Table 5_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（dose–response）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样本，共820名参与者（平均年龄21.5岁；女性占比51.8%），受试者佩戴腕部加速度计（wrist accelerometers）时长为7天。采用WHO-5量表（0~100分）评估主观幸福感（Subjective well-being, SWB）。构建受限立方样条（restricted cubic spline）模型，校正年龄、性别、睡眠质量、感知压力及社会经济地位等混杂因素。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（E-value）评估。通过delta法与bootstrap-BCa置信区间估算阈值峰值/平台期。
**结果**：每日步数与主观幸福感之间的关联呈非线性特征（总体*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；delta法95%置信区间：9394~14462）。与4000步/日相比，各分组的差值均未达到预先设定的最小临床重要差异（minimal clinically important difference, MCID=10分）。不同模型设定下的研究结果均保持一致；由于每日极高步数的样本量较少，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呈正相关，直至约8000~12000步/日；超过该阈值后，益处趋于平台期，呈现边际收益递减而非有害的特征。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（Introduction, Methods, Results, Discussion）版本。