BACKGROUND There has been limited longitudinal assessment of the relationship between moderate-to-vigorous physical activity (MVPA) and sedentary behaviour (SB) with frailty, and no studies have explored the possibility of reverse causality. This study aimed to determine the potential bidirectionality of the relationship between accelerometer-assessed MVPA, SB, and frailty over time in older adults. METHODS Participants were from the Toledo Study for Healthy Aging. We analysed 186 older people aged 67 to 90 (76.7 ± 3.9; 52.7% female participants) over a 4-year period. Time spent in SB and MVPA was assessed by accelerometry. Frailty Trait Scale was used to determine frailty levels. A cross-lagged panel model design was used to test the reciprocal relationships between MVPA/SB and frailty. RESULTS Frailty Trait Scale score changed from 35.4 to 43.8 points between the two times (P < 0.05). We also found a reduction of 7 min/day in the time spent on MVPA (P < 0.05), and participants tended to spend more time on SB (P = 0.076). Our analyses revealed that lower levels of initial MVPA predicted higher levels of later frailty [std. β = -0.126; confidence interval (CI) = -0.231, -0.021; P < 0.05], whereas initial spent time on SB did not predict later frailty (std. β = -0.049; CI = -0.185, 0.087; P = 0.48). Conversely, an initial increased frailty status predicted higher levels of later SB (std. β = 0.167; CI = 0.026, 0.307; P < 0.05) but not those of MVPA (std. β = 0.071; CI = -0.033, 0.175; P = 0.18). CONCLUSIONS Our observations suggest that the relationship between MVPA/SB and frailty is unidirectional: individuals who spent less time on MVPA at baseline are more likely to increase their frailty score, and individuals who are more frail are more likely to spent more time on SB at follow-up. Interventions and policies should aim to increase MVPA levels from earlier stages to promote successful aging.

中文翻译：

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哪个先出现：运动行为还是虚弱？托莱多健康衰老研究中的交叉滞后面板模型。

背景技术对中度至剧烈体力活动（MVPA）和久坐行为（SB）伴有虚弱的关系的纵向评估有限，并且没有研究探讨反向因果关系的可能性。这项研究旨在确定随着年龄的增长，加速度计评估的MVPA，SB和虚弱之间的关系具有潜在的双向性。方法参与者来自托莱多健康老龄化研究。我们在4年期间分析了186位67-90岁的老年人（76.7±3.9； 52.7％的女性参与者）。通过加速度计评估在SB和MVPA上花费的时间。脆弱特质量表用于确定脆弱水平。交叉滞后的面板模型设计用于测试MVPA / SB与脆弱之间的相互关系。结果脆弱特质量表得分从35.4变为43。两次之间为8分（P <0.05）。我们还发现，在MVPA上花费的时间减少了7分钟/天（P <0.05），并且参与者倾向于在S​​B上花费更多的时间（P = 0.076）。我们的分析表明，较低的初始MVPA水平可预测较高的后期虚弱水平。β= -0.126；置信区间（CI）= -0.231，-0.021; P <0.05]，而在SB上的最初花费时间并不能预测以后的虚弱（标准β= -0.049； CI = -0.185，0.087； P = 0.48）。相反，最初的脆弱状态增加会预测更高的SB水平（标准β= 0.167； CI = 0.026，0.307； P <0.05），而不是MVPA的水平（标准β= 0.071； CI = -0.033，0.175； P） = 0.18）。结论我们的观察结果表明，MVPA / SB与虚弱之间的关系是单向的：在基线时花在MVPA上的时间较少的人更有可能增加他们的虚弱评分，而虚弱的人在随访时更可能将更多时间花在SB上。干预措施和政策应旨在从早期开始提高MVPA水平，以促进成功的衰老。