Laboratory for Engineering of the Neuromuscular

System (LISiN), Politecnico di Torino, Italy

Taian Vieira, Ph.D. taian.vieira@polito.it

In che modo le griglie bidimensionali di elettrodi ci aiutano nell’interpretazione del

segnale EMG di superficie?

Nuove evidenze per l'acquisizione ed interpretazione del segnale EMG: dal bipolare al multicanale e ritorno

Centro Congressi Torino Incontra, Torino. Mercoledì 4 Ottobre 2017

Presentation outline

• From bipolar to high-density surface electromyograms (EMGs)

• How 2D grids of electrodes may help us with the unambiguous interpretation of surface EMGs

• Examples of applications exclusively focused on the use of 2D grids of electrodes

Time

+ -

0

100Temporal representation of surface action potentials:a single active motor unit

10 pps

Voltage

Skin

Fat

Muscle

Time

+ -

0

100

Voltage Temporal representation of surface action potentials:two active motor units

Skin

Fat

Muscle

motoneuron

(axon)

Tendon

Tendon

End-plate

Motor unit (MU)

Innervation Zone

(phase inversion)

Tendon location

(extinction of potential)

Waveform of motor unit action potentials (depend on the number of fibres, the jitter of end-plates, the depth of motor unit

territory and the conduction velocity, among other factors)

Conduction velocity (indicated by the “V” pattern)

Anatomical and physiological information provided by high-density electromyograms

Tendon location

(extinction of potential)

Different units are observed in different regions across gastrocnemius

4 6

3

6

200 μ

V

5

0

5

10

Po

sitio

n (

mm

)

Ro

ws

CoPCoG

forward

Columns

Medial

gastrocnemius

Lateral

gastrocnemius

Merletti et al 2010 (Crit Rev Biomed Eng 38:347-79)

0.5 s

10 s

+–

+–

Ankle

100 µ

V

1.4 1.8 2.2 2.6 3.0 3.4 3.8 4.2 4.6Time (s)

Grids of electrodes provide a representative

estimation of the timing of gastrocnemius activity

EMG detected proximally

RMS amplitude greater than the background, rest level

EMG detected distally

Dos Anjos et al 2017 (Front Hum Neurosci 11:190)

ACTIVENOT

ACTIVE ACTIVE

1.4 1.8 2.2 2.6 3.0 3.4 3.8 4.2 4.6Time (s)

Global, representative estimation of periods of activity

Fat tissue

Skin5 ms

A.U.

Pennation angle = 0°

Muscle unit parallel to

surface electrodes

Pennation angle = 20°

5 ms

A.U.

Mesin et al. – J Biomech 2011

Muscle unit pennate in

the depth direction

d

The spatial distribution of surface EMGs is

associated with the territory of motor units.

Tibial nerve

+

–

Skin

Fat tissueArray of electrodes

Muscle fibre

Motor unit with small territory Motor unit with large territory

Ankle+

–

Vieira et al 2011(J Physiol 589:431-43)

Topography of active fibres in the medial gastrocnemius muscle

Matrix of electrodes(1 cm IED)

8th stim. level (14-16 mA)

1 2 3 4 5 6 7

Columns of single differential, incremental M-waves

3.3

mV

10

20

30

40

50

AR

V a

mp

litu

de

(µV

)

Ro

ws

(cm

)

7th stim. level (12-14 mA)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

1 2 3 4 5 6 7

Stimulation electrode

US probe

Vieira et al 2015 (J Neurophysiol 114:1617-27)

Is it then not possible to detect propagating potentials from medial gastrocnemius?

20 ms

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Row

s o

f channels

(in

ter-

ele

ctr

ode d

ista

nce =

1 c

m)

Medial

Prints of

electrodes

on the skin

Rows

Columns

Raw surface EMGs

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

Insta

nta

ne

ou

s E

MG

am

plit

ud

e (

mV

)A

nkle

EMG ImageGallina et al 2013

(J Electromyogr Kinesiol 23:319-25)

Why can we observe propagating potentials onlyfor electrodes positioned at the more distal regions?

0.5

mV

0.3

mV

5 ms

20 ms

Knee

Medial

Gastrocnemius

Array of surface

electrodes

Electrodes

located over

the end of

different

muscle

fibres

Electrodes

running over

the same

group of

muscle

fibres+

–

+

–

gastrocnemius

fascicles

Fat tissueskin

Surface

electrodes

An

kle

Localised, atypical

motor unit action

potential (MUAP)

MUAP with typical

features of skin parallel-

fibered muscles

Hodson-Tole et al. 2013 (J Electromyogr Kinesiol 23(1):43-50)

Why is propagation appreciated only from top to bottom? Is it really unidirectional?And from bottom to top?

Propagation is not unidirectional.Potentials propagate in oblique direction

Muscle fascicles

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

Insta

nta

ne

ous E

MG

am

plit

ude

(m

V)

EMG ImageElectrodes’ and

muscle fibres'

location

Raw, surface EMGs

Gallina and Vieira 2015 (Muscle Nerve 52:1057-65)

Local representation of activity in different skeletal

muscles has been observed by different researchers and with

different technologies.

Kinugasa et al – J Appl Physiol 2005;

McLean and Goudy – Eur J Appl Physiol 2004;

Tamaki et al – J Appl Physiol 1998;

Segal and Song – Arch Phys Med Rehabil 2005;

Staudenmann et al – J Electromyogr Kinesiol 2009;

Watanabe et al – J Biomech 2016;

Wolf et al – J Electromyogr Kinesiol 1998;

Revisiting muscle function

from an electrophysiological

perspective

Some examples on the

application of 2D surface

electromyography

1 cm

1 cm

Pro

xim

al Lateral

16

ro

ws

8 columns

Patella

Vastusmedialis fibres

Axonal branch supplying proximal

fibres

20 msSubject 14, motor unit 80.2 mV

26 mV

Patella

Ro

ot

mea

n s

qu

are

amp

litu

de

of

mo

tor

un

it a

ctio

n p

ote

nti

als

Interpretation of surface EMGs demands prior knowledge on the architecture of specific muscles

and motor unit 10

52°

52°

51°

47°

48°

54°

65°

53°

74°73°

10mm

20 30 40 50 60 70

0

5

10

15

20

25

Fiber orientation (FO)

80

Median: 47°

10-90th perc.:

32° - 56°

Occurr

ences

Angle

(deg)

N = 77 MUs

10 15 20 25 30

0

4

8

12

16Estimated territory size (σ)

Median: 20 mm

10-90th perc.:

14 – 25 mm

Occurr

ences

Sigma

(mm)

N = 77 MUs

MUs have relatively small territories and a

range of fibres’ inclinationsGallina and Vieira 2015 (Muscle

Nerve 52:1057-65)

Propagation of action

potentials in oblique

direction is typically

observed for pinnate

muscles

What is so especial about the

pinnate, vastus medialis

muscles?

Intramuscular differences in fiber orientation

can be observed in vastus medialis

(Smith et al., 2009)

Proximal fibers: Knee extension

Distal fibers: Patellar tracking

(Lin et al., 2004)

VastusLateralis

RectusFemoris

VastusMedialis

Sartorius

Patella

Regionalised, rectus femoris function

during gait Watanabe et al 2014 (J Biomech 47:3502-8)

Myoelectric manifestation

of fatigue

Some examples on the

application of 2D surface

electromyography

Acromion

C7

Rotation of motor units delays

fatigue

Lateral

Cra

nia

l

0% 25% 28075% 100%50%

10

Columns of channels (8 mm IED)

1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5

1

2

3

4

5

6

7

8

9

10

11

12Ro

ws o

f ch

an

ne

ls (

8 m

m I

ED

)

RM

S a

mplit

ude (

uV

)

RMS images for different endurance times

Farina et al 2008 (J Electromyogr Kinesiol 18:16-25)

1 - WRIST SUPPORT

2 - FOREARM SUPPORT

3 - NO SUPPORT

MOUSE USING (30 seconds, mean ARV maps):

1

2

Max =6 μv

Max =2 μv

Max =9 μv

Max =34 μv

Max =9 μv

0 μV

10 μV

20 μV

30 μV3

1

2

3

4 cm

Max =33 μv

10.4 cm

LEFT RIGHT

LISi

N, T

ori

no

Do sweep

rowers activate

their back

muscles

asymmetrically?

Asymmetrical activation of

back muscles might lead

to back painParkin et al. 2010 J Sports Sci

Boat rotates to

the right side

Asymmetrical activation seems crucial for boat

stabilisation

Even in a laterally stable condition, 2D EMGs reveal side differences in the activation of back Readi et al 2015 (Scand J Med Sci Sports 25:e339-52)

Distinguishing the activity of

deep and superficial muscles

Some examples on the

application of 2D surface

electromyography

Is it possible to distinguish the activity of internal (IO) and external (EO)

oblique muscles?Ultrasound images taken during:

Rest Contraction

Transverse

abdominis

Internal

Oblique

External

Oblique

1 c

m Muscle

thickness

Brown and McGill (2010) Clin Biomech

Medial

12

11

10

9

8

7

6 5

Rectus

sheat

External

oblique

muscle(superficial)

Ilium

Internal

oblique

muscle(deep)

12

11

10

9

8

7

Ilium

Grid of 64

surface

electrodes(8 mm IED)

With a grid of electrodes we tested if,from propagation direction, internal and external oblique

activity may be distinguished in the surface EMGs

Contralateral

trunk rotation

Ipsilateral

trunk rotation

Our hypothesis

The amplitude of surface EMGs distributed along different directions during ipsilateral and

contralateral trunk rotations

1 2 3 4

1

2

3

4

5

6

7

8

9

10

11

12

Ro

ws o

f sin

gle

-diffe

ren

tia

lE

MG

s (

8 m

m I

ED

)

Columns (8 mm IED)Columns (8 mm IED)

1 2 3 4

1

2

3

4

5

6

7

8

9

10

11

12

Ro

ws o

f sin

gle

-diffe

ren

tia

lE

MG

s (

8 m

m I

ED

)

During ipsilateral trunk rotation, we could identify action potentials propagating towards the bottom-left corner

8 mm

Grid of 64 surface

electrodes(13 x 5 arrangement)

Active, IO

fibres

Missing electrode

Innervation zone

Action

potential

Instantaneous, interpolated

(4x) EMG image

During contralateral trunk rotation, we could identify action potentials propagating towards the bottom-right corner Instantaneous, interpolated

(4x) EMG image

8 mm

Missing electrode

Grid of 64 surface

electrodes(13 x 5 arrangement)

Innervation zone

Action

potential

Active, EO

fibres

Administration of botulinum toxin

Some examples on the

application of 2D surface

electromyography

Surface EMGs help in guiding the injection of the botulinum toxin Lapatki et al 2011 (Clin Neurophysiol 122:1611-6)

Myoelectriccontrol of prosthesis

Some examples on the

application of 2D surface

electromyography

Co-contractionNo action or lock

Hand Close

Ha

nd

Op

en

Off

FLEXOR ACTIVITY

EXTE

NSO

R A

CTI

VIT

Y

S1

S2

Two channels control of a hand prosthesis(near wrist amputation)

Wrist Extension

Wrist Extension

FingersExtension

ThumbExtension

What if EMGs from the forearm muscles could be collected with a grid of electrodes?

Bipolar detection (one or more pairs of electrodes):

- Timing of activity

- Amplitude

- Frequency

Carefully placed

Global information

Affected by crosstalk?Representative EMGs?

Linear array (transversal):

- Location of active muscle regions

Summary of the lecture: detecting surface EMGs

2D grid of electrodes:

- Surface EMG decomposition

- Muscle fiber orientation

- Regional activation indistincly for any muscle

Linear array (longitudinal):

- Innervation zone location

- Tendon location

- Conduction velocity

Skin-parellel-fibered muscle

- Location of active regions in pinnate muscles

Taian Vieira, T. Lemos, L. Oliveira, C. Horsczaruk, F. Tovar-Moll, E. Rodrigues

Motor unit plasticity in stroke survivors: altered distribution of gastrocnemius’

action potentials

taian.vieira@polito.it

Sessione 3 – Postura ed equilibrio – O.17 (05/10/17 18.11–18:23)

Laboratorio di Ingegneria del Sistema Neuromuscolare (LISiN),

Politecnico di Torino, Torino, Italia