The key finding
Researchers examining how different body functions decline with age in laboratory mice and fish have found that aging doesn’t affect all abilities simultaneously. A 2026 review of 32 studies revealed that sensory functions like hearing and vision deteriorate as early as midlife in mice, while movement abilities begin declining in middle age—particularly in female mice. Physical strength, measured by grip force, tends to weaken primarily in old age. These patterns in animal models closely parallel human aging trajectories, with sensory decline often preceding other functional losses. The research examined five key functional domains: movement, cognition, vitality (physical strength), psychological wellbeing, and sensory abilities.
What the study looked like
This narrative review analyzed 27 studies using mouse models and 5 studies using fish models, primarily killifish, which age rapidly in laboratory settings. Researchers searched three major scientific databases (PubMed, Embase, and Web of Science) to identify studies that tracked age-related changes in what scientists call “intrinsic capacity”—the combination of physical and mental abilities that determine healthy aging. The included studies measured various functions longitudinally, meaning they followed the same animals over time rather than just comparing young and old animals at a single point. Measurements included voluntary running wheel activity, rotarod performance (a rotating rod that tests balance and coordination), grip strength tests, maze navigation for memory assessment, and both behavioral and electrical recordings of sensory function. The review specifically focused on how these capacities evolved across the lifespan in these accelerated-aging animal models.
Why researchers think this happened
The researchers propose that different organ systems and biological processes age at different rates, explaining why sensory functions decline before physical strength. This aligns with the geroscience framework, which suggests that fundamental aging mechanisms—like cellular damage accumulation, inflammation, and declining repair systems—affect different tissues with varying timelines. The earlier onset of sensory decline in mice may reflect the particular vulnerability of specialized sensory cells to oxidative stress and reduced regenerative capacity. Gender differences in movement decline, with female mice showing earlier impairment, might relate to hormonal changes or sex-specific aging patterns. The review authors emphasize that understanding these sequential declines in animal models can help identify therapeutic windows for intervention in humans. The fact that killifish showed movement problems later in life (the final third) compared to mice suggests species-specific aging patterns, but both models demonstrated the principle that aging is not a uniform process across all body systems.
How to read this carefully
This review synthesized existing studies rather than conducting new experiments, meaning its conclusions depend on the quality and consistency of the included research. The studies used different measurement protocols, mouse strains, and housing conditions, making direct comparisons challenging. Laboratory animals live in controlled environments quite different from natural settings, and their aging may not perfectly mirror human aging processes. The review identified relatively few fish studies (only 5 compared to 27 mouse studies), limiting confidence in conclusions about aging patterns in aquatic models. Additionally, these are correlational observations—the studies tracked what declines when, but don’t definitively explain why certain functions deteriorate before others. Sample sizes and age ranges varied across studies, and not all studies measured all five functional domains, creating gaps in the longitudinal picture.
What this means for everyday life
These findings from animal research suggest that regular monitoring of different health aspects at different life stages might be valuable. If sensory decline precedes other aging signs in mammals generally, this could support the case for earlier hearing and vision screening in midlife humans, before obvious symptoms appear. The observation that movement abilities decline in middle age, particularly in females, might encourage earlier attention to physical activity and balance exercises rather than waiting until old age. The sequential nature of decline across different body systems suggests that “healthy aging” isn’t a single target but rather involves maintaining multiple capabilities that each follow their own timeline. While we can’t directly apply mouse and fish findings to human health recommendations, these animal models help researchers understand aging mechanisms and test interventions that might eventually translate to human therapies. Given this research, it might be worth considering comprehensive health assessments that evaluate multiple functional domains rather than focusing only on disease presence or absence.