This study is testing a device called the PNS Injectrode F1 to see if it can be safely placed on a nerve in your lower back. The goal is to check if it can help activate a muscle called the multifidus, which supports your spine. The study lasts for less than 28 days. You'll have the device in your back during this time and will visit the study team several times. The process involves using a type of gentle electrical pulse on your skin and under it to see if it helps with muscle activation. The study is for healthy adults aged 21 and older who can handle mild electrical stimulation and are stable in terms of health.

• **Duration**: The device stays in place for up to 28 days.
• **Visits**: You will need to attend 5 scheduled visits, including emails on some days.
• **Safety**: Designed as a non-significant risk study, focusing on safety and muscle activation.