Abstract
Little is known whether the assessment indexes or phenotypes to identify frailty in mice are capable of distinguishing important characteristics of the frailty syndrome. Therefore, the goals of this study were to identify the onset and the prevalence of frailty across the lifespan of mice and to determine if a frail phenotype predicts mortality. To accomplish these goals, we assessed body weight, walking speed, strength, endurance and physical activity levels in male C57BL/6 mice (n=29) from 14 months to 37 months of age. Mice with three or more positive frailty markers were identified as frail, mice with two positive markers were identified as pre-frail and mice with one or no positive frailty marker were considered non-frail. Using this approach, the mean survival age of the entire cohort was 31.83 months. The onset of frailty occurred at 17 months of age and represented 3.5% of the cohort. The prevalence of frailty increased from 3.5% at 17 months to 93.3% at 32 months of age. Frail, pre-frail, and non-frail mice had mean survival ages of 27.09 months, 29.48 months, and 33.75 months, respectively. Frail and pre-frail mice died earlier than non-frail mice (P=0.004 and P>0.001). Taken together, using a frailty phenotypic approach, we were able to identify that the onset of frailty begins the second half of life and steadily increases with age. Identifying the onset and prevalence of frailty across the lifespan, in addition to predicting mortality, has potential to yield information about susceptibility and resilience to the aging processes.