Rate Of Stretch Research Articles

Mono- versus biarticular muscle function in relation to speed and gait changes: in vivo analysis of the goat triceps brachii.

The roles of muscles that span a single joint (monoarticular) versus those that span two (biarticular) or more joints have been suggested to differ. Monoarticular muscles are argued to perform work at a joint, whereas biarticular muscles are argued to transfer energy while resisting moments across adjacent joints. To test these predictions, in vivo patterns of muscle activation, strain, and strain rate were compared using electromyography and sonomicrometry in two major elbow extensors, the long and lateral heads of the triceps brachii of goats (Capra hircus), across a range of speed (1-5 m s(-1)) and gait. Muscle recordings were synchronized to limb kinematics using high-speed digital video imaging (250 Hz). Measurements obtained from four goats (25-45 kg) showed that the monoarticular lateral head exhibited a stretch-shortening pattern (6.8+/-0.6% stretch and -10.6+/-2.7% shortening; mean+/-s.e.m. for all speeds and gaits) after being activated, which parallels the flexion-extension pattern of the elbow. By contrast, the biarticular long head shortened through most of stance (-16.4+/-3.4%), despite elbow flexion in the first half and shoulder extension in the last half of stance. The magnitude of elbow flexion and shoulder extension increased with increasing speed (ANCOVA, P<0.05 and P<0.001), as did the magnitude and rate of active stretch of fascicles in the lateral head (P<0.001 for both). In all individuals, shortening fascicle strain rates increased with speed in the long head (P<0.001), and, in three of the four individuals, strain magnitude increased. Few independent effects of gait were found. In contrast to its expected function, the biarticular long head appears to produce positive work throughout stance, whereas the monoarticular lateral head appears to absorb work at the elbow. The biarticular anatomy of the long head may mitigate increases in muscle strain with speed in this muscle, because strain magnitude in the second phase of stance (when the shoulder extends) decreased with speed (P<0.05).

Adductor longus mechanics during the maximal effort soccer kick

Groin pain is a common cause of athletic disability and often involves the adductor longus. A common complaint of patients with groin problems is pain while preparing to kick the ball. The purpose of this study was to examine muscle length and activation of the adductor longus while kicking a soccer ball. Three-dimensional joint positions and muscle activation were obtained from 15 National Collegiate Athletic Association (NCAA) Division 1 male soccer players during maximal effort kicks. Musculoskeletal modeling techniques incorporating joint position and muscle attachments were used to estimate adductor longus length from the beginning of the kicking leg's swing phase until ball strike. The maximum rate of stretch of the adductor longus (22.3 ± 5.3 cm/s) and maximum hip extension (23.3 ± 8.8°) occurred near 40% of swing phase. Activation of the adductor longus occurred between 10% and 50% of the swing phase. Adductor longus maximum length occurred at 65% of the swing phase. Maximum hip abduction (25.3 ± 5.4°) occurred at 80% of swing phase. The adductor longus appears to be at risk of strain injury during its transition from hip extension to hip flexion. This knowledge could be applied to muscle injury prevention and rehabilitation programs to aid with treatment of adductor longus related groin pain.

Stimulated calcium entry and constitutive RhoA kinase activity cause stretch-induced detrusor contraction

Urinary bladder wall muscle (i.e., detrusor smooth muscle; DSM) contracts in response to a quick-stretch, but this response is neither fully characterized, nor completely understood at the subcellular level. Strips of rabbit DSM were quick-stretched (5 ms) and held isometric for 10 s to measure the resulting peak quick-stretch contractile response (PQSR). The ability of selective Ca 2+ channel blockers and kinase inhibitors to alter the PQSR was measured, and the phosphorylation levels of myosin light chain (MLC) and myosin phosphatase targeting regulatory subunit (MYPT1) were recorded. DSM responded to a quick-stretch with a biphasic response consisting of an initial contraction peaking at 0.24 ± 0.02-fold the maximum KCl-induced contraction ( F o) by 1.48 ± 0.17 s (PQSR) before falling to a weaker tonic (10 s) level (0.12 ± 0.03-fold F o). The PQSR was dependent on the rate and degree of muscle stretch, displayed a refractory period, and was converted to a sustained response in the presence of muscarinic receptor stimulation. The PQSR was inhibited by nifedipine, 2-aminoethoxydiphenyl borate (2-APB), 100 μM gadolinium and Y-27632, but not by atropine, 10 μM gadolinium, LOE-908, cyclopiazonic acid, or GF-109203X. Y-27632 and nifedipine abolished the increase in MLC phosphorylation induced by a quick-stretch. Y-27632, but not nifedipine, inhibited basal MYPT1 phosphorylation, and a quick-stretch failed to increase phosphorylation of this rhoA kinase (ROCK) substrate above the basal level. These data support the hypothesis that constitutive ROCK activity is required for a quick-stretch to activate Ca 2+ entry and cause a myogenic contraction of DSM.

CAPACIDADE DE AUTODEPURAÇÃO DE UM TRECHO DO RIO CORUMBATAÍ, SP, BRASIL

O Índice de Depuração do baixo curso do Rio Corumbataí, SP, foi avaliado considerando a importância da água, quanto à qualidade e quantidade para abastecimento público através do índice K2. Sazonalmente nos períodos úmido/quente e seco/frio foram realizadas coletas em dois afluentes do Rio Corumbataí, o Rio Passa-Cinco e o Ribeirão Água Vermelha. As coletas foram realizadas no canal dos afluentes e após a foz de cada um deles junto ao rio Corumbataí, medindo-se a velocidade da água, vazão, profundidade, oxigênio dissolvido (OD), demanda bioquímica de oxigênio (DBO), demanda química do oxigênio (DQO) e nitrogênio total (NT). O curso de água do rio Corumbataí serve como receptor de grande quantidade de cargas orgânicas provenientes de fontes difusas tais como efluentes urbanos, rurais e industriais, lançados sem tratamento prévio, ocorrendo um grau de degradação acentuado. O rio Corumbataí, no trecho estudado, possui uma taxa de depuração alta, sendo no período seco/frio de aproximadamente 70,3%, provavelmente decorrente da declividade acentuada, que possui neste trecho, aos seus meandros e formações rochosas de fundo e pela presença de mata ciliar. Desta maneira, esse trabalho pode contribuir para a tomada de decisões de autoridades dos Municípios e da sociedade civil pertencentes ao Comitê da Bacia Hidrográfica PCJ, visando à preservação do manancial e da água de abastecimento público.

Interstitial cells of Cajal mediate mechanosensitive responses in the stomach

Changes in motor activity are a basic response to filling of smooth muscle organs. Responses to gastric filling, for example, are thought to be regulated by neural reflexes. Here, we demonstrate a previously uncharacterized aspect of stretch-dependent responses in visceral smooth muscles that is mediated by mechanosensitive interstitial cells of Cajal. Length ramps were applied to the murine antral muscles while recording intracellular electrical activity and isometric force. Stretching muscles by an average of 27 +/- 1% of resting length resulted in 5 mN of force. Increasing length caused membrane depolarization and increased slow-wave frequency. The responses were dependent on the rate of stretch. Stretch-dependent responses were not inhibited by neuronal antagonists or nifedipine. Increases in slow-wave frequency, but not membrane depolarization, were inhibited by reducing external Ca(2+) (100 microM) and by Ni(2+) (250 microM). Responses to stretch were inhibited by indomethacin (1 microM) and were absent in cyclooxygenase II-deficient mice, suggesting that cyclooxygenase II-derived eicosanoids may mediate these responses. Dual microelectrode impalements of muscle cells within the corpus and antrum showed that stretch-induced changes in slow-wave frequency uncoupled proximal-to-distal propagation of slow waves. This uncoupling could interfere with gastric peristalsis and impede gastric emptying. Stretch of antral muscles of W/W(V) mice, which lack intramuscular interstitial cells of Cajal, did not affect membrane depolarization or slow-wave frequency. These data demonstrate a previously uncharacterized nonneural stretch reflex in gastric muscles and provide physiological evidence demonstrating a mechanosensitive role for interstitial cells of Cajal in smooth muscle tissues.

A Device to Study the Initiation and Propagation of Calcium Transients in Cultured Neurons After Mechanical Stretch

The brain is generally considered protected from mechanical forces. However, during traumatic events, cells in brain tissue are exposed to complex mechanical events including transient acceleration, pressure, and direct stretch. This paper presents a model to expose cultured cells of the central nervous system (CNS) to a defined stretch insult. The system is designed to apply a single transient uniaxial stretch to cultured cells; control of both the magnitude and rate of stretch allows study of a broad range of conditions, from physiologic to traumatic. Distinct from previous cell-stretching systems, we control the fraction of cells deformed and examine the response of stretched cells or the surrounding population of unstretched cells, the "mechanical penumbra," of the same culture. Finally, we use this new model with cultured neurons, measuring the acute calcium response in traumatically stretched cells and the propagation of this calcium influx in neighboring, but unstretched cells. Stretched neurons exhibit a strain rate and magnitude-dependent response, unstretched exhibit an "all-or-none" response. This model will further our understanding of the complex interaction between mechanical stimuli, resulting biochemical cascades, and interaction between mechanical and other challenges, thereby furthering our understanding of the initiation and evolution of cellular damage following traumatic CNS injury.

The "best" tidal volume for managing acute lung injury/acute respiratory distress syndrome.

An inappropriate tidal volume setting can overstretch and injure the lung. Maximal stretch, tidal stretch, frequency of stretch, and rate of stretch are all implicated in such injury. Moreover, the stretch injury produces systemic injury by liberating cytokines and translocating bacteria in the lung. Clinical trials have shown that limiting maximal and tidal stretch improves outcomes, even if gas exchange is partially compromised. Current strategies should focus on limiting tidal and maximal stretch as much as possible.

Openings in frog microvascular endothelium at different rates of increase in pressure and at different temperatures.

Experiments were carried out on single mesenteric capillaries and venules of pithed frogs to determine whether the rate of increase in intravascular pressure (dP/dt) influenced the critical pressure (P(B)) which increases wall permeability. Vessels, microperfused with frog Ringer solutions containing 0.1% bovine serum albumin and red cells, were occluded downstream before pressure was raised either as a ramp or in a series of 13.6 cmH2O steps. By varying step duration, the mean dP/dt could be matched to dP/dt applied as a steady ramp. P(B) was recorded as the pressure at which there was an abrupt increase in filtration with red cells passing to and through one or more sites in the vessel wall. In all vessels, increasing dP/dt raised P(B), with no differences between steps and ramps. The relation between P(B) and dP/dt was linear, consistent with a latent period, T (the slope), between a critical pressure being reached and the abrupt increase in permeability being observed. Direct observation confirmed this latent period. Between 12 and 20 (o)C, T was 8.5 +/- 0.47 s; between 0 and 5 degrees C, T was 11.5 +/- 0.97 s. Tissue cooling did not influence the time constant, tau, describing the rate of stretch of wall following a step increase in pressure and used to measure wall visco-elastic properties. Nor was the value of tau (1.15 +/- 0.06 s, n = 42) consistent with T being accounted for by visco-elasticity. It is suggested that the latent period may indicate an active response of the endothelium.

Skeletal muscle is sensitive to the tension–time integral but not to the rate of change of tension, as assessed by mechanically induced signaling

Mechanical forces regulate many cellular processes. Mechanotransduction, however, is poorly understood. In skeletal muscle, mechanical forces have a major impact on the regulation of cellular volume, yet the nature of the mechanical stimulation to which muscle is most sensitive is unknown. It was recently demonstrated that activation of the mechanically-sensitive kinase p54 jun- N-terminal-kinase (JNK), is a quantitative marker of mechanical stimulation in skeletal muscle. This marker was shown to be more sensitive to peak tension than to other tension-related parameters such as the tension–time integral (TTI) and the rate of change of tension (d T/d t). The purpose of the present study was to parcel out the contribution of TTI and d T/d t to mechanical stimulation of muscle under conditions of constant peak tension. The rat medial gastrocnemius in situ was subjected to one of four 5-min passive stretch protocols consisting of equal length excursions, but differing in displacement–time integral (4%, 40%, or 100%) and/or rate of stretch (0, 3, or 30 mm/s), and the resulting p54-JNK phosphorylation was assessed. A linear relationship between TTI and p54-JNK signaling was observed. However, no effect of d T/d t was observed. It is concluded that peak tension and TTI are necessary parameters for modeling the mechanical stimulus-response of muscle. Additionally, the mechanism of mechanotransduction is sensitive to peak tension and TTI, but not to d T/d t, and thus exhibits spring-like behavior. These findings may contribute to the refinement of disuse atrophy countermeasures.

Neuromuscular neutral zones associated with viscoelastic hysteresis during cyclic lumbar flexion.

The reflexive EMG from the L3-L4 to L5-L6 multifidus of the in vivo feline was recorded during application of single passive flexion-extension cycle of the lumbar spine. To determine the effect of viscoelastic hysteresis associated with a single-cycle flexion-extension and of increasing cycle frequency on the initiation and cessation displacement and tension thresholds of reflexive EMG from the multifidus muscles. It is known that reflexive EMG can be recorded from some paraspinal muscles as a result of mechanical stimulation of lumbar ligaments and other viscoelastic structures. It is also known that mechanical neutral zones exist in the spine, that viscoelastic hysteresis is associated with a stretch-release cycle, and that the rate of stretch and release has a profound impact on viscoelastic tissue responses. It is unknown what are the neurologic neutral zones of the spine within which reflexive EMG does not exist, as well as the dependence of such neurologic neutral zones on viscoelastic hysteresis and increasing frequency of a flexion-extension cycle. Single passive flexion-extension cycles of frequencies ranging from 0.1 to 1.0 Hz were applied to the lumbar spine of the feline while recording intramuscular EMG from the L3-L4 to L5-L6 multifidus. The displacement and tension thresholds associated with the initiation and cessation of EMG activity during the cycle were analyzed with respect to the cycles' viscoelastic hysteresis and frequency. The peak EMG discharge was tested for relationships with cycle frequency. The displacement and tension thresholds during the flexion phase of the cycle were significantly lower than the corresponding thresholds in the extension phase of the cycle. As the cycle frequency increased, EMG was triggered significantly earlier (lower displacement and tension thresholds) in the flexion phase and terminated earlier (higher displacement and tension thresholds) in the extension phase. The peak EMG was significantly larger as cycle frequency increased. Reflexive muscle forces are triggered at lower displacement or tension during flexion but diminish early during extension, leaving the spine unprotected for a substantial part of the extension movement. The muscle forces are recruited earlier and with larger intensity as the velocity of the movement increases, lending more protection to the spine. Faster extension movement, however, creates a larger window during which the spine is exposed to instability and injury because of lack of muscle forces.

Flame acceleration due to flame-induced instabilities in large-scale explosions

Large-scale explosions of initially quiescent methane-air and propane-air mixtures at atmospheric pressure are reported, in which the flame speed of a hemispherical flame is measured up to radii just beyond 3 m. A cellular flame is developed fairly soon and thereafter the flame speed increases continually with the square root of the time. The range of unstable wavelengths that wrinkle the flame increases as the flame propagates and this increases the flame speed. Two flame propagation regimes can be discerned. First, there is an initial stable regime, in which the flame is stabilized by thermo-diffusion and flame stretch, and the burning velocity is related to the Markstein length and rate of flame stretch. This is followed by a second regime in which, after a critical Peclet number has been attained, the flame is no longer stable, instabilities grow, wrinkle the flame, and increase the flame speed. Theoretical expressions for flame speed are presented for both regimes. That for the second rests on flame instability theory, with an increasing range of unstable wavelengths as the flame propagates. The theoretical predictions of flame radius with time over both regimes are in good agreement with those observed experimentally. Cell sizes are measured photographically as the flame progresses. These are fairly close to the theoretical wavelengths at which the rate of growth of the unstable flame amplitudes are a maximum.

Brownian dynamics simulations of a DNA molecule in an extensional flow field

The unraveling dynamics of long, isolated, molecules of DNA subjected to an extensional flow in a crossed-slot device [, “Single polymer dynamics in an elongational flow,” Science 276, 2016–2021 (1997); “Response of Flexible Polymers to a Sudden Elongational Flow,” Science 281, 1335–1340 (1998)] are predicted by Brownian dynamics simulations using measured elastic and viscous properties of the DNA as the only inputs. Quantitative agreement is obtained both in the percentages of various unraveling states, such as “folds,” “kinks,” “dumbbells,” half-dumbbells,” and “coils,” and in the ensemble-averaged stretch and rate of stretch. Under fast flows (De≳10), unraveling is initially nearly affine, but for fractional stretch greater than ≈1/3, stretching is delayed to an extent that varies widely from molecule to molecule by flow-induced folded states, which are far-from-equilibrium kinetic hindrances not predicted by dumbbell models. From the computer simulations, the source of the high molecule-to-molecule heterogeneity in the experiments is traced to variability in the initial polymer configuration, which sets the unraveling path the molecule must take at De≳10. Formation of folds and kinks during unraveling can be predicted fairly reliably just by examining the initial state. The high-De unraveling behavior is consistent with the predictions of one-dimensional “kink dynamics” simulations.

Avulsion fracture of the ischium

Avulsion of the ischial apophysis is well known to occur from puberty until final fusion at around 25 years of age. The mechanism of injury varies but is usually strenuous, resulting in a high rate of stretch or contraction of the hamstrings. Minimally displaced fractures have a good prognosis when managed non-operatively. Where the fracture separation is wide there is less certainty. Union sometimes occurs but more commonly fibrous non union is the result. Consequently surgical intervention may be appropriate. Authors have suggested that displacements of more than two centimetres should be openly reduced and fixed. Too few cases have been reported to provide definitive management protocols. It remains unlikely that athletes can return to their former standards without surgical intervention but even accurate reduction and internal fixation does not guarantee a return to previous levels of achievement. One author reports of a semi professional American footballer who after excision of the avulsed ischial tuberosity and reattachment of the hamstrings was able to return to the same standard of play. It would be logical to suppose that restoration of the hamstrings to their original length by accurate reduction would make them more efficient. We report the case of a 32 year old athletic male who avulsed his inferior pubic ramus and ischial tuberosity whilst water-skiing who was treated by open reduction and internal fixation.

Crossbridge viscosity in activated frog muscle fibres

Force responses to fast ramp stretches at various velocities were recorded in single muscle fibres isolated from tibialis anterior muscle of the frog ( Rana esculenta) at a sarcomere length between 2.15 and 3.25 μm at 15°C. Stretches were applied at the tetanus plateau and during tetanus rise. Length changes were recorded at the sarcomere level using either a laser diffractometer or a striation follower apparatus. The immediate force response to the stretch is not simply elastic, as is usually assumed, but is composed of the sum of at least two components: (i) elastic (force proportional to the amount of stretch); and (ii) viscous (force proportional to the rate of stretch). The viscous response is associated with a short (about 10 μs) relaxation time. The amplitude of the viscous component increases progressively with tension during the tetanus rise and scales down with sarcomere length approximately in the same way as the tetanic tension. These results suggest that the viscosity of activated fibres may arise from crossbridge kinetics.

The relationship between the kinematics of passive movement, the stretch of extensor muscles of the leg and the change induced in the gain of the soleus H reflex in humans

The gain of the H reflex attenuates during passive stepping and pedalling movements of the leg. We hypothesized that the kinematics of the movement indirectly reflect the receptor origin of this attenuation. In the first experiment, H reflexes were evoked in soleus at 26 points in the cycle of slow, passive pedalling movement of the leg and at 13 points with the leg static (the ankle was always immobilized). Maximum inhibition occurred as the leg moved through its most flexed position ( P < 0.05). Inhibition observed in the static leg was also strongest at this position ( P < 0.05). The increase in inhibition was gradual during flexion movement, with rapid reversal of this increase during extension. In the second experiment, the length of stretch of the vasti muscles was modelled. Variable pedal crank lengths and revolutions per minute (rpm) altered leg joint displacements and angular velocities. Equivalent rates of stretch of the vasti, achieved through different combinations of joint displacements and velocities, elicited equivalent attenuations of mean reflex magnitudes in the flexed leg. Reflex gain exponentially related to rate of stretch ( R 2 = 0.98 P < 0.01). The results imply that gain attenuation of this spinal sensorimotor path arises from spindle discharge in heteronymous extensor muscles of knee and/or hip, concomitant with movement.

Absence of mechanical evidence for attached weakly binding cross‐bridges in frog relaxed muscle fibres.

1. Passive force responses to ramp stretches at various velocities were measured in intact and skinned single muscle fibres isolated from the lumbricalis muscle of the frog. Force was measured using a fast capacitance transducer and sarcomere length was measured using a laser light diffraction technique at a point very close to the fixed end so as to avoid effects of fibre inertia. Experiments were performed at 15 degrees C with sarcomere length between 2.13 and 3.27 microns under high (170 mM) and low (20 mM) ionic strength. 2. The analysis shows that the force response is the sum of at least three components: (i) elastic (force proportional to the amount of stretch), (ii) viscous (force proportional to rate of stretch), and (iii) viscoelastic (resembling the response of a pure viscous element in series with an elastic element). 3. The amplitude of all these components increased progressively with sarcomere length in the whole range measured. 4. A further component, attributable to the short-range elasticity (SREC), was present in the force response of the intact fibres. 5. The amplitude of the force response decreased substantially upon skinning at high ionic strength but increased again at low ionic strength. The SREC was completely abolished by skinning. 6. None of the components of the force response was found to have the properties expected from the previously postulated 'weakly binding bridges'.

Extinction of Counterflow Premixed Flames Under Periodic Variation of the Rate of Stretch

Abstract The influence of periodic oscillations of the rate of stretch on the extinction of lean methane-air and butane-air premixed flames in stagnation-point flow and counterflow is experimentally investigated. The periodic variation of the rate of stretch is achieved by means of two speakers that are attached to the conventional counterflow burners. It is found that for a given frequency, increasing the amplitude of the velocity oscillations tends to weaken the lean flames such that the critical minimum fuel concentration at extinction increases. The effects of oscillating stretch rates on flame position and extinction characteristics are found to diminish with the frequency. The extinction data are also obtained as a function of the frequency of velocity oscillations for given mean flow through the burners. Higher frequency flow oscillations are found to render more robust premixed flames since larger amplitudes of velocity oscillations are needed to extinguish the flames. For the counterflow methane-air and butane-air premixed flames the temperature profiles between the opposing burners with and without periodic velocity oscillations are determined. Periodic velocity fields arc found to reduce the temperatures throughout the flow field resulting in closer approach of the counterflow flames to the stagnation plane.

Regularity in the generation of discharge patterns by primary and secondary muscle spindle afferents, as recorded under a ramp-and-hold stretch.

The discharge frequency of primary (Ia) and secondary (II) muscle spindle afferents from the tibial anterior muscle of the cat were recorded under a ramp-and-hold stretch of the host muscle. The rate of ramp stretch and the prestretch of the muscle were varied systematically. The degree of stretch was kept constant. For a discharge pattern recorded at a ramp rate of 10 mm/s, the peak dynamic discharge, the maximum static value and the final static value were determined. These three discharge rate values were plotted against the maximum static value. In the resulting charts the II afferents presented themselves as a homogeneous group of spindle afferents, whereas the Ia fibers separated into three subgroups. The existence of three subpopulations of Ia fibers was verified by the method of Hald. Furthermore, it is shown that each subpopulation generated its discharge patterns in its own regularly systematic manner. It was concluded that, as one of the three Ia subpopulations exhibits much the same dynamic and static stretch properties as the II fibers, the encoder of this subpopulation must receive its receptor current from the sensory terminals of passive intrafusal chain fibers. The encoder of a second Ia subpopulation indicates its action potentials using the receptor current stemming from the bag1 sensory terminals, these Ia fibers eliciting a slow adaptation component of a high magnitude which is assumed to be the consequence of a high level of "creep" in the passive intrafusal bag1 fiber. The third Ia subpopulation initiates its action potential sequences by means of the receptor current stemming from the passive bag2 fiber, producing behavior patterns that lie between those of the other two Ia subpopulations.

Acceleration waves in an extensible elastica

We consider here the propagation of acceleration waves in planar elastic rods that are capable of bending and stretching. The moment-curvature and force-stretch relations used have sufficient generality as to afford a description of materially inhomogeneous, geometrically non-uniform, slender elastic rods undergoing finite deformations. It is shown that either the curvature of the rod or its rate of stretch suffers a jump discontinuity at an acceleration wave. The former wave is shown to have the characteristics of a longitudinal shock wave propagating into an inhomogeneous elastic body. Speeds of propagation and conditions governing the evolutionary behavior of these waves are derived. Discontinuities induced by these waves, and higher order waves are also considered.

The Strain Exerted by a Vortex on a Flame—Determined from Velocity Field Images

Abstract Velocity field imaging techniques were used to observe how a single toroidal vortex, which represents one eddy in a turbulent flow, exerts aerodynamic strain on a premised flame. By achieving dense seeding of the flow, the spatial derivatives of velocity were determined accurately, which allows the following to be measured as a function of space and time: the aerodynamic strain rate that is tangential to the flame, the rate of flame stretch, the vorticity field, the shear strain rate field and the flow pattern near the forward stagnation point. The vortex strength was sufficient to cause quenching of the flame. An unexpected result is that the maximum strain on the flame does not occur on the centerline near the forward stagnation point. Instead the strain rate distribution is significantly different from numerical simulations of Poinsot, et al., for which strain is maximum on centerline. The difference is due to the different vortex sizes considered, which indicates that small vortices exert a different strain rate distribution on a flame than larger vortices, and that the process cannot be modelled as being self-similar. During flame quenching, the maximum local strain rate is measured to be 35 sec-1, which is similar to the value of 42 sec-1 that is required to quench a steady, planar counterflow flame of the same equivalence ratio The velocity field images also show how the flame creates vorticity in the products. This flame-generated turbulence results from the gas expansion and baroclinic torque terms in the vorticity transport equation. The velocity field ahead of the flame also is affected by the flame, but no vorticity is generated in the reactants; this validates the assumption made in many models that the turbulence in the reactants is undisturbed by the flame