The goal of this clinical trial is to assess the effectiveness of isokinetic rehabilitation training under optimal stiffness in patients undergoing knee joint rehabilitation. The main questions it aims to answer are:

• Does isokinetic training under optimal stiffness lead to greater force exertion compared to traditional bodyweight training?
• What are the long-term (6-week) effects of isokinetic training under optimal stiffness on joint flexibility and muscle strength? Researchers will compare the effects of isokinetic training under optimal stiffness to traditional bodyweight training to see if isokinetic training produces superior improvements in muscle strength, flexibility, and overall functional recovery.

Participants will:

• Perform regular training sessions using a portable knee joint isokinetic trainer, customized to their optimal stiffness for maximum force exertion.
• Engage in a 6-week rehabilitation program, with assessments at the beginning, and end of the study to evaluate changes in muscle strength, and functional recovery.

Inclusion Criteria:

1. Age between 20-60 years.
2. Patients with unilateral anterior cruciate ligament (ACL) rupture (with or without meniscus injury), posterior cruciate ligament (PCL) rupture, meniscal tear (M), and patellar dislocation (PD).

4. Postoperative period of 3-6 months. 5. No restriction in knee extension or flexion movements.

Exclusion Criteria:

1. Patients with major diseases or conditions such as coronary heart disease, myocardial infarction, heart failure, cerebral infarction, cerebral hemorrhage, or malignant tumors.
2. Pregnant or breastfeeding women and other special populations.
3. Patients who refuse to sign the informed consent form or are unable to complete the entire study process.
4. Patients currently infected with human immunodeficiency virus (HIV), or with a history of infectious hepatitis B or C.
5. Patients with concurrent medical issues, including but not limited to: (1) Uncontrolled hypertension (systolic blood pressure ≥160 mmHg and/or diastolic blood pressure ≥95 mmHg), congestive heart failure (New York Heart Association functional classification of stage III or IV). (2) Patients with mental incapacity or an inability to comprehend the study requirements.