Effects of a Smartphone-Based Mindfulness Intervention on Momentary Stress Among First Responders: a Micro-Randomized Trial.

First responders face extreme workplace stressors that can increase symptoms of distress. While mindfulness-based interventions are well-established for stress management, their time-intensive formats may pose barriers for those with long shifts and unpredictable schedules. Smartphone-delivered mindfulness interventions offer a flexible alternative. This study used a micro-randomized controlled trial design to test the effectiveness of two smartphone-delivered mindfulness interventions in reducing momentary stress and stress reactivity to a self-reported stressor. The two interventions included: (1) a text message reminder to engage in a mindfulness practice (brief message) and (2) a prompt to complete an app-based guided mindfulness practice (MYAPT.MIND). Participants were 75 first responders (M = 38.9, SD = 6.8) who completed ecological momentary assessments twice a day (EMA 1 and EMA 2) and received 1 of 3 conditions daily (i.e., no-intervention, brief message, or MYAPT.MIND) between EMA 1 and EMA 2 for 30 days. Multilevel modeling was used to estimate the proximal effects of the daily intervention assignments and to test whether the interventions dampened the impact of stressor exposures on momentary stress at EMA 2. Results indicated no direct effect of interventions on momentary stress. However, participants who were assigned to MYAPT.MIND reported smaller increases in momentary stress following a stressor exposure than for the brief message or control groups. These findings highlight the potential of app-based mindfulness interventions as a "just-in-time" tool for acute stress management.