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Biomedical subjects

V Baltzopoulos

Publications and source records attributed to V Baltzopoulos.

34 records · Page 2Linked to original sources
PubMed1997

The effects of antagonist moment on the resultant knee joint moment during isokinetic testing of the knee extensors.

The purpose of this study was to examine the effects of moment of antagonistic muscle on the resultant joint moment during isokinetic eccentric and concentric efforts of the knee extensors. Ten males performed maximum eccentric and concentric knee extension and flexion efforts on a Biodex dynamometer at 0.52 rad.s-1 (30 degrees.s-1). Electromyographic (EMG) activity of vastus medialis and biceps femoris (hamstrings) was also recorded. The antagonistic moment of the hamstrings was determined by recording the integrated EMG (iEMG)/ moment relationship at different levels of muscle effort. The iEMG/moment curves were fitted using second-degree polynomials. The polynomials were then used to predict the antagonistic moment exerted by the hamstrings from the antagonist iEMG. The antagonistic moment had a maximum of 42.92 Nm and 28.97 Nm under concentric and eccentric conditions respectively; paired t-tests indicated that this was a significant difference (P < 0.05). These results indicate that the resultant joint moment of knee extensors is the result of both agonist and antagonist muscle activation. The greater antagonist muscle activity under concentric activation conditions may be partly responsible for the lower resultant joint concentric moment of knee extensors compared with the corresponding eccentric activation. The antagonist moment significantly affects comparisons between the isokinetic moments and agonist EMG and in vitro force measurements under different testing (muscle action and angular velocity) conditions.

Adult↗
PubMed1997

A comparison of automatic filtering techniques applied to biomechanical walking data.

The purpose of this study was to compare and evaluate six automatic filtering techniques commonly used in biomechanics for filtering gait analysis kinematic signals namely: (1) power spectrum (signal-to-noise ratio) assessment; (2) generalised cross validation spline; (3) least-squares cubic splines; (4) regularisation of Fourier series; (5) regression model and (6) residual analysis. A battery of 1440 signals representing the displacements of seven markers attached upon the surface of the right lower limbs and one marker attached upon the surface of the sacrum during walking were used; their original signal and added noise characteristics were known a priori. The signals were filtered with every technique and the root mean square error between the filtered and reference signal was calculated for each derivative domain. Results indicated that among the investigated techniques there is not one that performs best in all the cases studied. Generally, the techniques of power spectrum estimation, least-squares cubic splines and generalised cross validation produced the most acceptable results.

Artifacts↗
PubMed1997

Optimal digital filtering requires a different cut-off frequency strategy for the determination of the higher derivatives.

The present study investigated four different filtering and differentiation sequences for the calculation of the higher derivatives from noisy displacement data when using a second-order Butterworth filter and first-order finite differences. These were: (1) the conventional sequence (i.e. filtering the displacement data and then differentiating); (2) filtering the displacement with a different cut-off frequency depending upon optimal 0th, 1st and 2nd derivatives; (3) double filtering and differentiation (only for acceleration); and (4) differentiation and then filtering separately in each derivative domain, i.e. treating the noisy higher derivatives as individual signals. Thirty levels of time domain and 30 levels of frequency domain computer-generated pure noise signals, were superimposed on 24 reference signals which simulated the medial-lateral, anterior-posterior and vertical displacement patterns of eight markers attached to the lower extremity segments during walking. The optimum cut-off frequency for the displacement velocity and acceleration data was calculated as the one that produced the minimum root mean square error between the reference and noisy data in each derivative domain. The results indicated that the conventional strategy has to be reconsidered and modified, as the best results were obtained by the second strategy. The optimum cut-off frequency for acceleration was lower than that required for the velocity which in turn was lower than the optimum cut-off frequency for displacement. The findings of the present study will contribute to the development of existing and future automatic filtering techniques based on digital filtering.

Acceleration↗
PubMed1997

Inverse optimization: functional and physiological considerations related to the force-sharing problem.

This paper is a review of the optimization techniques used for the solution of the force-sharing problem in biomechanics; that is, the distribution of the net joint moment to the force generating structures such as muscles and ligaments. The solution to this problem is achieved by the minimization (or maximization) of an objective function that includes the design variable (usually muscle forces) that are subject to certain constraints, and it is generally related to physiological or mechanical properties such as muscle stress, maximum force or moment, activation level, etc. The usual constraints require the sum of the exerted moments to be equal to the net joint moment and certain boundary conditions restrict the force solutions within physiologically acceptable limits. Linear optimization (objective and constraint functions are both linear relationships) has limited capabilities for the solution of the force sharing problem, although the use of appropriate constraints and physiologically realistic boundary conditions can improve the solution and lead to reasonable and functionally acceptable muscle force predictions. Nonlinear optimization provides more physiologically acceptable results, especially when the criteria used are related to the dynamics of the movement (e.g., instantaneous maximum force derived from muscle modeling based on length and velocity histories). The evaluation of predicted forces can be performed using direct measurements of forces (usually in animals), relationship with EMG patterns, comparisons with forces obtained from optimized forward dynamics, and by evaluating the results using analytical solutions of the optimal problem to highlight muscle synergism for example. Global objective functions are more restricting compared to local ones that are related to the specific objective of the movement at its different phases (e.g., maximize speed or minimize pain). In complex dynamic activities multiobjective optimization is likely to produce more realistic results.

Biomechanical Phenomena↗
PubMed1996

Comparison of gait patterns between healthy and scoliotic patients using time and frequency domain analysis of ground reaction forces.

STUDY DESIGN: The walking gait in 20 healthy adolescent girls and 20 adolescent girls with idiopathic scoliosis was compared using time and frequency domain analysis of the ground reaction forces. OBJECTIVES: To investigate the support phase mechanics of walking gait in health subjects and those with scoliosis. SUMMARY OF BACKGROUND DATA: Previous studies have demonstrated the important role of gait in the etiology of scoliosis, although, to date, there are no detailed reports that examine kinetic gait parameters. METHODS: Selected force-time parameters were used to investigate time domain patterns. The frequency content of the vertical, anterior-posterior, and medial-lateral components was used to examine frequency characteristics. Inter- and intrasubject variability and bilateral symmetry also were examined. RESULTS: The findings indicated no significant difference between the two groups for the time domain variables. However, the frequency content of the group with scoliosis was significantly higher han that of the control group, especially in the medial lateral component, suggesting presence of a balance control misfunction. In addition, substantially higher inter- and intrasubject variability and asymmetry was found within the frequency content of the group with scoliosis compared with the control group in the medial-lateral and anterior-posterior directions. CONCLUSIONS: Patients with scoliosis exhibit balance problems during the stance phase of gait and have significant asymmetry in the frequency characteristics. These findings could be a primary effect that contributes to the medial-lateral deformity of the spine and its initiation and progression.

Adolescent↗
PubMed1996

Muscle tenderness and peak torque changes after downhill running following a prior bout of isokinetic eccentric exercise.

Unaccustomed exercise (usually of an eccentric nature) is often followed by delayed onset muscle soreness (DOMS). Previous studies have found that prior eccentric activity produces a training effect which reduces DOMS and morphological changes. The aim of this study was to examine the effects of a prior bout of maximal isokinetic eccentric exercise on DOMS, strength loss and plasma creatine kinase (CK) changes following a downhill run. Ten male subjects with a mean (+/- S.D.) age of 22.5 +/- 2.8 years, body mass of 62.67 +/- 0.05 kg and height of 176 +/- 3 cm were allocated to either a treatment group or a control group. The treatment group performed 100 maximal eccentric activations of the knee extensors in the dominant leg at 0.52 rad s-1. Two weeks later, the downhill run was performed on a motor-driven treadmill. This consisted of five bouts of 8 min at a gradient of -10% at a speed corresponding to 80% of the predicted maximal heart rate. The untrained group performed the downhill run as above but without the prior isokinetic session. Tenderness measurements, plasma CK activity and concentric and eccentric isokinetic peak torque measurements of the knee extensors at 0.52 and 2.83 rad s-1 were recorded prior to, immediately following and 2, 4 and 7 days after each protocol. The isokinetic protocol caused an increase (P < 0.01) in CK and tenderness and a decrease (P < 0.05) in concentric and eccentric torque at both speeds in the treatment group. Following the downhill run, a reduction in peak torque (P < 0.01) was observed in the eccentric and concentric modes at both isokinetic speeds in the control group. For the treatment group, the decrease in peak torque occurred only at the faster eccentric speed. With the exception of the faster eccentric speed, the decrement in peak torque was greater in the control group in all post-exercise isokinetic strength tests. There was less tenderness (P < 0.01) in the trained knee extensor muscle group. Peak torque also returned to pre-downhill values earlier for the trained group. Although plasma CK activity increased in both groups after downhill running, it was much lower (P < 0.01) in the trained group. The results suggest that a prior bout of isokinetic eccentric training reduces muscle damage, reduces the amount of strength loss and decreases the sensation of DOMS after downhill running.

Adult↗
PubMed1996

Gravitational moment correction in isokinetic dynamometry using anthropometric data.

The purpose of this study was to compare different methods of gravity correction in isokinetic dynamometry. The gravitational moment of the left leg-foot segment of 25 males was measured on a Biodex dynamometer at 30 degrees of knee flexion statically, and as the segment was passively falling from 0 degree to 90 degrees with a constant velocity of 0.035 rad.s-1. The tests were performed in a supine and a seated position. The gravitational moments were also estimated from anthropometric data and directly, using a reaction board method that was considered as the criterion measurement. Furthermore, the isokinetic maximum moment output of the knee flexors and extensors was measured and corrected for gravity using the above methods at angular velocities of 0.52 rad.s-1 and 2.62 rad.s-1 during eccentric, and at 0.52 rad.s-1, 2.62 rad.s-1, and 4.71 rad.s-1 during concentric activations. One-way repeated-measures analysis of variance tests revealed significant differences (P < 0.05) between the gravitational moments obtained on the isokinetic dynamometer and those estimated from anthropometric data or by the reaction board method. The maximum extensor and flexor moments were significantly different, corrected using the gravity correction methods on the dynamometer relative to the anthropometric model or the reaction board (P < 0.05). These results suggest that the determination of gravitational moments based on anthropometric data is more accurate than current gravity correction methods. This new proposed method should be implemented in isokinetic dynamometry applications.

Analysis of Variance↗
PubMed1996

Resistive eccentric exercise: effects of visual feedback on maximum moment of knee extensors and flexors.

One of the most important features of isokinetic dynamometry is the accurate assessment of muscular function. One of the main factors affecting the accuracy of isokinetic parameters during maximum activation efforts is visual feedback. The purpose of this study was the examination of the effects of visual feedback on maximum moment measurements of the knee extensors and flexors during isokinetic eccentric activations. Twenty-five males performed five maximal efforts at angular velocities of 30 degrees/sec and 150 degrees/sec with and without visual feedback on a Biodex dynamometer. Visual feedback was provided as real time display of the moment output. A three-factor analysis of variance test revealed significant differences between the moments recorded with visual feedback and the nonvisual feedback maximum moments of knee extensors and flexors at both speeds. The mean extension peak moments at 30 degrees/sec and 150 degrees/sec under visual feedback condition were approximately 7.2 and 6.4% higher than the nonvisual feedback moments, respectively. The increase for the knee flexor moment was 8.7 and 9% for slow and fast speeds, respectively. These findings suggest that visual feedback can improve maximum eccentric output and should be provided during assessment of maximum eccentric strength on an isokinetic dynamometer.

Adult↗
PubMed1995

Muscular and tibiofemoral joint forces during isokinetic concentric knee extension.

The purpose of this study was the examination of muscular and tibiofemoral forces during concentric isokinetic knee extension at angular velocities ranging from 30 to 210 deg s(-1), using a two-dimensional biomechanical model. Five males without knee joint injury history participated in the study. The maximum moment ranged from 226.2 Nm at 30 deg s(-1) to 166.4 Nm at 210 deg s(-1). The maximum muscular force ranged from 7.5 times body weight at 30 deg s(-1) to 5.7 at 210 deg s(-1). The compressive tibiofemoral force ranged from 7.5 times body weight at 30 deg s(-1) to 5.7 at 210 deg s(-1) and the shear tibiofemoral force ranged from 0.9 to 0.8 times body weight respectively. These results indicate that the forces developed during maximal isokinetic knee extension are significantly reduced relative to other powerful dynamic activities but are higher than joint forces during simple walking and cycling activities. Appropriate precautions and adjustment of the isokinetic protocol are required in the final phases of joint injury rehabilitation. RELEVANCE: Isokinetic dynamometry has widespread applications in rehabilitation and training of muscle function. It is therefore important to examine the joint and muscular forces under different conditions in order to alter rehabilitation and training programmes and prevent exercise-induced injuries.

Journal Article↗
PubMed1995

A videofluoroscopy method for optical distortion correction and measurement of knee-joint kinematics.

Image distortion in video and image intensifier X-ray systems requires appropriate distortion correction methods to obtain accurate biomechanical quantitative measurements for joint kinematics applications. This paper presents an algorithm for coordinate reconstruction and distortion correction using a modified polynomial method. This algorithm was used for the measurement of patellar tendon moment arm, tibial plateau-tibial axis angle and patellar tendon-tibial axis angle during knee extension using videofluoroscopy in vivo. These parameters allow the determination of a two-dimensional biomechanical model of the knee for the measurement of muscle and joint forces during dynamic activities. Five males without knee joint injury history participated in the study. The mean measurement error obtained using an image intensifier-video system was 0.246 +/- 0.111 mm over a 180-mm x 180-mm field of view. The mean maximum patellar tendon moment arm was 39.87 mm at 44.9 degrees of knee flexion. The patellar tendon-tibial plateau angle was 112.9 degrees at full extension and decreased linearly to 87.6 degrees at 90 degrees of knee flexion. The mean angle between the tibial plateau and the tibial long axis was 84.8 degrees. Applications of the method include motion analysis using video and X-ray fluoroscopy systems with non-linear distortion problems. RELEVANCE: Accurate measurement of anatomical parameters from videofluoroscopy systems is important for the determination of joint biomechanical models and measurement of muscular and joint forces.

Journal Article↗
PubMed1995

Eccentric activation and muscle damage: biomechanical and physiological considerations during downhill running.

An eccentric muscle activation is the controlled lengthening of the muscle under tension. Functionally, most leg muscles work eccentrically for some part of a normal gait cycle, to support the weight of the body against gravity and to absorb shock. During downhill running the role of eccentric work of the 'anti-gravity' muscles--knee extensors, muscles of the anterior and posterior tibial compartments and hip extensors--is accentuated. The purpose of this paper is to review the relationship between eccentric muscle activation and muscle damage, particularly as it relates to running, and specifically, downhill running.

Biomechanical Phenomena↗
PubMed1995

Isokinetic eccentric exercise.

The development of active isokinetic dynamometers has allowed the assessment of muscular moment under eccentric activations that have different characteristics to concentric actions. It is well documented that at a given angular velocity the eccentric moment is greater than the corresponding concentric moment. The moment-velocity relationship under eccentric conditions has been investigated, with conflicting results. Particularly, eccentric moment was reported to remain similar to, or to increase or decrease with, increasing angular velocity. As with concentric actions, the reliability of isokinetic eccentric measurements is influenced by a number of factors such as gravity, preload force and testing position. The velocity-specific effects of eccentric training have not been extensively investigated. Based on current knowledge, eccentric exercise does not appear to be velocity-specific. Although the mode specificity of both concentric and eccentric exercises have been investigated, the resultant observations are conflicting. Eccentric training has been found to improve both concentric and eccentric strength: yet, it has also been reported to improve only concentric or eccentric strength. The reciprocal muscle group ratios under eccentric actions were found not to be influenced by angular velocity, but the significant role of the eccentric/concentric moment ratio of each muscle has not been examined thoroughly. It is well documented that eccentric activations are associated with delayed muscle soreness and muscle damage. A limited number of studies have reported that isokinetic eccentric efforts may result in a lower amount of muscle soreness compared with other exercise modalities. Isokinetic dynamometers provide some unique characteristics for rehabilitation applications. Examination of the clinical application of eccentric exercise is limited. Consequently, the use of this exercise modality in prevention and assessment of musculoskeletal injuries should be investigated further.

Athletic Injuries↗
PubMed1993

Early mobilization after operative repair of ruptured Achilles tendon.

The results of 19 patients in a pilot study in which early mobilization after operative repairs of ruptured Achilles tendons are presented. Serial ultrasound scanning of the repaired tendon showed satisfactory healing. Muscle function was analysed isokinetically and gait symmetry was examined using kinetic analysis. Normal strength of plantarflexion and dorsiflexion was achieved with almost normal range of ankle movement. All patients had normal gait kinetic parameters and symmetry. Normal activities were regained rapidly, and 15 out of 19 patients returned to their pre-injury status. There were no reruptures.

Achilles Tendon↗
PubMed1992

Effect of very low calorie diet on body composition and exercise response in sedentary women.

The effect of very low calorie diet (VLCD) on fat-free mass (FFM) and physiological response to exercise is a topic of current interest. Ten moderately obese women (aged 23-57 years) received VLCD (1695 kJ.day-1) for 6 weeks. FFM, estimated by four conventional techniques, and heart rate (fc), blood lactate (la(b)), mean arterial pressure (MAP), respiratory exchange ratio (R) and rating of perceived exertion (RPE) were measured during a submaximal cycle ergometry test 1 week before, in the 2nd and 6th week, and 1 week after VLCD treatment. Strength and muscular endurance of the quadriceps and hamstrings were tested by isokinetic dynamometry. The 11.5-kg reduction in body mass was approximately 63% fat and 37% FFM. The latter was attributed largely to the loss of water associated with glycogen. Whilst exercise fc increased by 9-14 beats.min-1 (P < 0.01), there were substantial decreases (P < 0.01) in submaximal MAP (1.07-1.73 kPa), la(b) (0.75-1.00 mmol.l-1 and R (0.07-0.09) during VLCD. R and fc returned to normal levels after VLCD. Gross strength decreased (P < 0.01) by 9 and 13% at 1.05 rad.s-1 and 3.14 rad.s-1, respectively. Strength expressed relative to body mass (Nm.kg-1) increased (P < 0.01) at the lower contraction velocity, but there was no change at the faster velocity. Muscular endurance also decreased (P < 0.01) by 62 and 82% for the hamstrings and quadriceps, respectively. We concluded that the strength decrease was a natural adaptation to the reduction in body mass as the ratio of strength to FFM was maintained.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Isokinetic dynamometry. Applications and limitations.

Isokinetic contraction is the muscular contraction that accompanies constant velocity limb movements around a joint. The velocity of movement is maintained constant by a special dynamometer. The resistance of the dynamometer is equal to the muscular forces applied throughout the range of movement. This method allows the measurement of the muscular forces in dynamic conditions and provides optimal loading of the muscles. However, during movements in the vertical plane, the torque registered by the dynamometer is the resultant torque produced by the muscular and gravitational forces. The error depends on the angular position and the torque potential of the tested muscle group. Several methods have been developed for the correction of gravitational errors in isokinetic data. The torque output also contains artefacts that are associated with the inertial forces during acceleration and deceleration periods before the development of the constant preset angular velocity. For an accurate assessment of muscle function, only constant velocity data should be analysed. The most frequently used isokinetic parameters are the maximum torque and the angular position where it was recorded, the torque output at different angular velocities of movement, the torque ratio of reciprocal muscle groups and the torque output during repeated contractions. The unique features of isokinetic dynamometry are optimal loading of the muscles in dynamic conditions and constant preselected velocity of movement. These features provide safety in the rehabilitation of patients with muscular and ligamentous injuries. Isokinetic dynamometry has also been used for the training of various muscle groups in order to improve the muscular performance in dynamic conditions. The movement velocity of different activities can be simulated during training in order to improve the training effect. Data acquisition and analysis have been improved by using computer systems interfaced to isokinetic dynamometers. Recently developed computer systems provide correction for gravitational and inertial errors, accurate computation of isokinetic parameters and real-time display of the torque output.

Biomechanical Phenomena↗