Biomedical subjects

A Arampatzis

Publications and source records attributed to A Arampatzis.

11 recordsLinked to original sources

PubMed2005

Strain and elongation of the human gastrocnemius tendon and aponeurosis during maximal plantarflexion effort.

Regarding the strain and elongation distribution along the tendon and aponeurosis the literature is reporting different findings. Therefore, the purpose of this study was to examine in vivo the elongation and the strain of the human gastrocnemius medialis tendon and aponeurosis simultaneously at the same trial during maximal voluntary plantarflexion efforts. Twelve subjects participated in the study. The subjects performed isometric maximal voluntary contractions of their left leg on a Biodex-dynamometer. The kinematics of the leg were recorded using the Vicon 624 system with 8 cameras operating at 120 Hz. Two ultrasound probes were used to visualise the tendon (myotendinous junction region) and the distal aponeurosis of the gastrocnemius medialis respectively. The main findings were: (a) the absolute elongation of the gastrocnemius medialis tendon was different to that of the aponeurosis, (b) the strain of the gastrocnemius medialis tendon did not differ from the strain of the aponeurosis, (c) during the "isometric" plantarflexion the ankle angle exhibited significant changes, and (d) the non-rigidity of the dynamometer arm-foot system and the coactivity of the tibialis anterior both have a significant influence on the moment exerted at the ankle joint. Thus the strain of the human gastrocnemius medialis tendon and aponeurosis estimated in vivo using two-dimensional ultrasonography is uniform. To calculate the elongation of the whole tendon it is necessary to multiply the strain calculated for the examined part of the tendon by the total length of the tendon.

Achilles Tendon↗

PubMed2005

[Conservative versus operative treatment after ACL-rupture: influence on the muscle strength capability of the lower extremity].

PURPOSE: In this study two groups of ACL-rupture patients having had a conservative or an operative treatment and a similar rehabilitation were compared regarding their muscle strength capabilities, and the clinical outcome. METHODS: Thirty-three patients (mean age 31 years) were selected according to the Lysholm-scores. Twelve patients were conservatively treated (Group I) and were examined between six and 16 months post trauma. Group II consisted of 21 operatively treated patients which were examined between 6 and 16 months post surgery. All patients underwent a clinical exam following the OAK evaluation form and were tested on a Cybex 6000 isokinetic machine. The subjects had to perform concentric contractions of the extensor and flexor muscles of the knee, hip and ankle at 60 and 120 degrees /s. In addition the knee musculature was isometrically tested at knee angles of 0 and 45 degrees . RESULTS: The clinical examination revealed significant (P < 0.05) differences between groups. The operatively treated patients scored better at the tests for ligamentous stability, whereas the testing of the muscular capabilities revealed significant differences (P < 0.05) favouring the conservatively treated patients in the isokinetic measures, (maximal concentric torque M (max,con)) of the knee extensors, knee flexors, and ankle plantarflexors. CONCLUSION: Whereas the clinical examination only revealed the ligamentous stability to be better results in the operatively treated patients, the conservatively treated patients showed better results in the isokinetik strength measures of the knee extensors, knee flexors, and ankle plantarflexors. The better muscular profiles found for the conservatively treated patients suggest that a better regeneration of the corresponding muscular capabilities after an ACL rupture is possible, provided a specific and controlled rehabilitation program is performed. This seems to be more difficult in operatively treated patients even six to 16 months after the surgical intervention.

Adult↗

PubMed2004

[Development of muscle strength in knee, hip and ankle joints after ACL reconstruction].

INTRODUCTION: We searched for answers for following questions: How does the knee muscle strength change in dependence of post OP time after the same ACL-rehabilitation's program? Which changes in muscle strength occur in hip and ankle muscles after ACL? METHODS: In this study 69 patients with ACL-Reconstruction participated, mean 31 years. The Lysholm- and OAK-scores of all were good respectively very good. 28 patients were 3 - 6 months post OP (Gr. I), 20 were 6 - 12 months post OP (Gr. II), 21 was 12 - 24 months post OP (Gr. II). All patients were tested on the isokinetic Cybex 6000, for dynamic concentric strength and endurance. The evaluation parameters chosen were: max.moment at angle speed of 60 degrees /sec and endurance index at 120 degrees /sec, RESULTS: The analysis of the max. moment showed significant (P < 0.05) changes in both knee extension and flexion in all groups, in the hip flexors and extensors in group I, and hip flexors in group II and III. In the ankle joint we only found significant changes in the plantarflexors of group I. Looking at the endurance index we observed that many muscle groups of the injured leg presented higher values, however the difference is only significant in the knee flexors and extensors of group I and in the hip flexors of group III. CONCLUSION: Our study showed strength loss in both knee extensors and knee flexors in all patients who had undergone reconstruction surgery after the same ACL-rehabilitation's program. We can state that there is strength loss in hip and ankle muscles in 3 - 6 months post OP patients. A reduction of muscle strength at the hip flexor from all patients was seen after 12 months post-OP. It is suggested that the strength loss in the hip flexors could be due to bi-articular muscles surrounding the knee.This results has to be consider on the planning of strength training after ACL injuries.

Adult↗

PubMed2001

Mechanical energetic processes during the giant swing before the Tkatchev exercise.

The goal of this study was to examine the possibility of the utilization of high bar and uneven parallel bar elasticity by the gymnasts through muscular work during the giant swing before the Tkatchev exercise on the high bar or uneven parallel bars. The performances were gathered during the Gymnastic World Championship in 1994. The set up consisted of two video cameras (50Hz) and two force measuring bars (500Hz). Twenty giant swings before the Tkatchev exercise, nine giant swings before the Tkatchev exercise after Tkatchev on the high bar and 15 giant swings before the Tkatchev exercise on the uneven parallel bars were analyzed. The giant swings were performed by 20 male and 15 female gymnasts. There are three phases during the giant swing exercise before the Tkatchev in which the systems (high bar-human body) total energy can be changed. During the first phase, energy is transferred from the gymnast's body into the bar. A clearly effective use of the bar's elasticity during the first phase could not be found. During the second phase, energy is transferred from the bar's back into the gymnast's body whose total energy increases. An increase in the energy of the system can only be achieved through muscular work. During the second phase of the various giant swing techniques no significant (p<0.05) difference in the energy increase through muscular work could be found. During the third phase, energy is once again produced by the gymnast through extension at the hip and shoulder joints.

Adult↗

PubMed2001

Influence of leg stiffness and its effect on myodynamic jumping performance.

The purposes of this study are: a) to examine the possibility of influencing the leg stiffness through instructions given to the subjects and b) to determine the effect of the leg stiffness on the mechanical power and take-off velocity during the drop jumps. A total of 15 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". The jumps were performed at each height until the athlete could not achieve a shorter ground contact time. The ground reaction forces were measured using a "Kistler" force plate (1000 Hz). The athletes body positions were recorded using a high speed (250 Hz) video camera. EMG was used to measure muscle activity in five leg muscles. The data was divided into 5 groups where group 1 was made up of the longest ground contact times of each athlete and group 5 the shortest. The leg and ankle stiffness values were higher when the contact times were shorter. This means that by influencing contact time through verbal instructions it is possible to control leg stiffness. Maximum center of mass take-off velocity the can be achieved with different levels of leg stiffness. The mechanical power acting on the human body during the positive phase of the drop jumps had the highest values in group 3. This means that there is an optimum stiffness value for the lower extremities to maximize mechanical power.

Ankle Joint↗

PubMed2001

Leg stiffness and mechanical energetic processes during jumping on a sprung surface.

PURPOSE: The purposes of this study were: a) to examine the effect of verbal instructions given to the subjects on the control of lower extremity stiffness and b) to determine the effect of leg stiffness on mechanical energetic processes during drop jumps on a sprung surface. METHODS: A total of 10 female athletes performed a series of drop jumps on a sprung surface from heights of 20 and 40 cm. The instructions given to the subjects were a) "jump as high as you can" and b) "jump high a little faster than at your previous jump." The jumps were performed at each height until the athlete could not achieve a shorter ground contact time. Four jumps per subject per height were analyzed. The ground reaction forces were measured using a "Kistler" force plate (1000 Hz). The athletes' body positions were recorded using a high-speed (250 Hz) video camera. The deformation of the sprung surface was determined by another high-speed camera operating at 500 Hz. Surface EMG was used to measure muscle activity in five leg muscles. RESULTS: The contact time showed high correlation with leg stiffness as well as with ankle and knee stiffness. The change in leg stiffness was not due to the duration of the preactivation but rather to the level of activation during this phase. An increase in leg stiffness caused an increase in the energy stored and recovered in and by the sprung surface and a decrease of the energy produced by the subjects. CONCLUSIONS: By influencing contact time through verbal instructions, it is possible to control leg stiffness. Maximal vertical take-off velocity of the center of mass and maximal take-off body energy can be achieved having different levels of leg stiffness. The maximization of mechanical power is achieved by optimal leg stiffness values and leg muscle preactivation levels.

Adult↗

PubMed2000

Influence of different approaches for calculating the athlete's mechanical energy on energetic parameters in the pole vault.

The purposes of this study were as follows: (1) To determine the differences between two- and three-dimensionally calculated energy of the athlete in the pole vault. (2) To determine the differences between CM energy and total body energy. (3) To examine the influence of these different approaches of calculating the athlete's energy on energetic parameter values during the pole vault. Kinematic data were gathered during the pole vault final of the track and field world championships in 1997. Two video cameras (50Hz) covered the last step of the approach including the pole plant and 2 cameras covered the pole phase up to bar clearance, respectively. Twenty successful jumps were analysed. The characteristics of the energy development is similar for the different approaches. Initial energy, energy at maximum pole bend and energy at pole release (primary parameters) show significant differences (p<0.05). The findings indicate that rotatory movements and movements relative to the CM have a larger influence on the primary parameters than movements apart from the main plane of movement. For analysing the energy exchange between the athlete and the elastic implement pole only the differences among the secondary parameters (initial energy minus energy at maximum pole bend, final energy minus energy at maximum pole bend) are needed (Arampatzis et al., 1997 Biomechanical Research Project at the Vth World Championships in Athletics, Athens 1997: Preliminary Report. New Studies in Athletics 13, 66-69). For those parameters the relative differences between the calculation approaches range only between 1.47 and 0.04%. This indicates that the influence of the different approaches for calculating the athlete's energy on the analysis of energy exchange is negligible.

Biomechanical Phenomena↗

PubMed2000

Mechanical power in running: a comparison of different approaches.

The purposes of the present study were: (1) to compare four different methods of calculating mechanical power in running on the basis of comparable data over a wide range of running velocity; (2) to examine the linearity of the relation between mechanical power as calculated with the four methods and running velocity. Eight runners participated in the investigation (height: 1.82 +/- 0.03 m, body mass: 81.05 +/- 4.69 kg). A Kistler force platform registered all components of the ground reaction force (1000 Hz) during one foot ground contact, which was additionally video taped using two high-speed video cameras running at 120 Hz. Four different methods were used to calculate mechanical power. Two methods determined the mechanical power due to the work done on the athletes' center of mass and two were calculated from the motion of the athletes' segments. The four different methods provided different relations between mechanical power and running velocity. The calculations on the basis of kinematic data cannot be recommended to determine efficiency of movement. The methods based on ground reaction force measurements revealed significant linear relations (r = 0.90, r2 = 0.84) between running velocity and mechanical power.

Biomechanical Phenomena↗

PubMed1999

Mechanical energetic processes during the giant swing exercise before dismounts and flight elements on the high bar and the uneven parallel bars.

The purposes of this study were as follows: (1) To study the energy exchange between the body of the gymnast and the high bar and uneven parallel bars during forward and backward giant swings. (2) To examine the differences between the mechanical energy produced and the mechanical energy absorbed by the muscles during forward and backward giant swings on the high bar and the uneven parallel bars. The data were gathered during the gymnastic world championships in 1994. The experimental set up consisted of two video cameras (50 Hz) and two force measurement bars (500 Hz). A total of 101 giant swings before dismounts and flight elements performed by 33 male and 34 female gymnasts were analyzed. There are characteristically two main phases during forward and backward giant swings before dismounts and flight elements. During the first phase energy is transferred from the gymnast's body into the bar. During this phase of the backward giant swing the energy of the system decreases because the amount of energy decrease of the gymnast's body is more than the energy transferred into the high bar. An exception can be seen during the giant swings in which the gymnast used the power technique. During forward giant swings the energy of the system increases during the first phase. This occurs through active flexion of the hipjoint which produced the extra muscular energy. During the second phase energy is transferred from the bar back into the gymnast's body whose total energy increases. An increase in the energy of the system can only be achieved through muscular work. During the second phase of the backward giant swing the energy of the system increases. The forward giant swings performed on the uneven parallel bars showed a large energy loss during this phase. The energy deficit seen during the first phase of the backward giant swing can be improved by using the power technique. To achieve this the athlete must be in a bent position at the start of the giant swing exercise. Through extension at the shoulder and hip joints muscular energy can be put into the system.

Biomechanical Phenomena↗

PubMed1999

The effect of speed on leg stiffness and joint kinetics in human running.

The goals of this study were to examine the following hypotheses: (a) there is a difference between the theoretically calculated (McMahon and Cheng, 1990. Journal of Biomechanics 23, 65-78) and the kinematically measured length changes of the spring-mass model and (b) the leg spring stiffness, the ankle spring stiffness and the knee spring stiffness are influenced by running speed. Thirteen athletes took part in this study. Force was measured using a "Kistler" force plate (1000 Hz). Kinematic data were recorded using two high-speed (120 Hz) video cameras. Each athlete completed trials running at five different velocities (approx. 2.5, 3.5, 4.5, 5.5 and 6.5 m/s). Running velocity influences the leg spring stiffness, the effective vertical spring stiffness and the spring stiffness at the knee joint. The spring stiffness at the ankle joint showed no statistical difference (p < 0.05) for the five velocities. The theoretically calculated length change of the spring-mass model significantly (p < 0.05) overestimated the actual length change. For running velocities up to 6.5 m/s the leg spring stiffness is influenced mostly by changes in stiffness at the knee joint.

Ankle Joint↗

PubMed1998

A mathematical high bar-human body model for analysing and interpreting mechanical-energetic processes on the high bar.

The aims of this study were: 1. To study the transfer of energy between the high bar and the gymnast. 2. To develop criteria from the utilisation of high bar elasticity and the utilisation of muscle capacity to assess the effectiveness of a movement solution. 3. To study the influence of varying segment movement upon release parameters. For these purposes a model of the human body attached to the high bar (high bar-human body model) was developed. The human body was modelled using a 15-segment body system. The joint-beam element method (superelement) was employed for modelling the high bar. A superelement consists of four rigid segments connected by joints (two Cardan joints and one rotational-translational joint) and springs (seven rotation springs and one tension-compression spring). The high bar was modelled using three superelements. The input data required for the high bar human body model were collected with video-kinematographic (50 Hz) and dynamometric (500 Hz) techniques. Masses and moments of inertia of the 15 segments were calculated using the data from the Zatsiorsky et al. (1984) model. There are two major phases characteristic of the giant swing prior to dismounts from the high bar. In the first phase the gymnast attempts to supply energy to the high bar-humanbody system through muscle activity and to store this energy in the high bar. The difference between the energy transferred to the high bar and the reduction in the total energy of the body could be adopted as a criterion for the utilisation of high bar elasticity. The energy previously transferred into the high bar is returned to the body during the second phase. An advantageous increase in total body energy at the end of the exercise could only be obtained through muscle energy supply. An index characterising the utilisation of muscle capacity was developed out of the difference between the increase in total body energy and the energy returned from the high bar. A delayed and initially slow but even reduction of hip and shoulder angles provided more advantageous release conditions. The total body energy could be improved by up to 15%, the vertical CM release velocity by up to 10% and the angular momentum by up to 35%.

Algorithms↗