Physiological Mechanisms of Therapeutic Horseback Riding Intervention Effects in a Psychiatric Population of ASD Youth

This randomized control trial (RCT) seeks to assess the mechanisms underlying Therapeutic Horseback Riding's (THR) previously observed significant positive effects on ASD youth, particularly those with co-occurring psychiatric disorders, and to refine information on the durability, dose and sub-population effects of the intervention.

Inclusion Criteria: * documented ASD diagnosis and a co-occurring psychiatric disorder * ABC Irritability subscale score ≥8 * Leiter-III Nonverbal IQ ≥ 40 * meet Symptom Criterion score (minimum number of symptoms necessary for a DSM-V (mood, anxiety, or ADHD diagnosis) on CASI-5) * meet ASD cut-offs on the SCQ (≥ 11) and on ADOS-2 * Only one child with ASD per family to maintain independent observations * a consistent caregiver (i.e., parent or legal guardian) to complete study outcome measures Exclusion Criteria: * medical or behavioral issues that prevent participation * ward of the state * judged during riding center screen to have significant riding experience * smoking or regular use of oral, inhaled, or topical steroids on a regular basis, factors known to affect cortisol levels * Participants weighing 200 pounds or greater will be excluded due to the riding center's safety policies * Participants will not be allowed to begin baseline assessments until at least six months have passed from the time they last engaged in mounted EAAT, given pilot evidence for the six-month maintenance of THR effects.