DROP JUMP TRAINING STIMULUS INDUCES DIFFERENT QUALITATIVE ADAPTATIONS ON THE ELECTROMYOGRAPHIC (EMG) PATTERN OF THE LEG EXTENSOR MUSCLES

INTRODUCTION Jumping technique can dramatically affect drop jump performance (Warren et al., 1995), which suggests that the quality of the training stimulus may also influence the neuromuscular control of drop jump exercises. The present study was designed to investigate the changes in performance characteristics and in neuronal activation patterns, induced by different drop jump training stimulus. Thirteen healthy males were involved in an 8 weeks training program, followed by a detraining period o 4 weeks and a new training period of 4 additional weeks. The subjects exercised 3 to 4 times per week. They performed reactive.DJ from their best drop height. All the training sessions were supervised. During the sessions of the first 4 weeks the subjects were informed on the flight time of each jump and a reactive jump with maximal effort with a short contact time were continuously demanded by the supervisor. On the training sessions from week 4 to week 8 the supervisor only informed the subjects about the flight time of the jump. Finally, on the last 4 weeks the subjects were informed both on the flight and contact time of each jump. The testing procedures took place before and after each 4 weeks. The subjects performed reactive drop jump (DJ) exercises from the heights of 25, 40, 55 and 70 cm. The vertical ground reaction forces and the surface electromyograms (EMG) of the triceps surae muscles (GAS and SOL) were recorded. The EMGs were full-wave rectified and integrated (iEMG) over different functional phases (Schmidtbleicher et al., 1988): Preactivation phase (PRE) (100ms before ground contact); Reflex Induced Activation phase (i.e. the activation phase from 40 ms to 120 ms after impact); Late EMG Response phase (LER) (activity from 120 ms until the end of contact). RESULTS Table 1 summarises the results observed on the jump heightlcontact time ratio (JHCT) during the training process. Table 1- Mean and standard deviation of the jump height contacV contact time ratio (JHICT), for drop jump exercises from 25 cm (DJ25), 40 cm (DJ40), 55 cm (DJ55) and 70 cm (DJ70), during the training The increase on the jump height/contact time ratio (JHCT) corresponds to the training periods where the subjects were continuously instructed to jump reactively and received feedback information on the jump height and contact time of each individual drop jump. A decrease on the jump height/contact time ratio (JHCT) occurred when the feedback was only the jump height of the drop jumps. The EMG results showed a qualitative shifting in the EMG-patterns toward an accented RIA-phase activation, when the JHCT ratio increased. Additionally the changes in contact time were correlated negatively (r=-0.70 ; -0.85, pc0.001) with the iEMG of the RIA-phase for GAS and SOL muscles. CONCLUSION These results revealed that feedback on the jumping performance, produced clear differences on the biomechanics of the jump. Qualitative adaptations on the EMG pattern induced by a strength training program with drop jump exercises, are only observed if the jumping technique allows for a good jump height/contact time ratio. These parameter should be used to monitor the quality of reactive strength training stimulus

KINETIC ENERGY OF BODY SEGMENTS IN DROP JUMP

INTRODUCTION - In sport movements, such as sprinting and jumping, where the ability to produce explosive movement is extremely important, the elastic characteristics of the muscle-skeletal system are decisive. Drop jump (DJ) exercises are often used as a training method to develop the mechanical and control capabilities of the neuromuscular system. DJ has also been used to obtain very important data about the degree of adaptability of the locomotor system to increasing amounts of mechanical load, using different dropping heights. The purpose of this study is to analyse the changes of the kinetic energy of body segments (KE) in relation to the increase o! mechanical load, both in the stretching and push-off phases. These changes are related to the angular kinematics of joints and to the relative length changes on some of the extensor muscles. METHODS - Four elite sprinters (height 17855 cm, body mass 69.34.5 kg) performed 6 DJ from 25, 40, 55 and 70 cm. Ground reaction forces were recorded at 500Hz and vertical peak and vertical net impulse were calculated. Simultaneously, angular kinematic data of the ankle, knee and hip joints were calculated using video analysis system (120 Hz). We used Visser et al. (1990) model to calculate the relative length changes (%L) of gastrocnemius (G), rectus femoris (RF) and biceps femoris (BF) muscles. The joint angular velocity (~)) and relative muscle length changes velocity (%L.s-') were also calculated. The KE energy of the foot, lower leg, thigh and upper body mass centres were calculated from the kinematic and anthropometric data. RESULTS - The basic results are showed on the table, AVG and SD values, both for the stretching and shortening phases of the ground contact period. CONCLUSION - The KE of the body segments at the end of push-off was higher on DJ25 and DJ40, Wen compared with the KE at touchdown, presenting a positive energetic balance. At DJ55, the energetic balance was null and at DJ70 was negative. The stretching and shortening velocities increased in all muscles with the increase of DJ height. Nevertheless, no differences were found on vertical jumping achievement between DJ executed from different heights. The subjects were able to reduce the increasing stretching load producing higher vertical net impulses during the downward movement. REFERENCES Visser J.J.. Hoogkamer, J., Bobbert, M.F. and Huijing, P.A.(1990). Eur J Appl Physiol, 61: 453-46

THE ANTAGONIST MUSCLE PATTERN IN ELBOW EXTENSION OFA THROWING TASK

INTRODUCTION The myoelectric activity in fast human movements is characterised by a phasic pattern with two fundamental events: the first agonist burst, responsible for the initial limb acceleration, and an antagonist impulse. The accurate definition of the antagonist burst role, and the relative participation of peripheral and central sources on its control, are not clearly defined in the literature (Angel, 1977; Marsden et al., 1983). The purpose of the present study was (1) to characterise the antagonistic pattern on the elbow extension when subjects had to throw a dart onto a target, and (2) to analyse the antagonist changes when subjects throw with different accuracy/speed demands. Experiments were performed on 13 subjects. Surface EMG were recorded from triceps and biceps brachii with active bipolar electrodes. Electrogoniometers wore used on shoulder and elbow joints. RESULTS The antagonist EMG contained a phasic burst (ANT) which began between the movement onset and the end of the agonist activation, with an usual co-contraction duration of less than 30 ms. The time interval between the movement onset and the beginning of ANT was normally higher than the EMG latency necessary for spindle influences, considered to be less than 20 ms (Tarkka, 1986). In our results, ANT always began during the acceleration phase and, in most cases, developed its maximum intensity around the moment of elbow peak velocity. So, the antagonist burst represents more than an impulse braking preventing full extension, and we must admit its participation in the control of the duration of the acceleration phase. Antagonist modifications with velocity indicated an amplitude increase, measured by the integrated EMG. without relevant temporal changes. Two subjects presented an alternative way of braking the movement, when the accuracy constraints were absent, based, on the increase of the joint stiffness through the co-contraction of agonist and antagonist muscles. This kind of movement braking resulted in a reduced timing accuracy demand when compared with the active braking, produced by the antagonist phasic burst (Ghez & Martin, 1 982). CONCLUSION The timing of the antagonist phasic burst invite us (1) to associate it with the control of the end of the acceleration phase and (2) to accept that it could be influenced by the muscular response to stretch, although modulated by higher central commands. (3) The general tendency was to maintain the temporal structure of antagonist EMG among conditions and to increase its intensity with the increase of the throwing velocity. (4) Two subjects presented an alternative way of braking the movement when the accuracy constraints wers absent. REFERENCES Angel, R. (1977). Antagonist muscle activity during rapid arm movements. Central versus proprioceptive influences. J. Neuroi, Neuros., Psychia t., 40: 683-686. Ghez, C., & Martin, J. (1 982). The control of rapid limb movement in the cat. Ill - Agonist- Antagonist coupling. Exp: Br. Res., 45: 1 15 - 125. Marsden, C., Obeso, J., & Rothwell, J. (1983). The function of the antagonist muscle during fast limb movements in man. J. Physiol., 335: 1 - 13. Tarkka, 1. (1986). Short and long latency reflexes in human muscles following electrical and mechanical stimulation. Acta Physiol. Scand., 128. Supplem. 557: 1-32

A KINEMATIC ANALYSIS OF ROWING PERFORMANCE DURING A 2000M ERGOMETER TEST

The aim of this study was to investigate how force, velocity and power change during a maximum 2000m-rowing test, and to examine the relationship between 2-D joint kinematics and performance. Ten male rowers performed a 2000m test, which was analysed in five periods, considering also the mean final results. One-way ANOVA for repeated measures showed that force, velocity and power changed significantly along the 2000m test. Hip, and elbow joint kinematic parameters remained unchanged throughout the test but knee’s angular displacement and angular position at the catch, changed significantly during the 2000m test. A stepwise multiple regression analysis evidenced that the knee angular position at the catch is in relationship with time to finish the 2000m rowing and remained the single predictor of performance

Test-retest reliability of three-dimensional gait analysis in chronic low back pain individuals: a preliminary study

Trabalho apresentado no 1st Clinical Movement Analysis World Conference, 29 setembro a 4 outubro 2014, Roma, Itáli

TRAINING INDUCED QUALTI'ATIVE ADAPTATIONS ON THE ELECTROMYOGRAPHIC (EMG) PATTERN OF TI-IE LEG EXTENSOR MUSCLES

The combination of eccentric and concentric actions forms a natural type of muscle. function called a stretch-shortening cycle or SSC (Komi, 1984). Such SSC exercises are more efficient than pure concentre exercises (Aura and Komi, 1986). The prestretching increases the stiffness of the muscle-tendon complex and thus favors conditions that allow performance potentiation in the subsequent concentric phase. The fact that both the facilitator). and inhibitory sensory inputs from the muscle take part in the stiffness regulation implies that there is a great potential for adaptation. For training purposes, it is relevant that training could cause not only quantitative changes of the neuronal input to the muscle but also a qualitative shifting in the electromyogaphic (EMG) patterns (Schmidtbleicher et al. 1988). The present study was designed to investigate the changes in force-time characteristics in neuronal activation patterns before and after a training period using SSC exercises. Thirteen healthy males were involved in a 4 week training program. The subjects exercised 3 to 4 times per week. They performed reactive Dl from their best drop height. In each training unit they exercised 3 - 4 sets with 10-20 repetitions each and a rest interval of 5 minutes illbetwee11 sets. The testing procedures took place before and after the mining period. The subjects performed squat jumps (SJ), conter-movement jumps (CMJ) and reactive drop jump (Dl) exercises from the heights of 25, 40, 55 and 70 cm. The vertical ground reaction forces, the angular displacement of the knee and ankle joints as well as the surface electromyograms (EMG) of the triceps surae muscles (GAS and SOL), vastus medialis (VM) and biceps femoris (RF) were recorded. Each jump was performed six times. After normalization, force, angle displacement and EMG signals, were averaged for each jumping condition. The EMGs were fullwave rectified and integrated (iEMG) over different functional phases (Dietz et a].. 1979): Preactivation phase (PRE) (looms before ground contact); Reflex Induced Activation phase (i.e. the activation phase from 40 ms to 120 ms after impact); Late EMG Response phase (LER) (activity from 120 ms until the end of contact). The significance of the differences between means were tested with t-test for paired samples. The results of the height of rise of center of gravity (HRCG) showed non significant differences in SJ and CMJconditions. In DJ conditions the HRCG incresed from 38.1f3.9 cm ro 41.5f4.2 cm (

A dynamic method for charging-up calculations: the case of GEM

The simulation of Micro Pattern Gaseous Detectors (MPGDs) signal response is an important and powerful tool for the design and optimization of such detectors. However, several attempts to simulate exactly the effective charge gain have not been completely successful. Namely, the gain stability over time has not been fully understood. Charging-up of the insulator surfaces have been pointed as one of the responsible for the difference between experimental and Monte Carlo results. This work describes two iterative methods to simulate the charging-up in one MPGD device, the Gas Electron Multiplier (GEM). The first method uses a constant step for avalanches time evolution, very detailed, but slower to compute. The second method uses a dynamic step that improves the computing time. Good agreement between both methods was reached. Despite of comparison with experimental results shows that charging-up plays an important role in detectors operation, should not be the only responsible for the difference between simulated and measured effective gain, but explains the time evolution in the effective gain.Comment: Minor changes in grammatical statements and inclusion of some important information about experimental setup at section "Comparison with experimental results

Endoscopic Submucosal Dissection of Early Gastric Cancer Using the Insulated Tip Knife

AbstractEndoscopic submucosal dissection (ESD) is an endoscopic technique in which a gastrointestinal mucosal neoplasm can be excised by cutting through the submucosa with an endoscopic knife. It can be used with diagnostic or therapeutic intent and allows en bloc removal of the specimen. ESD usually begins with identification and evaluation of the lesion and assessment of the margin with chromo-endoscopy. The subsequent steps include marking, submucosal injection, and circumferential and submucosal dissection. Complications should be promptly recognized and dealt with immediately if necessary.This video demonstrates the main steps of the technique and management of complications. This article is part of an expert video encyclopedia

Simulation of gain stability of THGEM gas-avalanche particle detectors

Charging-up processes affecting gain stability in Thick Gas Electron Multipliers (THGEM) were studied with a dedicated simulation toolkit. Integrated with Garfield++, it provides an effective platform for systematic phenomenological studies of charging-up processes in MPGD detectors. We describe the simulation tool and the fine-tuning of the step-size required for the algorithm convergence, in relation to physical parameters. Simulation results of gain stability over time in THGEM detectors are presented, exploring the role of electrode-thickness and applied voltage on its evolution. The results show that the total amount of irradiated charge through electrode's hole needed for reaching gain stabilization is in the range of tens to hundreds of pC, depending on the detector geometry and operational voltage. These results are in agreement with experimental observations presented previously

Pressure effect in the X-ray intrinsic position resolution in noble gases and mixtures

A study of the gas pressure effect in the position resolution of an interacting X- or gamma-ray photon in a gas medium is performed. The intrinsic position resolution for pure noble gases (Argon and Xenon) and their mixtures with CO2 and CH4 were calculated for several gas pressures (1-10bar) and for photon energies between 5.4 and 60.0 keV, being possible to establish a linear match between the intrinsic position resolution and the inverse of the gas pressure in that energy range. In order to evaluate the quality of the method here described, a comparison between the available experimental data and the calculated one in this work, is done and discussed. In the majority of the cases, a strong agreement is observed