Effects of Short-Term Resistance Training on Diaphragm Thickness, Hepatic Fat Density, and Quality of Life in Healthy Older Men: A Randomized Controlled Trial

Background: The aging process leads to multidimensional physiological changes affecting respiratory muscles, metabolic health, and quality of life. While the effects of resistance training on the musculoskeletal system in older adults are well documented, its short-term effects on less studied physiological parameters, such as diaphragm muscle morphology and hepatic steatosis, are only partially understood. This study aims to investigate the effects of a resistance training-based intervention in healthy elderly men on diaphragm thickness, liver fat content, and health-related quality of life. Methods: This study was conducted using a randomized controlled pre-test–post-test design involving 30 healthy men aged 60–75 years. Participants were randomly assigned to either the intervention group (IG; resistance training) or the control group (CG). The intervention consisted of a moderate-intensity structured resistance training program performed three days per week for four weeks. Diaphragm thickness and liver fat content were assessed using non-contrast computed tomography (CT) scans, and quality of life was measured using the SF-12 questionnaire. Time effects and group × time interactions were analyzed using repeated measures analysis of variance. Results: In the intervention group, diaphragm thickness significantly increased after training (10.25%), while a slight decrease was observed in the control group. Both the effect of time (p = 0.002) and the group × time interaction (p = 0.014) was statistically significant for diaphragm thickness. Although the effect of time was not significant for liver fat density, the group × time interaction was strong and significant (p < 0.001). Physical and mental health scores increased over time in both groups, but the group × time interaction was not statistically significant for these changes. Conclusions: Short-term resistance training induces early and measurable structural adaptations in the diaphragm muscle of healthy elderly men. This finding indicates that respiratory muscles are exercise-responsive target structures in older individuals and provides important implications for clinical exercise prescriptions. Outcomes related to quality of life and hepatic steatosis primarily reflect general time-dependent changes or exploratory responses. This study reveals the physiological effects of low-cost and feasible exercise interventions in elderly individuals and lays a foundation for longer-term studies involving advanced imaging techniques.