Regular physical activity is a cornerstone of healthy aging, offering a wide range of benefits, including the modulation of immune regulation and reduction of chronic inflammation. With aging closely linked to persistent, low-grade inflammation, i.e. inflammaging, the effects of exercise intensity on acute immune responses in older adults remain not fully understood. In this study, we explored how moderate and intense acute continuous exercise impact immune cell activation, cytokine production and large extracellular vesicle (lEV) release in healthy elderly individuals. Fourteen participants completed a moderate continuous exercise intervention (60% VO2max for 30 minutes), while nineteen engaged in an intense continuous exercise session until exhaustion. Blood samples were collected at baseline, and at 1- and 24-hours post-exercise. Immune cell characterization by flow cytometry revealed distinct changes in monocyte subsets and NK cells activation across both exercise intensities. Intense exercise was associated with elevated proinflammatory TNFα levels, accumulation of circulating plasma-derived lEV and changes in their surface marker expression after 24 hours. Additionally, we identified sex-specific differences, including distinct activation profiles in innate immunity, alterations in EV release from CD4+ and HLA+ cells, and an exercise-induced increase in IL-6 observed exclusively in females. These findings suggest that moderate continuous acute exercise enhances immune cell activation without altering cell counts, while intense continuous exercise triggers acute proinflammatory immune response. Further research should clarify the long-term implications and fundamental mechanisms of exercise-induced immune modulation in aging populations.

The authors have declared no competing interest.

This work was supported by the following grants: German Center for Mental Health (DZPG) (funded by BMBF (to PM & ID), European Regional Development Fund (EFRE) (ZS/2024/02/184014, to RBD, SS, ID & PM), Graduate scholarship from the Novartis Foundation (to PM), Polycarp-Leporin-Program (PLP23/5,to PM).

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The study protocol was approved by the Ethics Committee of the Medical Faculty at Otto-von-Guericke University in Magdeburg, Germany (reference number: 07/20). All the procedures were conducted in accordance with the ethical standards outlined in the Declaration of Helsinki. Prior to participation, each individual provided written informed consent following a comprehensive explanation of the study, and all queries were addressed satisfactorily.

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

All data produced in the present study are available upon reasonable request to the authors