Supplementary Material for: Subjective Health and Physical-Activity Engagement across Adulthood: Distinguishing between Within-Person and Between-Person Associations

<b><i>Introduction:</i></b> It is assumed that age-related increases in loss (e.g., health decline) motivate behavioral changes (e.g., prevention of health decline) across adulthood. This assumption has rarely been directly tested in empirical research, and the current study seeks to fill this gap. <b><i>Methods:</i></b> By performing random intercept cross-lagged panel model and multilevel modeling analyses on a three-wave longitudinal dataset from the Midlife in the United States survey (<i>N</i> = 7,108; 51.6% female; between 20 and 75 years at T1), we examined the between-person and the within-person associations between subjective health and engagement in physical activity. Chronic conditions, difficulty in performing daily activities, and demographic variables were controlled for. <b><i>Results:</i></b> At the between-person level, subjective (i.e., self-rated) health was positively associated with physical activity in the whole sample and the older subgroup (T1 age &gt;55 years), but not in the younger subgroup (T1 age &lt;35 years). At the within-person level, the association between subjective health and subsequent physical activity was negative in the whole sample and the older subgroup, but nonsignificant (between T1 and T2) or positive (between T2 and T3) in the younger subgroup. <b><i>Discussion:</i></b> This study revealed various associations between subjective health and engagement in physical activity across levels (the within- vs. between-person level) and across age groups (younger vs. older group). The finding contributes to a better understanding of people’s health behavior in reaction to health decline at different ages. It also supports the proposition that age-related intraindividual increases in losses (e.g., health decline) motivate behaviors that counteract such losses (e.g., physical activity that protects health).

<b><i>引言：</i></b> 学界普遍假设，整个成年期内与年龄相关的损失（如健康衰退）会促使个体做出行为调整（如预防健康衰退）。这一假设尚未在实证研究中得到直接验证，本研究旨在填补这一研究空白。
<b><i>方法：</i></b> 本研究针对来自美国中年调查（Midlife in the United States survey）的三波纵向数据集（样本量<i>N</i>=7108，女性占比51.6%，T1时年龄介于20至75岁之间），采用随机截距交叉滞后面板模型（random intercept cross-lagged panel model）与多层模型分析，考察了主观健康与体育锻炼参与度之间的个体间和个体内关联。研究控制了慢性疾病、日常活动能力障碍以及人口统计学变量。
<b><i>结果：</i></b> 在个体间层面，全样本与老年亚组（T1时年龄＞55岁）的主观健康（即自我评定健康状况）与体育锻炼呈正相关，但年轻亚组（T1时年龄＜35岁）未出现这一关联。在个体内层面，全样本与老年亚组的主观健康与后续体育锻炼呈负相关；而年轻亚组中，该关联在T1至T2间无统计学意义，在T2至T3间则呈正相关。
<b><i>讨论：</i></b> 本研究揭示了主观健康与体育锻炼参与度之间的关联在不同分析层面（个体内与个体间层面）以及不同年龄组（年轻与老年组）中存在差异。该研究结果有助于更深入地理解不同年龄个体针对健康衰退所做出的健康行为反应。同时，本研究也支持如下命题：与年龄相关的个体内损失（如健康衰退）的增加，会促使个体做出抵消该损失的行为（如保护健康的体育锻炼）。