Irisin and brain-derived neurotrophic factor (BDNF) are considered potential biomarkers for sarcopenia; however, their interplay and relationship with oxidative stress remain unclear. Therefore, the aim of this study was to assess the serum concentration of irisin and BDNF in patients over 60 years of age, as well as their relationship with dynapenia and redox homeostasis. Dynapenia was diagnosed using the Five Times Sit-to-Stand Test (5TSST). Serum levels of irisin, BDNF, total oxidative status (TOS), and total antioxidative status (TAS) were measured, and the oxidative stress index (OSI) was calculated. A total of 110 patients from a geriatric ward (72.7% women, mean age 78.2 ± 7.1 years) participated in the study. BDNF concentration was negatively associated with dynapenia, irisin, and the irisin/BDNF ratio. TOS, TAS, and OSI were negatively associated with BDNF and positively associated with irisin and dynapenia. No significant association was found between irisin and sarcopenia parameters. In regression analysis, significantly higher odds of dynapenia were observed for older age, female sex, a greater number of chronic diseases, and higher OSI values, after adjusting for TOS, BDNF, and the irisin-to-BDNF ratio. These results confirm redox imbalance as an independent predictor of sarcopenia. A lower BDNF concentration and a higher irisin-to-BDNF ratio may indicate a protective role of BDNF in the development of sarcopenia in geriatric patients; however, this finding requires further confirmation.

Background: Dynapenia is an age-related decline in muscle strength that leads to unfavorable outcomes, decreased functional capacity, and increased mortality. The study aimed to measure total oxidative status (TOS) and total antioxidative status (TAS), and to explore the role of oxidative stress in dynapenia, with consideration of sex differences and dehydroepiandrosterone (DHEA) influence. Methods: The study was performed in geriatric ward patients over 60 years of age, who were able to take part in the functional assessment. Dynapenia was diagnosed if grip strength was <27 kg in men, and <16 kg in women. DHEA, TOS, and TAS were assayed in the serum. The severity of oxidative stress was expressed as the oxidative stress index (OSI). One hundred and thirty-four patients (73.9% women, mean age 79.1 ± 7.3 years) took part in the study. Results: Dynapenia was observed in 37.3% of cases, with similar prevalence in women (35.4%) and men (42.9%). The logistic regression analysis identified older age, higher OSI, lower BMI, and lower DHEA as significant determinants of dynapenia, while sex was not a significant factor. Conclusions: The study demonstrates a significant association between oxidative stress and dynapenia in older adults, independent of sex and comorbidity burden. The observed sex-specific patterns—especially the stronger association in women—and the link between lower DHEA levels and dynapenia underscore the importance of hormonal regulation in this process.