Background: Running can improve health status from a biopsychosocial perspective. However, isolation strategies, like the COVID-19 pandemic-induced lockdown, produce deleterious effects on both health status and sport performance. The aim of our study was to investigate recreational runners’ sporting habits, subjective vitality (SV), and well-being after the COVID-19 pandemic-induced lockdown. Methods: After data filtration, 5542 recreational runners (74.5% men and 25.5% women, >18 years) were selected for further analyses. The participants answered preliminary questions regarding sporting habits and completed the validated Spanish version of the Subjective Vitality as a Dynamic Reflection of Well-Being questionnaire for assessing their SV after lockdown. Results: Subjective vitality scores did not differ between men and women, nor between age groups (p = 0.41 and p = 0.11, respectively). Subjective vitality was greater with weekly training frequency up to 5 days/week, where this enhancement plateaued, while average training session duration was positively related to SV, stabilizing at 91–120 min/session (p < 0.001 for both). Conclusions: There is a dose–response relationship between both weekly training frequency and training session duration, and mental health benefits in recreational runners. Further longitudinal studies are needed in order to determine the optimal dose–response relationship for simultaneously enhancing mental health outcomes and running performance in recreational runners, especially regarding weekly training frequency, training session duration, and exercise intensity.