Abstract

Background and Purpose: Chronic low back pain (CLBP) is the leading cause of years lived with disability worldwide. Several risk factors, such as psychosocial and body composition, are associated with CLBP. However, the isokinetic strength and trunk muscle quality index (MQI) have been poorly explored. Thus, this study aimed to compare clinical, body composition, and functional variables between healthy people and CLBP patients by sex and to determine the relationship between clinical and body composition variables according to sex. Methods: Cross-sectional study. Twenty-eight healthy (22.0 ± 1.3 years, 72.5 ± 14.3 kg, and 1.70 ± 0.1 m) and 25 CLBP (24.1 ± 5.8 years, 72.1 ± 11.7 kg, and 1.67 ± 0.1 m) participants were evaluated for pain (Numeric Rating Scale), disability (Oswestry disability index), kinesiophobia (Tampa scale), body composition (DXA), isometric and isokinetic trunk strength, and trunk MQI. Results: Pain, disability, and kinesiophobia were greater in the CLBP group, but no differences in body composition were found independent of sex. The CLBP group had less extensor and flexor relative strength, differences maintained in females, but higher rotator strength, a difference that is only maintained in males. Trunk MQI is lower in the CLBP group for flexors and extensors but higher for trunk rotators, a difference maintained only in males. No correlation between body composition and clinical variables was found; however, a significant large correlation between kinesiophobia and fat mass and distribution existed for males with CLBP. Discussion: Compared to healthy people, CLBP patients have greater pain, disability, and kinesiophobia independent of sex, but they are not different in body composition. CLBP patients show fewer extensors and flexors strength and MQI; however, they have greater rotator strength and MQI, differences that are only maintained in males. Despite this, males present with pain and disability, so the role of trunk strength and MQI should be explored. © 2025 John Wiley & Sons Ltd.