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The kinematic location of the hip joint centre in gait studies
Ahtracts THE
I~IXEZ~ATIC
LOCATIOI~
GAIT
OF THE STUDIES
HIP
JOIXT
CEXTRE
I) Gait & Posture
S (1997)
IN
85
76-89
TOWARDS
A QUANTITATIVE EMG PA’ITERNS
M. Hulliger.
ANALYSIS IN CEREBRAL
A. Wojciechowski, I. O’Callaghan
Dept. of Clinical Neumsciences. Calgary, and Alberm Children’s
OF MULTIVARIATR PALSY
H.Z. Darwish’, K.&M. and G. Bishop
Human Rrfmmance Hospital’, Calgary.
Genitscn’.
Laboratory’. Univenity of Alberta, Canada RN 4Nl
Quantification of global (multivariate) EMG patterns is a non-trivial problem, espccially in the case of pathological EMG. While characteristic constellations of mubiple EMG profiles may be recognized by eye and described qualitatively. such patterns have proven tea be difficult to quantify. We investigated whether principal component analysis, a method which has previously been used successfully for quantification of multivariate kinematic gait patterns (1,2). could be applied in modified form for data reduction and subsequent pattern analysis of global (multi-channel) EMG signals in healthy children and patients with cerebral palsy. Surface EMG recordings wc~e made ftnm 8 leg muscles on one side while normal subjects and patients with cerebral palsy walked at a comfortable self-selected speed. F’tincipal components (PCs) were calculati as optimally weighted sums of rectified and low-pass tiltwed EMG signals. For PC analysis to be a useful tool, it has to meet minimally five criteria: it should permit significant data reduction (i); PCs should be consistent within subjects (ii) and between subjects (iii); PC analysis should capture alterations in global EMG patterns in pathological gait (iv); and EMG PCS should be interpretable, functionally (v). Results so far indicate that by calculating the fust 4 (of maximally 8) PCs appreciable data reduction could be achieved with limited loss of information (IO-20%). PC waveforms wete generally consistent bath within and between (normal) subjects, featuring reproducible pmfilcs of the 8 EMG weight factors. Rcliminary analysis of EMG patterns in cerebral palsy yielded distinctly different yet, for each patient, generally consistent PC wavefnms, indicating that the pathological alumtions of the cerebral oalsv ~attems were mosdv cantwed in the PC reoresentations. However. the f&&l i&pretation of PCwav~fonns is not stmigt&wvd. Judging horn tbc weight factor profiles it is evident that individual PCs do not reflect simple anatomical (e.g. flexor/extensor) synergies. Instead they appear to ~present functional synergies of anatomically hetetvgenous muscle groups. Attempts are under way to determine whether useful kinematic equivalents of EMG PCs can be identified, using computer simulations of human gait (3). Bell
AL, Pedersen rrni hy rrnirr Assessment
DR and Brand lorniion mrlhods. of the inherent Greenpark
RA. 1, /,. ., B,o,rrect,an,rs.X( o,. 6,~.L’,, 1940.
accuracy of a kinematic analysis R Baker Care Trust, Belfast
system
Health
Referenas 1. 2. 3.
Introduction
Mah, CD., Hulliaer. M., Lee. R.G. & O’Callarhan. I (1994). Ouamitative analysis of humah nmvement synergies: consm&e pattern analyds for gait. Journal of Motor Behavior 26, 83-102. Mab, CD., Hulliger, M.. O’Callaghan, I. & Lee, R.G. (1996). Quantitative kinematics of gait patterns during the recovery period following smoke. Stroke (submitted). Gcrritsen, K.G.M., van den Bogen, A.J. & Hulliger, M. (19%). Direct dynam its simulation of FES-assisted locomotion. In Proceedings of the Inter~ti~l Symposium on Smofl Structures and Materials (in press).
Supported
by NCE Canada, AHIMR
It is a generally accepted principle of measwement theory that the inherent error in the measurement equipment should be an order of magnitude lower than the smallest significant increment in the quantity being measured For many systems reccrding the kinematics of human gait this is not the case and an undestanding ofthese errors and their sowces is required for intelligent interpretation of the dataThis study attempts to determine the relative contribution to errors in determination of marker position from different sources of inaccuracy.
E.M. Laassel, Ch. Guibal, Gart Laboratory
Method
Tel A series of tests has been carried out to calculate the error in both absolute and relative measurements of marker position. Absolute measurements relate to tixed markers placed on the floor of the laboratory at measured positions, relative measurements relate to markers fixed to a frame which was moved through the measuring space The effect of repeated calibration, repeated data capture. system noise and masking of combinations of cameras was assessed The system used in this evaluation was a six camera Vicon VX system (Oxford Metrics, Oxford. UK) An a.se~~rnent of the effects of skin mcwement was also made by measuring the variation in distance between markers “fixed” to the same body segment during the gait cycle for comparative purposes
Results show that repeated calibration and data capture of fixed markers do not introduce appreciable errms into the system System noise causes a standard deviation of less than 0 Smm in determination of absolute position but a range of +/I m m The error in the average measurement of absolute marker position was of the order of +/lmm Masking cameras PO that only two cameras could see a marker introduced a range of measurement of absolute position of up to IOmm This was reduced to less than 3mm when viewed by four cameras
Conclusion With care the overall inherent accuracy of the kinematic measurement system assessed was of the order of +/-I 5 m m if all camems detected a marker The largest swrce of error occurs when markers are masked from several cameras
and NSERC.
J. PClissier. A. Dimeglio
Inrtnut Saint Pxrre 34250 Palwas
w (33) 67 07 75 56
Les - Flats.
FXUlCe
Fax xx(33)67680990
Introduction A quantitative method is presented for evaluating the development of stance phase, using kmetic and kinematic data Results obtained from normal and pathological subjects are presented and discussed, together with a study of amputee gait using a variety of prostheses Materials
and Methods
Subjects are assessed in the gait laboratory usmg a Vicon reflective-marker kinematic measurement system, with tw ANTI force plates providing synchronised kmetic data One marker is placed on the lateral malleolus and one on the second metatarsal joint The displacements of the two markers and the cent~e of pressure are plotted together as a function of time. with sagittal and lateral components show separately The resulting diagrams are a useful aid for analysing the development of stance phase
Results Twenty normal subjects were studied Figure 1 is typical of normal mature gait From the moment of heel contact, the centre of pressure moves steadily forward past the malleolus during weight acceptance, continuing forward at a nearly constant rate during the footflat phase, slowing as the heel rises, and moving ahead ofthe metatarsal joints at the end of stance. The Forresponding curves for a subject diagnosed as hemiplegia who displays equinus gat IS shown in figure 2 The centre of pressure remains under the metatarsal joint tbrougbout stame phase, moving by less than 15 mm. Figure 3 represents a diagram of a spma bifida patient who displays talus gait The centre of pressure remains within a range of 11 mm, just fonvard of the lateral malleolus
I~IXEZ~ATIC
LOCATIOI~
GAIT
OF THE STUDIES
HIP
JOIXT
CEXTRE
I) Gait & Posture
S (1997)
IN
85
76-89
TOWARDS
A QUANTITATIVE EMG PA’ITERNS
M. Hulliger.
ANALYSIS IN CEREBRAL
A. Wojciechowski, I. O’Callaghan
Dept. of Clinical Neumsciences. Calgary, and Alberm Children’s
OF MULTIVARIATR PALSY
H.Z. Darwish’, K.&M. and G. Bishop
Human Rrfmmance Hospital’, Calgary.
Genitscn’.
Laboratory’. Univenity of Alberta, Canada RN 4Nl
Quantification of global (multivariate) EMG patterns is a non-trivial problem, espccially in the case of pathological EMG. While characteristic constellations of mubiple EMG profiles may be recognized by eye and described qualitatively. such patterns have proven tea be difficult to quantify. We investigated whether principal component analysis, a method which has previously been used successfully for quantification of multivariate kinematic gait patterns (1,2). could be applied in modified form for data reduction and subsequent pattern analysis of global (multi-channel) EMG signals in healthy children and patients with cerebral palsy. Surface EMG recordings wc~e made ftnm 8 leg muscles on one side while normal subjects and patients with cerebral palsy walked at a comfortable self-selected speed. F’tincipal components (PCs) were calculati as optimally weighted sums of rectified and low-pass tiltwed EMG signals. For PC analysis to be a useful tool, it has to meet minimally five criteria: it should permit significant data reduction (i); PCs should be consistent within subjects (ii) and between subjects (iii); PC analysis should capture alterations in global EMG patterns in pathological gait (iv); and EMG PCS should be interpretable, functionally (v). Results so far indicate that by calculating the fust 4 (of maximally 8) PCs appreciable data reduction could be achieved with limited loss of information (IO-20%). PC waveforms wete generally consistent bath within and between (normal) subjects, featuring reproducible pmfilcs of the 8 EMG weight factors. Rcliminary analysis of EMG patterns in cerebral palsy yielded distinctly different yet, for each patient, generally consistent PC wavefnms, indicating that the pathological alumtions of the cerebral oalsv ~attems were mosdv cantwed in the PC reoresentations. However. the f&&l i&pretation of PCwav~fonns is not stmigt&wvd. Judging horn tbc weight factor profiles it is evident that individual PCs do not reflect simple anatomical (e.g. flexor/extensor) synergies. Instead they appear to ~present functional synergies of anatomically hetetvgenous muscle groups. Attempts are under way to determine whether useful kinematic equivalents of EMG PCs can be identified, using computer simulations of human gait (3). Bell
AL, Pedersen rrni hy rrnirr Assessment
DR and Brand lorniion mrlhods. of the inherent Greenpark
RA. 1
accuracy of a kinematic analysis R Baker Care Trust, Belfast
system
Health
Referenas 1. 2. 3.
Introduction
Mah, CD., Hulliaer. M., Lee. R.G. & O’Callarhan. I (1994). Ouamitative analysis of humah nmvement synergies: consm&e pattern analyds for gait. Journal of Motor Behavior 26, 83-102. Mab, CD., Hulliger, M.. O’Callaghan, I. & Lee, R.G. (1996). Quantitative kinematics of gait patterns during the recovery period following smoke. Stroke (submitted). Gcrritsen, K.G.M., van den Bogen, A.J. & Hulliger, M. (19%). Direct dynam its simulation of FES-assisted locomotion. In Proceedings of the Inter~ti~l Symposium on Smofl Structures and Materials (in press).
Supported
by NCE Canada, AHIMR
It is a generally accepted principle of measwement theory that the inherent error in the measurement equipment should be an order of magnitude lower than the smallest significant increment in the quantity being measured For many systems reccrding the kinematics of human gait this is not the case and an undestanding ofthese errors and their sowces is required for intelligent interpretation of the dataThis study attempts to determine the relative contribution to errors in determination of marker position from different sources of inaccuracy.
E.M. Laassel, Ch. Guibal, Gart Laboratory
Method
Tel A series of tests has been carried out to calculate the error in both absolute and relative measurements of marker position. Absolute measurements relate to tixed markers placed on the floor of the laboratory at measured positions, relative measurements relate to markers fixed to a frame which was moved through the measuring space The effect of repeated calibration, repeated data capture. system noise and masking of combinations of cameras was assessed The system used in this evaluation was a six camera Vicon VX system (Oxford Metrics, Oxford. UK) An a.se~~rnent of the effects of skin mcwement was also made by measuring the variation in distance between markers “fixed” to the same body segment during the gait cycle for comparative purposes
Results show that repeated calibration and data capture of fixed markers do not introduce appreciable errms into the system System noise causes a standard deviation of less than 0 Smm in determination of absolute position but a range of +/I m m The error in the average measurement of absolute marker position was of the order of +/lmm Masking cameras PO that only two cameras could see a marker introduced a range of measurement of absolute position of up to IOmm This was reduced to less than 3mm when viewed by four cameras
Conclusion With care the overall inherent accuracy of the kinematic measurement system assessed was of the order of +/-I 5 m m if all camems detected a marker The largest swrce of error occurs when markers are masked from several cameras
and NSERC.
J. PClissier. A. Dimeglio
Inrtnut Saint Pxrre 34250 Palwas
w (33) 67 07 75 56
Les - Flats.
FXUlCe
Fax xx(33)67680990
Introduction A quantitative method is presented for evaluating the development of stance phase, using kmetic and kinematic data Results obtained from normal and pathological subjects are presented and discussed, together with a study of amputee gait using a variety of prostheses Materials
and Methods
Subjects are assessed in the gait laboratory usmg a Vicon reflective-marker kinematic measurement system, with tw ANTI force plates providing synchronised kmetic data One marker is placed on the lateral malleolus and one on the second metatarsal joint The displacements of the two markers and the cent~e of pressure are plotted together as a function of time. with sagittal and lateral components show separately The resulting diagrams are a useful aid for analysing the development of stance phase
Results Twenty normal subjects were studied Figure 1 is typical of normal mature gait From the moment of heel contact, the centre of pressure moves steadily forward past the malleolus during weight acceptance, continuing forward at a nearly constant rate during the footflat phase, slowing as the heel rises, and moving ahead ofthe metatarsal joints at the end of stance. The Forresponding curves for a subject diagnosed as hemiplegia who displays equinus gat IS shown in figure 2 The centre of pressure remains under the metatarsal joint tbrougbout stame phase, moving by less than 15 mm. Figure 3 represents a diagram of a spma bifida patient who displays talus gait The centre of pressure remains within a range of 11 mm, just fonvard of the lateral malleolus