Older patients with less skeletal muscle mass gain more skeletal muscle in rehabilitation wards after fractures.

Background: We hypothesized that old patients could increase skeletal muscle mass after fractures by exercise rehabilitation, even if they have a low initial muscle mass.

Aim: This study aimed to evaluate the relationship between skeletal muscle mass and skeletal muscle changes in older patients after fractures.

Methods: This case-control study took place in rehabilitation wards and included 807 patients aged ≥ 65 years with fractures. Patients were divided into two groups based on the skeletal muscle index (SMI) on admission by the sarcopenia cut-off points: low SMI group included patients with SMI < 7.0 for men and < 5.7 for women and high SMI group included patients with SMI ≥ 7.0 for men and ≥ 5.7 for women. Analysis of comparison between the two groups and multivariate logistic regression analyses were performed.

Results: The SMI gain was significantly higher in the low SMI group (0.20) than in the high SMI group (0.00, p  < 0.001). There were also the differences in age, BMI, mini nutritional assessment short form, Charlson comorbidity index, length of hospital stay, and protein intake. The SMI on admission was significantly associated with increased SMI after rehabilitation (odds ratio 0.569, 95% confidence interval 0.455‒0.710). Length from onset to transfer to the hospital, hospital stay, and period of exercise therapy were also significantly associated with increased SMI.

Conclusions: We found that older patients with low SMI after fracture gained more skeletal muscle mass than those with high SMI following exercise rehabilitation. In addition, SMI on admission was one of the factors independently associated with increased SMI.