Group-based versus individual-based circuit training in elderly women with knee osteoarthritis: study protocol for a non-inferiority randomized controlled trial

Abstract

Background

Knee osteoarthritis (KOA) is one of the most prevalent health issues, affecting approximately 67% of women over 60 years old. Clinical guidelines recommend individualized muscle training to treat this condition. However, a lack of human and financial resources hinders the delivery of this treatment. In response to this limitation, group training may be an alternative. Although a few studies have compared group and individual exercise for knee OA, none have tested the non-inferiority of group-delivered circuit training specifically in elderly women. Therefore, this study aims to compare the non-inferiority of a group-delivered muscle training program to the same individually delivered training in clinical and functional aspects in elderly women with KOA.

Methods

This is a randomized controlled non-inferiority trial with two arms, parallel groups, blinded evaluator, conducted in Petrolina—PE, evaluating women aged 60 or older. Participants randomly assigned will undergo an 8-week training, either in individual sessions (control group—IB) or as part of a group (intervention group—GB) of four participants, supervised by a physical therapist. Blind assessments at baseline, immediately post-intervention, and 4 weeks post-intervention will include feasibility, safety, and satisfaction analysis of the training program; pain; quality of life; and physical function. Data will be analyzed using the Statistical Package for Social Sciences (SPSS) version 22. Estimated marginal means of each clinical and functional outcome for both groups (IB and GB) will be compared using mixed-effects generalized linear models. The primary analysis will test our main hypothesis that group training is non-inferior to individualized training regarding the primary outcome: relative reduction (%) in the WOMAC questionnaire pain subscale. Confidence intervals of 95% will be calculated. A significance level of p < 0.05 will be adopted in all analyses.

Discussion

Expected results suggest that a group-based approach is not inferior to an individual one in this population.

Trial registration

Brazilian Registry of Clinical Trials (ReBEC) ID: RBR-5bq9jh3. Registered on 18 August 2023. Link: http://www.ensaiosclinicos.gov.br; Universal Trial Number (UTN) of World Health Organization: U1111-1289–2580.

Administrative information

Note: the numbers in curly brackets in this protocol refer to SPIRIT checklist item numbers. The order of the items has been modified to group similar items (see http://www.equator-network.org/reporting-guidelines/spirit-2013-statement-defining-standard-protocol-items-for-clinical-trials/).

Title {1}	Group-based versus individual-based circuit training in elderly women with knee osteoarthritis: study protocol for a non-inferiority randomized controlled trial.
Trial registration {2a and 2b}.	RBR-5bq9jh3 Effects of group training in elderly women with knee osteoarthritis https://ensaiosclinicos.gov.br/rg/RBR-5bq9jh3 [registered on 18–08–2023] Universal Trial Number U1111-1289-2580.
Protocol version {3}	Version 1 of 18-08-2023; Version 2 (recruitment date updated—under review).
Funding {4}	Not applicable. This trial will be conducted with the authors’ own funding and no external sources.
Author details {5a}	C.L.L.; Department of Physical Therapy, University of Pernambuco (UPE), Brazil. A.V.S.L.L.; Department of Physical Therapy, University of Pernambuco (UPE), Brazil. R.C.A.; Department of Physical Therapy, University of Pernambuco (UPE), Brazil. F.T.S.; Department of Physical Therapy, University of Pernambuco (UPE), Brazil. T.F.A.S.; Department of Physical Therapy, University of Pernambuco (UPE), Brazil..
Name and contact information for the trial sponsor {5b}	Investigator initiated clinical trial; C.L. Lopes (Principal Investigator) clecio.limalopes@upe.br.
Role of sponsor {5c}	This is an investigator initiated clinical trial. Therefore, this trial will be conducted with the authors’ own funding and no external sources.

Introduction

Background and rationale {6a}

Knee osteoarthritis (KOA) is a prevalent and debilitating manifestation of osteoarthritis (OA) and a leading cause of pain and functional impairment in older adults. Approximately 43% of individuals with KOA encounter challenges in performing daily activities, with 25% unable to complete them [1, 2]. According to Magnusson [3], women aged 55 and above exhibit a higher incidence, prevalence, and severity of OA than men and younger adults, reaching around 67%. Pain and muscle weakness emerge as primary consequences of KOA, drawing attention due to the hindrance they cause and their association with joint wear and tear [4].

Various therapeutic measures are recommended for treating the disease. Among non-pharmacological approaches, physical exercise proves effective in alleviating pain, enhancing physical function, and improving the quality of life for those with KOA [5]. International guidelines recommend diverse exercise types, including resistance, isolated or combined; aerobic, isolated or coupled with resistance exercise; balance or neuromuscular exercises; and mind-body exercises like Tai Chi or Yoga [6–12]. Despite several recommended exercises, a consensus is yet to be reached in the literature regarding the optimal interruptions for exercise performance [5].

Circuit muscle training (MT) is a type of physical exercise that combines the benefits of both aerobic and resistance exercises. This training has demonstrated positive effects on various chronic conditions, such as weight reduction, improvement in abdominal health, increased strength and muscle mass, ultimately enhancing body composition [13]. Beyond these advantages, MT serves as a non-pharmacological treatment method that accommodates multiple participants in a single session. Compared to other modalities, this type of training requires less time, fostering high adherence among participants [13–17].

Few studies investigate the effects of circuit muscle training on individuals with KOA [18–20]. Moreover, existing studies present noteworthy considerations. Samples varied significantly in terms of age groups and anthropometric characteristics, and diverse training protocols were employed, with training durations ranging from 6 to 14 weeks. Consequently, an optimal exercise therapy program for this population remains undetermined.

Additionally, a few studies have compared group and individual exercise for knee OA, but neither have they aimed to compare the effectiveness of group-delivered MT versus individual delivery nor have they tested the non-inferiority of group-delivered circuit training specifically in elderly women [21, 22]. Further, group-based exercise programs may offer advantages over individual sessions, including lower delivery costs, greater efficiency of therapist time, and enhanced social support that can improve adherence and motivation [19, 20]. However, results are conflicting, and no studies have evaluated the non-inferiority of group-delivered circuit training in elderly women. This trial seeks to address this gap.

Thus, the outcomes of this research may contribute to the development of intervention strategies for the disease. By examining the effects of a cost-effective, non-pharmacological, and non-invasive treatment, the research can offer insights for better planning in the rehabilitation of patients with knee OA.

Objectives {7}

The primary aim of this randomized controlled trial is to determine if an eight-week circuit muscle training protocol conducted in a group will not be inferior to the same protocol carried out individually in elderly individuals with knee osteoarthritis in terms of reducing pain (as a primary outcome), improving function, enhancing quality of life, and declining in analgesic intake.

Trial design {8}

The present protocol is a non-inferiority randomized, two-arm, parallel-group, single-blind trial. This study was prospectively registered in the Brazilian Registry of Clinical Trials (ReBEC) under identifier RBR-5bq9jh3 and with Universal Trial Number U1111-1289–2580. The following methodology is in full agreement with the OARSI (Osteoarthritis Research Society International) recommendations for randomized controlled trials (RCTs) [23], the Consolidated Standard of Reporting Trials (CONSORT) [24–27], and the SPIRIT (Standard Protocol Items for Randomized Trials) [28] (Fig. 1).

Fig. 1.

Consolidated Standard of Reporting Trials flow chart illustrating the process of the study. GB, group-based circuit training; IB, individual-based circuit training; SF-12, 12-item short-form health survey; WOMAC, Western Ontario McMaster Universities Osteoarthritis Index

Methods: participants, interventions, and outcomes

Study setting {9}

Participants from the community of Petrolina, Brazil, will be invited to participate in this study. Recruitment will occur through community health centers, local print media, and social media in Petrolina, Pernambuco. This location was selected due to the availability of physiotherapy facilities and a high prevalence of knee OA among its elderly population. Participants will be recruited by ads in local newspapers, magazines, and social media. After declaring interest, participants will be phone interviewed by the Trial Coordinator to verify if they meet the eligibility criteria. If they are deemed eligible, a face-to-face evaluation will be scheduled to confirm the eligibility criteria.

Eligibility criteria {10}

The trial will be conducted in patients with KOA who fulfill the following eligibility criteria.

Inclusion criteria

1. Female gender.

2. Age between 60 and 80 years [29].

3. Diagnosis of knee osteoarthritis (KOA) based on the criteria of the American College of Rheumatology (ACR) [30].

4. Medial femorotibial KOA, as assessed by radiography and classified as grade 2 or 3 according to the Kellgren and Lawrence criteria [31], with a neutral or varus mechanical axis.

5. Reported average knee pain score between 4.0 and 9.0 on the Numeric Rating Scale (NRS)—to reduce variability and the possibility of overestimating baseline pain levels [23].

We limited the sample to women because KOA is more prevalent and severe in women. This homogeneity reduces variability in this pilot non-inferiority trial; future studies will include men. Participants with bilateral KOA are eligible; the most symptomatic knee will be assessed.

Exclusion criteria

1. Body mass index (BMI) ≥ 30 kg/m² [32].

2. Cognitive deficits, as screened by the Mini-Mental State Examination [33].

3. Currently undergoing physiotherapy or engaging in regular physical exercise (more than twice a week) in the last 6 months [34].

4. History of joint infiltration in the last 3 months or planning to receive infiltration in the next 6 months [34].

5. History of knee arthroplasty or hip arthroplasty within the last 12 months or persisting postoperative restrictions [34].

6. History of knee surgery in the last 6 months or planning to undergo surgery in the next 6 months [34].

7. Presence of other diseases that threaten safety or prevent participation in interventions or tests (symptomatic or severe coronary artery disease, dementia, use of walking aids, other types of arthritis such as rheumatoid arthritis) [34].

8. History of knee trauma in the last 30 days [34].

9. Diagnosis of diseases characterized by chronic pain such as fibromyalgia.

10. Inability to perform the training protocol (inability to walk short distances or need for assistance from another person to complete activities of daily living) [34].

We will exclude participants with BMI ≥ 30 kg/m² to minimize cardiometabolic risk and ensure safety during higher intensity circuit training. Participants with cognitive impairment will be excluded to ensure they could follow complex circuit instructions and maintain safety. Cognitive status will be assessed using the Mini-Mental State Examination (MMSE), with education adjusted cut offs (< 20 for individuals with no formal education, < 25 for 1–4 years of education, < 27 for 5–8 years, < 28 for 9–11 years, < 29 for ≥ 12 years). The effect of group circuit training in individuals with obesity warrants evaluation in future studies. Regular use of walking aids (e.g., cane, walker) will be excluded to ensure participants can safely perform multi station circuit exercises involving rapid positional changes. Participants undergoing other structured exercise programs or who had knee/hip surgery or intra articular injections in the past 6 months will be excluded to avoid confounding influences on outcomes [6, 35].

Screening eligible criteria

Mini-Mental State Examination (MMSE)

MMSE will be used as a screening test for cognitive loss, exclusion criteria of the present study. The MMSE consists of 11 items, divided into 2 sections. The first section requires verbal answers and questions for guidance, memory, and attention, and the second section is for reading and writing questions. The questions are performed in the order in which they are listed and can total a maximum score of 30. Thus, the following individuals will be considered to have cognitive impairment: illiterate with a total score of less than 20, individuals with 1 to 4 years of study with a total score less than 25, individuals with 5 to 8 years of study with a total score of less than 26.5, individuals with 9 to 11 years of study with a total score of less than 28, and individuals who studied for more than 11 years with a total score of less than 29 [33].

Who will take informed consent? {26a}

All participants considered eligible will receive oral and written information about the research procedures. The purpose, potential risks (e.g., muscular pain after doing the exercise protocol and physical assessments), and possible benefits (e.g., improvement in daily activities and pain relief) involved in the study will be explained by the Trial Coordinator. After agreeing to participate, participants will sign an informed consent form. This study protocol has been approved by the Human Research Ethics Committee from the University of Pernambuco (CAAE: 69032023.6.0000.5191) and will be conducted according to the norms of National Health Council Resolution 466/2012 on research involving human beings.

Additional consent provisions for collection and use of participant data and biological specimens {26b}

This randomized controlled trial will not use participant data and biological specimens from ancillary studies.

Interventions

Explanation for the choice of comparators {6b}

According to the OARSI Clinical Trials Recommendations [35], usual care is a recommended comparator for interventions involving exercise. Thus, participants allocated to the control group will receive the circuit muscle training protocol modified from what was proposed by Almeida [36], which has demonstrated improved physical function and muscle strength in patients with knee OA [20].

Intervention description {11a}

The treatments will be conducted at the Physical Therapy Department of the University. Participants will undergo an 8-week circuit training program supervised by licensed physiotherapists. Prior to the trial, all physiotherapists will receive standardized training on the protocol.

Patients allocated to the intervention group (GB) will participate in an 8-week circuit exercise program supervised by a physiotherapist, conducted in small groups comprising three to four elderly individuals. On the other hand, patients allocated to the control group (IB) will also engage in the same 8-week circuit exercise program under the guidance of a physiotherapist, but the sessions will be conducted individually.

The exercise protocol is simple and easy to perform. The exercise protocol will be performed three times a week, for 8 weeks, totaling 24 sessions [36]. Each session will consist of 5 min of warm-up (stationary bike or walk), circuit protocol, and 5 min of stretching exercises (cool down). Immediately after the warm-up, participants will begin the circuit protocol consisting of exercises for the lower limbs and trunk.

Participants will be instructed to perform each exercise as fast as possible, with the maximum number of repetitions during the time set for the training phase (light, moderate, or intense), in order to ensure the aerobic component [36]. After the first exercise, the participant should move to another station, following a specific order and allowing different muscle groups to alternate between rest and work, favoring recovery and minimizing the risk of muscle fatigue [36].

In the first, second, and third weeks of training, participants will perform exercises stratified as light; each exercise will last 20 s. Moderate exercises will be performed in the fourth, fifth, and sixth weeks, lasting 30 s each. Intense exercises will be performed in the seventh and eighth weeks, lasting 40 s each. For all intensities, a maximum transition interval of 30 s between stations will be implemented [36].

Participant safety will be continually monitored. Sessions will be stopped or modified if (a) the participant reports pain > 8 on a 0–10 numeric rating scale, (b) heart rate exceeds 85% of age-predicted maximum (220 – age), or (c) the participant experiences dizziness, chest pain, severe shortness of breath, or any other adverse symptom. Should a session be stopped, the episode will be documented, and the participant will be reassessed before resuming the program.

The exercises that comprise each of the circuit training phases, as well as the execution time, are presented in Appendix 1.

Criteria for discontinuing or modifying allocated interventions {11b}

Participants are free to withdraw from the study at any time and for any reason without penalty. The participant data that have been collected up to that moment will be included in the analysis.

Strategies to improve adherence to interventions {11c}

Adherence reminders will take place during the sessions of circuit training for both groups. The researcher/physical therapist will provide support by increasing participants’ knowledge and understanding of knee OA, such as the causes of pain and the benefits of exercise. This will provide strategies for stimulating activity and dealing with pain during exercise, providing realistic expectations of likely outcomes, reaffirming that pain does not need to be feared, and helping the participant to build confidence in their ability to perform exercises.

To promote adherence, participants will be contacted weekly by telephone to address concerns, reinforce session schedules, and provide motivation. They will receive links to instructional videos demonstrating proper technique for each exercise. Additionally, a moderated group messaging platform (e.g., WhatsApp) will be used to share reminders, offer encouragement, and answer questions in real time. Attendance will be recorded for each session, and participants who miss a session will be contacted within 24 h to reschedule and address barriers to participation.

Relevant concomitant care permitted or prohibited during the trial {11d}

Permitted concomitant care comprises all drug prescriptions for medical conditions that do not meet the exclusion criteria of the present study. The prohibited care includes the uptake of new physical therapeutic measures.

Provisions for post-trial care {30}

Trial center insurance will compensate for those who suffer harm from trial participation.

Outcomes {12}

An orthopedic surgeon blinded to group allocation will perform all assessments. The first will consist of collecting personal details, anthropometric data, and all clinical outcomes. After baseline assessment (T1), all subjects will be scheduled for two further assessments: postintervention (T2), 8 weeks, and follow-up (T3), 12 weeks.

Primary outcome

Pain subscale of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC).

Clinical parameters will be evaluated by the investigator at T1, T2, and T3. The primary outcome is the average difference in the WOMAC pain subscale. WOMAC is a self-rated questionnaire that assesses three dimensions (pain, stiffness, and disability) using a 24-question, 5-point Likert protocol. The higher the score, the worse the condition. The Brazilian Portuguese versions of the WOMAC have been validated and show good reliability and validity [37]. Pain is the primary outcome of this study protocol and the main symptom that drives individuals with knee OA to seek physical therapy care. In addition, assessing this symptom is strongly recommended as an outcome of change in clinical trials with individuals with knee OA [38].

Secondary outcomes

All secondary outcomes will also be also calculated using data measured at baseline and 8 weeks. Only WOMAC and SF-12 questionnaires will be measured at 8 weeks and 12 weeks.

Self-rated stiffness and function

WOMAC stiffness and disability domains will be used to evaluate the average difference in self-rated stiffness and function. The higher the score, the worse the condition [37]. The total WOMAC score will also be calculated [37].

Quality of life

We will assess quality of life using the 12-Item Short-Form Health Survey (SF-12). The SF-12 is a shortened version of the Short Form-36 Health Survey, which is a widely used instrument to assess health-related quality of life. The SF-12 consists of 12 questions across eight domains (physical function, social function, physical role, emotional role, mental health, vitality, body pain, and general health status), and higher scores indicate a better health-related quality of life [39]. In this study, we will use the Brazilian version of the SF-12, which has been previously validated [40].

Physical function

Physical function will be evaluated applying three tests. Two tests recommended by OARSI [41]: (I) 30 s chair stand test and (II) 40 m fast-paced walk test. Also, we will apply the (III) sitting–rising test [42]. All tests will be conducted by a single blinded evaluator at baseline and the first end-point.

30-s chair stand test

The 30-s chair stand test consists of rising from a chair as many times as possible, for 30 s. From the sitting position, with feet flat on the floor and arms crossed over the chest, the participant should stand up completely from the chair and then sit down as quickly as possible for 30 s. The total number of repetitions (standing up and sitting represents one repetition) performed will be recorded. In this test, the more repetitions volunteers perform, the better their condition [41].

40 m fast-paced walk test

Participants 40 m fast-paced walk testwill be instructed to walk as fast as possible without running for a distance of 10 m (marked by ribbons and bounded by cones), returning to the starting point and repeating the walk for a total distance of 40 m. The test will be timed, and the speed in meters/second (m/s) will be used for analysis. The faster volunteers perform, the better their condition [41, 43].

The sitting–rising test

The sitting–rising test (SRT) was developed in the 1990 s as a simple and safe tool to simultaneously evaluate all the major non-aerobic components of physical fitness – muscle strength/power, flexibility, balance, and body composition. A recent epidemiological study showed that SRT score is strongly associated with all-cause mortality in subjects aged 51 to 80 years [42]. To the best of our knowledge, this is the first randomized controlled trial that uses SRT in knee osteoarthritis patients. The SRT consists of an evaluation of the subject’s ability to sit and to rise from the floor. It should be administered on a non-slippery flat surface, in a space equal to or larger than 2 m × 2 m, and with the subject standing barefoot and wearing clothing that does not restrict his/her movements. In order to standardize the conditions of SRT application, the evaluator should instruct the subject in a very straightforward manner: “Without worrying about the speed of the movement, try to sit and then to rise from the floor, using the least support that you believe is needed.”

The ability of sitting and rising from the floor is measured according to the number of supports needed to perform each of the movements and the presence or absence of instability when sitting and rising. The score for each of the actions ranges from a minimum of 0 to a maximum of 5, with half-point intervals. Starting from 5, one point is subtracted for each support utilized, that is, for each hand, forearm, knee, or side of the leg used, and an additional 0.5 point is subtracted if the evaluator notices an unsteady execution (partial loss of balance) during the actions. In addition, if the subject places one hand on the knee in order to sit or rise, this is also considered as one support and, therefore, one point is subtracted. Crossing the legs for either sitting or rising from the floor is allowed if the sides of the subject’s feet are not used for support. Independently of the number of attempts performed, the best score for each one of the two actions is considered the resulting SRT score for sitting and rising from the floor. Moreover, a composite SRT score—the sum of sitting and rising scores—is also calculated and ranges from 0 to 10. A score of 10 indicates the ability to sit and to rise from the floor without using any support—hand or knee—or presenting instability. A video illustrating SRT performance and scoring is available at: https://www.youtube.com/watch?v=MCQ2WA2T2oA&t=149s [44].

Medication intake

At baseline, patients from both groups will receive a diary to record medication intake, and these diaries will be collected at 8 weeks. Paracetamol (500 mg) intake every 4 h will be suggested as a support drug to both groups for pain management, according to American College of Rheumatology recommendations for OA treatment [45]. If individuals are taking another medication before T1 (non-steroidal anti-inflammatory drugs, for example), they will continue to take it, and we will record the amount. Individuals will be excluded if they modify the pharmacological treatment during the study period.

Adherence, satisfaction, and safety

The attendance rate (adherence) will be calculated as the average percentage of completed sessions by the participants. The level of satisfaction will be assessed through a structured questionnaire with five items on a five-point Likert scale, where scores of 4 or 5 indicate a positive response regarding participant satisfaction. The perception of safety will be evaluated through an 18-item questionnaire. This questionnaire was recently validated for safety assessment [46], and we will use eight of these items with a five-point Likert scale. The exercise program will be considered safe if 70% of individuals score positively on eight items of the Likert scale (i.e., rating 1 or 2 for questions 1, 2, 3, 4, 5; and rating 4 or 5 for questions 6, 7, 8). Adverse events were reported when necessary. These outcomes will be self-reported on a paper form only during the end-point (T2).

Participant timeline {13}

Figure 2 summarizes the schedule of enrollment, interventions, and assessments for this study protocol according to SPIRIT recommendations [28].

Fig. 2.

Schedule protocol. WOMAC, Western Ontario and McMaster Universities; BMI, body mass index

Sample size {14}

Sample size was based on detecting non-inferiority of group-based circuit training in comparison to the individual method at 8 weeks after randomization, considering the primary outcome pain (WOMAC pain sub-scale). For change in WOMAC pain sub-scale, a non-inferiority margin (NIM) of 2.2 units (11% of scored 0–20) was chosen as this is less than the minimum clinically important difference (MCID) of 12% (2.4) of improvement from baseline in OA research [47]. Assuming standard deviations (SD) for changes from baseline of 2.7 units for pain intensity [34], 80% power and a one-sided 2.5% significance level, we needed 24 people per arm for change in pain intensity. However, considering 25% loss to follow-up, we needed 30 people per arm for change in pain intensity. Thus, a total of 60 people will be included in the trial. The sample size calculation was performed using the Sealed Envelope Ltd software [48], employing the formula proposed by Julious [49].

Recruitment {15}

Participants from the community of Petrolina (PE, Brazil) will be recruited via advertisements in local newspapers, magazines, and social media platforms. This location was selected due to the availability of physiotherapy facilities and a high prevalence of knee OA among its elderly population. Potential participants will be identified by the project manager and the research assistant. A researcher will be trained on how to determine eligibility criteria during initial telephone contact and how and when to contact them for follow-up and data collection.

Assignment of interventions: allocation

Sequence generation {16a}

Participants will be randomly assigned to the intervention group through the stratified randomization method. This method can be used to achieve balance among groups in terms of participants’ baseline characteristics. Thus, participants will be paired into two groups (allocation 1:1) considering similar baseline characteristics, such as age, BMI, and knee OA grade. Once paired, a simple randomization will be performed through a randomization site (http://www.random.org/) to define the intervention method of each group (GB and IB).

Concealment mechanism {16b}

A single investigator, who will have access only to participants’ baseline characteristics, such as sex, age, BMI, and knee OA grade, will be responsible for pairing participants as explained under the sequence generation section. Then, the same investigator will perform a simple randomization through a website that will decide the intervention received by each participant (GB or IB). The investigator will inform both the participants and the physical therapist responsible for the interventions.

Implementation {16c}

All patients who give consent for participation and who fulfill the inclusion criteria will be randomized. Randomization will be requested by the Trial Coordinator after conclusion of the baseline assessments and after pairing participants (1:1). The estimated time between baseline assessments and allocation will not exceed 7 days. To ensure quality control and feasibility given limited staff and equipment, recruitment will occur in two waves: 20 participants in wave one to refine procedures, followed by 40 participants once the protocol is validated.

Assignment of interventions: blinding

Who will be blinded {17a}

Due to the nature of the interventions, it will not be possible to blind neither the patients nor the physical therapist responsible for the interventions. Thus, the patients will be instructed not to discuss their experience during the exercise if they incidentally encounter other participants. It is important to note that the primary outcome (pain intensity, WOMAC pain sub-scale), as well as self-rated stiffness and function (WOMAC physical function sub-scale), quality of life, medication intake, adherence, satisfaction, and safety are patient reported, and hence they cannot be blinded. Furthermore, the study interventions and measurements will occur in separate locations to facilitate assessor blinding.

The outcome assessors and the data analysts will be blinded to the treatment groups.

Procedure for unblinding if needed {17b}

The trial design is a single-blinded study; thus, only the outcome assessors and the data analysts will be blinded. Thus, there is no unblinding procedure foreseen.

Data collection and management

Plans for assessment and collection of outcomes {18a}

Assessments will be conducted face-to-face at the Biomechanics and Human Functional Activity Laboratory (LABIAFH) at the University of Pernambuco (UPE) and in the orthopedic outpatient clinic of the Polyclinic at the University Hospital of the University of Vale do São Francisco (Polyclinic HU-Univasf) and will take 1 day.

At the assessment day, participants will complete an evaluation form (personal, anthropometric, socioeconomic, medication, knee pain data, and previous medical history). In this visit, the WOMAC questionnaire and the Short Form 12 (SF-12) will be participant-reported on a paper form. In addition, the performance-based tests will be held in the same visit. This day of assessment will be performed by the same researcher and will have a total duration time of approximately 1 h. More detailed information on the data collection for these study outcomes was provided in the “Outcomes” section.

Medication intake, adherence, satisfaction, and safety will be self-evaluated during the endpoints (8 weeks and 12 weeks). Thus, questions related to these outcomes will be included on the first day of assessment post-intervention.

The assessments will be conducted at all timepoints (baseline, 8 weeks, and 12 weeks) by the same researcher. The researcher will be blinded to the intervention’s groups. In addition, all randomized participants will be invited to attend all timepoints of the study, even if they do not adhere to the interventions.

Plans to promote participant retention and complete follow-up {18b}

Participants will receive extensive information about the study design and requirements during the recruitment. The importance of the follow-up completion will be informed. Participants are allowed to withdraw from the study at any time and for any reason without penalty. However, if possible, participants will be invited to attend the end-point assessment of the present study (8 weeks and 12 weeks).

Data management {19}

After checking for completeness, the data will be entered in an electronic password-accessible database by a blinded collaborator of this study. In a separate step, the correct transfer and coding of the data will be checked by a different blinded collaborator. All research data will be archived for 5 years after the study has ended according to the local ethics committee.

Confidentiality {27}

The present study data will be documented and archived using an identification code for each participant. All personal information will be stored in a locked, password-accessible database. Paper forms and exam reports containing personal information will be locked in a lockable metal cabinet. Physical and electronic personal documents will be safeguarded by the Trial Coordinator for 5 years as recommended by the local ethics committee; after that, they will be destroyed and deleted.

Plans for collection, laboratory evaluation and storage of biological specimens for genetic or molecular analysis in this trial/future use {33}

No biological specimens will be collected.

Statistical methods

Statistical methods for primary and secondary outcomes {20a}

A blinded data analyst will perform all analysis using the Statistical Package for Social Science, version 20.0 (SPSS Inc, Chicago, IL, USA). Baseline characteristics of participants will be presented using descriptive statistics. The between-group differences and 95% confidence interval (CI) for the post-treatment outcomes at 8-week and 12-week end points will be calculated using generalized mixed linear models. The linear mixed effects model with random intercepts for participants and fixed effects for group, time, and group × time interaction will be used. Baseline covariates (age, BMI, baseline WOMAC) will be included for sensitivity analyses. The non-inferiority margin is − 2.2 WOMAC pain points, and non-inferiority will be concluded if the lower bound of the 95% confidence interval for group minus individual lies above − 2.2 for change in WOMAC pain subscale at 8 weeks after randomization. Missing data will be handled using multiple imputation function in SPSS [50], and an intention-to-treat analysis [51] (including all randomized participants) will be conducted. No adjustments for multiplicity will be made.

It is important to note that, if appropriate, a full statistical plan will be finalized prior to analysis.

Interim analyses {21b}

There are no interim analyses planned.

Methods for additional analyses (e.g., subgroup analyses) {20b}

There are no subgroup analyses planned. Baseline covariates (age, BMI, baseline pain) will be assessed for their effect on outcomes. Interaction terms will be explored to identify potential effect modifiers.

Methods in analysis to handle protocol non-adherence and any statistical methods to handle missing data {20c}

The primary and secondary outcomes will be assessed using an intention-to-treat analysis. Multiple imputation method will be used to impute missing data.

Plans to give access to the full protocol, participant level-data and statistical code {31c}

The full protocol, participant-level data, and statistical code can be made available by the Trial Coordinator upon reasonable request.

Oversight and monitoring

Composition of the coordinating center and trial steering committee {5d}

The coordinating center is located at the Department of Physical Therapy at the University of Pernambuco and comprises the Trial Coordinator, the principal investigator, 1 nurse, 1 physical therapy degree student, 4 physical therapists, and the data analysts. The study team meets weekly. There is no trial steering committee or public involvement group.

Composition of the data monitoring committee, its role and reporting structure {21a}

A data monitoring committee was not considered as this study adopts a low-risk intervention, and an interim analysis is not planned in this study.

Adverse event reporting and harms {22}

Participants who experience any adverse event are instructed to report these to their physical therapist. All adverse events reported by the participant or observed by the physical therapist during sessions will be recorded. In this RCT, adverse events are defined as any problem experienced during the execution of the study as a result of the assessments, exercise protocol, and/or advice given by the physical therapist.

Frequency and plans for auditing trial conduct {23}

The researcher group meets every week to discuss the trial development and upcoming issues. The study documents, such as informed consents, inclusion and exclusion criteria, and source data, are checked four times a year by an independent researcher, who is not involved with the present study. If a document is found to be missing or information is inconsistent, the local ethics committee is notified immediately.

Plans for communicating important protocol amendments to relevant parties (e.g., trial participants, ethical committees) {25}

All amendments to the protocol will be communicated and approved by the Human Research Ethics Committee from the University of Pernambuco.

Dissemination plans {31a}

The results of this RCT will be disclosed completely in international peer-reviewed journals. Both positive and negative results will be reported. In addition, participants will receive a report with all the results of the study.

Discussion

In this study, we have outlined the rationale and design of a Randomized Controlled Trial (RCT) investigating the impact of an 8-week group-based circuit training exercise program on patients with knee osteoarthritis (OA). The study is characterized by high methodological quality, featuring randomization, prospective registration, masked assessors, allocation concealment, and an intention-to-treat approach.

Moreover, the sample size was carefully calculated to ensure sufficient statistical power for detecting potential differences in the primary outcome of the study. Although previous trials have involved larger samples, none have evaluated noninferiority of circuit training in elderly women. Our sample size of 60 participants, derived from noninferiority calculations, is appropriate for a pilot trial to inform future multicenter studies.

Our intervention involves a group-based circuit training exercise program specifically tailored for individuals with knee OA. We anticipate positive outcomes such as alleviation of knee pain, improved functionality in daily activities, and reduced medication usage among participants. The exercise intensities in our program will be adjusted periodically to adhere to the overload principle of strength training.

This clinical trial aims to contribute new data and insights into the effectiveness of circuit training, shedding light on its impact on both clinical and functional aspects of knee OA. Should our hypothesis be confirmed, group exercises could be considered an additional component to the structured land-based exercise programs already recommended by international guidelines, offering a conservative treatment option for those with knee OA.

The trial’s external validity is another notable strength. We deliberately chose not to restrict participant inclusion based on unilateral or bilateral involvement, or the use of medications, allowing for the generalization of study findings to a broader segment of the population.

However, it is essential to acknowledge certain limitations. The study’s focus on female patients with knee OA might limit generalizability, although this decision was based on the higher incidence, prevalence, and severity of OA in women. Additionally, the inability to mask the therapist or individuals involved in the study is recognized as a limitation.

Trial status

The protocol for this study was registered on August 18, 2023, under the registration RBR-5bq9jh3. As of now, we are currently in the initial two blocks of recruitment, allocation, and analysis. However, the commencement of the final block of participants (n = 40) is pending and has not yet begun.

Data recruitment for the study began on December 13, 2023. Data when recruitment will be completed: 31 March 2024—Version 2 (recruitment date updated—under review).

Abbreviations

ACR

American College of Rheumatology

BMI

Body mass index

CI

Confidence interval

CONSORT

Consolidated Standard of Reporting Trials

GB

Group-based circuit training

IB

Individual-based circuit training

KOA

Knee osteoarthritis

LABIAFH

Biomechanics and Human Functional Activity Laboratory

MCID

Minimum clinically important difference

MMSE

Mini-Mental State Examination

MT

Circuit Muscle Training

NIM

Non-inferiority margin

NRS

Numeric Rating Scale

OA

Osteoarthritis

OARSI

Osteoarthritis Research Society International

Polyclinic HU-Univasf

Orthopedic outpatient clinic of the Polyclinic at the University Hospital of the University of Vale do São Francisco

RCT

Randomized controlled trials

ReBEC

Brazilian Registry of Clinical Trials

SD

Standard deviations

SF-12

12-Item short form health survey

SPIRIT

Standard Protocol Items for Randomized Trials

SPSS

Statistical Package for Social Sciences

UPE

University of Pernambuco

UTN

Universal Trial Number

WOMAC

Western Ontario McMaster Universities Osteoarthritis Index

Appendix 1

Circuit muscle training program—selected exercises descriptions

Mild exercises—from 1^st to 3^rd week

Lower body exercises
1. Sitting position—knee flexion light elastic band
2. Standing position—step-up and down
3. Standing position—hip abduction with 0.5 kg ankle weight
4. Standing position—calf strengthening without extra weight
5. Supine position—single leg raises with 0.5 kg ankle weight
6. Supine position—traditional bridge
Trunk exercises
7. Ventral position—knee plank (isometric)
8. Knee side plank (isometric)
9. Supine position—abdominal curl with legs leaning on the ball

Moderate exercises—from 4 to 6th week

Lower body exercises
1. Standing position—hip abduction with light elastic band
2. Stand up position—hip adduction with light elastic band
3. Sit-to-stand
4. Siting position—knee extension with 0.5 kg ankle weight
5. Standing position—knee flexion with 0.5 kg ankle weight
Trunk exercises
6. Supine position—abdominal curl up holding a small ball
7. Supine position—bridge exercise with hip adduction holding a small ball between the knees
8. Plank (isometric)
9. Side plank (isometric)

Intense exercises—from 7^th to 8^th week

Lower body exercises
1. Standing position—hip abduction	With hard elastic band
2. Stand up position—hip adduction	With hard elastic band
3. Standing position—knee flexion	With 1.0 kg ankle weight
4. Forward lunge with elastic band medially traction
Trunk exercises
5. Supine position—bridge with single leg static hold—one foot on the floor and contralateral limb with knee extension
6. Supine position—oblique abdominal strengthening holding a small ball
7. Supine position—bridge on bosu
8. Supine position—abdominal curl with hip flexion and knee extension holding a small ball

Authors’ contributions {31b}

CLL, AVSLL, and RCA conceptualized the protocol; CLL and TFAS established the selection criteria; CLL and FTS provided statistical knowledge in the study design and conducted the primary statistical analysis; CLL, AVSLL, and RCA are responsible for the organization and implementation. All authors read and made comments on previous drafts of the manuscript and approved the final manuscript.

Funding {4}

Not applicable.

This trial will be conducted with the authors’ own funding and no external sources.

Data availability {29}

The datasets produced and/or analyzed during the current study are not available since they are not complete. However, the protocol and procedures are available on the website www.ensaiosclinicos.gov.br, under registration RBR-5bq9jh3 or U1111-1289–2580.

Declarations

Ethics approval and consent to participate {24}

The study was approved by the Human Research Ethics Committee from the University of Pernambuco (CAAE: 69032023.6.0000.5191). Participants will be invited to participate voluntarily in the study and sign the Informed Consent Form explaining all research procedures.

Consent for publication {32}

All participants will give written and oral informed consent to participation in the study. The Informed Consent Form includes information that the data will be anonymously published.

Competing interests {28}

The authors declare that they have no competing interests.