Autism Spectrum Disorder (ASD) is characterized by significant impairments in social and communication skills, as well as restricted and repetitive patterns of behavior. Individuals with ASD often struggle with regulating emotions, such as anger and anxiety, which poses considerable challenges in their daily lives. Difficulties in social and communication abilities frequently lead to complex interpersonal situations [1] [2] , underscoring the importance of managing emotions like anger, confusion, anxiety, and tension in these contexts. Furthermore, research has shown that stress and trauma can have profound effects on the psychological well-being of individuals with ASD [3] .

Some scholars suggest that behaviors often perceived as “unusual” among individuals with ASD are not simply attempts to seek attention but are instead mechanisms to fulfill fundamental needs, such as safety, affection, and acceptance [4] . However, despite progress in formal inclusion within educational settings, many individuals with ASD still do not receive adequate support in practice [5] . These systemic gaps exacerbate the emotional and psychological challenges faced by individuals with ASD, significantly impacting their overall well-being.

Hippotherapy, a supplementary therapeutic approach, leverages interactions with animals to provide therapeutic benefits for a variety of dysfunctions and disabilities. It has been demonstrated to improve motor functions in children with cerebral palsy [6] [7] , enhance cardiac functions [8] [9] , increase physical capabilities in elderly individuals [10] [11] , and aid gait recovery in stroke patients [12] . Additionally, psychological benefits have been observed in individuals with PTSD [13] and those with neurodegenerative diseases [14] . These findings highlight the diverse therapeutic applications of hippotherapy, indicating its potential relevance to the ASD population.

In the context of ASD, several studies have explored the relationship between hippotherapy and the social behaviors of children with ASD [15] - [17] . However, most assessments rely on subjective evaluations from parents or instructors. While Ward et al. have noted that the benefits of hippotherapy diminish when the intervention is discontinued [18] , Coman et al. reported that the positive effects persisted for up to eight weeks post-intervention [19] . These discrepancies may stem from differences in intervention protocols, participant diversity, and evaluation methods. This highlights the need for research employing standardized and validated psychological and physiological assessment tools. Furthermore, unlike typically developing children, ASD youth exhibit independent development of executive functions and emotional intelligence, which can impede their ability to effectively adapt when confronted with stress [20] . As a result, objective investigations into the effects of hippotherapy on stress management in young individuals with ASD are warranted.

To address these gaps, the present study aims to comprehensively evaluate the psychological and physiological effects of hippotherapy on young individuals with ASD. Utilizing validated assessment tools, namely the Profile of Mood States-Second Edition (POMS2) and salivary amylase activity as a physiological stress marker, this study seeks to provide reliable evidence for the effectiveness of hippotherapy. The findings are expected to contribute valuable insights for the development of treatment and support programs tailored to individuals with ASD.

This study included 23 children and adolescents aged 7 to 18 years who had been diagnosed with ASD. The participants had a mean age of 11.8 ± 2.7 years and a median age of 12 years. Hippotherapy sessions, along with pre- and post-intervention measurements, were conducted between June 2022 and February 2025. Of the 23 participants, 14 were male and 9 were female. All participants successfully completed SAA measurements and responded to POMS2 questionnaire before and after undergoing hippotherapy.

No significant differences were observed in SAA levels before and after hippotherapy ( Figure 1 ). Similarly, no significant differences were found in the POMS2 T scores ( Figure 2 ) for Anger-Hostility (A-H), Confusion-Bewilderment (C-B), Depression-Dejection (D-D), Fatigue-Inertia (F-I), and Vigor-Activity (V-A). However, a significant decrease was detected in Tension-Anxiety (T-A) (p < 0.05), while a significant increase was observed in Friendliness (F) (p < 0.01). Additionally, Total Mood Disturbance (TMD) demonstrated a significant decrease (p < 0.01).

The increase in POMS2 Friendliness scores and the decrease in Tension-Anxiety and Total Mood Disturbance scores observed in this study suggest that the hippotherapy intervention fosters a tendency toward friendliness and a calmer mood in young individuals with ASD. These findings may be attributable to mechanisms such as hormonal regulation and the promotion of emotional stability through interactions with horses. Evidence from diverse populations underscores the multifaceted impact of hippotherapy; for example, studies involving elderly individuals have demonstrated hormonal regulation effects, such as serotonin and cortisol adjustment to optimal levels [29] , while research focusing on veterans [30] has highlighted improvements in self-efficacy. Additionally, studies involving at-risk adolescents [31] point to emotional stabilization achieved through interactions with horses. These results collectively indicate that hippotherapy can offer beneficial effects across varied demographics and contexts.

ASD youth often face challenges in emotional regulation, exhibit reduced use of adaptive emotion regulation strategies [32] , and show a heightened focus on stress-inducing factors [33] . It is hypothesized that hippotherapy, by inducing calming effects, may support the development and adoption of adaptive emotion regulation strategies in response to stressors. The observed improvements in POMS2 scores may reflect an overall enhancement in mood and positive energy. These changes could have further implications for emotional regulation and stress-coping mechanisms, potentially strengthening self-regulatory capacities. Previous studies have highlighted that children with ASD, even those with relatively high functioning, often experience significant impairments in self-regulation, leading to reduced social interactions in school and peer environments [34] . Since improvements in self-regulation are closely tied to the development of social skills and adaptability in educational settings, the observed changes in POMS2 scores may signal meaningful progress in these areas. If such changes are recognized as markers of enhanced self-regulatory abilities, they could inform the design of additional support programs to further nurture this capability.

The newly introduced Friendliness (F) subscale in POMS2 has been reported to strongly correlate with the Vigor-Activity subscale, indicating positive mood states [24] . An increase in F scores suggests a positive shift in mood, which prior research links to improved emotional regulation [35] . Emotional regulation is a critical factor for social adaptation in children with ASD [36] , and hippotherapy may contribute to improvements in social functioning, potentially mediated by its impact on emotional regulation.

Regarding physiological stress markers, salivary amylase activity was assessed, with values below 30 KU/L classified as indicating no stress, and levels above 30 KU/L reflecting varying degrees of stress [28] . Among the participants, seven individuals exhibited salivary amylase levels above 30 KU/L ( Table 1 ). A Wilcoxon signed-rank test comparing pre- and post-intervention salivary amylase levels for these participants revealed no significant differences (Z = −0.524, p = 0.600). However, further analysis showed that participants P21 and P22, whose salivary amylase levels increased after the intervention, exhibited a higher tendency for tantrums when exposed to situations that did not align with their expectations.

The values in the table represent salivary amylase activity, expressed in KIU/L. Out of the 23 participants, seven individuals with values exceeding 30, indicative of stress, were selected for analysis. Among these, P2 showed little to no change, while P5, P14, P17, and P20 exhibited decreases. Conversely, P21 and P22 demonstrated increases.

For some individuals with ASD, factors such as unpredictability, sensory overstimulation, or hypersensitivity may act as irritability triggers. While prior studies have suggested that hippotherapy may alleviate such tendencies [37] , it is important to consider that riding a horse and guiding its movements—particularly during the first session—can present significant challenges. In this study, the potential stress induced by the initial session, especially for participants prone to tantrums in unpredictable situations, underscores the importance of carefully adapting hippotherapy to minimize stress during early sessions and to optimize its therapeutic benefits.

The findings of this study demonstrate the potential of hippotherapy to enhance emotional regulation and mood among children with ASD, as evidenced by increased Friendliness scores and reduced Tension-Anxiety and Total Mood Disturbance scores. Ward et al. identified positive associations between therapeutic horseback riding and improvements in social communication and sensory responses in children with ASD [18] . Similarly, Gabriels et al. explored the relationship between repetitive behaviors and sensory abnormalities, revealing that sensory-based therapies could mitigate such challenges [37] . These findings align with the notion that hippotherapy fosters emotional stability and social adaptability in individuals with ASD, thereby underscoring the novelty and potential implications of this study.

Further examination is required regarding the lack of significant changes observed in the Vigor-Activity subscale, despite improvements in the Friendliness subscale. One possibility is that the T-value score for the Vigor-Activity subscale in this study approached the threshold for statistical significance (p = 0.053, Figure 1 ), suggesting that additional data collection may confirm significant changes. Alternatively, initial apprehension or sensory overload during the first session might have influenced the Vigor-Activity outcomes. Participants who exhibited elevated salivary amylase levels tended to experience higher stress, indicating that individualized interventions may be necessary to optimize the therapeutic benefits of hippotherapy. Future studies should consider incorporating gradual adaptation protocols to account for these individual differences, thereby enhancing the effectiveness of intervention. Further research is essential to gain a more comprehensive understanding of the emotional and physiological impacts of hippotherapy on the well-being of children with ASD.

The sample size of this study was limited to 23 participants. Future research should aim to include a larger sample, ideally exceeding (e.g., 50 or 100 participants), to enhance statistical validity and generalizability of the findings. Moreover, variability in participant characteristics, such as age, severity of ASD symptoms, and prior exposure to similar interventions, may have affected the outcomes and should be considered in future studies.

The present study utilized a single-session pre- and post-intervention comparison design. While this approach provided valuable preliminary insights into the potential psychological and physiological effects of hippotherapy on young individuals with ASD, it limits the ability to assess long-term outcomes and sustained effects of the intervention. To develop more effective programs aimed at enhancing the well-being of young individuals with ASD, future research should incorporate longitudinal designs and multiple intervention sessions, along with appropriate control groups. This would allow for a comprehensive understanding of the cumulative and lasting benefits of hippotherapy.

Finally, environmental factors such as the setting of the hippotherapy sessions and differences in horse behavior may have influenced participant responses. Future studies should aim to standardize these variables to ensure consistency and better interpret the impact of hippotherapy.

To investigate the psychological and physiological effects of hippotherapy on young individuals with ASD, we compared pre- and post-intervention POMS2 scores and salivary amylase activity. Significant differences were observed in some subscales of POMS2, suggesting the potential psychological benefits of hippotherapy, including improvements in self-regulation abilities and social skills. While no significant changes in salivary amylase activity were observed overall, individual analysis indicated that, in cases with relatively high pre-intervention stress levels, hippotherapy may help reduce stress. However, for individuals with ASD who have a predisposition toward tantrums, the initial session might exacerbate irritability, potentially increasing stress levels.

Based on these findings, future efforts should focus on developing programs designed to enhance stress reduction and improve self-regulation skills, ultimately contributing to the well-being of young individuals with ASD.

The authors thank the participants and their caregivers in this study.

This manuscript was subsidized by JSPS KAKENHI (Grant No. 21K7394).