The impact of obesity on muscle function in older adults: from clinical evaluation to lifestyle management

In the geriatric population, obesity and sarcopenia constitute two important public concerns due to their association with disability, loss of independence, comorbidity, and mortality. Only few studies previously evaluated the impact of obesity on the in vivo muscle strength, power, and physical function in the older population, particularly on the lower extremities. This is surprising, since particularly the decline of lower body physical function negatively affects important daily activities. In older adults the role of obesity and adipose tissue on muscle function decline is complex and not completely understood. Furthermore, the possible contribution of lower limb muscles in the evaluation of muscle weakness has been poorly investigated. Finally, various studies exist on the possible approaches using exercise and nutrition to treat and to ameliorate obesity, dynapenia and sarcopenia; discrepancies are instead presented on the potential beneficial effects associated with the supplementations compared to exercise alone, leaving open questions about the best treatments to adopt in this population. Therefore, the goals of this thesis are: i) to determine the impact of obesity on the in vivo lower limbs muscle strength and function in older adults of both sexes; ii) to investigate the associations between lower limbs muscle strength and function and the handgrip dynamometer and the possible contribution to predict the appendicular muscle mass; iii) to propose an intervention protocol aimed at improving or reversing obesity and sarcopenia condition. Chapter one explored the literature around the effects of obesity in the geriatric population. A particular emphasis is made on the important role of maintaining and assessing muscle strength, muscle mass and function. Additionally, an overview of different strategies for treating or reversing obesity and sarcopenia through exercise and nutrition are provided. Chapter two presents the consequences of obesity on the lower limbs’ muscles, adding new reference data of knee extensors and knee flexors strength and power in geriatric population of both sexes. Chapter three focuses on the tools used for evaluating muscle weakness. In this context, the role of handgrip dynamometer as a proxy of muscle strength is argued with a comprehensive narrative review and an experimental study. In the latter, the associations between upper vs lower limbs muscle strength and physical function are discussed looking at the possible sex differences in geriatric population. Chapter four describes the preliminary results on the role of a 5-month controlled diet plus strength training alone or amino acids supplementation in older adults with obesity, dynapenia and sarcopenia. After the intervention, the changes in several outcomes (i.e., on body composition, upper and lower limbs muscle strength and power, physical performance) are described, by comparing the different interventional groups. Lastly, chapter five outlines the main results of each study and presents a general conclusion with proposals for future directions needed on these research topics.