Which of the following indicates a successful outcome of the TENS treatment?

The most appropriate indicator of a successful outcome of Transcutaneous Electrical Nerve Stimulation (TENS) treatment is a decrease in pain levels as reported by the client. TENS is primarily used for pain relief; it works by delivering electrical impulses through the skin that interfere with the body's ability to perceive pain. When a client reports reduced pain levels, it signifies that the TENS treatment is effectively fulfilling its primary purpose.

While improvements in mobility or strength, as well as reduction of swelling, may indicate overall progress in the client's condition, they are not direct measures of TENS effectiveness. This treatment modality specifically targets pain management, making the patient's self-reported pain reduction the most relevant outcome to assess its success.