Muscle Activity During Aquatic and Land Exercises in People With and Without Low Back Pain

Abstract

Background:
Chronic low back pain (CLBP) is the most prevalent musculoskeletal disorder. Aquatic exercises are commonly used by physical therapists for CLBP treatment and management; however, there are no data on trunk muscle activation during aquatic exercises in people with CLBP.

Objective:
We quantified activation of trunk and gluteal muscles, exercise intensity, pain, and perceived exertion in people with and without CLBP when performing water and land exercises.

Design:
The study used a cross-sectional design.

Methods:
Twenty participants with non-specific CLBP and 20 healthy participants performed 15 aquatic exercises and 15 similar land exercises. Mean and peak muscle activation were measured bilaterally from erector spinae, multifidus, gluteus maximus, gluteus medius, rectus abdominis, external oblique, and internal oblique, using waterproof and wireless surface electromyography. Exercise intensity (heart rate), perceived exertion (Borg scale), and for the CLBP group, pain (visual analog scale) were recorded.

Results:
There were no significant between-group differences. Significant between-environment differences were found in heart rate (always higher on land), exertion (higher in the water for 3 exercises and on land for 6 exercises) and muscle activation (higher on land in 29% and in the water in 5% of comparisons). Pain levels were low, but pain was reported more than twice as frequently on land than in water (7.7% vs 3.7%, respectively).

Limitations:
People with high levels of disability and CLBP classification were not included.

Conclusions:
People with mild-to-moderate CLBP had similar exercise responses to healthy controls. Aquatic exercise produced sufficient muscle activation, intensity, and exertion, and should not be assumed to be less strenuous or less effective in activating trunk and pelvic muscles than exercise on land. These data can be used to inform design and prescription of rehabilitation programs and interventions.

Full text

Original Research
S.G. Psycharakis, MSc, PhD, Institute
of Sport, Physical Education and
Health Sciences, University of Edin-
burgh, St Leonard’s Land, Holyrood
Road, Edinburgh EH8 8AQ, United
Kingdom. Address all correspon-
dence to Dr Stelios Psycharakis at:
Stelios.Psycharakis@ed.ac.uk.
S.G.S. Coleman, PhD, Institute of Sport,
Physical Education and Health Sci-
ences, University of Edinburgh.
L. Linton, PT, MSc, FASIC Sport and Ex-
ercise Medicine Clinic, University of Ed-
inburgh.
K. Kaliarntas, PhD, School of Applied
Sciences, Edinburgh Napier University,
Edinburgh, United Kingdom.
S. Valentin, MSc, PhD, Institute of
Sport, Physical Education and Health
Sciences, University of Edinburgh; and
Institute for Clinical Exercise and Health
Science, University of the West of Scot-
land, Hamilton, United Kingdom.
[Psycharakis SG, Coleman SGS, Lin-
ton L, et al. Muscle activity during
aquatic and land exercises in people
with and without low back pain. Phys
Ther. 2019;99:297–310.]
C
American Physical Therapy Asso-
ciation 2019. Published by Oxford
University Press [on behalf of the
American Physical Therapy Associa-
tion]. This is an Open Access article dis-
tributed under the terms of the Creative
Commons Attribution Non- Commer-
cial License (http://creativecommons.
org/licenses/by-nc/4.0/), which per-
mits non-commercial re-use, distribu-
tion, and reproduction in any medium,
provided the original work is properly
cited. For commercial re-use, please
contact journals.permissions@ou
Published Ahead of Print:
January 23, 2019
Accepted: July 16, 2018
Submitted: March 1, 2018
Muscle Activity During Aquatic and
Land Exercises in People With and
Without Low Back Pain
Stelios G. Psycharakis, Simon G.S. Coleman, Linda Linton,
Konstantinos Kaliarntas, Stephanie Valentin
Background. Chronic low back pain (CLBP) is the most prevalent musculoskeletal dis-
order. Aquatic exercises are commonly used by physical therapists for CLBP treatment
and management; however, there are no data on trunk muscle activation during aquatic
exercises in people with CLBP.
Objective. We quantied activation of trunk and gluteal muscles, exercise intensity, pain,
and perceived exertion in people with and without CLBP when performing water and land
exercises.
Design. The study used a cross-sectional design.
Methods. Twenty participants with nonspecic CLBP and 20 healthy participants per-
formed 15 aquatic exercises and 15 similar land exercises. Mean and peak muscle acti-
vation were measured bilaterally from erector spinae, multidus, gluteus maximus, glu-
teus medius, rectus abdominis, external oblique, and internal oblique using waterproof
and wireless surface electromyography. Exercise intensity (heart rate), perceived exertion
(Borg scale), and, for the CLBP group, pain (visual analog scale) were recorded.
Results. There were no signicant between-group differences. Signicant between-
environment differences were found in heart rate (always higher on land), exertion (higher
in the water for 3 exercises and on land for 6 exercises), and muscle activation (higher on
land in 29% and in the water in 5% of comparisons). Pain levels were low, but pain was
reported more than twice as frequently on land than in water (7.7% vs 3.7%, respectively).
Limitations. People with high levels of disability and CLBP classication were not in-
cluded.
Conclusions. People with mild-to-moderate CLBP had similar exercise responses to
healthy controls. Aquatic exercise produced sufcient muscle activation, intensity, and
exertion, and should not be assumed to be less strenuous or less effective in activating
trunk and pelvic muscles than exercise on land. These data can be used to inform design
and prescription of rehabilitation programs and interventions.
2019 Volume 99 Number 3 Physical Therapy 297
Downloaded from https://academic.oup.com/ptj/article-abstract/99/3/297/5299588 by Edinburgh University Library user on 21 February 2019

Muscle Activity in People With and Without LBP
Low back pain (LBP) is the most prevalent
musculoskeletal disorder, affecting nearly everyone at
some point during their lifetime and 4% to 33% of the
population at any given time.1,2LBP has a major impact on
quality of life and is also a cause of disability and absence
from work. For example, about 150 million working days
are lost annually in the United States because of back
pain,3whereas in the United Kingdom over 200,000
people report back pain at work at least once every year.4
LBP has also a very high economic cost, with the annual
cost in the United States, for instance, estimated at $100
billion to $200 billion.5The majority (85%) of LBP cases
are described as “nonspecic” due to a mismatch between
symptoms and radiological ndings.6Recurrence and
chronicity are common, with less than 40% of patients
being pain-free 12 months after an acute LBP episode.7
Exercise therapy on land targeting spinal and trunk
musculature commonly forms the foundation of clinical
programs for people with chronic LBP (CLBP) and has
been shown to reduce pain and disability and improve
muscle function and strength.8,9Approaches in exercise
programs include generalized graded exercise and
exercises that target the recruitment of specic muscles to
improve lumbopelvic stability, because altered neuromotor
control of the spine and pelvis10 and generalized
weakness around the hip and abdominal muscles have
been identied in this population.11 Aquatic exercise is
also often used in the management and treatment of LBP
because it has some important benets compared with
land exercise and can assist with balance, mobility, and
pain control. For example, warm water can facilitate
muscle relaxation,12 buoyancy reduces joint loads,11 and
hydrostatic pressure provides support.1Studies on aquatic
exercise have reported positive effects on patient
outcomes, such as improved function and muscular
endurance, increased spinal exibility, and reduced
absence from work.13–18
With the positive effects of exercise well documented,19
leading bodies, such as the UK’s National Institute of
Health and Care Excellence, recommend exercise in all its
forms for people with LBP.20 However, it is not yet known
which form of exercise could be superior for the
management or treatment of LBP.21 Aquatic exercise has
been reported to have similar14,18 or greater
improvements1,13,16,17 than land programs and might be
more appropriate for people with LBP, in particular for the
initial stages of rehabilitation and for those who have
difculties performing land exercises.22
Nevertheless, despite the evidence on aquatic exercise
usefulness for people with LBP, practical application of
research ndings in this area is still limited. One reason is
that the programs and exercises used in aquatic studies
are typically not well reported or not reported at all.1
Moreover, to maximize program effectiveness and
specicity, it is vital that exercises target directly the
muscles of interest. However, due to the complexities of
electromyography (EMG) measurements in the water,
knowledge of trunk muscle activation during aquatic
rehabilitation exercises is very limited. The most
commonly tested exercises are underwater walking or
deep-water running,23,24 with just a few studies
investigating a small number of rehabilitation
exercises.22,25 Furthermore, EMG studies have typically
used electrodes on 1 side of the body directly linked by
cables to external receivers. Such systems cause active
drag, affect exercise execution, and inhibit movement
disproportionally between left and right. They also provide
only unilateral information on muscle activity, a potentially
important limitation, particularly for asymmetrical
exercises.26 Finally, to our knowledge, no aquatic studies
have measured trunk muscle activity in people with CLBP.
With studies on land reporting maladaptations of the
neuromuscular system of the spine for people with CLBP27
and also differences in muscle activation between people
with and without CLBP,10 EMG data during aquatic
exercises are required for people with CLBP.
Considering the above limitations, exercise selection by
physical therapists is often arbitrary or based on anecdotal
evidence. Further research in this area with improved
methods is therefore needed to advance knowledge and
facilitate generalizability of ndings. This would provide
an evidence base to inform clinical practice and exercise
prescription, which could then lead to improved quality,
efciency, and effectiveness of exercise interventions and
rehabilitation. Thus, the aim of this study was to
investigate trunk and gluteal muscle activation, pain,
intensity, and perceived exertion during aquatic and land
exercises in people with and without CLBP.
Methods
See supplementary material online (available at
https://academic.oup.com/ptj) for full methodological
details on inclusion/exclusion criteria, exercise selection
process and rationale, identication of repetition onset,
participant familiarization, and EMG normalization and
processing.
Participants
Power calculations using GPower 3.1 showed that for a
power of 80% to detect a medium effect (f =0.25,
α-level =.05), a total sample of 34 participants would be
required.28 Therefore, 40 men volunteered for this study,
20 with nonspecic CLBP of more than 12 weeks’ duration
(mean [standard deviation, SD] values: age =33.1[6.3]
years; height =1.81[0.07] m; weight =82.6[23.4] kg; body
mass index [BMI] =23.6[1.9] kg/m2) and 20 without
musculoskeletal disorders but similar group characteristics
to those of the CLBP group (age =28.5[7.8] years; height
=1.78[0.07] m; weight =77.5[8.5] kg; BMI =24.4[2.3]).
The CLBP group mean (SD) values for the Oswestry
Disability Index questionnaire, the TAMPA scale for
kinesiophobia, and the STarT back screening (total and
298 Physical Therapy Volume 99 Number 3 2019
Downloaded from https://academic.oup.com/ptj/article-abstract/99/3/297/5299588 by Edinburgh University Library user on 21 February 2019

Aquatic vs Land Exercises for LBP
subscore) were, respectively, 21.1(11.5)%, 32.5(6.0),
1.5(1.2), and 0.7(0.7). Ethical approval was obtained from
the institutional ethics committee. All participants read the
participant information sheet and signed an informed
consent form before commencing the study.
Exercise Selection Process and Rationale
Exercises were selected based on appropriateness for
rehabilitation, following a thorough multistage process
that included open consultation with physical therapists
and beneciaries. Body movements, instructions to
participants, and cadence were standardized. The 14
exercises with upper extremity dynamic movements and
16 exercises with lower extremity dynamic movements
used in this study are described in Figure 1. Exercises will
be referred to according to their numbering in Figure 1
(eg, Ex1L, Ex1R, Ex2, etc).
The land and water environments have some fundamental
differences; eg, buoyancy acts in the opposite direction to
gravity, and water resistance is extremely difcult to
replicate on land. Therefore, when selecting land
exercises, the intention was not to create identical
conditions between the 2 environments—something that
would probably be impossible. Instead, by selecting
commonly used land rehabilitation exercises that have
very similar movement patterns to those in the water, the
aim was to provide comparisons that would be particularly
useful for professional practice and would further inform
rehabilitation program prescription for both environments.
Experimental Setup
Aquatic testing took place in a 25-m indoor pool
(depth =1.25 m, average water temperature =28◦C). For
EMG measurements, a 16-channel Mini-Wave Waterproof
EMG system (Cometa SRL, Milan, Italy) was used. This
system was wireless and waterproof, substantially
reducing active drag and movement inhibition compared
with systems with external cables connecting electrodes to
ampliers. Standard Ag-AgCl electrodes (Ambu Blue
Sensor Electrode, Ambu Ltd, St Ives, UK) were placed on
the skin on the left and right sides of the body over the
muscles erector spinae (ES), multidus (M), rectus
abdominis (RA), external oblique (OE), internal oblique
(OI), gluteus maximus (GMax), and gluteus medius
(GMed) using SENIAM guidelines29 for spinal extensors
and gluteal muscles and, in the absence of SENIAM
guidelines, recommendations by Boccia and Rainoldi30
and Huebner et al31 for abdominal muscles. EMG data
were sampled at 2000 Hz. Aquatic exercises were recorded
by 2 underwater and 2 above-water cameras (ELMO
PTC-400c, Promotivations Visual Technology, Nuneaton,
UK, 25 Hz, synchronized and genlocked). Land exercises
were recorded through a 9-camera motion capture system
(100 Hz; Qualisys Inc., Gothenburg, Sweden). These
recordings were used to identify the onset of each
repetition for subsequent EMG processing.
Data Collection
Participants undertook familiarization for the water and
land exercises in separate sessions and on different days
to those of the experimental data collection. On testing
days, each participant performed a 5-minute warm-up on
a Monarch-814 bike (Monark Exercise AB, Vansbro,
Sweden; power output 30 W at 60 rpm), followed by 12 to
15 repetitions of the exercises subsequently used for the
submaximal contractions at a self-selected comfortable
intensity. The EMG electrodes were then applied and
land-based submaximal isometric contractions performed
for EMG data normalization. Maximum voluntary isometric
contractions (MViC) were not used to normalize EMG data
due to the limitations of obtaining MViC data in a LBP
population.32 For the main data collection, exercise order
was randomized and data were collected for 10 repetitions
per exercise. The mean and peak EMG values were
calculated for repetitions 2 to 9. At the end of each
exercise, the rate of perceived exertion (RPE; Borg scale,
scored from 6 to 20), the intensity of exercise (heart rate
[HR], beats per minute; Polar Monitor, Kempele, Finland),
and, for the CLBP group, pain (visual analog scale, scored
from 0 to 10) were also recorded.
Statistical Analysis
Data normality and homogeneity of variance were
checked through Shapiro-Wilk and Levene tests (α=.05).
For each exercise, EMG comparisons between the CLBP
and control groups, and between the water and land
environments, were made using 2-way analysis of variance
with 1 between-factor and 1 within-factor
(group ×environment). Bootstrapping for non-normal
data was carried out using ttests in the post hoc
investigation of main effects of group or environment.
Because of the volume of comparisons, the post hoc
α-level was set at .01 to mitigate for the experiment-wise
error rate. Post hoc analyses were not carried out for the
interactions because the analysis of variance showed no
signicant differences. Effect sizes were calculated using
partial eta squared33 (η2), with small, medium, and large
effects classied as values of 0.0099, 0.0588, and 0.1379.
Differences between CLBP and control groups for HR and
RPE were carried out separately in water and land
environments using independent ttests (α=.05). Pain
data for land and water exercises were compared using
nonparametric methods (Wilcoxon matched-pairs
signed-rank tests; α=.05) due to skewed distributions
resulting from the many zero scores obtained.
Role of the Funding Source
The present study was funded by the Chief Scientist Ofce
in Scotland, project reference number ETM/378. The
funding source had no role in the study’s design, conduct,
and reporting.
Results
Examples of EMG data recorded during the exercises are
shown in Figures 2and 3.Figure2illustrates the mean
2019 Volume 99 Number 3 Physical Therapy 299
Downloaded from https://academic.oup.com/ptj/article-abstract/99/3/297/5299588 by Edinburgh University Library user on 21 February 2019

Muscle Activity in People With and Without LBP
Figure 1.
Description of the aquatic and land exercises used in the present study. For Exercises 1–5 (Ex 1–5), participants had the same starting position
for water and land, with feet a shoulder-width apart and knees in slight flexion (15–30◦). This lower limb position with a static pelvic posture
was maintained throughout the exercises (except Ex4 where the static foot position only was maintained). For Ex 7–11, the participants were
instructed not to move their trunk. bpm =beats per minute.
300 Physical Therapy Volume 99 Number 3 2019
Downloaded from https://academic.oup.com/ptj/article-abstract/99/3/297/5299588 by Edinburgh University Library user on 21 February 2019

Aquatic vs Land Exercises for LBP
Figure 2.
Mean muscle activity for the chronic lower back pain (CLBP) group and control group during dynamic lower limb exercise 7 (hip abduction).
ESL =left erector spinae; ESR =right erector spinae; GMaxL =left gluteus maximus; GMaxR =right gluteus maximus; GMedL =left gluteus
medius; GMedR =right gluteus medius; ML =left multifidus; MR =right multifidus; OEL =left external oblique; OER =right external
oblique; OIL =left internal oblique; OIR =right internal oblique; RAL =left rectus abdominis; RAR =right rectus abdominis.
EMG data and Figure 3the peak EMG data recorded in the
water and on land for Ex7 (hip abduction). eFigures 1 and
2 (available at https://academic.oup.com/ptj) show the
mean and peak EMG data for all exercises. The RPE, HR,
and pain data are shown in Table 1.
Differences Between CLBP and Control Groups
In most cases, muscle activation, RPE, and HR values were
not different between the CLBP and control groups. The
only exceptions were the mean left ES activations in Ex2
(P=.007; 95% CI =0.59–4.83; partial η2=0.105) and
2019 Volume 99 Number 3 Physical Therapy 301
Downloaded from https://academic.oup.com/ptj/article-abstract/99/3/297/5299588 by Edinburgh University Library user on 21 February 2019

Muscle Activity in People With and Without LBP
Figure 3.
Peak muscle activity for the chronic lower back pain (CLBP) group and control group during dynamic lower limb exercise 7 (hip abduction).
ESL =left erector spinae; ESR =right erector spinae; GMaxL =left gluteus maximus; GMaxR =right gluteus maximus; GMedL =left gluteus
medius; GMedR =right gluteus medius; ML =left multifidus; MR =right multifidus; OEL =left external oblique; OER =right external
oblique; OIL =left internal oblique; OIR =right internal oblique; RAL =left rectus abdominis; RAR =right rectus abdominis.
RPE in Ex6 (P=.022; 95% CI =0.26–3.12; partial
η2=0.133), which were greater in the CLBP group.
Differences Between Aquatic and Land
Environments
Signicant differences between environments are shown
in Table 2forEMGandinTable3for HR and RPE. There
were no differences in muscle activation between water
and land in about two-thirds of the cases. Signicantly
higher mean or peak activation for some muscles on land
was observed in ∼29% and in the water in ∼5% of
comparisons. Higher activation in the water was recorded
for left and right external oblique muscles (Ex3, Ex5), for
left rectus abdominis (Ex3, Ex4), and for erector spinae
302 Physical Therapy Volume 99 Number 3 2019
Downloaded from https://academic.oup.com/ptj/article-abstract/99/3/297/5299588 by Edinburgh University Library user on 21 February 2019

Aquatic vs Land Exercises for LBP
Tab l e 1.
Heart Rate, Rate of Perceived Exertion, and Paina
Water Exercises Land Exercises
ExercisebHRcRPEdPaine
ExercisebHRcRPEdPaine
CLBP
Group
Control
Group
CLBP
Group
Control
Group
CLPB Group CLBP
Group
Control
Group
CLBP
Group
Control
Group
CLPB Group
1L 75 (8) 70 (11) 10 (2) 9 (2) 3.4, 3.8 1L 86 (9) 89 (15) 11 (2) 10 (2) 0.9, 1.1, 1.4, 3.1
1R 73 (8) 68 (13) 10 (2) 10 (2) 1R 89 (9) 90 (15) 10 (2) 10 (2) 1.3, 1.9, 3.4
275 (9) 70 (14) 10 (2) 10 (2) 2.6 285 (11) 85 (13) 8 (2) 8 (2)
377 (9) 73 (11) 10 (2) 9 (2) 1.8 382 (11) 82 (15) 9 (2) 9 (2) 2.9
485 (7) 81 (11) 11 (2) 10 (2) 4100 (10) 99 (16) 12 (2) 11 (2) 6.9
579 (10) 76 (12) 11 (3) 10 (2) 585 (10) 89 (11) 10 (2) 9 (2) 1.6, 1.7
674 (11) 68 (11) 14 (3) 12 (3) 691 (9) 90 (12) 13 (2) 12 (3) 1.1
7L 76 (11) 72 (12) 9 (2) 9 (2) 1.4 7L 87 (10) 88 (13) 11 (2) 11 (2) 1.5
7R 76 (9) 73 (12) 10 (2) 9 (2) 0.8, 1.9 7R 87 (8) 90 (15) 11 (2) 10 (2)
8L 68 (9) 70 (12) 9 (2) 9 (2) 1.2 8L 85 (8) 88 (13) 10 (2) 9 (2) 1.8, 2.0, 6.8
8R 69 (9) 70 (13) 9 (2) 9 (2) 0.9, 1.1, 1.1 8R 85 (8) 89 (15) 10 (2) 9 (2) 1.4, 1.6, 2.4
9L 75 (11) 72 (14) 10 (2) 10 (2) 9L 89 (9) 94 (14) 12 (2) 11 (3)
9R 76 (10) 74 (12) 10 (2) 10 (3) 9R 89 (9) 92 (14) 12 (2) 11 (3)
10 80 (12) 82 (11) 10 (3) 11 (3) 10 88 (11) 90 (14) 11 (3) 10 (2) 1.2, 3.9, 4.2
11 74 (11) 70 (13) 11 (3) 11 (3) 11 80 (8) 80 (12) 12 (2) 10 (3) 1.3
aAs recorded at the end of dynamic exercises with upper extremity (exercises 1–6) and lower extremity (exercises 7–11) movements. Values are reported
as mean (SD) unless otherwise indicated. CLBP =chronic low back pain; HR =heart rate; L =left side; R =right side; RPE =rate of perceived exertion.
bRefer to Figure 1 for descriptions of exercises.
cReported as beats/min.
dReported as scores on the Borg scale (from 6 to 20).
ePain values shown are all of the nonzero values reported (on the visual analog scale, scored from 1 to 10), with blank cells indicating no pain report.
and rectus abdominis (Ex11). With the exception of Ex5,
higher activation on land was recorded for some muscles
in all other exercises. HR was higher on land for all
exercises. Perceived exertion was higher in the water for 3
exercises (Ex2, Ex3, Ex5), higher on land for 6 exercises
(Ex7L/R, Ex8L/R, Ex9L/R), and not different for the
remaining 6 exercises.
Pain in the CLBP Group
Pain level was generally low and not signicantly different
between environments (mean [SD] water pain
level =1.8[1.0]; land pain level =2.4[1.6]). Pain was
reported more than twice as frequently when exercising
on land, with 23 reports of pain on land (7.7% of cases)
and 11 reports of pain in the water (3.7% of cases).
Discussion
Low back pain affects millions of people worldwide and
causes pain, disability, and a decrease in quality of life.
Although exercise is recommended for the treatment and
management of CLBP, information on appropriateness of
rehabilitative aquatic exercises in activating trunk and
gluteal muscles is lacking. To our knowledge, this was the
rst study to measure trunk and gluteal muscle activation
in people with CLBP when performing rehabilitative
aquatic exercises, and to report the associated pain,
intensity, and perceived exertion. The inclusion of similar
land exercises and of a group of healthy controls, as well
as the use of rigorous advanced methods, provide
condence in the ndings and their practical applications.
This robust set of data can positively affect practice,
inform exercise prescription, and improve effectiveness of
rehabilitation.
In summary, the between-group comparison in the present
study showed no differences between CLBP and control
groups. The between-environment comparison revealed
no differences in muscle activation in two-thirds of the
cases, but activation was higher on land in 29% and in the
water in 5% of comparisons. HR was higher on land than
in the water, but perceived exertion showed a mixed
pattern, with neither environment producing consistently
higher values than the other. Pain levels were low but pain
was reported more than twice as frequently when
exercising on land.
2019 Volume 99 Number 3 Physical Therapy 303
Downloaded from https://academic.oup.com/ptj/article-abstract/99/3/297/5299588 by Edinburgh University Library user on 21 February 2019

Muscle Activity in People With and Without LBP
Tab l e 2.
Significant Differences Between Land and Water Environments in Mean and Peak Electromyographic (EMG)
Amplitudes for Dynamic Exercisesa
ExercisebMuscle
Significant Differencescin:
Mean EMG Peak EMG
P95% CI Effect Size P95% CI Effect Size
1L ESR .001 −6.68 to −3.56 0.529
MR .001 −4.70 to −1.97 0.358
GMaxR .001 −1.39 to −0.40 0.268
GMedR .001 −2.06 to −0.71 0.284
OER .001 −7.49 to −2.63 0.297
OIL .001 −7.59 to −3.15 0.384
OIR .001 −4.63 to −1.94 0.391 .006 −8.32 to −1.69 0.238
1R ESL .001 −6.89 to −3.58 0.493 .004 −8.14 to −2.19 0.234
ML .001 −5.80 to −2.52 0.415 .001 −8.00 to −1.60 0.250
GMedL .003 −3.49 to −1.18 0.295
OIR .008 −8.39 to −2.95 0.309
2GMaxL .004 −1.44 to −0.41 0.266
GMaxR .001 −1.65 to −0.65 0.384 .001 −2.43 to −0.87 0.293
GMedL .002 −2.22 to −0.78 0.284 .008 −3.11 to −0.89 0.201
GMedR .001 −1.98 to −0.84 0.381 .003 −2.75 to −0.84 0.254
3GMedR .002 −1.59 to −0.58 0.283
RAL .008 0.57–2.11 0.220 .003 1.97–5.48 0.257
OEL .004 1.64–3.85 0.349 .002 3.43–7.98 0.362
OER .009 1.10–2.80 0.269 .004 2.29–6.11 0.277
OIR .005 −2.78 to −0.60 0.219
4 ESL .001 −8.37 to −3.62 0.425 .002 −16.64 to −5.06 0.265
ESR .001 −9.26 to −4.10 0.373
ML .001 −7.55 to −4.10 0.536 .001 −17.07 to −8.39 0.387
MR .001 −8.88 to −4.89 0.572 .001 −21.57 to −11.41 0.444
GMaxL .001 −3.75 to −2.26 0.625 .001 −12.74 to −7.91 0.637
GMaxR .001 −3.61 to −2.44 0.715 .001 −12.53 to −8.20 0.728
GMedL .001 −3.18 to −1.28 0.358 .001 −9.88 to −3.89 0.404
GMedR .001 −2.79 to −1.08 0.341 .001 −8.74 to −3.62 0.323
RAL .001 3.07–6.91 0.418 .001 19.17–36.46 0.476
5OEL .001 1.98–3.72 0.437 .002 4.34–8.80 0.454
OER .002 1.69–3.35 0.442 .001 3.90–8.38 0.465
6 ESL .005 −4.20 to −1.37 0.299
ESR .002 −4.91 to −1.85 0.288
ML .002 −2.10 to −0.74 0.345
MR .001 −2.83 to −1.28 0.439 .001 −5.65 to −1.85 0.336
RAL .001 −35.29 to −8.76 0.517 .001 −139.60 to −72.92 0.556
RAR .001 −24.8 to −12.7 0.521 .001 −95.11 to −54.98 0.602
(continued)
304 Physical Therapy Volume 99 Number 3 2019
Downloaded from https://academic.oup.com/ptj/article-abstract/99/3/297/5299588 by Edinburgh University Library user on 21 February 2019

Aquatic vs Land Exercises for LBP
Tab l e 2.
Continued
ExercisebMuscle
Significant Differencescin:
Mean EMG Peak EMG
P95% CI Effect Size P95% CI Effect Size
OER .002 −7.78 to −1.68 0.242 .002 −27.94 to −6.31 0.267
OIL .001 −13.90 to −7.90 0.559 .001 −48.82 to −26.05 0.571
OIR .001 −15.82 to −8.38 0.545 .001 −58.28 to −29.99 0.491
7L ML .001 −5.00 to −1.74 0.288 .001 −10.32 to −3.65 0.290
GMaxR .001 −5.15 to −2.06 0.357 .002 −10.01 to −3.38 0.291
GMedR .001 −16.98 to −10.10 0.569 .002 −28.90 to −12.15 0.343
OIL .001 −6.91 to −2.93 0.376 .001 −11.27 to −4.14 0.323
OIR .001 −8.53 to −5.15 0.570 .001 −14.07 to −6.95 0.417
7R MR .001 −3.85 to −1.40 0.307 .001 −9.18 to −4.29 0.411
GMaxL .004 −5.59 to −2.04 0.352 .007 −12.66 to −4.70 0.342
GMedL .001 −11.38 to −4.99 0.349
GMedR .003 −7.31 to −2.77 0.301
OER .002 −3.32 to −1.31 0.361
OIL .001 −8.85 to −4.88 0.500 .001 −15.70 to −8.00 0.451
OIR .001 −5.90 to −3.37 0.535 .001 −10.77 to −5.86 0.515
8L ML .009 −4.04 to −0.62 0.175
GMaxL .006 −3.79 to −0.60 0.184
GMaxR .002 −2.14 to −0.73 0.250
GMedR .001 −14.42 to −9.06 0.677 .001 −24.09 to −14.24 0.589
OIL .001 −6.76 to −3.43 0.450 .001 −11.85 to −5.33 0.385
OIR .001 −7.41 to −4.41 0.574 .002 −11.40 to −6.21 0.524
8R GMaxR .008 −3.73 to −0.60 0.170
GMedL .001 −9.70 to −5.71 0.591 .001 −14.43 to −6.27 0.400
GMedR .004 −5.84 to −1.43 0.251
OER .003 −1.88 to −0.63 0.283 .007 −3.31 to −0.78 0.201
OIL .002 −7.75 to −4.15 0.495 .001 −12.56 to −6.24 0.453
OIR .001 −5.60 to −2.94 0.506 .001 −9.80 to −4.93 0.462
9L GMaxL .001 −4.45 to −2.07 0.426 .001 −10.12 to −3.67 0.347
GMedL .001 −12.21 to −6.92 0.581 .001 −20.43 to −8.84 0.392
OIL .001 −7.23 to −3.61 0.443 .001 −11.95 to −4.80 0.354
OIR .001 −3.98 to −2.02 0.490 .001 −5.97 to −2.69 0.410
9R GMaxR .001 −5.25 to −2.82 0.496 .002 −10.99 to −4.72 0.377
GMedR .001 −15.99 to −9.58 0.602 .001 −26.88 to −11.33 0.338
OIL .001 −5.29 to −2.05 0.315 .001 −8.35 to −2.83 0.296
OIR .001 −7.44 to −4.10 0.619 .001 −12.18 to −5.93 0.534
10 OIL .001 −7.57 to −3.87 0.460 .002 −19.83 to −9.44 0.441
OIR .001 −7.44 to −3.79 0.520 .001 −20.72 to −10.85 0.549
11 ESL .001 2.43–5.32 0.390 .005 1.94–7.39 0.231
ESR .002 2.49–6.09 0.328 .008 0.95–8.17 0.184
(continued)
2019 Volume 99 Number 3 Physical Therapy 305
Downloaded from https://academic.oup.com/ptj/article-abstract/99/3/297/5299588 by Edinburgh University Library user on 21 February 2019

Muscle Activity in People With and Without LBP
Tab l e 2.
Continued
ExercisebMuscle
Significant Differencescin:
Mean EMG Peak EMG
P95% CI Effect Size P95% CI Effect Size
MR .004 −3.58 to −0.56 0.201
GMedR .001 −3.04 to −1.33 0.376 .001 −9.20 to −3.55 0.349
RAL .001 3.13–6.14 0.510 .001 5.84–10.67 0.507
RAR .001 3.66–7.02 0.520 .001 6.44–12.44 0.547
aExercises included upper limb (exercises 1–6) and lower limb (exercises 7–11) movements. ESL =left erector spinae; ESR =right
erector spinae; GMaxL =left gluteus maximus; GMaxR =right gluteus maximus; GMedL =left gluteus medius; GMedR =right
gluteus medius; ML =left multifidus; MR =right multifidus; OEL =left external oblique; OER =right external oblique;
OIL =left internal oblique; OIR =right internal oblique; RAL =left rectus abdominis; RAR =right rectus abdominis.
bRefer to Figure 1 for descriptions of exercises.
cNegative 95% CIs indicate greater EMG amplitudes on land. Positive 95% CIs (shown in bold type) indicate greater EMG amplitudes in
water. Empty cells indicate no significant difference.
Tab l e 3.
Significant Differences Between Land and Water Environments in Heart Rate and Rate of Perceived Exertion During Dynamic
Exercisesa
Exerciseb
Significant Differencescin:
Heart Rate Rate of Perceived Exertion
P95% CI Effect Size P95% CI Effect Size
1L <.001 10.05–19.35 0.533
1R <.001 13.07–24.11 0.565
2<.001 7.64–16.13 0.465 <.001 −2.63 to −0.94 0.331
3<.001 2.91–12.08 0.228 .001 −1.09 to −0.13 0.151
4<.001 12.44–20.83 0.643
5<.001 4.57–13.65 0.321 .033 −1.35 to −0.06 0.117
6<.001 16.87–26.32 0.705
7L <.001 6.63–17.24 0.559 <.001 0.79–2.27 0.320
7R <.001 10.05–17.68 0.594 .001 0.63–2.08 0.278
8L <.001 13.76–20.57 0.744 .046 0.01–1.42 0.103
8R <.001 13.42–20.81 0.711 .026 0.09–1.38 0.127
9L <.001 12.90–22.73 0.600 .001 0.92–2.49 0.344
9R <.001 10.10–19.18 0.543 <.001 0.63–2.26 0.259
10 <.001 3.16–12.57 0.237
11 <.001 4.32–12.24 0.347
aExercises included upper extremity (exercises 1–6) and lower extremity (exercises 7–11) movements. L =left side; R =right side.
bRefer to Figure 1 for descriptions of exercises.
cHeart rates were always significantly higher on land. Rates of perceived exertion were significantly higher on land unless indicated otherwise. Rates of perceived
exertion (shown in bold type) were significantly higher in water. Empty cells indicate no significant difference.
Differences Between CLBP and Control Groups
The only signicant differences between the 2 groups
were the mean ES values for 1 exercise (out of 840 EMG
comparisons) and RPE for 1 exercise (out of 30
comparisons). This is well within the experiment-wise
error rate of false signicant differences expected due to
possible statistical type I error (approximately 8 false
signicant differences for EMG and 2 for RPE). Hence, it
can be stated that participants with CLBP had the same
muscle activation, HR, and perceived exertion as healthy
306 Physical Therapy Volume 99 Number 3 2019
Downloaded from https://academic.oup.com/ptj/article-abstract/99/3/297/5299588 by Edinburgh University Library user on 21 February 2019

Aquatic vs Land Exercises for LBP
controls when exercising in the water and on land.
Because this is the rst such data set for an aquatic
environment, it suggests that exercising in the water can
be benecial for rehabilitation and strengthening by
allowing people with CLBP to perform the exercises and
activate muscles without their condition adversely
affecting them.
In previous studies comparing muscle activity between
CLBP and control groups during similar land exercises,
∼80% of the comparisons showed no differences.34–36
When differences were reported, the patterns were mixed,
at times even within the same exercise, with no group
displaying consistently higher activation. Ng et al35 stated
that this possibly relates to the variance in impaired
coordination of people with CLBP and the fact that trunk
muscles can act as prime movers, antagonists, or
stabilizers. In line with some of their ndings, and
considering that several different exercises have been
tested among studies, it is also possible that slight
variations in exercises could elicit different patterns of
activation for some muscles in CLBP groups.
It is worth noting that, in the present study, participants
with CLBP exercised recreationally despite their CLBP and
were classied as having moderate disability and low risk
of kinesiophobia. This implies that they would typically
respond well to self-management37 and could further
explain the absence of between-group differences. It has
been suggested that subgrouping people with LBP based
on clinical ndings might be useful in helping to select the
most appropriate treatment.38 Thus, future research should
seek to conrm if the current ndings reect CLBP
populations with greater disability and/or fear of
movement, or even a subgroup of acute sudden-onset
pain.
Differences Between Aquatic and Land
Environments
Muscle activation. No signicant differences were found
between environments in ∼66% of all muscle activation
comparisons. There was greater activation on land in
∼29% of comparisons and greater activation in the water
in ∼5% of comparisons.
Mean Ex1 activity was greater on land for the contralateral
spinal extensors, whereas the ipsilateral spinal extensors
were not signicantly different. There was not the same
consistency for the remaining muscles, as activation was
greater on land for 3 of the 4 oblique abdominal muscles
in Ex1L, but just 1 in Ex1R. One of the reasons for the side
differences could be that there were 3 reports of pain for
Ex1R on land but none in the water. Interestingly, Ex2
showed differences for the gluteal muscles only (greater
on land), suggesting that hydrostatic pressure probably
offers sufcient support to maintain balance during
sagittal upper extremity movement despite the drag and
turbulence created. Ex3 and Ex5 that incorporated
alternating upper extremity movements required similar
activation in the water and land for the spinal extensors
and majority of gluteal muscles (except that external
oblique activation was greater in the water). Greater
activation on land was needed in spinal extensors and
gluteal muscles for Ex4, which involved a movement
assisted by gravity (land) or buoyancy (water) in the rst
phase. Hence, performing a squat with upper extremity
movement, similar to a lifting task, is perhaps initially
better trained in an aquatic environment if spinal extensor
overactivity is problematic or painful. Ex6 might pose
similar benets due to greater abdominal and spinal
extensor activity on land. If an abdominal strengthening
exercise was required for rehabilitation but a land
program was too advanced, then this water exercise could
offer a suitable intermediate step.
In the unilateral lower extremity exercises of hip
abduction, extension, and single-leg squat (Ex7–9), gluteal
activity was the same or greater on land. This might not be
surprising due to the effects of buoyancy assisting the
concentric phase, which would normally require increased
gluteal effort in the dynamically moving lower extremity
on land to control against gravity. In addition, hydrostatic
pressure offers greater support in the water, thereby
attenuating the need for gluteal activity to maintain
balance in the static supporting lower extremity. These
ndings might suggest that, to increase gluteal activity,
unilateral hip exercises should be performed on land
rather than in the water, as gluteal weakness has been
observed in patients with CLBP.11,39 The ES and RA had
greater activation in the water for Ex11, perhaps
suggesting a greater “splinting” or coactivation of the large
force-producing sagittal trunk muscles. Such a trunk
stiffening strategy has been observed in people with LBP40
and might not be desirable. However, it is also possible
that the ES and RA activity implied abdominal bracing,
because with the body being partially supported by the
dumbbells, muscles such as latissimus dorsi and iliopsoas
might have been activated more. Finally, another
possibility is that the water alternative of this exercise
required greater postural control due to buoyancy effects
displacing the dumbbells, thus making it more
challenging. In this case, the aquatic version of the
exercise could be considered as a progression of the land
exercise.
Overall, muscle activation in the water was at least similar
to that on land in 71% of all muscle comparisons. This is
contrary to some previous research ndings and
assumptions that aquatic exercise produces lower muscle
activation.22,24 It is important to note that lower activation
in the water in previous research had sometimes been
partially attributed to the challenges of waterproong
electrodes, which could cause a decrease in the recorded
EMG values in the water. The EMG system in the present
study was waterproof by design, minimizing such
2019 Volume 99 Number 3 Physical Therapy 307
Downloaded from https://academic.oup.com/ptj/article-abstract/99/3/297/5299588 by Edinburgh University Library user on 21 February 2019

Muscle Activity in People With and Without LBP
problems. Introducing an element of added resistance in
several of the aquatic exercises in the present study could
also be another reason that, contrary to previous
assumptions, activation in the water was usually not lower
than that on land. This suggestion is consistent with some
other studies, where higher muscle activity has often been
reported when resistance was added in aquatic
exercises.24,25 Although research ndings in this area
should always be interpreted with caution given the
limitations of comparing aquatic and land exercises, the
present data suggest that aquatic exercise should not be
regarded as less effective than land exercise in activating
trunk and gluteal muscles. The level of activation can be
muscle-, exercise-, or resistance-dependent. Finally, as
summarized by Bressel et al,22 levels of activation of 25%
or less have been shown to be sufcient to improve motor
control and endurance aspects of some trunk muscles, and
are of an intensity that maximally stiffens segmental joints
of the spine. Thus, the exercises that were used in the
present study seem, overall, to produce sufcient levels of
activation for subsequent improvements.
Heart rate and perceived exertion. Heart rate was
lower in the water. This was anticipated as water
immersion is generally expected to reduce HR.41 Although
comparison of HR values in the water and on land has
been reported in other studies,41 to our knowledge, the
present study is the rst in this area to compare perceived
exertion between these 2 environments. A mixed pattern
was observed, with no environment producing
consistently higher values than the other. Perceived
exertion scores for individual participants ranged from 6
to 19 (“no exertion” to “extremely hard”) in both
environments. In some exercises, when higher exertion
was recorded in 1 environment there were also more
muscles with higher activation in that environment.
However, in most exercises, higher perceived exertion for
an environment was not accompanied by higher muscle
activation, so differences in muscle activation did not
seem to be linked to differences in perceived exertion.
Pain in the CLBP group. Pain level was generally low
and not different between environments, despite a
tendency for the nonzero values to be higher on land (2.4
vs 1.8). Pain was reported more than twice as often on
land (7.7%) than in the water (3.7%), suggesting that an
aquatic environment could be more appropriate than land
for avoiding the adverse effects of pain when exercising.
In previous studies, pain level has been reported to be
either similar between environments or lower in an
aquatic environment,13,18 with 1 study reporting that the
aquatic environment produced about half the reports of
pain of the land environment.17
Right hip extension was the only aquatic exercise to have
more than 2 pain reports, albeit with the pain level being
very low (1.0). In contrast, at least 3 participants (≥15% of
the group) reported pain in one-third of all land exercises
(mean level from 1.6 to 3.5). Although this requires further
investigation to be conrmed for other CLBP groups, such
ndings are potentially relevant for patients with CLBP of
greater severity or irritability of symptoms, where
exercising in water could be the only medium where pain
can be maintained below a manageable threshold. It is
also possible that the water provided better support in
exercises such as Ex8, helping to maintain a more stable
and neutral trunk and pelvis.
Limitations and Future Directions
We examined a male CLBP population that had
mild-to-moderate disability, using exercises with specic
cadence and resistance. Future studies could expand to
participants of both sexes with different levels of disability
and classication, and explore any differences when
resistance or speed of movement are altered. The exercises
in the present study should now be used to inform
rehabilitation programs in the water and on land, and to
evaluate their effectiveness and cost-effectiveness
compared with other types of CLBP treatment and
management.
Conclusion
There were no differences between people with and
without CLBP when exercising in the water or on land.
For the between-environment comparison, HR was higher
on land but no environment produced consistently higher
values than the other for perceived exertion. Muscle
activation was different between environments in about
one-third of comparisons (greater on land in 29% and in
the water in 5% of cases). This diversity indicates that
aquatic exercises should not be assumed to be less
strenuous or less effective in activating muscles than land
exercises. Pain was reported more than twice as frequently
when exercising on land, suggesting that the aquatic
environment might be more appropriate for patients with
kinesiophobia or when pain is a limiting factor.
Author Contributions
Concept/idea/research design: S.G. Psycharakis, S.G.S. Coleman, L. Linton,
K. Kaliarntas, S. Valentin
Writing: S.G. Psycharakis, S.G.S. Coleman, L. Linton, S. Valentin
Data collection: S.G. Psycharakis, S.G.S. Coleman, L. Linton, K. Kaliarntas,
S. Valentin
Data analysis: S.G. Psycharakis, S.G.S. Coleman, S. Valentin
Project management: S.G. Psycharakis, S.G.S. Coleman, S. Valentin
Fund procurement: S.G. Psycharakis
Providing participants: S.G. Psycharakis, S.G.S. Coleman, L. Linton,
K. Kaliarntas, S. Valentin
Providing facilities/equipment: S.G. Psycharakis, S.G.S. Coleman
Providing institutional liaisons: S.G. Psycharakis, S.G.S. Coleman, L. Linton
Clerical/secretarial support: S.G. Psycharakis
Consultation (including review of manuscript before submitting):
S.G. Psycharakis, S.G.S. Coleman, L. Linton, K. Kaliarntas
308 Physical Therapy Volume 99 Number 3 2019
Downloaded from https://academic.oup.com/ptj/article-abstract/99/3/297/5299588 by Edinburgh University Library user on 21 February 2019

Aquatic vs Land Exercises for LBP
Ethics Approval
Ethical approval was obtained from the ethics committee of the Moray
House School of Education, at the University of Edinburgh. All participants
read the participant information sheet and signed an informed consent form
before commencing the study.
Funding
The present study was funded by the Chief Scientist Office in Scotland,
project reference number ETM/378.
Disclosures
The authors completed the ICJME Form for Disclosure of Potential Conflicts
of Interest and reported no conflicts of interest.
DOI: 10.1093/ptj/pzy150
References
1. Waller B. Therapeutic aquatic exercise in the treatment of low
back pain: a systematic review. Clin Rehabil. 2009;23:3–14.
2. Woolf AD, Peger B. Burden of major musculoskeletal
conditions. Bull World Health Organ. 2003;81:646–656.
3. Guo HR, Tanaka S, Halperin WE et al. Back pain prevalence
in US industry and estimates of lost workdays. Am J Public
Health. 1999;89:1029–1035.
4. Health and Safety Executive. LFS- Labour Force Survey:
self-reported work-related ill health and workplace injuries.
Index of LFS tables.
http://www.hse.gov.uk/statistics/lfs/index.htm. Accessed July
19, 2018.
5. Katz JN. Lumbar disc disorders and low-back pain:
socioeconomic factors and consequences. J Bone Joint Surg
Am. 2006;88:21–24.
6. O’Sullivan P. Diagnosis and classication of chronic low
backpain disorders: maladaptive movement and motor
control impairments as underlying mechanism. Manual Ther.
2005;10:242–255.
7. Costa LC, Maher CG, McAuley JH, et al. Prognosis for patients
with chronic low back pain: inception cohort study. BMJ.
2009;339:b3829.
8. Hides JA, Stanton WR, Mendis MD et al. Effect of motor
control training on muscle size and football games missed
from injury. Med Sci Sports Exerc. 2012;44:1141–1149.
9. Macedo LG, Latimer J, Maher CG, et al. Effect of motor
control exercises versus graded activity in patients with
chronic nonspecic low back pain: a randomized controlled
trial. Phys Ther. 2012;92:363–377.
10. D’Hooge R, Hodges P, Tsao H et al. Altered trunk muscle
coordination during rapid trunk exion in people in
remission of recurrent low back pain. J Electromyogr
Kinesiol. 2013;23:173–181.
11. Nourbakhsh MR, Arab AM. Relationship between mechanical
factors and incidence of low back pain. J Orthop Sports Phys
Ther. 2002;32:447–460.
12. Eversden L, Maggs F, Nightingale P et al. A pragmatic
randomised controlled trial of hydrotherapy and land
exercises on overall well being and quality of life in
rheumatoid arthritis. BMC Musculoskelet Disord. 2007;8:23.
13. Dundar U, Solak O, Yigit I et al. Clinical effectiveness of
aquatic exercise to treat chronic low back pain: a randomized
controlled trial. Spine. 2009;34:1436–1440.
14. Baena-Beato PA, Ártero EG, Arroyo-Morales M et al. Aquatic
therapy improves pain, disability, quality of life, body
composition and tness in sedentary adults with chronic low
back pain. A controlled clinical trial. Clin Rehabil.
2014;28:350–360.
15. Bayraktar D, Guclu-Gunduz A, Lambeck J et al. A comparison
of water-based and land-based core stability exercises in
patients with lumbar disc herniation: a pilot study. Disabil
Rehabil. 2016;38:1163–1171.
16. Bello A, Kalu NH, Adegoke BOA, et al. Hydrotherapy versus
land-based exercises in the management of chronic low back
pain: a comparative study. J Musculoskelet Res.
2010;13:159–165.
17. Granath AB, Hellgren MSE, Gunnarsson RK. Water aerobics
reduces sick leave due to low back pain during pregnancy. J
Obstet Gynecol Neonatal Nurs. 2006;35:465–471.
18. Sjogren T, Long N, Story I et al. Group hydrotherapy versus
group land-based treatment for chronic low back pain.
Physiotherapy Res Int. 1997;2:207–217.
19. Hettinga DM, Jackson A, Moffett JK, et al. A systematic review
and synthesis of higher quality evidence of the effectiveness
of exercise interventions for non-specic low back pain of at
least 6 weeks’ duration. Phys Ther Rev. 2013;12:221–232.
20. National Institute of Health and Care Excellence. Low back
pain and sciatica in over 16s: assessment and management.
https://www.nice.org.uk/guidance/ng59/chapter/Recommen
dations. Published November 2016. Accessed July 19,
2018.
21. Van Middelkoop M, Rubinstein SM, Verhagen AP et al.
Exercise therapy for chronic nonspecic low-back pain. Best
Pract Res Clin Rheumato. 2010;24:193–204.
22. Bressel E, Dolny DG, Gibbons M. Trunk muscle activity
during exercises performed on land and in water. Med Sci
Sports Exerc. 2011;43:1927–1932.
23. Kaneda K, Sato D, Wakabayashi H et al. EMG activity of hip
and trunk muscles during deep-water running. J
Electromyogr Kinesiol. 2009;19:1064–1070.
24. Masumoto K, Takasugi S, Hotta N et al. Muscle activity and
heart rate response during backward walking in water and
on dry land. Eur J Appl Physiol. 2005;94:54–61.
25. Colado JC, Tella V, Triplett NT. A method for monitoring
intensity during aquatic resistance exercises. JStrengthCond
Res. 2008;22:2045–2049.
26. Bressel E, Dolny DG, Vandenberg C et al. Trunk muscle
activity during spine stabilization exercises performed in a
pool. Phys Ther Sport. 2012;13:67–72.
27. Cholewicki J, Siles SP, Shah RA, et al. Delayed trunk muscle
reex responses increase the risk of low back injuries. Spine.
2005;30:2614–2620.
28. Faul F. GPower 3.1.9.2. Universität Kiel: 2014.
29. Seniam. Recommendations for sensor locations on individual
muscles. http://www.seniam.org. Accessed July 19, 2018.
30. Boccia G, Rainoldi A. Innervation zones location and optimal
electrodes position of obliquus internus and obliquus
externus abdominis muscles. J Electromyogr Kinesiol.
2014;24:25–30.
31. Huebner A, Faenger B, Schenk P et al. Alteration of surface
EMG amplitude levels of ve major trunk muscles by dened
electrode location displacement. J Electromyogr Kinesiol.
2015;25:214–223.
32. Dankaerts W, O’Sullivan PB, Burnett AF et al. Reliability of
EMG measurements for trunk muscles during maximal and
sub-maximal voluntary isometric contractions in healthy
controls and CLBP patients. J Electromyogr Kinesiol.
2004;14:333–342.
33. Richardson JTE. Eta squared and partial eta squared as
measures of effect size in educational research. Educ Res
Review. 2011;6:135–147.
34. Marshall PWM, Desai I. Electromyographic analysis of upper
body, lower body, and abdominal muscles during advanced
swiss ball exercises. J Strength Cond Res. 2014;24:
1537–1545.
35. Ng JKF, Richardson CA, Parnianpour M et al. EMG activity of
trunk muscles and torque output during isometric axial
rotation exertion: a comparison between back pain patients
and matched controls. JOrthopRes. 2002;20:112–121 02.
2019 Volume 99 Number 3 Physical Therapy 309
Downloaded from https://academic.oup.com/ptj/article-abstract/99/3/297/5299588 by Edinburgh University Library user on 21 February 2019

Muscle Activity in People With and Without LBP
36. Siles SP, Squillante D, Maurer P, Westcott S et al. Trunk
muscle recruitment patterns in specic chronic low back
pain populations. Clin Biomech. 2005;20:465–473.
37. Foster NE, Mullis R, Hill JC, et al. Effect of stratied care for
low back pain in family practice (IMPaCT Back): a
prospective population-based sequential comparison. Ann
Fam Med . 2014;12:102–111.
38. Long A, Donelson R, Fung T. Does it matter which exercise?
A randomized control trial of exercise for low back pain.
Spine. 2004;29:2593–2602.
39. Cooper NA, Scavo KM, Strickland KJ et al. Prevalence of
gluteus medius weakness in people with chronic low back
pain compared to healthy controls. Eur Spine J.
2016;25:1258–1265.
40. Brumagne S, Janssens L, Knapen S et al. Persons with
recurrent low back pain exhibit a rigid postural control
strategy. Eur Spine J. 2008;17:1177–1184.
41. Lazar JM, Khanna N, Chesler R, Salciccioli L et al. Swimming
and the heart. Int J Cardiol. 2013;168:19–26.
310 Physical Therapy Volume 99 Number 3 2019
Downloaded from https://academic.oup.com/ptj/article-abstract/99/3/297/5299588 by Edinburgh University Library user on 21 February 2019