**Lumbar Injectrode Feasibility Evaluation** This study checks if the PNS Injectrode F1, a device placed near the spine, can safely and effectively help activate the multifidus muscle. The multifidus is a small muscle in the back that helps stabilize the spine. The device uses electrical signals to stimulate the lumbar medial branch nerve, which is a nerve in the lower back. Healthy adults will have the device inserted for up to 28 days under the skin near this nerve. Doctors will use ultrasound (a type of imaging) to see if the muscle moves or is activated. **Key Points:** - **Study Length:** The device will be in place for up to 28 days, with several check-ins and emails for follow-up. - **Participation Requirements:** Participants must be over 21, able to attend all visits, and understand English well enough to complete forms and follow instructions. - **Exclusions:** People with certain medical issues, like severe cognitive impairments or active infections, and women who are pregnant or not using birth control, cannot join the study. The study aims to ensure the device is safe and works as expected, with visits scheduled on specific days to monitor progress.