The impact of disease-related immobilization on thigh muscle mass and strength in frail older hospitalized patients

Abstract Background: We assessed the quantitative changes in muscle mass and strength during two weeks of hospitalization in immobile and mobile acutely ill hospitalized older adults. Methods: 41 patients (82.4±6.6 years, 73.0% females) participated in this prospective longitudinal observational study. Mobility status was defined according to walking ability as described in the Barthel-Index. Functional status, including handgrip strength and isometric knee-extension strength, and mid-thigh magnetic resonance imaging (MRI) measurements of cross-sectional area (CSA) were conducted on admission and at discharge. Results: Twenty-two participants (54%) were immobile and 19 (46%) mobile. In all, 54.0% and 12.0% were at risk of malnutrition and malnourished, respectively. The median time between baseline and follow-up for MRI scans were 13 days in mobile and immobile participants (P=0.072). Mid-thigh muscle and subcutaneous fat CSA significantly decreased by 3.9cm 2 (5.0%, P=0.002) and 5.3cm 2 (5.7%, P=0.036) during hospitalization whereas intermuscular fat remained unchanged in immobile subjects. No significant changes were observed in mobile patients. In a regression analysis, mobility was the major independent risk factor for changes in mid-thigh muscle CSA as a percentage of initial muscle area (P=0.022) whereas other variables such as age (P=0.584), BMI (P= 0.879), nutritional status (P=0.835) and inflammation (P=0.291) were not associated with muscle mass changes. There was a significant decrease in isometric knee extension strength (P=0.002) and no change in handgrip strength (P=0.167) in immobile patients whereas both parameters increased significantly over time in mobile patients (P=0.048 and P=0.012, respectively). Conclusions : Two weeks of disease-related immobilization result in a significant loss of thigh muscle mass and muscle strength in older patients with impaired mobility. Concomitantly, there was a significant reduction of subcutaneous adipose tissue in immobile older hospitalized patients whereas no changes were observed in intermuscular fat among these patients. These data highlight the importance of mobility support in maintaining muscle mass and function in older hospitalized patients.