Physical Activity as an Indicator of Frailty in Chronic Acquired Brain Injury: A Cutoff Point Proposal

Frailty is a frequent complication in individuals with chronic acquired brain injury (CABI), associated with functional decline and higher disability risk. Identifying an indicator based on physical activity may contribute to earlier detection and targeted management strategies. Our study aimed to evaluate the indicative capacity and identify threshold values of physical activity associated with frailty in patients with CABI. Patients were assessed and classified into frail or non-frail groups according to the Physical Performance Test. Main variables included objective physical activity levels measured by an accelerometer and subjective physical activity levels evaluated with the Physical Activity Scale for the Elderly (PASE). Additional measures included exercise self-efficacy, disability, and falls efficacy. A total of 316 participants were included. Significant differences were found among groups (p < 0.05), with the frail CABI group showing the worst outcomes. Significant differences (p < 0.05) also emerged between frail and non-frail groups in favor of the latter. Regarding indicative values, the cutoff point for steps per day was ≤1313.50 (AUC: 0.962; sensitivity: 0.96; specificity: 0.20). For subjective physical activity, the cutoff point for the PASE score was ≤2.20 (AUC: 0.581; sensitivity: 0.97; specificity: 0.80). Objective and subjective physical activity levels can indicate frailty in CABI patients, supporting their clinical utility.