Research Paper

Progressive Resistance Training Improves Overall Physical Activity Levels in Patients With Early Osteoarthritis of the Knee: A Randomized Controlled Trial Joshua N. Farr, Scott B. Going, Patrick E. McKnight, Shelley Kasle, Ellen C. Cussler, Michelle Cornett

Background. Prescription of resistance training (RT) exercises is an essential aspect of management for knee osteoarthritis (OA). However, whether patients with knee OA who are randomly assigned to receive RT simply substitute RT for other modes of physical activity remains unclear.

Objective. The aim of this study was to determine the effect of a structured RT intervention on overall levels of moderate- and vigorous-intensity physical activity (MVPA) in patients with early-onset knee OA. The study compared patients with early-onset OA who participated in an RT program, those who participated in a self-management (SM) program, and those who participated in both RT and SM. Because participants randomly assigned to receive the RT intervention may simply switch activity modes, resulting in little net effect, we assessed total MVPA in addition to tracking changes in strength (force-generating capacity).

Design and Intervention. This study was a randomized controlled trial com- paring the effectiveness of SM alone, RT alone, and combined RT�SM on MVPA in patients with early OA of the knee.

Setting. The study was conducted on a university campus, with patient recruit- ment from the local community.

Participants. The participants in this study were 171 patients (74% women, 26% men) with knee OA. They had a mean age of 55.1 (SD�7.1) years, a mean body mass index of 27.6 (SD�4.2) kg/m2, and radiographic status of grade II OA (and no higher) in at least one knee, as defined by the Kellgren and Lawrence classification. They wore an accelerometer while awake (X�14.2 [SD�2.2] hours) for 5 to 7 contiguous days (X�6.8 [SD�0.5] days) at baseline and at 3 and 9 months of intervention.

Results. The participants engaged in MVPA a mean of 26.2 (SD�19.3) minutes per day at baseline. Both groups significantly increased their MVPA from baseline to 3 months (RT group by 18% [effect size (d)�0.26]; SM group by 22% [effect size (d)�0.25]), but only the RT group sustained those changes at 9 months (RT group maintained a 10% increase [effect size (d)�0.15]; SM group maintained a 2% increase [effect size (d)�0.03]). A significant group � time interaction for MVPA indicated that the RT group maintained higher MVPA levels than the SM group.

Limitations. Lack of direct measures of energy expenditure and physical function was a limitation of the study.

Conclusions. Patients with early-onset OA of the knee can engage in an RT program without sacrificing their overall MVPA levels. These results support the value of RT for management of knee OA.

J.N. Farr, MS, is Research Assistant, Department of Physiological Sci- ences, University of Arizona, 1713 E University Blvd #93, Tucson, AZ 85721 (USA). Address all corre- spondence to Mr Farr at: jfarr@ email.arizona.edu.

S.B. Going, PhD, is Professor, De- partment of Nutritional Sciences, University of Arizona.

P.E. McKnight, PhD, is Assistant Professor of Psychology, Depart- ment of Psychology, George Ma- son University, Fairfax, Virginia.

S. Kasle, PhD, is Research Assistant Professor, Arizona Arthritis Center, College of Medicine, University of Arizona.

E.C. Cussler, MS, is Data Manager, Department of Physiological Sci- ences, University of Arizona.

M. Cornett, RN, is Senior Research Nurse, Arizona Arthritis Center, College of Medicine, University of Arizona.

[Farr JN, Going SB, McKnight PE, et al. Progressive resistance train- ing improves overall physical ac- tivity levels in patients with early osteoarthritis of the knee: a ran- domized controlled trial. Phys Ther. 2010;90:356 –366.]

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The primary goals of knee osteo-arthritis (OA) treatment are toreduce pain and improve func- tion and quality of life. Declining en- thusiasm for cyclo-oxygenase 2 in- hibitors for knee OA pain relief and unsuccessful clinical trials of disease- modifying OA drugs have contrib- uted to increased interest in non- pharmacologic treatments for OA.1

Resistance training (RT) exercise programs and educational self- management (SM) programs are 2 mainstays of nonpharmacologic treatment.

Physical activity (PA) refers to any bodily movement that results in en- ergy expenditure. Physical activity is an essential recommendation in- cluded in all guidelines for manage- ment of knee OA.2– 4 Moreover, PA is recommended by the US Centers for Disease Control and Prevention (CDC) and the American College of Sports Medicine (ACSM) for general health to reduce risks of obesity- linked health problems, including di- abetes and cardiovascular disease,5,6

which often coexist with knee OA. Work group recommendations from the 2002 Exercise and Physical Ac- tivity Conference (EPAC)7 advise pa- tients with knee OA to accumulate 30 minutes of at least moderate- intensity (�3 metabolic equivalents [METs]*) PA on at least 3 days of the week. The expert EPAC panel con- cluded that promotion of PA in adults with arthritis should empha- size aerobic moderate- and vigorous- intensity physical activity (MVPA, �3 METs) and muscle strengthening resistance exercise. In a more recent statement, an expert consensus panel provided evidence-based rec- ommendations for practical delivery of exercise therapy for patients with knee OA, stating that “both general (aerobic fitness training) and local (strengthening) exercises are essen-

tial, core aspects of management for every patient with knee OA.”8(p69)

In recent years, it has become clear that RT can have a positive effect on resting energy expenditure (REE), to- tal free-living energy expenditure (TEE), and activity-related energy ex- penditure (AEE). Withers et al9 com- pared REE, TEE, and AEE of chroni- cally active women who engaged in RT and chronically inactive women, aged 49 to 70 years. They reported that the chronically active women had increased REE, TEE, and AEE compared with the chronically inac- tive women. Hunter et al10 addressed this concern in elderly men and women who were healthy, aged 61 to 77 years. They found increases in REE, TEE, and AEE in response to 26 weeks of RT and showed that the TEE increase remained significant even after adjustment for the energy expenditure of the RT. These find- ings suggest that RT has value in in- creasing energy expenditure and lipid oxidation rates in older adults.

A potential concern when structured RT programs are prescribed is that participants may simply switch activ- ity modes, resulting in a decrease in aerobic MVPA. For example, Goran and Poehlman11 and Meijer et al12

both observed a compensatory de- crease in free-living PA levels of older adults after engaging in RT pro- grams. However, we found no stud- ies that have addressed this concern in a patient population such as pa- tients with early OA of the knee. Al- though controlling mode is desirable for study purposes, in clinical and public health settings, replacement of one mode with another may de- feat efforts to increase overall MVPA. In contexts such as the present study, participants randomly as- signed to receive RT might engage in less overall MVPA, substituting RT for other modes of MVPA. Alterna- tively, if participants randomly as- signed to receive RT increased or at

least maintained their MVPA levels, they would benefit from both RT and aerobic MVPA. However, if RT inhib- ited participants from achieving rec- ommended MVPA levels, the net re- sult could interfere with exercise interventions aimed at improving cardiovascular function, insulin ac- tion, energy metabolism, and psy- chological health in patients with OA of the knee.13,14 Therefore, in the present analysis, we aimed to deter- mine the effect of a structured RT intervention on overall daily levels of activity by using accelerometry to measure MVPA in individuals with early-onset knee OA who partici- pated in an RT program and in those who participated in an SM program. We hypothesized that in addition to improving muscle strength (force- generating capacity), the RT groups would maintain similar levels of MVPA compared with the SM group.

Method Design Overview The data used for this analysis were obtained from the Multidimensional Intervention for Early Osteoarthritis of the Knee Study (the Knee Study), a randomized clinical trial comparing the effectiveness of SM alone, RT alone, and combined RT�SM on rel- evant knee OA outcomes over 24 months. After preliminary analyses of the 3 groups, the RT groups (RT alone and RT�SM) were collapsed into a single group and compared with the SM only group to test the

* 1 MET�3.5 mL O2�kg �1�min�1.

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question of whether participants ran- domly assigned to the RT group would substitute RT for MVPA. The analysis presented here was based on data from the first phase (baseline to 9 months) of the interventions described. Outcome measurements were obtained at baseline and at 3 and 9 months of intervention.

Participants Participants were recruited from the Tucson, Arizona, general community and surrounding areas using mass mailings, media advertisements, pe- riodic media coverage, and requests to local physicians for patient refer- rals. A total of 1,726 people were assessed for eligibility. Eligibility cri- teria were: age between 35 and 68 years to ensure an early-onset knee OA sample; pain on 4 or more days of the week in one or both knees for at least 4 months during the previous year; less than 5 years’ symptom du- ration15,16; radiographic status of grade II OA (and no higher) in at least one knee, as defined by the Kellgren and Lawrence classifica- tion17; and disability due to knee OA, as assessed with the Western Ontario and McMaster Universities Osteo- arthritis (WOMAC) Index.18 Partici-

pants gave written informed consent and self-reported demographic char- acteristics (Tab. 1). All participants enrolled in the study met American College of Rheumatology classifica- tion criteria for early OA of the knee.19

A CONSORT flowchart describing the progress of participants through the 9-month intervention is pre- sented in Figure 1. Of the 1,726 peo- ple who were assessed for eligibility, 293 eligible participants were strati- fied by sex and randomly assigned via a random number table to 1 of the 3 treatment groups (SM, RT, or RT�SM). Concealed allocation was accomplished using envelopes to conceal computer-generated values. Manifest transparency of the treat- ments rendered blinding unfeasible. Essentially, given our outcome mea- sures, interrater agreement bias was deemed a smaller threat to internal validity than ensuring treatment fi- delity, which precluded effective blinding. Of the 293 eligible partici- pants, 39 did not receive any of the allocated intervention and 33 discon- tinued the intervention prior to 9 months (Fig. 1).

Interventions Resistance training. The overall goal of the RT intervention was to encourage participants to maintain a long-term exercise program to in- crease muscle strength, decrease im- pairment, maintain and restore func- tion, and protect joint structures from further damage. The RT inter- vention paralleled programs devel- oped by the ACSM5 and the National Strength Training and Conditioning Association20 and was designed to test expert panel recommenda- tions.8 Sessions targeted improve- ment in each of 4 core areas: (1) stretching and balance, (2) range of motion (ROM) and flexibility, (3) iso- tonic muscle strengthening, and (4) aerobics. Participants met with cer- tified physical trainers 3 times per week for 9 months, with a minimum of 1 day of rest between training ses- sions, to complete a 1-hour exercise regimen that emphasized RT. Super- vised, small-group sessions were held to improve adherence. Each ses- sion consisted of: (1) 10-minute warm-up on either a bicycle ergome- ter or treadmill at 50% maximum heart rate, (2) 5 to 10 minutes of stretching and balance exercises, (3) 10 minutes of ROM exercises, (4) 30

Table 1. Baseline Descriptive Characteristics of Participants by Intervention Groupa

Characteristic SM Group

(n�57) RT Group (n�52)

RT�SM Group (n�62)

Collapsed RT and RT�SM Group

(n�114) Noncompleters

(n�83)

Female (%) 72 73 79 76 83

Age (y), X (SD) 55.8 (6.1) 55.5 (7.3) 54.2 (7.3) 54.7 (7.3) 55.5 (7.7)

Height (cm), X (SD) 169.5 (8.1) 169.6 (10.6) 167.2 (9.4) 168.3 (10.0) 166.7 (10.1)

Weight (kg), X (SD) 80.6 (13.7) 80.1 (19.4) 76.1 (13.4) 77.8 (16.6) 78.2 (15.2)

BMI (kg/m2), X (SD) 28.0 (4.0) 27.5 (4.5) 27.2 (4.2) 27.3 (4.3) 28.1 (4.3)

Normal (�25) 30% 35% 32% 33% 33%

Overweight (25–30) 40% 36% 40% 39% 39%

Obese (�30) 30% 29% 28% 28% 28%

Knee OA severity

Grade 11 unilateral knee OA 59% 46% 56% 52% 55%

Grade II bilateral knee OA 41% 54% 44% 48% 45%

a SM�self-management, RT�resistance training, RT�SM�resistance training � self-management, BMI�body mass index, OA�osteoarthritis.

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Figure 1. Flowchart describing the progress of participants through the Knee Study trial. RT�resistance training, SM�self-management, RT�SM�resistance training � self-management.

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minutes of RT exercises, and (5) 5 minutes of cool-down. Specific RT exercises included leg press, leg curl, hip abduction and adduction, straight leg lift, incline dumbbell press, seated row, and calf raise. The exercises were chosen primarily to directly strengthen the muscles sup- porting the knee, but also to im- prove the strength of muscles most involved in activities of daily living.

The strength protocol progressed through 2 phases: (1) resistance from body weight and Thera-Band exercise bands† and (2) free weights and machine weights. Participants started with one set per exercise, 6 to 8 repetitions per set, at an inten- sity of 50% of each individual’s 3-repetition maximum (3-RM). Dur- ing an orientation session, partici- pants were familiarized with the equipment and instructed by certi- fied trainers on proper lifting tech- niques for all exercises. All partici- pants began training at a comfortable weight with proper form for each exercise based on standardized pro- tocols developed by the ACSM.5 The program progressed from 1 to 2 sets, along with increases in load when participants were able to complete all repetitions with proper body po- sition and joint alignment for 3 con-

secutive sessions.21 They then pro- gressed to loads between 60% and 75% of their 3-RM and continued to increase loads to maintain vigorous intensity. The ROM exercises were increased for each participant when the exercises could be completed with a Borg scale score of difficulty of �6.22 Participants completed training logs during all sessions and reported sets, repetitions, and loads for each exercise. Certified physical trainers supervised all RT sessions, monitored progression, and tested participants following standard pro- tocols.5 Throughout the interven- tion, trainers emphasized good form and encouraged participants to re- port soreness or pain during and af- ter RT sessions. Changes in load from baseline to 9 months for the RT groups (RT and RT�SM) are shown in Table 2.

Self-management. The SM inter- vention was designed to target cop- ing skills, promoting the use of more adaptive strategies and fewer avoid- ance or passive strategies based on existing self-help programs.23 The in- tervention also targeted self-efficacy through a variety of educational and behavioral techniques. Self-efficacy skills focused on increasing percep- tions of control for physical function- ing, pain management, and other ancillary arthritis symptoms. The

9-month program began with 12 weekly, 90-minute classroom ses- sions in which participants com- pleted SM education modules ad- dressing an overview of OA, general exercise principles and PA recom- mendations, stress management, foot care, pain management, analge- sic and anti-inflammatory medica- tions, nutrition for health, coping mechanisms, communication with health care providers, and healthy lifestyle practices. As part the of the exercise module, participants were introduced to the benefits of MVPA and RT for patients with OA of the knee and were given instructions for establishing a regular PA program. They also were provided with PA recommendations implemented by the CDC6 and the ACSM5 and work group PA recommendations from the 2002 EPAC for people with ar- thritis,7 but no further exercise in- struction was given. Classroom ses- sions were followed by 24 weeks of a structured telephone intervention program that reinforced SM skills.

Combined treatment. The com- bined treatment group (RT�SM) en- gaged in both the RT and SM inter- ventions, with slight alterations to ensure equivalence of contact time across treatment groups. Specifi- cally, participants in the RT�SM group were contacted by staff less during the 24 weeks of the tele- phone intervention program that fol- lowed classroom sessions.

Anthropometry. Anthropometric measurements were obtained at baseline following standard proto- cols outlined in the Anthropometric Standardization Reference Manu- al.24 Total body mass was measured to the nearest 0.1 kg using a cali- brated scale (Seca model 770),‡ and height was measured to the nearest 0.1 cm using a portable stadiometer

† The Hygenic Corp, 1245 Home Ave, Akron, OH 44310-2575.

‡ Seca GMBH and Co KG, Hammer Steindamm 9 25, 20089 Hamburg, Germany.

Table 2. Change (�) in Weight Lifted From Baseline to 9 Months of Intervention for All Resistance Trainersa

Exercise RT

Group � RT�SM Group �

All (n�114) � P b

Leg press 112.7 (72.1) 91.9 (67.3) 101.6 (69.3) .19

Incline dumbbell press 11.4 (8.5) 10.7 (8.0) 11.0 (8.2) .69

Seated row 27.2 (15.8) 20.1 (18.2) 23.3 (17.4) .08

Leg curl 41.2 (35.5) 33.7 (39.6) 37.3 (37.7) .40

Calf raise 13.4 (15.1) 10.9 (15.2) 12.2 (15.0) .60

a Values are means (SD) for change in load (pounds) from baseline to 9 months of intervention based on 1 to 2 sets of 6 to 8 repetitions. RT�resistance training, RT�SM�resistance training � self-management. b Independent t test for group difference.

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(Shorr Height Measuring Board)§ af- ter full inspiration.

Pain. Knee pain was assessed us- ing the WOMAC Index, which has been validated in patients with OA of the knee.18 The WOMAC pain sub- scale comprises 5 items eliciting pa- tient ratings on visual analog scales (0 –100) of pain severity during walk- ing, stair use, lying in bed at night, sitting, and standing. The pain sub- scale has a maximum summed score of 500, with higher scores reflecting more pain.

Physical activity. Baseline PA lev- els of the Knee Study participants have been published previously.25

Physical activity was measured using the MTI Actigraph accelerometer (model 7164).� The uniaxial Acti- graph accelerometer measures vertical-plane accelerations and de- celerations and records them as “counts” over a specific time interval (epoch), which provides informa- tion regarding the intensity of PA as- sociated with movement.26 The ac- celerometer assesses accelerations ranging from 0.05 to 2.0g, with a frequency ranging from 0.25 to 2.5 Hz.27 These specifications allow for detection of normal body motion, while filtering out high-frequency vi- bration movements. Actigraph reli- ability and validity have been re- viewed in detail.28 Counts have been shown to be highly correlated (r�.77–.88) with steady-state oxy- gen consumption during ambulatory activities26,29 and have been shown to be dependent upon movement frequency in a mechanical setup.30

For each assessment, the accelerom- eter was initialized and downloaded according to the manufacturer’s specifications30 and set to record

data in 60-second epochs. Partici- pants were instructed to wear the accelerometer for 7 contiguous days during all waking hours, except while in water. A previous study31

has shown that when the Actigraph accelerometer is worn for 7 consec- utive days, PA can be assessed with 90% reliability. The accelerometer was firmly secured to a belt worn around the waist and positioned on the right hip because this site per- mits measurement of whole-body movement, does not interfere with daily activities, and is the most fre- quently used site in epidemiological studies.25 The following measure- ments were obtained: days worn; registered wear time in hours per day; and average minutes per day spent in moderate-intensity physical activity (MPA, 3– 6 METs), vigorous- intensity physical activity (VPA, �6 METs), and MVPA (�3 METs). A number of studies26,29,32–34 have used criterion methods such as indi- rect calorimetry and heart rate mon- itoring to demonstrate the reliability and validity of the Actigraph acceler- ometer. As described in detail previ- ously,25 we minimized sampling error by averaging the cutoff points reported by calibration studies us- ing the MTI Actigraph model 716426,29,32–34 and applied the result- ing cutoff points to differentiate among PA intensities. The applied cutoff points for MPA and VPA inten- sities were accelerometer recordings of 2,225 to 5,950 and �5,950 counts per minute, respectively. Moderate- and vigorous-intensity physical activ- ity was defined as �2,225 counts per minute.

Leisure time PA and exercise habits were assessed at baseline and at 3 and 9 months of intervention using the Aerobics Center Longitudinal Study Physical Activity Question- naire (ACLS).35 The ACLS elicits self- reports of frequency (sessions per week) and duration (minutes per ses- sion) of activities such as walking,

running, treadmill, cycling, swim- ming, aerobics, yoga, weight lifting, and other sports (eg, golf, tennis, soccer).

Data Analysis For the analyses presented here, a valid day of PA was defined as having 10 or more hours of accelerometer wearing, based on previous recom- mendations from analyses of the National Health and Nutrition Exam- ination Survey (NHANES) accelerom- eter database.36 Furthermore, 5 to 7 days of valid accelerometer wearing was required for inclusion in the present analysis. We chose a mini- mum of 5 days of accelerometer wearing because PA levels vary greatly throughout the week and 1 to 4 days of PA may not be representa- tive of habitual PA.28

In order to address the question of whether participants randomly as- signed to receive RT would substi- tute RT for MVPA, the RT groups (RT and RT�SM, n�114) were collapsed into a single group and compared with the SM group (Tab. 1). Descrip- tions of the 171 participants ran- domly assigned to each of the 3 in- tervention groups (SM, RT, RT�SM) and the 114 participants who re- ceived the RT intervention (col- lapsed RT and RT�SM group) are shown in Table 1. Means, standard deviations, and 95% confidence in- tervals were calculated for continu- ous variables, and frequencies were calculated for categorical variables. Data were checked for missing values and normality prior to analy- ses. Moderate- and vigorous-intensity physical activity (minutes per day), which was skewed, was natural log transformed for analysis, resulting in a normal distribution.

Preliminary tests for baseline differ- ences in descriptive characteristics among the 3 intervention groups were performed using an analysis of variance or the chi-square test for

§ Shorr Productions, 17802 Shotley Bridge Place, Olney, MD 20832. � Manufacturing Technologies Inc, 70 Ready Ave NW, Fort Walton Beach, FL 32548.

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proportions as appropriate. For all subsequent analyses, the RT groups (RT and RT�SM) were collapsed into a single group and compared with the SM group to address the question of whether RT affects MVPA. The RT groups were com- bined because both groups of partic- ipants engaged in the RT interven- tion and no significant (P�.05) group differences using independent t tests were observed for any vari- ables at any time point. Effect sizes representing the magnitude of differ- ence between baseline and 3 and 9 months were calculated using Co- hen’s method37 based on adjusted means of MVPA for the 2 groups (SM and collapsed RT).

A repeated-measures analysis of co- variance was performed with group (SM and collapsed RT) as the between-subjects factor and time (3 and 9 months) as the within-subjects factor. Baseline MPVA, age, BMI, knee OA pain, and sex were entered as covariates to account for baseline between-group differences in MVPA and the putative influence of these variables on MVPA. The specific ef- fect of interest in this analysis was the group � time interaction. A sig- nificant group � time interaction would indicate that the degree of change in MVPA over time was dif- ferent for the 2 groups (SM and col- lapsed RT). Statistical significance was set at P�.05 for all tests. Analy- ses were conducted using the Statis- tical Package for the Social Sciences, version 17.0.#

Results At baseline, 3 months, and 9 months, 5, 17, and 26 participants, respec- tively, either did not wear an accel- erometer or did not meet the inclu- sion criteria. Comparisons of baseline descriptive characteristics for noncompleters (n�83) versus

completers (n�171) showed no sig- nificant (P�.05) differences (Tab. 1). After 9 months of intervention, the numbers of participants who suc- cessfully completed all measures at baseline, 3 months, and 9 months were as follows: SM group�57, RT group�52, RT�SM group�62 (Fig. 1). The final sample of partici- pants with early onset OA of the knee who successfully adhered to the accelerometer protocol com- prised 171 participants (74% women, 26% men; mean age�55.1 (SD�7.1) years, and mean BMI�27.6 (SD�4.2) kg/m2). Preliminary base- line analyses of the 3 intervention groups showed no significant (P�.05) difference among groups or between completers (n�171) and noncompleters (n�83) at baseline for any variables (Tabs. 1 and 3). Par- ticipants wore the accelerometer, on average, 6.8 (SD�0.5) days and 14.2 (SD�2.2) hours per day over all 3 PA assessments. There were no signifi- cant group differences (P�.05) in number of days the accelerometer was worn or in accelerometer wear- ing time at any time interval. Signifi- cant differences were not observed for any of the measured variables (P�.05) when participants with 5 to 6 days of accelerometer data were compared with participants with 7 days of data. Unadjusted means, stan- dard deviations, and 95% confidence intervals for MPA, VPA, and MVPA for the collapsed RT group and the SM group at baseline, 3 months, and 9 months are presented in Table 3.

Exercise session attendance was 75.9% (SD�17.9%) for the collapsed RT group, and SM class attendance was 85.9% (SD�14.2%) for the SM group. However, attendance did not significantly (P�.48) differ between the collapsed RT group and the SM group. The RT groups significantly (P�.001) increased their leg press, leg curl, incline dumbbell press, seated row, and calf raise loads from baseline to 9 months (Tab. 2). Data

from the ACLS questionnaire showed that few SM group partici- pants (n�11, 19%) reported engag- ing in any form of resistance exercise throughout the intervention.

Despite high exercise session atten- dance and significant improvements in muscle strength, very little time (minutes per day) was spent in VPA as measured by the accelerometer, and there were no significant (P�.05) differences in VPA among the intervention groups at any time interval (Tab. 3). Consequently, aver- age daily MVPA (�3 METs) was rep- resentative of total time spent in health-enhancing PA intensities. The collapsed RT group participants in- creased their MVPA by 18% at 3 months (P�.001, effect size [d]� 0.26) and by 10% at 9 months (P�.047, effect size [d]�0.15) com- pared with baseline levels. The SM group participants increased their MVPA by 22% at 3 months (P�.023, effect size [d]�0.25) and by 2% at 9 months (P�.80, effect size [d]�0.03) compared with baseline levels. After adjusting for baseline MVPA, age, BMI, sex, and knee OA pain, there was a significant (P�.034) group � time interaction for MVPA, which indicated that lon- gitudinal MVPA decreased at a greater rate in the SM group than in the collapsed RT group (Fig. 2).

Discussion The overall increase in MVPA by the RT groups suggests that patients with early-onset OA of the knee can engage in a structured resistance exercise program without a compen- satory decrease in MVPA levels. Compared with baseline, MVPA in- creased in the collapsed RT group by 18% at 3 months and 10% at 9 months, and the SM group showed a 22% increase in MVPA at 3 months but only a 2% increase at 9 months. These findings indicate that both SM and RT programs are effective for increasing short-term MVPA in pa-

# SPSS Inc, 233 S Wacker Dr, Chicago, IL 60606.

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tients with early OA of the knee, which is consistent with the findings of previous studies.38 – 40 The greater 3-month increase in MVPA in the SM group compared with the RT group may have resulted from differences in adherence (SM group�86%, RT group�76%) or because both pro- grams encouraged PA. Although both treatments were effective in in- creasing short-term MVPA, RT was better than SM for maintaining long- term MVPA levels. Indeed, a signifi- cant group � time interaction indi- cated that the degree of change in MVPA was different between groups (ie, MVPA in the RT groups re- gressed between 3 and 9 months at a slower rate than in the SM group). Thus, rather than simply substituting RT for MVPA, the RT groups were

able to maintain MVPA levels in ad- dition to attaining strength benefits from RT. It is possible that participa- tion in the RT sessions may have con- tributed to the long-term mainte- nance of MVPA levels. On the other hand, adherence and MVPA in the SM group may have dropped off be- cause of the intervention content. For example, early sessions focused on developing SM skills, whereas later sessions focused on reinforcing those skills. Thus, those participants who already mastered the skills may have seen less utility in the contin- ued support.

Previous studies have shown that when older adults participate in structured RT programs, there is a tendency for a compensatory de-

crease in aerobic MVPA.11,12 For ex- ample, Goran and Poehlman11 ob- served a decrease of �544 kJ per day in free-living PA in elderly adults who were healthy after an 8-week high-intensity (85% of maximal oxy- gen consumption) training program. It is possible that the high intensity of the exercise program used in that study was too vigorous, thereby fa- tiguing the participants to the extent that they were no longer able to en- gage their regular PA throughout the remainder of the day. Meijer et al12

reported that a 12-week, moderate- intensity combined aerobic and RT program resulted in improved phys- ical fitness but had no effect on total daily PA (ie, after subtracting the PA of the exercise training sessions, this study showed that training PA was

Table 3. Means (SD) and 95% Confidence Intervals for Average Time Spent in the 3 Physical Activity Intensities and for Knee Osteoarthritis Paina

Measure

SM Group (n�57)

RT Group (n�52)

RT�SM Group (n�62)

Collapsed RT and RT�SM Group

(n�114)

X (SD) [95%CI] X (SD) [95%CI] X (SD) [95%CI] X (SD) [95%CI]

MPAb (min/d)

Baseline 23.4 (18.2) [18.9–28.6] 24.6 (17.8) [19.8–29.7] 27.9 (18.3) [23.2–32.6] 26.5 (18.1) [23.1–29.8]

3 mo 29.0 (22.5) [23.1–35.0] 27.9 (19.4) [23.1–32.7] 32.1 (17.1) [27.7–36.4] 30.2 (17.2) [27.0–33.4]

9 mo 24.1 (17.5) [19.4–28.7] 26.1 (17.7) [21.2–31.1] 30.1 (15.0) [26.3–33.9] 28.3 (16.3) [25.3–31.3]

VPAc (min/d)

Baseline 0.8 (2.9) [0.0–1.6] 0.8 (2.6) [0.1–1.6] 1.0 (2.0) [0.5–1.5] 0.9 (2.3) [0.5–1.4]

3 mo 0.7 (1.7) [0.3–1.2] 2.1 (4.9) [0.7–3.5] 1.6 (2.5) [0.9–2.2] 1.8 (3.8) [1.1–2.5]

9 mo 0.7 (2.1) [0.1–1.2] 1.6 (4.2) [0.4–2.8] 1.9 (3.7) [26.3–33.9] 1.8 (4.0) [1.0–2.5]

MVPAd (min/d)

Baseline 24.2 (19.3) [19.4–29.7] 25.4 (19.4) [20.2–31.0] 28.6 (19.4) [24.0–33.8] 27.4 (19.4) [23.8–31.0]

3 mo 29.7 (23.1) [23.6–35.9] 30.0 (19.7) [24.5–33.3] 33.6 (18.2) [29.0–38.3] 32.0 (18.9) [28.5–35.5]

9 mo 24.8 (18.7) [19.7–29.6] 27.7 (20.0) [22.2–33.3] 31.8 (16.8) [27.7–36.2] 30.1 (18.3) [26.7–33.5]

Knee OA paine

Baseline 82.2 (68.3) [64.1–100.3] 84.3 (70.1) [64.8–103.8] 81.9 (67.3) [64.8–99.0] 83.0 (68.3) [70.3–95.6]

3 mo 72.0 (66.3) [54.4–89.6] 47.6 (50.9) [33.5–61.8] 67.1 (68.8) [49.5–84.7] 58.2 (61.8) [46.6–69.7]

9 mo 62.9 (81.0) [41.4–84.4] 48.6 (61.3) [31.4–65.9] 56.2 (75.3) [36.7–75.6] 52.7 (29.1) [39.7–65.7]

a SM�self-management, RT�resistance training, RT�SM�resistance training � self-management, CI�confidence interval, OA�osteoarthritis. b MPA�moderate-intensity physical activity (3– 6 metabolic equivalents [METs]). c VPA�vigorous-intensity physical activity (�6 METs). d MVPA�combined moderate- and vigorous-intensity physical activity (�3 METs). e Knee OA pain assessed with Western Ontario and McMaster Universities Osteoarthritis (WOMAC) Index pain subscale comprising 5 items eliciting patient ratings on visual analog scale (0 –100) of pain severity during walking, stair use, lying in bed at night, sitting, and standing. The pain subscale has a maximum summed score of 500, with higher scores reflecting more pain.

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compensated for by a decrease in nontraining PA, consistent with the findings of Goran and Poehlman11). In contrast, a 26-week RT program in a study by Hunter et al10 was not associated with a compensatory drop in free-living PA. The findings of Hunter et al are consistent with our findings because participants were able to engage in RT without substituting RT for MVPA.

Although accelerometers allow for accurate measurements of daily time spent in various health-enhancing PA intensities (ie, MPA, VPA, and MVPA),26 hip placement may under- estimate energy expenditure during certain activities (ie, biking, climbing stairs, and weight lifting) and pro- vide no estimate of PA during water activities (eg, swimming) because ac- celerometers cannot be worn.28

Given the time spent standing, sit- ting, and lying during RT, this mode of activity is not measured well by accelerometers.28 This finding was evident in the present study because

despite rather high exercise session attendance (RT group�76%) and sig- nificant (P�.001) increases in load from baseline to 9 months for a num- ber of RT exercises (eg, leg press, leg curl, seated row, incline dumbbell press, calf raise), average daily VPA in the RT group remained extremely low at 3 months (1.8 [SD�3.8] min- utes per day) and 9 months (1.8 [SD�4.0] minutes per day). Thus, based on the observed improve- ments in strength, the RT groups likely received additional benefits of RT compared with the SM group, such as improved REE, TEE, AEE, lipid oxidation rates, musculoskele- tal function, and body composition, which have been observed in re- sponse to RT in older adults.9,10,41

Furthermore, the ACLS question- naire indicated that few SM group participants (n�11, 19%) engaged in any form of RT, and thus the majority of participants in this group did not receive additional benefits of RT.

In addition to increasing TEE,10 RT has been shown to improve a num- ber of functional limitations that lead to disability in patients with OA of the knee, such as quadriceps muscle weakness,42 neurological deficits,43

and decreased knee ROM.44 Further- more, RT programs have been shown to improve psychological fac- tors such as mood, self-efficacy, anx- iety, and depression.45,46 Aerobic MVPA also can improve some of the same functional limitations in pa- tients with OA of the knee and can reduce risks of obesity-linked health problems, including diabetes and cardiovascular disease,5,6 which of- ten coexist with knee OA. There- fore, in clinical settings, the ability to engage in RT without sacrificing MVPA is important.

We acknowledge several limitations of our study. For example, 5 to 7 days of contiguous accelerometer re- cordings may not be representative of habitual PA, and adipose tissue around the waist might affect the validity of the accelerometer out- puts.25 Furthermore, accelerometers may underestimate PA during activi- ties such as biking, climbing stairs, and weight lifting and cannot be worn during water activities (eg, swimming).28 Thus, PA may be un- derestimated in individuals who en- gage in these activities on a regular basis. More detailed physiological studies are needed in patients with OA of the knee to measure directly different energy expenditures (ie, REE, TEE, and AEE), which have been shown to be elevated in older adults in response to RT.9,10 Lastly, we cannot establish a causal relation- ship between increased levels of MVPA and improved physical func- tion because we did not measure functional changes. However, a number of randomized controlled trials8,39,40,47,48 in patients with OA of the knee have shown a strong asso- ciation between increased levels of MVPA and RT and improved physical

Figure 2. Average daily moderate- and vigorous-intensity physical activity (MVPA, �3 metabolic equivalents) at 3 and 9 months of intervention for the self-management group (SM) and collapsed resistance training (RT) groups (RT and RT�SM). Values were adjusted for baseline MVPA, age, body mass index, sex, and knee osteoarthritis pain. There was a significant group � time interaction (P�.034) for MVPA.

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function, which provides support for improved knee function of indi- viduals who undertook the RT intervention.

Conclusion Patients with early-onset knee OA were able to engage in an RT pro- gram without a compensatory de- crease in their overall MVPA levels. Because RT has been shown to in- crease energy expenditure in adults9,10,41 and has been shown to improve muscle strength and physi- cal function and to reduce pain in patients with OA of the knee,8 it is a vital component of knee OA therapy. Given the relevant health benefits of RT and aerobic MVPA for manage- ment of knee OA, future studies are necessary to improve adherence to both modes of exercise.

Dr Going and Dr McKnight provided con- cept/idea/research design. Mr Farr, Dr Mc- Knight, and Dr Kasle provided writing. Mr Farr, Dr McKnight, Dr Kasle, and Dr Cornett provided data collection. Dr Kaske provided data management. Mr Farr, Dr McKnight, and Ms Cussler provided data analysis. Dr Going, Dr McKnight, and Dr Cornett pro- vided project management. Dr McKnight provided fund procurement. Dr Going and Ms Cussler provided consultation (including review of manuscript before submission).

The authors thank the men and women with knee OA who generously volunteered their time, the project coordinators for their over- sight of all aspects of the study, and the other members of the Knee Study investiga- tive team. Dr Isidro Villanueva is gratefully acknowledged for his contributions to the Knee Study.

This study was approved by the University of Arizona Institutional Review Board and con- ducted in accordance with the Helsinki Declaration.

This project was supported by National In- stitutes of Health/National Institute of Arthri- tis and Musculoskeletal and Skin Diseases grant R01-AR-047595. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institute of Arthritis and Mus- culoskeletal and Skin Diseases or the Na- tional Institutes of Health.

NIH Clinical Trials Registry: NCT00586300.

This article was received February 10, 2009, and was accepted October 30, 2009.

DOI: 10.2522/ptj.20090041

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