BACKGROUND Age-related accumulation of chronic medical conditions increases disability in older adults. Physical activity potently combats chronic conditions and disability. However, it is unclear whether activity maintenance alleviates the effects of chronic conditions on disability and if this buffering effect differs with age. This study examined whether long-term physical activity can forestall functional limitations in the face of accumulating chronic conditions among middle-aged and older adults. METHODS Participants (n = 2,119; 54.7% female) were from the Survey of Midlife Development in the United States. Self-reported physical activity, number of chronic conditions, and functional limitations were obtained across 18-20 years. Functional limitations were regressed against the change in chronic conditions, physical activity, and their interaction over time in a multilevel model of change. Baseline age was added as an additional moderator. RESULTS Faster accumulation of chronic conditions [B(SE) = 2.08(0.32), p < .001] and steeper declines in activity [B(SE) = -2.29(0.41), p < .001] were associated with greater increases in functional limitations over time. Among those with faster-than-average increases in conditions, those who maintained activity had a slower progression of functional limitations, compared to those whose activity declined more rapidly [B(SE) = -11.18(3.96), p = .005]. Baseline age moderated the buffering effect of activity maintenance; older adults were protected against functional limitations only when conditions accumulated slowly [B(SE) = 0.23(0.08), p = .005]. CONCLUSION This study provides evidence for an age-dependent buffering effect of activity maintenance on the longitudinal relationship between chronic conditions and functional limitations. Intervention strategies using physical activity to forestall disability should target midlife adults and consider the rate of condition accumulation.

中文翻译：

---

随着时间的推移，身体活动对慢性疾病和功能限制之间关联的调节作用：年龄的影响。

背景技术与年龄相关的慢性疾病的累积会增加老年人的残疾。体育活动有效地对抗慢性病和残疾。然而，目前尚不清楚活动维持是否能减轻慢性病对残疾的影响，以及这种缓冲作用是否随年龄而异。本研究探讨了长期体育活动是否可以预防中老年人在慢性病累积的情况下的功能限制。方法 参与者（n = 2,119；54.7% 女性）来自美国中年发展调查。在 18-20 年间获得了自我报告的身体活动、慢性病数量和功能限制。功能限制随着慢性病、身体活动、以及它们在多层次变化模型中随时间的相互作用。添加了基线年龄作为额外的调节器。结果 慢性病的更快积累 [B(SE) = 2.08(0.32), p < .001] 和活动的急剧下降 [B(SE) = -2.29(0.41), p < .001] 与更大的增加有关随着时间的推移功能限制。在条件增加快于平均水平的人中，与活动下降更快的人相比，保持活动的人功能限制进展较慢 [B(SE) = -11.18(3.96)，p = .005]。基线年龄缓和了活动维持的缓冲作用；只有当条件缓慢累积时，老年人才能免受功能限制 [B(SE) = 0.23(0.08), p = .005]。结论 本研究为活动维持对慢性病和功能限制之间的纵向关系的年龄依赖性缓冲作用提供了证据。使用身体活动预防残疾的干预策略应针对中年成年人并考虑病情累积的速度。