10.1016@j.clinbiomech.2018.09.016

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Accepted Manuscript
The effect of quadriceps-strengthening exercise on quadriceps and
knee biomechanics during walking in knee osteoarthritis: A two-
centre randomized controlled trial
Paul DeVita, Jens Aaboe, Cecilie Bartholdy, Joshua M. Leonardis,
Henning Bliddal, Marius Henriksen
PII: S0268-0033(18)30090-1
DOI: doi:10.1016/j.clinbiomech.2018.09.016
Reference: JCLB 4605
To appear in: Clinical Biomechanics
Received date: 12 February 2018
Accepted date: 12 September 2018
Please cite this article as: Paul DeVita, Jens Aaboe, Cecilie Bartholdy, Joshua M.
Leonardis, Henning Bliddal, Marius Henriksen , The effect of quadriceps-strengthening
exercise on quadriceps and knee biomechanics during walking in knee osteoarthritis:
A two-centre randomized controlled trial. Jclb (2018), doi:10.1016/
j.clinbiomech.2018.09.016
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THE EFFECT OF QUADRICEPS-STRENGTHENING EXERCISE ON QUADRICEPS 
AND KNEE BIOMECHANICS DURING WALKING IN KNEE OSTEOARTHRITIS: A 
TWO-CENTRE RANDOMIZED CONTROLLED TRIAL 
 
Paul DeVita
1
, Jens Aaboe
 2
, Cecilie Bartholdy
2
, Joshua M Leonardis
1
, Henning Bliddal
2
, Marius 
Henriksen
2
 
 
1
Biomechanics Laboratory, Department of Kinesiology, East Carolina University, Greenville, NC, 
USA. 
2
The Parker Institute, Department of Rheumatology, Copenhagen University Hospital Bispebjerg-
Frederiksberg, Copenhagen, Denmark. 
 
Correspondence: 
Paul DeVita, Ph.D. 
332 Ward Sports Medicine Building 
Department of Kinesiology 
East Carolina University 
Greenville, NC 27858 
Tel: (252) 737 - 4563 
Fax: (252) 737 - 4689 
Email: devitap@ecu.edu 
 
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ABSTRACT 
Objective 
To assess the effect of quadriceps strengthening on quadriceps muscle force, power, and work and 
tibio-femoral compressive loads during walking in adults with knee osteoarthritis. 
Methods 
Study design: Two-center, randomized, controlled trial. Intervention: Patients with knee 
osteoarthritis were randomly allocated to quadriceps strengthening program (3 times weekly) or no 
attention control group. Main outcome measures: Primary outcome was change from baseline in 
peak quadriceps force during walking at 12 weeks. Secondary outcomes included quadriceps power 
and work, knee compression forces during walking estimated with musculoskeletal modeling, 
muscle strength and pain and function. Outcomes were measured at baseline and 12 weeks. 
Results 
30 patients were randomized to receive either training (n=15) or no attention (n=15). At follow-up, 
there were no statistical differences between groups for maximum quadriceps force, quadriceps 
positive power, negative work, and positive work, and knee compressive force. Maximum negative 
quadriceps power in early stance was statistically significantly increased 36% in the training group 
compared to the control group which was most likely partially a response to faster walking velocity 
at follow-up. Muscle strength and patient reported pain and function were improved in the training 
group compared to the control group. 
Conclusions 
Quadriceps strength training leads to increased muscle strength and improved symptomatic and 
functional outcomes but does not change quadriceps or knee joint biomechanics during walking. 
The biomechanical mechanism of improved health with strength training in knee osteoarthritis 
patients remains unknown. 
ClinicalTrials.gov Identifier: NCT01538407 
 
 
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Keywords: muscle force, muscle power, muscle work, knee compressive force, strength training, 
musculoskeletal model, WOMAC, pain, function 
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INTRODUCTION 
 Quadriceps muscle strength is typically lower in people with knee osteoarthritis (OA) compared 
to healthy adults and quadriceps weakness is a risk factor for initiation and progression of knee OA 
(Hurley, 1999; Oiestad et al., 2015; Serrao et al., 2015; Slemenda et al., 1997; Slemenda et al., 
1998). Accordingly, strengthening exercise regimens increase quadriceps muscle strength and 
sensorimotor function and reduce neural inhibition (all tested isokinetically) and also improve 
clinical outcomes, such as pain, physical function and quality of life (Baker et al., 2001; Hurley and 
Newham, 1993; Hurley and Scott, 1998; McAlindon et al., 2014). Thus, quadriceps strengthening 
programs are firmly entrenched in the rehabilitation literature (McAlindon et al., 2014; Zhang et al., 
2007) and in public health policy in the United States by the National Institutes of Health (NIH-OA) 
and the Center for Disease Control and Prevention (CDC-OA). Absolute quadriceps strength and 
quadriceps strengthening in particular are thought to stabilize the knee against undesirable 
displacement forces (Markolf et al., 1978) and to protect the knee from pathologic loadings thus 
preventing structural damage during daily activities (Brandt et al., 2009; Hurley, 1999; Segal et al., 
2010; Topp et al., 2002). It is theorized that quadriceps strength training will increase quadriceps 
force during locomotion and thereby enable the muscle along with the patellar tendon to more 
effectively unload the knee joint (Anwer and Alghadir, 2014; Hurley, 1999; Vincent and Vincent, 
2012). Further, the theory suggests that increased quadriceps force would also increase its energy 
absorbing capacity (i.e. negative work) potentially reducing the stress reaching the knee joint 
surfaces (Hurley, 1999; Mikesky et al., 2000). Intuitively, this would theoretically explain the 
suggested shock absorbing function of periarticular knee muscle strength (Brandt et al., 2009; 
Mikesky et al., 2000). 
 While one or more biomechanical responses elicited through quadriceps strength training may 
be linked to reduced pain and improved physical function in people with knee OA, no empirical 
evidence has causally identified any underlying biomechanical mechanisms associated with 
increased quadriceps strength. This point was highlighted by Bennell et al in their comprehensive 
meta-analyses of nearly 500 related publications (Bennell et al., 2011). For example, Knoop et al 
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(Knoop et al., 2015) concluded after a thigh muscle strengthening program, that muscle 
strengthening is one of the mechanisms responsible for the beneficial effects of exercise. However, 
they reported only correlational data showing associations between improved thigh muscle strength 
and symptomatic improvements but they did not identify any change in quadriceps muscle function 
or knee joint loads after strengthening. The maximum knee adduction moment (KAM) during 
walking, has often been used as a proxy for the medial to lateral load distribution in people with 
knee OA (Aaboe et al., 2011; Baliunas et al., 2002; Chang et al., 2015) and potentially could 
identify the biomechanical outcomes of quadriceps strengthening. However, the KAM is typically 
neither related to maximum quadriceps strength nor is it influenced by strength
training (Foroughi 
et al., 2011; Hunt et al., 2013; Lim et al., 2008; Lim et al., 2009; Sled et al., 2010; Thorp et al., 
2010) although Karamanidis et al did show reduced KAM during inclined walking after 14 weeks 
of strength training (Karamanidis et al., 2014). More directly related to quadriceps muscle function, 
increased strength through training did not change the sagittal plane knee moments during step-up 
(McQuade and de Oliveira, 2011), level walking (Chang et al., 2016) or inclined walking 
(Karamanidis et al., 2014) tasks. 
 We suggest there is a disparity between the theoretical notion that quadriceps strengthening 
improves quadriceps function and knee biomechanics during locomotion and the data to support it. 
In fact, to our knowledge no study has yet investigated the effects of quadriceps strengthening 
exercises on quadriceps muscle power and work muscle during locomotion. The aim of the study 
was to assess the effect of quadriceps muscle strengthening on quadriceps muscle force, power, and 
work production and tibio-femoral compressive joint loads during walking in adults with knee OA. 
By demonstrating whether or not increasing the capacity of the quadriceps muscle through 
strengthening changes quadriceps biomechanics during walking, we will provide original data that 
directly investigates possible biomechanical pathways to symptomatic improvement in knee OA 
patients with exercise. 
 
 
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METHODS 
Study design 
This was a two-center study based on the collaboration between The College of Health and Human 
Performance, East Carolina University, USA and The Parker Institute, Bispebjerg-Frederiksberg 
Hospital, Denmark. The study was conducted at two separate motion analysis laboratories, using 
identical test protocols, methodology and study design in order to cluster all data and to publish the 
results in a pooled analysis. Accordingly, this study is a randomized controlled two-center trial 
including adults with tibio-femoral OA (ClinicalTrials.gov/ NCT01538407). All study procedures 
were approved by the Institutional Review Boards at both sites and all research participants at each 
site provided written informed consent to participate. Each subject was entered into the study after 
the presence of tibio-femoral knee OA was verified by a rheumatologist or orthopedist according 
the criteria of the American College of Rheumatology (Altman et al., 1986) . At each center 
participants were randomly and equally (1:1) allocated to a 12 weeks of quadriceps strengthening 
group or a control group (no attention) by two of the co-authors (J.A. and J.L.). The randomization 
sequence was made before commencement of study activities by a computer random number 
generator. Participants allocated to the training group had to complete a minimum of 80% of the 
training bouts (30 out of 36 possible bouts) to be considered adherent to the protocol. All methods 
were applied consistently for all participants throughout the study; no procedures were altered 
during the study. 
Participants 
Participants were included if clinical symptoms and radiographic findings of tibio-femoral OA were 
verified in one or both knees. Otherwise participants were in general good health aged between 45 
and 70 years and with body mass index (BMI) of 19<BMI<34 kg/m
2
. Exclusion criteria included 
(but were not limited to) knee joint effusion, subjects dependent on walking device or signs and 
symptoms of clinically significant cardiovascular diseases, autoimmune disorders, diabetes or 
neurologic disorders. 
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Strength training Quadriceps strengthening consisted of supervised and facility based sessions (3 
times/week) including leg extension, leg press and forward lunge exercises each performed in 3 sets 
of 10 repetitions with loads. The initial two weeks were performed at 60% 3RM, the following two 
weeks at 70% 3RM and the remaining 8 weeks at 85% 3RM. Training load was progressed by 
means of bi-weekly estimates of muscle strength (3RM test) to ensure a consistent training load 
between 60%–85% 3RM. Muscle strengthening exercises on both lower extremities were 
performed according to the standard progressive resistance and overload principle (36). Before each 
session participants performed 5-10 minutes of warming up on a treadmill or stationary bicycle. 
Each training session lasted about 60 minutes. 
Gait analysis Gait analysis data were acquired using infrared 3D motion analysis systems (Qualisys 
MacReflex 240, Gothenburg, Sweden and Vicon MX13, Oxford, UK, both operating at 100 Hz) in 
combination with adhesive reflective markers placed directly on the skin of the subjects in a 
modified Helen Hayes configuration. Force platforms (AMTI, LG6-4-2000, Newton, MA, USA 
operating at 1,000 Hz) embedded in the laboratory floor captured ground reaction forces which 
were temporarily and spatially synchronized with the kinematic data. The digitized Cartesian 
coordinates of the reflective markers were digitally filtered bi-directionally through a second order 
low-pass Butterworth digital filter with a 6-Hz cut-off frequency. In cases of bilateral OA, the knee 
with more pain at baseline based on patient report was measured and analyzed. During all trials 
subjects walked in their own comfortable shoes. Subjects were familiarized to the task by walking 
at a self-selected speed across the walkways for 10 m and until a self-selected target walking speed 
was determined. Since exercise increases walking speed in people with knee OA (e.g. (Messier et 
al., 2004), self-selected and not a standard speed was used to provide greater ecological validity and 
to maximize the potential for observing altered quadriceps and knee joint forces. Walking speed 
was monitored with a set of two photocells connected to a clock at each site. Subsequently, 10 
acceptable trials per person (clean force plate hits) were collected and used for statistical evaluation. 
We examined the quality of the ten-trial procedure by calculating all within-participant 
coefficients of variation (CV) for the locomotion variables in this study. The trials within each ten-
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trial sample were highly consistent with extremely low inter-trial CVs which averaged 14% 
compared to the between participant CVs which averaged 44%. Three dimensional joint angular 
kinematics were determined from the filtered linear position data and joint reaction forces and 
moments were calculated using standard inverse dynamics approach and Visual 3D software (C-
Motion, Rockville, MD). The analyses focused on the stance phase of the gait cycle which was 
defined as heel strike to toe-off as determined by the vertical ground reaction force with a 10 N 
threshold. All trials were analyzed individually and subsequently each variable was averaged across 
trials for each participant. 
Outcome measures 
All participants had body mass and height, 3D gait analyses, isokinetic muscle strength, functional 
performance tests and data from the Western Ontario and McMaster Osteoarthritis Index 
(WOMAC) collected before and after a 12-week intervention period. The primary outcome 
variables were maximum quadriceps muscle force and power and quadriceps work and the 
maximum total knee (tibio-femoral) compressive force during 1
st
 half of stance, the period of 
maximum quadriceps activation and knee extensor torque. Estimates of muscle forces and joint 
compressive forces were calculated using the kinematic and kinetic data from the gait analyses in
combination with a biomechanical model used previously and described in detail (DeVita and 
Hortobagyi, 2001; Messier et al., 2011) and used extensively for knee OA individuals (Messier et 
al., 2005; Messier et al., 2011; Messier et al., 2013b). The muscle and joint force predictions 
compare favorably to those from other biomechanical models (see (Messier et al., 2011) for 
summary) and the knee joint force predictions were highly similar to the measured forces from an 
individual with an above knee prosthesis (Messier et al., 2013a). We extended the calculations 
from previous work to include quadriceps muscle power. Quadriceps length was determined in each 
kinematic frame based on knee joint angular position from equations by Chow et al (Chow et al., 
1999) and quadriceps shortening or lengthening velocity was then derived as the time derivative of 
muscle length. Quadriceps power was calculated as the product of quadriceps muscle force and 
velocity. To further investigate the effects of strengthening exercises on knee mechanics, maximum 
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knee flexion and maximum internal knee extensor torque both occurring at approximately 20% of 
the stance phase were also included in the analyses. 
 The maximal isokinetic muscle strength (MVC) was measured at 60 °/sec using a dynamometer 
(HUMAC NORM, CSMi, Stoughton, MA and KinCom, Chattex, Chattanooga, TN). The subjects 
were seated and firmly strapped into the dynamometer chair, and the axis of rotation was aligned 
with the axis of joint rotation (knee flexion/extension). The distal part of the subject’s leg was held 
against the dynamometer with a cuff. The subjects were asked to perform the given movement in a 
full range of motion with maximal effort and force, and loud verbal encouragement was given 
during the tests, as well as visual feedback from the dynamometer computer monitor. After 
familiarization with the test protocol, each test series consisted of 3 maximum torque values and the 
maximum value was extracted for statistical analysis. 
 
Radiographic evaluation 
Standard semi-flexed anterior posterior standing radiograph was taken (Philips Optimus). A trained 
musculoskeletal radiologist performed the Kellgren-Lawrence (K/L) score in all standing 
radiographs as originally described by Kellgren and Lawrence (Kellgren and Lawrence, 1957). 
Using this method the medial knee tibio-femoral joints were categorized into 5 grades from 0 to 4, 
assessing the stage of knee OA. 
 
Statistical analysis 
The sample in this study was set to 40 in total. However during the trial it became apparent that we 
would not reach this enrolment level, thus it was decided only to enroll a total of 30 with 15 
participants in each group. The statistical analyses are based on per protocol population defined as 
participants with gait analysis data at baseline and at follow-up after the 12 weeks intervention 
period and adherence to the strength training program (minimum 80%). Gait variables were 
averaged across the 10 trials per participant at each test session and these mean values were 
statistically analyzed. We performed one-way ANCOVAs on the change scores within each group 
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with the baseline values used as the co-variate. Level of statistical significance was accepted if 
p<0.05. To further explore possible relationships among clinical and biomechanical variables we 
correlated the change in maximum quadriceps isokinetic strength with the change in WOMAC pain 
and function scores and these three variables with changes in knee joint and quadriceps force, 
power, and work variables. 
 
Figure 1 
 
 
RESULTS 
Thirty-five adults with knee OA volunteered for the study, four were excluded at screening due 
to knee joint effusion (n=1), excessive BMI (n=1), or they declined to participate upon further 
information (n=2; Figure 1). In total we included 31 participants, 18 females and 13 males; one 
male left the study however after changing employment because he could not meet the training 
schedule. The 30 remaining participants had a mean age of 57.1 (SD 7.7) years and BMI 27.1 (4.0) 
kg/m
2
 (Table 1). Following randomization the groups were as expected comparable at baseline, and 
differed by less than 4%, on average, in age, height, BMI and K/L score (Pre-test K/L for all 
subjects was 2.65). All participants in the strength training group adhered to the protocol and 
completed at least 30 sessions (80%) of the possible 36 training sessions. All included participants 
completed the follow-up tests; however, 1 subject did not perform the WOMAC questionnaire. Four 
subjects (two in each group) had incomplete muscle strength test data, which were accounted for by 
multiple imputations. One participant in the training group left the study after ~50% of the training 
sessions because of a change in employment and this person could no longer meet the training 
schedule. All participants were recruited, trained and analyzed between September, 2011 and April, 
2013. 
Table 1 
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Quadriceps strength training produced significant group differences in quadriceps strength and 
pain, function and total WOMAC scores (Table 2), Quadriceps muscle strength increased 25% in 
the training group compared to only 2% in the control group. The effect size for this difference was 
0.90. Changes in pain, function, and total WOMAC scores were 43%, 62% and 55% larger in 
training compared to control group with effect sizes over 1.00 for each variable and with non-
overlapping 95% confidence intervals for the pre-test – post-test difference scores for each group 
(data not shown). The analysis showed statistically non-significant differences in the group 
difference scores for maximum quadriceps force and maximum compressive knee force during 
walking (figure 2). A statistically significant effect in the difference score was evident for 
maximum negative quadriceps power in early stance, with a 36% increase (i.e. more negative) in 
the training group compared to 1% decrease in the control group and an effect size of 0.91. The 
group differences in negative quadriceps work and maximum positive quadriceps power and work 
in early stance however were not statistically significant. Maximum knee flexion and knee internal 
extension torque during loading phase were also not statistically significantly different between 
groups after the treatment period. Self-selected walking velocity during the gait tests was 
statistically significantly increased by 3% in the training group compared to a 3% decrease the 
control group with a large effect size for the difference of 0.98. 
Eighteen of the twenty correlation coefficients between changes in clinical and biomechanical 
gait scores were statistically non-significant (p>0.05, Table 3). Changes in maximum knee 
compression and maximum quadriceps force were inversely related to changes in pain and function 
(p<0.05), meaning that higher knee compression and quadriceps forces were associated with less 
pain and improved function. None of the participants reported any pain or discomfort associated 
with the training during or after the study period. 
Table 2 
Figure 2 
Table 3 
 
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DISCUSSION 
 In this randomized controlled trial we investigated the effects of quadriceps strength training 
on quadriceps muscle force, power and work, and knee compression force during walking in people 
with knee OA. To our
knowledge this study is the first attempt to directly investigate the 
proposition that quadriceps strength training alters quadriceps locomotor function in people with 
knee OA. Specifically, we explored the idea that these symptomatic improvements were mediated 
through enhanced quadriceps muscle function and reduced knee joint loads during walking. Indeed, 
quadriceps strength training did improve the mechanical capacity of the muscle by increasing its 
maximum strength. Strength training also reduced the participants’ pain and disability and increased 
self-selected walking velocity and these results well agree with previous work (Chang et al., 2016; 
Fransen et al., 2003; Juhl et al., 2014; McAlindon et al., 2014). Additionally, quadriceps 
strengthening greatly improves underlying neural control and reduces neural inhibition of the 
quadriceps strongly suggesting that quadriceps capacity during locomotion would be enhanced 
(Hurley and Newham, 1993; Hurley and Scott, 1998). With one or possibly two exceptions however 
and within the limitations of our protocol (e.g. a moderate 12 weeks of training, testing at only one 
walking speed), the increased quadriceps strength was not reflected in the walking biomechanics: 
quadriceps force, maximum positive power, negative work and positive work were all statistically 
unchanged after the training period. The exception was that maximum negative quadriceps power in 
early stance was increased in the training group compared to the control group. The possible 
exception was that quadriceps negative work in the early portion of stance may have increased and 
we may have had a type II statistical error since the associated negative power was increased and 
the p-value for the work comparison was 0.061. We suggest however that the increased negative 
power and possibly work functions were direct responses to the increased walking velocity likely 
due to reduced pain as observed only in the training group and not primary responses of increased 
quadriceps strength. In fact, changes in maximum negative quadriceps power and negative work 
were uncorrelated to the change in quadriceps strength as were changes in maximum quadriceps 
force, positive power and work and knee joint compressive force across all participants (all p>0.05). 
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Further, we observed only two significant relationships out of 18 examined among changes in the 
clinical WOMAC variables and the biomechanical variables of knee joint and quadriceps force, 
power and work suggesting that improvements in pain and function were associated with increases 
in knee compression forces and quadriceps forces, respectively (table 3). However, these 
associations need confirmation as they may have occurred by chance due to multiple testing. We 
conclude that improved clinical and symptomatic outcomes after quadriceps strength training were 
not due to altered or improved quadriceps muscle function or knee joint loads in level walking. Our 
results refute the theory that strength training induces a biomechanical unloading mechanism at the 
knee joint (Segal et al., 2010; Topp et al., 2002). This conclusion supports the observation of 
Bennell et al (Bennell et al., 2011) who showed the literature cannot support the idea that exercise 
can alter the mechanical load in the knee. Our results also support Sharma et al (Sharma et al., 
2003) who conjectured that muscle strength may be a poor measure of muscle contribution to joint 
function in people with knee OA. Also, a recent study showed that exercise therapy had no effects 
on a range of ankle, knee and hip gait biomechanics variables (Henriksen et al., 2014). The 
mechanism through which quadriceps strength training elicits favorable responses in people with 
knee OA remains elusive and unknown. Further, our results are analogous to those of Beijersbergen 
et al (Beijersbergen et al., 2013) who showed from an extensive literature review the biomechanical 
mechanism of how strength and power training improves walking speed in old adults also remains 
unknown. It appears that the biomechanics-rehabilitation literature has yet to connect improved 
neuromuscular and physiological properties elicited through physical activity or exercise and the 
manifestation of reduced symptoms and disability in the OA or aged populations during activities of 
daily living. 
Messier et al reported quadriceps muscle and knee joint compressive forces in response to diet, 
exercise, and diet and exercise treatments. They showed that a general exercise regimen including 
aerobic training and quadriceps strength training did not reduce maximal quadriceps force and knee 
joint compressive force during walking in the absence of weight loss in knee OA participants 
(Messier et al., 2011). Further, general exercise alone had minimal change in knee compression (i.e. 
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3%) compared with diet (10%) and diet and exercise (10%) programs in a large sample of knee OA 
participants (Messier et al., 2013b). Combined with our results, improved pain and function seem to 
be more strongly mediated through reduced body weight than improved muscle function. 
 We respectfully submit that biomechanical mechanisms in OA should distinguish between force 
and energy issues. Muscles generate or produce force and mechanical energy but they dissipate only 
energy. Thus, improved muscle function should not be considered to absorb forces to reduce joint 
loads (Baker et al., 2001; Igawa and Katsuhira, 2014). As identified in both the OA and healthy gait 
literature, increased muscle force would clearly increase load on the joint surfaces because muscles 
compress joints (Baker et al., 2001; Kim et al., 2009; Sasaki et al., 2008; Schipplein and 
Andriacchi, 1991; Shelburne et al., 2006). Through eccentric lengthening contractions, such as 
performed by the quadriceps in the loading phase of gait, muscles reduce mechanical energy 
associated with total body mass (DeVita et al., 2007) but not with joint surfaces, a proposed, 
protective outcome of muscle contraction (Brandt et al., 2009). Indeed, knee joint loading during 
gait directly loads the joint surfaces, performing work on the cartilage inducing cartilage strain and 
thinning in knee OA patients and in individuals with injured anterior cruciate ligaments (Andriacchi 
et al., 2009; Chehab et al., 2014). Our data showed that strength training increased walking 
dynamics by increasing walking velocity while at the same time reduced pain and improved 
function. With a lack of associated knee joint and quadriceps muscle adaptations to increased 
maximal muscle strength, we conjecture the beneficial effects of strength training may be mediated 
through a broader, systemic response to the physical activity and not a specific, joint and muscle 
centered response. For example, higher levels of physical activity were associated with lower levels 
of inflammatory markers in knee OA patients (Penninx et al., 2004). 
 This work was conducted as a two-center study, and even though we used identical test- 
protocols and laboratory set-up, there may be subtle differences in the methods that we could not 
control for. This is a possible limitation, but gathering data from more than one laboratory is also a 
strength; we showed similar outcomes in WOMAC (ECU 6.8; Parker 5.6), isokinetic strength (ECU 
0.93; Parker 1.21 Nm/kg), gait biomechanics (maximum knee force: ECU 35.3; Parker 38.9 N/kg; 
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maximum quadriceps force: ECU 19.0, Parker 20.7 N/kg) and quadriceps
muscle responses to 
strength training at both sites (data not shown). We also draw note to the fact that the present 
participants were limited on average to middle-aged adults who were overweight but not obese. 
Older and obese adults may respond differently to the training program. Our prediction of 
quadriceps muscle length and subsequently muscle power were based solely on the sagittal plane 
angular position of the knee joint. As such, we cannot distinguish individual contributions from 
muscle fiber and tendon components or include potentially influential effects of muscle activation 
and tendon mechanical properties nor how these properties may have changed over the training 
period. Otherwise, we expect our results are generalizable to the adult population with knee OA but 
with few other health ailments. 
Certainly muscle strength and muscle function are pivotal for knee OA patients in terms of 
improvements in pain and physical function (Fransen et al., 2003; Juhl et al., 2014; McAlindon et 
al., 2014). However, while quadriceps weakness may increase the risk of structural deterioration in 
knee OA (Oiestad et al., 2015) and while high muscle strength may protect against knee OA 
progression, our results do not support the underlying mechanism of exercise induced knee 
unloading through improved muscle function leading to reduced pain and disability. This outcome 
is novel and demonstrates for the first time responses in quadriceps muscle power and work during 
locomotion to quadriceps strength training exercise in knee OA patients. The findings of this study 
suggest that pain relief and improvements in function are not explained by altered quadriceps forces 
or knee joint loads after strengthening the quadriceps through strength training. 
 
 
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ACKNOWLEDGEMENTS 
The authors thank Mr. Patrick Rider for his technical assistance in data collection and analysis 
at East Carolina University. Mr. Lars Bo Jørgensen (Physical Therapist) is acknowledged for his 
assistance in exercise delivery at The Parker Institute. We thank senior biostatistician and professor 
of clinical epidemiology Robin Christensen for his assistance when designing the study, for 
providing guidance on the statistical analyses, and for providing editorial recommendations. 
 
AUTHOR CONTRIBUTIONS 
 All authors made substantial contributions to 1) the conception and design of the study, or 
acquisition of data, or analysis and interpretation of data; 2) drafting the article; and 3) final 
approval of the version to be submitted 
 
ROLE OF THE FUNDING SOURCE: 
 This work was funded by the Biomechanics Laboratory in the Department of Kinesiology at 
East Carolina University, The Danish Rheumatism Association and The Oak Foundation 
 
CONFLICT OF INTEREST 
 The authors report no conflicts of interest. 
 
 
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REFERENCES: 
Aaboe, J., Bliddal, H., Messier, S.P., Alkjaer, T., Henriksen, M., 2011. Effects of an intensive 
weight loss program on knee joint loading in obese adults with knee osteoarthritis. Osteoarthritis 
Cartilage 19, 822-828. 
Altman, R., Asch, E., Bloch, D., Bole, G., Borenstein, D., Brandt, K., Christy, W., Cooke, T.D., 
Greenwald, R., Hochberg, M., et al., 1986. Development of criteria for the classification and 
reporting of osteoarthritis. Classification of osteoarthritis of the knee. Diagnostic and Therapeutic 
Criteria Committee of the American Rheumatism Association. Arthritis Rheum. 29, 1039-1049. 
Andriacchi, T.P., Koo, S., Scanlan, S.F., 2009. Gait mechanics influence healthy cartilage 
morphology and osteoarthritis of the knee. J. Bone Joint Surg. Am. 91 Suppl 1, 95-101. 
Anwer, S., Alghadir, A., 2014. Effect of Isometric Quadriceps Exercise on Muscle Strength, Pain, 
and Function in Patients with Knee Osteoarthritis: A Randomized Controlled Study. Journal of 
physical therapy science 26, 745-748. 
Baker, K.R., Nelson, M.E., Felson, D.T., Layne, J.E., Sarno, R., Roubenoff, R., 2001. The efficacy 
of home based progressive strength training in older adults with knee osteoarthritis: a randomized 
controlled trial. J. Rheumatol. 28, 1655-1665. 
Baliunas, A.J., Hurwitz, D.E., Ryals, A.B., Karrar, A., Case, J.P., Block, J.A., Andriacchi, T.P., 
2002. Increased knee joint loads during walking are present in subjects with knee osteoarthritis. 
Osteoarthritis Cartilage 10, 573-579. 
Beijersbergen, C.M., Granacher, U., Vandervoort, A.A., DeVita, P., Hortobagyi, T., 2013. The 
biomechanical mechanism of how strength and power training improves walking speed in old adults 
remains unknown. Ageing Res Rev 12, 618-627. 
Bennell, K., Hinman, R.S., Wrigley, T.V., Creaby, M.W., Hodges, P., 2011. Exercise and 
osteoarthritis: cause and effects. Comprehensive Physiology 1, 1943-2008. 
Brandt, K.D., Dieppe, P., Radin, E., 2009. Etiopathogenesis of osteoarthritis. Med. Clin. North Am. 
93, 1-24, xv. 
ACCEPTED MANUSCRIPT
AC
CE
PT
ED
 M
AN
US
CR
IP
T
18 
 
 
Chang, A.H., Moisio, K.C., Chmiel, J.S., Eckstein, F., Guermazi, A., Prasad, P.V., Zhang, Y., 
Almagor, O., Belisle, L., Hayes, K., Sharma, L., 2015. External knee adduction and flexion 
moments during gait and medial tibiofemoral disease progression in knee osteoarthritis. 
Osteoarthritis Cartilage 23, 1099-1106. 
Chang, S.Y., Lin, Y.J., Hsu, W.C., Hsieh, L.F., Lin, Y.H., Chang, C.C., Chou, Y.C., Chen, L.F., 
2016. Exercise Alters Gait Pattern but Not Knee Load in Patients with Knee Osteoarthritis. BioMed 
research international 2016, 7468937. 
Chehab, E.F., Favre, J., Erhart-Hledik, J.C., Andriacchi, T.P., 2014. Baseline knee adduction and 
flexion moments during walking are both associated with 5 year cartilage changes in patients with 
medial knee osteoarthritis. Osteoarthritis Cartilage 22, 1833-1839. 
Chow, J.W., Darling, W.G., Ehrhardt, J.C., 1999. Determining the force-length-velocity relations of 
the quadriceps muscles: I. anatomical and geometrical parameters. J. Appl. Biomech. 15, 182-190. 
DeVita, P., Helseth, J., Hortobagyi, T., 2007. Muscles do more positive than negative work in 
human locomotion. J. Exp. Biol. 210, 3361-3373. 
DeVita, P., Hortobagyi, T., 2001. Functional knee brace alters predicted knee muscle and joint 
forces in persons with ACL reconstruction during walking. J. Appl. Biomech. 17, 297-311. 
Foroughi, N., Smith, R.M., Lange, A.K., Baker, M.K., Fiatarone Singh, M.A., Vanwanseele, B., 
2011. Lower limb muscle strengthening does not change frontal plane moments in women with 
knee osteoarthritis: A randomized controlled trial. Clin Biomech (Bristol, Avon) 26, 167-174. 
Fransen, M., McConnell, S., Bell, M., 2003. Exercise for osteoarthritis of the hip or knee. Cochrane 
Database Syst Rev, CD004286. 
Henriksen, M., Klokker, L., Graven-Nielsen, T., Bartholdy, C., Schjodt Jorgensen, T., Bandak, E., 
Danneskiold-Samsoe, B., Christensen, R., Bliddal, H., 2014. Association of exercise therapy and 
reduction of pain sensitivity in patients with knee osteoarthritis: a randomized controlled trial. 
Arthritis care & research 66, 1836-1843. 
ACCEPTED MANUSCRIPT
AC
CE
PT
ED
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AN
US
CR
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T
19 
 
 
Hunt, M.A., Pollock, C.L., Kraus, V.B., Saxne, T., Peters, S., Huebner, J.L., Sayre, E.C., Cibere, J., 
2013. Relationships amongst osteoarthritis biomarkers, dynamic knee joint load, and exercise: 
results from a randomized controlled pilot study. BMC musculoskeletal disorders 14, 115. 
Hurley, M.V., 1999. The role of muscle weakness in the pathogenesis of osteoarthritis. Rheum. Dis. 
Clin. North Am. 25, 283-298.
Hurley, M.V., Newham, D.J., 1993. The influence of arthrogenous muscle inhibition on quadriceps 
rehabilitation of patients with early, unilateral osteoarthritic knees. Br. J. Rheumatol. 32, 127-131. 
Hurley, M.V., Scott, D.L., 1998. Improvements in quadriceps sensorimotor function and disability 
of patients with knee osteoarthritis following a clinically practicable exercise regime. Br. J. 
Rheumatol. 37, 1181-1187. 
Igawa, T., Katsuhira, J., 2014. Biomechanical analysis of stair descent in patients with knee 
osteoarthritis. Journal of physical therapy science 26, 629-631. 
Juhl, C., Christensen, R., Roos, E.M., Zhang, W., Lund, H., 2014. Impact of exercise type and dose 
on pain and disability in knee osteoarthritis: a systematic review and meta-regression analysis of 
randomized controlled trials. Arthritis Rheumatol 66, 622-636. 
Karamanidis, K., Oberlander, K.D., Niehoff, A., Epro, G., Bruggemann, G.P., 2014. Effect of 
exercise-induced enhancement of the leg-extensor muscle-tendon unit capacities on ambulatory 
mechanics and knee osteoarthritis markers in the elderly. PLoS One 9, e99330. 
Kellgren, J., Lawrence, J., 1957. Radiological assessment of osteo-arthrosis. Am. rheum. Dis. 16, 
494-501. 
Kim, H.J., Fernandez, J.W., Akbarshahi, M., Walter, J.P., Fregly, B.J., Pandy, M.G., 2009. 
Evaluation of predicted knee-joint muscle forces during gait using an instrumented knee implant. J. 
Orthop. Res. 27, 1326-1331. 
Knoop, J., Steultjens, M.P., Roorda, L.D., Lems, W.F., van der Esch, M., Thorstensson, C.A., 
Twisk, J.W., Bierma-Zeinstra, S.M., van der Leeden, M., Dekker, J., 2015. Improvement in upper 
leg muscle strength underlies beneficial effects of exercise therapy in knee osteoarthritis: secondary 
analysis from a randomised controlled trial. Physiotherapy 101, 171-177. 
ACCEPTED MANUSCRIPT
AC
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PT
ED
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AN
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CR
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T
20 
 
 
Lim, B.W., Hinman, R.S., Wrigley, T.V., Sharma, L., Bennell, K.L., 2008. Does knee malalignment 
mediate the effects of quadriceps strengthening on knee adduction moment, pain, and function in 
medial knee osteoarthritis? A randomized controlled trial. Arthritis Rheum. 59, 943-951. 
Lim, B.W., Kemp, G., Metcalf, B., Wrigley, T.V., Bennell, K.L., Crossley, K.M., Hinman, R.S., 
2009. The association of quadriceps strength with the knee adduction moment in medial knee 
osteoarthritis. Arthritis Rheum. 61, 451-458. 
Markolf, K.L., Graff-Radford, A., Amstutz, H.C., 1978. In vivo knee stability. A quantitative 
assessment using an instrumented clinical testing apparatus. J. Bone Joint Surg. Am. 60, 664-674. 
McAlindon, T.E., Bannuru, R.R., Sullivan, M.C., Arden, N.K., Berenbaum, F., Bierma-Zeinstra, 
S.M., Hawker, G.A., Henrotin, Y., Hunter, D.J., Kawaguchi, H., Kwoh, K., Lohmander, S., 
Rannou, F., Roos, E.M., Underwood, M., 2014. OARSI guidelines for the non-surgical 
management of knee osteoarthritis. Osteoarthritis Cartilage 22, 363-388. 
McQuade, K.J., de Oliveira, A.S., 2011. Effects of progressive resistance strength training on knee 
biomechanics during single leg step-up in persons with mild knee osteoarthritis. Clin Biomech 
(Bristol, Avon) 26, 741-748. 
Messier, S.P., Gutekunst, D.J., Davis, C., DeVita, P., 2005. Weight loss reduces knee-joint loads in 
overweight and obese older adults with knee osteoarthritis. Arthritis Rheum. 52, 2026-2032. 
Messier, S.P., Legault, C., Loeser, R.F., Van Arsdale, S.J., Davis, C., Ettinger, W.H., DeVita, P., 
2011. Does high weight loss in older adults with knee osteoarthritis affect bone-on-bone joint loads 
and muscle forces during walking? Osteoarthritis & Cartilage 19, 272-280. 
Messier, S.P., Loeser, R.F., Miller, G.D., Morgan, T.M., Rejeski, W.J., Sevick, M.A., Ettinger, 
W.H., Jr., Pahor, M., Williamson, J.D., 2004. Exercise and dietary weight loss in overweight and 
obese older adults with knee osteoarthritis: the Arthritis, Diet, and Activity Promotion Trial. 
Arthritis Rheum. 50, 1501-1510. 
Messier, S.P., Mihalko, S.L., Beavers, D.P., Nicklas, B.J., DeVita, P., Carr, J.J., Hunter, D.J., 
Williamson, J.D., Bennell, K.L., Guermazi, A., Lyles, M., Loeser, R.F., 2013a. Strength Training 
for Arthritis Trial (START): design and rationale. BMC Musculoskeletal Dis 14, 208. 
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Messier, S.P., Mihalko, S.L., Legault, C., Miller, G.D., Nicklas, B.J., DeVita, P., Beavers, D.P., 
Hunter, D.J., Lyles, M.F., Eckstein, F., Williamson, J.D., Carr, J.J., Guermazi, A., Loeser, R.F., 
2013b. Effects of intensive diet and exercise on knee joint loads, inflammation, and clinical 
outcomes among overweight and obese adults with knee osteoarthritis: the IDEA randomized 
clinical trial. Journal of the American Medical Association 310, 1263-1273. 
Mikesky, A.E., Meyer, A., Thompson, K.L., 2000. Relationship between quadriceps strength and 
rate of loading during gait in women. J. Orthop. Res. 18, 171-175. 
Oiestad, B.E., Juhl, C.B., Eitzen, I., Thorlund, J.B., 2015. Knee extensor muscle weakness is a risk 
factor for development of knee osteoarthritis. A systematic review and meta-analysis. Osteoarthritis 
Cartilage 23, 171-177. 
Penninx, B.W., Abbas, H., Ambrosius, W., Nicklas, B.J., Davis, C., Messier, S.P., Pahor, M., 2004. 
Inflammatory markers and physical function among older adults with knee osteoarthritis. J. 
Rheumatol. 31, 2027-2031. 
Sasaki, K., Neptune, R.R., Burnfield, J.M., Mulroy, S.J., 2008. Muscle compensatory mechanisms 
during able-bodied toe walking. Gait Posture 27, 440-446. 
Schipplein, O.D., Andriacchi, T.P., 1991. Interaction between active and passive knee stabilizers 
during level walking. J. Orthop. Res. 9, 113-119. 
Segal, N.A., Glass, N.A., Felson, D.T., Hurley, M., Yang, M., Nevitt, M., Lewis, C.E., Torner, J.C., 
2010. Effect of quadriceps strength and proprioception on risk for knee osteoarthritis. Med. Sci. 
Sports Exerc. 42, 2081-2088. 
Serrao, P.R., Vasilceac, F.A., Gramani-Say, K., Lessi, G.C., Oliveira, A.B., Reiff, R.B., Mattiello-
Sverzut, A.C., Mattiello, S.M., 2015. Men with early degrees of knee osteoarthritis present 
functional and morphological impairments of the quadriceps femoris muscle. Am. J. Phys. Med. 
Rehabil. 94, 70-81. 
Sharma, L., Cahue, S., Song, J., Hayes, K., Pai, Y.C., Dunlop, D., 2003. Physical functioning over 
three years in knee osteoarthritis: role of psychosocial, local mechanical, and neuromuscular 
factors. Arthritis Rheum. 48, 3359-3370. 
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Shelburne, K.B., Torry, M.R., Pandy, M.G., 2006. Contributions of muscles, ligaments, and the 
ground-reaction force to tibiofemoral joint loading during normal gait. J. Orthop. Res. 24, 1983-
1990. 
Sled, E.A., Khoja, L., Deluzio, K.J., Olney, S.J., Culham, E.G., 2010. Effect of a home program of 
hip abductor exercises on knee joint loading, strength, function, and pain in people with knee 
osteoarthritis: a clinical trial. Phys. Ther. 90, 895-904. 
Slemenda, C., Brandt, K.D., Heilman, D.K., Mazzuca, S., Braunstein, E.M., Katz, B.P., Wolinsky, 
F.D., 1997. Quadriceps weakness and osteoarthritis of the knee. Ann. Intern. Med. 127, 97-104. 
Slemenda, C., Heilman, D.K., Brandt, K.D., Katz, B.P., Mazzuca, S.A., Braunstein, E.M., Byrd, D., 
1998. Reduced quadriceps strength relative to body weight: a risk factor for knee osteoarthritis in 
women? Arthritis Rheum. 41, 1951-1959. 
Thorp, L.E., Wimmer, M.A., Foucher, K.C., Sumner, D.R., Shakoor, N., Block, J.A., 2010. The 
biomechanical effects of focused muscle training on medial knee loads in OA of the knee: a pilot, 
proof of concept study. Journal of musculoskeletal & neuronal interactions 10, 166-173. 
Topp,
R., Woolley, S., Hornyak, J., 3rd, Khuder, S., Kahaleh, B., 2002. The effect of dynamic 
versus isometric resistance training on pain and functioning among adults with osteoarthritis of the 
knee. Arch. Phys. Med. Rehabil. 83, 1187-1195. 
Vincent, K.R., Vincent, H.K., 2012. Resistance exercise for knee osteoarthritis. PM & R : the 
journal of injury, function, and rehabilitation 4, S45-52. 
Zhang, W., Moskowitz, R.W., Nuki, G., Abramson, S., Altman, R.D., Arden, N., Bierma-Zeinstra, 
S., Brandt, K.D., Croft, P., Doherty, M., Dougados, M., Hochberg, M., Hunter, D.J., Kwoh, K., 
Lohmander, L.S., Tugwell, P., 2007. OARSI recommendations for the management of hip and knee 
osteoarthritis, part I: critical appraisal of existing treatment guidelines and systematic review of 
current research evidence. Osteoarthritis Cartilage 15, 981-1000. 
 
 
 
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FIGURE LEGENDS: 
 
Figure 1. Participant flow schematic diagram. 
 Figure 2. Pre- and post-test group mean curves for A) quadriceps muscle force, B) quadriceps 
muscle power, and C) knee compressive force during the support phase of walking. Solid, dashed 
lines are pre- and post-tests. Dotted lines are ± 1 standard deviation of baseline values. 
 
 
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 Table 1. Baseline characteristics of knee OA participants 
 
Control Group Training Group 
 (n = 15) (n = 15) 
Gender 
 Females no. (%) 8 (53.3) 10 (66.7) 
 Males no. (%) 7 (46.7) 5 (33.3) 
Age (years 56.2 ± 8.9 58.1 ± 6.5 
Height (m) 1.73 ± 0.11 1.73 ± 0.07 
Body mass (kg) 83.8 ± 18.7 79.4 ± 14.8 
BMI (kgm
-2
) 27.9 ± 3.9 26.4 ± 4.0 
Kellgren Lawrence score* 
 Score 1 3 2 
 Score 2 1 4 
 Score 3 8 7 
 Score 4 3 2 
 
Except where indicated results are mean ± standard deviation 
 
 
 
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Table 2. Pre- and post-test means (standard deviations) of primary and secondary variables and ANCOVA probability 
 
 Control 
Group 
 Traning 
Group 
 P* 
 Pre-test Post-test Pre-test Post-test 
Isokinetic quadriceps muscle strength (Nm/kg) 1.12 1.17 0.96 1.21 0.037 
 (0.35) (0.40) (0.39) (0.42) 
WOMAC Pain 6.67 7.33 6.43 3.64 0.001 
 (3.31) (4.72) (3.18) (2.55) 
WOMAC Function 22.9 21.1 17.7 6.8 0.003 
 (10.7) (12.9) (9.7) (9.5) 
WOMAC Total 33.1 31.6 27.3 12.4 0.001 
 (14.5) (18.2) (13.1) (12.3) 
Gait Variables: 
Maximum quadriceps force (N/kg) 21.7 20.9 17.4 20.2 0.125 
 (5.9) (5.4) (5.4) (6.0) 
Maximum knee compressive force (N/kg) 40.7 38.4 34.6 37.5 0.161 
 (5.4) (6.2) (6.7) (6.2) 
Maximum negative quadriceps power (W/kg) -1.40 -1.38 -1.00 -1.36 0.003 
 (0.68) (0.86) (0.80) (1.05) 
Quadriceps negative work (J/kg) -0.114 -0.113 -0.091 -0.118 0.061 
 (0.063) (0.070) (0.061) (0.078) 
Maximum positive quadriceps power (W/kg) 0.804 0.806 0.632 0.770 0.153 
 (0.390) (0.401) (0.445) (0.513) 
Quadriceps positive work (J/kg) 0.087 0.102 0.071 0.086 0.354 
 (0.056) (0.065) (0.055) (0.063) 
Maximum knee flexion (deg) -19.0 -19.6 -16.4 -16.4 0.236 
 (6.5) (6.7) (7.5) (5.6) 
Maximum internal knee extensor torque (Nm/kg) 0.673 0.692 0.522 0.639 0.187 
 (0.278) (0.257) (0.267) (0.279) 
Walking velocity (m/s) 1.49 1.45 1.43 1.47 0.014 
 (0.16) (0.17) (0.21) (0.23) 
mean values across participants and sd in () 
P*: probability value from ANCOVA with adjustment for baseline scores, BOLD : P<0.05 
 
 
 
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Table 3. Correlation coefficients among changes from baseline in clinical (isokinetic strength) 
and biomechanical gait variables (all participants, n = 30) 
 
Correlation with: 
Variable Pain Function Strength 
Maximum isokinetic strength -0.111 -0.046 
 Maximum knee compression -0.515 -0.478 0.161 
Maximum quadriceps force -0.474 -0.522 0.032 
Maximum negative quadriceps power 0.306 0.098 -0.211 
Negative quadriceps work 0.283 0.124 -0.119 
Maximum positive quadriceps power -0.416 -0.361 0.065 
Positive quadriceps work -0.231 -0.222 -0.106 
Absolute values > 0.497 statistically significantly different than 0, p<0.05 
 
 
 
 
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Highlights: 
Quadriceps strength training or no training were given to groups of knee osteoarthritis patients. 
 
Training increased strength and reduced pain but did not change quadriceps or knee forces in 
walking 
 
Biomechanical mechanism of improved health with strengthening in knee OA patients remains 
unknown. 
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Figure 1
Figure 2