Comparison of Two Techniques for Lifting Low-lying Objects

on a Table

Part I: Setup, ECG and Motion Measurement

Harald Loose, Katja Orlowski, Angelina Thiers and Laura Tetzlaff

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

Magdeburger Str. 50, 14770 Brandenburg, Germany

Keywords: Stoop and Squat Lifting, ECG, EMG and Motion Measurement, Kinect, Shimmer Sensors, Procomp Infiniti.

Abstract: “There is a strong belief that stoop lifting is ‘bad’ and squat lifting is ‘good’.”

In this paper we research a combined motion: lifting and putting a beer crate into a car trunk. This real life

task was chosen in the biosignal analysis course at the Brandenburg University of Applied Sciences. We

started with the hypothesis that ‘the squat lifting technique is more ergonomic, healthy and less exhausting’.

Our study was scheduled for one semester including the experiments and a first preliminary analysis of the

data to prove or disprove three partial hypotheses. Four male and four female untrained subjects were

involved in the experimental part of the study. Physiological parameters like the heart and the respiration

rate, the activity of various muscles as well as the motion of the whole body were measured. Questionnaires

were developed and carried out before, immediately after and one week after the experiment to acquire

information about the fitness of the subjects and the effects of the exercises on their state of wellness and

health. First conclusions result in no clear preference for one lifting technique.

1 INTRODUCTION

The purpose of this study was to determine

differences in effectiveness, health benefits and

fatigue when using various lifting techniques.

In the community “there is a strong belief that

stoop lifting is ‘bad’ and squat lifting is ‘good’.”

(Straker, 2002). Dieen et al. (1999) gave a review of

biomechanical studies on lifting techniques

concluding that both techniques have positive and

negative effects. Straker (2002 and 2003) published

a research review regarding both techniques for

lifting low-lying objects. In the first paper different

criteria of evaluation from about 80 references were

discussed. The second paper showed that there is no

technique with clear validity summarizing

psychophysical, physiological, biomechanical,

performance and

clinical aspects. Recommendations

for correct lifting of low-lying objects are given:

keep the load close, use a secure grip and a stable

base as well as a smooth movement of moderate

pace (Straker, 2003). A biomechanical study of the

kinematics of the lower extremity joint, the lumbar

lordosis based on three-dimensional motion analysis

and the measured EMG is described in (Hwang,

2009). No significant differences in the maximum

lumbar joint movements between the two techniques

were found. Still, the squat lifting technique is

generally recommended as the “correct” one.

In this paper we research a combined motion of

‘lifting and putting a beer crate into a car trunk’. We

started with the hypothesis that ‘the squat lifting

technique is more ergonomic, healthy and less

exhausting’. Our study was scheduled for one

semester including the experiments and a first

preliminary analysis of the data to prove or disprove

the three partial hypotheses concerning ergonomics,

health and exhaustion. First conclusions result in no

clear preference for one lifting technique.

2 METHODS AND MATERIALS

This chapter describes the experimental setup (task,

phases and selection of subjects) as well as the

measurements (equipment, parameters, sensors, data

acquisition and analysis).

388

Loose H., Orlowski K., Thiers A. and Tetzlaff L..

Comparison of Two Techniques for Lifting Low-lying Objects on a Table - Part I: Setup, ECG and Motion Measurement.

DOI: 10.5220/0004327603880391

In Proceedings of the International Conference on Bio-inspired Systems and Signal Processing (BIOSIGNALS-2013), pages 388-391

ISBN: 978-989-8565-36-5

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

2.1 Experimental Setup

After preliminary tests, some discussions and a

literature review the task to do for each test subject

was defined as follows: lifting a crate of bottles,

putting it on a table, taking it again and placing it on

the ground. Male subjects handled a full filled crate,

females a half filled one.

Figure 1: Stoop technique – half of the cycle.

Figure 2: Squat technique – half of the cycle.

Task. Figure 1 and 2 show half a cycle of the task

the subjects need to repeat at least five times per

minute for a period of ten minutes

Each cycle starts

and ends upstanding, then the subject takes the crate

of 15 kg for males and 8.4 kg for females

respectively, lifts it up to a position in front of the

stomach, puts it on the table with a height of 0.72 m

and reverse. While using the stoop technique the

legs are stretched during the whole procedure.

During the squat technique the body is more or less

upright. Before and after the lifting cycle the subject

stands upright for one minute to calibrate the sensors

and to acquire the vital parameters during the rest.

Phases. Before starting the practical part of the

course, the experiment was scheduled and

standardized to exclude as many random failures as

possible during the preparation of the subject. The

sequence is split into four phases. During the first

phase (25 minutes) the subject is prepared for the

experiment. During the second phase (35 minutes)

the electrodes are tested and the maximum voluntary

contractions of determined muscles are captured.

The experiment starts immediately after the

configuration of all involved equipment and

software. After one minute rest the subject begins to

execute the exercise. After ten minutes the subject

rests again for one minute, the protocol is continued

and the data are saved (21 minutes). During the

wrap-up phase (16 minutes) the blood pressure is

measured and the test subject is interviewed to

capture his/her subjective impression of the task. All

phases take about 98 minutes per subject. Therefore

one day is needed to process eight subjects in one

technique. The questionnaire was to be filled out

immediately after the experiment and during the

following seven days. The second technique was

executed one week later.

Test Subjects.

Eight young and healthy volunteers

were enlisted as test subjects in this study: four male

and four female subjects of normal weight, between

18 and 26 years old and with a height of 160 to 188

cm. The fitness level of the subjects varied between

average and very good. The subjects were asked to

take part in a questionnaire to capture their fitness.

2.2 Measurements

Vital and Motion Parameters.

To answer the three

hypotheses, data about the physiological state of the

subject, his/her muscle activities and the motion of

the body were captured. The ECG, pulse and blood

pressure measurements are standard approaches to

evaluate the behaviour of the heart: the heart rate, its

variability and adaptability to constant or rising

loads. Changes in the respiration rate and surface

temperature reflect the rising demand of oxygen and

the heat build-up during lifting of high load. EMGs

are used to estimate the activities of various muscles

or groups of muscles. The RGB video and the

skeleton stream of the KINECT sensor are captured

to estimate the executed lifting process.

Equipment and Data Acquisition. In this

investigation various devices and sensor systems are

used to observe the execution as well as the vital

parameters of the test person. The data acquisition

from all devices running on five computers is

synchronized manually by starting the software on

demand. The data are sampled with five different

rates: 30 Hz on the KINECT (RGB video, depth and

the skeleton stream), 256 Hz for respiration,

temperature and filtered EMG from ProComp

Infiniti, 1024 Hz SHIMMER-EMG, 2048 Hz from

ProComp Infiniti ECG and EMG and 51200 Hz

from the NEUROWERK-EMG. The KINECT, the

ProComp Infiniti encoder as well as the

NEUROWERK-EMG sensors are connected by

wire. The data of SHIMMER sensors are send

wireless (Bluetooth). The data acquisition process is

observed in real time using the original software

(running plots, RGB video stream). All data are

transferred sequentially to the host PC and converted

into integer formats to save storage on memory and

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hard discs.

The skeletal tracking of the KINECT

immediately delivers the 3D-positions of 20 points

on a fictive skeleton. In the experiment only the left

half of the test subject is observed. Our software

called KinectStreamer is connected to the device and

receives the skeleton data stream as well as the RGB

and the depth streams.

Sensors and their Placement. All available sensor

systems are used to get a maximum of information

about the physiological state of the test subject. The

EMG electrodes are placed on those muscles mostly

involved in the squat and stoop lifting (for details

see Thiers et al., 2013). Both ECG sensors are

applied ventral. The KINECT sensor is placed 2.5 m

right of the test subject, so that the optical axis is

perpendicular to the sagittal plane of the test person.

Signal Analysis.

The primary analysis of each signal

is processed by programs written in the MATLAB

environment. First of all, the quality and

completeness was checked by visual inspection of

generated plots. Some signals were corrupted

because of failures in data transmission, artefacts or

software errors. That data was excluded from further

investigation. In a second step signals were filtered

and smoothed using band pass filters to reduce high

frequency noise and to exclude low frequency drifts.

In this paper we focus on the change of all signals or

their characteristics over the 10 minute long

experiment while the test subject processed more

than 50 lifting cycles. The execution of the stoop

and lifting technique during one cycle is not

evaluated here, no kinematic or kinetic analysis was

done.

3 RESULTS

In this section selected results are presented to allow

a preliminary answer to the question what lifting

technique is to be preferred.

In this paper we explain only results we got from

observation and single measurements from ECG and

motion capture devices. Results in relation to muscle

activities and psychological aspects are discussed by

Thiers et al. (2013).

3.1 Observation

All information about the subjects and their

individual characteristics (gender, age, height,

fitness, performance, impression, pain, pulse, blood

pressure before and after the experiment), the

number of executions per minute counted by one

examiner as well as abnormalities during the

measurement (loss of electrodes, interruption of

software) were collected in a file. In table 1 some of

these data are presented. 50% of the subjects are

female, only one does not regularly work out. The

pulse measured immediately after the squat

technique is for most of the subjects higher than

after the stoop cycle - a first indication that squat

lifting is more exhausting or less familiar.

Table 1: Selected data of the test subjects (gender and

regular sport activities) and their pulse (in beats per

minute) immediately before and after the experiment (f-

female, m-male).

No. Gender Sports

Pulse

before/after

Stoop Squat

01 f yes 68/108 76/112

02 f yes 84/116 80/120

03 m yes 84/120 72/132

04 f yes 80/132 76/132

05 m yes 72/88 64/96

06 m no 72/120 92/136

07 f yes 68/107 60/132

08 m yes 76/116 64/140

3.2 Electrocardiogram (ECG)

The electrocardiogram was captured parallel using

the ProComp Infiniti encoder and SHIMMER ECG

sensor. Both sensors recorded similar data.

Figure 3: Change of the heart rate of subject 1 (filled) and

6 (dashed) over time using the stoop (black) and squat

(gray) technique.

Figure 3 shows the dependency of the heart rate

of two test subjects on the repetitions (time).

Obviously the heart rate rises rapidly at the

beginning of the execution (no warm up). Then the

increase becomes moderate and after the lifting was

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

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stopped it falls rapidly what is an indicator for the

good fitness of the subject. The curves of subject 1

are below the corresponding curves of subject 6 who

was the only one not regularly working out.

The slower decrease of the heart rate at the end

(last 1.5 minute) supports this fact. More important,

the heart rate of the squat lifting is at all times higher

than that of the stoop technique.

All effects indicate that the squat lifting

technique is more exhausting than the stoop

technique.

3.3 Motion

The following results are derived from the vertical

motion of the head. During every repetition the

subject stoops or squats twice, once to lift the crate

and once to drop it. Therefore there are two local

minima of the vertical position in each cycle. These

minima are detected and used to count the

repetitions.

Table 2 lists the number of repetitions counted

by an examiner and calculated from skeletal data.

Both numbers coincide well, i.e. to use the minimum

of the height of the head to split the whole execution

into single cycles works satisfactory.

Table 2: Number of repetitions counted and calculated.

No.

Number of repetitions

counted

Number of repetitions

calculated

Stoop Squat Stoop Squat

01 73 59 73 60

02 52 80 56 81

03 78 54 79 55

04 91 104 92 104

05 54 96 54 96

06 66 94 67 94

07 76 70 77 70

08 78 94 78 95

The heights of the head (not shown in this paper)

are more or less constant. While the cycle time

increases for subject 1 for both techniques, for

subject 2 it increases in the stoop technique and

decreases in the squat technique. At the same time

the repetitions were executed faster. It seems that

subject 2 became tired in the course of the

experiment.

Analyzing the motion of the head no clear

preference for one of the techniques can be

concluded.

4 CONCLUSIONS

In this paper the hypothesis that ‘the squat lifting

technique is more ergonomic, healthy and less

exhausting’ is investigated in a real life example of a

lifting and putting a beer crate onto a table. The

conditions of our study are described, a number of

experimental results analyzing the ten-minute

repetition, not a single cycle, are presented. The

observation and the ECG measurements indicate that

the squat lifting technique is more exhausting than

the stoop technique. That thesis is partly attested by

motion analysis. Anyway there is no clear

preference for one or the other technique from the

prospect of performance.

Further measurements (EMG, interviews),

results, discussions and final conclusions are to be

found in part II of this paper (Thiers et al., 2013).

The analysis of the data captured during the

experiment as well as the study itself will be

continued. Single cycles will be evaluated

statistically, SHIMMER motion data will be

included, kinematics and kinetics will be covered.

The experiment with another group of volunteers

will be repeated skipping, replacing or adding some

sensors.

REFERENCES

Dieen van, J. H., Hoozemans, M. J. M., Toussaint, H. M.,

1999. Stoop or squat: a review of biomechanical

studies on lifting techniques. In: Clinical

Biomechanics 14 (1999), pp. 685-696, Elsevier

Science.

Hwang, S., Kim, Y., Kim Y., 2009. Lower extremity joint

kinetics and lumbar curvature during squat and stoop

lifting. In: BMC Musculoskeletal Disorders, 2009, pp

10-15.

Loose, H. Orlowski, K., 2012. Measurement of Human

Locomotion: Evaluation of Low-Cost KINECT and

SHIMMER Sensors. In: MSM 2012, The 8

International Conference Mechatronics Systems and

Materials, July 8-13, 2012, Bialystok.

Straker, Leon M., 2002. A review of research on

techniques for lifting low-lying objects: 1. Criteria for

evaluation. In: Work 19(2002), pp. 9-18, IOS Press.

Straker, Leon M., 2003. A review of research on

techniques for lifting low-lying objects: 2. Evidence

for a correct technique. In: Work 20(2003), pp. 83-96,

IOS Press.

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

Wallmann M., 2013. Comparison of two techniques

for lifting low-lying objects on a table: Part II: EMG

and Psychological Measurement, BIOSIGNALS 2013,

Barcelona, 11.-14.02.2013 (in print).

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