Download Each muscle contraction starts with the excitation of an upper motor

The 2nd International Conference
Computational Mechanics
and
Virtual Engineering
COMEC 2007
11 – 13 OCTOBER 2007, Brasov, Romania
PROTOCOL FOR GAIT ANALYSIS BASED ON LABORATORY
INVESTIGATIONS
Mirela Toth-Taşcău, Dan Ioan Stoia, Mircea Dreucean
Politehnica University of Timisoara, ROMANIA, [email protected], [email protected],
[email protected]
Abstract: The present study assigns a protocol for human gait investigations. In order to find a protocol, the gait cycles of a
number of 20 healthy patients were recorded. The basic concept was to use three different systems in order to achieve the desired
protocol. The protocol idea arises from the necessity to compare a record of a healthy person with a diseased one. The
establishing of a normal gait pattern was also a main concern. The recording equipments used are: the human gait analysis
system Zebris, the plantar force measurement system Zebris FDM and the electromyography system from ADInstruments. All of
these systems are dedicated or can be adapted to our study purpose. The combination of the measurement and investigation
concepts of the equipments involved in the study, lead us to a protocol for human gait evaluation.
Keywords: kinematical analysis, gait, force distribution, electromyography
1. INTRODUCTION
The gait is one of the main abilities of the human body. During a life time, different motion abnormalities can occur.
The human lower limb skeleton may be considered a complex system composed of rigid bodies (bones), joints
(articulations) and actuators (muscles). According to the complexity of the lower limb construction, the movement
capacities at this level are really vast. The gait abnormalities can be caused by problems in bones, joints, muscles,
ligaments or nerves. An investigation based on kinematical analysis is not sufficient for a diagnostic. The physicists
can add their own medical experience to the results of the gait analyze system in order to define a diagnostic and to
evaluate the level of the rehabilitation process.
2. KINEMATICAL GAIT ANALYSIS USING ZEBRIS CMS-HS MEASURING SYSTEM
Figure 1: Geometrical model
The Zebris measuring system allows an objective kinematical
analysis of the human gait by means of analyzing the tracks
of body surface markers [4]. The measuring method is based
on the determination of spatial coordinates of miniature
ultrasound receivers (markers) by measuring the delay
between the emission of sonic pulses by the transmitters and
their reception at the microphone sensors. The exact spatial
position of the markers is determined by triangulation
method.
The measurement starts with the attachment of the two
markers on the body in two key points. The first marker
triplet is attached on the thigh and the second one on the
upper part of the foot. In the next step, the anatomic
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landmarks are marked with the pointer, and the dedicated software creates the geometrical model (figure 1). After
this point, the recording can start.
The steps number was isolated from the large data recorded and used to calculate the velocity, cadence and double
support time. In a normal gait, the step time is about 1.3 seconds, but in this case the subject made small and short
steps (figure 2). One can say that this parameter is characteristic for the investigated person. Another important
parameter is the balance between the gait phases. For a normal gait, the swing phase must be around 40% of the gait
cycle and the stance phase 60%. This case underlines an abnormality of the gait, with around 25% of swing and 75%
of stance (figure 3). The difference between the left and right limb in gait phases is still insignificant.
Figure 3: Swing –Stance phases
Figure 2: Step diagram during gait cycles
The joint angles recorded during the gait cycle are presented in the figure 4.
Figure 4: Angular variation in lower limb joints during a gait cycle
The diagram shows the angular variation for each individual joint in all the possible movements: flexion-extension,
abduction-adduction and rotations. The flexion-extension movements of the thigh, knee and ankle present the highest
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amplitudes, with the values included in the normal range for a gait cycle. The diagrams for the left limb joint
variations are highlighted in the upper part of the figure 4, and at the bottom of the same figure, the same parameters
for the right limb. The angular variations of the left and right limbs prove also, the similitude between the limbs. So,
the angular parameters indicate a gait movement close to the normal one.
3. FORCE DISTRIBUTION MAPPING USING ZEBRIS FDM SYSTEM
The Zebris FDM measuring system functions using high-quality capacitive force sensors that are arranged in matrix
form. The measuring plate enables both the static and dynamic plantar force distribution to be analyzed during the
patient standing and walking [5].
In order to compare the resulting gait parameters with the parameters from the first recording method the same
subject was investigated.
The general parameters indicate a particular type of gait (like in the first case), with large stance periods up to 78%
on the right limb, and large stride time of 1.58 sec (a normal gait has a stride time of 1.3 sec).
The specific parameter of the system is the plantar pressure distribution. The pressure distribution looks like a
colored footprint (tracking). The values of the pressures are provided in N/cm² units and can be identified in
comparison with a reference color bare (figure 5).
Figure 5: Long platform picture
Another specific parameter recorded with FDM system is the reaction force. The reaction forces at the plantar level
vary like in the figure 6. The capacitive sensors of the system measure the instantaneous pressure and calculate the
force F=P*S (S represents stance for the contact area between foot and platform). The graphic below reveal three
major points for the force distribution: peaks, flat middle lines and valleys.
The peaks on the graphic correspond to the double support of the limbs at the moment when the first initial heal
contact happens. At this moment, the force is greater then the force of gravity because of the small contact area and
the inertial forces caused by the movement.
The valleys correspond to the double support of the limbs, with a large contact, when one foot is completely on the
ground and the other one is in toe-off position. This large contact area explains the low values of the pressure.
The flat lines between peaks and valleys indicate a single support. Because the movement is fully generated by the
other limb, the forces correspond to a static loading. In this case, the force represents the gravity force of the subject.
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Figure 6: Variation of the reaction forces during the gait
Other parameters provided by this method are presented in the figure 7. The first one, the GLL (gait line length)
parameter is the length of the line that describes the course of the pressure center, when only the individual ground
contacts of the side of the body are taken into consideration. This parameter comprises the course of the pressure
center for all the steps recorded of one by one sides of the body.
Figure 7: GGL - Gait line length diagram
Figure 8: Steps cyclogram
In the steps cyclogram (figure 8), another two parameters are drawn. The SSL-single support line is equivalent to the
average length of the lines that describe the course of the pressure center, when all the ground contacts are taken into
consideration. The A/PP (anterior/posterior position) parameter describes the shift forwards/backwards of the
intersection point of the CoP trajectory in the cyclogram, taking all the steps into consideration.
4. ELECTROMYOGRAPHIC INVESTIGATIONS USING AD INSTRUMENTS SYSTEM
In addition to the first two investigations methods, EMG analysis can be used to discern a subtle gait disorder such as
muscles or ligaments injuries. Each muscle contraction starts with the excitation of an upper motor neuron (UMN) in
the motor cortex of the brain, which travels down the spinal cord to synapse with a lower motor neuron (LMN) in the
vertebral horn of the spinal cord (figure 9) [1].
Figure 9: Muscle control: 1 Motor cortex, 2 Upper motor neuron; 3 Spinal cord; 4 Lower motor neuron; 5 Muscle
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The summation of many bioelectrical signals from all the motor units active at a given time results in electrical
activity called electromyogram. This can be picked up over the skin surface over the muscle (EMG), or by
percutaneous fine needle electrodes inserted into the muscle belly. The signal recorded by surface electrodes is very
small (less than 1mV) so, in order to analyze this, it must be amplified.
During gait, different muscle groups are actuated in a certain order to perform skeleton movement. The main muscles
groups of the lower limbs are:
- iliopsoas, gluteus maximus, and gluteus medius – for hip joint
- rectus femoris, adductor longus, vastus lateralis, vastus medialis, and biceps femoris – for knee joint
- gastrocnemius, soleus, tibialis anterior, peroneus longus – for ankle joint
In order to record and acquire an EMG signal, the ADInstruments measurement system can be used. The system is
composed by the PowerLab data acquisition system suitable for a wide range of applications; the Dual Bio
Amplifier/Stimulator dedicated to measure a wide variety of biological signals like EEG, ECG, and EMG; the EMG
electrodes and Chart 5 software.
EMG activity can be recorded using either a monopolar or bipolar recording arrangement. In monopolar recordings,
one electrode is placed directly over the muscle and a second electrode is placed at an electrically neutral site, such
as a bony prominence. Generally, monopolar signals yield lower frequency responses and less selectivity than
bipolar recordings. The monopolar recordings are frequently used during static contractions and in a variety of
clinical investigations. Monopolar recordings are appropriate for the assessment of H and T reflex and muscle M
waves, however [1], [2].
Bipolar recordings are considerably more common. In a bipolar recording arrangement, two electrodes are placed in
the muscle or on the skin overlaying the muscle and a third neural, or ground, electrode placed at an electrically
neutral site.
The amplitude and frequency spectrum of the EMG signal is affected by the location of the electrode with respect to
the innervation zone (figure 10).
Figure 10: EMG signals according to the electrode positions
Placing the electrodes at the extremity of the muscle (insertion points) the acquired signal has small amplitude. The
preferred location is in the midline of the belly of the muscle between the nearest innervation zone and the
myotendonous junction. In this location the EMG signal with the greatest amplitude is detected (figure 10).
Evaluating the muscular activities of the lower limb by electromyography some typical wave forms can be
established (figure 11).
a). Thigh muscles group
b). Leg muscles group
c). Foot muscles group
Figure 11: Typically wave forms for the lower limb muscular activity
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5. CONCLUSIONS
The human gait can be successfully evaluated using the presented methods. The three methods succeed to evaluate
the gait from three different points of view. First, the investigations using Zebris CMS-HS system leads to a
kinematical approach by analyzing the angular variation of each joint. The second investigation method consisting of
a force distribution measurement (Zebris FDM system) provides important data about the reaction forces acting at
the plantar level. The third investigation succeeds to evaluate the gait from the electrical activity point of view. This
last approach was possible using the ADInstruments electromyographic system. Combining the three methods in an
investigation of a subject, a diagnostic can be more easily established. The different approaches allow discovering of
all the gait abnormalities, helping to correct the problems in initial phase.
Methods
Kinematical analysis
Table 1: Protocol for gait analysis
Parameters
Joints angles [deg]
Double support time [sec]
Velocity [cm/sec]
Swing time [%]
Stance time [%]
Force distribution investigation
Plantar pressure [N/cm²]
Pressure center’s trajectory
Gait line length [m]
Single support line [m]
Anterior/Posterior position [m]
Electromyographic investigation
Electrical activity of the muscles
[mV]
Evaluation of the parameters
Kinematic parameters of the
investigated limb
Comparison with reference values
Identification of the possible
problems
Determination of the real plantar
pressure distribution
Detection of the influences from gait
analyze
Detection of the influences from
spine mobility
Formulation of partial conclusions
for diagnostic
Clarification of suspicions provided
by the kinematic analyze
Definition of a most probable
diagnostic based on multicriterial
analyze
REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]
KIRTLEY C.: Clinical Gait Analysis, theory and practice. Churchill Livingstone Elsevier 2006.
GORDON D.E. ROBERTSON et al., Research Methods in Biomechanics, Human Kinetics,USA,2004
FISH D J.; NIELSEN J-P.: Clinical assessment of the human gait. Journal of Prosthetic and Orthotics 1993
*Zebris CMS-HS: Operating Instructions.
*Zebris FDM: Operating Instructions.
*ADInstruments: Operating Instructions.
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