Inertial measurement units (IMUs) provide benefits over the traditional optoelectronic motion capture (OMC) systems in measuring kinematics for the low back pain population. The reliability and validity of IMUs to quantify three-dimensional motion for multiple hip/spine segments have not been systematically evaluated. The purpose of this study was to determine the repeated-measures reliability and concurrent validity of an IMU system for measuring the three-dimensional spine/hip kinematics in six common movement assessments. Seventeen participants (32.3 (14.7) years; 11 female) performed two trials each of six range-of-motion assessments while fitted with four IMUs (T1/T2, T12/L1, L5/S1, and femur). The IMUs showed good–excellent reliability for most of the movements in the primary plane and poor–moderate reliability in the non-primary planes. The IMU and OMC systems showed generally good–excellent agreement in the primary plane and RMSE values between 3.03° and 15.75°. The removal of outliers based on the Bland–Altman analysis resulted in RMSE values between 2.44° and 10.30°. The system agreement in the non-primary planes was generally poor–moderate, and the RMSE values ranged from 2.19° to 45.88°. Anomalies in the proprietary sensor fusion algorithm or calibration may have contributed to the large RMSE values, highlighting the importance of assessing data for physiological relevance. The results suggest that these IMUs may be best suited for population-based studies measuring movement in the primary plane and point toward the need for the development of more robust approaches for broader implementation.

Importance: Chronic low back pain (cLBP) is associated with reduced gait speed and other gait quality impairments. Fear-avoidance and pain catastrophizing impact movement in cLBP, but their specific impact on gait quality is unknown. Objective: This study aimed to determine associations between fear-avoidance or pain catastrophizing and gait quality in cLBP. Design: This was a cross-sectional study. Setting: This study occurred at a university. Participants: There were 500 individuals (56.6 [SD = 16.5] years old; 311 female) with cLBP. Interventions: Participants completed the Fear-Avoidance Beliefs Questionnaire – Physical Activity (FABQ-PA) and 6-item Pain Catastrophizing Scale. Participants were divided into high and low fear-avoidance subgroups based on an established FABQ-PA cutoff (>14). Main Outcomes and Measures: Gait speed was measured during a 4-meter walk test, while step time average, step time variability, and symmetry were derived from a lumbar inertial measurement unit worn during a 2-minute walk test. Multiple linear regression models were used to determine relationships between fear-avoidance or pain catastrophizing and gait quality. T tests were used to determine gait quality differences between high versus low fear-avoidance subgroups. Results: High fear-avoidance was associated with reduced gait speed (B = −0.0039), but pain catastrophizing was not. The high fear-avoidance subgroup had slower gait speed (mean difference = 0.05 m/s), longer step time (mean difference = 0.02 s), and higher step time variability (mean difference = 0.004 s) compared to the low fear-avoidance subgroup. Conclusions: Fear-avoidance is associated with slower gait speeds, even after adjusting for demographics, pain, and disability. The established FABQ-PA cutoff is robust in detecting gait differences between high versus low fear-avoidance subgroups. Relevance: It may be important to consider fear-avoidance in the delivery of multi-modal interventions to address gait impairments. Future studies are needed to determine the impact of addressing fear-avoidance alongside traditional gait interventions in cLBP.

Gait is a complex motor skill requiring high-level cognitive resources such as attention. Chronic low back pain (cLBP) is associated with attention impairments that may impact gait. Fear-avoidance and pain catastrophizing in cLBP may additionally contribute to attention impairments that affect gait. Forty-five participants with cLBP (age 37.0±11.5 (21-59), 64% female) completed a gait task with and without a concurrent auditory information processing choice reaction time task (IP-CRT). Dual-task cost (DTC) was computed for gait and cognitive performance metrics. Participants also completed the Fear-Avoidance Beliefs Questionnaire-Physical Activity subscale (FABQ-PA), the Pain Catastrophizing Scale (PCS), and the Numeric Pain Rating Scale (NPRS). PCS was positively associated with DTC for step length (r=0.32, p=0.04), and NPRS was positively associated with DTC for harmonic ratio (anterior-posterior direction) as a measure of symmetry (r=0.41, p<0.01). Higher NPRS scores were associated with reduced step length during single- (r=-0.37, p=0.02) and dual-task (r=-0.35, p=0.02), higher stance time variability during single- (r=0.36, p=0.02) and dual-task (r=0.35, p=0.02), lower harmonic ratio (vertical direction) during dual-task (r=-0.31, p=0.049), and slower reaction time during dual-task (r=0.41, p<0.01). Individuals with high pain catastrophizing or high pain severity may alter step length and gait symmetry differently than their peers in response to increased cognitive loading. Pain severity, but not pain-related psychological factors, appears to be related to gait and cognitive performance, emphasizing the importance of reducing pain burden. Results support the continued study of intersections between pain, attention, and pain-related psychological burden in cLBP.

Background: Approximately 1 in 5 children and adolescents live with chronic pain, with musculoskeletal (MSK) pain being one of the most prevalent subtypes. Unfortunately, some studies show that less than half of youth (<18 years) experience improvements with existing evidence-based treatments. Self-report measures—the current gold standard for monitoring the pain experience—are limited in their use as a single point-of-care assessment and their vulnerability to recall bias. The ubiquitous adoption of wearable technology presents a promising solution for improved monitoring of the pain experience via real-time tracking through a multisystemic lens. Objective: The purpose of this study is (1) to develop a digital biosignature of the pain experience in youth with chronic MSK pain and (2) to assess the feasibility, acceptability, and appropriateness of the captured data for future applications. Methods: All aspects of this study were designed in partnership with people with lived experience and patient advocacy partners. This is a longitudinal observational cohort study, with all study activities taking place remotely over a 12-week period. Up to 500 youth (between 14 and 24 years old) with chronic MSK pain will be enrolled through a multipronged recruitment strategy to ensure a representative sample. The participants will wear an Apple Watch throughout the study to continuously monitor physiological, sleep, and physical activity metrics. In addition, participants will complete brief “daily check-in” surveys that include gold-standard measures of the pain experience (eg, pain interference, mood, fatigue) and the option to report a “pain flare” (ie, a temporary but noticeable worsening of the usual pain symptoms). Participants will also complete a modified online Trier Social Stress Test and a 30-second sit-to-stand task to capture individual responses to standardized challenges. Traditional machine learning and deep representation learning methods will be used to develop a digital biosignature of the pain experience. The accuracy of the biosignature will be assessed through measures of model performance as compared to gold-standard self-reports. Results: This study was funded in September 2024, with data collection beginning in March 2025. As of December 15, 2025, 190 participants are enrolled, with data collection and analysis ongoing. Conclusions: This is the first study to leverage wearable health technology for real-time monitoring of the pain experience in youth with chronic MSK pain. The resulting digital end points are expected to heighten the rigor of clinical trials and provide opportunities for individually tailored interventions. The second phase of this study will investigate the implementation of “wellness alerts” triggered by abnormal smartwatch readings. Alerts would empower users toward preemptive self-management strategies, thereby enhancing self-efficacy in those living with chronic MSK pain. International Registered Report Identifier (IRRID): DERR1-10.2196/84781

BACKGROUND Approximately 1 in 5 children and adolescents live with chronic pain, with musculoskeletal (MSK) pain being one of the most prevalent subtypes. Unfortunately, some studies show that less than half of youth (<18 years) experience improvements with existing evidence-based treatments. Self-report measures—the current gold standard for monitoring the pain experience—are limited in their use as a single point-of-care assessment and their vulnerability to recall bias. The ubiquitous adoption of wearable technology presents a promising solution for improved monitoring of the pain experience via real-time tracking through a multisystemic lens. OBJECTIVE The purpose of this study is (1) to develop a digital biosignature of the pain experience in youth with chronic MSK pain and (2) to assess the feasibility, acceptability, and appropriateness of the captured data for future applications. METHODS All aspects of this study were designed in partnership with people with lived experience and patient advocacy partners. This is a longitudinal observational cohort study, with all study activities taking place remotely over a 12-week period. Up to 500 youth (between 14 and 24 years old) with chronic MSK pain will be enrolled through a multipronged recruitment strategy to ensure a representative sample. The participants will wear an Apple Watch throughout the study to continuously monitor physiological, sleep, and physical activity metrics. In addition, participants will complete brief “daily check-in” surveys that include gold-standard measures of the pain experience (eg, pain interference, mood, fatigue) and the option to report a “pain flare” (ie, a temporary but noticeable worsening of the usual pain symptoms). Participants will also complete a modified online Trier Social Stress Test and a 30-second sit-to-stand task to capture individual responses to standardized challenges. Traditional machine learning and deep representation learning methods will be used to develop a digital biosignature of the pain experience. The accuracy of the biosignature will be assessed through measures of model performance as compared to gold-standard self-reports. RESULTS This study was funded in September 2024, with data collection beginning in March 2025. As of December 15, 2025, 190 participants are enrolled, with data collection and analysis ongoing. CONCLUSIONS This is the first study to leverage wearable health technology for real-time monitoring of the pain experience in youth with chronic MSK pain. The resulting digital end points are expected to heighten the rigor of clinical trials and provide opportunities for individually tailored interventions. The second phase of this study will investigate the implementation of “wellness alerts” triggered by abnormal smartwatch readings. Alerts would empower users toward preemptive self-management strategies, thereby enhancing self-efficacy in those living with chronic MSK pain. INTERNATIONAL REGISTERED REPORT DERR1-10.2196/84781