“ Measuring complexity at the behavioral level may yield clinically relevant markers of declining adaptability near the transition to frailty .”
BUFFALO, NY — October 8, 2026 — A new commentary was published in Volume 18 of Aging on September 12, 2026, titled “ Complexity, variability, and the behavioral layer of gerophysics: a commentary on Unfried et al. (2026) .”
The commentary proposes expanding the emerging field of gerophysics to include behavioral complexity, offering a way to understand how aging affects the ability to adapt to everyday challenges. The authors argue that measuring changes in movement, physiological rhythms and other behavioral patterns could complement molecular and biological markers of aging, potentially helping researchers identify declining resilience and the transition toward frailty.
The commentary was authored by Jean-Jacques Temprado and Rita Sleimen-Malkoun, both affiliated with Aix Marseille Université, CNRS, and the Institute of Movement Sciences (ISM), Marseille, France . Temprado is also the corresponding author.
Gerophysics is an emerging interdisciplinary field that applies concepts from physics, mathematics and complex systems science to the study of aging. It draws on dynamical systems, entropy, network theory and stochastic processes to understand how biological systems change over time. A recent report from the Global Conference on Gerophysics, discussed by Unfried and colleagues, outlined a framework connecting aging processes across biological scales, from individual cells to the whole organism.
Temprado and Sleimen-Malkoun suggest that this framework could be strengthened by explicitly incorporating behavioral dynamics, particularly how people interact with and adapt to their environments. While molecular and physiological measurements reveal important aspects of aging, behavioral patterns may provide additional information about how effectively the body responds to changing demands in everyday life.
The authors build on earlier research suggesting that healthy physiological and behavioral systems exhibit complex fluctuations across multiple time scales. These patterns are neither entirely random nor perfectly regular. Instead, their variability reflects the flexibility needed to respond to different situations. With aging, this complexity may decline, producing patterns that become either more predictable or more random, potentially indicating a reduced capacity for adaptation.
Evidence from brain activity, muscular signals and movement variability supports the relevance of complexity measurements to aging. Previous studies have also explored whether changes in movement patterns can help predict future falls. The commentary argues that these findings should be viewed as interconnected aspects of aging rather than isolated observations.
An important distinction concerns how complexity changes across biological levels. The authors discuss preliminary, unpublished findings suggesting that network entropy may decrease with age even as molecular entropy increases. If confirmed, this would indicate that complexity at one biological level cannot necessarily be inferred from measurements at another. Behavioral complexity may therefore provide information that molecular biomarkers alone cannot capture.
The commentary also introduces the concept of “complexity reserve,” describing the remaining capacity of a biological system to maintain flexible, adaptive behavior before reaching a point of functional decline. This concept extends existing ideas of cognitive and physical reserve by focusing on how behavior changes dynamically in response to challenges.
The authors suggest that complexity reserve could be evaluated by examining how well individuals maintain organized behavioral patterns when exposed to progressively demanding tasks or environmental changes. Another approach would be to measure how close a person’s current functional state is to a transition where even a relatively small stressor could disrupt stability.
This framework could have implications for understanding frailty, a condition characterized by reduced physiological reserve and increased vulnerability to stress. Rather than relying exclusively on isolated health measurements, continuous behavioral monitoring might eventually help identify declining adaptability before more obvious functional deterioration occurs.
The proposed concept also considers how past experiences may shape resilience and how complexity reserve might help predict responses to future interventions. Exposure to stimulating environments and varied physical or cognitive challenges could contribute to maintaining behavioral flexibility. Conversely, complexity reserve might help explain why individuals respond differently to exercise or environmental enrichment. However, these possibilities remain hypotheses requiring empirical validation.
Another research direction involves “complexity matching,” the idea that interactions between systems may be influenced by the similarity of their temporal patterns. The authors propose investigating whether exposure to stimuli with fractal-like structures could help restore aspects of age-related behavioral complexity. They emphasize that this remains a theoretical possibility, not an established intervention for reversing aging-related decline.
“ We propose the notion of complexity reserve to denote the residual buffer of dynamical flexibility available before the system crosses into irreversible functional decline. ”
The commentary is conceptual rather than experimental. It does not present new clinical trial results or demonstrate that behavioral complexity measurements can reliably predict frailty or improve health outcomes. The proposed relationships between behavioral complexity, biological resilience and responses to interventions will require carefully designed studies, including longitudinal measurements and standardized assessments of adaptive behavior.
The authors also caution against assuming that different measures of complexity represent the same underlying biological process. Establishing how molecular, network and behavioral dynamics relate to one another will be essential before these concepts can be translated into practical assessments or interventions.
Overall, the commentary highlights behavioral complexity as a potentially valuable addition to gerophysics. By integrating measurements of how organisms respond to environmental challenges with molecular and physiological models, researchers may gain a more complete understanding of aging, resilience and functional decline. The proposed framework offers new, testable directions for studying how adaptability changes with age and how future interventions might help preserve it.
Paper DOI : https://doi.org/10.18632/aging.206421
Corresponding author: Jean-Jacques Temprado – jean-jacques.temprado@univ-amu.fr
Video preview: https://www.youtube.com/watch?v=7v2X8axjdgI
Keywords: aging, dynamical systems, complexity, behavior
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Complexity, variability, and the behavioral layer of gerophysics: a commentary on Unfried et al. (2026)
12-Sep-2026
The authors declare no conflicts of interest related to this study.