For the treatment of individuals with knee osteoarthritis (KOA), the American College of Rheumatology recommends conservative modalities and, among them, are muscle strengthening (MS) and aerobic exercise (AE), the latter usually associated with MS, which makes it difficult to know what the effective contribution of AE is to this population. In addition, psychological factors are also important to be considered for KOA and how much they influence physical performance and symptom improvement is still uncertain.

To evaluate and compare MS and AE protocols on intensity and pain awareness, muscle strength, self-reported and objective physical performance in individuals with KOA, considering the influence of age, BMI and psychological factors.

Ninety-eight individuals (mean ± SD = 63.2 ± 8.4 years, 72 women) with KOA participated in the study. Three protocols were performed over an 8-week period, 3 times a week. 1) MS protocol: It consisted of strengthening the hip abductor muscles, quadriceps and tibialis anterior, through 4 sets of 6 repetitions; 2) AE Protocol: It consisted of 40 minutes of ergometric bicycle, in which the individual should maintain the range of 50-70% of the maximum heart rate; 3) Control Protocol (CT): It consisted of education through a booklet and 60-minute lectures on the characteristics of KOA and execution of part of the physiotherapeutic protocol to be carried out at home. The main assessment measures were Numerical Pain Scale (NPS), Pressure Pain Threshold (PPT), Beck Depression Inventory (BDI), Pain Catastrophizing Scale (PCS), Western Ontario and McMaster Universities Osteoarthritis Questionnaire (WOMAC), Isometric Muscle Strength and Gait Speed.

The MS and AE protocols produced a positive short-term effect on pain intensity and sensitization, muscle strength, self-reported and objective physical performance, even when considering the influence of age, BMI and psychological factors. However, the MS protocol proved to be more effective than the AE and CT protocol for pain intensity, in addition to increasing tibialis anterior (TA), quadriceps (QD) and hip abductor (ABD) muscle strength. Peripheral and central sensitization decreased after MS, AE and CT protocols, however, there was no significant difference between groups. Likewise, self-reported physical performance increased after MS, AE and CT interventions, however, there was no significant difference between groups. As for the objective physical performance variables, both the MS group and the AE group increased the comfortable speed (CS), slow speed (SS) and fast speed (FS) compared to the CT group.

MS is the most effective protocol to improve the symptoms of individuals with KOA when compared to AE and CT, even when considering the influence of age, BMI and psychological factors.

This study reveals that muscle strengthening was more effective when compared to aerobic exercise in improving the symptoms of knee osteoarthritis.