Table 9_Inverted-U association between daily steps and WHO-5 in university students: non-linear modeling and robustness checks.xlsx

BackgroundPhysical activity is linked to mental health, yet the dose–response shape remains debated.
MethodsIn a cross-sectional sample of Chinese university students, 820 participants (mean age 21.5 years; 51.8% women) wore wrist accelerometers for 7 days. Subjective well-being (SWB) was measured with the WHO-5 (0–100). Restricted cubic spline models adjusted for age, sex, sleep quality, perceived stress, and socioeconomic status. Sensitivity analyses included quadratic and segmented models, trimming/winsorization, and E-value assessment. Peaks/plateaus were estimated via the delta method and bootstrap-BCa confidence intervals.
ResultsThe steps–SWB association was non-linear (overall p<0.05). SWB rose steeply up to ~8,650 steps/day and then leveled off, with a statistical plateau near ~19,300 steps/day (bootstrap-BCa 95% CI: 7,997–17,896; delta-method 95% CI: 9,394–14,462). No contrast versus 4,000 steps/day exceeded the prespecified minimal clinically important difference (MCID=10 points). Findings were consistent across specifications; right-tail precision was limited due to few very high step counts.
ConclusionAmong university students, higher daily steps are associated with better SWB up to ~8,000–12,000 steps/day, beyond which benefits plateau with diminishing returns rather than harm. Results support range-based, progressive step guidance for student mental health. Please replace the current abstract with the structured IMRaD version provided above.

背景：体力活动与心理健康存在关联，但其剂量-反应关系的具体形态仍存在争议。
方法：本研究纳入中国大学生的横断面研究样本，共820名参与者（平均年龄21.5岁，女性占比51.8%），所有参与者佩戴腕部加速度记录仪时长为7天。采用世界卫生组织幸福量表（WHO-5，评分范围0~100）评估主观幸福感（Subjective Well-Being, SWB）。采用校正了年龄、性别、睡眠质量、感知压力及社会经济地位的限制性立方样条（Restricted Cubic Spline）模型进行分析。敏感性分析涵盖二次模型、分段模型、截尾/缩尾处理（trimming/winsorization）以及E值评估。采用德尔塔法（delta method）与bootstrap-BCa置信区间估计峰值/平台期。
结果：每日步数与主观幸福感的关联呈非线性特征（整体p<0.05）。主观幸福感随每日步数快速上升，直至约8650步/日后趋于平缓，在约19300步/日处达到统计学平台期（bootstrap-BCa 95%置信区间：7997~17896；德尔塔法95%置信区间：9394~14462）。与4000步/日相比，各组差值均未达到预先设定的最小临床重要差异（MCID=10分）。不同模型设定下的研究结果保持一致；由于每日步数极高的参与者数量极少，右尾区间的估计精度有限。
结论：在大学生群体中，每日步数增加与主观幸福感提升相关，这一关联在约8000~12000步/日时达到增益峰值，超过该范围后，益处趋于平稳且边际效益递减，而非产生负面影响。本研究结果支持针对学生心理健康制定基于区间范围的渐进式步数指导方案。请将当前摘要替换为上述结构化IMRaD（引言、方法、结果、讨论）版本。