Literatura académica sobre el tema "Contraction's velocitie"

This study was performed to clarify in detail the behavior of the propagation velocities and frequencies of contractions along the canine small intestine. In conscious dogs, duodenal, jejunal, and ileal contractions were recorded by multiple, closely spaced strain gauges and analyzed by a computerized method. During both the interdigestive and postprandial states, the propagation velocity increased from the duodenal bulb to the distal duodenum and declined aborally within the jejunum, reaching rather constant values in the ileum. The decrease was steepest in the proximal part of the jejunum. In contrast to the propagation velocities, the contraction frequencies were almost constant in the upper small intestine. In the ileum, the contraction frequencies were markedly lower than in the upper small intestine, indicating that the aboral decrease in frequency occurred in the distal parts of the jejunum. We conclude that both the propagation velocities and the frequencies of contractions decline aborally in a nonlinear fashion. However, the nonlinear patterns of the frequency and the propagation velocity gradients are different.

The aim of this study was to analyze of hamstring to quadriceps peak torque ratio (H:Q) measured in isokinetic testing with respect to different angular velocities (60, 180, 300°/s), gender, dominant side and mode of contraction (concentric, eccentric) in volleyball players. Twenty male and ten female healthy volleyball players participated in this study. An independent t-test was used to compare the differences between gender. One-way analysis of variance test was conducted to test for differences by effecting factors. There was a statistically significant difference between dominant and non-dominant side in H:Q ratio at 300°/s in males (p<0.05). There was no statistically significant difference between dominant and non-dominant side in H:Q ratio between female and male volleyball players (p>0.05). There was no statistically significant difference between at 60-180-300°/s velocities by Hconc:Qconc contractions and at 60°/s by Hconc:Qecc contractions for male and female’s peak torques in dominant side (p>0.05). There was a statistically significant difference between at 60°/s by Hconc:Qconc and Hconc:Qecc contractions for male and female’s peak torques in dominant side (p<0.05). There was a statistically significant difference H:Q ratio obtained by concentric contraction between at 60-300°/s and 180-300°/s velocities (p<0.05), whereas there was no statistically significant difference between 60-180°/s in male and female’s peak torques in dominant side (p>0.05). It was found in our study that H:Q ratio increases with increasing angular velocity. The findings of the present study indicated that angular velocity, type of contraction and leg dominance influence isokinetic strength profiles of male and female, consequently, muscular balance that is H:Q at the knee. This implies that isokinetic concentric knee strength plays more role in high intensity contractions and has more effect at high velocities of contraction in maximal performance.

The aim of the present study was to investigate the behavior of human muscle fascicles during dynamic contractions. Eight subjects performed maximal isometric dorsiflexion contractions at six ankle joint angles and maximal isokinetic concentric and eccentric contractions at five angular velocities. Tibialis anterior muscle architecture was measured in vivo by use of B-mode ultrasonography. During maximal isometric contraction, fascicle length was shorter and pennation angle larger compared with values at rest ( P < 0.01). During isokinetic concentric contractions from 0 to 4.36 rad/s, fascicle length measured at a constant ankle joint angle increased curvilinearly from 49.5 to 69.7 mm (41%; P < 0.01), whereas pennation angle decreased curvilinearly from 14.8 to 9.8° (34%; P < 0.01). During eccentric muscle actions, fascicles contracted quasi-isometrically, independent of angular velocity. The behavior of muscle fascicles during shortening contractions was believed to reflect the degree of stretch applied to the series elastic component, which decreases with increasing contraction velocity. The quasi-isometric behavior of fascicles during eccentric muscle actions suggests that the series elastic component acts as a mechanical buffer during active lengthening.

Background During labor, ephedrine is widely used to prevent or to treat maternal arterial hypotension and restore uterine perfusion pressure to avoid intrapartum fetal asphyxia. However, the effects of ephedrine on uterine blood flow have not been studied during uterine contractions. The purpose of the study was to assess the effects of ephedrine on uterine artery velocities and resistance index using the Doppler technique during the active phase of labor. Methods Ten normotensive, healthy parturients with uncomplicated pregnancies at term received intravenous ephedrine during labor to increase mean arterial pressure up to a maximum of 20% above their baseline pressure. Peak systolic and end-diastolic Doppler flow velocities and resistance indices were measured in the uterine artery before and immediately after administration of bolus intravenous ephedrine and after ephedrine washout. Umbilical and fetal middle cerebral arterial resistance indices and fetal heart rate were also calculated. Results After ephedrine administration, mean arterial pressure increased by 17 +/- 4%. End-diastolic flow velocity in the uterine artery at peak amplitude of uterine contraction was restored to 74% of the value observed in the absence of contraction. The systolic velocity was totally restored, and the uterine resistance index was significantly decreased, compared with the values in the absence of contraction. Between uterine contractions, ephedrine induced similar but less marked effects. Fetal hemodynamic parameters were not altered by ephedrine administration. Conclusions Bolus administration of intravenous ephedrine reversed the dramatic decrease in diastolic uteroplacental blood flow velocity and the increase in resistance index during uterine contraction, without altering fetal hemodynamic parameters. This suggests that the increase in uterine perfusion pressure during labor could in part restore uterine blood flow to the placenta during uterine contraction.

The objective of this study was to examine the response and recovery to a single set of maximal, low and high angular velocity isokinetic leg extension-flexion contractions with boys. Sixteen boys (11–14 yrs) performed 10 isokinetic contractions at 60°.s−1 (Isok60) and 300°.s−1 (Isok300). Three contractions at both velocities, blood lactate and ratings of perceived exertion were monitored pretest and at 2, 3, 4, and 5 min of recovery (RI). Participants were tested in a random counterbalanced order for each velocity and recovery period. Only a single contraction velocity (300°.s−1 or 60°.s−1) was tested during recovery at each session to remove confounding influences between the recovery intervals. Recovery results showed no change in quadriceps’ power at 300°.s−1, quadriceps’ power, work and torque at 60°.s−1 and hamstrings’ power and work with 60°.s−1. There was an increase during the 2 min RI in hamstrings’ power, work and torque and quadriceps’

Contractions of a segment of bowel result in alterations of its blood flow. However, the precise temporal and spacial relationships between contractions and mucosal blood flow are unknown. Rats were fitted with strain gauge force transducers and implanted with silver wire electrodes into the muscularis externa of the stomach. In vivo microscopic observation of motility and of the gastric mucosal blood flow was performed during electrical field-stimulated contractions. Contractions originated in the midcorpus, were 0.237 +/- 0.018 cm wide, traveled along the corpus at 0.133 +/- 0.024 cm/s, and had a duration of 5.9 +/- 0.1 s. Antral contractions were 0.174 +/- 0.032 cm wide, traveled at 0.070 +/- 0.009 cm/s, and had a duration of 5.6 +/- 0.7 s. During the contraction, capillary flow velocity in the corpus decreased from a basal value of 410 +/- 105 to 206 +/- 104 microns/s at the peak of a contraction. Five seconds after the contraction was released hyperemia was observed with the flow velocity increasing to 570 +/- 102 microns/s. In the antrum, flow stopped completely during the contraction irrespective of the initial flow velocity and no hyperemia occurred with release of the contraction; rather, flow velocity slowly returned to baseline values. In both regions the flow reductions were in phase with the contractions as measured by the force transducers. These studies provide direct evidence that strong gastric contractions can effectively reduce or stop gastric mucosal blood flow.

The purpose of the study was to assess the effect of movement velocity on the relation between fluctuations in acceleration and the ability to achieve a target velocity during voluntary contractions performed by young (29.5 ± 4.3 yr) and old (74.9 ± 6.2 yr) adults. Subjects performed concentric and eccentric contractions with the first dorsal interosseus muscle while lifting a submaximal load (15% of maximum) at six movement velocities (0.03–1.16 rad/s). Fluctuations in acceleration, the accuracy of matching the target velocity, and electromyographic (EMG) activity were determined from three trials for each contraction type and movement velocity. The fluctuations in acceleration increased with movement velocity for both concentric and eccentric contractions, but they were greatest during fast eccentric contractions (∼135%) when there was stronger modulation of acceleration in the 5- to 10-Hz bandwidth. Nonetheless, EMG amplitude for first dorsal interosseus increased with movement velocity only for concentric and not eccentric contractions. Consistent with the minimum variance theory, movement accuracy was related to the fluctuations in acceleration for both types of contractions in all subjects. For a given level of fluctuations in acceleration, however, old subjects were three times less accurate than young subjects. Although the EMG amplitude at each speed was similar for young and old adults, only the young adults modulated the power in the EMG spectrum with speed. Thus the fluctuations in acceleration during voluntary contractions had a more pronounced effect on movement accuracy for old adults compared with young adults, probably due to factors that influenced the frequency-domain characteristics of the EMG.

The aim of this study is to elucidate the nature of ileal interdigestive contractile patterns by the computerized analysis of the contraction spread and by videofluoroscopy. Conscious dogs equipped with closely spaced strain-gauge force transducers were used. Two patterns of repetitive, phasic contractions were recorded, migrating clusters and phase IIIs; both patterns consisted of repetitive, propagated contractions. Both patterns migrated aborad by sequential movement of contraction waves down the bowel. Consequently, the rate of migration of either of the entire patterns was slower than the propagation velocity of constituent, individual contraction waves. Both patterns differed in several parameters, especially the propagated contractions of the clusters spread over shorter distances (1.47 +/- 0.4 cm) than those of phase III (4.65 +/- 0.99 cm). Compared with these complex patterns, propagating power contractions represented single contractions that propagated aborad at the same velocity as the contraction waves of the complex patterns. All three patterns propelled luminal contents distally.

This study aimed to identify areas of reduced surface EMG amplitude and changed frequency across the phase space of a maximal dynamic knee extension task. The hypotheses were that (1) amplitude would be lower for eccentric contractions compared with concentric contractions and unaffected by fiber length and (2) mean frequency would also be lower for eccentric contractions and unaffected by fiber length. Joint torque and EMG signals from the vasti and rectus femoris were recorded for eight athletic subjects performing maximum knee extensions at 13 preset crank velocities spanning ±300°⋅s−1. The instantaneous amplitude and mean frequency were calculated using the continuous wavelet transform time–frequency method, and the fiber dynamics were determined using a muscle model of the knee extensions. The results indicated that (1) only for the rectus femoris were amplitudes significantly lower for eccentric contractions (p= .019) and, for the vasti, amplitudes during eccentric contractions were less than maximal but this was also the case for concentric contractions due to a significant reduction in amplitude toward knee extension (p= .023), and (2) mean frequency increased significantly with decreasing fiber length for all knee extensors and contraction velocities (p= .029). Using time–frequency processing of the EMG signals and a muscle model allowed the simultaneous assessment of fiber length, velocity, and EMG.

Incidence of double discharges (DDs; >100 Hz) and short interspike intervals (ISIs; >50 to <100 Hz) is reported to vary widely among different muscles and tasks, with a higher incidence in motor unit (MU) trains of fast muscles and for the production of fast contractions in humans. However, it is unclear whether human muscles with a large composition of slower motor units exhibit DDs or short ISIs when activated with maximal synaptic drive, such as those required for maximal velocity dynamic contractions. Thus the purpose of this study was to determine the effect of increasing peak contraction velocity on the incidence of DDs and short ISIs in the anconeus muscle. Seventeen anconeus MUs in 10 young males were recorded across dynamic elbow extensions ranging from low submaximal velocities (16% of maximal velocity) up to maximal velocities. A low incidence of DDs (4%) and short ISIs (29%) was observed among the 583 MU trains recorded. Despite the low incidence in individual MU trains, a majority (71% and 94%, respectively) of MUs exhibited at least one DD or short ISI. The number of short ISIs shared no variance with MU recruitment threshold ( R2 = 0.02), but their distribution was skewed toward higher peak velocities ( G = −1.26) and a main effect of peak elbow extension velocity was observed ( P < 0.05). Although a greater number of short ISIs was observed with increasing velocity, the low incidence of DDs and short ISIs in the anconeus muscle is likely related to the function of the anconeus as a stabilizer rather than voluntary elbow extensor torque and velocity production.

Lengthening contraction velocity appears to be one of the factors affecting the magnitude of muscle damage, however limited human studies have investigated this issue. The purpose of this thesis was to clarify the effect of lengthening contraction velocity on changes in indirect markers of muscle damage after maximal voluntary lengthening exercise of the elbow flexors. This thesis incorporates five individual studies that have been published or submitted for publication in peer review journals. The first study investigated the hypothesis that the variability of changes in indirect markers of muscle damage would be explained by work performed and/or torque generated during lengthening contraction exercise. Fifty-three subjects performed 60 maximal lengthening contractions of the elbow flexors through a range of movement from 60° to 180° of elbow flexion at a constant angular velocity of 90°·s -1 • Pearson's correlation coefficient was used to examine relationships between exercise parameters (total work, change in total work, torque produced during exercise, change in peak torque) and markers of muscle damage (maximal voluntary isometric contraction torque, range of motion, plasma creatine kinase activity and muscle soreness) were measured before, immediately after, and 24 - 96 hours after exercise. The analysis revealed that a large inter-subject variability was evident for both work and torque during exercise, and for changes in all markers of muscle damage. Contrary to the hypothesis, total work (normalised for individual pre-exercise MVC) absorbed during the exercise did not correlate significantly with any markers of muscle damage, with the exception of MVC (r = 0.3). Total work absorbed and changes in total work showed higher correlations with some markers, but nor-values exceeded 0.4. Normalised exercise torque and the changes in peak torque during exercise were not correlated with changes in MVC, nor other markers. The findings from this investigation suggested that the large inter-subject variability in responses to maximal voluntary lengthening exercise is not associated with work performed or torque generated during lengthening exercise. The aim of the second study was to verify the lengthening torque-velocity relationship of human elbow flexors by considering whether muscle damage induced in maximal lengthening torque measurements influences the relationship. Twenty subjects were tested twice, separated by seven days, for maximal isometric strength at 90° of elbow flexion and maximal dynamic strength during lengthening contractions at velocities of 30°·s-1 followed by 90°, 150°, 210°·s-1 , and a repeated 30°·s-1 using a range of movement from 60° to 140°, where 180° was considered full extension. Assessment of maximal isometric strength preceded each lengthening contraction to assess the effects of muscle damage and/or fatigue on the measures. The difference in lengthening contraction strength at 30°·s-1 between the first and second attempts was used to adjust the torque values. The reliability of the measurements was supported by high intra-class correlation coefficients (0.96 - 0.99) and low coefficient of variation (6.3 - 9.1 %). Peak lengthening contraction strength across all velocities was significantly greater than maximal isometric strength (14 - 16%), but no significant differences were evident within velocities. The second lengthening contraction performed at 30°·s-1 was significantly lower (-10%) than the first, and maximal isometric strength decreased significantly over the measurements (-10%). Following adjustment, no significant differences in maximal dynamic lengthening torque among velocities were evident. It was concluded that lengthening contraction torque is approximately 15% higher than isometric torque without an influence of angular velocity for the elbow flexors in an untrained population. The purpose of the third study was to investigate the effect of lengthening contraction velocity on muscle damage. Sixteen men were placed into two groups performing either 30 (n = 8) or 210 (n = 8) maximal lengthening contractions of the elbow flexors on an isokinetic dynamometer. Dominant and non-dominant arms were randomly assigned for a slow (S: 30°·s-1 ) or a fast (F: 210°·s-1 ) velocity exercise separated by 14 days. Maximal voluntary strength of isometric contractions (iMVC) and isokinetic concentric contractions ( cMVC), range of motion (ROM), upper arm circumference, muscle soreness and serum creatine kinase (CK) activity were measured before, immediately after, and 1 - 120 hours following exercise. Changes in these measures over time were compared by a two-way repeated measures ANOV A to examine the effect of velocity in the same number of contractions (S30 vs F30; S210 vs F210) or the effect of contraction number at the same velocity (S30 vs S21 O; F30 vs F210). A significant interaction effect was evident only for iMVC (90° P = 0.020 and 150° P = 0.033) between S30 and F30, but for iMVC (90° P = 0.040 and 150° P= 0.000), cMVC (150°·s-1 P= 0.042), ROM (P= 0.001) and CK (P = 0.000) between S210 and F210. Changes in most of the measures were significantly smaller after 30 (S30 and F30) than 210 contractions (S210 and F210). These results suggest that the effect of contraction velocity on the magnitude of muscle damage following 30 contractions is minor; however, when 210 lengthening contractions were performed, the effect of contraction velocity became conspicuous. It is concluded that fast velocity lengthening contractions are likely to induce greater muscle damage than slow velocity contractions; however, muscle fatigue appears to be a confounding factor for the velocity effect. The fourth study tested the hypothesis that the first bout of exercise consisting of slow velocity (30°·s- 1 ) maximal lengthening contractions would not confer protection against a subsequent bout of exercise consisting of fast velocity (210°·s- 1 ) lengthening contractions. Eighteen men (26.3 ± 4.2 yrs) were randomly placed into two groups; repeated bout group (n = 10) and control group (n = 8). The repeated bout group performed two bouts of exercise consisting of 210 (3 5 sets of 6) maximal lengthening contractions of the elbow flexors separated by 14 days using their nondominant arm at a velocity of 30°·s-1 for the first bout and 210°·s-1 for the second bout. The control group performed the fast velocity bout only. Changes in maximal isometric strength, range of motion, upper arm circumference, muscle thickness, muscle soreness, serum creatine kinase and lactate dehydrogenase activities were measured before, immediately after, and 24 - 96 hours after exercise. Changes in the measures over time after the fast velocity exercise were compared between groups by a two-way repeated measure ANOV A. For the repeated bout group, changes in the measures were compared between bouts by a two-way repeated measure ANOV A. The repeated bout group showed significantly smaller changes or faster recovery of all criterion measures except for muscle soreness after the fast velocity exercise compared with the control group. A significant difference in the changes in the criterion measures between the slow and fast velocity bouts of the repeated bout group was evident only for range of motion. These results suggest that a bout of slow velocity lengthening contractions confers protection against muscle damage induced by fast velocity lengthening contractions, although the magnitude of protective effect conferred by the slow velocity exercise is not strong. The final study investigated the hypothesis that muscle damage induced by fast velocity lengthening contractions would be greater for old than young men. Ten old ( 64 ± 4 yrs) and 10 young (25 ± 6 yrs) men performed 5 sets of 6 maximal voluntary lengthening contractions, through a range of movement from 60° to 180° at the angular velocity of 210°·s-1 • Changes in maximal isometric strength, optimum angle, elbow joint range of motion (ROM), upper arm circumference, muscle thickness and echo intensity assessed by B-mode ultrasonography, muscle soreness, and serum CK and LDH activities before, 1, 24 - 96 hrs post exercise were compared between the young and old groups by a two-way repeated measure ANOV A. Prior to exercise no significant differences were observed between groups for criterion measures, and for the work performed during exercise. A significant group x time interaction effect was found for isometric strength and muscle soreness, with the old group showing significantly slower recovery of strength and less development of soreness compared with the young group. Changes in other measures were not significantly different between groups. The results of this study refuted the hypothesis that old men are more susceptible to muscle damage, but confirmed the previous studies reporting that recovery of muscle strength is slower for old than young individuals. The mechanical factors, work absorbed and torque developed during lengthening contractions were not related to the magnitude of muscle damage. In addition it was determined that the torque developed during voluntary lengthening contractions with increasing velocities did not differ significantly. These works were used to justify the major findings from these studies indicating that lengthening contraction velocity has a significant effect on the magnitude of muscle damage with fast velocity lengthening contractions resulting in significantly greater damage than slow velocity lengthening contractions. It was proposed that the results are indicative of a stress susceptible group of muscle fibres that may not be fibre type specific but consists of a greater proportion of type II muscle fibres.

Los jugadores de tenis necesitan una combinación de habilidades técnicas, tácticas, psicológicas y físicas. Respecto a las habilidades físicas, es esencial una combinación de velocidad, agilidad y potencia, incluyendo un nivel aeróbico de medio a elevado. El entrenamiento de fuerza en tenis principalmente se ha utilizado para aumentar la velocidad de golpeo, la velocidad de desplazamiento y para prevenir lesiones. El objetivo principal de esta tesis doctoral fue evaluar los métodos de lanzamientos de balón medicinal y de entrenamiento con sobrecargas en la velocidad y precisión de golpeo y los efectos a largo plazo (Estudio I) y efectos agudos (Estudio II), también investigando la potenciación post-activación (Estudio III) en jugadores jóvenes. Para los efectos a largo plazo se evaluó la velocidad de golpeo durante 8 semanas de entrenamiento con sobrecargas y lanzamientos de balón medicinal con ejercicios de banda elástica. Se observó una mejora en la velocidad de servicio después del entrenamiento con sobrecargas después de 8 semanas aunque no se dio a las 4 semanas, mientras que el entrenamiento con lanzamientos de balón medicinal con ejercicios de banda elástica aumentó la velocidad de lanzamiento de balón medicinal, pero no obtuvo ningún efecto en la velocidad de golpeo. Se encontró una correlación moderada entre los lanzamientos de balón medicinal con la velocidad de servicio (Estudio I). Con respecto a los efectos agudos y retardados, se evaluó la velocidad y precisión de golpeo de una sesión de fuerza de lanzamientos de balón medicinal y de entrenamiento con sobrecargas midiendo el rendimiento antes de la sesión y 3 minutos (efectos agudos) y 24 y 48 horas después (efectos retardados). No se observaron efectos en la velocidad y precisión de golpeo, sugiriendo que estos métodos con protocolos parecidos no causan fatiga neuromuscular en los músculos involucrados en la cadena cinética de los golpeos en tenis (Estudio II). Dentro de los efectos agudos, la potenciación post-activación se investigó mediante el uso de un entrenamiento complejo realizando ejercicios con sobrecargas pesadas (pres de banca, media sentadilla y ambos al 80% 1RM). No se encontraron efectos en la velocidad y precisión de servicio (Estudio III).
Tennis players need a compound of technical, tactical, psychological and physical skills. Regarding physical skills for a high tennis performance, a mixture of speed, agility and power, together with a medium to high aerobic level is essential. As a consequence, strength training has achieved an important role in the tennis training program. Although tennis evolution has led to an increased interest in tennis research, the methodology used by tennis coaches or strength and conditioning coaches is still sometimes based on their intuition and experience rather than on scientific research. Strength training has mainly been used to increase ball velocity and speed displacement and, in addition, for injury prevention. The main aim of this doctoral thesis was to evaluate different strength training methods in ball velocity and accuracy and their long- term (Study I) and acute-term effects (Study II), also investigating the post-activation potentiation (PAP) (Study III) in young players. Long-term effects were investigated by assessing stroke ball velocity during 8-weeks tennis program of resistance training (RT) and medicine ball throws (MB) with elastic tubing. Although ball velocity changes have not been observed after 4 weeks, serve (S) velocity improvement was found at the end of 8-weeks training period of RT, meanwhile, MB and elastic tubing training increased medicine ball velocity but had no effect in stroke ball velocity (Study I). It has also been found a moderate correlation between one-arm and two-arms overhead MB with S velocity (Study I). Regarding acute and delayed effects, they were investigated by evaluating assessing stroke ball velocity and accuracy of MB and RT sessions, assessing the performance before training, after 3 minutes (acute effects) and 24 and 48 hours later (delayed effects). No effects were found in ball velocity and accuracy, suggesting that these methods using similar protocols (i.e., exercises, volume, intensity or repetitions in reserve) do not cause a neuromuscular fatigue to the involved muscles in the tennis stroke’s kinetic chain (Study II). Within the acute effects, PAP in S velocity and accuracy was investigated by using a complex training performing heavy load resistance exercises (80% 1RM). Bench press, half squat and both of them were performed to find PAP. No effects were found in S performance (Study III).

This thesis aims to determine the impact of slowed myocardial conduction velocity and depressed myocyte contractility on the duration of isovolumic contraction time (ICT) of the left ventricle by carrying out simulations using finite element method. A 3D finite element model enabling to simulate both physiological and pathological states of myocardium was created. The model is based on simplified ellipsoidal geometry and accounts for anisotropic behavior of myocardium, its asynchronous contraction and variations in the arrangement of muscle fibers. Slowing of conduction velocity to a half of its physiological value resulted in prolongation of ICT by 27 %; slowing of shortening velocity of myocytes by the same percentage prolonged ICT by 73 %. It is therefore concluded that ICT can be much more prolonged due to depressed contractility than due to conduction slowing. The presented results give an idea of the extent to which ICT can be prolonged due to depressed contractility and conduction slowing and therefore can be useful in identifying the causes of decreased myocardial performance in heart disease.

In der vorliegenden Studie wurde daher den Einfluss exzentrischen Trainings, mit unterschiedlicher Reizmagnitude, Bewegungsgeschwindigkeit und Muskellänge bei Reizapplikation, auf die Adaptation des M. vastus lateralis (VL) untersucht. Die 31 Studienteilnehmer wurden randomisiert in zwei Trainings- und eine Kontrollgruppe aufgeteilt. Die Trainingsgruppen führten 30 Trainingseinheiten mit exzentrischem Training der Knieextensoren an einem Isokineten durch. Gruppe 1 (n=10) trainierte ein Bein mit 65% der maximalen willkürlichen isometrischen Kontraktion (MVC) und das andere Bein mit 100% MVC, bei einer Winkelgeschwindigkeit von 90°/s und einem Kniewinkel von 25°-100°. Gruppe 2 (n=10) trainierte beide Beine mit 100% MVC, ein Bein aber mit einer Winkelgeschwindigkeit von 90°/s in einem Kniewinkel von 25°-65° und das andere Bein mit 240°/s und 25°-100°. In der Pre- und Postmessung wurde die VL Muskelfaserlänge mittels Ultraschall bestimmt und die Moment-Winkel- und Leistungs-Winkelgeschwindigkeitsrelation mit einem Dynamometer erfasst. Die Ergebnisse zeigen nur für Bein mit 240°/s eine signifikante (p
The present study investigated the effects of magnitude, velocity and muscle length at which the eccentric stimulus is applied on the longitudinal adaptation of the vastus lateralis muscle (VL). The 31 participants were randomly assigned into two experimental groups to perform 30 sessions of eccentric training for the knee extensors (3 times/week) and one control group. The first experimental group (n=10) exercised one leg at 65% of maximum voluntary isometric contraction (MVC) and the second leg at 100% MVC at 90°/s from 25° to 100° knee angle on an isokinetic device (Biodex 3). The second experimental group (n=10) exercised one leg at 100% MVC at 90°/s from 25° to 65° knee angle and the other leg at 100% MVC at an angular velocity of 240°/s from 25° to 100° knee angle. In pre and post measurements the fascicle length of the VL was examined by ultrasonography and the moment-angle and power-angular velocity relationship of the knee extensors with a dynamometer. The results showed an increase (p

Background: Gait initiation is a major issue in Parkinson’s disease (PD). Moreover, the effect of current treatment on motor deficits vary alongside individual differences and disease severity. In some cases, postural instability has been documented as a major side-effect and refractory symptom to dopaminergic medication. Despite these shortcomings, research involving other forms of therapy including deep brain stimulation (DBS) and transcranial magnetic stimulation (TMS), has evidenced the improvement of postural deficits in PD. In this regard, there is a strong rational for the modulation of subcortical brain activity via the application of non-invasive transcranial direct current stimulation (tDCS) to interconnected cortical brain structures. Purpose: Therefore, we sought to determine the effect of tDCS applied to the supplementary motor area (SMA), on gait initiation preparation and performance in PD. Methods: A within subjects repeated measures quasi-experimental design was used to investigate the effects of a 10-minute sham-controlled tDCS intervention. Clinically diagnosed participants (n=12) with idiopathic PD were tested on medication during two sessions that bookended one week. Those who had previously undergone other forms of brain stimulation, had diabetes, severe freezing of gait, or any other neurological or functional limitations that could interfere with gait initiation were excluded from the study. Statistical Analyses/Results: Two-way repeated measures ANOVAs with Bonferroni corrections and a post-hoc analyses when appropriate, revealed a significant reduction in the magnitude of center of pressure (CoP) displacement and velocity in the mediolateral (ML) direction following tDCS. Conclusions: Findings from this study provide insights that may guide scientific research regarding the effects of tDCS on gait initiation among those with PD. Additionally, our work may highlight the importance of ML postural stability for individuals with comorbid and/or pharmacologically induced postural instabilities.

Background e obiettivi L’intolleranza all’esercizio fisico (ES), la sintomatologia e gli effetti extra-polmonari incrementano il rischio di disabilità, bassa qualità della vita (QoL) e sedentarietà nel paziente affetto da Broncopneumopatia Cronica Ostruttiva (BPCO). In riabilitazione respiratoria l’ES è considerato il principale intervento non farmacologico per incrementare la salute e la capacità di esercizio nei pazienti. Sfortunatamente, si rilevano pochi interventi strutturati di attività fisica (AF). Inoltre, un numero elevato di pazienti declina la partecipazione. Le ragioni di abbandono o non partecipazione sono state poco investigate. Inoltre, esiste un considerevole dibatto riguardo l’efficacia dei diversi modelli applicativi di AF nell’incrementare i parametri salute correlati (PSC) dei pazienti BPCO e il loro impatto sul mantenimento a lungo termine di uno stile di vita attivo. Infine, l’AF quotidiana, i PSC, la forza muscolare e la performance motoria dei pazienti BPCO sono intimamente correlati. Sebbene la disfunzione muscoolare sia presente in tutti i pazienti BPCO, è stato osservato che la contrazione eccentrica (ECC) è più elevata nei BPCO rispetto ai soggetti sani (HC). La maggior parte delle ricerche del settore hanno utilizzato parametri isometrici i concentrici (CON), però poco è conosciuto riguardo all’associazione tra forza ECC e alte velocità di contrazione nei pazienti BPCO. Pertanto gli studi proposti vogliono evidenziare le motivazioni e le barriere che riducono il reclutamento e impediscono a pazienti BPCO di acquisire uno stile di vita attivo. Inoltre, si vogliono verificare le modifiche ai PSC ottenute da due modelli di attività fisica adattata (AFA) specifici per BPCO e il loro impatto nell’acquisizione di uno stile di vita attivo. Infine si vogliono investigate le performance muscolari CON ed ECC degli arti inferiori dei pazienti BPCO a diverse velocità di contrazione. Metodi 1° studio: single-centre, multi-practice, parallel-group trial clinico randomizzato. 269 maschi affetti da BPCO males sono stati sottoposti a screening per individuare 132 pazienti elegibili. I 38 soggetti reclutati hanno compilato il questionario EMI-2. 2° studio: trial longitudinale, randomizzato. Sono state effettuate valutazioni ad inizio (T1), dopo 3 mesi (T2), 6 mesi (T3) and a 3 mesi di follow up (T4). La composizione corporea e il contenuto minerale osseo (BMC) tramite DXA, i parametri motori (6MWT, Leg press, leg extension, chest press e biceps curl 1RM, flessibilità del cingolo scapolo-omerale e della schiena, e l’equilibrio), lo stile di vita (IPAQ e registrazione SenseWear PRO-2) e la QoL (questionario MRF-26) sono stati investigati. 3° stadio: studio osservazionale, caso/controllo, cross over. Misure di architettura muscolare, contrazione CON ed ECC del quadricipite a diverse velocità (30deg/sec, 210 deg/sec), stile di vita e PSC di 35 pazienti con BPCO sono state confrontati con quelli rilevati in 25 soggetti sani di controllo (HC). Risultati 1° studio: la principale causa che impedisce la partecipazione è dovuta al non rispetto dei criteri di inclusione (65.53%). La mancanza di interesse (8.94%), di tempo disponibile (6.81%) e la difficoltà a raggiungere le strutture sportive (1.7%) sono le principali ragioni che inducono il paziente ad abbandonare il programma. Il reclutamento dello studio ha un’aderenza molto elevata (25.7%) in confronto alla letteratura di riferimento, confermato anche dal numero esiguo di drop out (10.52%). Bassi livelli iniziali di motivazione intrinseca da parte dei pazienti con BPCO sono stati rilevati (media 81.69pt ±48.08), sebbene miglioramenti statisticamente significativi si osservino solo nel gruppo FC dopo la partecipazione ad interventi di AF dopo 3 mesi (+43.99%, p<0.05) e 6 mesi (+47.42%, p<0.05). A 3 mesi modificano gli item socio/emotivi (p<0.01), di gestione ponderale (p<0.05) e di piacevolezza (p<0.01), riconfermandosi a 6 mesi (socio/emotivi p<0.01, piacevolezza p<0.05). 2° studio: 7 pazienti abbandono il programma nei 9 mesi. A breve termine, il gruppo FC incrementa significativamente i parametri di %BMC (0.112 ±0.029, p<0.01), Biceps curl 1RM (1.9kg ±0.6, p<0.05), Chest press 1RM (8.1kg ±1.7, p<0.001) ed equilibrio (48.5sec ±14.2, p<0.05). Modificazioni significative si rilevano nel gruppo EDU, i.e. grasso corporeo (-736.4g ±240.0, p<0.05), BMI (-0.332 ±0.106, p<0.05), Leg Extension 1RM (7.2kg ±2.4, p<0.05), Chest Press 1RM (6.1kg±1.7, p<0.05) e mobilità della spalla (2.7cm ±0.7, p<0.01). Il gruppo CG modifica i parametri di BMI (-0.588 ±0.157, p<0.01), grasso corporeo (-1086.4g ±365, p<0.05), and massa totale (-1849.8g ±494.1 p<0.01). A lungo termine, FC modifica significativamente %BMC (0.071 ±0.024 p<0.05), Chest Press 1RM (9.8kg ±2.4, p<0.01), equilibrio (57.0sec±13.3, p<0.01), quantità di attività moderata (1024 ±272, p<0.01), tempo totale in attività sedentaria (-3.3 ±0.7, p<0.01) and MRF-26 (-2.3 ±0.7, p<0.05). Il gruppo EDU riduce la percezione di sforzo al 6MWT (-1.37 ±0.41 p<0.05) e il tempo totale in attività sedentaria (-3.6 ±0.7, p=0.000), aumentando l’attività di cammino (618 ±208, p<0.05) e l’MRF-26 (-2.1 ±0.7, p<0.05). Al termine del follow up, il gruppo FC riduce i parametri di %BMC (-0.069 ±0.020 p<0.05), 6MWT (-48.2 ±14.8, p<0.05), Leg Extension 1RM (-9.3 ±2.8, p<0.05), Chest Press 1RM (-11.6 ±2.1, p=0.000), flessibilità del busto (-3.8 ±0.9, p<0.01) ed equilibrio (-21.0 ±7 p<0.05). Il gruppo EDU group riduce i parametri di Leg Press 1RM (-32.6 ±9.1, p<0.05), Leg Extension 1RM (-10+5 ±1.9, p<0.001), Chest Press 1RM (-14.3 ±1.3, p=0.000), flessibilità del cingolo scapolo-omerale (-4.3 ±1.3, p<0.05), tempo totale in attività sedentaria (-3.5 ±0.9, p<0.01) and MRF-26 (-2.9 ±0.8, p<0.05). anche il gruppo CG dimostra riduzioni al Chest Press 1RM (-10.9 ±2.6, p<0.01). Nessuna modificazione è stata osservata con il SenseWear PRO-2. 3° studio: I soggetti del gruppo HC presentano valori più elevati in termini di capacità d’esercizio, i.e. 6MWT (p<0.001) e 1RM alla Leg Press (p<0.05), rispetto ai pazienti BPCO. Solo il torque CON a 30deg/s è più elevato nei soggetti HC rispetto ai BPCO (p<0.05). Nessuna differenza statisticamente significativa è stata rilevata tra i gruppi per i parametri di architettura muscolare, torque CON a 210 deg/sec e nei toque ECC. Differenze significative si evidenziano nel rapporto tra torque ECC e CON (30 deg/sec p<0.001; 210 deg/sec p<0.01). Correlazioni significative sono state osservate tra FEV1 e 6MWT (0.719 p<0.001), 1RM Leg Press (0.449 p<0.001), torque a 30 deg/sec (0.427 p<0.01; 0.280 p<0.05), a 210 deg/sec (0.285 p<0.05; 0.276 p<0.05) and rapporto ECC/CON di torque ad entrambe le velocità (-0.562 p<0.001; -0.292 p<0.05). Le medesime osservazioni sono state rilevate tra FEV1/FVC e i parametri investigati. Conclusioni La principale barriera è rappresentata dai criteri di inclusione. La pratica di reclutamento effettuata da un singolo specialista sembra essere la più efficace. La supervisione dello specialista in AFA e l’aumento della collaborazione tra clinici e specialisti AFA potrebbe incrementare la partecipazione dei pazienti BPCO. Semplici modelli applicativi di AFA possono risultano efficaci ad incrementare sia la motivazione all’ES e sia alcuni dei PSC specifici per BPCO. Questi miglioramenti sembrano essere apportati prevalentemente dai “well rounded program”. Il supporto dello specialista APA risulta necessario per poter mantenere a lungo termine i guadagni ottenuti con l’ES. Invece, i miglioramenti di capacità funzionale non sembrano modificare lo stile di vita. Sebbene i pazienti BPCO siano caratterizzati da basse performance dei PSC, ridotta capacità di contrazione CON e stile di vita inattivo rispetto ai soggetti HC, sembrano preservare la contrazione ECC e il torque nelle contrazioni ad alta velocità. Ulteriori ricerche sembrano essere necessarie.
Background and aims Exercise intolerance, symptoms and extra-pulmonary effects may increase patients disabilities, affecting quality of life (QoL) and reducing maintenance of an active lifestyle. Exercise training (ExT) is considered the most effective non-pharmacological intervention to improve COPD patients health and exercise capacity. Unfortunately, there are few available health-care structured programs of physical activity (PA) and a considerable proportion of eligible patients decline participation or drop out. Reasons for decline and drop-out from ExT programs have seldom been investigated. Moreover, a considerable debate continues about what kind of model of PA and ExT intervention is more effective to improve COPD patients’ health related parameters (HRQL), and to maintain long-term active lifestyle. Finally, evidences support notions that daily physical activity (DPA), HRQL, muscle strength and performance are likely intimately interlinked. Although, muscle wasting is common in COPD patients across all disease stages, it has been observed that eccentric contraction (ECC) results greater compared to healthy control subjects. Majority of COPD leg muscle function’s research has used isometric or concentric (CON) quadriceps torque, but there is lack of knowledge about associa¬tion between ECC muscle strength and fast-velocity muscle contractions in COPD patients. Therefore, we would to outline motivation and barriers which reduced COPD patients recruitment in ExT program and hindered an active lifestyle acquisition. Secondly, it would be verify short and long-term modifications of several HRQL provided by two different and easily applied-field models of adapted fitness activity (APA) for COPD patients to evaluate long-term active-lifestyle maintenance. Finally, we would to investigate COPD patients lower limb strength performances as a function of contraction modalities and velocities comparing with healthy control (HC). Methods Fist study: single-centre, multi-practice, randomized, parallel-group clinical trial. 269 COPD males were screened to establish 132 eligible patients. 38 recruited COPD patients were administrated by EMI-2 questionnaire. Recruitment steps were recorded in order to assess patients’ motivation of decline or drop out. Second study: longitudinal randomized controlled trial, in which baseline (T1), 3 months (T2), 6 months (T3) and 3 months of follow up (T4) evaluations were performed. Body composition and bone mass content, i.e. BMC (DXA scanner), functional health-related (6MWT, Leg press, leg extension, chest press and biceps curl 1RM, shoulder and lower back flexibility and balance), lifestyle (IPAQ questionnaire and SenseWear PRO-2 assessment) and quality of life (MRF-26 questionnaire) parameters were administrated. 38 COPD patients were randomized and assigned to one of the three evaluation groups: Fitness Center based group (FC=13), Educational PA group (EDU=12) and Control group (CG=13). Third study: case/control research, cross over and observational trial. Architectural muscle measurements, CON and ECC quadriceps contractions at different velocities (30deg/sec, 210 deg/sec), lifestyle and health-related parameters of COPD patients (N=35) and HC (N=25) subjects were recorded. Results First study: major cause of not-participation was mismatched inclusion criteria (65.53%). No-interest in exercise training (8.94%), lack of available time (6.81%) and inability to access at the PA structures (1.7%) were most commonly cited reasons to drop out. Recruitment showed higher adherence (25.7%) compared to literature, also confirmed by lower number of drop out (10.52%). Low score of intrinsic motivation towards PA were recorded (mean 81.69pt ±48.08) and significant improvements in EMI-2 were observed after 3 months (+43.99%, p<0.05) and 6 months of ExT (+47.42%, p<0.05) by FC group. Significant increases in Socio/Emotional (p<0.01), Weight management (p<0.05) and Enjoyment items (p<0.01) were recorded after 3 months. Socio/Emotional aspects (p<0.01) and Enjoyment items (p<0.05) improved after 6 months. Second study: 7 patients dropped out. At short term, FC group shows significant improvement in %BMC (0.112 ±0.029, p<0.01), Biceps curl 1RM (1.9kg ±0.6, p<0.05), Chest press 1RM (8.1kg ±1.7, p<0.001) and Balance test (48.5sec ±14.2, p<0.05). EDU group shows significant modification in Fat (-736.4g ±240.0, p<0.05), BMI (-0.332 ±0.106, p<0.05), Leg Extension 1RM (7.2kg ±2.4, p<0.05), Chest Press 1RM (6.1kg±1.7, p<0.05) and Shoulder flexibility (2.7cm ±0.7, p<0.01). The CG group shows significant differences in BMI (-0.588 ±0.157, p<0.01), Fat (-1086.4g ±365, p<0.05), and Total Body Mass (-1849.8g ±494.1 p<0.01). At long-term, FC modified significantly %BMC (0.071 ±0.024 p<0.05), Chest Press 1RM (9.8kg ±2.4, p<0.01), Balance (57.0sec±13.3, p<0.01), IPAQ moderate activity (1024 ±272, p<0.01), IPAQ sedentary hours (-3.3 ±0.7, p<0.01) and MRF-26 (-2.3 ±0.7, p<0.05). EDU group recorded modifications in 6MWT Borg scale (-1.37 ±0.41 p<0.05), IPAQ walking activity (618 ±208, p<0.05), IPAQ sedentary hours (-3.6 ±0.7, p=0.000) and MRF-26 (-2.1 ±0.7, p<0.05). CG group did not shows significant differences. At follow up, FC shows significant changes in %BMC (-0.069 ±0.020 p<0.05), 6MWD (-48.2 ±14.8, p<0.05), Leg Extension 1RM (-9.3 ±2.8, p<0.05), Chest Press 1RM (-11.6 ±2.1, p=0.000), Sit & Reach (-3.8 ±0.9, p<0.01), Balance (-21.0 ±7 p<0.05). EDU group shows significant modification in 6MWT Borg score (-1.36 ±0.41 p<0.05), Leg Press 1RM (-32.6 ±9.1, p<0.05), Leg Extension 1RM (-10+5 ±1.9, p<0.001), Chest Press 1RM (-14.3 ±1.3, p=0.000), Back Scratch (-4.3 ±1.3, p<0.05), IPAQ sedentary hours (-3.5 ±0.9, p<0.01) and MRF-26 (-2.9 ±0.8, p<0.05). CG group shows significant difference in Chest Press 1RM (-10.9 ±2.6, p<0.01). No significant modification were observed in SenseWear PRO-2 administration. Third study: HC subjects were significantly different in exercise capacity, i.e. 6MWT (p<0.001) and 1RM Leg Press (p<0.05), than COPD patients. Only CON 30deg/s peak torque was significantly higher in HC compared to COPD (p<0.05). No differences in muscle architecture, fast CON and/or e ECC torque were observed between groups. Significant differences were found between groups in ECC/CON torque ratio (30 deg/sec p<0.001; 210 deg/sec p<0.01). Finally, significant correlations were found between FEV1 and 6MWT (0.719 p<0.001), 1RM Leg Press (0.449 p<0.001), peak torque contraction at 30 deg/sec (0.427 p<0.01; 0.280 p<0.05), at 210 deg/sec (0.285 p<0.05; 0.276 p<0.05) and ECC/CON peak torque ratio at both velocities (-0.562 p<0.001; -0.292 p<0.05). Same results were observed between FEV1/FVC and parameters assessed. Conclusions Recruit COPD patients becomes very challenging. Cause of not-participation was related to mismatched inclusion criteria. Great effort practice of recruitment, managed by only one person, seems to be more effective. Supervision of ExT specialist and incresed level of liaison between specialist physicians and healthcare professionals could be useful to increase participation. An easily applied-field models of COPD specific APA training could be efficient in order to improve some of COPD-specific HRQL. These improvements seem to be better provide by a “well rounded” APA program. APA exercise specialist support is necessary to maintain long-term significant health’s gains. Whereas, improvement in functional exercise capacity does not automatically turn into a more active lifestyle. COPD patients are characterized by lower health related parameters and lifestyle. Also COPD performed lower CON contraction compared to HC. COPD preserved ECC contractions and fast concentric torque. We hypothesize that COPD males develop a favorable profile to minimize strength loss likely due to neural-muscular modification. Further studies are aimed.

碩士
中國文化大學
體育學系運動教練碩博士班
99
Purpose: The aim of this study was to compare the response of the muscle damage on knee extensors by using one set of maximal fast (FV) or slow velocity (SV) eccentric exercise. Methods: Twleve healthy untrained male students were recruited in the study. By the counter-balance method, each subject with right and left legs of FV or SV eccentric exercise (rest interval between a set of FV or SV eccentric exercise at least two weeks ) performed a set of 120 s-1 maximal voluntary isokinetic eccentric contractions (MAX; SV: at angular velocity of 30°·s-1 for 6 sets 5 repetitions; FV: at angular velocity of 210°·s-1 for 6 sets 35 repetitions; and range of knee joint angle was set at 5° to 125°, both) in order to compare the induced muscle damage in SV and FV. Maximal muscle soreness (SOR), leg circumference (CIR) , rang of motion of knee (ROM) , maximal isometric voluntary contraction strength (MVC), plasma creatine kinase activity (CK) were measured before, immediately after, 1, 2, 3, 4 and 5 days after MAX. All data were analyzed by a two-way repeated measures ANOVA. Results: After MAX, all the variables (SOR↑, CIR↑, ROM↓, MVC↓, CK↑) of FV were more significant than SV (p<.05). Conclusion: These results suggest that, when FV and SV have the same time under tension FV would cause more muscle damage than SV after MAX in untrained subject.

In this chapter it is shown how Bernoulli’s equation can be applied to practical fluid-flow problems. In the case of internal flows, such as that through a Venturi tube, it is also necessary to use the continuity equation to relate changes in cross-sectional area to changes in flow velocity. For liquid flows it is shown that for sufficiently high flowspeeds the static pressure could fall below the saturated vapour pressure and lead to cavitation. The designs of various flow-measuring devices, including the orifice-plate flowmeter, the Venturi-tube flowmeter, and the Pitot tube, are based on Bernoulli’s equation. The changes in flow velocity occurring in flow through a wind-tunnel contraction are explained by Bernoulli’s equation.

In-line measurements and sample stream withdrawals for on-line and/or at-line measurements of slurries flowing in horizontal pipes can be complicated by nonuniform slurry profiles. More uniform profiles would improve measurements. Area contractions are a common means used to produce more uniform velocity fields for single phase flows. For example, contractions are used to condition the flow entering wind tunnel test sections and make velocity profiles more uniform at venturi throats. It was desired to determine whether area contractions could be used to make slurry concentration profiles more uniform in horizontal pipe flows. An ASME flow nozzle with a contraction diameter ratio of 0.5 was chosen as a well defined geometry to consider in a Computational Fluid Dynamic (CFD) study of the effects of a contraction on slurry concentration profiles. The pipe was 2.8 m long with a 50.8 mm diameter. The entrance of the contraction was placed at 35 pipe diameters from the inlet in fully developed flow. A length of 20 diameters followed the contraction. The slurry had a xylene liquid phase and an ADP solid phase with a density ratio of 1.7. The simulations were performed at primary phase velocities of 2 m/s and 4 m/s, corresponding to Reynolds numbers of 1.4E05 and 2.8E05. Spherical particle diameters of 38, 75, and 150 μm were used at concentrations of 0.05, 0.2, and 0.3. ANSYS FLUENT 12 software was used with the standard k-ε turbulence model and standard wall function. The mixture multi-phase model was used for the two-phase flow. An unstructured tetrahedral meshing scheme was used with 1.4 million elements. The grid was adjusted until the condition 30 < y+ <60 for the mesh point nearest the wall was satisfied. A grid refinement study was performed to insure grid independence. The computational scheme first was validated by comparing pipe flow velocity and concentration profiles to results in the literature. The computations performed with the contraction showed that in all cases the concentration profiles of the solid particles displayed greater uniformity than the profiles in the pipe upstream of the contraction. The effect of the contraction was more pronounced for the larger particles. As in the case of single phase flows, the contraction caused the axial turbulence intensity to decrease. The greater uniformity of the concentration profiles at the exit plane of the nozzle, suggest that the contraction can provide better conditions for performing measurements of a particle-laden slurry.

Direct measurement techniques are employed to quantify the kinematics of DNA flows in micro-contraction devices. Flow through micro-contractions subjects the fluid to large spatial gradients in velocity, thereby eliciting viscoelastic effects. Additionally, in this microfluidic flow environment, the fully extended length of the macromolecule L will approach the characteristic length scale of the channel geometry h. This is a unique flow environment that is not yet well understood. Knowledge of the fundamental physics that govern this flow regime will have a profound impact on optimization of lab-on-a-chip systems incorporating macromolecular flows. This study investigates the flow of semi-dilute λ-DNA solutions in a 2:1 micro-contraction where L/h ∼ 0.32. Video microscopy and streak images of semi-dilute DNA flows reveal large vortex regions in the corners of the contraction, which are indicative of strong elastic behavior. Velocity fields constructed using Digital Particle Image Velocimetry (DPIV) demonstrate the first use of this tool for obtaining velocity measurements of viscoelastic flows in microfluidic systems.

Abstract There is a contraction portion in the water supply pipe line system, and cavitation may occur in the contraction when the flow velocity is increased. Such a situation occurs widely in the throat of the fluid machineries and in the vicinity of the valve body of the valve. In operation of the valve, it is well known that a phenomenon occurs in which the flow rate does not increase even if the static pressure difference upstream and downstream of the valve is increased due to the growth of cavitation in the contraction, which is well known as choking . It is not clear what phenomena occurs when cavitation surge occurs in the pipe system in the situation where choking is occurring in the contraction. In this study, cavitation CFD was performed on pipes those have three different geometry contractions. It was revealed that choking occurred when cavitation occurred in any shape. Also, in the case with the sharp contraction part and the sudden expansion, the flow fluctuation at the upstream of the contraction is much weaker than that at the downstream, but in the contraction with the bent part where the centrifugal force acts on the flow, the flow fluctuation at the upstream was found to be strong.

Inspired by the physiological network of insects, which have dimensions on the order of micrometers to millimeters, we study the airflow within a single model insect tracheal tube. The tube undergoes localized rhythmic wall contractions. A theoretical analysis is given to model the airflow within the tracheal tube. Since flow motions at the microscale are dominated mainly by viscous effects, and the tube has radius, R, that is much smaller than its length, L, (i.e. δ = R/L ≪ 1), lubrication theory for axisymmetric, viscous, incompressible flows at low Reynolds number (Re ∼ δ) is used to model the problem mathematically. Expressions for the velocity field, pressure gradient, wall shear stress and net flow produced by the driving tube wall contractions are derived. The effect of the contraction amplitudes, time lag, and spacing between two sequences of contractions on the time-averaged net flow over a single cycle of wall motions is investigated. The study presents a new, insect-inspired mechanism for valveless pumping that can guide efforts to fabricate novel microfluidic devices that mimic these physiological systems. A x-ray image that shows the tracheal network of the respiratory system of an insect (Carabid beetle) and the associated locations of these rhythmic contractions are shown in figure (1) to promote this study.

Power generating gas turbines employ an inlet duct or contraction to accelerate air to the operating inlet velocity of the compressor. Multiple passages of this kind are necessary in gas turbines with cycle modifications such as intercooling. An experimental investigation was carried out to obtain flow characteristics of a curved wall annular contraction. The results are described in terms of the velocity vectors, surface pressure coefficients, static and stagnation pressure distributions, and profiles of mean velocities, turbulence intensity, and Reynolds shear stress. The upstream flow conditions were changed to evaluate how they affected the flow development in the passage. Results show that the static pressure and axial velocity profiles at the contraction exit were uniform. Higher inlet turbulence increased the Reynolds shear stress although the effect on the static and total pressure fields was negligible. The overall stagnation pressure loss was approximately 2 to 3 percent of the dynamic head at the contraction exit.

Xurography is an inexpensive rapid prototyping technology for the development of microfluidic systems. Imprecision in the xurographic tape cutting process can result in undesired changes in channel dimensions near features that require a change in cutting direction, such as 90° miter bends. An experimental study of water flow in rectangular xurographic microchannels incorporating 90° miter bends with different channel widths in each leg is reported. A set of twelve microchannels, with channel depth approximately 105 micrometers and aspect ratio ranging from 0.071 to 0.435, were fabricated from double-sided adhesive Kapton® polyimide tape and two rectangular glass plates. The channels were reinforced with a mechanical clamping system, enabling high Reynolds number, Re, flows (up to Re = 3200) where Re was based upon hydraulic diameter and average velocity. Reported data include friction factor and critical Reynolds number for straight microchannels and loss coefficients for flow through 90° miter bends that contain either a contraction or expansion with cross-sectional area ratios of 0.5, 0.333 and 0.2. The critical Reynolds number, Recr, ranged from 1750 to 2300 and was found to be dependent on channel defects such as sidewall roughness, adhesive droplets, and corner imperfections. Loss coefficients through 90° miter bends with expansion decrease rapidly for Re < Recr. At the transition, the loss coefficient suddenly drops and approaches an asymptotic value for Re > Recr. For 90° miter bends with contractions, loss coefficients gradually decrease with increasing Re for 150 < Re < 1400. In addition, the loss coefficient decreases with decreasing area ratio through the contraction or expansion. The minor loss coefficient data were found to be dependent on Reynolds numbers and area ratio of contraction/expansion at the bend. The results suggest that the effect of the contraction/expansion was the dominant mechanism for minor losses in the 90° miter bend.

A numerical model is developed and used to simulate gas-liquid two-phase flow through a plate orifice in a millimeter-scale channel. The channel width is 50 mm and the height is varied from 1.00 mm to 2.00 mm. The contraction ratio and thickness of the orifice are varied over the range 0.04–0.4 and 5–20 mm respectively. The model utilized is based on the multiphase-mixture principle in which transport equations are solved for the mixed phase velocities with allowance for interpenetration of phases and intra-phase transfer processes. The predicted velocity profiles are successfully validated by comparison with the available experimental data for the mixture velocity. The predictions also extend beyond the experimental data to provide the detailed effect of contraction ratio on the flow and gas fraction distribution in the channel. In the range of parameters investigated, the predictions indicate that the flow in such channels will produce no wake in the lee of the orifice for contraction ratios >0.2.

In a recent work, a protocol to measure the relaxation time of dilute polymer solutions, known to be challenging,has been established [1]. This protocol is based on a 2D multi-scale description of free-falling low velocity viscoelastic liquid jets. Although the relaxation time reached an asymptotic value for high jet velocities, a significant dependence with the jet velocity is observed for low velocities. The present work reconsiders these previous experimental data using a 3D multi-scale analysis in order to identify the origin of the dependence between the relaxation time and the jet velocity. The 3D analysis demonstrates the importance of a velocity–dependent coalescence mechanism in the jet behaviour. Thanks to a simple model of jet deformation it is demonstrated that this coalescence mechanism prevents the elasto-capillary contraction of the smallest scales from occurring whenthe jet velocity is reduced.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4700