Resistance training is the primary intervention for managing patellofemoral pain (PFP). However, the impact of exercise volume remains unclear.
ObjectiveTo compare the effects of a resistance training program with a single set per exercise versus the conventional three-set approach on pain, self-reported function, muscle strength, and hop performance in women with PFP.
MethodsIn this randomized controlled trial, 42 women with PFP were allocated to either a single-set (SS, n = 21) or three-set (TS, n = 21) group. Both groups completed a nine-week, twice-weekly lower limb resistance training program. The SS group performed one set per exercise, while the TS group followed the conventional three-set protocol. Primary outcomes included self-reported function (Anterior Knee Pain Scale, AKPS) and usual pain over the past week (Numeric Pain Rating Scale, NPRS). Secondary outcomes included stair ascent/descent pain, unilateral leg press and knee extension one-repetition maximum tests, and single-leg hop performance. Group comparisons were analyzed using mixed linear models under an intention-to-treat approach.
ResultsNo significant differences in any outcome were observed between the SS and TS groups. Participants achieved significant improvements in AKPS [SS: + 16 points (95% CI: 10, 22); TS: + 17 points (95% CI: 11, 23)] and NPRS [SS: – 5 points (95% CI: – 6, – 4); TS: –4 points (95% CI: – 5, – 3)] over the intervention period. Significant enhancements were also observed in all secondary outcomes.
ConclusionWomen with PFP who completed a 9-week resistance training program achieved comparable improvements in health status whether performing one or three sets per exercise.
Patellofemoral pain (PFP) is one of the most common painful musculoskeletal conditions affecting the adult knee, with an estimated prevalence of 29% in the female population.1 This condition is characterized by pain around or behind the patella that is aggravated by weight-bearing activities on a flexed knee, such as squatting, stair ambulation, jogging/running, and hopping/jumping.2 Patients with PFP frequently report persistent knee pain after 5–8 years,3 impacting their ability to perform sports, physical exercises, and some work-related activities pain-free.4 As a consequence, patients with PFP tend to have markedly reduced knee- and health-related quality of life compared to pain-free individuals.5
The pathogenesis of PFP is complex, with interactive biopsychosocial pathways suggested to contribute to its onset and persistence.4 Exercise-based therapy is currently recognized as the primary intervention for treating this condition.6,7 A series of randomized clinical trials have reported improvements in knee pain, patient-reported outcomes and functional performance for patients with PFP undergoing lower limb resistance exercise programs.8–12 According to current clinical practice guidelines, PFP should be managed with a combination of knee- and hip-targeted resistance exercises that focus on the quadriceps and the posterolateral hip musculature, incorporating both weight-bearing (e.g., squats, leg press) and non–weight-bearing exercises (e.g., knee extension, hip abduction).7 Surveys have found that physical therapists widely employ these exercises to treat patients with PFP.1,13 Nonetheless, exercise prescriptions in PFP studies are poorly reported,14 impairing their implementation in clinical practice.
In the extensive resistance training literature, 'load' typically refers to the intensity relative to an individual’s maximum capacity (e.g., percentage of one-repetition maximum), while 'volume' is commonly defined by the number of sets (per exercise, session, or week) or the number of repetitions (per set, exercise, session, or week).15,16 In the general population, the number of sets performed per week appears to be the most influential volume variable for health-related outcomes, particularly gains in muscle size and strength.17,18 This makes it somewhat intriguing that rehabilitation programs for women with PFP have included anywhere from nine to 81 lower limb resistance exercise sets per week—a ninefold difference in weekly set volume.19 Two recent systematic reviews have examined the role of resistance training volume in individuals with PFP.19,20 Both the meta-regression conducted by Oliveira et al.19 and the meta-analysis by Almeida et al.20 reported greater improvements in self-reported function among patients engaged in higher-volume training programs. Additionally, higher training volumes may lead to greater reductions in pain intensity.20 Nevertheless, the role of resistance exercise set volume in PFP outcomes remains uncertain given the lack of randomized clinical trials specifically designed to isolate the effects of weekly set volume in this population.
International organizations have issued guidelines for prescribing resistance training in healthy youth, adults, and elderly populations,16,21–23 as well as for individuals with various chronic diseases.24–26 While it is generally recommended to use multiple sets per exercise during each training session, opting for a single set instead represents a reduced-volume training strategy aimed at achieving the ‘minimal dose’.27 This approach involves a lower exercise volume compared to those from guidelines but is still able to produce positive effects on target outcomes.27 Evidence suggests that resistance training programs including a single set per exercise may result in comparable muscular strengthening to multiple-set approaches during the initial stages (i.e., up to 12 weeks) in untrained healthy individuals.28 From a practical standpoint, shorter and less fatiguing sessions of resistance training may help individuals attain initial benefits and improve adherence to exercise programs. Accordingly, this study aimed to compare the effects of a resistance training program with a single set per exercise versus the conventional three-set approach on pain, self-reported function, muscle strength, and hop performance in women with PFP.
MethodsStudy designIn this single-center, assessor-blinded, randomized clinical trial with two parallel intervention groups, we compared a single-set (SS) and a three-set (TS) resistance training program in women with PFP. Participants were engaged in a 9-week intervention employing identical resistance exercises targeting the lower limbs muscles. The SS group completed a single set per exercise, while the TS group completed the three-set conventional approach. Primary and secondary outcomes were evaluated at baseline and after the training program.
The study was conducted entirely within the facilities of a partner training center. Data collection was carried out between March 2022 and November 2023. The study was approved by the Federal University of Health Sciences of Porto Alegre Ethics Committee (#3.935.996). The study was conducted in accordance with the plan prospectively registered in the Brazilian Registry of Clinical Trials (#RBR-8648fg), with no significant deviations from the approved protocol. All participants signed an informed consent document. This report follows the CONSORT (Consolidated Standards of Reporting Trials).
ParticipantsWomen with anterior knee pain between 18 and 40 years were recruited from the general population through social media advertisements. A preliminary assessment conducted by a physical therapist was performed to determine the volunteers’ suitability for participation in the study, and the inclusion criteria were based on established guidelines for PFP diagnosis and management:7 (1) presence of peripatellar or retropatellar pain in at least two functional tasks (running, kneeling, jumping, squatting, climbing or descending stairs, sitting for a long time, sitting with knees flexed); (2) ongoing patellar pain for at least 3 months; (3) beginning of symptoms not related to trauma; (4) a minimum of 3 points in the 0-to-10 Numeric Pain Rating Scale (NPRS); (5) not participating in any PFP treatment or lower limb resistance training program in the last year. Volunteers were not included if they had a history of lower limb orthopedic surgery, knee conditions (e.g., meniscal or ligament tears, tendinopathies), were pregnant, using corticosteroids or anti-inflammatory medication, or had contraindications to resistance exercises or strength and hop tests.
Sample size, randomization, and blindingSample size estimation was determined using G*Power (version 3.1, Universität Kiel, Germany). Anterior Knee Pain Scale (AKPS) and Numeric Pain Rating Scale (NPRS) scores, collected before and after 6 weeks of intervention in the standard rehabilitation group (i.e., resistance training focused on the quadriceps and posterolateral hip muscles) from Pompeo et al.12 were used to inform the sample size estimation. Considering a significance level of 0.05, statistical power of 0.80, and a correlation among repeated measures of 0.5, the minimum required sample size to detect effects in both outcomes was estimated at 17 participants per group. To account for a potential sample loss of up to 20%, recruitment continued until 21 participants were obtained per group, resulting in a total of 42 women with PFP initially enrolled in the trial.
Participants were randomly assigned to one of two groups (1:1) using a free online tool (random.org). The allocation sequence was generated in advance by an investigator not involved in recruitment, assessment, or intervention. Participants and the physical therapist delivering the interventions were informed of the group assignment only on the day of the first training session. Assessors, who were not involved with the interventions, remained blinded to group allocation until data collection was completed.
Outcome measuresThe primary outcomes were self-reported function and usual pain in the last week, assessed through AKPS and NPRS, respectively. Secondary outcomes comprised knee pain experienced during ascending and descending stairs, unilateral leg press and knee extension one-repetition maximum (1RM) tests, and performance on the single-leg hop and the single-leg triple hop tests. In participants with bilateral pain, assessments were conducted on the most affected side, defined as the knee with the greatest pain. Assessments took place one week before the start of the 9-week resistance training program and again one week after its completion.
Self-reported functionThe AKPS is a validated 13-item questionnaire used to assess symptom severity and physical limitations in individuals with PFP.30 Scores range from 0 to 100, with higher scores indicating a lesser impact on function. The minimal clinically important difference (MCID) for the AKPS is 10 points.29 Participants completed the questionnaires independently, with an evaluator present to answer questions.
Pain intensityThe 11-point NPRS, where 0 represents “no pain” and 10 indicates “worst imaginable pain”, has shown reliability, validity, and responsiveness in individuals with PFP.7 The MCID for the NPRS is 2 points.29 The usual pain during the last week was used as a primary outcome.8,12,29 while secondary outcomes included a step-up and step-down test to assess knee pain intensity during these activities.9,10
Muscle strengthThe 1RM test measures the maximum load an individual can lift for a single repetition of an exercise and has shown excellent reliability with the knee extension chair and leg press machine.31 In this study, unilateral 1RM tests were performed using the same equipment as in the intervention programs. Participants received instructions and familiarized themselves with the exercises on at least two occasions. In the first attempt, the participant self-selected the load and was encouraged to perform as many repetitions as possible. The load was adjusted for the second attempt using an equivalence equation.32 Additional load adjustments were made as needed to ascertain the true 1RM value. A minimum of 3 min rest was provided between attempts, with a maximum of 4 attempts conducted to define the 1RM load.31 Verbal encouragement was given to motivate participants to lift the heaviest weight possible.
Hop performanceThe single-leg hop and the single-leg triple hop tests were administered to assess participants' functional performance by measuring the horizontal distance covered in one and three successive unilateral jumps, respectively. Both tests demonstrated excellent reliability.33 Participants completed two familiarization attempts followed by three maximal-effort attempts, with a two-minute rest between attempts. Distances were measured using a tape fixed to the ground, and the mean of the three trials was used for statistical analysis.
InterventionsThe resistance training program consisted of 18 sessions, conducted twice a week over a 9-week period, with at least 48 h between sessions. All sessions were supervised by a single physical therapist with 8 years of experience managing individuals with PFP and other knee disorders, ensuring a 1:1 patient-to-therapist ratio. Participants were directed not to engage in lower-limb resistance exercises beyond those specified in the study intervention and were instructed to avoid using medications for knee-related issues.
The intervention followed current guidelines for managing PFP, emphasizing resistance exercises to strengthen the lower limb muscles, particularly the knee extensors and posterolateral hip complex.7 The same five resistance exercises were prescribed for SS and TS groups: unilateral leg press, unilateral knee extension, split squat, hip abduction, and clam (Fig. 1). Participants performed leg press and knee extension exercises using resistance training equipment, split squat with body weight and free weights (i.e., dumbbells), and hip abduction and clam exercises with elastic bands. The leg press, knee extension, and split squat exercises were performed from approximately 90° of knee flexion to near-complete knee extension. For all exercises, participants were instructed to execute each movement repetition in approximately 4 s: 2 s for the concentric phase and 2 s for the eccentric phase. A one-minute rest interval was provided between sets.
The resistance training program was divided into three blocks, each lasting 3 weeks, with a target number of repetitions for each exercise set: 15 repetitions in block 1; 12 repetitions in block 2; and 8 repetitions in block 3 (Fig. 1). The load for each exercise was adjusted based on the participant's individual response using self-reported repetitions in reserve.34 After each set, participants reported the number of additional repetitions they felt capable of performing with that load. The load was increased if the participant reported being able to perform >2 additional repetitions beyond the established number for that training block.35 Conversely, the load was decreased if the participant was unable to complete the predetermined number of repetitions due to muscle fatigue or knee discomfort.35 The load adjustment in the elastic resistance exercises was achieved by either changing the color and the number of elastic bands. The elastic bands were replaced with new ones every six weeks to prevent significant losses in elastic resistance capacity due to continuous use.
Statistical analysisThe primary analysis was performed using the intention-to-treat population; patients were assessed and analyzed as members of their randomized groups, irrespective of adherence to the planned course of treatment. Between-group differences (treatment effects) and their 95% confidence intervals (CIs) were calculated by using mixed linear models with group (two levels), time (two levels; baseline and post-intervention evaluation) and the corresponding interaction as fixed effects and participants as random effects (normal distribution assumed). Linear mixed models automatically adjust the between-group differences taking baseline data differences into account, even if these differences are very small.36 The analysis adjusted the between-group differences considering all moments of evaluation. Within-group effect sizes (ES; baseline to follow-up) were assessed through the Cohen’s d: ES = [M2 – M1]/SDpooled, where M2 is the mean follow-up measure, M1 is the mean baseline measure, and SDpooled is the pooled SD of M1 and M2. Training effects were considered as “trivial” (ES<0.2), “small” (ES>0.2), “moderate” (ES>0.5), “large” (ES>0.8) or “very large” (ES>1.2).12 For all statistical analyses, SPSS 20.0 software (Statistical Package for the Social Sciences Inc., Chicago, IL, USA) was used, with a significance of α ≤ 0.05.
ResultsSeventy-six women volunteered for the study. Forty-two eligible volunteers were randomized: 21 to the SS group and 21 to the TS group (Fig. 2). Baseline characteristics were comparable between groups (Table 1). During the 9-week intervention program, four participants discontinued intervention in the SS group and two in the TS group. None of the withdrawals were attributed to symptom exacerbation or other complications arising during the intervention. At follow-up, 15 out of 17 participants in the SS group attended all 18 training sessions, while 2 participants attended 16 and 17 sessions, respectively. In the TS group, all 19 participants attended every session.
Baseline demographic and anthropometric characteristics [mean (SD)].
Abbreviations: IPAQ, International Physical Activity Questionnaire; MET, Metabolic Equivalent of Task; SS, single-set group; TS, three-set group.
No significant group or group-by-time effects were detected for the primary outcomes (Table 2). SS and TS groups exhibited significant improvements in self-reported function and pain in the last week (Table 2). Following the 9-week intervention period, participants demonstrated a notable 16-point improvement in AKPS scores, alongside a corresponding reduction of 4 points in NPRS (Table 3).
Primary and secondary outcomes at baseline and follow-up.
Abbreviations: AKPS, Anterior Knee Pain Scale; CI, confidence interval; SS, single-set group; TS, three-set group; 1RM, one-maximum repetition.
Within-group analyses.
Abbreviations: AKPS, Anterior Knee Pain Scale; CI, confidence interval; SS, single-set group; TS, three-set group; 1RM, one-maximum repetition.
No significant group or group-by-time effects were detected for the secondary outcomes (Table 2). Participants experienced significant decreases in pain during step-up and step-down tasks, accompanied by a notable increase in maximum strength and hop distance (Table 2). SS and TS programs yielded similar changes across all secondary outcomes (Table 3).
DiscussionThis groundbreaking study brings to the field of rehabilitation a topic that has long been discussed in resistance training for healthy individuals. The main finding revealed that women with PFP achieved similar outcomes after participating in a 9-week resistance training program, regardless of whether they followed a single-set or a conventional three-set per exercise approach. Participants improved knee pain, self-reported function, muscle strength, and hop performance with both interventions.
Comparisons between resistance training programs utilizing single-set versus multiple-set in healthy individuals has generated a substantial body of research since the 1990s. There seems to exist a gradual dose-response relationship in individuals with some resistance training experience, supporting that a greater training volume leads to increased strength gains.17 However, single-set training programs appear to yield similar muscle strengthening initial effects compared to multiple sets in untrained individuals.28 After 2 to 3 months of training in healthy untrained women, no differences in 1RM knee extension were observed between those who trained with one set versus three sets per exercise.37–39 In contrast, by the 6-month follow-up, the three-set groups exhibited significantly greater strength gains.38,40 This evidence supports earlier recommendations that low-volume training can effectively produce significant initial improvements, but higher-volume training is likely more beneficial for strength development once a baseline fitness level is achieved.21
Participants in this study, like many women with PFP, were not regularly engaged in resistance training. Thus, similar strength responses between the SS and TS groups following a 9-week intervention were somewhat expected. Notably, to the best of our knowledge, this is the first study to demonstrate that resistance exercise set volume is not a key factor in the health benefits of this intervention for individuals with PFP, particularly during the first two months of training. These findings could significantly impact clinical practice. Although current guidelines recommend managing PFP with a combination of hip- and knee-targeted resistance exercises,7 patient adherence to this type of intervention is often challenging. Exercises performed in either closed- or open-kinetic chain may exacerbate symptoms in people with PFP, representing a barrier for a population often characterized by kinesiophobia and pain catastrophizing.41 Therefore, the prospect of achieving similar benefits with a time-efficient program requiring only one-third of the typical number of resistance exercise sets per session may be appealing for patients.
The baseline health status of participants in this study was consistent with the expected profile for women with PFP, as prior trials reported average pain scores between 4 and 8 on the NPRS or visual analogue scale (VAS), accompanied by self-reported function scores between 58 and 77 points on the AKPS.19 A recent meta-analysis indicated that resistance training programs lasting 3 to 12 weeks reduced pain by an average of 3.1 points (95% CI 2.6 to 3.6) and improved self-reported function by 12.4 points (95% CI 9.8 to 15.1) in women with PFP.19 The average improvements of approximately 4 points in NPRS and 16 points in AKPS observed in our study were comparable to previous resistance training research and exceeded the MCID of 2 and 10 points for this population.29 The novelty of this study, therefore, lies in demonstrating that clinically relevant benefits for patients with PFP can be achieved in the first two months applying one-third of the typical number of sets prescribed per resistance exercise. Following this initial intervention period, as patients become more accustomed to resistance training and experience significant symptom relief, increasing the training volume may be beneficial for optimizing muscle strengthening.
This study had certain limitations. First, the 9-week intervention duration limits our ability to assess whether the long-term benefits of higher training volumes observed in healthy individuals also apply for women with PFP. Consistent with previous PFP studies involving up to 12 weeks of resistance training,19,20 our interventions did not fully eliminate symptoms or restore participants’ function. These findings suggest that longer interventions may be needed for the complete recovery, thereby framing this study as an investigation into the ‘initial management’ of individuals with PFP. Second, the lack of follow-up after the intervention prevents us from determining whether the improvements were sustained equally in both the SS and TS groups. Third, given the characteristics of the participants, caution is needed when extrapolating our findings to well-trained female athletes or to male subjects.
In contrast, a notable strength of this study is its ecological validity, as real patients were treated with an intervention that requires minimal resources and can be easily implemented in a clinical setting. Additionally, the individualized supervision of all training sessions by a physiotherapist ensured strict adherence to the prescribed intervention, allowing for effective control of key variables such as exercise technique and load management. Further research is needed to elucidate the effects of single-set training, as well as other forms of low-volume resistance training, on the health status of individuals with PFP. Trials that include both men and women with varying fitness levels (e.g., athletes vs. physically active individuals) and involve longer intervention periods will help clinicians make more informed decisions.
ConclusionThis randomized clinical trial showed that women with PFP who completed a 9-week resistance training program achieved comparable improvements in pain, self-reported function, muscle strength, and hop performance regardless of whether they performed one or three sets per exercise. Single-set resistance training emerges as a viable and time-efficient option for the initial management of PFP in clinical settings.
Ethical standingEthical approval was obtained from Federal University of Health Sciences of Porto Alegre Ethics Committee (#3.935.996).
Trial registryBrazilian Registry of Clinical Trials (#RBR-8648fg).
Declaration of generative AI in scientific writingThe authors used ChatGPT for grammatical review. After using this tool, the authors reviewed and edited the content as needed and takes full responsibility for the content of the publication.
Data sharingAll data presented in the manuscript are available, with a reasonable request, by contacting the corresponding author. Data will be shared in anonymized form and can be used for meta-analytical purposes.
Funding informationThis research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
The authors certify that they have no affiliations with or financial involvement in any organization or entity with a direct financial interest in the subject matter or materials discussed in the article.
The authors express their sincere gratitude to the Studio Fitsul Training Center (Porto Alegre, Brazil) for collaboration with this study. L.S.S. thanks CNPq-Brazil for the scholarship. F.V.S. thanks CNPq-Brazil for the research productivity fellowship.
