Background Low physical activity is an important risk factor for common physical and mental disorders. Physical activity interventions delivered via smartphones can help users maintain and increase physical activity, but outcomes have been mixed. Purpose Here we assessed the effects of sending daily motivational and feedback text messages in a microrandomized clinical trial on changes in physical activity from one day to the next in a student population. Methods We included 93 participants who used a physical activity app, “DIAMANTE” for a period of 6 weeks. Every day, their phone pedometer passively tracked participants’ steps. They were microrandomized to receive different types of motivational messages, based on a cognitive-behavioral framework, and feedback on their steps. We used generalized estimation equation models to test the effectiveness of feedback and motivational messages on changes in steps from one day to the next. Results Sending any versus no text message initially resulted in an increase in daily steps (729 steps, p = .012), but this effect decreased over time. A multivariate analysis evaluating each text message category separately showed that the initial positive effect was driven by the motivational messages though the effect was small and trend-wise significant (717 steps; p = .083), but not the feedback messages (−276 steps, p = .4). Conclusion Sending motivational physical activity text messages based on a cognitive-behavioral framework may have a positive effect on increasing steps, but this decreases with time. Further work is needed to examine using personalization and contextualization to improve the efficacy of text-messaging interventions on physical activity outcomes. ClinicalTrials.gov Identifier NCT04440553.

中文翻译：

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促进大学生体育活动的每日励志短信：微随机试验的结果

背景 低体力活动是常见身心障碍的重要危险因素。通过智能手机提供的身体活动干预可以帮助用户保持和增加身体活动，但结果好坏参半。目的 在这里，我们评估了在一项微随机临床试验中发送每日激励和反馈短信对学生群体一天到一天的身体活动变化的影响。方法 我们纳入了 93 名参与者，他们使用了一个体育活动应用程序“DIAMANTE”，为期 6 周。每天，他们的手机计步器都会被动地跟踪参与者的步数。基于认知行为框架，他们被微随机化以接收不同类型的激励信息，并对其步骤进行反馈。我们使用广义估计方程模型来测试反馈和激励信息对从一天到下一天的步骤变化的有效性。结果 发送任何短信与不发送短信最初会导致每日步数增加（729 步，p = .012），但这种影响会随着时间的推移而减少。分别评估每个文本消息类别的多变量分析表明，最初的积极影响是由激励消息驱动的，尽管效果很小且趋势显着（717 步；p = .083），但不是反馈消息（-276 步） , p = .4)。结论 发送基于认知行为框架的激励性身体活动短信可能对增加步数有积极影响，但随着时间的推移而减少。需要进一步的工作来研究使用个性化和情境化来提高短信干预对身体活动结果的效果。ClinicalTrials.gov 标识符 NCT04440553。