Background:

Spinal cord injury (SCI) results in profound changes in body composition characterised by muscular atrophy below the level of injury (LoI) and increased adiposity. Paralysis of the lower limbs increases reliance on upper limbs for daily mobility and physical activity. Whether this compensatory increase in upper limb activity affects upper limb and total fat-free mass is currently unclear.

Objectives: 

To compare whole body and regional (upper limbs, lower limbs and trunk) FFM between individuals with chronic SCI (>1 year) and non-injured controls adjusted for age, sex and height.

Methods:

A retrospective cross-sectional study included individuals with chronic SCI (n=54;M=32,F=22; time since injury [TSI] 15±10 years; lesion level C5–L3; tetraplegia, n=2, high paraplegia n=22, low paraplegia n=30; American Spinal Injury Association Impairment Scale [AIS] A–C) and non-injured controls (n=37; M=19, F=18). Whole-body dual-energy X-ray absorptiometry (DEXA) quantified total and regional (upper-limb, lower-limb and trunk) FFM. Between-group differences in FFM were assessed using general linear models, with group (SCI vs CON) as a fixed factor and age, sex, and height as covariates. Independent-samples t-tests compared age, body mass index (BMI), and body fat percentage between groups. Associations between LoI, TSI, and FFM were examined using Spearman’s rank correlation coefficients (rₛ). Data are presented as mean±standard deviation and 95% confidence intervals (CI).

 

Results:

Age did not significantly differ between SCI and controls (SCI: 47±8 years vs CON: 47±10 years; p=0.746). BMI was lower in SCI than controls (25.7±4.4 kg/m² vs 28.4±3.1 kg/m², respectively; p=0.001). Body fat percentage did not significantly differ between groups (SCI: 33±10% vs CON: 33±9%; p=0.904). After adjusting for age, sex, and height, individuals with SCI demonstrated significantly reduced lower-limb FFM compared with controls (-9.6 kg, -10.9 to -8.3 kg; p<0.001). Adjusted trunk FFM was also significantly lower in SCI (-2.9 kg, -4.1kg to -1.7 kg; p<0.001), as was upper-limb FFM (-1.2 kg, -1.9 to -0.6 kg; p<0.001). Adjusted total FFM was 10.5 kg lower in SCI compared with controls (8.3 to 12.7 kg; p<0.001). No associations were observed between TSI and upper-limb (rₛ=0.069, p=0.620) or lower-limb FFM (rₛ=-0.166, p=0.232), nor between LoI and lower-limb (rₛ=-0.113, p=0.417), upper-limb (rₛ=-0.131, p=0.347), or total FFM (rₛ=-0.124, p=0.372).

 

Conclusion: 

These data suggest that SCI is associated with lower FFM across all body compartments; however, the reduction is disproportionately greater in the lower-limbs than the upper-limbs. These findings highlight reduced metabolically active FFM and limited compensatory adaptation, with important implications for health and exercise prescription in SCI. For example, such findings may support targeted interventions including neuromuscular electrical stimulation, resistance training (NMES) and/or hybrid exercise modalities such as NMES-RT and functional electrical stimulation aimed at eliciting lower-limb muscular contractions to preserve lean mass and potentially improve metabolic health.