Search results for "eccentric"
showing 10 items of 182 documents
Interaction between fascicle and tendinous tissues in short-contact stretch-shortening cycle exercise with varying eccentric intensities
2005
The interaction between fascicle and tendinous tissues (TT) in short-contact drop jumps (DJ) with three different drop heights [low (Low), optimal (OP), and high (High)] was examined with 11 subjects. The ground reaction force (F z) and ankle and knee joint angles were measured together with real-time ultrasonography (fascicle length) and electromyographic activities of the medial gastrocnemius (MG) and vastus lateralis (VL) muscles during the movement. With increasing drop height, the braking force and flight time increased from Low to OP ( P < 0.05). In High, the braking force increased but the flight time decreased compared with OP ( P < 0.05). During contact of Low and OP conditi…
Geometric optimal control of elliptic Keplerian orbits
2005
This article deals with the transfer of a satellite between Keplerian orbits. We study the controllability properties of the system and make a preliminary analysis of the time optimal control using the maximum principle. Second order sufficient conditions are also given. Finally, the time optimal trajectory to transfer the system from an initial low orbit with large eccentricity to a terminal geostationary orbit is obtained numerically.
Acute (0-2h) and delayed (2-8D) effects of exercise-induced muscle damage and soreness on elbow target movements.
2011
The aim was to examine the acute and delayed effects of exercise-induced muscle damage and soreness on elbow target movements (TM) performance and control. Ten males performed an exercise of 50 maximal eccentric elbow actions. TMs were performed at three movement ranges. Maximal forces, active stretch reflex and TM were tested, and muscle soreness, creatine kinase and elbow joint stiffness were determined acute (after and 2 h) and delayed (2, 4, 6, 8d) postexercise. Both the long lasting muscle soreness and force drop were observed after the exercise. Joint stiffness was increased at 2 h postexercise. The highest deterioration in flexion-TM performance was found at the time (2 h) and at the…
Chaotic dynamics around cometary nuclei
2017
We apply a generalized Kepler map theory to describe the qualitative chaotic dynamics around cometary nuclei, based on accessible observational data for five comets whose nuclei are well-documented to resemble dumb-bells. The sizes of chaotic zones around the nuclei and the Lyapunov times of the motion inside these zones are estimated. In the case of Comet 1P/Halley, the circumnuclear chaotic zone seems to engulf an essential part of the Hill sphere, at least for orbits of moderate to high eccentricity.
Brancati su Pirandello e il pirandellismo
2019
Nel romanzo breve "Sogno di un valzer" uscito a puntate su “Quadrivio”, dal 5 giugno al 14 agosto 1938, Vitaliano Brancati mette in scena, tra osservazione dei luoghi e rilevamento di costume, un’umanità fuori misura, continuamente in bilico tra realtà e sogno. A Caltanissetta (Nissa) la città nel cui Istituto magistrale lo scrittore, voltate le spalle alla Roma fascista, è venuto a insegnare, personaggi non appariscenti, insignificanti, che tuttavia covano desideri, si arrovellano in domande metafisiche. Prende così forma il leitmotiv delle critica al pirandellismo che più volte con ironia sottile affiora negli scritti brancatiani. Il saggio mostra come esso si intrecci con la comicità sul…
Concentric force enhancement during human movement
2001
In order to understand the possible mechanisms contributing to enhanced concentric performance in stretch-shortening cycle exercises in vivo the present study examined knee extension torque, electromyogram (EMG) activity and fascicle length of the vastus lateralis muscle in maximal and submaximal human movements. Maximal concentric knee extensions (120 degrees s(-1)) were done after pre-stretch and pre-isometric conditions by nine volunteers. During shortening at the knee angle of 115 degrees (180 degrees = extended) the knee extension torque was found to be greater in pre-stretch condition (272 vs. 248 N m, P < 0.05) although the torque level prior to shortening was smaller than in pre-iso…
Viscosity of the elbow flexor muscles during maximal eccentric and concentric actions.
1996
The aim of the present study was to estimate the damping coefficient (B factor) of the elbow flexor muscles during both eccentric and concentric muscle actions. We used a muscle model consisting of a viscous damper associated in parallel with a contractile component, both in series with an elastic component. The viscous damper allowed the concentric loss and the eccentric gain of force to be modelled. Eight volunteer subjects performed maximal eccentric and concentric elbow movements on an isokinetic dynamometer at angular velocities of 0.52, 1.04 and 2.09 rad*s(-1). Torques at an elbow joint angle of 90 degrees were recorded. Electromyogram (EMG) signals from the belly of the right elbow f…
Effect of Training-Induced Changes in Achilles Tendon Stiffness on Muscle–Tendon Behavior During Landing
2018
During rapid deceleration of the body, tendons buffer part of the elongation of the muscle–tendon unit (MTU), enabling safe energy dissipation via eccentric muscle contraction. Yet, the influence of changes in tendon stiffness within the physiological range upon these lengthening contractions is unknown. This study aimed to examine the effect of training-induced stiffening of the Achilles tendon on triceps surae muscle–tendon behavior during a landing task. Twenty-one male subjects were assigned to either a 10-week resistance-training program consisting of single-leg isometric plantarflexion (n = 11) or to a non-training control group (n = 10). Before and after the training period, plantarf…
A Pluto-like radius and a high albedo for the dwarf planet Eris from an occultation
2011
The dwarf planet Eris is a trans-Neptunian object with an orbital eccentricity of 0.44, an inclination of 44 degrees and a surface composition very similar to that of Pluto. It resides at present at 95.7 astronomical units (1ĝ€‰au is the Earth-Sun distance) from Earth, near its aphelion and more than three times farther than Pluto. Owing to this great distance, measuring its size or detecting a putative atmosphere is difficult. Here we report the observation of a multi-chord stellar occultation by Eris on 6 November 2010 ut. The event is consistent with a spherical shape for Eris, with radius 1,163±6 kilometres, density 2.52±0.05 grams per cm 3 and a high visible geometric albedo,. No nitro…
Effects of eccentric phase velocity of plyometric training on the vertical jump.
2004
The aim of this study was to compare the effects of plyometric training performed with rapid or slow stretch contraction on jump performance and muscle properties. Thirty males between the ages of 19 and 22 volunteered for the 8-week experiment. Subjects were divided into the following three groups: training group 1 (TG1), training group 2 (TG2), and control group (CG). Each of the two experimental groups underwent a unique training regimen. For the first group (TG1, n = 12): from a standing position the subject flexed his knees to a 90 degrees angle with velocity standardized and controlled at 0.4 m/s and immediately performed a leg extension as quickly as possible. For the second group (T…