S T U D Y P R O T O C O L Open Access
The PICO project: aquatic exercise for knee
osteoarthritis in overweight and obese individuals
, Margarida Espanha
, Filomena Vieira
, Stephen P Messier
, Cristina Monteiro
and Antonio P Veloso
Background: Aquatic exercise is recommended by the Osteoarthritis Research Society (OARSI), by the
American College of Rheumatology (ACR) and by the European League Against Rheumatism (EULAR) as a
nonpharmacological method of controlling the knee osteoarthritis (KOA) symptoms. Moreover, given that weight
loss results in a reduction of the load that is exerted upon the knee during daily activities, obesity is also considered
to be a modifiable risk factor for the development and or exacerbation of KOA. The implementation of an exercise
based weight loss program may, however, itself be limited by the symptoms of KOA. The aquatic program against
osteoarthritis (termed “PICO”in Portuguese) prioritizes the control of symptoms and the recovery of functionality,
with an attendant increase in the patient’s physical activity level and, consequently, metabolic rate. Our laboratory is
assessing the effectiveness of 3 months of PICO on the symptoms of KOA, on physical function, on quality of life
and on gait. In addition, PICO shall examine the effects of said exercise intervention on inflammatory biomarkers,
psychological health, life style and body composition.
Methods/Design: The trial is a prospective, single-blinded, randomized controlled trial, and involves 50 overweight
and obese adults (BMI = 28–43.5 kg/m
; age 40–65 yrs) with radiographic KOA. The participants are randomly
allocated into either an educational attention (control) group or an aquatic (exercise program) group. This paper
describes the experimental protocol that is used in the PICO project.
Discussion: The PICO program shall provide insight into the effectiveness of an aquatic exercise program in the
control of KOA symptoms and in the improvement of the quality of life. As such, they are likely to prove a useful
reference to health professionals who intend to implement any kind of therapeutic intervention based around
Trial registration: NCT01832545.
Keywords: Aquatic exercise, Knee osteoarthritis, Exercise, Pain, Obesity
Although rheumatic diseases (RD) have low death rates,
they are one of the primary causes of compromised
quality of life and absenteeism from work, with attend-
ant economic and social consequences . In Portugal,
RD are responsible for 40 to 60% of situations of pro-
longed physical incapacity in daily activities, for 43% of
cases of absenteeism from work, and for 35 to 41% of
early retirements due to illness .
Osteoarthritis (OA) is the most prevalent rheumatic
disease and represents a great risk to the quality of life
of the individual, given the consequent loss of autonomy
that can be precipitated by its effect on lower extremity
based activities (such as walking up and down stairs,
climbing and squatting) [1,3,4]. Although the causes of
OA are not completely understood, it is thought to be a
complex, adaptive response of the joints to biomechan-
ical, genetic and environmental stresses . Recent stud-
ies demonstrated that that low-grade inflammation plays
a pathophysiological role in OA. The severity, the symp-
toms, the impairment in physical function and the
* Correspondence: email@example.com
Department of Sports and Health, Univ de Lisboa, Fac Motricidade Humana,
CIPER, LBMF, P-1499-002 Lisbon, Portugal
Full list of author information is available at the end of the article
© 2013 Yázigi et al.; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited.
Yázigi et al. BMC Musculoskeletal Disorders 2013, 14:320
progression of OA may also be partly mediated by the
extent of chronic inflammation in OA patients [6,7].
The knee is the most commonly affected weight bear-
ing joint, being considered the 4
main cause of
disability in women and men, respectively . KOA is
more common in the medial tibiofemoral compartment
than in other sites of the knee, probably due to a higher
frequency of varus malalignment . Inflammation and
joint loading are commonly believed to cause or to ex-
acerbate the disease process . Obesity, prior knee
injury, physical activity levels, physical strength and the
extent of alignment/misalignment of body segments are
the most often cited potential risk factors for KOA in
the academic literature. The latter risk factor seems to
have more importance in the radiographic progression
than in the incidence of KOA [11-14].
Knee Osteoarthritis (KOA) is highly prevalent in obese
individuals . The International Association for the
study of Obesity (IASO)/International Obesity Taskforce
(IOTF) analysis (2010) estimated that approximately 1.0
billion adults are currently overweight and a further 475
million are obese, worldwide . Obese individuals
have higher concentrations of the inflammatory markers
(such as TNF-αand leptin) that are predominantly se-
creted by adipose tissue and can induce the production
of IL-6 and C-reactive protein (CRP) . The patho-
genesis of obesity is characterized by hypothalamic in-
flammation and subsequent central resistance to leptin.
High leptin concentrations then compromise the reduc-
tion of food intake and increase in energy expenditure.
In addition, leptin increases the synthesis of a stimulator
of osteophyte formation, TNF-β. The resulting low-
grade inflammation plays a pathophysiological role in
OA, because it can affect muscle function and lower the
individual’s pain threshold. It can also affect chondrocyte
homeostasis and cause degenerative changes in cartilage
Besides its effect on the individual’s quality of life,
KOA uses up considerable health care resources. The
consequences of KOA make it a public health problem
in many countries [1,20-22]. Pain is the symptom that
markedly affects quality of life in KOA patients. Gait
tests are an important measure of mobility and KOA pa-
tients may adapt their gait and adjust body alignment to
reduce pain. However, the latter adaptations may in-
crease the loading on the joint and result in increased
disease progression. In addition, the pain that is con-
comitant with KOA causes irritability, sleeplessness, de-
pression and other physical and psychological changes
that may aggravate the disease and incur both a general
loss of functionality and a drop or maintenance in phys-
ical activity levels to below the recommended levels .
The main consequences of inactivity are weight gain and
the obesity installation . The combination of obesity
and KOA create a vicious cycle of pain, loss of function-
ality, and disease progression. To interrupt this cycle,
KOA symptoms should be reduced. Physical activity and
weight loss can make an important contribution.
Current therapy most often focuses on pain relief, using
mainly analgesics and nonsteroidal anti-inflammatory med-
ications that have only a modest functional benefit and do
not slow disease progression, whilst causing serious cardio-
vascular and gastrointestinal side effects [25,26]. The rec-
ommendations of the Osteoarthritis Research Society
International (OARSI), the American College of Rheuma-
tology (ACR), and the European League Against Rheuma-
tism (EULAR) also include exercise as an important
treatment [27-29]. Aerobic, aquatic, and resistance training
exercise are recommended .
Exercise program and Knee OA
Appropriate exercise can provide an improvement in
symptoms and reduce pain, preventing OA-associated dis-
abilities and increasing quality of life. In addition, there
seems to be a positive effect of exercise on the chondro-
protective anti-inflammatory cytokine response , me-
diated by IL-10 and IL-4. The weight loss and body
composition improvements that can induced by exercise,
reduce the thigh fat depots and may have a positive effect
on the secretion of pro-inflammatory cytokines, lowering
IL-1 and leptin levels in individuals with KOA .
The literature indicates that an exercise intervention
for KOA should be broadly based and include aerobic
training, lower limb-strengthening, gait training, flexibil-
ity, stability and posture training, weight reduction, pa-
tient education and psychosocial intervention [27,31-34].
Aquatic exercise is at this moment one of the main
non pharmacological interventions that is suggested by
the OARSI, ACR and EULAR guidelines as a means of
controlling the symptoms and to prevent or slow down
the progression of KOA [26,27,35]. Various studies have
demonstrated that controlled aquatic exercise classes
can be effective for KOA symptom control and to im-
prove function [36-43]. In addition, a person in pain has
difficulty with weight bearing exercise. Aquatic exercise
allows aerobic exercise to be accomplished with less load
on the joints .
Several studies have examined the effects of exercise
in water (hydrotherapy, aquatic exercise) on the symp-
toms of knee arthritis [36-40,44-51]. However, said stud-
ies are inconsistent as regards the quality and quantity
of exercise that was performed. There is a lack of defin-
ition of what is involved in hydrotherapy and what is
performed in aquatic exercise classes. Aquatic Exercise
(AE) is an exercise modality which can be defined as a
group of exercises performed in the water, mainly in the
vertical position, with or without music, with or without
equipment added and in shallow or deep water. Its main
Yázigi et al. BMC Musculoskeletal Disorders 2013, 14:320 Page 2 of 14
characteristics are the utilisation of hydrostatic pressure
and hydrodynamics to work on the aerobic and neuro-
muscular system. AE has been used for rehabilitation
(hydrotherapy) [52-59], for athletic training [60-64] or
for general fitness activity [65-71].
Aerobic training is very important for pain control and
to improve functionality in individuals with KOA .
According to the guidelines of the Aquatic Exercise As-
sociation (AEA) , aerobic aquatic exercise classes
with fitness goals, should be performed in water between
28-30°C so as not to compromising the endocrine
responses. Water temperatures above 32°C are recom-
mended for passive work, relaxation techniques or for
individuals with low movement levels, but are not advis-
able temperature for aerobic or strength based exercise
. In cases of patients with low aquatic abilities, the
Arthritis Foundation Guidelines suggest a superior limit
range of water temperature of 31°C .
The PICO program is an overall body fitness and
mind based intervention through aquatic exercise in-
volving an educational component that has been specif-
ically created for individuals with KOA. Two recent
studies regarding the aquatic exercise in KOA should be
referred to [38,39], as they have a controlled method-
ology and were performed according to the AEA guide-
To design an aquatic exercise program specific to knee
osteoarthritis, with the goal of management of OA
symptoms and the improvement of physical fitness.
The PICO program is based around the first step for
weight loss interventions in individuals with KOA be-
ing the control of pain and other symptoms. When
KOA symptoms are controlled, patients learn that it is
possible to live with the disease which in turn moti-
vates lifestyle changes. The increase of physical activity
due to lifestyle changes may then cause improvement
in body composition. In this way 6 hypotheses are for-
mulated: H1. 3 months of aquatic exercise will improve
KOA symptoms (pain and stiffness) and physical func-
tion in obese individuals with KOA; H2. The gait pa-
rameters (gait speed, gait cycle, ground reaction forces
and knee forces moments) of obese individuals with
KOA can be improved by aquatic exercise; H3. Beyond
fitness component and the exercises skills, aquatic ex-
ercise group classes can work as an educational com-
ponent and to promote lifestyle changes. H4: The
aquatic exercise program can improve mental status
and quality of life. H5: The aquatic exercise program
can cause a weight reduction or body composition
change. H6: 3 months of aquatic exercise can have a
positive effect on selected inflammatory biomarkers of
PICO is a single-blinded, randomized controlled trial with
3 months duration. Participants will be randomly assigned
to one of two groups: aquatic exercise (AE) and control
group (CG). Figure 1 provides a flowchart of PICO design.
Researchers and personnel responsible for data collection
will be blinded four the group classes. The study protocol
was approved by the Ethical Committee of the Faculty of
Human Kinetics, Technical University of Lisbon. All partic-
ipants will be informed about the procedures and potential
risks and an informed consent will be obtained from them.
Considering the calculation of the sample size, the studies
of Messier (2009)  and Wang (2007)  were used as
a reference, because they had a sample with similar charac-
teristics and studied similar outcomes. Both showed that a
reduction of symptoms in patients with OA of the knee led
to a significant improvement (α< 0.05) of the primary out-
come measure of self-reported physical function. To find
an analogous improvement of self-reported physical func-
tion of approximately 25% between the baseline and final
measurements in patients with KOA, the minimum num-
ber of patients that are required is 20 for the main out-
comes. The latter number is based on a power (1-B) of
0.80 and a significance level of 5% (two-sided). When a
dropout rate of 20% is taken into account, at least 25 par-
ticipants must be involved at study onset.
The study sample will consist of 56 community-dwelling
adults from the Lisbon area with: (1) age between 40
and 65 years; (2) 28.0 ≤BMI ≤45 kg/m
; (3) unilateral or
bilateral KOA diagnosed by knee pain and grade I-III
radiographic tibiofemoral OA or tibiofemoral plus patel-
lofemoral OA (4) a sedentary lifestyle, defined as not
participating in a program that incorporates more than
30 minutes per week of formal exercise, within the
6 months leading up to the study; (5) being independ-
ently mobile; and (6) literate.
The exclusion criteria are: subjects with skin diseases, with
unstable medical conditions and or who have undergone
hip or knee replacement, or knee surgery within the
6 months prior to the study; and participants who had any
type of knee injections within the past 3 months.
The recruitment and selection process will be done ac-
cording to the aforesaid eligibility criteria. To avoid
Yázigi et al. BMC Musculoskeletal Disorders 2013, 14:320 Page 3 of 14
convenience sampling different documents will be cre-
ated for advertising and publicizing the PICO project.
Social networks, television interviews, newspapers and
the collaboration of entities/companies will be the main
channels for PICO announcements.
All eligible individuals who contact the study secretariat
will go through the same selection process, namely: a tele-
phone based pre–selection stage followed by a face to face
interview and completion of the screening questionnaire
which will supply information about demographics and
symptoms, signs and risk factors for KOA occurrence.
Volunteers who, after completing the questionnaire, fulfill
the ACR criteria for clinical diagnosis  will receive a
request for an x-ray examination. The exams will be re-
ferred to a rheumatologist who will make the final diagno-
sis according to ACR radiological criteria. In the case of
confirmation of the KOA diagnosis, the subject will be
invited to a further interview the purpose of which is
Figure 1 PICO flowchart.
Yázigi et al. BMC Musculoskeletal Disorders 2013, 14:320 Page 4 of 14
detailed explanation of the project, obtaining his/her in-
formed consent and familiarization with both the locale
and the equipment which shall be used in the tests.
Aquatic exercise (AE)
The aquatic program is based on the guidelines of
OARSI and EULAR for KOA management [28,29], on
the Aquatic Exercise Association Guidelines (AEA) ,
on the Arthritis Foundation Aquatics Program instruc-
tor’s manual , on the ACSM’s Guidelines for Exercise
Prescription  and on analysis of the protocols of pre-
vious studies [36,38,39,44,77,78].
The strategies in the PICO proposal to produce a high
quality aquatic exercise intervention are structured ac-
cording to AEA guidelines  and include overload
assessment and managements, impact level control (level
1, 2 or 3), exercise cadence control and adequate music
according to exercise goals. In addition the use of differ-
ent and pre-defined cool-down sessions each week, a
strong motivational component and pain assessment
should make the difference in this protocol. Educational
themes shall also be addressed during the classes. One
educational theme per week shall be reinforced, such as:
What did you have for breakfast? Let’s try, during this
week, to improve the quality of our breakfast. Next class
I will check what you ate; remember that you should as-
sess yourself about knee pain, let’s try to learn how to live
Another aspect that will be considered is the level of
aquatic ability of each participant. Exercises like under-
water breathing and flotation will be used in small doses
to reduce fear of water and to ensure that participants
are comfortable moving around the pool.
The aquatic program will be organized into 24 sessions
distributed over 12 consecutive weeks, with a frequency
of twice a week. The duration of each session will be
60 minutes, being that 10 minutes are for patient recep-
tion, blood pressure control, pain registry etc., and the
effective time inside the water is 45 minutes. The indoor
pool works with an air temperature around 27 ± 1°C and
water temperature is controlled at 30.5 ± 0.5°C.
Table 1 describes the aquatic exercise class format for
the first four weeks. Workouts are organized in order to
have a progressive overload every week. Water is the
main instrument to create resistance and only in the last
week, according to the level of progression of the partic-
ipants and whether their self-reported pain is controlled,
Table 1 The aquatic exercise protocol design for the first 4 weeks of the PICO program
Music BPM Week1-5
(128 bpm) Week 1 Week 2 Week 3 Week 4
Walking combined with
static and gentle movements
of main joints. Use hands
to keep thermal comfort
with static and gentle
movements of main
Walking combined with
static and gentle
movements of main joints
with static and gentle
of main joints
Aquatic adaptation Vertical balance Vertical balance Submersion Submersion
Travellings Travellings Underwater breathing Underwater breathing
Duration 3x5min 4x5′4x5′(1x10′)+5′+5′
Exercise pattern Walking patterns with variation
of upper limb patterns
Walking patterns with
variation of upper limb
Walking patterns with
variation of upper limb
10′walking patterns + (2x5′)
de basic aquatic patterns
(Jumping jack, Ski, Leg
Curl and Kicks)
57%-67% RPE 4-6 57%-67% RPE 4-6 57%-67% RPE 4-6 64-74% RPE 5-6
Impact level 1111
Repetitions 2x8 1 x16 2x16 2x16
Cadence t1 = water tempo t1 = water tempo t1 = water tempo t1 = water tempo
tt = land tempo
Sets interval Active 1-2′Active 1-2′Active 1-2′Active 1-2′
added No No No No
(Omni-RES) 6-7 6-7 6-7 6-7
(5-6′)Static stretching on the wall Static stretching
(center) Dance + Dynamic/static
RPE- Rate of perceived exertion scale.
Yázigi et al. BMC Musculoskeletal Disorders 2013, 14:320 Page 5 of 14
will additional equipment be added to increase the water
resistance and consequently, the exercise overload. The
Omni - Perceived Exertion Scale for Resistance Exercise
(OMNI-RES) and for aerobic target zone (0–10 Borg
Scale) will be used according guidelines for exercise
intensity management .
The exercise instructors will use behavioral techniques:
1) to encourage social contact between participants; 2) to
promote frequent contact during all intervention phases;
3) to define clear behavioral goals and allow feedback on
achievements; 4) to help participants to self-monitor their
pain and exercise intensity to complete activity; 5) to
establish personal commitment to the project through the
Educational program: control group (CG)
The control group will not be enrolled in any exercise pro-
gram but will participate in the educational program
“PESO comunitário”. This program is based on appropri-
ate clinical guidelines and on validated behavior change
principles . Implemented by an intervention team with
expertise gained from current scientific research in weight
control determinants, this program, as is PICO, is free of
charge for all interested adults who wish to manage their
weight and health. It has operated since 2005 with the ob-
jective of preventing obesity or reducing excess weight as
well as some of the risk factors for adult obesity, via
through a change to steady healthy habits, attitudes and
behaviors. PESO lasts 3 months and comprises 12 sessions
of one and a half hour, on a weekly basis.
The Knee Osteoarthritis Pre-Screening questionnaire
(KOPS) was validated by the authors and considered use-
ful for this purpose (article in submission process). KOPS
addresses physical function, activity level, co-morbid dis-
eases, KOA risk factors and symptoms, height and weight
(to determine BMI) as well as caregiver status. The demo-
graphic data that are collected include data on occupation,
income, and educational level. The medical form is used
to determine co-morbidities and to analyze any self-
reported information on medications. The overall KOPS
score has acceptable to good reliability with a Cronbach’s
Alpha of 0.747 and satisfactory internal consistency with
an Intraclass Coefficient (ICC) for average measures of
0.646. The results for test-retest of one-week interval for
each component ranged from 0.895-0.992 for ICC and
from 0.894 to 0.979 for Cronbach’sAlpha.
Osteoarthritis diagnosis and severity classification
To confirm OA and classify its severity the same X-ray
protocol will be used for all subjects. Bilateral, anterior-
posterior, weight-bearing knee radiographs will be used
to identify OA in the tibiofemoral joint, and sunrise
views to identify OA in the patellofemoral compartment.
Severity of tibiofemoral OA will be measured using the
K-L grading scale .
Outcomes, measures and instruments
All tests will be performed by all subjects at both base-
line and 3 month later, at the end of the exercise inter-
vention, using the same protocols and evaluated by the
PICO team member(s). Tests list can be checked in the
Table 2. The tests and questionnaires will be distributed
over two nonconsecutive days, taking the fatigue levels
of the subject and the need to avoid overload into ac-
count. Therefore the knee strength test and the Six
Minute Walking Test will be conducted on different days.
The main outcomes will be KOA symptoms (pain and
stiffness) and quality of life, physical function (aerobic
Table 2 Tests list
ASSESSMENT (TEST) Screening Baseline 3
KOPS x x
Knee X-ray (lateral and
KOA symptoms and quality of life
Pain assessment (Brief pain inventory) x x
Knee osteoarthritis associated quality
of life (KOOS) xx
MOS (SF-12v2) x x
(Beck depression inventory) xx
Weight and lifestyle inventory x x
Physical function and gait
Aerobic capacity (6MWT) x x
Strength x x
Functional (FRSTS) x x
Knee (BIODEX dynamometer) x x
Hand (grip dynamometer) x x
Flexibility (CRS and BS tests) x x
Gait Analysis (Kinematics and kinetics) xx
Morphology and body composition
Body composition (DXA scan) x x
Physical activity level (IPAQ) x x
Cytokines (blood drawn) x x
Yázigi et al. BMC Musculoskeletal Disorders 2013, 14:320 Page 6 of 14
capacity, strength, and flexibility) and gait (kinetics and
kinematics). The secondary outcomes are body compos-
ition, morphology, physical activity level, and inflamma-
tory biomarkers. During the study, all participants will be
allowed to maintain their usual medication, including an-
algesics and NSAIDs. A detailed record of medication will
be done at baseline and 3 month post-intervention testing.
Knee OA symptoms and health quality of life
Brief Pain Inventory (BPI) –short version. A
consensus panel, the Initiative on Methods,
Measurement, and Pain Assessment in Clinical Trials
(IMMPACT) recommended the inclusion of the short
version of Brief Pain Inventory (BPI) in all trials that
intend to assess chronic pain . It is a widely used,
reliable, valid instrument that assesses pain history,
location, intensity and its interference with daily
activities in individuals with osteoarthritis . The
Portuguese version was validated and recent studies
have provided strong support for its reliability and
Numerical Rating Scale (NRS). The subjects shall
learn to self-assess their knee intensity pain via the
0–10 point NRS. The NRS should be used to control
pain intensity before and after the aquatic exercise class
and whenever is necessary.
Knee Injury and Osteoarthritis Outcome Score
(KOOS). This questionnaire includes 5 dimensions to
measure KOA specific health-related quality of life
(QOL), knee pain (Pain), other disease-specific
symptoms (Other Symptoms), activities of daily living
(ADL), sport/recreation function (Sport/Rec). A score
in each of the five dimensions is calculated as the sum
of the items included and then converted according to
a0–100 scale, with 0 representing extreme knee
problems and 100 representing no knee problems. The
KOOS is validated for patients with knee injury or with
knee OA and is a reliable and responsive self-administered
instrument for short-termfollow-up . The
Portuguese validation has acceptable reliability with
Cronbach’s alpha coefficients between 0.77 and 0.95,
Medical Outcomes Study (MOS) Short-Form Health
Survey (SF-12v2). SF-12 v2 consists of a subset of 12
items to assess health status, organized into two
domains: Physical (Physical Component Summary,
PCS) and Psychological (Mental Component Summary,
MCS) that make up the original SF-36 . It has been
shown that the SF-12 correlates highly with SF-36
in both obese and non-obese patients . The
Portuguese version of SF-12 has satisfactory reliability
and validity [89,90].
Beck Depression Inventory (BDI-II). This
instrument, developed by Beck and colleagues has
21 items to rate the severity of depression according to
the clinical definition. It is one of the most popular and
widely used instruments for assessing the severity of
depressive symptomatology. The Portuguese version
 shows a good internal consistency, a factor
structure very similar to the original version [91,93],
and an adequate convergent validity.
Six Minutes Walking Test (6MWT). The distance (d)
and gait speed (v) of the 6MWT is used to assess the
aerobic capacity and the walking ability. It will be
performed individually and according to the American
Thoracic Society protocol (ATS) , in a controlled
indoor environment 46 meters in length and
rectangular in shape. The 6MWT is highly
reproducible in obese individuals (r = 0.926; 95% CI
0.816-0.972, P < 0.001) , and it has been used in
studies with KOA [75,96-100].
Chair Sit and Reach test (CSR). The CSR test is a
safe and socially acceptable alternative to traditional
floor sit-and-reach tests as a reasonably accurate and
stable measure of hamstring flexibility . The sub-
jects shall be allowed three attempts for each limb and
the best of these scores shall be recorded to the nearest
The Back Scratch Test (BS). The BSS is a measure of
overall shoulder range of motion which involves
measuring the distance between (or overlap of ) the
middle fingers behind the back with a ruler . After
a familiarization trial, this test is assessed twice,
alternately with both hands, and the best value of each
Five-Repetition Sit-To-Stand Test (FRSTST). This is a
widely used measure of functional strength. ICC values
for it demonstrate from good to high test-retest
reliability for adults and subjects with osteoarthritis
Knee Strength. A dynamometer Biodex System III
(Biodex Medical Inc., Shirley, NY, U.S.A.) will be used
for isokinetic assessment of knee strength (flexor and
extensor muscles) and isometric knee strength,
bilaterally. The first leg to be tested shall be the less
affected leg or, in doubtful cases, the dominant leg.
Gravity correction to torque is calculated at 45 degrees
(0 = straight leg). The range of motion for testing is
pre-determined from 20° to 80° for all subjects. The
exclusion of extreme ranges of knee motion was
Yázigi et al. BMC Musculoskeletal Disorders 2013, 14:320 Page 7 of 14
established due to the fact that they are known to be
painful and frequently non-executable by these patients,
namely full extension due to quadriceps weakness
Similar procedures, according to the dynamometer
used, have been adopted in other surveys involving the
same population [105-110].
Maximal Isokinetic Strength is measured on a
concentric/concentric mode, at angular velocity of 60°/s.
Among the low velocities’group, the 60°/s have been
used in other studies and should provide better stability
for this population . The subjects should perform
one set with minimum overload for habituation and 2
sets of 3 repetitions with a 120-second rest between sets.
The subjects should be oriented to perform the test by
exerting maximum pressure on the isokinetic arm
through the entire range of movement. During the test
vigorous verbal encouragement shall be given to each
subject. The set with higher extension peak torque
together with the lowest coefficient of variation will be
chosen for analysis.
The angle of best torque of the knee extension
obtained from each subject in the isokinetic test should
be chosen for the isometric test. Maximal knee
extension isometric test will be applied in one set of 3
repetitions during 5 seconds with 30 seconds relaxation
interval between repetitions. The best of the three
force-time curve will be chosen according to the higher
Prior to measurement, the subject shall be are seated
on the dynamometer with knee and hip joints at 90°.
Crossover shoulder, belly and knee straps, as well as a
lap belt will be used to restrain the subjects movement.
The lever arm pad is strapped around the lower leg, 2
centimeters above the lateral malleolus of the fibula.
The axis of rotation of the dynamometer should be
aligned with knee joint’s axis of rotation. Joint warm-up
will be done by gentle free movements of flexion and
extension of the knee.
The Handgrip Strength Test (HST). This test evaluates
maximal isometric force of the muscles of the hand
and forearm. Although the sample of this study will not
have hand OA, this test has been used in obese
individuals as an indicator of total body strength and
functionality [112,113]. The adopted protocol for this
project is the same that was used for Portuguese adults
in the national observatory . Prior to the test, the
grip dynamometer should be adjusted to the size of the
hand of each subject. Subject will be standing with
arms along the body without contact with the trunk
and elbow slightly bent at 200°. Testing is first done by
dominant hand followed by the non-dominant one.
The force must be performed during the expiratory
phase and valsalva maneuver should be avoided. After
three trials, if the difference between each value is
within 3 kg, the test is considered completed. If a
bigger difference is observed, then the test will be
repeated after sufficient rest time. The best repetition
will be chosen for further analysis.
Morphology and body composition
Body composition. Body mass index will be calculated
as mass (measured in kilograms by a standard
calibrated scale) divided by height squared (measured
in meters). A DXA scanner (QDR 4500A, fan-beam
densitometer, software version 8.21; Hologic, Waltham,
USA) will be used to measure whole body lean mass
(LM), fat mass (FM) and bone mineral content (BMC).
DXA measures the attenuation of X-rays pulsed
between 70 and 140 kV synchronously with the line
frequency for each pixel of the scanned image. According
to the protocol described by the manufacturer, a step
phantom with six fields of acrylic and aluminum of
varying thickness and known absorptive properties
shall be scanned alongside each subject to serve as an
external standard for the analysis of different tissue
components. The same technician shall position the
subjects, perform the scans and execute the analysis
using the standard analysis protocol. Based on test-retest
using 10 subjects, the coefficient of variation (CV)
in PICO staff for FM and FFM was 2.6 and 1.5%
respectively, and the total error of measurement (TEM)
and the CV were 0.02 kg and 1.7% respectively.
Anthropometry. The anthropometric measurements
that shall be collected by this study shall include
height, body mass, perimeters (waist, hip, middle thigh,
patella shank and foot breadth. The aforesaid measures
shall be collected by an ISAK accredited
anthropometrist using procedures established by ISAK
 except in the case of patellar circumference, foot
diameter and abdominal sagittal diameter, which shall
be obtained according to previously validated
procedures [116-118]. The intra-observer technical
error for circumferences and diameters measures in the
pilot study ranged from 0.2 -0.4.
The gait protocol used on the present study was adapted
from IDEA study , taking into account our labora-
tory specific equipment.
Data collection and analysis: Motion capture of the gait
will be collected with 10 cameras Qualisys (Oqus-300)
operating at a frame rate of 200Hz. Forty six reflective
markers should be placed in predefined anatomical pro-
tuberances and used for the reconstruction of lower
limb segments using Visual 3D software (C-Motion,
Inc., Germantown, MD). To reduce noise, the motion
data is filtered, using a low pass Butterworth filter,
Yázigi et al. BMC Musculoskeletal Disorders 2013, 14:320 Page 8 of 14
with a cutoff frequency of 15Hz . Ground reaction
force will be collected with two force platforms (Kistler
AG, Winterthur, Switzerland) and AMTI (Advanced
Mechanical Technology, Inc, Watertown, MA), synchro-
nized with the motion capture system.
The test will be performed in a fifteen meters walkway,
six successful trials are collected from each participant
and three should be chosen for subsequent analysis. A
trial consists of starting on the platform approximately 2
meters behind the initial timer and walking past the first
beam of light to activate the timer. As the participant
walks and passes the second beam of light the timer will
stop and speed will be recorded. The participant will
turn around and wait for orientations to perform similar
trial in the opposite direction.
In general, KOA subjects walk at a slower speed and
cadence, with a prolonged stance phase, presenting a
static and dynamic varus alignment, showing smaller
flexion and greater knee adduction moment (KAM)
[12,34,120,121]. The following kinematic and kinetic
outcomes should be analyzed from the gait test:
Freely chosen speed is slower in individuals with Knee
OA being correlated with high ground reaction forces
during heel strike ;
Gait cycle characteristics
Swing and stance phase duration, stride frequency, stride
length, knee and hip ROM and angular velocity;
Ground reaction forces
The vertical, anteroposterior and mediolateral force
components will be recorded with a force platform.
Computer software will be used to calculate duration,
amplitude and impulse of the reaction forces;
Knee adduction moment (KAM)
Knee adduction moment (KAM) is considered a valid
parameter to infer the level of mechanical loading .
Healthy subjects show substantially higher abduction
moments than OA subjects and the external adductor
moment has been linked to the development and pro-
gression of medial compartment OA in association with
the varus alignment installation by increasing the com-
pressive forces across the knee . In addition, there
is a significant inverse association between the peak of
knee adduction moment during late stance and the
amount of knee pain which may represent a compensa-
tory mechanism to reduce medial tibiofemoral joint load
in the setting of knee pain ;
Adduction angular impulse (AddImp)
The integral of the frontal plane external joint moments
(adduction and abduction) over time during the stance
phase, providing a functional measure of gait rather than
normalized KAM. This measure has been useful to dis-
tinguish loads in different OA severity [125,126];
Knee extension moment
Individuals with knee pain and weak muscles, as a pro-
tective mechanism, seem to avoid the quadriceps muscle
recruitment during load acceptance in stance phase,
showing a reduced knee peak extension moment;
Hip extensor moment
OA subjects walking at similar speeds of healthy one’s
maintain their walking speed by increasing hip range of
motion and its speed. Greater hip extensor moments
may indeed help to maintain walking speed, but this
does not appear to be the case with the hip flexor and
ankle plantar flexor moments, which were substantially
Hip external abduction moment
Individuals with knee OA seems to have a higher in-
volvement of hip adductor muscles to compensate a
weak quadriceps and hip abductors [12,127].
Since this is a longitudinal study, walking speed may
change and should be measured at each testing moment
(baseline and after intervention). One successful trial is
defined as the one in which the participant’s entire foot
is placed on the surface area of the force platform while
walking within ± 3.5% of the freely chosen speed.
The freely chosen speed should be assessed in the bio-
mechanical test day before the placement of markers, in
so far as each subject shall walk barefoot in the walkway
until a stabilization of walking speed is observed. Usually
the latter stabilization occurs after crossing of the walkway
5–6 times. The speed is monitored using an infrared
photocell control system (Model E3F2-R4B4-M, OMRON)
set with 7.3 m apart at the hip level, interfaced with a pro-
cessor specifically built to record the time and calculate the
speed as a function of the distance.
International physical activity questionnaire (IPAQ)
The short form of IPAQ was chosen because it is easy to
apply. Despite its liability having been verified in many
countries and with different populations [128-130], studies
have indicated that the IPAQ-SF typically overestimates
physical activity . However, this instrument will be
used for controlling the amount of physical activity along
the study, and not for any classification of physical activity
level. All participants shall receive a previous explanation
about how to complete the questionnaire, and their
Yázigi et al. BMC Musculoskeletal Disorders 2013, 14:320 Page 9 of 14
answers will be confirmed during the interview. Data will
be processed according to IPAQ guidelines .
The weight and lifestyle inventory (WALI)
The WALI is designed to obtain demographics informa-
tion, weight and dieting histories, eating and exercise
habits, and relationships with family and friends .
The Portuguese version (IPEV) and the process by which
it was translated is published in a national book .
The PICO project will use only the sections G, K and Q
of the Portuguese version (IPEV) for controlling alcohol
and tobacco consumption, dietary patterns and clinical
Our primary measures are IL-6 and IL-10. These cyto-
kines are consistently implicated in OA pathogenesis
and showed significant improvement with weight loss in
ADAPT. We will also measure hsCRP as an overall
marker of chronic inflammation and TNFαand TNFα
soluble receptor 1 (sTNFR1) because they are also impli-
cated in OA pathogenesis. Leptin, an adipokine that
increases synthesis of TGFβ, a known stimulator of
osteophyte formation, will also be measured.
For assessing IL-6, IL-10, hsCRP, TNFα, sTNFαR1 and
leptin, venous blood samples (approximately 10 ml per
visit) will be collected into dry tubes and EDTA tubes by
standard procedures in the morning after a minimum of
4 h fast without any type of exercise.
Blood will be centrifuged at 1500 x g for 10 min to
separate serum from the cloth in the dry tubes and
plasma from red blood cells in the EDTA tubes. Serum
and plasma will be frozen at 80°C for posterior analysis
by ELISA using commercially available kits.
Descriptive statistics, including frequencies for categor-
ical variables and means with standard deviations (SD)
for continuous variables with normal distribution and
median for skewed distributions will be used to describe
subject’s characteristics. Normality will be tested using
the Kolmogorov-Smirnov test. For continuous outcome
measures, differences in mean change (baseline minus
post-intervention) will be compared between groups
using analysis of covariance adjusted for baseline values of
the outcome. Comparisons between groups (CG and
AEG) at baseline and post intervention will be conducted
by Independent-sample t-tests or Mann–Whitney U test if
equal variance is not assumed. Changes within group will
be analyzed by paired Student’s t tests or by the Wilcoxon
Signed Rank test when normality is not assumed. A mixed
model analyses of covariance (ANCOVAs) will be con-
ducted for interaction analyses adjusted for BMI with
two within-participant factors of 6MWT (baseline) and
6MWT (post-intervention) and between two groups (CG
and AE). Statistical analysis will be performed using IBM
SPSS Statistics 20.0 and MedCalc Statistical Software
(MedCalc Software, Mariakerke, Belgium). Multiple Linear
regression analyses will be performed to understand the
potential covariates that could improve the explanation of
the variability of outcomes (6MWT, strength and KOOS
dimensions). Statistical significance will be set at P <0.05
(2- tailed) for all analyses. Effect sizes will be calculated for
all measures with an effect size of 0.2 considered small, 0.5
medium and 0.8 large.
The need to improve non-pharmacological intervention
for patients with KOA is obvious, and aquatic exercise is
an option for obese patients since it minimizes joint
load. Although water exercise is frequently encouraged,
relatively little research has been conducted in this area
as compared to land-based exercise.
There are several strengths to the design of this study.
The first one, is the detailed exercise prescription proto-
col concerning dosage (frequency, duration and intensity
of the exercise), the fulfillment of overload and individu-
ality principles of training (e.g., gradual increase of the
number of sets and repetitions on strength training), and
the control of exercise intensity during the sessions
using rating perception effort scales (e.g., Borg RPE and
Secondly, the pool where the program will be delivered
is easily accessed by train or bus. This aspect is crucial
as the access to appropriate facilities and patient motiv-
ation to undertake water exercise, might be a barrier to
adherence. Additionally, the fact of our sample being
adult and not elderly should facilitate the displacement
to our facilities.
Thirdly, the exercise program will be delivered by high
qualified aquatic exercise instructors, all of whom shall
be graduates in Sports Science at the Faculty of Human
Kinetics who have specialized in exercise and health and
fitness group skills. The exercise program will be deliv-
ered similarly to both classes regarding exercises, over-
loads and leading strategies according to the predefined
plan. Four instructors will be organized in pairs, and
each pair will take care of one aquatic exercise group
during the entire program.
With the exception of the knee radiographs for OA
diagnosis, all measures will be obtained in the same fa-
cility at the baseline and immediately after the end of
the program. One barrier at each visit/measuring point
will be the capacity to asses all participants in a short
interval. Due to the specificity of the outcomes will be
necessary to manage the schedule among four different
labs. Therefore, to support the project, staff team in-
cludes one secretary responsible for administrative work,
Yázigi et al. BMC Musculoskeletal Disorders 2013, 14:320 Page 10 of 14
four technicians conducting the dynamometer tests, gait
analysis, body composition and anthropometry assess-
ments and one professional for collecting blood samples.
Each technician received the responsibility to be special-
ized in two test’s group plus questionnaires and, to avoid
inter-rater error, the same technician should lead its ap-
plication in both assessments, baseline and post-exercise
intervention. Participant adherence to exercise is one of
the main challenges, therefore to avoid drop outs, motiv-
ational cues, intra-group social interaction, frequent tele-
phone calls and the quality of instructors are the main
strategies chosen to contribute to adherence rates. Besides,
since our sample will include adults that may still be work-
ing which will create some difficulties in the definition of
class schedules, one extra class, every 15 days, will be pro-
vided to enhance high compliance, and to allow that all
participants might attend to 24 sessions during the
3 month period over which the study shall run.
One possible constraint to the success of the aquatic ex-
ercise programs would be the level of water skills of each
participant. Although it is not necessary to know how to
swim, the autonomy and the ability to apply power against
the water are essential to get benefits from this type of ac-
tivity, especially when performing strengthening exercises.
Therefore some aquatic adaptation exercises will be intro-
duced in the class format (Table 1).
Our study is based on the premise that individuals
with KOA need a wide exercise intervention, adapted
not only to the affected joint but to the health status of
the patient, working the whole body and the mind sim-
ultaneously. In addition, we expect that aquatic exercise,
beyond the improvement of KOA symptoms, can in-
crease the symmetry between forces in the lower-limb
joints (adduction/abduction and flexion/extension mo-
ments at knee and hip joints), so improving gait.
The format of the sessions, the study duration and the
weekly frequency of exercise classes are organized in
such a way as to make sure that this proposal is execut-
able, not only for this project but also for future imple-
mentations by communities or in private pools. The
sample size of this protocol are reduced because we con-
sider that, before implementing the program in the gen-
eral community, for public health, the exercise protocol
should be validated by a very controlled process.
This study is a Randomized Controlled Trial (RCT) using
aquatic exercise specially designed with a very controlled
methodology. It is expected that the results will enable
evidence-based recommendations for the treatment of pa-
tients with KOA through aquatic-exercise. Future studies
would aim to reproduce the protocol contained herein
and implement it in a larger sample and in different com-
munities. The findings of PICO’saquaticprogramfor
KOA should inform the development of an effective and
reproducible exercise protocol, available for use by any
professional with aquatic exercise and exercise and health
The authors declare that they have no competing interests.
FY conceived the study, participated in its design and coordination, shall
carry out the biomechanical gait tests, the intervention team coordination
and drafted the manuscript. ME participated in its design, coordinates staff,
and improved both the manuscript improvement and data management.
SM participated in the protocol development, and in training staff for
biomechanics tests. FV participated in the design of the body composition
and anthropometry based protocols and their coordination. CM coordinates
and carries out the biomarker analyses. AV participated in the study design
and manuscript improvement. All authors read and made comments on
previous drafts of the manuscript, and approved the final manuscript.
We gratefully acknowledge the contributions to this paper of our colleagues
and also, a special thanks to Professor Veronica Vleck for the final revision.
Department of Sports and Health, Univ de Lisboa, Fac Motricidade Humana,
CIPER, LBMF, P-1499-002 Lisbon, Portugal.
Department of Health and
Exercise Science, Wake Forest University, Winston-Salem, NC, USA.
Received: 29 May 2013 Accepted: 7 November 2013
Published: 13 November 2013
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Cite this article as: Yázigi et al.:The PICO project: aquatic exercise for
knee osteoarthritis in overweight and obese individuals. BMC
Musculoskeletal Disorders 2013 14:320.
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