Thoracolumbar fascia thickness and body mass index as predictors of pain sensitivity: a single-blinded experimental hypertonic saline study

Abstract Background The thoracolumbar fascia (TLF) is a key connective tissue structure that is involved in biomechanics of the lumbar spine and nociceptive processing. Growing evidence indicates that body mass index (BMI) is associated with connective-tissue remodeling, that may influence pain sensitivity and may thus contribute to musculoskeletal pain. However, the extent to which BMI-related differences in fascia morphology predict pain responses under controlled experimental conditions remains insufficiently understood. This study investigated thoracolumbar fascia thickness and BMI as predictors of pain sensitivity using a single-blinded experimental hypertonic saline pain model. Methods Twenty healthy adult volunteers (mean age 23.6 ± 2.4 years) received injections of hypertonic saline (5.8% NaCl) into the TLF to evoke low back pain. Induced Pain intensity was assessed using numerical rating scales (0–100 NRS) and the TLF thickness was measured via ultrasound at injection and contralateral site by a person blinded to pain ratings. Results TLF thickness was a significant predictor of experimentally induced pain sensitivity, demonstrating a moderate positive correlation with the individual peak pain (Pearson’s r = 0.606, P < 0.01), accounting for approximately 37% of the variance in pain response. Furthermore, BMI was positively associated with TLF thickness ( r = 0.495, P < 0.05), indicating that higher body mass predicts increased fascial thickness. Notably, BMI was positively correlated with induced pain intensity ( r = 0.565, R 2 = 0.320, P < 0.05), supports the notion that body composition may contribute to inter-individual variability in pain sensitivity. No significant side-to-side differences in TLF thickness were observed. Conclusion These findings identify both thoracolumbar fascia thickness and BMI as potential predictors of low back pain sensitivity and demonstrate significant associations between structural fascial characteristics, body composition, and nociceptive responses. The results are consistent with clinical observations linking higher BMI to increased musculoskeletal pain burden and suggest that fascial structural characteristics may be related to nociceptive sensitivity. Furthermore, ultrasound-based assessment of fascial thickness may represent a clinically accessible parameter associated with pain sensitivity and may be useful for characterizing musculoskeletal outcomes in the context of weight-related interventions.