Horsepower: equine-assisted interventions are associated with reduced PTSD symptoms, improved sleep quality, and quality of life in military veterans with treatment-resistant PTSD.

Introduction: Military veterans are at an elevated risk of developing posttraumatic stress disorder (PTSD), while first-line trauma-focused treatments are less effective in this population. This highlights the need for novel, evidence-based complementary interventions for military veterans with treatment-resistant PTSD. Although equine-assisted interventions (EAIs) are increasingly popular and appear promising, many studies suffer from methodological issues. Therefore, further research incorporating both psychometric and physiological parameters is warranted. Methods: Nine consecutive groups of eight veterans ( Results: Psychometric questionnaires demonstrated a significant decrease in PTSD symptoms (PCL-5), an improvement in sleep quality (Pittsburgh Sleep Quality Index [PSQI]), and an improvement in quality of life (EuroQol 5-Dimension 5-Level questionnaire [EQ-5D-5L]), with effects persisting at least until the 3-month follow-up session. No significant differences in heart rate (HR) or heart rate variability (HRV) were observed between pre- and post-intervention. However, during EAI sessions, patterns consistent with physiological adaptation were observed, as HR decreased and HRV increased after the first week during free interactions with the horse. Discussion: In conclusion, the EAI program was associated with long-term effects on PTSD, sleep quality, and quality of life in veterans with treatment-resistant PTSD. No structural changes in physiological parameters were found, only evidence for successful adaptation to acute stress during EAI sessions. We hypothesize that adaptation to physiological arousal during acute stress may represent a possible working mechanism of EAI.