Fit & Strong! (F&S!) is a non-pharmacological intervention designed for older people with osteoarthritis with proven efficacy. This program was developed and implemented among American patients. It is composed by two components: physical exercise with health education. In total, the program last eight weeks, and meets three times per week (24 sessions), for 90 minutes per session. The nationals and internationals statistics showed that Portugal has a high prevalence of OA, in particular in the knee or hip. Considering this fact and the negative impact in OA patients' lives the F&S! program was culturally adapted for Portugal, which constitutes its first formal adaptation to an international population and setting.

Therefore, a randomized controlled trial was developed to the effects of F&S! among Portuguese older adults with lower-extremity OA, particularly, with respect to physical performance (walking speed, balance, lower body strength), pain, stiffness, functionality, physical activity, anxiety, depression and fear of movement. Participants were identified and referred from the electronic medical record maintained by general practitioners in Health Care Centers. Participants were randomly allocated to the experimental or to the control and were assessed three times (baseline, posttest and 4-months follow-up). Data analysis included descriptive statistics (medians and interquartile ranges) to describe participants' characteristics. The comparison between the experimental and the control group at baseline was performed using the Mann-Whitney U test for continuous variables and the Fisher test for categorical variables. Within each group, changes over time (pretest, posttest, follow-up) were analyzed using the Wilcoxon signed-rank test. Between group comparisons of differences in outcome variables between pretest, posttest and 4-month follow-up were analyzed using the Mann-Whitney U test.

Fit & Strong! (F&S!) is an evidence-based intervention for OA in the U.S. developed at the University of Illinois, Chicago. This program was designed for older adults who have lower extremity joint pain and stiffness caused by OA. It is a pioneer multi-component intervention that incorporates physical exercise with health education for long lasting behavior change. The intervention last 8 weeks, and meets three times per week (24 sessions), for 90 minutes per session. Each session includes one hour of stretching, low-impact aerobics/ fitness walking, and strengthening exercises using adjustable ankle cuff weights and exercise bands, and balance exercises. The class was structured to begin with a warm-up activity, then, an aerobic activity and balance exercises, strengthening exercises, end a cold down activity with stretching and relaxation exercises were performed. The last 30 minutes of each session include structured, manual-based group discussion/health education. The educational component aims to facilitate symptom management, increase confidence in ability to exercise, and commitment to lifestyle change. Toward the end of the eight weeks, each participant meets individually with the instructor to develop a tailored adherence contract (a core element of the program). Participants received a "Participant Manual" with the description of the all program and the logs that have to fill during the program.

In Portugal, similar to other developed countries, the prevalence of OA is high. It is estimated that the self-reported prevalence of knee OA in adults 18 years and older was 11.1%, 5.9% in men and 14.2% in women. Rates of hip OA were 5.5%, 2.2% in men and 7.4% in women. The National Rheumatic Diseases Observatory (ONDOR) that based its findings on radiographic evidence, found a prevalence of knee OA in adults 40 years of age or older of 56.9% in men and 57.7% in women; radiographic hip OA was 54.8% in men and 24.5% in women.

Considering the high prevalence and the negative impact that OA has on patients' lives, in contrast to the positive effects demonstrated by F&S! in U.S., the program was culturally adapted in Portugal, which constitutes its first formal adaptation to an international population and setting. Therefore, a randomized controlled trial was developed to analyze the effects of the Portuguese version of the F&S!. This study sought to analyze the effects of F&S! among Portuguese older adults with lower-extremity OA, particularly, with respect to physical performance (walking speed, balance, lower body strength), pain, stiffness, functionality, physical activity, anxiety, depression and fear of movement.

Participants were identified and referred from the electronic medical record maintained by general practitioners in Health Care Centers.This phase of the study was conducted in two waves: the first wave lasted for three months (May 2017 to July 2017) and the second took place over five months (March 2018 to July 2018). After the identification of the potential participants by general practitioners, the principal investigator contacted the potential participants by phone to reinforce the invitation and to schedule a face-to-face interview (baseline assessment). During the phone contact an eligibility screen was used to confirm the presence of inclusion/exclusion criteria. Participants were randomly allocated by the researcher to the experimental or to the control group after the baseline assessment.

We used face-to-face interviews to collect the data in three distinct moments: baseline, posttest (at the end of the program) and 4-months follow up. Experimental group was enrolled in the Portuguese F&S! Program. The program was provided in two classes, the first class took place from October to December 2017 and the second class took place from October to November 2018.

Thirty one participants who were eligible and consented to participate, using a 2:1 randomization scheme, 23 participants were assigned to the experimental group and eight to the control group.

Regarding the data analysis, the descriptive statistics, including medians and the interquartile ranges were used to describe participant characteristics. The comparison between the experimental and the control group at baseline was performed using the Mann-Whitney U test for continuous variables and the Fisher test for categorical variables.

Within each group, changes over time (pretest, posttest, follow-up) were analyzed using the Wilcoxon signed-rank test. Between group comparisons of differences in outcome variables between pretest, posttest and 4-month follow-up were analyzed using the Mann-Whitney U test. Participants with an attendance rate of less than 50% were included in the baseline analyses but then were considered to be drop-outs and were excluded from posterior analyses. Results from these analyses are presented as medians and IQRs. Statistical analyses were performed using the Statistical Package for the Social Sciences for Windows (SPSS, version 25, IBM) and α=0.05 was used to determine significance level.

Inclusion Criteria:

• age 50 years or older,
• lower extremity OA diagnosed according to the clinical criteria of the American College of Rheumatology (ACR) [14,15], and
• doctor's authorization to participate.

Exclusion Criteria:

• no recent (<6 months) joint replacements,
• no steroid injections in the last 3 months,
• no moderate to severe cognitive impairment,
• no rheumatoid arthritis,
• no diabetes mellitus and/or uncontrolled hypertension,
• no other health condition for which multicomponent physical exercise is not recommended.

Experimental and control group had no interaction to each other during the study. For data collection was used an individual interview in a place that guarantee privacy. None participant were aware about the group that they will be allocated before the baseline assessment.