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Biomedical subjects

A Cappozzo

Publications and source records attributed to A Cappozzo.

At least 19 recordsLinked to original sources
PubMed2003

Femoral anatomical frame: assessment of various definitions.

The reliability of the estimate of joint kinematic variables and the relevant functional interpretation are affected by the uncertainty with which bony anatomical landmarks and underlying bony segment anatomical frames are determined. When a stereo-photogrammetric system is used for in vivo studies, minimising and compensating for this uncertainty is crucial. This paper deals with the propagation of the errors associated with the location of both internal and palpable femoral anatomical landmarks to the estimation of the orientation of the femoral anatomical frame and to the knee joint angles during movement. Given eight anatomical landmarks, and the precision with which they can be identified experimentally, 12 different rules were defined for the construction of the anatomical frame and submitted to comparative assessment. Results showed that using more than three landmarks allows for more repeatable anatomical frame orientation and knee joint kinematics estimation. Novel rules are proposed that use optimization algorithms. On the average, the femoral frame orientation dispersion had a standard deviation of 2, 2.5 and 1.5 degrees for the frontal, transverse, and sagittal plane, respectively. However, a proper choice of the relevant construction rule allowed for a reduction of these inaccuracies in selected planes to 1 degrees rms. The dispersion of the knee adduction-abduction and internal-external rotation angles could also be limited to 1 degrees rms irrespective of the flexion angle value.

Algorithms↗
PubMed2002

The sensitivity of posturographic parameters to acquisition settings.

The objective of this study was to evaluate the sensitivity of posturographic parameters (PP) to changes in acquisition settings. A group of eight young adults underwent a set of typical orthostatic posture trials, and selected PP were then calculated from a set of centre of pressure (CoP) displacement time series obtained by applying different cut-off frequencies to the same set of raw data. Four PP out of 11 showed significant changes with respect to cut-off frequency. Statistical mechanics parameters exhibited smaller sensitivity than summary measures. On the basis of the results obtained, a proposal for a standard cut-off frequency and a sampling rate value is embodied in the paper together with some suggestions on measurement settings, with a view to standardized use of instrumentation for quantitative analysis in orthostatic posturography.

Acceleration↗
PubMed2001

Hemodynamics as a possible internal mechanical disturbance to balance.

The postural control system is assessed by observing body sway while the subject involved aims at maintaining a specified up-right posture. Internal masses generate internal reaction forces that constitute an internal mechanical stimulus that may contribute to cause segmental displacements, i.e. body sway. Thus, gaining knowledge about the amplitude and direction of these reaction forces would contribute to gain insights into the mechanisms that influence the maintenance of balance and into its control. The 3-D force vector that acts on the body centre of mass (COM) and is associated with the transient blood movement at each cardiac cycle was assessed in a population sample of 20 young adults during the maintenance of a quiet up-right posture. Typical patterns of the three components of this force vector were identified. Relevant parameters were selected and submitted to sample statistics. For a number of them, linear correlation with subject-specific parameters was found. The antero-posterior force component was characterised by a triphasic major wave, the peaks of which had values up to 0.40 N. The vertical component showed a repeatable triphasic wave with peak-to-peak values in the range 1.3-3.0 N. The medio-lateral component showed relatively low peak-to-peak values (in the range 0.05-0.10 N). The resultant vector had an amplitude that underwent several oscillations during the cardiac cycle and reached its maximal value in the range 0.6-1.7 N.

Adaptation, Physiological↗
PubMed2000

A spot check for estimating stereophotogrammetric errors.

Good practice rules in the management of a movement analysis laboratory recommend that photogrammetric measurement errors are assessed, prior to every experimental session, using an ad hoc experiment referred to as a spot check. The paper proposes an inexpensive and easy to make spot check. The test uses a rigid rod carrying two markers and a target point taken on the line joining them and coinciding with the rod tip. The latter point is placed in a fixed and measured position in the laboratory frame and the markers are tracked while the rod is kept stationary and while it is manually made to rotate about the target point. Several target points are used within the measurement volume. The instantaneous errors with which the laboratory co-ordinates of the latter points are reconstructed are determined and submitted to statistical analysis. A normalisation procedure is illustrated that aims at making the test results independent from the geometry of the test object. The experimental and analytical methods underlying the proposed spot check were validated experimentally in two movement analysis laboratories using repeated tests. A rod, 1.5 m long, carrying four markers was used. In this way, several test-object geometries were tested. Results confirmed that the photogrammetric error could be divided into a zero-mean random and a systematic component. It was shown that the normalisation procedure was effective for the standard deviation of both error components when the two markers were located at a distance between them 1.5 times larger than the distance of their centroid from the tip of the rod. The systematic component bias could not be normalised, however a conservative value of it could be estimated. The two above-mentioned normalised standard deviations and the bias value can be taken as descriptors of the photogrammetric error of the specific measuring system tested. These parameters may also be used to assess the precision and the accuracy with which the laboratory position of a target point, defined relative to any specified marker cluster, may be reconstructed during movement analysis.

Humans↗
PubMed2000

Sit-to-stand motor strategies investigated in able-bodied young and elderly subjects.

For the execution of a certain motor task, a motor strategy is chosen by each individual among those that are consistent with the structural and functional constraints of his/her locomotor system, and that tends to maximise the effectiveness of the motor act. The identification of this strategy allows for the assessment of the individual's functional status. This study aimed at identifying the motor strategies adopted for the execution of the sit-to-stand motor task, at different speeds and initial postures, in a sample of 35 community-dwelling elders and in a sample of 16 young able-bodied individuals. This was done using a method, least perceivable to the test subject and "economical" for the experimenter, which entailed the recording of external forces only. A musculo-skeletal system model, based on a telescopic inverted-pendulum (TIP) moved by a linear and two rotational muscle-equivalent actuators, was then used. Parameters describing the kinematics and dynamics of these actuators were extracted and submitted to statistical analysis. Different motor strategies were identified in the two age groups, as well as associated with both a different initial posture (ankle dorsiflexion angle) and speed of execution of the motor task. In particular, the elder group, as compared with the young group, prior to seat-off tended to flex the trunk more, thus bringing the CM closer to the base of support, and at a higher velocity, thus gaining a higher momentum. After seat-off, elders rotated the body forward and, only after having brought their CM over the base of support, effectively started elevation. Both global muscular effort and coordination effort associated with the achievement of balance and raising were lower. However, maximal speed was also lower. The above results indicated that the elders could count on a lower functional reserve than the young individuals and, from the methodological viewpoint, that the TIP approach is a good candidate for subject-specific functional evaluation in a clinical context.

Adult↗
PubMed2000

Effects of hip joint centre mislocation on gait analysis results.

Methods to determine the hip joint centre (HJC) location are necessary in gait analysis. It has been demonstrated that the methods proposed in the literature involve large mislocation errors. The choice should be made according to the extent by which HJC location errors distort the estimates of angles and resultant moments at the hip and knee joints. This study aimed at quantifying how mislocation errors propagate to these gait analysis results. Angles and moments at the hip and knee joint were calculated for five able-bodied subjects during level walking. The nominal position of the HJC was determined as the position of the pivot point of a 3D movement of the thigh relative to the pelvis. Angles and moments were then re-calculated after having added to HJC co-ordinates errors in the range of +/-30 mm. Angles and moments at both hip and knee joints were affected by HJC mislocation. The hip moments showed the largest propagation error: a 30 mm HJC anterior mislocation resulted in a propagated error into flexion/extension component of about -22%. The hip abduction/adduction moment was found the second largest affected quantity: a 30 mm lateral HJC mislocation produced a propagated error of about -15%. Finally, a 30 mm posterior HJC mislocation produced a delay of the flexion-to-extension timing in the order of 25% of the stride duration. HJC estimation methods with minimum antero-posterior error should therefore be preferred.

Adult↗
PubMed1999

Pelvis and lower limb anatomical landmark calibration precision and its propagation to bone geometry and joint angles.

Human movement analysis using stereophotogrammetry is based on the reconstruction of the instantaneous laboratory position of selected bony anatomical landmarks (AL). For this purpose, knowledge of an AL's position in relevant bone-embedded frames is required. Because ALs are not points but relatively large and curved areas, their identification by palpation or other means is subject to both intra- and inter-examiner variability. In addition, the local position of ALs, as reconstructed using an ad hoc experimental procedure (AL calibration), is affected by photogrammetric errors. The intra- and inter-examiner precision with which local positions of pelvis and lower limb palpable bony ALs can be identified and reconstructed were experimentally assessed. Six examiners and two subjects participated in the study. Intra- and inter-examiner precision (RMS distance from the mean position) resulted in the range 6-21 mm and 13-25 mm, respectively. Propagation of the imprecision of ALs to the orientation of bone-embedded anatomical frames and to hip, knee and ankle joint angles was assessed. Results showed that this imprecision may cause distortion in joint angle against time functions to the extent that information relative to angular movements in the range of 10 degrees or lower may be concealed. Bone geometry parameters estimated using the same data showed that the relevant precision does not allow for reliable bone geometry description. These findings, together with those relative to skin movement artefacts reported elsewhere, assist the human movement analyst's consciousness of the possible limitations involved in 3D movement analysis using stereophotogrammetry and call for improvements of the relevant experimental protocols.

Biomedical Engineering↗
PubMed1999

Validation of a functional method for the estimation of hip joint centre location.

The present study assesses the accuracy with which the subject specific coordinates of the hip joint centre (HJC) in a pelvic anatomical frame can be estimated using different methods. The functional method was applied by calculating the centre of the best sphere described by the trajectory of markers placed on the thigh during several trials of hip rotations. Different prediction methods, proposed in the literature and in the present investigation, which estimate the HJC of adult subjects using regression equations and anthropometric measurements, were also assessed. The accuracy of each of the above-mentioned methods was investigated by comparing their predictions with measurements obtained on a sample of 11 male adult able-bodied volunteers using roentgen stereophotogrammetric analysis (RSA), assumed to provide the true HJC locations. Prediction methods estimated the HJC location at an average rms distance of 25-30 mm. The functional method performed significantly better and estimated HJCs within a rms distance of 13 mm on average. This result may be confidently generalised if the photogrammetric experiment is carefully conducted and an optimal analytical approach used. The method is therefore suggested for use in motion analysis when the subject's hip range of motion is not limited. In addition, the facts that it is not an invasive technique and that it has relatively small and un-biased errors, make it suitable for regression equations identification with no limit to sample size and population typology.

Adult↗
PubMed1999

A telescopic inverted-pendulum model of the musculo-skeletal system and its use for the analysis of the sit-to-stand motor task.

For field applicability of biomechanical methodologies aiming at assessing motor ability in disabled, or at risk of disablement (e.g. elderly), subjects, measurements must be carried out using a least perceivable to the subject and essential experimental apparatus. Since data thus obtained do not necessarily lend themselves to straightforward interpretation, they should be fed to a model of the portion of the musculo-skeletal system involved that already embodies the invariant aspects of both the modelled system and the motor task. Through such a minimum measured-input model, richer, physiology-related, and thus easier to interpret, information may be expected. In this framework, the present study investigated the sit-to-stand motor task using information obtained only from a force plate located under seat and subject's feet, a seat uniaxial load-cell and basic anthropometric parameters. Data were collected in a sample of 12 able-bodied subjects while executing the motor task at different speeds. The musculo-skeletal system was modelled as a telescopic inverted pendulum (TIP) that could vary its length (shortening or elongation) by effect of a force actuator and its orientation in space by effect of two couple actuators that were looked upon as muscle equivalent effectors. The TIP model output consisted in the kinematics and dynamics of these actuators. It allowed the identification of four functional phases in which the seat-to-stand motor task could be divided, and a detailed description of the relevant mechanics in terms of balance control and centre of mass elevation. Motor strategy modifications associated with speed variation could also be identified. For a global evaluation of the motor act it showed to be no less informative than more demanding multi-segment models. Although it is true that specific musculo-articular functions can only be inferred, the more compact information yielded by the TIP model is expected to facilitate subject and/or disability classification.

Adult↗
PubMed1999

Inter- and intra-individual variability of ground reaction forces during sit-to-stand with principal component analysis.

Variable reduction is an important issue in biomechanics, because the definition of a non-redundant set of variables necessary for a complete description of a given motor act provides information about the motor strategy. A systematic tool for dealing with variable reduction problems is Principal Component Analysis. In this paper, as an example of an application of this technique, the set of Ground Reaction Forces (GRFs) provided by a six-component force plate, gained during standing up in a heterogeneous population of 82 normal individuals, was reduced to a set of fewer variables. Each subject was required to stand up from a chair five times at different, randomly self selected, speeds, obtaining a data set of 410 trials. Principal Components (PCs) of GRFs were computed for each trial. On average, over the ensemble of trials, first and second PCs (PC1 and PC2) explained together 90% of PCs. Inter- and intra-individual repeatability of the first two PCs was investigated by examining the correlation coefficient between PC waveforms obtained from the whole set of trials and within the set of trials performed by the same subject, respectively. While the PC1 exhibited repeatable patterns, the second one, although repeatable within the group of trials performed by the same subject, displayed marked inter-individual variability. Therefore, PC1 was related to intrinsic aspects of the motor task and PC2 to inter-subject features.

Adult↗
PubMed1998

Skin movement artefact assessment and compensation in the estimation of knee-joint kinematics.

In three dimensional (3-D) human movement analysis using close-range photogrammetry, surface marker clusters deform and rigidly move relative to the underlying bone. This introduces an important artefact (skin movement artefact) which propagates to bone position and orientation and joint kinematics estimates. This occurs to the extent that those joint attitude components that undergo small variations result in totally unreliable values. This paper presents an experimental and analytical procedure, to be included in a subject-specific movement analysis protocol, which allows for the assessment of skin movement artefacts and, based on this knowledge, for their compensation. The effectiveness of this procedure was verified with reference to knee-joint kinematics and to the artefacts caused by the hip movements on markers located on the thigh surface. Quantitative validation was achieved through experimental paradigms whereby prior reliable information on the target joint kinematics was available. When position and orientation of bones were determined during the execution of a motor task, using a least-squares optimal estimator, but the rigid artefactual marker cluster movement was not dealt with, then knee joint translations and rotations were affected by root mean square errors (r.m.s.) up to 14 mm and 6 degrees, respectively. When the rigid artefactual movement was also compensated for, then r.m.s errors were reduced to less than 4 mm and 3 degrees, respectively. In addition, errors originally strongly correlated with hip rotations, after compensation, lost this correlation.

Adult↗
PubMed1997

Surface-marker cluster design criteria for 3-D bone movement reconstruction.

When three-dimensional (3-D) human or animal movement is recorded using a photogrammetric system, bone-embedded frame positions and orientations are estimated from reconstructed surface marker trajectories using either nonoptimal or optimal algorithms. The effectiveness of these mathematical procedures in accommodating for both photogrammetric errors and skin movement artifacts depends on the number of markers associated with a given bone as well as on the size and shape characteristics of the relevant cluster. One objective of this paper deals with the identification of marker-cluster design criteria aimed at the minimization of error propagation from marker coordinates to bone-embedded frame position and orientation. Findings allow for the quantitative estimation of these errors for any given cluster configuration and suggest the following main design criteria. A cluster made up of four markers represents a good practical compromise. Planar clusters are acceptable, provided in quasi-isotropic distribution. The root mean square distance of the markers from their centroid should be greater than ten times the standard deviation of the marker position error. The second objective of this paper deals with the identification of the optimal cluster position and orientation on the limb aimed at the minimization of error propagation to anatomical landmark laboratory coordinates. Cluster position should be selected to minimize skin movement artifacts. The longest principal axis of the marker distribution should be oriented toward the relevant anatomical landmark position.

Animals↗
PubMed1996

Position and orientation in space of bones during movement: experimental artefacts.

This paper deals with the experimental problems related to the reconstruction of the position and orientation of the lower limb bones in space during the execution of locomotion and physical exercises. The inaccuracies associated with the relative movement between markers and underlying bone are analysed. Quantitative information regarding this movement was collected by making experiments on subjects who had suffered fractures and were wearing either femoral or tibial external fixators. These latter devices provided frames that were reliably rigid with the bone involved, and hence the possibility of assessing the relative movement between markers mounted on the skin and this bone. Anatomical frames associated with thigh and shank were reconstructed using technical frames based on different clusters of skin markers and their rotation with respect to the relevant bone evaluated. Marker movement was also assessed in subjects with intact musculoskeletal structures using digital videofluoroscopy.

Journal Article↗
PubMed1995

Position and orientation in space of bones during movement: anatomical frame definition and determination.

This paper deals with methodological problems related to the reconstruction of the position and orientation of the human pelvis and the lower limb bones in space during the execution of locomotion and physical exercises using a stereophotogrammetric system. The intention is to produce a means of quantitative description of joint kinematics and dynamics for both research and application. Anatomical landmarks and bone-embedded anatomical reference systems are defined. A contribution is given to definition of variables and relevant terminology. The concept of anatomical landmark calibration is introduced and relevant experimental approaches presented. The problem of data sharing is also addressed. This material is submitted to the scientific community for consideration as a basis for standardization. RELEVANCE: In order to make movement analysis effective in the solution of clinical problems, a structured conceptual background is needed in addition to standardized definitions and methods. Technical solutions which make data sharing and relevant data banks possible are also of primary importance. This paper makes suggestions in this context.

Journal Article↗
PubMed1991

Prediction of ramp traversability for wheelchair dependent individuals.

The purpose of this research was to obtain a single objective criterion that would constitute a reliable prediction of length and grade limits for ramps that can be traversed by any special category of wheelchair dependent individuals (WDI). The maximal voluntary force (MVC) is the main limiting factor of the performance of WDI, thus the force required to traverse a ramp has been established by means of a simple mechanical model. The real time course of force application during ascent was experimentally obtained. Then, a simplified law of force application was introduced in a computer simulation program of kinetics and kinematics of ascent. Inputs to the model were also the mass of the subject plus wheelchair, the initial velocity of the chair, and the ramp length. The output of the program was the force requirement for any given length/grade. When capsizing conditions were encountered the simulation ended. We tested the results thus obtained having some selected WDI successfully traversing ramps with the predicted length/grade specifications.

Architectural Accessibility↗
PubMed1985

Lumbar spine loading during half-squat exercises.

Evaluation of the compressive load acting on the lumbar spine (L3-L4) during half-squat exercises executed with a barbell resting on the subject's shoulders was undertaken. The kinematics of the upper body segments of two male and two female subjects as well as the barbell were described using data obtained by means of an optoelectronic system (CoSTEL). L3-L4 compressive load was calculated using a model of the anatomy of the trunk musculoskeletal system. Filtered surface electromyographic trunk flexor recordings from the obliquus externus and rectus abdominis and trunk extensor erectores spinae muscles as well as measurement of the ground reaction forces were also carried out for predicted result validation. During half-squat exercises with barbell loads in the range 0.8 to 1.6 times body weight the compressive loads on the L3-L4 segment vary between 6 and 10 times body weight. Erectores spinae contraction force was predicted to be between 30 and 50% of the relevant maximal isometric force. The magnitude of trunk flexion was found to be the variable which influenced most spinal compression load.

Adult↗
PubMed1984

Compressive loads in the lumbar vertebral column during normal level walking.

The longitudinal compressive load acting on the L3-L4 spinal motion segment was investigated during normal level walking for a range of speeds of progression. Forces were predicted using experimental data from photogrammetric measurements of upper body segmental motion and inertial properties, along with a biomechanical model of the trunk. A partial validation of the results was obtained using records of the electrical activity of the trunk muscles and intradiscal pressure information available in the literature. Experiments were carried out in five normal young male subjects. Results showed that the L3-L4 motion segment is subjected to cyclic compressive loads. The maximum and minimum values of this load vary with walking speed from approximately 1.0 to 2.5 and from 0.8 to 0.2 times body weight, respectively. Relevant peaks occur with a frequency ranging approximately from 1.3 to 2.5 Hz. Muscular action is mostly concentrated in the trunk extensors, which show a burst of activity at the time of ipsilateral toe-off.

Adult↗