Mimicking Ankle EMG and Kinetics Of Walking While Sitting

1
Mimicking Ankle EMG and Kinetics Of Walking While
Sitting

• Master Student
• (Biomedical Engineering)
• Xiaoliang Yue
• Supervisors
• Bram Zuur
• Michael Grey

2
About This Presentation

• Introduction (Background)
• Method
• Results
• Discussion
• Conclusion

3
Introduction

• What is this project about?
• Ankle Kinetics.
• Electromyograph (EMG) .
• Transcranial Magnetic Stimulation (TMS).
• MEP Modulation and factors influencing MEP.

4
What is this project about?

• Human walking is a highly complex automated
  movement.
• The role of Motor cortex during our walking is
  still poorly understood.
• Sitting situation create a more controllable
  environment and thus reduce variability.
• Differences in cortical excitability between
  sitting and
• walking will be evaluated.

5
Ankle Angle

• Ankle angle Definition.
• Dorsiflexion and Plantar Flexion.
• 4 Phases.

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The Role of Muscles During Gait Cycle

• Dorsiflexors
• Tibialis Anterior (TA), Extensor digitorum
  longus,
• Extensor hallucis longus . They have similar
  length, but size varies
• Plantar Flexors
• Seven muscles as plantar flexors. Soleus and
  gastrocnemius are responsible for about 93 of
  plantar flexor torque.

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Ankle Function During The Gait

• Initial Contact
• Loading Response
• 1.Loading of 60 of body weight in 2 of
  gait cycle.
• 2. TA decelerates rate of plantar flexion.
• 3. TA draws body move forward.

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Ankle Function During The Gait
From planter Flexion to dorsi- flexion
Soleus Restrains the Fast rate of dorsiflexion.
Together with Body weight, Dorsiflexion
torque Reaches maximum
Soleus and Gastrocnemius act 2 times Stronger,
Lock the ankle, Decelerate dorsi- -flexion,
provide Stabitlity.
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Ankle Function During The Gait
Body weight Is transferred To the other Limb
rapidyly.
Toe off and The ankle starts Dorsiflexion.
TA functions to Make ankle dorsi- Flexion to
neutral Position.
Keep neutral Position for heel Contact.
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Electromyograph (EMG)

• Movement of muscles are controlled by the nerves.
• The nerves send electrical impulses to the
  muscles and make the muscles to contract.
• Electromyograph can measure these electrical
  discharges.
• EMG signals are very small, just a few hundred
  microvolts.

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EMG Electrodes

• Type Surface and implanted.
• Differential amplification is employed.
• Electrode placement between a motor point and
  the tendon insertion..

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Electrodes Placement
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Recording of EMG

• Amplifier Gain.
• Gain from 100 to 10,000
• Input Impedance.
• In range of Millions of Ohms
• Frequency Response.
• 10 - 1000Hz
• Processing of EMG.
• Rectification
• Linear envelope (lt10Hz, 3-6Hz, second order
  LP filter)

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LP Filter Selection

• FIR and IIR filter.
• FIR Always stable.
• IIR Lower order is needed
• IIR filters
• Chebyshev ideal LP filter response.
• Butterworth fast transition.
• Elliptic Filter fast transition.

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Transcranial Magnetic Stimulation (TMS)

• TMS and TES.
• Coils Large/Small.
• Double Circular Coils.

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TMS and MEP

• TMS evokes MEP in contra lateral muscles.
• Parameters
• Threshold
• Amplitude
• Latency

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TMS Response Modulation during Walking
(M.Schubert 97)
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TMS NET Response Modulation during Walking
(M.Schubert 97)
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Factors Influencing MEP
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Method

• EMG Recording.
• Training on MTS machine.
• TMS investigation.

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EMG And Ankle Angle Recording

• EMG from TA and Soleus, ankle angle.
• Speed 2.3-3.2Km/h.
• Recording was triggered by right heel contact.
• EMG was sampled at 3000Hz, ankle angle was at
  1000Hz
• EMG was LP filtered(5-1000Hz), rectified and LP
  filtered at 6Hz.

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Training Design

• Reproduce ankle angle movement.
• Training on MTS.
• To match muscle control during walking.
• Feedback is applied.

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Experiment Setup
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Feedback Selection

• Force
• 1. Easy recording.
• 2. Body weight problem.
• EMG
• 1. Direct reflection of muscle activity.
• 2. Signal Processing is needed.

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EMG Feedback
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Recording Synchronization
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TMS Experiment

• Subject head was fixed while sitting in a chair,
  his knee ankle was kept around 120 degree.
• Subject right foot was placed on the MTS pedal
  and Ankle at its neutral position.
• Optimal TMS coil position was found, intensity at
  69(0.828T).
• Safety check up before fully attach subjects
  foot to MTS pedal.
• Recording started at the same time MTS started to
  move. TMS was triggered with the reference to the
  start time of each movement.
• Stimulation was applied at 100ms, 200ms..For
  each time point, 15 stimuli were delivered in a
  random way.
• 50 sweeps are recorded without TMS.

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Control Recording

• To eliminate influence from muscle activities on
  the MEP.
• Control experiments were carried out right after
  TMS recording with same experiment setup.
• Subjects were asked to do tonic contraction.
• 15 stimuli were applied for each EMG level.
• MEP from different level EMG were recorded.

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Data Analysis

• MEP was obtained by averaging all 15 sweeps at
  each stimulation time point.
• MEP was cut from 100ms before stimulation time to
  100ms after.
• MEP amplitude was calculated by peak-peak value.
• Background EMG level in control experiment was
  measured using root mean square.

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Results

• Training Performance.
• MEP modulation.
• Tonic contraction MEP and EMG level.
• Net effect on MEP facilitation.

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Training Performance

• Only soleus was examined.
• Results from 50 sweeps without MEP.
• Results from both subjects.

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MEP Modulation

• MEP was normalized.
• EMG was normalized.
• MEP in different phases of mimicked walking is
  shown.
• Significant modulation presents.
• Some points are different.

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Tonic Contraction MEP
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Net Effect on MEP Facilitation

• Walking MEP/Tonic MEP 100.
• Only a rough modulation exists in subject 1.
• Most of points are below 100.
• Points exceed 100 happen in the earlier phase in
  both cases.

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Discussion(1)

• Recording on left, MTS on right leg.
• The walking speed, one gait around 1.5sec is good
  on MTS.
• EMG Recording and Training were done separately
  (electrodes position problem).
• Only soleus was applied in this project.
• Training in this project should be too short to
  change cortical excitability.
• TMS intensity was constant for all.
• TMS pulse delivery time can be changed for better
  comparison between subjects.
• A better coil placement system could be better.

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Discussion(2)

• MEP Modulation exists in mimicked walking as
  reported in real walking (Schubert).
• NET MEP is below 100, similar to the study by
  Capaday on real walking.
• Cortical interests in TA more than soleus.
• H- reflex experiment is needed to study the exact
  cortical excitability.

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Conclusion

• Easily reproduce soleus activity in walking.
• Phase dependent modulation exists as happen in
  real walking.
• Linear relationship between Tonic Contraction and
  MEP.
• Soleus MEP in mimicked walking is smaller than
  tonic contraction.
• More experiments are needed (including on TA).

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Thank You
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Mimicking Ankle EMG and Kinetics Of Walking While
Sitting

• Master Student
• (Biomedical Engineering)
• Xiaoliang Yue
• Supervisors
• Bram Zuur
• Michael Grey