Comparison of Two Techniques for Lifting Low-lying Objects on a Table

Part II: EMG and Psychological Measurement

Angelina Thiers, Harald Loose, Katja Orlowski, Mildred Bl

asing and Marco Wallmann

Department of Informatics and Media, Brandenburg University of Applied Sciences,

Magdeburger Str. 50, 14770 Brandenburg, Germany

Keywords:

Back Pain, Load Lifting, Stoop Lifting, Squat Lifting, Electromyography, Psychological Criteria.

Abstract:

The purpose of this study was to determine differences in health beneﬁts and fatigue when using various

lifting techniques. Worldwide, back pain is a common disease. In this context, muscular tension in shoulder

and neck areas as well as tension-type headaches are the most common side effects. One frequent cause for

this pain is connected with the wrong lifting and carrying of loads. To avoid these types of back pain numerous

recommendations concerning the right lifting technique already exist. The most common recommendation is

that one should use squat lifting instead of stoop lifting. By means of this technique a relief for the back

should be obtained. However, these beneﬁts have not been proven yet. For this study eight healthy subjects

were evaluated. The test persons had to lift a load for ten minutes. During the lifting task the muscle activity of

nine muscles was documented. At the same time, psychological data were collected in a questionnaire. Both,

the physiological and psychological data revealed differences between the lifting techniques. During the stoop

lifting, a higher burdening of the back muscles was measured. In addition, following the exercise, a greater

and prolonged discomfort in the back muscles was documented.

1 INTRODUCTION

People who had not at least once in their lifetime

low back pain are the minority. A survey of German

health insurances companies showed that back pain is

one of the ﬁve most frequent illnesses. Almost 80%

of all people in Central Europe have reported at least

once in their lifetime about back problems. Espe-

cially, the number of children involved highlights the

increasing importance of prevention programs (Lez-

ius, 2004).

Frequently, the affected persons do not only suffer

from low back pain but also from muscular tensions

in the spine, shoulder and neck areas. Additionally,

back pain often leads to tension-type headache. Com-

mon causes of these pain patterns are incorrect or ex-

cessive pressure to the back as well as psychological

factors like stress. In everyday life, heavy lifting and

moving of loads are equally as responsible for an in-

creased stress of the back as wrong postures during

lifting (Kempf, 2009; Buhr, 2011).

The current recommendations for avoiding back

pains consist primarily of guidelines for a correct lift-

ing technique. The often suggested squat lifting is

done by bent knees and erected back. In contrast, the

stoop lifting is characterized by straight legs and a

bent back. However, the advantages of squat lifting

in terms of effectiveness and positive health beneﬁts

have not been sufﬁciently proven (Dietrich, 2009).

To proof the suspected superiority of the squat lift-

ing technique different studies have been made. Re-

vuelta et al. (Revuelta et al., 2000) as well as Straker

and Duncan (Straker and Duncan, 2000) were able

to show that using the squat lifting leads to a higher

heart rate response than the stoop lifting. A different

physical strain of the lifting techniques was also con-

ﬁrmed by analyzing the muscle activity. Besides dif-

ferent activity and fatigue patterns, recorded datasets

also showed that a heavy pressure caused a changed in

the lifting technique from squat to stoop (Troup et al.,

1983; Hagen et al., 1994; Dietrich, 2009).

The aim of the current study was to show that there

is a difference in effectiveness, health beneﬁts and fa-

tigue between both techniques. For the veriﬁcation

of these assumptions a loading test was conducted.

Analyzing psychological data as well as physiologi-

cal data should show the differences between squat

and stoop lifting.

248

Thiers A., Loose H., Orlowski K., Bläsing M. and Wallmann M..

Comparison of Two Techniques for Lifting Low-lying Objects on a Table - Part II: EMG and Psychological Measurement.

DOI: 10.5220/0004327802480253

In Proceedings of the International Conference on Bio-inspired Systems and Signal Processing (BIOSIGNALS-2013), pages 248-253

ISBN: 978-989-8565-36-5

 2013 SCITEPRESS (Science and Technology Publications, Lda.)

2 EXPERIMENTAL SETUP

2.1 Subjects

Eight students were recruited through personal con-

tact. An equal distribution of the sexes was given. The

ages ranged from 18 to 27 years. The average body

height of the test persons was 173.5 (SD 8.6) cm.

All were healthy, without back pain symptoms and

gave their written consent to participate after being

informed about the experiment.

2.2 Test Procedure

On the ﬁrst day of the experiment the subjects had to

execute the stoop lifting. Test persons returned one

week later to perform the squat technique.

Initially, the test persons were briefed about the

selected lifting technique (Loose et al., 2013). A max-

imum voluntary contraction (MVC) test for all ana-

lyzed muscles followed. Afterwards, the subjects did

a test lift with the aim to practice the correct motion

sequence while it was being made sure that the test

person is not restricted. The lifting task itself con-

sisted of three different stages. Firstly, the test person

had to remain still for one minute. During the second

phase, the subject performed the lifting of the load

for ten minutes. The requirements included both, the

correct motion sequence and a lifting frequency of at

least ﬁve lifts per minute. The ﬁnal stage was equal

to the initial phase, one minute rest. A different load

weight for the sexes was given (male: 15 kg , female:

8.4 kg) (Loose et al., 2013). For the post-processing

of the lifting task an immediate survey about the sub-

jective effort and discomfort was conducted. Further-

more, a questionnaire about the same topics was ﬁlled

out on each of the seven following days.

2.3 Measurement

The used Shimmer

sensors are characterized by

their small form and their low power consump-

tion. The Bluetooth technology offers real-time data

streaming. The basic module consists of an on-board

micro-controller, wireless communication modules, a

microSD slot and an integrated three-axis accelerom-

eter. In this study the used daughterboard was the

electromyography (EMG). The EMG module records

the electrical activity of a muscle with a sampling fre-

quency of 1024 Hz. The sensor disposes of three con-

nectors which allow to measure two or three chan-

nel pre-ampliﬁcated EMG-signal (Shimmer Research

Support, 2012).

2.4 Sensor Placement

Muscular contraction data were collected for nine

muscles. The EMG was recorded from the follow-

ing trunk and extremities muscles: M. gastrocnemius

medialis and lateralis, M. biceps femoris, M. vastus

lateralis, M. rectus femoris, M. gluteus maximus, M.

erector spinae, M. trapezius ascendes and M. biceps

brachii. The muscles were chosen based on their

function to carry out the deﬁned motion sequences.

Ag/AgCl surface electrodes were applied after a stan-

dard skin preparation considering the recommenda-

tions from the SENIAM project (SENIAM project,

2012).

2.5 Data Analysis

The ﬁrst questionnaire was completed immediately

after the lifting task. The second questionnaire was

completed on a daily basis at home over a period of

seven days. The content included questions regard-

ing the effort and discomfort in general and in spe-

cial parts of the body. Using an eleven-point answer

scale, the test persons had to judge from 0 (no ef-

fort/discomfort) to 10 (very high effort/discomfort).

The statistical evaluation was performed by using

mean values to compare the two lifting techniques.

The raw EMG signal was band-pass ﬁltered from

15 to 500 Hz (Merletti and Parker, 2004). Addition-

ally, a notch ﬁlter with a blocking frequency of 50 Hz

was applied.

For analyzing the signal in the time domain a full-

wave rectiﬁcation was carried out. Statistical parame-

ters like maximal or mean amplitude were calculated

over the time. They were calculated over an inter-

val of seven seconds, which is the average length of

a lifting cycle. Additionally, the parameters were cal-

culated for ten detected liftings. Using the MVC data

for the standardization of the EMG an inter-proband

analysis was possible. A second standardization was

made by using time normalization.

Transformation of the EMG signal from the

time to the frequency domain was achieved by the

Fast Fourier Transformation over signal segments of

512 ms (Grimshaw et al., 2006; Kaplanis et al., 2009).

The Frequency-Analysis included the computation of

the median frequency as well as the computation of

the total power. Both parameters were used as indi-

cators for muscle fatigue (Merletti and Parker, 2004;

Lukas, 2000).

The accumulation of the power density spectrum

for all frequencies is deﬁned as the total power, ﬁg-

ured in equation 1 (Kaplanis et al., 2009).

ComparisonofTwoTechniquesforLiftingLow-lyingObjectsonaTable-PartII:EMGandPsychologicalMeasurement

249

totalPower

∞

( f )d f (1)

The median frequency is the frequency where the

accumulated power spectrum energy is 50 % of the

total power spectrum, ﬁgured in equation 2 (Chang

et al., 2012; Kaplanis et al., 2009).

medianFrequency

∞

( f )d f (2)

3 RESULTS

3.1 Physiological Data

For the comparison of the course of the maximum am-

plitude of the M. rectus femoris in stoop and squat the

measured values of all subjects were averaged. Fig-

ure 1 shows the changes in the maximum amplitude

(normalized values) of the M. rectus femoris through-

out the lifting task. A comparison of the stoop and

squat values illustrates the higher strain of the M. rec-

tus femoris in squat lifting. On average, using squat

technique produces threefold greater voltage values

than using stoop technique. That corresponds to the

characteristic that in squat the load is lifted from the

knees and not from the back.

Figure 1: M. rectus femoris - Comparison of the maximum

amplitude in stoop and squat.

As in the previous calculation, the maximum am-

plitudes of all subjects were averaged. The visualiza-

tion of the averaged values (normalized values) of the

M. erector spinae is shown in ﬁgure 2. Both tech-

niques have in common that on average the values

rise over time. This observation supports the asser-

tion that load lifting leads to a fatigue in the back

muscle. The ﬁgure further indicates that the stoop

technique involves a higher participation of the back

muscle. The consideration of ﬁgure 2 together with

ﬁgure 1 points out for both techniques that the mea-

sured values reﬂect the strain in the suspected body

areas. The relative measurements in stoop show a

threefold higher effort in M. erector spinae than in M.

rectus femoris. The measured values in squat tech-

nique show a strongly contrasting distribution. M.

rectus femoris is producing twice as high values as

M. erector spinae.

Figure 2: M. erector spinae - Comparison of the maximum

amplitude in stoop and squat.

Fatigue is deﬁned in muscle physiology as a state

when a subject can no longer maintain a required

force (Merletti and Parker, 2004). Hence the main-

tenance demands an increasing recruitment of motor

units (Lukas, 2000). Figure 3 shows the course of

the total power of one test person during the load lift.

The difference between the absolute values for both

techniques are clearly visible. Furthermore, there is

a noticeable course difference. For the total power in

stoop nearly static values were recorded. In contrast,

the calculated total power when using squat technique

shows a steady increase. Both observations indicate a

higher strain in M. rectus femoris during squat lifting.

Additionally, the course of the total power illustrates

the fatigue of the muscle when using squat lifting.

Figure 3: M. rectus femoris - Comparison of the total power

in stoop and squat.

One of the most widely applied indexes for muscle

fatigue is the median frequency. In the state of mus-

cle fatigue the EMG spectrum is compressed towards

BIOSIGNALS2013-InternationalConferenceonBio-inspiredSystemsandSignalProcessing

250

lower frequencies (Merletti and Parker, 2004). The

development of the median frequency of M. erector

spinae for both lifting techniques is represented in ﬁg-

ure 4. Both graphs show descending median frequen-

cies. Hence, squat lifting is as well as stoop lifting

fatiguing for the back muscles. However, a close-up

look at the values shows that the decrease of the fre-

quency in stoop lifting is higher than in squat. The al-

legation that stoop lifting causes a higher strain on the

back is supported by ﬁgure 4. The course of the me-

dian frequency of this subject is similar to the curves

of the other test persons.

Figure 4: M. erector spinae - Comparison of the median

frequency in stoop and squat.

To assess the fatigue of the M. gastrocnemius lat-

eralis during the execution of both techniques the

maximum amplitude (time normalized) of ten de-

tected repetitions was considered. According to

Werner (Werner, 2006), the fatigue of a muscle ac-

crues as a result of strain and is recognizable by the

increase of the electrical activity. On average, the test

persons showed higher maximum values during the

squat than the stoop technique. Figure 5 illustrates the

behavior of the maximum amplitude of the M. gas-

trocnemius lateralis for both techniques over the ten

detected repetitions. Because of the higher electrical

Figure 5: Maximum values of the electrical activity of the

averaged curves of the ten repetitions, M. gastrocnemius lat-

eralis.

activity during the squat technique it can be assumed

that this technique led to a higher strain. However,

if the behavior of the maximum values is considered

over the ten repetitions, no continuous increase or de-

crease is visible. Referring to the ﬁrst and the last de-

tected repetition, there is an increase of the values in

both techniques. Hence, a fatigue of the M. gastroc-

nemius lateralis could not be proven. This could be

due to either none of the techniques causing a fatigue

of the M. gastrocnemius lateralis or too many factors

being present that inﬂuence EMG signals.

3.2 Psychological Data

The immediately conducted survey of all test persons

after the lifting task (ﬁg. 6) revealed as part of the

comparison of stoop and squat lifting that the sub-

jective general effort in squat lifting is higher than in

stoop. A detailed look at the distribution in ﬁgure 6

shows that both, the effort in quadriceps and biceps

femoris in squat lifting are higher than in stoop lift-

ing. A contrary result is shown in terms of subjec-

tive exertion in low and upper back. In both cases

the perceived effort in stoop lifting is several times

higher than in squat lifting. The information gath-

ered from the test persons consultation presents the

expected results in dependency to the described mo-

tion sequences of the lifting techniques.

Figure 6: Comparison of the general effort in stoop and

squat

In addition, the surveys sought information about

the actual discomfort. In general, all test persons suf-

fered a higher discomfort after using the squat tech-

nique. However, a more detailed analysis of this

point revealed that while some body areas led to a

higher discomfort when using the squat technique

other body areas had a higher discomfort following

the stoop technique. Firstly, the look at discomfort of

the thigh in ﬁgure 7 shows that using the squat tech-

nique caused higher values, especially in the quadri-

ceps. The discomfort is nearly seven times higher

ComparisonofTwoTechniquesforLiftingLow-lyingObjectsonaTable-PartII:EMGandPsychologicalMeasurement

251

than using the stoop technique. Therefore, the use of

the stoop technique can be expected to have a higher

discomfort in the back. Figure 7 conﬁrms the assump-

tion that the subjective pain after using stoop is in the

lower as well as in the upper back many times higher

than after using the squat lifting.

Figure 7: Comparison of the general discomfort in stoop

and squat.

The assessment of general discomfort one day af-

ter the lifting tasks showed similar values to those ob-

tained immediately after the lifting. The comparison

of the course of the complaints differs (ﬁg. 8). The

discomfort on the ﬁrst days after using the squat tech-

nique shows a decreasing level. In contrast, the com-

plaints in the back after using stoop are still growing

on the second day. Compared to the squat technique,

the pain level in the lower back is in stoop over ten

times higher.

Figure 8: Following day 1 and 2 - Comparison of the gen-

eral discomfort in stoop and squat.

The course of the general pain levels shows a

faster regeneration after using squat technique. On

the third day after the lifting task the comparison of

the general pain shows for the ﬁrst time lower values

for the squat lifting. Already on the fourth day af-

ter using the squat technique, the test person reported

scarcely any complaints. The values of the subjective

pain in the back after using stoop are comparatively

high.

Figure 9: Following day 3 and 4 - Comparison of the gen-

eral discomfort in stoop and squat.

4 DISCUSSION

The main ﬁnding in this experimental study is that the

EMG patterns of stoop and squat lifting differ. On

one hand, high values in muscle activity were sus-

pected for the M. rectus femoris. On the other hand,

the presumption for the squat lifting was a high per-

formance of the M. erector spinae. Both assumptions

are proven with the analyzed EMG courses. More-

over, in the frequency domain the typical properties

of the lifting techniques are visible. The comparison

of the course of total power of the M. rectus femoris

in stoop and squat showed a great difference in the ef-

fort of the muscle. The increase of the total power in

squat indicates the fatigue of the muscle. The higher

voltage values as well as the fatigue point out that the

effort in squat is higher than in stoop. The detailed

observation of the maximum amplitudes and the fa-

tigue of the M. erector spinae show lower differences.

Although stoop technique creates higher voltage val-

ues and a steeper decrease of the median frequency of

the M. erector spinae, the differences are not as pow-

erful as the differences in squat technique. This can

be caused by the deﬁnition of the motion sequence of

Loose et al. (Loose et al., 2013). A lifting and lower-

ing of weights without placing the weights on a table

might be useful for a more conclusive result. Addi-

tionally, the placement of the sensors can be more ef-

fectively. As the investigation of the muscle activity

of the M. gastrocnemius lateralis shows that this mus-

cle is less important for the evaluation of the lifting

techniques. Instead, the placement of additional sen-

sors at the back can be useful.

The analysis of the subjective pain impressions

recorded via the questionnaires support the statement

that squat lifting is healthier than stoop lifting. Es-

pecially the course of the discomfort in the four days

following the lifting shows that complaints after using

stoop are more intensive and the regeneration takes

BIOSIGNALS2013-InternationalConferenceonBio-inspiredSystemsandSignalProcessing

252

longer. Furthermore, the observation of the general

effort and general discomfort immediately after the

lifting task conﬁrms the thesis that squat is more fa-

tiguing than stoop lifting.

5 CONCLUSIONS

This paper investigated the hypothesis that the squat

lifting technique is more ergonomic, healthy and less

exhausting on a real life example of a combined mo-

tion of lifting and putting a beer crate into a car trunk.

The analysis of the physiological and psychological

data indicates on the one hand that squat causes a

higher effort in the upper legs and on the other hand

that the effort of the back is higher in stoop. Fur-

thermore, the investigation of the discomfort in the

back shows that the intensity and duration of the com-

plaints are higher when using stoop. In contrary, the

ECG analyzed in Loose et al. (Loose et al., 2013)

showed a higher physical stress when using squat. In

summary, it can be concluded that no general assump-

tion for an optimal lifting technique can be made.

Further assumptions about the lifting techniques

can be reached by an individual analysis of the lifting

cycles. This can be realized by an observation of the

EMG patterns or by the use of the Kinect data (Loose

et al., 2013).

The feature of the characterized motion sequence

is that it represents an everyday situation like lifting a

beer (or similarly shopping) crate into a car. However,

the experimental study was not able to show a signiﬁ-

cant beneﬁt of the squat lifting with regards to the fa-

tigue of the M. erector spinae. Due to that reason the

validity of the statement that squat lifting is healthier

has to be proven in everyday situations. Another con-

tinuation of the study could focus on the behavior of

the muscle activity when lifting different loads using

various lifting techniques.

Further measurements (Kinect and ECG data), re-

sults, discussions and ﬁnalizing conclusions are in-

cluded in Loose et al. (Loose et al., 2013).

REFERENCES

Buhr, M. (2011). Der gesunde R

ucken: R

uckenschmerzen

vorbeugen und heilen. humboldt.

Chang, K.-M., Liu, S.-H., and Wu, X.-H. (2012). A wireless

semg recording system and its application to muscle

fatigue detection. Sensors, pages 489–499.

Dietrich, R. (2009). Zeitaufgel

oste Frequenzanalyse

von EMG-Signalen bei dynamischen Hebevorg

angen

mit zunehmenden Lasten. PhD thesis, Humboldt-

Universit

at zu Berlin.

Grimshaw, P., Lees, A., and Fowler, N. (2006). Sport and

Exercise Biomechanics (BIOS Instant Notes). Bios

Scientiﬁc Publ.

Hagen, K. B., Harms-Ringdahl, K., and Hall

en, J. (1994).

Inﬂuence of lifting technique on perceptual and car-

diovascular responses to submaximal repetitive lift-

ing. European Journal of Applied Physiology, pages

477–482.

Kaplanis, P., Pattichis, C., Hadjileontiadis, L., and Roberts,

V. (2009). Surface emg analysis on normal subjects

based on isometric voluntary contraction. Journal of

Electromyography & Kinesiology, pages 157–171.

Kempf, H.-D. (2009). Die Neue R

uckenschule. Springer.

Lezius, T. (2004). Volkskrankheit r

uckenschmerzen - ein

forschungsprojekt unter gesundheitspsychologischen

aspekten. Master’s thesis, Evangelische Hochschule

urnberg.

Loose, H., Orlowski, K., Thiers, A., and Tezlaff, L. (2013).

Comparison of two techniques for lifting low-lying

objects on a table: Part i: Setup, ecg and motion mea-

surement. BIOSIGNALS 2013.

Lukas, C. M. (2000). Kraftverhalten und elektromyo-

graphische Untersuchungen an der Unterschenkel-

muskulatur bei Patienten nach operativ versorgter

Achillessehnenruptur. PhD thesis, Eberhard-Karls-

Universit

at zu T

ubingen.

Merletti, R. and Parker, P. A. (2004). Electromyography.

John Wiley & Sons.

Revuelta, N., Dauphin, A., Kowslowski, O., Dubois, D.,

and Thevenon, A. (2000). Heart rate response to two

lifting techniques. Archives of Physical Medicine and

Rehabilitation, 81:958–959.

SENIAM project (2012). Sensor placement. Website.

Available online at http://www.seniam.org; visited on

October 25th 2012.

Shimmer Research Support (2012). EMG User Guide Rev

1.2. Shimmer Research.

Straker, L. and Duncan, P. (2000). Psychophysical and psy-

chological comparison of squat and stoop lifting by

young females. Australian Journal of Physiotherapy,

pages 27–32.

Troup, J., Leskinen, T. P. J., Stalhammar, H. R., and

Kuorinka, I. A. A. (1983). A comparison of intraab-

dominal pressure increases, hip torque, and lumbar

vertebral compression in different lifting techniques.

Human Factors: The Journal of the Human Factors

and Ergonomics Society, pages 517–525.

Werner, F. (2006). Auswirkungen differenzieller

Erm

udungsprogramme auf ausgew

ahlte Bewe-

gungsparameter und die Muskelaktionspotenziale von

Triceps surae und Quadriceps femoris. PhD thesis,

Friedrich-Schiller-Universit

at Jena.

ComparisonofTwoTechniquesforLiftingLow-lyingObjectsonaTable-PartII:EMGandPsychologicalMeasurement

253