Assessment of Muscle Fatigue, Strength andMuscle Activation During Exercises with theUsage of Robot Luna EMG, Among Patients with
Multiple Sclerosis
Krystyna Stańczyk1 , Anna Poświata2 , Anna Roksela2 , and Michał Mikulski2
1

Neurological Rehabilitation Ward, Medical University of Silesia, Katowice, Poland,
2
EGZOTech Sp. z o.o., Gliwice, Poland,stanczykkrystyna@op.pl, anna@poswiata.com, anna.roksela@egzotech.com,
michael.mikulski@egzotech.com

Abstract. Objective measurement of fatigability in patients with neurological diseases remains a problem rarely described in the research.
The quick and easy assessment of muscle fatigue among patients withmultiple sclerosis (MS) is a needed tool, which could be implemented
as a standard test among those patients, to better plan and conduct
physiotherapy. New devices, such as Luna EMG, allows to create precise environment, to carry out objective assessment and providing data
based on strength and electromyography (EMG) measurement, especiallymedian frequency (MDF), which is the standard parameter to indicate
fatigue. The experiment was performed among 25 MS patients. Subjects
were asked to perform 5 minutes isokinetic exercise of elbow flexion andextension and 2 minutes of isokinetic exercise of the same joint, witha 2 min break between. RMS value, median of frequency and its slope
during exercise, was assessed for biceps and triceps brachii. The mean
strength of both muscles were measured at the same time, accompaniedby the automated counting of repetition. The correlation concerning triceps brachii has been found, between the amount of repetition in firstexercise, with the slope of frequency in the first exercise (5 minutes isokinetic exercise). The same correlation for triceps brachii has been found
for the second isokinetic exercise (2 minutes isokinetic exercise). For biceps brachii different correlation has occurred. The correlation between
amount of repetition in 5 minutes isokinetic exercise and the slope insecond (2 minutes) exercise has been noted. The mean strength during flexion for 5 minutes exercise was 11.20 Nm and 9.5 for extension.
During 2 minutes exercise the mean values were 11.53 Nm and 10.18
Nm respectively. Assessment of MS patients performed with the usage ofnewest devices allows us to observe muscle fatigue, strength, muscle activation and relations between them among patients with MS. This quick
test, accompanied by functional assessment can be a base for patient
objective evaluation and a good foundation for planning and controllingtraining, in terms of muscle fatigue, applied force, muscle activation andcoordination.
Keywords: sclerosis multiplex (MS), fatigue, exercise, sEMG

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Krystyna Stańczyk et al.

Introduction

Multiple sclerosis is a chronic autoimmune, inflammatory neurological disease of
the central nervous system. This is an autoimmune disease, mounted by CD4+
T cells reactive against central nervous system (CNS) antigens. These T cells
are, ostensibly, primed in peripheral lymphoid tissues and cross the blood-brain
barrier to initiate inflammatory demyelination. MS attacks the myelinated axons in the CNS, destroying the myelin and the axons to varying degrees.The
course of MS is highly varied and unpredictable. In most patients, the disease
is characterized initially by episodes of reversible neurological deficits, which isoften followed by progressive neurological deterioration overtime [1].
The diagnosis of MS is typically made on the basis of a set of objective clinicalcriteria, which may be supplemented with other data obtained from MRI scans
and CSF (cerebrospinal fluid) analysis. The clinical presentation of MS is highlyvariable, relying on patient reported or objectively observed sensory, visual, or
motor signs and symptoms that reflect neurological damage and that have been
documented by a neurological exam and findings from visual evoked potential
testing or MRI.
Fatigue is one of the most disabling multiple sclerosis symptoms, significantly
impacting on patients’ daily life activities and quality of life and affecting up to
80% of MS patients [2–6]. It is present even in early stages of the disease, it
can precede other MS symptoms or predicts disease progression. The main characteristics of MS-related fatigue are enhanced perception of effort and limited
endurance of sustained physical and mental activities. The pathophysiology offatigue is still unclear. Damage of specific brain structures and strategic localization of MS lesions have been related to fatigue in MS patients [7].
The rehabilitation of patients with multiple sclerosis can not lead to overheating and excessive fatigue of the body. Exercise helps maintain muscle length andflexibility and lead to increase their strength, mass and endurance. Research on
the effectiveness of rehabilitation interventions is crucial for people with multiple
sclerosis. The content of rehabilitation programmes should be individualised andbased on an assessment of the patient’s unique needs [8–11].
Technologies can provide valid, reliable and sensitive assessment tools that,when used alongside clinical measures, can inform clinical decision-making andprovide richer data on patient outcomes [12]. There is now a clear need for
guidelines for clinicians and researchers to optimise technology-based assessment
and application of clinical measures and procedures [13].

2Material and Methods

The main goal of the study was to create and test a special protocol, using
innovative device, such as Luna EMG, to assess fatigue and other related factors
among patients with multiple sclerosis.

Assessment of Muscle Fatigue with the Usage of Robot, Among MS Patients

2.1

3

Luna EMG

Luna EMG is a rehabilitation robot manufactured by EGZOTech, with assessment and training options, especially useful in rehabilitation of neurological andorthopaedic patients (Fig. 1). It allows physiotherapists to measure muscle force,muscle activity (EMG), stiffness, coordination and proprioception during theexercises. The system allows to work with neurological patients in all stages ofrehabilitation, starting from patients, with no muscle force and no muscle activity, through patients with muscle activity, without muscle force, to patients withmuscle activity and muscle force. Luna EMG includes motor and extensionsexchangeable mechanical parts, that are connected to the patient by straps orby grip. The movement can be preprogramed based on sensors including: a position sensor, a torque sensor, a 6 channel electromyograph and column height
position sensor. It is controlled by a Windows Application from a tablet, throughUser Interface (UI). Luna EMG is able of facilitating the following basic control algorithms: Isokinetic movement, Isotonic movement, Isometric exercises.
To measure the muscle activity and muscle force of the patient, therapist canapply a special protocol of repetitive movements, using isokinetic mode. Withsurface EMG electrodes, attached to the muscle, the root mean square (RMS)
signal can be reported as a representation of muscle activity during the movement. On the other hand we can use EMG median frequency (MDF), which isthe standard parameter to indicate fatigue, due to theory that muscle fatigue
results in a downward shift of frequency spectrum of the EMG signal. Especially
due to the fact, that if the fatigue is increasing sharply, this can cause damage inthe muscles and influence the motoric functions of the patient. For that reason
this can be a useful tool for therapist working with MS patients on daily basis.

Fig. 1. Neurorehabilitation robot Luna EMG

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2.2

Krystyna Stańczyk et al.

Subjects

The experiment was performed among 25 patients, assessed with Expanded Disability Status Scale (EDSS) scale as 6 points or less (patient should have walked
independently) [14]. Patients were included regardless of the form of multiple
sclerosis or medication, but with understanding of the exercise protocol, therefore the patients with cognitive problems were excluded. In order to performisokinetic training, biceps and triceps brachii had to be rated on a Lovett scaleas 3 degree or higher. Lovett scale is commonly used method of muscle strength
assessment, with the scale of 0–5, where 0 – no visible or palpable muscle contraction, 1 – visible or palpable contraction but no range of motion, 2 – moves
full range of motion, gravity is eliminated, 3 – moves full range of motion against
gravity, 4 – moves full range of motion against gravity and moderate resistance,
5 – moves full range of motion against gravity and has maximal resistance [15].
Patients had to understand training with usage of Luna EMG robot and had tofollow the instructions.
2.3

Experiment

Subjects were asked to perform 5 minutes isokinetic exercise of elbow flexion andextension, followed by 2 minutes break and finished with 2 minutes of isokinetic
exercise of the same joint. The exercise was preceded with 2 minutes of passive
motion exercise. Surface EMG electrodes were placed on the biceps brachii andtriceps brachii, to assess the RMS value, median of frequency and its slope during
exercise. The mean strength of both muscles were measured at the same time,
accompanied by the automated counting of repetition. Setting of the patient ispresented on Fig. 2.

Fig. 2. Patient setting in Luna EMG

Assessment of Muscle Fatigue with the Usage of Robot, Among MS Patients

2.4

5

Data Processing

Acquired signals from Luna EMG – EMG signals from biceps brachii and triceps brachii, torque and position, were analysed by algorithm written in Python
3.7.0. The all readings were partitioned into sections responding to movement up(flexion) and down (extension) based on the extension’s position measurement.
EMG signals were filtered using bandpass filter and notch filter. After filtration,
RMS values of electromyography signal were computed with window 100 ms(Fig. 3). Median power frequency is frequency value at which the EMG power
spectrum is divided into two regions with an equal integrated power. It can be
expressed as:
M
M
DF
M
X
X
1X
Pj
(1)
Pj =
Pj =
2 j=1
j=1
j=M DF

where Pj is the EMG power spectrum at a frequency bin j and M is the lengthof the frequency bin. Median frequency was computed for each second of thesignal (Fig. 4). Then the line is fitted to these results using linear regression.

Fig. 3. EMG RMS signal from biceps brachii and triceps brachii during 2 minutes
exercise

2.5

Statistical Analysis

The tables present descriptive statistics: mean, standard error, median, standard
deviation, minimum and maximum value, and confidence level (95.00%). In orderto check the relationship between variables, Pearson’s correlation coefficient wasapplied. The following scale was used to assess the correlation coefficient:r = 0 variables are not correlated;
0 <r <0.1 slender correlation;
0.1 ≤ r <0.3 weak correlation;

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Krystyna Stańczyk et al.

0.3 ≤ r <0.5 average correlation;
0.5 ≤ r <0.7 high correlation;
0.7 ≤ r <0.9 very high correlation;
0.9 ≤ r <1 nearly full correlation.

Fig. 4. Triceps Brachii EMG Median frequency showing fatigue during extension in 5
minute exercise

The direction of correlation refers to the order of the value of one variable inrelation to the value of the other variable. In the case when the correlation ispositive, this means that high values of one variable correspond to the high valuesof the second variable. Correlation is negative, when one variable takes highvalues and the other low values. All the hypotheses considered in the study wereverified at the significance level of α = 0.05. The test results with a significancelevel of p <0.05 were considered statistically significant.

3

Results

The basic values of RMS for biceps brachii and triceps brachii, amount of repetitions and mean torque of both muscles are shown in Table 1. The mean strength
during flexion for 5 min exercise was 11.20 Nm and 9.5 for extension. During 2
min exercise the mean values were 11.53 Nm and 10.18 Nm respectively. Valuesof the median frequency and frequency slope among experimental group are presented in the Table 2. Data shows extensors are slightly weaker muscle group,
than flexors, in those patients, in both exercises. The correlation concerning triceps brachii has been found, between the amount of repetition in first exercise,Assessment of Muscle Fatigue with the Usage of Robot, Among MS Patients7with the slope of frequency in the first exercise (5 minutes isokinetic exercise).
The same correlation for triceps brachii has been found for the second isokinetic
exercise (2 minutes isokinetic exercise). For biceps brachii different correlation
has occurred – between amount of repetition in 5 minutes isokinetic exercise andthe slope in second 2 minutes exercise (Table 3). Beside the correlation between
mean torque in flexion and MDF slope of biceps brachii during the 2 minutes
exercise, when if patients applied more force, they were getting more tired, noother correlation between strength and fatigue was found (Table 4).
Table 1. EMG RMS and torque values among the group of multiple sclerosis patients

Mean
SE
MedianSD
Minimum
Maximum
Confidence level

Mean
SE
MedianSD
Minimum
Maximum
Confidence level4

Isokinetic exercise
Isokinetic exercise(5min) Flexion(2min) Flexion
EMG EMG Torque EMG EMG TorqueBiceps Tricpes
Biceps Tricpes
[uV]
[uV]
[Nm] [uV][uV][Nm]136.77 59.62 -11.20 139.54 60.52-11.53
24.31
7.38
0.76
23.49
7.99
0.89
87.30
50.67
10.84 97.63
49.27-10.68121.55 36.92
3.78 117.44 39.93
4.44
6.26
5.06
-19.16
4.82
21.95-19.56427.94 147.02 -4.90 407.28 170.70
-4.48
50.17
15.24
1.56
48.48
16.48
1.83
Isokinetic exercise
Isokinetic exercise(5min) Extension(2min) Extension
72.76 135.69
9.53
76.86 140.24
10.18
8.17
23.17
0.96
12.23
23.32
0.87
66.18 113.27
7.20
61.30 111.16
8.96
40.83 115.84
4.81
61.13 116.61
4.37
16.47
5.21
5.10
10.24
16.21
5.02
174.51 437.16 20.29 273.63 457.26
20.57
16.86
47.81
1.98
25.23
48.13
1.80

Discussion

Prevention of disability progression in patients with neurodegenerative diseases
such as multiple sclerosis is crucial. In the scientific literature, fatigability is
described as one of the symptoms of multiple sclerosis. Fatigue can be characterized as a form of general fatigue, drowsiness, lack of energy, mental andphysical fatigue, increasing of the muscle fatigue, and tiredness at rest. Thissymptom affects 30-50% of patients with MS. The accumulation of symptoms of
multiple sclerosis is observed during the first 10 years after diagnosis. Focusedrehabilitation introduced, when first syndromes occurs, creates an opportunity
for normal functioning. Rehabilitation in MS is extremely difficult. It is associated with a variable prognosis, depending on the course of the disease, the form,

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Krystyna Stańczyk et al.
Table 2. Mean frequency and frequency slope among experimental group

Mean
SEMedianSD
Minimum
Maximum
Confidence level 95.0%
MeanSE
MedianSD
Minimum
Maximum
Confidence level 95.0%

Exercise
Exercise(5min)(2min)(5min) (2min)
Mean Frequency [Hz] MDF Slope [%]Biceps Brachii
46.37
48.13
-1.94
-1.29
1.28
1.33
0.36
0.93
49.02
48.55
-1.61
-0.37
6.41
6.66
1.82
4.64
24.76
23.63
-6.34
-12.58
53.31
58.80
0.21
7.08
2.65
2.75
0.75
1.92
Triceps Brachii
54.32
56.99
-5.36
0.39
1.84
1.82
1.65
2.91
52.58
53.57
-2.34
0.08
9.18
9.10
8.26
14.53
35.85
45.60
-28.84-25.81
80.54
82.67
4.49
34.62
3.79
3.76
3.41
6.00

Table 3. Correlation between mean torque and MDF slope for biceps and triceps (inflexion and extension)
Amount of repetition in
5 min exercise
2 min exercise
MDF Slope in
p=0.6110
p=0.6742
5 min exercise
Biceps Brachii
MDF Slope in
p=0.0269 (r=0.4419)
p=0.8428
2 min exercise
MDF Slope in
p=0.0198 (r=0.4625)
p=0.8158
5 min exercise
Triceps Brachii
MDF Slope in
p=0.6932
p=0.0246 (r=0.4481)
2 min exercise
Table 4. Correlation between mean torque and MDF slope for Biceps Brachii andTriceps in flexion and extension

MuscleType of exercise
DurationCorr

MDF Slope [%] corr Mean torque [NM]Biceps Brachii Triceps Brachii Biceps Brachii Triceps Brachii
FlexionExtension
FlexionExtension
5 min
5 min
2 min
2 min
p=0.000193
p=0.8776
p=0.1433
p=0.2632(r=0.6784)

degree and location of the lesions. Due to the variety of forms of rehabilitation,

Assessment of Muscle Fatigue with the Usage of Robot, Among MS Patients

9both in the field of kinesiotherapy and physical procedures, there is a need toobjectify the results of rehabilitation [8–11].
Objective measurement of fatigability in patients with neurological diseases
remains a problem rarely described in the research. Many authors emphasize
the need for further research to determine the possibility of reliable, repeatablemeasurements of muscle fatigue in neurodegenerative diseases [13, 16].
According to Hughes et al. ”There is an urgent need for agreed guidelines
on measurement tools and assessment protocols. Furthermore, new technologybased measurement tools have the potential to be used alongside clinical measures of impairment, activity and participation, but need to be rigorously tested
for usability, validity, reliability and responsiveness. Technologies can provide
valid, reliable and sensitive assessment tools that, when used alongside clinicalmeasures, can inform clinical decision-making and provide richer data on patient
outcomes. There is now a clear need for guidelines for clinicians and researchers
to optimise technology-based assessment and application of clinical measuresand procedures” [17]. Motor fatigability is, however, important to consider inpatients with MS because it affects the ability to perform sustained activities ofdaily living. Furthermore, it will have an impact on the exercise capacity of patients with MS, limiting the possibility to exercise regularly. The assessment ofmuscle weakness is routinely performed, but muscle weakness and motor fatigability are different concepts. Patients with MS might not show muscle weakness
on a single assessment of muscle strength, but they might show increased motor
fatigability with a fast decline in muscle strength during longer or repeated test
protocols [18]. Physical activity which is tailored to the individual patient’s needs
can bring a lot of beneficial effects. The individualized and supervised exercise
program should be designed to patient to improve strength, endurance, balance,
coordination, fatigue, etc. It should consider a patient’s baseline impairments
and capabilities, should be safe and effective. The prescription should include all
the necessary components, such as frequency, duration, intensity, modalities tobe used, and precautions to be observed [19].
Consequently, it is important to quantify (pathological) motor fatigability
applying objective, valid, reliable, and responsive outcomes. To unravel the relation between motor fatigability and activities of daily living, it is, furthermore,
important to include outcome measures on both the body function level and theactivity level of the International Classification of Functioning, Disability and
Health (ICF), when assessing fatigability [18].
There is need of to objective evaluate the effects of neurorehabilitation,
standardized assessment protocols and outcome measures. Use of rehabilitation
robots during the process of improvement patients with neurological disease
could be useful not only for physiotherapist but also for the patients as a objective biofeedback and for treatment plan [20]. Among sclerosis multiplex patients
overloading with exercises is not allowed, but therapists goal is need to slow
down the weakness and disability progress. Due to information about fatigability, therapist can plan intensity and duration of training adapted to the patientindividually. During training with the use of the rehabilitation robot Luna EMG

10Krystyna Stańczyk et al.

patients show high motivation to perform exercises due to very good cooperation and biofeedback with the therapist. New technologies allows us to better
objectively assess and understand relations between muscle fatigue and otherfactors, like eg. amount of repetition, in context of applied force and muscle
activation. Data from the experiment shows, that there is a average correlation
between triceps muscle fatigue and amount of repetition, both for 5 minutes and2 minutes exercise. This was not the case for biceps brachii, where the slope insecond exercise was rather correlated with the amount of repetition in the firstone. This could indicated that biceps brachii, got more tired in the second training, being followed by the exhausting first one. High correlation between mean
torque in flexion and MDF slope of biceps brachii during the 2 minutes exercise
was noted, higher mean force, correlated with higher fatigue. No other correlation between strength and fatigue was found. According to study of Schwid andet. [13] fatigue is greater in MS patients, comparing to control group, even inmuscles that were not clearly weak. They have not found significant associations
between strength and fatigue in any of the muscles tested in their research, sothey conclude that motor fatigue appears to be distinct from weakness because
the degree of fatigue was not associated with the degree of weakness. In addition comparing with healthy control subjects, MS patients were weak in lower
extremity muscles, but upper extremity strength was relatively preserved. Since
fatigue of MS patients seems like a complex topic, our first results are the beginning and a first step for the further research, to develop exercises and right
protocols for MS rehabilitation. New technologies can be useful in applying rightamount of repetitions, accurate force and at the same time to monitor muscle
fatigue. Through objective measurements and understanding of the muscles conditions, we can create evidence based exercise protocols, which can be used inprecise exercise devices, like Luna EMG.
Acknowledgement. Research presented in this paper is co-financed by theEuropean Union from the European Regional Development Fund, Smart Growth
Operational Programme, grant no. POIR.01.01.01-00-2077/15 ”Development ofinnovative methods of automatic diagnostics and rehabilitation using robots andbioelectric measurements”.

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