Sensor-based measurement of fear avoidance and movement patterns of healthy individuals with mechanically induced lower back pain during movement tasks: Study protocol for an experimental non-interventional study

Background Chronic primary low back pain (CPLBP) is highly prevalent and associated with physical impairment and psychological distress. Fear avoidance (FA) is one contributing factor in the development and persistence of CPLBP. Previous studies proved existing connections between pain, physical activity, stress, and FA, which is also present in pain-free individuals. However, the roles of FA and psychophysiological stress responses have not been systematically disentangled and related to movement patterns combined in one standardized experiment involving pain induction. Methods To address this gap, 76 pain-free participants (20: phase 1; 56: phase 2) will perform standardized movement tasks (Back Performance Scale, Sit-To-Stand-Test) with and without wearing a back pain simulator in a within-subject design. Movement will be recorded with wearable sensor-based and novel radar-based motion capture technology. Additionally, psychophysiological stress parameters (e.g., salivary cortisol, heart rate variability), and self-reports on stress, pain, and FA will be assessed. This will be followed by a qualitative feasibility and acceptability interview in phase 1. In this phase, we will evaluate the feasibility and acceptability of a novel back pain simulator enabling a standardized simulation of low back pain, and the motion capture technology. Phase 2 will investigate the effects of pain induction on self-reported pain, back pain-related movement parameters, and stress responses. Associations of these factors with FA will be analyzed. We anticipate high feasibility and acceptability. We expect higher pain ratings, lower mobility, and higher stress responses in the pain condition compared to the control condition. We expect FA to moderate mobility and stress responses in the pain condition. Discussion This study protocol establishes an experimental paradigm to investigate the association of pain, FA, movement, and stress in healthy samples under controlled pain conditions. This paradigm aims to contribute to a deeper understanding of the interplay of psychological and physiological mechanisms in CPLBP. Trial registration OSF, osf-registrations-rt2ca-v1. Registered April 2, 2025, https://doi.org/10.17605/OSF.IO/RT2CA ; osf-registrations-vsmce-v1. Registered September 18, 2025, https://doi.org/10.17605/OSF.IO/VSMCE .