Association Between Body Composition, Muscle-to-Weight Ratio, and Functional Disability in Patients with Chronic Non-Specific Low Back Pain: A Cross-Sectional Study.
Tirla S, Gherle A, et al. • Medicina (Kaunas, Lithuania) • 2026
Pain intensity, age, and Muscle-to-Weight Ratio (MWR) were significantly associated with functional disability in patients with chronic non-specific low back pain, with lower MWR values associated with greater disability after adjustment for confounders.
Key Findings
Results
Pain intensity showed the strongest positive correlation with functional disability in patients with chronic non-specific low back pain.
Correlation coefficient r = 0.56, p < 0.001 between VAS pain scores and RMDQ disability scores
In multivariable regression, pain intensity had a standardized coefficient β = 0.49, p < 0.001
Pain intensity remained significant after adjustment for sex, age, body fat percentage, and MWR
Study sample included 98 adults with chronic non-specific LBP (mean age 61.9 ± 10.0 years)
Results
Muscle-to-Weight Ratio (MWR) was negatively correlated with functional disability, such that lower relative muscle mass was associated with greater disability.
Bivariate correlation: r = -0.34, p = 0.001 between MWR and RMDQ scores
In multivariable regression, MWR had a standardized coefficient β = -0.27, p = 0.018
MWR remained significantly associated with disability after adjustment for age, sex, body fat percentage, and pain intensity
MWR was calculated as skeletal muscle mass divided by body weight, expressed as a percentage, measured via bioelectrical impedance analysis (BIA)
Results
Age was independently associated with functional disability in patients with chronic non-specific low back pain.
In multivariable regression, age had a standardized coefficient β = 0.22, p = 0.013
Age remained significant after adjustment for sex, body fat percentage, pain intensity, and MWR
Mean participant age was 61.9 ± 10.0 years
53.1% of participants were female
Results
The multivariable regression model including pain intensity, age, MWR, sex, and body fat percentage explained 43.2% of the variance in disability scores.
R² = 0.432 for the full regression model predicting RMDQ scores
Significant independent predictors were pain intensity (β = 0.49, p < 0.001), age (β = 0.22, p = 0.013), and MWR (β = -0.27, p = 0.018)
Sex and body fat percentage were included as adjustment variables but are not reported as independently significant predictors
RMDQ (Roland-Morris Disability Questionnaire) was used to evaluate functional disability
Results
Female participants reported significantly higher pain intensity than male participants and showed a different distribution of disability severity categories.
Mean VAS pain score: females 60.5 ± 31.0 vs. males 44.2 ± 35.5, p = 0.021
Distribution of disability severity categories differed significantly by sex (Fisher-Freeman-Halton exact p = 0.021)
53.1% of the 98 participants were female
Sex comparisons were performed as part of the cross-sectional observational design
Methods
Body composition was assessed using bioelectrical impedance analysis (BIA) in a sample of 98 adults with chronic non-specific low back pain recruited from a rehabilitation department in Romania.
Cross-sectional observational study design
Participants were recruited from a rehabilitation department in Romania
Mean age 61.9 ± 10.0 years; 53.1% female
Pain intensity measured by Visual Analogue Scale (VAS); disability measured by Roland-Morris Disability Questionnaire (RMDQ)
The cross-sectional design precludes conclusions regarding causality, as noted by the authors
What This Means
This research examined how body composition — particularly the ratio of muscle mass to total body weight — relates to physical disability in people with long-lasting, non-specific low back pain. Researchers studied 98 adults (average age about 62 years) at a rehabilitation center in Romania, measuring their body composition with a bioelectrical impedance device, asking them to rate their pain on a scale, and assessing how much their back pain limited their daily activities. They found that people with lower relative muscle mass (a smaller proportion of their body weight being muscle) tended to have greater disability, even after accounting for how much pain they felt, their age, sex, and body fat levels.
The study found that pain intensity was the single strongest factor linked to disability, but muscle-to-weight ratio and age also independently contributed. Together, these three factors — along with sex and body fat percentage — explained about 43% of the differences in disability levels between patients. Women in the study reported notably higher pain levels than men and had a different pattern of disability severity. These findings suggest that body composition, and specifically the relative amount of muscle a person carries, may be a meaningful piece of information when clinicians are evaluating patients with chronic low back pain.
This research suggests that having proportionally less muscle mass may be relevant to how disabled a person with chronic low back pain feels in daily life, beyond what pain alone explains. However, because this was a snapshot-in-time (cross-sectional) study, it is not possible to determine whether low muscle mass causes greater disability, whether disability leads to muscle loss, or whether some other factor drives both. Future studies following patients over time would be needed to clarify the direction of this relationship and whether interventions aimed at improving muscle mass might reduce disability in this population.
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Tirla S, Gherle A, Bondar L, Osser B, Niculescu V, Iovanovici D, et al.. (2026). Association Between Body Composition, Muscle-to-Weight Ratio, and Functional Disability in Patients with Chronic Non-Specific Low Back Pain: A Cross-Sectional Study.. Medicina (Kaunas, Lithuania). https://doi.org/10.3390/medicina62081474