Frailty, physiological reserve, and surgical resilience: toward a dynamic stress–recovery model

Background: Chronological age remains widely used in perioperative decision-making but incompletely captures the biological heterogeneity that influences postoperative outcomes. Frailty has substantially advanced surgical risk assessment by shifting attention from age toward multidimensional vulnerability and diminished physiological reserve. Nevertheless, patients with similar frailty profiles often experience markedly different recovery trajectories, suggesting that baseline vulnerability alone may not fully explain postoperative adaptation. Methods: This narrative conceptual review was developed through a targeted search of PubMed/MEDLINE, Scopus, and Google Scholar, focusing on frailty, physiological reserve, physical resilience, intrinsic capacity, prehabilitation, and postoperative recovery. Peer-reviewed clinical studies, reviews, and conceptual frameworks from geroscience and perioperative medicine were synthesized to develop an integrated model of surgical resilience. Results: Emerging evidence indicates that frailty and resilience represent related but distinct constructs. Frailty primarily identifies vulnerability before stress exposure, whereas resilience reflects the dynamic capacity to withstand, adapt to, and recover from physiological perturbation. Recent perioperative studies suggest that postoperative outcomes are influenced not only by baseline reserve but also by the interaction between reserve, surgical stress exposure, and recovery capacity. Within this framework, skeletal muscle function, nutritional status, cognition, inflammatory burden, and functional independence appear to contribute to an individual's adaptive potential. Surgery represents a uniquely informative human model through which stress-response biology and recovery trajectories can be studied longitudinally. Conclusions: We propose surgical physiological resilience as a dynamic stress-recovery phenotype emerging from the interaction among three interconnected domains: baseline reserve, surgical stress load, and recovery capacity. This framework extends current frailty-based approaches by incorporating longitudinal adaptation and recoverability after surgical stress. Reframing perioperative medicine around resilience may support trajectory-based risk stratification, targeted prehabilitation strategies, longitudinal functional monitoring, and the future development of a dynamic Surgical Resilience Index capable of capturing postoperative heterogeneity more accurately than chronological age or static vulnerability measures alone.