# Physical Fitness Dynamics Shape Immune Remodeling in Healthy Aging: A 3‐Year Longitudinal Study

## TL;DR

This study shows that declining physical fitness in older adults is linked to immune changes typical of aging, even without noticeable inflammation.

## Contribution

The study identifies physical fitness as a modifiable factor influencing early immune aging in healthy elderly individuals.

## Key findings

- Declines in cardiorespiratory fitness and strength correlate with immune remodeling, including increased senescent T cells.
- Resting Tregs decrease while memory-like Tregs increase with declining physical fitness.
- Habitual physical activity is independently associated with effector T cell dynamics.

## Abstract

Aging is accompanied by functional decline and immune remodeling, yet the dynamics and early modifiability of these processes remain incompletely understood. Research suggests that lifestyle factors, particularly physical activity and fitness, influence immune aging. This study investigated longitudinal changes in physical performance and immune parameters in a well‐characterized cohort of clinically healthy elderly. In this study, 49 clinically healthy elderly underwent repeated assessments of cardiorespiratory fitness, muscular strength, body composition, immune cell phenotypes, and serum cytokines at baseline, 1‐year, and 3‐year follow‐up. We observed a shift toward an aged T cell profile, characterized by reductions in naïve and regulatory T cells (Tregs), alongside increases in differentiated and senescence‐associated subsets. Treg subsets followed divergent trajectories, with resting Tregs (rTregs) declining and memory‐like Tregs (mTregs) increasing. Serum levels of classical pro‐inflammatory cytokines remained largely stable over the study period. Despite stable self‐reported physical activity, participants showed declines in cardiorespiratory fitness and strength. Immune remodeling was primarily associated with declines in physical fitness, alongside an increase in highly differentiated CD4+ and senescent CD8+ T cell subsets, lower rTregs, higher mTregs, and increased CD4−CD8− lymphocyte frequencies, while habitual physical activity was independently related to effector T cell dynamics. Together, these findings indicate that subtle functional decline in clinically healthy older adults is paralleled by immune changes characteristic of early immunosenescence, occurring largely in the absence of overt systemic inflammation. These results highlight physical fitness as a potentially modifiable determinant of immune trajectories and immune resilience in healthy aging.

In a 3‐year longitudinal study of healthy older adults, intraindividual declines in physical fitness and strength were linked to dynamic immune remodeling, including shifts toward senescent and regulatory T cell phenotypes, despite stable activity levels. These findings identify physical fitness as a key, potentially modifiable driver of early and subclinical immune aging.