The goal of this clinical trial is to investigate the effect of the BTL-899M device on muscular system function in adult subjects seeking treatment for improving their muscular system function in the lower extremities. The main question it aims to answer is:

Whether the BTL-899M device is effective for muscular system function improvement 3 months posttreatment compared to the sham group, based on the dynamometer measurement.

Researchers will compare a sham group to see if the device is effective.

Participants will complete four treatment visits and two follow-up visits. Their strength will be recorded via a dynamometer.

This study will evaluate the clinical efficacy and safety of the BTL-899M device for changes in muscular system function through muscle strength measurement by hand-held dynamometer. The study is a prospective, multi-center, open-label, single-arm study. The subjects will be enrolled and assigned to two groups - active and sham in a 3:1 ratio. All patients will be required to complete four (4) treatment visits receiving the treatment with the study device and two follow-up visits at 1 month and 3 months. The sham group will be treated with 5% of both energies only. The treatment administration phase will consist of four (4) treatments, delivered 5-10 days apart. The applicators of BTL-899M will be applied over the designated area. The device will induce visible muscle contractions along with heating by radiofrequency (RF). Each therapy session will last 30 minutes. At baseline, after the last treatment, and all follow-up visits, the strength measurement of the treated area will be performed by hand-held dynamometer in all subjects. At the last therapy visit, the patients will receive the Subject Satisfaction Questionnaire and Therapy Comfort Questionnaire to fill in. Subject satisfaction questionnaire will be given to the subjects at all follow-up visits. Safety measures will include documentation of adverse events (AE), which will be assessed after each procedure and at all follow-up visits. During the post-procedure visits (at 1-month and 3-month follow-up visits), all subjects will receive the Lifestyle Change Questionnaire to fill in.

Inclusion Criteria:

• Age 22 years and older
• Voluntarily signed an informed consent form
• BMI ≤ 35 kg/m2
• Women of child-bearing potential are required to use birth control measures during the whole duration of the study
• Subjects willing and able to abstain from partaking in any treatments other than the pre-procedure therapy regime and the study procedure for improvement of the musculoskeletal system
• Subjects willing and able to maintain their regular (pre-procedure) diet, exercise and therapy regimen without affecting significant change in either direction during study participation

Exclusion Criteria:

• Electronic implants (such as cardiac pacemakers, defibrillators, and neurostimulators)
• Metal implants
• Drug pumps
• Malignant tumor
• Pulmonary insufficiency
• Application over muscles in the acute phase of injury
• Cardiovascular diseases
• Disturbance of temperature or pain perception
• Hemorrhagic conditions, blood coagulation disorders or anticoagulation therapy
• Septic conditions and empyema
• Acute inflammations
• Systemic or local infection such as osteomyelitis and tuberculosis
• Contagious skin disease
• Elevated body temperature
• Pregnancy, postpartum period, and nursing
• Graves' disease