Biomedical subjects

G Giakas

Publications and source records attributed to G Giakas.

16 recordsLinked to original sources

PubMed2007

The effect of eccentric exercise on position sense and joint reaction angle of the lower limbs.

Impaired position sense and impaired joint reaction angle of the lower limbs after muscle-damaging activities is a serious functional limitation that may lead to an increased risk of injury, particularly in older populations. The purpose of the present study was to examine whether position sense and joint reaction angle to release can be affected by eccentric exercise-induced muscle damage. Twelve women underwent an isokinetic exercise session of the lower limb. Isometric peak torque, delayed-onset muscle soreness, serum creatine kinase, position sense, and knee joint reaction angle to release were examined before, immediately after, and 24, 48, and 72 h post-exercise. Due to the effect of eccentric exercise, subjects persistently placed their lower limb at a more extended position, representing a shorter knee extensor muscle. Eccentric exercise increased the knee reaction angle of the lower limb after release from 0 degrees and 15 degrees but not from 30 degrees and 45 degrees . Position sense and joint reaction to release were similarly affected by eccentric exercise and independently of visual feedback. Position sense was impaired only immediately post-exercise (probably due to muscle fatigue), whereas impairment of the reaction angle to release persisted up to 3 days post-exercise (probably due to muscle damage). Attenuation of position sense and joint reaction angle of the lower limbs after damaging activities is a serious functional limitation that may lead to an increase risk of injury, particularly in older populations.

Adult↗

PubMed2006

Contact area inside the distal radioulnar joint: effect of axial loading and position of the forearm.

BACKGROUND: A biomechanical study was performed to define the normal profiles of contact area inside the distal radioulnar joint and how these profiles change as a result of damage to the distal radioulnar ligaments. METHODS: Twelve cadaver arms were used and a custom-made jig was designed to allow axial loading of the hand. Tekscan sensor film was used to measure the contact area inside the joint. Measurements were taken with different loads and in different positions of the forearm. The same measurements were taken after dividing either the volar or dorsal distal radioulnar ligament. Finally the measurements were repeated after reconstruction of the divided ligament. FINDINGS: The contact area increases with axial loading of the hand and is greater in supination than pronation. Division of a single distal radioulnar ligament increases the contact area inside the distal radioulnar joint (123% of normal) and reconstruction of the divided distal radioulnar ligament restores the contact patterns towards the normal values (113% of normal). INTERPRETATION: The results show that axial loading of the hand and position of the forearm has a significant effect on the contact area inside the distal radioulnar joint. The study also shows that injury of the distal radioulnar ligament disturbs the normal profiles of contact.

Aged↗

PubMed2006

The load-bearing characteristics of the forearm: pattern of axial and bending force transmitted through ulna and radius.

A biomechanical study was performed on 12 cadaveric arms to define the normal profiles of force transmission through the ulna and radius and demonstrate the effect on these of simulated injury of the distal radioulnar joint (DRUJ). Strain gauges were used to measure the axial and bending forces transmitted through each bone. Axial force transmitted through the ulna is, broadly, reciprocal to that seen in the radius, with the greatest force seen in supination. In all 12 arms, axial loading of the hand created an anterior bending force (to create a posterior convexity) in the distal radius. Axial loading of the hand created an anterior bending force in the distal ulna for half the specimens and a posterior bending force in the remaining half. Division and division with reconstruction of either the volar or the dorsal distal radioulnar ligament (DRUL) had no significant effect on force transmission through the ulna and radius, while excision of the ulnar head significantly disrupted the profiles of the axial and bending forces.

Aged↗

PubMed2004

Reliability of measurement of tempo-spatial parameters of gait after stroke using GaitMat II.

OBJECTIVE: (1) To find the inter-rater and intra-rater reliability of raters using GaitMat II to measure tempo-spatial gait parameters of stroke patients. (2) To find if reliability is related to abnormality of footprint patterns. DESIGN: A prospective agreement study. SETTING: A movement analysis laboratory. SUBJECTS: Nineteen adults who were at least six months after stroke and able to walk 4 metres with or without assistance participated as subjects in this study. There were five raters. METHODS: Subjects completed at least two walks along GaitMat II. The raw footprint data were analysed independently by each of the five raters. RESULTS: Mean intraclass correlation coefficients (ICCs) for each rater within subject ranged from 0.8398 to 0.9318. However eight of the 17 parameters tested showed significant differences between raters (p = 0.0029 to p < 0.0001). When the most inexperienced rater was excluded, differences between experienced raters (n = 4) was found to be statistically insignificant for all parameters. The association of the mean score and standard deviation of experienced raters was significant for nine parameters (r values 0.5087 to 0.9459), i.e., as walking pattern became more abnormal, variation in scoring between raters increased. CONCLUSIONS: GaitMat II may have acceptable inter-rater reliability if raters have experience of gait analysis but disagreement may increase when stroke patients exhibit more abnormal gait patterns.

Adult↗

PubMed2003

The effects of anterior cruciate ligament reconstruction on tibial rotation during pivoting after descending stairs.

Recent in vitro research suggests that ACL reconstruction does not restore tibial rotation. This study investigated rotational knee joint stability in vivo during a combined descending and pivoting movement that applies a high rotational load to the knee joint. We studied 20 ACL reconstructed patients (bone-patellar tendon-bone graft) and 15 matched controls with a six-camera optoelectronic system performing the examined movement. In the control group the results showed no significant differences in the amount of tibial rotation between the two sides. No significant differences were also found between the contralateral intact leg of the ACL group and the healthy control. However, a significant difference was found within the ACL reconstructed group and between the reconstructed and the contralateral intact leg. Therefore ACL reconstruction may not restore tibial rotation even though anterior tibial translation has been reestablished.

Adult↗

PubMed2003

Hamstring weakness as an indicator of poor knee function in ACL-deficient patients.

Anterior cruciate ligament (ACL) rupture causes instability to the knee joint which leads each patient to a different degree of disability. The purpose of this study was to examine the strength of the quadriceps and the hamstrings in ACL-deficient amateur soccer players at different levels of functional status. Thirty male amateur soccer players were separated into three groups according to their Lysholm score; the high-L1 (Lysholm > or =84), the intermediate-L2 (84> Lysholm > or =72) and the low-L3 (Lysholm <72) knee function groups. The control group consisted of 12 amateur soccer players. The strength of the quadriceps and hamstrings was assessed isokinetically at 60 degrees/s. The quadriceps demonstrated significant deficits of the injured knee compared to the intact knee in all groups, whilst the hamstrings showed significant weakness only in the low function group. Respective percentage deficits in groups L1, L2 and L3 were 13.7%, 16.0% and 18.6% for the quadriceps and 2.4%, 5.6% and 19.2% for the hamstrings. All groups had significant quadriceps weakness which did not differ between the groups. In contrast, the strength deficit of the hamstrings was an indicator of poor knee function, since they were significantly weak only in group L3, which represented patients who clearly failed to compensate for instability symptoms. In groups L1 and L2 the side-to-side differences were within the area of asymmetry measured in the control group. Clinical importance of the results is discussed.

Adult↗

PubMed2003

Fatigue analysis of the surface EMG signal in isometric constant force contractions using the averaged instantaneous frequency.

The averaged instantaneous frequency (AIF) is proposed as an alternative method for the frequency analysis of surface electromyography (EMG) in the study of muscle fatigue during sustained, isometric muscle contractions. Results from performance analysis using experimental EMG signals demonstrate the low variability of the proposed frequency variable. Indeed, the AIF measure is shown to perform significantly better than the widely used mean and median frequency variables, in terms of robustness to the length of the analysis window.

Action Potentials↗

PubMed2003

A hypothesis: self-propulsion in a wheelchair early after stroke might not be harmful.

BACKGROUND: There is often strong clinical resistance to patients self-propelling a wheelchair post stroke as this is believed to produce immediate increases in abnormal posture and movement. Research to support this viewpoint is limited. OBJECTIVE: To begin investigation of the immediate effects of self-propulsion on symmetrical sitting. DESIGN: Replicated single-case studies ABABA. SETTING: Movement analysis laboratory. SUBJECTS: Four patients, a maximum of eight weeks post stroke and six age-matched healthy volunteers. INTERVENTIONS: Subjects sat in the wheelchair during the A phases and self-propelled forwards during the B phases. The Manchester Active Position Seat (consists of 68 force transducers which transmit data at 10 Hz) measured the magnitude of peak force and the position of peak force on both sides of the seat. The mean symmetry index and standard deviation for each study phase were calculated and graphed for each subject. Interpretation was by visual inspection. RESULTS: Only one stroke patient and one volunteer increased asymmetry of magnitude of peak force following the two periods of self-propulsion. Only one of the stroke patients increased asymmetry of position of peak force following self-propulsion compared with three of the healthy volunteers. CONCLUSIONS: These results raise the hypothesis that self-propulsion early post stroke might not produce immediate detrimental effects on seated symmetry.

Aged↗

PubMed2002

Automatic algorithm for filtering kinematic signals with impacts in the Wigner representation.

An automatic filtering algorithm is proposed for the accurate estimation of the second derivatives of kinematic signals with impacts. The impacts considered here occur when a moving object hits a rigid surface. The algorithm performs time-frequency filtering in the Wigner representation, to deal efficiently with the non-stationarities caused by such impacts, and adjusts the parameters of its time-frequency filtering function so that the filtering process adapts to the individual characteristics of the signal in hand. Performance analysis and comparative evaluation with experimentally acquired kinematic impact signals demonstrated a higher accuracy, with performance advantages over two widely used conventional automatic methods: linear phase autoregressive model-based derivative assessment (LAMBDA) and generalised cross-validation using quintic splines (GCVQS). For high impacts, the average absolute relative error in estimating the peak acceleration was 5.7% with the proposed method, 17.2% with a Butterworth low-pass filter optimised to yield minimum overall acceleration RMS error (best-case result), 18.3% with the LAMBDA method, and 37.2% with the GCVQS method. For signals with low impacts, the average absolute relative error was 19.4%, 6.9%, 8.3% and 19.1%, respectively, in each case, which indicates that, for signals with a low-frequency content, there is no need for such time-frequency filtering.

Algorithms↗

PubMed2001

An exploration of the effects of weighted garments on balance and gait of stroke patients with residual disability.

OBJECTIVE: To explore the effects of weighted garments on the balance and gait of stroke patients. DESIGN: A pilot randomized controlled study with blinded measurement. SETTING: Weighted garments were worn by patients living in the community and measurement was made in a hospital-based gait laboratory. SUBJECTS: Twenty-four adults who were at least six months post stroke and were able to walk 10 metres with or without assistance or a walking aid. INTERVENTION: The six-week treatment-phase subjects were given a set of weighted garments which they were shown how to apply and instructed to wear on their paretic side. Subjects randomly allocated to the six-week control phase were not given any weighted garments. MAIN OUTCOME MEASURES: Balance was measured with the Berg Balance Scale. Gait was measured using GaitMat II, an instrumented walkway. Gait parameters of interest were velocity and symmetry of: step length; single support time; double support time; and support base width. Measures were made at baseline before randomization (baseline) and at the end of the six weeks of intervention (outcome). RESULTS: No statistically significant differences were found between the treatment and control groups at outcome for balance (Mann-Whitney U-test; p = 0.74), gait velocity (p = 0.68) or symmetry of gait parameters (p = 0.33 to p = 0.75). CONCLUSIONS: We found no evidence to support the clinical use of these weighted garments for stroke survivors.

Activities of Daily Living↗

PubMed2000

Time-frequency analysis and filtering of kinematic signals with impacts using the Wigner function: accurate estimation of the second derivative.

Biomechanical signals are represented in the time-frequency domain using the Wigner distribution function. Filtering of this representation for the case of a non-stationary displacement signal with impact is studied. Smoothed displacement data are then double differentiated and compared with references accelerometer data. It is shown that this technique is able to remove noise from these signals in a better way than conventional filtering techniques currently used in biomechanics.

Biomechanical Phenomena↗

PubMed1999

Fatigue profile: a numerical method to examine fatigue in cycle ergometry.

Fatigue Profile, a new numerical method for characterising fatigue in isokinetic cycle ergometry is presented and compared with the conventional fatigue index (FI). The new method describes the temporal development of muscle fatigue based on the decline of peak power output throughout a whole trial. The advantage of this method is demonstrated by the analysis of two 25 s maximum trials, separated by 90 s recovery, performed by a well-trained athlete at a pedal frequency of 120 revolutions per minute. A fourth degree polynomial was fitted to model the peak power data. Using the polynomial model coefficients the first derivative represented the rate of changing peak power which represented the Fatigue Profile. The conventional FI was calculated as -35 Ws(-1) and -32 Ws(-1) for trials 1 and 2 respectively, indicating minor differences in fatigue between trials. In contrast the Fatigue Profile revealed important numeric and temporal differences between the trials. For trial 1 a maximum rate of peak power decline of -65 Ws(-1) was reached at approximately 6 s into the trial. In marked contrast, in trial 2, maximum rate of peak power decline (-146 Ws(-1)) occurred immediately. The Fatigue Profile approach allows the characterisation of the temporal development of fatigue under different experimental conditions and in combination with other techniques may yield further insight into the underlying mechanisms of fatigue.

Adult↗

PubMed1998

Improved extrapolation techniques in recursive digital filtering: a comparison of least squares and prediction.

Two extrapolation techniques for recursive digital filtering are presented and compared with common padding methods such as linear and reflection (reverse mirror) extrapolation. The case in which the endpoints of position data lead to peak accelerations after filtering and differentiation is examined. The first technique, 'least squares', is based on fitting a third-degree polynomial to the final 10 data points in both the forward and backward directions and extending the signal by 20 data points using the polynomial coefficients. The second technique, 'prediction', is based on a linear autoregressive model with 20 coefficients, which is applied in both directions and the signal is extrapolated by 20 points. The lowest cumulative error of the endpoint accelerations (22.8 rad s(-2)) represented just one-third of the error when the common padding methods were used in optimal digital filtering (69.7 rad s(-2)). It also represented approximately half the lowest cumulative error in optimal smoothing with quintic splines (48.0 rad (s-2)).

Acceleration↗

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↗

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↗