Biomedical subjects

Adamantios Arampatzis

Publications and source records attributed to Adamantios Arampatzis.

33 records · Page 2Linked to original sources

PubMed2005

Differences between measured and resultant joint moments during isometric contractions at the ankle joint.

The purpose of this study was to examine two hypotheses: (a) during voluntary and electrically induced isometric contractions the moments measured at the dynamometer are different from the resultant moments in the same plane around the ankle joint and (b) at a given resultant moment during electrically induced isometric contractions the ankle angle while loading is different from the ankle angle while unloading. Twenty-seven long distance runners participated in the study. All subjects performed isometric maximal voluntary contractions (MVC) and contractions induced by electrostimulation at four different ankle-knee angle combinations on a Biodex-dynamometer. The kinematics of the leg were recorded using the vicon 624 system with eight cameras operating at 120 Hz. The main findings were: (a) the resultant moment at the ankle joint and the moment measured by the Biodex-dynamometer during isometric contractions are different, (b) during a plantar flexion effort the ankle angle changes significantly, whereas the knee angle shows only small and in most cases not significant changes, and (c) at identical resultant ankle joint moments the ankle angles are different between the loading and the unloading phases. The observed differences may lead to erroneous conclusions concerning the following: (a) diagnostic of muscle architecture, (b) estimation of the moment-ankle angle relationship and (c) estimation of the strain and hysteresis of tendons and aponeuroses.

Ankle Joint↗

PubMed2005

Joint stabilizing response to expected and unexpected tilts.

BACKGROUND: The results found in the literature regarding functional ankle joint stabilization are controversial possibly because of the testing methods used. METHODS: The responses of 22 subjects to unexpected and expected sudden inversions of the foot were compared for all subjects together, as well as grouped by their self-perceived stability. A three-dimensional foot model was used to describe ankle and foot motion. Electromyographic signals of six muscles of the lower limb as well as the horizontal ground reaction forces were recorded. RESULTS: Whereas unexpected and expected trials did not show significant differences (p > 0.05) in kinematics, higher activation and horizontal force integrals were found for the unexpected trials. In addition, no differences in electromyographic or ground reaction force parameters were found between stable and unstable ankles; however, the kinematics revealed higher amplitudes and velocities for the stable group. CONCLUSIONS: The awareness of the instant of tilt enhances stabilization in that the same motion is achieved with a lower muscle activation. Evidence suggests that this is triggered at supraspinal levels. We found that timing of the EMG signal is not as relevant to stabilization as the amplitude (which has often been disregarded in the literature).

Adult↗

PubMed2005

Mechanical and morphological properties of different muscle-tendon units in the lower extremity and running mechanics: effect of aging and physical activity.

The objectives of this work were (i) to investigate whether chronic endurance running is a sufficient stimulus to counteract the age-related changes in the mechanical and morphological properties of human triceps surae (TS) and quadriceps femoris (QF) muscle-tendon units (MTUs) by comparing runners and non-active subjects at different ages (young and old), (ii) to identify adaptational phenomena in running mechanics due to age-related changes in the mechanical and morphological properties of the TS and QF MTUs, and finally (iii) to examine whether chronic endurance-running exercise is associated with adaptational effects on running characteristics in old and young adults. The investigation was conducted on 30 old and 19 young adult males divided into two subgroups according to their running activity: endurance-runners vs non-active. To analyse the properties of the MTUs, all subjects performed isometric maximal voluntary (MVC) ankle plantarflexion and knee extension contractions at 11 different MTU lengths on a dynamometer. The activation of the TS and QF during MVC was estimated by surface electromyography. The gastrocnemius medialis and the vastus lateralis and their distal aponeuroses were visualized by ultrasonography at rest and during MVC, respectively. Ground reaction forces and kinematic data were recorded during running trials at 2.7 m s(-1). The TS and QF MTU capacities were reduced with aging (lower muscle strength and lower tendon stiffness). Runners and non-active subjects had similar MTU properties, suggesting that chronic endurance-running exercise does not counteract the age-related degeneration of the MTUs. Runners showed a higher mechanical advantage for the QF MTU while running (lower gear ratio) compared to non-active subjects, indicating a task-specific adaptation even at old age. Older adults reacted to the reduced capacities of their MTUs by increasing running safety (higher duty factor, lower flight time) and benefitting from a mechanical advantage for the TS MTU, lower rate of force generation and force generation per meter distance. We suggest that the improvement in running mechanics in the older adults happens due to a perceptual motor recalibration and a feed-forward adaptation of the motor task aimed at decreasing the disparity between the reduced capacity of the MTUs and the running effort.

Adult↗

PubMed2004

Choosing EMG parameters: comparison of different onset determination algorithms and EMG integrals in a joint stability study.

OBJECTIVE: The aim was to test various algorithms for onset determination and compare onset repeatability to that from integrals of the EMG signal. The information contained in both parameters is discussed. DESIGN: Onset times were calculated using six different algorithms. The integral of the EMG signal was calculated for seven intervals: from tilt start and from each of the resulting onsets to 200 ms after tilt start. BACKGROUND: EMG onset times are often utilised, especially regarding co-ordination patterns or joint stability. There are almost as many different procedures for onset determination as authors dealing with it. Results in the literature are contradictory. The determination and usage of onset times remains controversial. METHODS: EMG signals from six muscles of the lower leg of 23 subjects were recorded during three consecutive, expected and unexpected sudden inversion and eversion trials while standing on a tilting platform. RESULTS: In most cases the repeatability of the onset times was considerably lower than that of the integrals of the EMG for all studied algorithms. In some cases earlier onset times corresponded to lower integral values and constant onsets to variable integrals. CONCLUSIONS: In many cases onset times alone are not sufficient for describing onset phenomena. The additional calculation of the integrated EMG might provide relevant information regarding the quality of early activation.

Adult↗

PubMed2004

Differences between measured and resultant joint moments during voluntary and artificially elicited isometric knee extension contractions.

OBJECTIVE: Examine two hypotheses: (a) during isometric knee extension contractions the moment measured at the dynamometer is different from the resultant moment in the same plane around the knee joint and (b) during isometric contractions, at the same given resultant moment the knee angle while loading is different from the knee angle while unloading. DESIGN: Comparative study in which the geometrical and the kinetic differences between joint and dynamometer were determined. BACKGROUND: It is usually assumed that the moment measured by the dynamometer is equivalent to the resultant joint moment. The non-rigidity of the dynamometer-leg system can influence the equivalence of these two moments. METHOD: Twenty seven subjects performed isometric maximal knee extension contractions and contractions induced by electrostimulation on a dynamometer. The kinematics of the leg were recorded using 8 cameras (120 Hz). RESULTS: The resultant moment at the knee joint and the moment measured by the dynamometer are different. During a knee extension effort the knee angle changes significantly. At identical resultant knee joint moments the knee angles are different when comparing the loading and the unloading phases. CONCLUSIONS: The differences between the measured and the resultant joint moments might influence the estimation of parameters as: muscle forces, moment-angle relationship and strain and hysteresis of tendons and aponeuroses. RELEVANCE: Torque dynamometers have been often used to estimate muscle forces, to examine neuromuscular processes and to determine the mechanical properties of tendons and aponeuroses.

Biomechanical Phenomena↗

PubMed2004

Effect of the pole--human body interaction on pole vaulting performance.

The purposes of this study were: (a) to examine the interactions between the athlete and the pole and the possibility for the athlete to take advantage of the pole's elasticity by means of muscular work and (b) to develop performance criteria during the interaction between the athlete and the pole in pole vaulting. Six athletes performed 4-11 trials each, at 90% of their respective personal best performance. All trials were recorded using four synchronized, genlocked video cameras operating at 50 Hz. The ground reaction forces exerted on the bottom of the pole were measured using a planting box fixed on a force plate (1000 Hz). The interaction between athlete and pole may be split into two parts. During the first part, energy is transferred into the pole and the total energy of the athlete decreases. The difference between the energy decrease of the athlete and the pole energy is an indicator of the energy produced by the athletes by means of muscular work (criterion 1). During the second part of the interaction, energy is transferred back to the athlete and the total energy of the athlete increases. The difference between the returned pole energy and the amount of energy increase of the athlete defines criterion 2. In general, the function of the pole during the interaction is: (a) store part of the kinetic energy that the athlete achieved during the run up as strain energy and convert this strain energy into potential energy of the athlete, (b) allow the active system (athlete) to produce muscular work to increase the total energy potential.

Energy Transfer↗

PubMed2004

Effect of ankle joint position and electrode placement on the estimation of the antagonistic moment during maximal plantarflexion.

During maximal efforts, antagonistic activity can significantly influence the joint moment. During maximal voluntary "isometric" contractions, certain joint rotation can not be avoided. This can influence the estimation of the antagonistic moment from the EMG activity. Our study aimed to quantify the influence on the calculated agonistic moment produced during maximal voluntary isometric plantarflexions (a) when estimating antagonistic moments at different ankle angles and (b) when placing the EMG electrodes at different portions over the m. tibialis anterior. Ten subjects performed maximal voluntary isometric plantarflexions at 90 degrees ankle angle. In order to estimate the antagonistic moment, submaximal isometric dorsiflexions were performed at various ankle angles. Moment and EMG signals from mm. triceps surae and tibialis anterior were measured. The RMS differences between plantarflexors moment calculated considering the antagonistic cocontraction estimated at the same ankle angle at which the maximal plantarflexion moment was achieved and at different ankle angles ranged from 0.10 to 2.94 Nm. The location of the electrodes led to greater RMS differences (2.35-5.18 Nm). In conclusion, an angle 10 degrees greater than the initial plantarflexion angle is enough to minimize the effect of the change in length of the m. tibialis anterior during the plantarflexion on the estimation of the plantarflexors moment. The localisation of the electrodes over the m. tibialis anterior can influence the estimation of its cocontraction during maximal plantarflexion efforts.

Adult↗

PubMed2004

Reproducibility of electromyography and ground reaction force during various running techniques.

This study examined the validity of the assumption of electromyographic (EMG) and vertical ground reaction force (GRF) parameter reproducibility during running at different velocities and stride frequencies. Each of 12 female long distance runners ran on a treadmill in combinations of three velocities (2.5, 3.0 and 3.5 m/s) and three stride frequencies (preferred, +/-10% from preferred). Seven parameters from the GRF and five parameters from the EMG signals from five muscles of the lower extremity were evaluated (1000 Hz). The GRF was analysed by a pressure measuring insoles. A total number of three trials for each running condition were recorded. GRF parameters during all running conditions showed high intraclass correlation coefficients (ICC average 0.87). The ICC of the EMG parameters of gastrocnemius medialis and lateralis were high (r>0.69 in 73% of the data), while those for vastus lateralis (22%), hamstrings (42%) and tibialis anterior (51%) were clearly lower. The results revealed that GRF parameters were reproducible during all running techniques indicating that a single trial would provide reproducible GRF-data. The reproducibility of the EMG parameters was not influenced by the running technique but dependent on the parameter itself and on the muscle studied.

Adult↗

PubMed2004

Comparison of the men's and the women's pole vault at the 2000 Sydney Olympic Games.

The aim of this study was to identify differences between elite male and female pole vaulters in terms of their mechanical energy and angular momentum. The vaulter's total mechanical energy and angular momentum were calculated from the three-dimensional kinematic data of the pole vault finals at the Sydney 2000 Olympic Games. The development of total, kinetic and potential energy showed similar characteristics for men and women. The initial energy of the vault, the energy at maximum pole bend position and the final energy were significantly higher for male athletes (P <0.05), while the energy gain produced by the athletes during the vault showed no significant differences (male vaulters 5.88 +/- 1.02 J.kg(-1), female vaulters 5.74 +/- 1.63 J.kg(-1)). Time-related parameters relating to pole bending and recoiling also showed no significant differences (P <0.05). In contrast to the male vaulters, the female vaulters did not show a free upward flight phase. The angular momentum was significantly higher for the female vaulters during the initial pole bend and during the bar clearance (P <0.05). We conclude that the pole vaulting technique of female elite athletes is not a projection of the technique of male elite vaulters at a lower jump height, but rather a different way of jumping and interacting with the elastic pole. The current technique of elite female pole vaulters still has potential for further improvement.

Algorithms↗

PubMed2004

Interaction of the human body and surfaces of different stiffness during drop jumps.

PURPOSE: The purpose of this study was to examine two hypotheses: (a) the stiffness of the surface influences the leg stiffness of the subjects during drop jumps, and (b) drop jumping performance (jumping height and energy rates of the subject's center of mass during the contact phase) increases when decreasing surface stiffness due to a greater energy storage capacity of the surface for a given acting force. METHODS: Ten female subjects performed a series of drop jumps from 40-cm height onto two sprung surfaces with different stiffness. Those trials of each subject displaying the maximal mechanical power during the upward phase were analyzed. The ground reaction forces were measured using a force plate. Sagittal kinematics of the subject's body positions and the deformation of the surface were recorded using two high-speed video cameras. RESULTS: On the soft surface, the jumping height and the energy rates of the subjects during the contact phase were greater than on the hard one. The energy delivered by the subjects during the upward phase, the leg and joint stiffness, as well as the range of motion of the subjects remained unchanged for both surfaces. CONCLUSIONS: The absolute energy loss is lower for the hard surface, but the jumping performance is greater for the soft one. The reason is a higher ratio of positive to negative mechanical work done by the subjects during the contact phase. The adjustment of the subjects to different surfaces is not only dependent on the stiffness of the surface but also on the intensity of the movement.

Algorithms↗

PubMed2004

The effect of drop jump starting height and contact time on power, work performed, and moment of force.

The purposes of this study are (a) to examine the effects of contact time manipulation on jump parameters and (b) to examine the interaction between starting height changes and contact time changes on important jump parameters. Fifteen male athletes performed a series of drop jumps from heights of 20, 40, and 60 cm. The instructions given to the subjects were (a) "jump as high as you can" and (b) "jump high a little faster than your previous jump." Jumps were performed at each height until the athlete could not achieve a shorter ground contact time. The data were divided into 5 groups where group 1 was made up of the longest ground contact times of each athlete and groups 2-4 were composed of progressively shorter contact times, with group 5 having the shortest contact times. The jumps of group 3 produced the highest maximum and mean mechanical power (p <0.05) during the positive phase of the drop jumps regardless of starting jump height. The vertical takeoff velocities for the first 3 groups did not show significant (p < 0.05) differences. These results indicate that the manipulation of jump technique plays larger role than jump height in the manipulation of important jump parameters.

Ankle↗

PubMed2003

The effect of falling height on muscle activity and foot motion during landings.

The aims of this study were: (a) to examine the effect of falling height on the kinematics of the tibiotalar, talonavicular and calcaneocuboid joints and (b) to study the influence of falling height on the muscle activity of the leg during landings. Six female gymnasts (height: 1.63 +/- 0.04 m, weight: 58.21 +/- 3.46 kg) participated in this study. All six gymnasts carried out barefoot landings, falling from 1.0, 1.5 and 2.0 m height onto a mat. Three genlocked digital high speed video cameras (250 Hz) captured the motion of the left shank and foot. Surface electromyography (EMG) was used to measure muscle activity (1000 Hz) from five muscles (gastrocnemius medialis, tibialis anterior, peroneus longus, vastus lateralis and hamstrings) of the left leg. The kinematics of the tibiotalar, talonavicular and calcaneocuboid joints were studied. The lower-leg and the foot were modelled by means of a multi-body system, comprising seven rigid bodies. The falling height does not show any influence on the kinematics neither of the tibiotalar nor of the talonavicular joints during landing. The eversion at the calcaneocuboid joint increases with increasing falling height. When augmenting falling height, the myoelectric activity of the muscles of the lower limb increases as well during the pre-activation phase as during the landing itself. The muscles of the lower extremities are capable of stabilizing the tibiotalar and the talonavicular joints actively, restricting their maximal motion by means of a higher activation before and after touchdown. Maximal eversion at the calcaneocuboid joint increases about 52% when landing from 2.0 m.

Biomechanical Phenomena↗

PubMed2003

Symmetry and reproducibility of kinematic parameters during various running techniques.

PURPOSE: This study examined the validity of the assumption of lower-extremity kinematic parameter reproducibility and symmetry during running with different velocities and stride frequencies. METHODS: Each of 12 female long-distance runners ran on a treadmill in combinations of three different velocities (2.5, 3.0, and 3.5 m.s-1) and three different stride frequencies (preferred and +/- 10% from preferred). The left and right sides of the athletes were filmed using video cameras placed orthogonally to the sagittal plane. A total number of three step cycles for each running condition were recorded (250 Hz). For each side of the body, 19 sagittal kinematic parameters from the lower extremity were evaluated. RESULTS: Intraclass correlation coefficients (ICC) for both legs were high (generally > 0.80). Only the angular velocity parameters demonstrated correlation values below 0.70. The symmetry index for the linear and angular displacement parameters and the contact times during all running techniques were less than 8%, whereas those for the angular velocity parameters and flight times were higher than 15%. CONCLUSION: The present results suggested that the degree of reproducibility and symmetry of kinematic data do not vary with a deliberate change in running technique but rather depend on the parameter itself. With respect to the economy of data analysis, the present findings indicate that recording a single monolateral trial would provide reproducible and symmetric values for most kinematic parameters.

Adult↗

PubMed2002

Influence of 2D and 3D body segment models on energy calculations during kinematic analysis of running.

The aims of the present study were: (1) to examine the influence of two-dimensional (2D) and three-dimensional (3D) analysis on the body's total energy during the support phase of running, and (2) to examine the influence of the choice of anthropometric models on the body's total energy during running. A total of 14 runners participated in the investigation [mean (SD) height: 1.83 (0.03) m, body mass: 79.67 (5.65) kg]. Two genlocked high-speed cameras (120 Hz) filmed each athlete's movement during single-foot ground contact. The exact support time of the athletes was measured with a Kistler force plate (sampling frequency: 1000 Hz). The masses and moments of inertia of the various segments were estimated using the 2D and 3D models of Hanavan (1964) as well as the 3D model of Zatsiorsky et al. (1984). The influence of the 2D and 3D analysis on the calculations was evaluated by comparing of the total energies calculated using Hanavan's 2D and 3D models. The influence of the choice of the anthropometric model on the calculations was checked by comparing the results obtained using the Hanavan 3D model and those obtained using the 3D model of Zatsiorsky et al. (1984). The data show us that 2D and 3D analyses produce similar energy values during the entire support phase of running (only very small percentage energy differences were observed: e.g. from 0.23% for the energy of the body at the first contact with the ground, up to 0.31% for the energy of the body at the time the athlete leaves the ground, E(TO)). In addition, calculations made using the 3D models of Hanavan and Zatsiorsky also produced similar results for energy values (energy differences from 0.33% for energy minimum, up to 0.8% for E(TO)). It can be assumed, therefore, that neither the choice of the anthropometric model nor the calculations made on the basis of 3D coordinates are limiting factors in the calculation of body total energies for running.

Adult↗

PubMed2002

A three-dimensional shank-foot model to determine the foot motion during landings.

PURPOSE: The purposes of this study were a) to develop a model of the foot capable of describing the foot motion during dynamic movements and b) to study the influence of different mats on foot motion during landing in gymnastics. METHODS: Six female gymnasts (height: 1.63 +/- 0.04 m, weight: 58.21 +/- 3.46 kg) participated in this study. All six gymnasts carried out barefoot landings, falling from 80 and 115 cm onto three mats each with a different stiffness (hard, medium, and soft). Three synchronized digital high-speed video cameras (250 Hz) captured the motion of the left shank and foot. At the same time, the reaction forces between mat and foot at the forefoot and rearfoot were measured by two instrumented insoles (Paromed, 1000 Hz). The kinematics of the tibiotalar, talonavicular, and calcaneocuboid joints were examined. The lower leg and the foot were modeled by means of a multi-body system, comprising seven rigid bodies. For each joint, two joint coordinate systems attached on each of the connected segments were defined. RESULTS: The mat stiffness did not show any influence on the maximal reaction forces or on the kinematics of the tibiotalar joint. For the soft mat, higher maximal eversion angles at the talonavicular and the calcaneocuboid joints were measured. CONCLUSIONS: The relative motion between forefoot and rearfoot was influenced by changing mat stiffness. Therefore, the construction of the mat influenced the motion of the foot. The observation of only the tibiotalar joint is not enough when studying the influence of different mats on foot motion. The functional benefit of the mechanical advantages of a soft mat (higher energy absorption) includes a decrease in stability. The surface of the landing mat should, therefore, be reinforced by a stabilizing mechanism.

Adult↗