Development of EMG Indicators for Measuring and Analyzing

Pre-motor Activity on Muscles

Yosra Saidane

, Soﬁa Ben Jebara

, Tarak Driss

and Giovanni de Marco

COSIM Lab, Higher School of Communications of Tunis, University of Carthage

Route de Raoued KM 3.5, Cite El Ghazala Ariana 2083, Tunisia

UFR STAPS,Universit

e Paris Ouest de Nanterre La Defense,

200 Avenue de la R

epublique, 92001 Nanterre cedex, France

Keywords:

EMG Signal, Pre-motor activity, Movement preparation, Preparation’s duration, Behavior difference by

gender, by muscle.

Abstract:

In sport, it is well known that mental preparation to a physical effort increases drastically the performance.

In this paper, we present a study that aims to evaluate the effect of movement preparation during pre-motor

activity on the EMG signal. We considered the existence/no-existence of preparation and preparation duration

as indicators. The results of this study performed on different muscles of the forearm show: i) female are sen-

sitive to preparation warning whereas male are not sensitive, ii) contrary to deep muscles, superﬁcial muscles

are affected by preparation warning.

1 INTRODUCTION

ElectroMyoGraphy (EMG) is an electro diagnostic

technique used to evaluate and record electrical

activity produced by skeletal muscles (Gordon et al.,

2004).

For voluntary motions, all muscle contractions

(excluding reﬂexes) occur as a result of conscious

effort originating in the brain. In fact, the brain sends

signals, in the form of action potentials, through the

nervous system to the motor neuron that innervates

several muscle ﬁbers (Cacioppo et al., 2007).

The major studies in literature focused on the

study of the muscle activity during exercise. Most

studies considered the latency time (or refractory

time) which is the rest time preceding the muscle

activity. It is a short period during which the nervous

system is not excitable and can not respond to

stimulation or excitation.

At our knowledge, few studies discuss the mental

(psychological) stage before the motor task which

concerns the pre-motor period. It is deﬁned as the

small muscle activity (if it exists) which happens

between a warning signal motivating preparation and

initiating motion (anticipatory postural adjustment)

and the ”go” signal for motion execution.

Pre-motor activity represents the muscular activ-

ity during mental or psychological preparation. In

sport domain, researchers have begun to study the

effect of speciﬁc mental preparation on motor perfor-

mance. Some of the most popular techniques include

imagery, self efﬁcacy statements, attentional focus,

preparatory arousal, and relaxation (Weinberg, 1981).

Numerous studies have provided experimental,

correlational and anecdotal evidence that patterns of

thought can inﬂuence athletic performance (Corbin,

1967), (Richardson, 1967), (Shelton and Mahoney,

1978).

In this paper, we present a study that evaluates the

effect of movement preparation on EMG signals of

the forearm muscles during pre-motor activity. More

precisely, we will answer the following questions:

does movement preparation leads to effective prepa-

ration which appears as small contraction during

pre-motor activity? In case where no preparation

warning (instruction) is given, is there any sponta-

neous muscle preparation? If a cognitive preparatory

period exists, how long it activates the muscle and

what difference do we have in absence or presence

of attentional focus? Is it possible to discriminate

between both trials (absence or presence of attention)

using only preparation time as descriptor?

This paper is organized as follows: in the ﬁrst

part, we will identify and analyze the preparation

duration in all trials. In the second part, we will

describe the different indicators involved in the

preparation. Finally, we will discriminate between

the presence or absence of a preparation duration

Saidane, Y., Jebara, S., Driss, T. and Marco, G..

Development of EMG Indicators for Measuring and Analyzing Pre-motor Activity on Muscles.

In Proceedings of the 3rd International Congress on Sport Sciences Research and Technology Support (icSPORTS 2015), pages 41-47

ISBN: 978-989-758-159-5

using an analysis of variance statistical method.

2 EXPERIMENTAL PARADIGM

Surface EMG activity was recorded using bipolar sur-

face electrodes equipped with a preampliﬁer with an

inter-electrode distance of 25 mm (BIOPAC systems,

Aero Camino, Goleta, USA). Electrodes were ﬁxed

onto the skin over the muscle with Elastoplast bands.

Because no SENIAM guidelines are available for

these muscles, the electrodes were positioned during

a muscle contraction (Basmajian, 1979). EMG activ-

ity was recorded using Acknowledge data hardware

(Model MP100A; BIOPAC Systems, USA). EMG

signals were ampliﬁed, and sampled at a frequency of

10 kHz. A ground electrode was placed on the sub-

jects wrist during measurements.

10 males and 10 females volunteers have participated

in this study. Each volunteer realized maximal iso-

metric contractions of ﬁnger ﬂexors during a ”hand

grip” exercise. Two trials were carried. The ﬁrst one

needs attentional focus and the other one does not re-

quire attentional focus. All volunteers realized 5 con-

tractions for each trial.

In the ﬁrst trial, the EMG signal has three differ-

ent periods: a pre-motor activity in which the volun-

teer has to prepare mentally and carefully the activity

during 6.6 seconds until a hearing statement (bip) is

given to ask him to begin contraction. Then a motor

activity begins and lasts 4.4 seconds which is the ef-

fective contraction phase. Finally a rest period of 44

seconds ends the experiment.

In the second trial, the volunteer don’t have prepa-

ration warning, he executes the movement when he

wants during 4.4 seconds and the same rest period of

44 seconds follows.

In this study, we are interested only in he ﬁrst pe-

riod which is the pre-motor activity. The label of the

ﬁrst (resp. second) trial is ”With” (resp. ”Without”)

preparation warning. The studied muscles are: the

Flexor Digitorum Profundus (FDP), the Flexor Digi-

torum Superﬁcialis (FDS), the First Radial (FR) and

the Common Extensor Digitorum (CED).

Note that the Flexor Digitorum Profundus activity can

be measured by surface EMG (Bøg et al., 2011). Us-

ing temporal analysis, two indicators were selected:

the number and the duration of preparation.The goal

is to differentiate the two trials with these indicators.

3 STUDY OF NUMBER OF

PREPARATION

3.1 Subject Behavior to Preparation

In this section, the goal is to know if each volunteer

prepares its contraction during the time interval which

is called the pre-motor time.

Using the data presented in the experimental

paradigm section, Fig.1 shows the number of pre-

pared contractions for each subject. The dashed (resp.

solid) line concerns the trial ”with” (resp. without”)

preparation warning. The results of Fig 1.a (resp. Fig

1.e) corresponds to male FDP (resp. female). Fig 1.b

(resp. Fig 1.f) represents the data of male FDS (resp.

female ). The results of Fig 1.c (resp. Fig 1.g) are

addressed to male FR (resp. female). Finally, the Fig

1.d (resp. Fig1.h) gives the number of preparation of

male CED s(resp. female).

Note that all volunteers prepare muscle activity

even when no preparation warning is given. How-

ever, the number of prepared contractions is not al-

ways the same. When comparing the muscles, we can

note that, in the case of males, the number of prepa-

ration is important for the ﬂexor digitorum profundus

muscle (Fig 1.a) and for the ﬂexor digitorum super-

ﬁcialis muscle (Fig 1.b). In fact, 5 volunteers of 10

have a complete preparation (5 for both trials) during

contractions. The number of preparation decreases in

common extensor digitorum muscle to 3 preparations

(Fig 1.c). Hence, we can conclude that males have

an important number of preparation in ﬂexor muscles

than in extensor muscles (Fig 1.a,b,c,d).

In the case of female volunteers, the number of prepa-

ration is more important in extensor muscles (Fig

1.g,h) than in ﬂexor muscles (Fig 1.e,f). In fact,we

show one complete preparation in (Fig 1.f) but in (Fig

1.h), there is three complete preparations.

3.2 Analysis of the Number of Effective

Preparation

The objective of this section is to analyze the number

of effective preparation. To do it, this number is

used as input data. A simple statistical analysis using

the mean, the median and the standard deviation of

the number of preparation is carried and given in

Tab.1 in case of ﬁrst radial muscle. We show that

male volunteers are characterized by an important

median and mean values of preparation number in

the case of ”without preparation”. But, the results are

opposite in case of female volunteers: the number

of preparation is slightly higher in case of ”with

icSPORTS 2015 - International Congress on Sport Sciences Research and Technology Support

1 2 3 4 5 6 7 8 9 10

Number of subjects

Number of preparation

With preparation warning

Without preparation warning

1 2 3 4 5 6 7 8 9 10

Number of subjects

Number of preparation

With preparation warning

Without preparation warning

(a) (b)

1 2 3 4 5 6 7 8 9 10

Number of subjects

Number of preparation

With preparation warning

Without preparation warning

1 2 3 4 5 6 7 8 9 10

Number of subjects

Number of preparation

With preparation warning

Without preparation warning

1 2 3 4 5 6 7 8 9 10

Number of subjects

Number of preparation

With preparation warning

Without preparation warning

1 2 3 4 5 6 7 8 9 10

Number of subjects

Number of preparation

With preparation warning

Without preparation warning

(e) (f)

1 2 3 4 5 6 7 8 9 10

Number of subjects

Number of preparation

With preparation warning

Without preparation warning

1 2 3 4 5 6 7 8 9 10

Number of subjects

Number of preparation

With preparation warning

Without preparation warning

(g) (h)

Figure 1: Number of preparation for each subject. (a): male FDP, (b): male FDS, (c): male FR, (d): male CED, (e): female

FDP, (f): female FDS, (g): female FR, (h): female CED.

Development of EMG Indicators for Measuring and Analyzing Pre-motor Activity on Muscles

preparation warning” trial.

Table 1: Simple statistic values of number of preparation on

ﬁrst radial muscle.

Mean Median Standard

deviation

Males With 3.8 4 1.55

Without 4 5 1.5

Females With 3.4 3 1.5

Without 3.1 3 1.96

Tab.2 represents the number of preparation per-

centage in both trials, for both genders and for each

muscle separately.

For male volunteers, the percentage of number of

preparation is important when no preparation warn-

ing is given. We observe this result in three muscles

(FDP, FDS, CED) except the ﬁrst radial (FR) in case

of 5 preparations.

The sum of percentage of number of preparation is

equal to 80% for 3,4 and 5 contractions together.

This result is valid for all muscles except the com-

mon extensor digitorum muscle who had an impor-

tant percentage (100%) when no preparation warning

is given.

The results are opposite in the case of female vol-

unteers. We observed that the sum of percentage of

number of preparation are more important in case of

”with preparation warning” than in case of ”without

preparation warning” for 3,4 and 5 contractions to-

gether. We show this result in the three ﬁrst mus-

cles: CED, FDS, FR. The ﬁrst radial (FR) muscle had

90% (resp. 70%) preparations in case of ”with” (resp.

”without”) preparation, in FDS and CED .

However, for ﬂexor digitorum profundus muscle, the

percentage is equal to 70% between both trials. Ac-

cording to Tab. 2, we noticed that males prepare more

than females in both trials.

4 THE EFFECT OF

PREPARATION’S DURATION

4.1 Duration by Subject

This section aims to observe the dispersion of prepa-

ration’s duration in the both trials.

Fig.2 shows the duration of preparation for each

male and female volunteers of ﬁrst radial muscle. For

clarity reasons, symbols are discarded in the ﬁgure

from the central values. The triangle (resp. circle)

symbol represents ”With” (resp. ”Without”) prepara-

1 2 3 4 5 6 7 8 9 10

1000

2000

3000

4000

5000

6000

7000

8000

Number of subjects

Preparations duration (ms)

With preparation warning

Without preparation warning

(a)

1 2 3 4 5 6 7 8 9 10

1000

2000

3000

4000

5000

6000

7000

8000

Number of subjects

Preparations duration (ms)

With preparation warning

Without preparation warning

(b)

Figure 2: Preparation’s duration of ﬁrst radial muscle.(a):

male volunteers,(b): female volunteers.

(a)

(b)

Figure 3: Mean preparation

s duration of ﬁrst radial muscle.

(a): male volunteers, (b): female volunteers.

icSPORTS 2015 - International Congress on Sport Sciences Research and Technology Support

Table 2: Number of preparation percentage in both trials: with and without preparation warning.

Male volunteers Female volunteers

Number of preparations(%) 5 4 3 2 1 0 5 4 3 2 1 0

FDP With 50 20 10 0 10 10 20 50 0 10 20 0

Without 60 20 0 10 0 10 30 30 10 20 10 0

FDS With 70 10 0 10 0 10 20 30 40 10 0 0

Without 60 10 10 20 0 0 40 20 20 0 20 0

FR With 40 10 30 20 0 0 30 10 50 0 0 10

Without 70 0 10 10 10 0 40 0 30 10 0 20

CED With 40 30 10 0 20 0 50 30 10 10 0 0

Without 60 0 40 0 0 0 60 10 10 10 0 10

tion warning. These two genders have different val-

ues of preparation’s duration and don’t obey to any

obvious rules. Note that the range of all durations is

between 0 and 6600 milliseconds (we recall that the

duration of theoretical preparation is 6600 millisec-

onds).

Fig.3 illustrates the mean preparation’s duration

for each trial and for every volunteer. Fig 3.a (resp.

Fig 3.b) represents males (resp. female) volunteers.

The mean preparation’s duration is higher in case of

”with preparation warning” trial for 7 males and 9 fe-

males. Hence, we can conclude that volunteers pre-

pare longer their contraction when a warning signal is

given.

4.2 Boxplots of Preparation’s Duration

In statistic analysis, the boxplots is a useful tool for

studying large sets of data. It can provide informa-

tion about data range, median, normality and skew of

distribution. In this case, we deal with the distribu-

tion of preparation’s duration for the two trials for all

muscles.

In Fig. 4, we draw the preparation’s duration boxplots

for both gender when all muscles data are combined

together. We can see that the dispersion is large when

a preparation warning is given. For example, in Fig

4.a, the median duration value (line into rectangle) of

pre-motor activity is important in ”with preparation

warning” (3.83 s) than ”without preparation warning”

mode (1.987 s).

Fig.5 represents the preparation’s duration for each

muscle for male and female volunteers separately.

The results shows that the median duration value is

higher in ”with preparation warning” trial than in

”without preparation warning” trial except the Fig5.a

and Fig5.d who show that the median value is slightly

higher when no preparation warning is given.

5 STATISTIC ANALYSIS: ONE

WAY ANOVA TEST

In statistics, ANalysis Of VAriance (ANOVA)(Nuzzo,

2014) is a collection of statistical models used in or-

der to analyze the differences between group means

and their associated procedures (such as ”variation”

among and between groups). Anova test was used

to compare the preparation’s duration and try to sepa-

rate the two trials with signiﬁcance level equal to 5%.

Tab.3 gives the results of discrimination between

two trials. The symbol (6= ) (resp. (=)) means there is

a (resp. no) signiﬁcant difference between two trials.

Table 3: Difference inter-muscular between with and with-

out preparation warning.

Males Females Both gender

All muscles = 6= 6=

FDP = = =

FDS = 6= 6=

FR = 6= 6=

EDC = 6= =

5.1 Difference between ”With

preparation warning” and ”Without

preparation warning” on Muscles

The results of Tab.3 show that there is a signiﬁ-

cant difference between with and without preparation

warning for both genders and for all muscles con-

sidered together(T=14.48,p-value=0.0001). So, the

preparation warning has an inﬂuence on the pre-motor

activity.

Development of EMG Indicators for Measuring and Analyzing Pre-motor Activity on Muscles

With Without

2000

4000

6000

8000

Preparations duration (ms)

With Without

2000

4000

6000

8000

Preparations duration (ms)

With Without

2000

4000

6000

8000

Preparations duration (ms)

(a) (b) (c)

Figure 4: Boxplots of preparation’s duration for forearm muscles. (a):both gender, (b):male volunteers, (c):female volunteers.

With Without

2000

4000

6000

8000

Preparation’s duration (ms)

With Without

2000

4000

6000

8000

Preparation’s duration (ms)

With Without

2000

4000

6000

8000

Preparation’s duration (ms)

With Without

2000

4000

6000

8000

Preparation’s duration (ms)

(a) (b) (c) (d)

With Without

1 000

2 000

3 000

4 000

5 000

6 000

7 000

8 000

Preparation’s duration (ms)

With Without

2000

4000

6000

8000

Preparation’s duration (ms)

With Without

2000

4000

6000

8000

Preparation’s duration (ms)

With Without

2000

4000

6000

8000

Preparation’s duration (ms)

(e) (f) (g) (h)

Figure 5: Boxplots of preparation

s duration for forearm muscles. (a): male FDP, (b): male FDS, (c): male FR, (d): male EDC

(e): female FDM, (f): female FDS, (g): female FR, (h): female EDC.

5.2 Gender Difference in Pre-motor

Activity

Tab.3 shows that preparation’s duration differs by

gender. In fact, there is no difference between with-

out and with preparation warning for males (T=1.71,

p-value=0.1922) but there is a signiﬁcant difference

in females (T=16.32, p-value=0.00005) for all mus-

cles. These results conﬁrm the brain behavior. In fact,

in some previous studies such as (Ingalhalikar et al.,

2014), it was shown that the brain behavior is differ-

ent for each gender: the females outperform males

on attention, word and face memory, and social cog-

nition tests and males perform better on spatial pro-

cessing and motor and sensorimotor speed. In this

case and specially in ”with preparation warning” ,vol-

unteers must be attentional and concentrate. Female

were able to do it. However, male volunteers weren’t

sensitive to preparation warning.

5.3 Inter-muscular Difference in

Pre-motor Activity

When we separate the muscles, the results of Tab.3

show that there is no difference between with and

without preparation warning in pre-motor activity for

males (p-value ≥ 0.134). For females, we found

a signiﬁcant difference in Flexor Digitorum Super-

ﬁcialis, First Radial , Extensor Digitorum Commu-

nis muscles (T ≥ 4.72, p-value ≤ 0.032) but no dif-

ference in Flexor Digitorum Profundus (T=2.29, p-

value=0.1302).

The muscles are classiﬁed into two families: the

superﬁcial muscles and deep muscles. The superﬁ-

cial (resp. deep) muscles are Flexor Digitorum Su-

perﬁcialis, First Radial and Extensor Digitorum Com-

munis (resp. Flexor Digitorum Profundus). Due to

the anatomical and biomechanical differentiation of

the superﬁcial and deep muscle ﬁbers, a difference

in ﬁber type distribution can be hypothesized: it is

assumed that the deep muscle ﬁber has a higher por-

tion of type I ﬁbers compared to the superﬁcial mus-

cle ﬁber (MacDonald et al., 2006). Fibers of type I are

slow twitch ﬁbers, which are fatigue resistant and ide-

ally suited to provide low load tonic activity. Type II

ﬁbers, are fast twitch ﬁbers, are less fatigue resistant,

but able to produce a higher load activity(Henneman

et al., 1965).

During the pre-motor activity, the preparation was

done only for superﬁcial muscles.

icSPORTS 2015 - International Congress on Sport Sciences Research and Technology Support

6 CONCLUSION

In this work, we found two indicators that character-

ize the pre-motor activity. The ﬁrst one is the number

of preparation. It was shown to be important even

when no preparation warning is given.

The second indicator is preparation’s duration. It was

shown a signiﬁcant difference between ”with” and

”without” preparation modes for female in superﬁcial

muscles of the forearm. However, no difference of

behavior are observed between the two modes for

male.

Studying the motor behavior during the transition

between the pre-motor activity and the effective

motor activity and studying the brain activity using

fMRI will be the topic of further research.

REFERENCES

Basmajian, J. V. (1979). Biofeedback: Principles and prac-

tice for clinicians. Williams & Wilkins.

Bøg, M. F., Erkocevic, E., Niemeier, M. J., Mathiesen, J. R.,

Smidstrup, A., and Kamavuako, E. N. (2011). In-

vestigation of the linear relationship between grasp-

ing force and features of intramuscular emg. In 15th

Nordic-Baltic Conference on Biomedical Engineering

and Medical Physics (NBC 2011), pages 121–124.

Springer.

Cacioppo, J. T., Tassinary, L. G., and Berntson, G. (2007).

Handbook of psychophysiology. Cambridge Univer-

sity Press.

Corbin, C. B. (1967). Effects of mental practice on skill de-

velopment after controlled practice. Research Quar-

terly. American Association for Health, Physical Edu-

cation and Recreation, 38(4):534–538.

Gordon, R., Graham, C., and Joseph, H. (2004). Research

Methods in Biomechanics. Human Kinetics.

Henneman, E., Olson, and B., C. (1965). Relations between

structure and function in the design of skeletal mus-

cles. Journal of Neurophysiology, 28(3):581–598.

Ingalhalikar, M., Smith, A., Parker, D., et al. (2014). Sex

differences in the structural connectome of the human

brain. Proceedings of the National Academy of Sci-

ences, 111(2):823–828.

MacDonald, D. A., Moseley, Lorimer, G., H., and W., P.

(2006). The lumbar multiﬁdus: does the evidence sup-

port clinical beliefs. Manual therapy, 11(4):254–263.

Nuzzo, R. (2014). Scientiﬁc method: Statistical errors. nat,

506:150–152.

Richardson, A. (1967). Mental practice: a review and dis-

cussion part i. Research Quarterly. American Associ-

ation for Health, Physical Education and Recreation,

38(1):95–107.

Shelton, T. O. and Mahoney, M. J. (1978). The content

and effect of psyching-up strategies in weight lifters.

Cognitive Therapy and Research, 2(3):275–284.

Weinberg, R. S. (1981). The relationship between mental

preparation strategies and motor performance: A re-

view and critique. Quest, 33(2):195–213.

Development of EMG Indicators for Measuring and Analyzing Pre-motor Activity on Muscles