Knee osteoarthritis is a chronic joint disease and one of the leading causes of disability among adults, resulting in irreversible damage to articular cartilage and subchondral bone, osteophyte formation, joint pain and stiffness.The purpose of the study is to evaluate the acute responses of lower limb strengthening on physical function and pain, in patients operated on by total knee arthroplasty.Candidates for this study will be men and women over 55 years of age who have undergone total knee arthroplasty, who are admitted to the University Clinical Hospital of Valencia, with an intervention date in 2022-2023, and who begin their physiotherapy treatment between days 1-2 post-surgical.

Knee osteoarthritis (OA) is a chronic joint disease and one of the leading causes of disability among adults, resulting in irreversible damage to articular cartilage and subchondral bone, osteophyte formation, joint pain and stiffness. Knee osteoarthritis often makes it difficult to participate in activities of daily living, which can make work difficult or even impossible, especially when it comes to physical activities that impose a great mechanical strain on the knee. For example, when climbing stairs, the pressure on the knees is six times greater than body weight, which is a known risk factor for knee OA due to occupational activities.Given the increasing prevalence of knee OA with the ageing population and the increasing state retirement age in most European countries, the implications of knee OA need to receive special attention.The most common surgical solution is the placement of a total knee arthroplasty, There are several reasons why your doctor might recommend knee replacement surgery. Recommendations for surgery are based on the patient's pain and disability, not age. Most patients who undergo a total knee replacement are between the ages of 55 and 80, but orthopedic surgeons evaluate patients individually. Usually, the surgical procedure takes between 1 and 2 hours. The orthopedic surgeon will remove the damaged cartilage and bone, and then place the new metal and/or plastic implants to restore knee alignment and function.The purpose of the study is to evaluate the acute responses of lower limb strengthening on physical function and pain, in patients operated on by total knee arthroplasty. Candidates for this study will be men and women over 55 years of age who have undergone total knee arthroplasty, who are admitted to the University Clinical Hospital of Valencia, with an intervention date in 2022-2023, and who begin their physiotherapy treatment between days 1-2 post-surgical. Patients will voluntarily participate in the study. All of them will be informed about the objectives and content of the research and written informed consent will be obtained. The study will conform to the Declaration of Helsinki and will be approved by the local ethics committee.Participants will be excluded if they have any involvement in the contralateral lower limb, if they have already had/have any other knee injury or other anatomical part of the intervened MI (in the last year), and if they have any other condition or disease in which there is a contraindication to physical exercise. Also if they participate in other research studies. In addition, if severe neural or vascular injury is evident.In a previous study, initial WOMAC scores had a standard deviation of 11. If the difference between the means of the intervention and control groups is at least 10, a sample size of 20 patients in each group is adequate to reject the null hypothesis with a power of 80% and a significance level of p < 0.05.If possible, two days before the surgical intervention, a video will be sent to the participants with the performance of the exercises to be performed, so that they can check the technique to be executed. Likewise, they will be sent the following information about guidelines to follow for the realization of the tests:

• Try to rest at least 8 hours the post-surgical night. Patients will be treated while admitted to the hospital (between 3 and 4 days), through 1 session / day of approximately 40 minutes.

Evaluation 1 will be performed on the first day after surgery (1st postoperative day) and evaluation 2 on the day of hospital discharge (3rd postoperative day).EXERCISE PROGRAM WITH ELASTIC RESISTANCE:

• All exercises are done until the maximum number of repetitions is reached, since they will only be done once / day.
• During the first day, each exercise should begin with 2 sets of 2 repetitions as a warm-up and calculation of the appropriate intensity. The appropriate intensity will be the one where the patient tells us that he perceives 5-6 out of 10 on the Borg CR10 scale after finishing 2 repetitions.CONTROL GROUP EXERCISE PROGRAM:

The patients of the control group will perform the physiotherapy exercises following the RHB protocol in ATR of the University Clinical Hospital of Valencia.

Inclusion Criteria:

• Men and women over 55 years of age.
• Total knee arthroplasty
• Intervention date in 2022, and who begin their physiotherapy treatment between days 1-2 post-surgical.

Exclusion Criteria:

• Participants have any involvement in the contralateral lower limb.
• Participants have already had/have any other knee injury or other anatomical part of the intervened LM (in the last year).
• Participants have any other condition or disease in which there is a contraindication to physical exercise.