Short-Term Effect of Negative Verbal Language Versus Positive Verbal Language on Physical and Functional Capacity and Pain in People With Chronic Primary Low Back Pain.

BACKGROUND: Low back pain (LBP) is the leading cause of years lived with disability. While education is recommended by most guidelines, the type of language used can lead to a placebo or nocebo effect. This study aims to compare the short-term effect of negative language versus positive language on physical and functional capacity in individuals with chronic primary LBP. METHODS: Forty-six adults with chronic primary LBP were recruited and received standardized negative (n = 23) or positive (n = 23) messages about LBP immediately before physical (isometric/isokinetic trunk flexion and extension) and functional capacity (Back Performance Scale (BPS); five times sit-to-stand (FTSTS)) tests. Pain intensity and pressure pain threshold (PPT) of trunk muscles were also measured before (T0) and after intervention (T1). RESULTS: Groups were comparable at baseline for sociodemographic, psychobehavioral (Start Back Screening Tool) characteristics, and disability (Oswestry Disability Index). No between-group differences were detected for physical (all p > 0.18) or functional capacity (FTSTS: p = 0.781; BPS: p = 0.665). Pain intensity increased from T0 to T1 in both groups (p < 0.001), without minimal clinically important difference and with no group or interaction effect. PPT showed no main effects or interactions across the seven measurement sites (all p > 0.08). CONCLUSION: No significant short-term difference was found between negative and positive language on physical and functional capacity, pain intensity, or PPT in individuals with chronic primary LBP. Future studies should examine tailored negative or positive language delivered over multiple sessions to clarify the effect of language type on physical and functional outcomes in individuals with chronic primary LBP. SIGNIFICANCE STATEMENT: There is growing evidence suggesting that the type of language used may influence various clinical outcomes, such as anxiety, catastrophizing, or disability, in people with chronic primary LBP. However, no study has shown whether language style can influence trunk strength and functional capacity in this population. This study shows that there is no short-term difference in physical and functional capacity among people with chronic primary LBP exposed to negative or positive language.