ABSTRACT The life expectancy of people with HIV (PWH) in the U.S is increasing. HIV, together with normal aging, imposes additional challenges to an extended healthspan (i.e., the length of time that the person is healthy and not just alive) in this population. This includes an earlier occurrence of geriatric conditions such as sarcopenia, a musculoskeletal disease that can lead to falls, morbidity, loss of independence, disability, and mortality. Sarcopenia poses a significant economic burden, generating higher healthcare costs and more extended hospital stays for the sarcopenic population. Sarcopenia is highly prevalent (24%) among PWH, and we recently demonstrated that PWH are six times more likely to develop sarcopenia than people without HIV. Despite being prevalent among this population, few observational studies in PWH have included sarcopenia as a primary outcome, and we lack interventional studies targeting sarcopenia among PWH. The causes of sarcopenia are multifactorial, and despite being recognized as a debilitating disease, it has no effective pharmacological treatment. In the general population, physical inactivity and malnutrition are recognized contributors to sarcopenia, and exercise and diet interventions are the best ways to prevent and treat it. Among PWH, the causes of sarcopenia can include different HIV-associated factors. Lifestyle factors such as physical inactivity, sedentary behavior, and malnutrition are prevalent among PWH and can potentially contribute to sarcopenia in this population. However, these associations in HIV remain poorly explored, and whether these are the primary contributors to sarcopenia among PWH is unknown. This proposed study is uniquely positioned to address such gaps in the science by leveraging the ongoing multi-site PROSPER-HIV study (R01-NR-018391) focused on the association between physical activity, diet, and HIV symptoms in PWH by adding a whole-body dual-energy X‐ray absorptiometry scan. This will provide data on the amount of lean body mass and allow us to rigorously determine the presence of sarcopenia among PWH. The PROSPER-HIV study provides an ideal opportunity to explore the importance of these modifiable lifestyle behaviors on the healthspan of PWH and to answer how physical activity and diet can help in the multifactorial development and management of sarcopenia. Specifically, in 130 PWH ≥50 years of age, we will: 1) Examine the cross-sectional relationship between modifiable lifestyle factors (i.e., habitual physical activity levels and diet quality) and the presence of sarcopenia; and 2) Investigate to what extent current or prior exposures (i.e., symptom burden; medication adherence; smoking, alcohol, and drug use; the presence of depression and anxiety; clinical and demographic characteristics) predicts sarcopenia. Our scientific premise is that, on top of other factors leading to HIV-associated sarcopenia, lifestyle factors play an essential role and can be harnesseed as a non...