摘要：Objectives. This prospective longitudinal study investigated the association between baseline objectively measured sedentary time and 2-year onset of physical frailty. Methods. We studied 1333 Osteoarthritis Initiative participants 55 to 83 years of age who were at risk for physical frailty, as assessed via low gait speed (< 0.6 m per second) or inability to perform a single chair stand. Baseline sedentary time was assessed through accelerometer monitoring. Hazard ratios (HRs) for physical frailty onset were estimated with discrete survival methods that controlled for moderate physical activity, sociodemographic characteristics, baseline gait and chair stand functioning, and health factors. Results. The incidence of physical frailty in this high-risk group was 20.7 per 1000 person-years. Greater baseline sedentary time (adjusted HR = 1.36 per sedentary hour; 95% confidence interval [CI] = 1.02, 1.79) was significantly related to incident physical frailty after control for time spent in moderate-intensity activities and other covariates. Conclusions. Our prospective data demonstrated a strong relationship between daily sedentary time and development of physical frailty distinct from insufficient moderate activity. Interventions that promote reductions in sedentary behaviors in addition to increases in physical activity may help decrease physical frailty onset. New health care challenges fueled by an aging population are on the horizon. By 2030, 1 in 5 people living in the United States will be older than 65 years. 1 Largely as a result of this oncoming wave of aging, a substantial increase in disability is anticipated. Physical frailty, a medical syndrome, 2 is a strong risk factor for disability, dependency, and death. 3–8 Physical frailty (assessed according to functional performance) reflects decreased physical reserves and vulnerability in old age. 9 The demographically aging society of the United States makes prevention and delay of physical frailty a public health priority. Regular physical activity reduces the risk of physical frailty 2,8,10 and promotes health benefits, including better quality of life and reduced risk for chronic diseases. 11–14 Despite the important publicized benefits of physical activity, US adults primarily engage in sedentary behaviors. 15,16 In contrast to the recommendation that people engage in physical activities of moderate intensity or greater (3.0 or more metabolic equivalents), sedentary behavior involves activities at the resting level of energy expenditure (1.0–1.5 metabolic equivalents). 17 Working on a computer and watching television 18 are common sedentary activities. Prolonged sedentary time has been associated with an increased risk of functional decline and such conditions as obesity, metabolic syndrome, and type 2 diabetes. 19–21 Physical activity interventions designed to improve health outcomes have largely focused on increasing recommended moderate-intensity activities 13 and have addressed sedentary behavior only to a limited degree. Recently, however, there has been a growing interest in the role of sedentary behavior as a separate risk factor for poor health. Sedentary behavior, already associated with poor health outcomes, may have a unique relationship to the development of physical frailty or may reflect only a lack of moderate-intensity physical activity. This is an essential issue to address because if sedentary behavior is demonstrated to be an independent risk factor, reducing such behavior may increase the effectiveness of behavior interventions, particularly among people with activity-inhibiting chronic conditions such as arthritis. However, the limited available information on the relationship between sedentary behavior and physical frailty is problematic owing to a reliance on recall of sedentary behaviors or physical activity. We tested the hypothesis that increased sedentary behavior is related to an increased risk of physical frailty independent of time spent in moderate physical activity. We focused on community-dwelling adults with or at high risk for knee osteoarthritis (OA) who participated in the multisite Osteoarthritis Initiative (OAI). Using detailed, objective physical activity accelerometer monitoring, we investigated the association between time spent in sedentary behavior and the development of physical frailty as determined via longitudinal objective function tests.
