriceps strength ratio was higher for the 40° flexion isometric test (P = 0.01), and this difference may be explained by the lower knee pain intensity elicited during the isometric tests (P's < 0.001). All strength measures were closely associated with fast gait speed after adjustment for knee pain and covariates (P's < 0.001). ConclusionsEarly in the post-TKA period, isometric and isotonic strength tests may be used to assess quadriceps strength but these tests are not interchangeable. Isometric quadriceps testing may be preferable to isotonic testing as it was associated with lower knee pain intensity.

Paper #14 - The distal biceps deficient arm, “the short arc syndrome”

Introduction: Long term functional loss following a distal biceps rupture is difficult to quantify. Despite the 40% supination strength loss, some patients can successfully adjust to their weakness. 2 Freeman C.R. McCormick K.R. Mahoney D. Baratz M. Lubahn J.D. J Bone Joint Surg Am. 2009; 91: 2329-2334 Crossref PubMed Scopus (119) Google Scholar , 3 Morrey B.F. Askew L.J. An K.N. Dobyns J.H. J Bone Joint Surg Am. 1985; 67: 418-421 Crossref PubMed Scopus (431) Google Scholar , 5 Schmidt C.C. Brown B.T. Sawardeker P.J. DeGravelle Jr, M. Miller M.C. J Shoulder Elbow Surg. 2014; 23: 68-75 Abstract Full Text Full Text PDF PubMed Scopus (21) Google Scholar Their adaptation may occur by changing their supination movement. 5 Schmidt C.C. Brown B.T. Sawardeker P.J. DeGravelle Jr, M. Miller M.C. J Shoulder Elbow Surg. 2014; 23: 68-75 Abstract Full Text Full Text PDF PubMed Scopus (21) Google Scholar The purpose of this study is to measure the kinematic adaptation following a distal biceps rupture by using a novel timed isotonic supination test. We hypothesize that biceps deficient arms will compensate by shortening the forearm arc of supination, shifting the center of supination to a pronated position, and increasing the shoulder contribution. This kinematic adjustment could result in less supination power.

Modeling and compensation control of asymmetric hysteresis in a pneumatic artificial muscle

Pneumatic artificial muscle is a novel compliance actuator, and it has many excellent actuator characteristics, such as high power density, safety, and compliance. However, it also has strong nonlinear and asymmetric hysteresis, which makes the accurate trajectory control for a pneumatic artificial muscle very difficult. In this article, the pressure/length hysteresis of a pneumatic artificial muscle was analyzed via an isotonic test. And then, it was described using extended unparallel Prandtl–Ishlinskii model, and the model parameters were identified by an adaptive weight particle swarm optimization with a mutation portion algorithm. For the comparison, the classical Prandtl–Ishlinskii was also considered, and its parameters were identified by least square method. Based on the hysteresis model built by extended unparallel Prandtl–Ishlinskii model, an integral inverse compensator was proposed, and then a proportional–integral–derivative controller with the integral inverse compensator (integral inverse-proportional–integral–derivative) was designed. The simulations and experiments validated that the integral inverse-proportional–integral–derivative controller has good dynamic performance. Compared with conventional proportional–integral–derivative controller without a hysteresis compensator, the control precision of integral inverse-proportional–integral–derivative controller is improved by 43.86%.

Modelling Length/Pressure Hysteresis of a Pneumatic Artificial Muscle using a Modified Prandtl-Ishlinskii Model

Pneumatic artificial muscles have been widely used in various fields owing to their inherent compliance and high power-to-weight ratio. However, the natural hysteresis nonlinearity including length/pressure hysteresis and force/pressure hysteresis degrades their performance in precise tracking control, making it necessary to build a mathematical hysteresis model for hysteresis compensation. This paper deals with the modelling of length/pressure hysteresis of pneumatic artificial muscles. The length/pressure hysteresis loops measured by the isotonic test are found to be asymmetric and independent of the external load when the load is small. Considering that the classical Prandtl-Ishlinskii model is only effective for symmetric hysteresis, a modified Prandtl-Ishlinskii model is proposed to describe the length/pressure hysteresis behaviour. The developed model utilizes two asymmetric operators with simple mathematical forms to independently model the ascending branch and descending branch of hysteresis loops. The model parameters are identified using the recursive least square algorithm. Comparisons between simulation results and experimental measurements demonstrate that the proposed model can characterize the asymmetric major hysteresis loop and minor hysteresis loops with high accuracy.

NOVA SOLUÇÃO ELETROLÍTICA INTRAVENOSA PARA USO VETERINÁRIO: EFEITOS SOBRE O PERFIL ELETROLÍTICO E ÁCIDO BASE EM BOVINOS ADULTOS HÍGIDOS

Resumo Objetivou-se avaliar os efeitos de uma nova solução hidratante intravenosa sobre os equilíbrios eletrolítico e ácido-base de bovinos. Para tanto, oito animais adultos hígidos, mestiços taurinos foram submetidos a dois tratamentos em delineamento cross-over: solução salina isotônica (SI) e solução teste (ST) composta por 145 mEq de Na+, 5 mEq de K+, 4 mEq de Ca++, 2 mEq de Mg++, 96 mEq de Cl-, 60 mEq de lactato, 50 g de dextrose e 4 mg de cianocobalamina por litro. As soluções foram administradas por via intravenosa, em volume correspondente a 5% do peso corporal, durante três horas de infusão contínua. Amostras de sangue venoso foram colhidas antes da infusão e três, seis, nove e 24 horas após o início da infusão para determinações de glicose, lactato L, Ca, P, Mg, pH, pCO2, HCO3-, BE, Na+, K+, Cl- e Ca++. Os resultados foram analisados por análise de variâncias de medidas repetidas. Ao contrário da SI, que causou hipercloremia e redução da diferença de íons fortes no plasma (SID), determinando efeito acidificante, a ST gerou alcalinização leve e transitória e não provocou alteração das concentrações de Na+ e de Cl-. A hipopotassemia e a hiperglicemia, presentes ao final da infusão da ST, foram transitórias e não determinaram sinais clínicos evidentes. Conclui-se que a ST é uma alternativa segura para a terapia com fluidos em bovinos, tendo a vantagem de provocar alterações iatrogênicas de baixa magnitude.

Is the ball velocity dependent on expertise? A multidimensional study in handball

The goals of this study are to 1) compare the differences in anthropometric and physical fitness characteristics between elite and skilled players, 2) investigate these parameters and ball velocity in three conditions (standing position, with a three-step run and the difference between them) and 3) predict ball-throwing velocity. We measured general anthropometric parameters and upper-limb dynamic strength using medicine ball throwing tests. Lower-limb power, strength and reactivity were assessed using a hopping-in-place jumping test and a squat-jump test. Elite players are taller (+7.75%) and heavier (+24%) than skilled players, and have greater upper-limb strength (+23%), all p< .05. The ANOVA revealed a significant effect of expertise (p < .001) and of the type of overarm throw (p < .0001) on ball velocity, but with no interaction effect. The improvement obtained through a three-step run is 2.19 ± 0.72 m.s-1. Additionally, the best multiple regression models explained 73% of total variability including at least an isotonic test and an anthropometric variable. Finally, we validate the equations found on a 24-player independent sample (T(46)<1, n.s.) and they all are very stable whatever the sample.

Mechanical characteristics of intact Middle Pleistocene Epoch loess in northwestern China

In order to research the mechanical characteristics of intact Middle Pleistocene Epoch loess, triaxial shear tests and isotonic compression test of intact Middle Pleistocene Epoch loess were conducted by improved SJ-1A triaxial shear equipment. According to test results, it can be found that the intact Middle Pleistocene Epoch loess has the properties of shear dilatancy and shear shrinkage. With the increase of confining pressure, stress-strain curve develops from softening to hardening. The failure mode of intact Middle Pleistocene Epoch loess is shear failure with the rupture angle between 55° and 61°. And it is better to determine the yield stress (py, qy) of the intact loess under different confining pressures by using the ɛv-q/p curve. Along with the increase of confining pressure, yield deviatoric stress qy and yield spherical stress py present logarithmic relationship. Besides, the strength parameters, elastic modulus K and G of intact loess, are obtained, which are benefit for loess projects design.

The Difference in Output Properties Between Dominant and Nondominant Limbs as Measured by Various Muscle Function Tests

Recently, right and left output properties exerted from specific muscle groups have been evaluated using special measurement devices such as an isokinetic dynamometer. However, it remains unclear whether the coach can properly evaluate muscle function corresponding to lateral specificity in athletes. This study aimed to examine the different output properties between the dominant (D) and nondominant (ND) upper limbs as measured by muscle function tests with various muscle contraction patterns. Fifteen right-handed young men participated in this study. Each subject carried out isometric, isokinetic, and isotonic muscle power tests by elbow flexion with right and left arms. When calculating the laterality index, the laterality of the isotonic test (1.17) was the highest. In all tests, significant correlations were found between the measurements of the D and ND limbs. The isometric test was the highest (r = 0.93), followed by the isokinetic test (r = 0.66-0.83) and the isotonic test (r = 0.55). To examine the ratio of the laterality of measurements provided by each muscle function test, each measurement was converted to a standard score (Z-score). There were significant differences between D and ND limbs in the isometric (D:ND = 55.0:45.0) and the isotonic (54.1:45.9) tests but not in the isokinetic test (60°·s⁻¹, 51.4:48.6; 180°·s⁻¹, 50.7:49.2; 300°·s⁻¹, 51.8:48.2). Particularly, the D (right) limb exerted greater muscle power in the isometric and the isotonic tests than in the isokinetic test. Occupational therapists or strength and conditioning professionals should understand that the D-ND differences shown by these muscle function tests may differ because of measurement conditions.

Effect of baclofen on liquid and solid gastric emptying in rats

Gamma-aminobutyric acid (GABA) is a potent inhibitory neurotransmitter. There is evidence that GABA(B) receptors located in the dorsal complex and in afferent fibers of the vagus nerve participate in the control of gastrointestinal motility. To assess the intracerebroventricularly (ICV) and intravenously (IV) effect of baclofen, a GABA(B) receptor agonist, on liquid and solid gastric emptying in rats. Adult male Wistar rats weighing 250-300 g (n = 6-8 animals) were used. Gastric emptying of liquid test meals labeled with phenol red was evaluated by the determination of percent gastric retention (%GR) 10 and 15 min after orogastric administration of saline and 10% glucose meals, respectively. Baclofen was injected ICV (1 and 2 µg/animal) through a tube implanted into the lateral ventricle of the brain and was injected IV (1 and 2 mg/kg) into a tail vein. The gastric emptying of liquid was determined 10 or 30 min after ICV and IV baclofen administration, respectively. The gastric emptying of the solid meal was assessed by the determination of percent gastric retention 2 h after the beginning of the ingestion of the habitual ratio by the animal, consumed over a period of 30 min. Baclofen was administered ICV (1 and 2 µg/animal) or IV (1 and 2 mg/kg) immediately after the end of the ingestion of the solid meal. The control groups received vehicle (sterile saline solution) ICV or IV. The group of animals receiving baclofen ICV (2 mg/animal) presented a significantly lower (P<0.05, Tukey test) %GR (mean ± SEM) of the saline (18.1 ± 2.5%) compared to control (33.2 ± 2.2%). In the group receiving the drug IV, the gastric retention of the same test meal did not differ from control. ICV and IV administration of baclofen had no effect on the gastric emptying of the 10% glucose solution compared to control. ICV administration of 1 or 2 mg baclofen/animal significantly increased the gastric retention of the solid test meal (57.9 ± 6.5% and 66.6 ± 6.3%, respectively) compared to control (35.1 ± 4.4%). The same phenomenon was observed only with the IV dose of 2 mg/kg (71.9 ± 2.6%) compared to control (52.7 ± 2.8%). Baclofen administered: 1. ICV (2 µg/animal), but not IV, increased gastric emptying of a non-caloric isotonic liquid test meal (saline); 2. when administered ICV or IV, it had no effect of gastric emptying of a 10% glucose solution; 3) when administered ICV (1 and 2 mg/animal) and IV (2 mg/kg) it delayed the gastric emptying of the solid meal.

A constitutive model for smooth muscle including active tone and passive viscoelastic behaviour

A new constitutive model for the biomechanical behaviour of smooth muscle tissue is proposed. The active muscle contraction is accomplished by the relative sliding between actin and myosin filaments, comprising contractile units in the smooth muscle cells. The model includes a chemical part, governing the cross-bridge (myosin head) cycling, that is responsible for the filament sliding. The number of activated cross-bridges govern the contractile force generated and also the contraction speed. A strain-energy function is used to describe the mechanical behaviour of the smooth muscle tissue. Besides the active contractile apparatus, the mechanical model also incorporates a passive viscoelastic part. The constitutive model was calibrated with respect to experiments on smooth muscle tissue from swine carotid artery and guinea pig taenia coli, in terms of isometric and isotonic tensile test results. The model was fully able to reproduce the experimental results.

Performance monitoring during isotonic leg training and analysis of movement

To evaluate improvements during leg training on an isotonic leg extension system, we analyzed the modality of exercise performance by building power-angle curves for each leg. Ten subjects underwent a two-month training protocol on a leg extension device. Maximal theoretical forces were evaluated to set the protocols for each subject. Each training session was monitored in real time by the acquisition of angles and building power-angle curves for each leg during sub-maximal exercise. Maximal theoretical strength, maximal speed values and slopes between the first and last training sessions differed significantly (p<0.001). Constant monitoring of exercise performance allows physical training efficiency to be improved over time. Adequate training exercises can be devised by prompt analysis of movement by power-angle curves. The isotonic test for monitoring performance is a good solution directly correlated to isokinetic methodology.