Objective: The main aim of the study was to explore muscle mass changes and to investigate musculoskeletal inflammation in critically ill patients.Methods: A pure observational study that comprised two musculoskeletal analyses was conducted. Ultrasonography was used to determine the inflammatory process and muscle mass modifications. We assessed the presence of musculoskeletal inflammation and muscles area reduction. We recruited 26 patients and we performed both imaging investigations (shoulder and hip joints, biceps brachii and rectus femoris areas) and anthropometric measurements (mid-upper arm circumference).Results: More than 70% of patients were classified with low muscle mass, over one half of sarcopenic patients being over-weight and 17% being obese. The relationship between the length of stay in intensive care unit, mechanical ventilation and presence of low mid-upper arm circumference, highlighted a significant difference when comparing sarcopenic and non-sarcopenic groups. Musculoskeletal inflammation expressed by step-down lesions, calcifications and osteophytes, is common in these patients. Statistically significant results were obtained when comparing the dimensions of the investigated muscles. Good inter-observer variability in day 3 of assessment for biceps brachii and rectus femoris was noticed.Conclusions: More than 1/3 of critically ill patients included in the present study was classified with low muscle mass. The length of stay in intensive care unit and the length of mechanical ventilation had an important impact on sarcopenic patients. Musculoskeletal impairment was frequent, reflected by presence of enthesitis lesions in joints and by dynamic reduction of muscle area.