Objectives <p>The purpose of this study was to investigate the comparative effects of mindfulness running versus mindfulness sitting on general mental and immune health when practice is brief but daily after work.</p> Method <p>A 4-week intervention was conducted in two training centers for Civil Guard officers in Spain (total sample <i>n</i> = 208). There were three experimental conditions: sitting mindfulness meditation (SM), mindful running (MR), and a control group (CG). Each active group practiced daily after work for between 15 and 30 min with audio-guided meditations.</p> Results <p>Two studies were conducted: a longitudinal study with five measurement time points and a daily study involving repeated assessments over 16 days. Firstly, a mixed ANOVA data analysis (baseline, pre-test, post-test, 1-month follow-up, and 3-month follow-up) was performed to measure salivary immunoglobulin A (IgA), general mental health, work stress, affect, and need for recovery from work. Secondly, the daily growth curve analyzed attention deficit, fatigue, sleep quality, detachment from work, and stress. The results showed significant differences between the SM and the CG in positive affect, need for recovery, and fatigue. SM-MR comparison was also significant for stress. On the other hand, MR significantly improved IgA levels and reduced fatigue.</p> Conclusions <p>This study sheds light on the different effects of different mindfulness practices when practiced daily for a short period of time. SM yielded results that were related to improving psychological aspects. MR practice was associated with improvements in physical aspects, such as fatigue sensation and the immune system (IgA). Future studies are needed to confirm these findings in the general population and with more extended practice periods.</p> Preregistration <p>This study was preregistered on ClinicalTrials.gov (Ref No: NCT05557266).</p>