Investigation into the effect of static stretching on the active stiffness and damping characteristics of the ankle joint plantar flexors

2001 ◽  
Vol 2 (1) ◽  
pp. 15-22 ◽  
Author(s):  
D.Glenn Hunter ◽  
Vince Coveney ◽  
Jonathon Spriggs
Keyword(s):  
Ankle Joint ◽  
Static Stretching ◽  
Plantar Flexors ◽  
Damping Characteristics ◽  
Stiffness And Damping

scholarly journals Acute Effects of Two Different Static Stretching Protocols on Performance Parameters in Professional Ballet Dancers

Proceedings ◽  
2019 ◽  
Vol 25 (1) ◽  
pp. 20
Author(s):  
Eleni Kotsala ◽  
Ioli Panidi ◽  
Gregory C. Bogdanis ◽  
Athena Androulidaki ◽  
Georgia Giannakopoulou ◽  
...  
Keyword(s):  
Ankle Joint ◽  
Motor Coordination ◽  
Muscle Power ◽  
Acute Effect ◽  
Static Stretching ◽  
Acute Effects ◽  
Plantar Flexors ◽  
Countermovement Jump ◽  
Ballet Dancers ◽  
Long Duration

AIM: Ballet dancers’ performance is based on the execution of complex technical skills that require an unusually large range of motion (ROM) and increased muscular power. Static stretching is commonly used to increase ROM, but it may induce a transient decrease in muscle power. However, this may depend on the population and stretching protocol. The purpose of this study was to compare the acute effect of a short (20 s) vs. a long (60 s) static stretching protocol on joint ROM and jumping performance in ballet dancers. MATERIAL & METHOD: Sixteen female professional ballet dancers (age, 25.9 ± 2.7; dancing experience, 19.6 ± 3.8 y) performed 5 days of testing using a single-leg stretching and jumping design. Baseline measurements of one-leg countermovement jump (CMJ) and a ballet technical jump with one leg (“temps levé”, TL) were performed on the first visit. On the other four visits, dancers stretched their hamstrings, quadriceps and plantar flexors for 20 or 60 s per muscle group and then performed a CMJ or a TL in a counterbalanced order. This combination of stretching and jumping resulted in four conditions: long stretch-CMJ, long stretch-TL, short stretch-CMJ and short stretch-TL. In all conditions, ankle joint ROM was measured at rest and immediately after stretching. RESULTS: ROM significantly increased following stretching (p = 0.01) with no difference between stretching protocols (p = 0.505). CMJ height decreased post-stretching following both stretching protocols (p = 0.01); however, the long-duration static stretching induced a larger decrease in jump height (p = 0.020). TL height remained unchanged after the short and the long stretching protocols (7.7 ± 2.1 to 7.4 ± 2.2 vs. 7.7 ± 2.1 to 7.2 ± 2.0 cm, respectively, p = 0.701). CONCLUSION: Both stretching protocols similarly increased ankle joint ROM and decreased one-leg CMJ height immediately post-stretching. Also, both stretching protocols did not decrease TL height, probably because dancers are able to compensate for the stretch-induced deficit in muscle power through motor coordination.

Changes in H-reflex amplitude to muscle stretch and lengthening in humans

2016 ◽  
Vol 27 (5) ◽  
pp. 511-522 ◽  
Author(s):  
Francesco Budini ◽  
Markus Tilp
Keyword(s):  
Human Movement ◽  
Careful Consideration ◽  
H Reflex ◽  
Spinal Reflex ◽  
Neural Pathways ◽  
Static Stretching ◽  
Plantar Flexors ◽  
Reflex Excitability ◽  
Apparent Disagreement ◽  
Shed Light

AbstractSpinal reflex excitability is traditionally assessed to investigate neural adjustments that occur during human movement. Different experimental procedures are known to condition spinal reflex excitability. Among these, lengthening movements and static stretching the human triceps have been investigated over the last 50 years. The purpose of this review is to shed light on several apparent incongruities in terms of magnitude and duration of the reported results. In the present review dissimilarities in neuro-spinal changes are examined in relation to the methodologies applied to condition and measure them. Literature that investigated three different conditioning procedures was reviewed: passive dorsiflexion, active dorsiflexion through antagonists shortening and eccentric plantar-flexors contractions. Measurements were obtained before, during and after lengthening or stretching. Stimulation intensities and time delays between conditioning procedures and stimuli varied considerably. H-reflex decreases immediately as static stretching is applied and in proportion to the stretch degree. During dorsiflexions the inhibition is stronger with greater dorsiflexion angular velocity and at lower nerve stimulation intensities, while it is weaker if any concomitant muscle contraction is performed. Within 2 s after a single passive dorsiflexion movement, H-reflex is strongly inhibited, and this effect disappears within 15 s. Dorsiflexions repeated over 1 h and prolonged static stretching training induce long-lasting inhibition. This review highlights that the apparent disagreement between studies is ascribable to small methodological differences. Lengthening movements and stretching can strongly influence spinal neural pathways. Results interpretation, however, needs careful consideration of the methodology applied.

Rotordynamic Performance of a Rotor Supported on Bump Type Foil Gas Bearings: Experiments and Predictions

2006 ◽  
Vol 129 (3) ◽  
pp. 850-857 ◽  
Author(s):  
Luis San Andrés ◽  
Dario Rubio ◽  
Tae Ho Kim
Keyword(s):  
High Speed ◽  
Critical Speed ◽  
Load Capacity ◽  
Test System ◽  
Foil Bearings ◽  
Rotor Imbalance ◽  
Synchronous Motion ◽  
Damping Characteristics ◽  
Rotor Surface ◽  
Stiffness And Damping

Gas foil bearings (GFBs) satisfy the requirements for oil-free turbomachinery, i.e., simple construction and ensuring low drag friction and reliable high speed operation. However, GFBs have a limited load capacity and minimal damping, as well as frequency and amplitude dependent stiffness and damping characteristics. This paper provides experimental results of the rotordynamic performance of a small rotor supported on two bump-type GFBs of length and diameter equal to 38.10mm. Coast down rotor responses from 25krpm to rest are recorded for various imbalance conditions and increasing air feed pressures. The peak amplitudes of rotor synchronous motion at the system critical speed are not proportional to the imbalance introduced. Furthermore, for the largest imbalance, the test system shows subsynchronous motions from 20.5krpm to 15krpm with a whirl frequency at ∼50% of shaft speed. Rotor imbalance exacerbates the severity of subsynchronous motions, thus denoting a forced nonlinearity in the GFBs. The rotor dynamic analysis with calculated GFB force coefficients predicts a critical speed at 8.5krpm, as in the experiments; and importantly enough, unstable operation in the same speed range as the test results for the largest imbalance. Predicted imbalance responses do not agree with the rotor measurements while crossing the critical speed, except for the lowest imbalance case. Gas pressurization through the bearings’ side ameliorates rotor subsynchronous motions and reduces the peak amplitudes at the critical speed. Posttest inspection reveal wear spots on the top foils and rotor surface.

Nonlinear Isolator Optimization Using RMS Cost Function

2004 ◽  
Author(s):  
A. Narimani ◽  
M. F. Golnaraghi
Keyword(s):  
Closed Form Solution ◽  
Optimization Method ◽  
Relative Displacement ◽  
Form Solution ◽  
Jump Phenomenon ◽  
Nonlinear Parameters ◽  
Strongly Nonlinear ◽  
Damping Characteristics ◽  
Stiffness And Damping ◽  
Boundary Limits

In this paper using a modified averaging method the frequency response of a general nonlinear isolator is obtained. Stiffness and damping characteristics are considered cubic functions of displacement and velocity through the isolator. Analytical results are compared with those obtained by numerical integration in order to validate the closed form solution for strongly nonlinear isolator. While increasing the nonlinearity in the system improves the response of the isolator, stability and jump avoidance conditions set boundary limits for the parameters. The effects of nonlinear parameters to avoid jump phenomenon are discussed in detail. The set of parameters where the system behaves regularly are found and the nonlinear isolator is optimized based on RMS optimization method. Using this method the RMS function of absolute acceleration of the sprung mass is minimized versus the RMS function of relative displacement.

Research on Stiffness and Damping Characteristics of Fixed Oily Porous Materials Joint Interface

2011 ◽  
Vol 422 ◽  
pp. 575-579
Author(s):  
Chong Nian Qu ◽  
Liang Sheng Wu ◽  
Jian Feng Ma ◽  
Yi Chuan Xiao
Keyword(s):  
Porous Material ◽  
Porous Materials ◽  
Parallel Plate ◽  
Joint Interface ◽  
Force Model ◽  
Equivalent Stiffness ◽  
Contact State ◽  
Damping Characteristics ◽  
Stiffness And Damping ◽  
Damping Model

In this document, using the anti-squeezed force model in the narrow parallel plate when fluid is squeezed, the equivalent stiffness and damping model is derived. It is further verified that it can increase the stiffness and damping while there are oil between the joint interfaces theoretically. Because the contact state of oily porous material can divide into liquid and solid parts, the document supposes that it is correct and effective to think the stiffness and damping of the two parts as shunt connection.

Modelling Fluid Inertia Forces of Short Journal Bearings for Rotordynamic Applications

1993 ◽  
Author(s):  
A. El-Shafei
Keyword(s):  
Momentum Equation ◽  
Journal Bearings ◽  
Fluid Inertia ◽  
Radial Acceleration ◽  
Damping Characteristics ◽  
Energy Approximation ◽  
Form Model ◽  
Fluid Inertia Effect ◽  
Stiffness And Damping ◽  
Inertia Forces

Abstract It has been recently suggested that fluid inertia may play an important role in the dynamic behavior of rotors supported on journal bearings. This paper presents a model for fluid inertia forces in short cylindrical journal bearings based on an energy approximation. The inertialess velocity profiles predicted by the solution of Reynolds’ equation are inserted in the axial momentum equation multiplied by the axial velocity profile and integrated across the film thickness, to obtain the pressure in short journal bearings including the fluid inertia effect. The pressure is then integrated to obtain the fluid inertia forces. It is shown that the inertia forces thus obtained are proportional to the usual radial, centripetal, tangential and coriolis accelerations of the journal, in addition to a nonlinear radial acceleration. Moreover, it is shown that the inertia forces contribute to the stiffness and damping characteristics of the journal bearings. The inertia coefficients of the bearings are obtained in cartezian and cylindrical coordinates, for both uncavitated and cavitated bearings, and are plotted versus the eccentricity ratio. The model thus obtained is an analytical closed form model for fluid inertia forces in short journal bearings. Such a model is the most suitable for rotordynamic applications, particularly for time transient rotordynamic simulations.

A simulation investigation of helicopter ground resonance phenomenon

2019 ◽  
Vol 91 (3) ◽  
pp. 484-497
Author(s):  
Jaroslaw Stanislawski
Keyword(s):  
Simulation Method ◽  
Landing Gear ◽  
Rotor Blades ◽  
Resonance Phenomenon ◽  
Content Type ◽  
Damping Characteristics ◽  
Runge Kutta Method ◽  
Ground Resonance ◽  
Lumped Masses ◽  
Stiffness And Damping

Purpose The purpose of this paper is to present a simulation method applied for investigation of helicopter ground resonance phenomenon. Design/methodology/approach The considered physical model of helicopter standing on ground with rotating rotor consists of fuselage and main transmission gear treated as stiff bodies connected by elastic elements. The fuselage is supported on landing gear modeled by spring-damper units. The main rotor blades are treated as set of elastic axes with lumped masses distributed along blade radius. Due to Galerkin method, parameters of blades motion are assumed as a combination of bending and torsion eigen modes. A Runge–Kutta method is applied to solve equations of motions of rotor blades and helicopter fuselage. Findings The presented simulation method may be applied in preliminary stage of helicopter design to avoid ground resonance by proper selection of landing gear units and blade damper characteristics. Practical implications Ground resonance may occur in form of violently increasing mutual oscillations of helicopter fuselage and lead-lag motion of rotor blades. According to changes of stiffness and damping characteristics, simulations show stable behavior or arising oscillations of helicopter. The effects of different blade balance or defect of blade damper are predicted. Originality/value The simulation method may help to determine the envelope of safe operation of helicopter in phase of take-off or landing. The effects of additional disturbances as results of blades pitch control as swashplate deflection are introduced.

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