Cohort-Defined Low Skeletal Muscle Mass and Functional Dependency After Critical Illness: A 12-Month Longitudinal Study

Objective: To evaluate the association between low skeletal muscle mass at intensive care unit (ICU) enrollment and functional dependency at 1, 3, 6, and 12 months after enrollment. Design: Prospective longitudinal observational cohort with follow-up at 1, 3, 6, and 12 months after enrollment. Exposure: Sex-defined low muscle mass (LMM), using L3 skeletal muscle index (SMI) thresholds of <33.2 cm2/m2 in men and <28.3 cm2/m2 in women, derived from the cohort distribution. Main outcome and analysis: Need for assistance with activities of daily living, transfers, or toileting. Logistic generalized estimating equations (GEE) included LMM-by-time interactions, adjustment for sepsis, sex, and age <65 years, and mortality-derived inverse probability weights. Results: Among 217 participants, 148 had SMI measurements and 15 had sex-defined LMM. The functional GEE included 404 assessments from 121 patients, including 12 with LMM. Observed dependency at 1 month was 8/12 (66.7%) with LMM versus 35/108 (32.4%) without LMM. The adjusted 1-month odds ratio (OR) was 3.52 (95% confidence interval [CI], 0.99-12.44; p=0.051); the 12-month OR was 1.67 (95% CI, 0.41-6.81; p=0.475). The joint LMM-by-time test gave p=0.076. A model imposing a common effect across visits gave OR 2.04 (95% CI, 0.79-5.24). Sensitivity analyses were imprecise and did not establish a persistent association. Conclusions: Low muscle mass may identify patients with greater early functional dependency after critical illness. Sparse exposed numbers, mortality, and incomplete follow-up limit inference about persistence and recovery trajectories. The data do not establish equivalent recovery patterns or a causal effect of muscle mass.