Aim To examine changes in lean mass during hospitalization in geriatric patients and the effect of muscle activation by neuromuscular electrical stimulation. Methods Thirteen patients (69-94 years) at a geriatric ward completed tests at hospital admission (day 2-3) and discharge (day 8-10). One leg received daily stimulation of the knee extensors while the other leg served as a control leg. Lean mass was evaluated by DEXA scans and muscle thickness by ultrasound scans. Muscle biopsies were collected from both legs at admission and discharge in 9 patients and analyzed for fibre size, satellite cell number and activation and expression of genes associated with muscle protein synthesis and breakdown, connective tissue and cellular stress. Results The relative decline in leg lean mass and midthigh region lean mass was larger in the control (-2.8±1.5%) vs. the stimulated leg (-0.5±1.4%, p