Impact of equine interactions on human acute pain perception: Two cross sectional studies.

Chronic pain, defined as pain lasting over 3 months, is a global public health problem that impairs well-being and quality of life. 1 Treating chronic pain can involve pharmacology; however, such treatments can cause side effects like hyperalgesia and addiction. 2 Recent research promotes alternative therapies in conjunction with biomedical treatment, 3 which can reduce pain more effectively than medication alone. 4 The current study is the first of its kind to investigate whether interacting with horses can reduce pain perception. This horse-interaction involves ground-based activities with horses and does not involve riding. Given the novelty of the study, we investigated the effect of horse-interaction on acute pain perception rather than testing a patient group with chronic pain. Our longer-term research aims are to investigate interactions with horses in the treatment of chronic pain, in which the necessity of non-pharmaceutical interventions becomes of particular importance. Recognition of the importance of psychosocial factors in pain perception has led to development of psychotherapies for chronic pain. 5 One form of psychosocial intervention for pain management is Animal-Assisted Therapy (AAT). AAT can improve various health conditions, often more effectively than traditional treatments. 6 , 7 Interaction with therapy animals can trigger the release of β-endorphins 8 , 9 – neuropeptides that act as natural painkillers. 10 The Dynamic Model of Affect (DMA 11 ) is also consistent with this explanation, hypothesizing that the ability to sustain positive states decreases vulnerability to pain. Studies supporting this model demonstrate that AAT is linked to decreased stress, mood disturbance and fatigue, alongside reduction in pain perception (PP). 8 , 12 Horses have been integrated into therapeutic interventions (including therapeutic riding and hippotherapy) to treat various conditions including chronic pain. 13 , 14 In a review of the literature, White-Lewis et al. (2017) 15 report that while 94% of the studies they looked at reported significant benefits to people with chronic pain, the majority of studies lacked methodological rigour (e.g. not including an adequate control) and therefore results must be treated with some caution. Equine Assisted Learning (EAL), a non-riding (ground-based) activity involving horses, has not yet been used in the treatment or study of pain. Equine Assisted Psychotherapy (EAP) includes a psychotherapeutic component. 16 , 17 As a social prey animal, horses are attentive to environment changes, including micro and macro body movements in humans, as seen in the classic study of Clever Hans. 18 Some researchers have suggested that horses are instinctively attentive to mood, 19 reacting sensitively to humans. 20 This can have psychological benefits for humans, including improved communication, confidence and emotion regulation. 21 The benefits of interacting with horses may subsequently affect cognitive and psychosocial factors that moderate acute pain perception. It is proposed that task and pain processing compete for attentional resources, 22 , 23 thus pain-related brain activation can be reduced through interactive (rather than passive) distraction. 24 Psychosocial factors can bias attention away from pain sensation, aiding pain management 25 – 29 in both chronic and acute pain. The two studies reported here investigate whether interacting with horses with psychotherapeutic input (EAP) and without psychotherapeutic input (general horse-interaction and EAL) can reduce acute pain perception. Pain was administered to participants using a blood-pressure cuff 30 and pre- and post-activity pain ratings were taken. Follow-up questionnaires and interviews explored participants’ subjective experiences. We hypothesized that EAL, EAP and HI activities would lead to significant reductions in acute pain ratings.

Participants were recruited via volunteer sampling, using a research participation scheme and word-of-mouth. All testing was done in the autumn/winter of 2023-24. To sign up participants were required to be over the age of 18 and have no history of vascular disease. None of these participants had taken part in Study 1. Fifty-three participants (43 females, 9 males, 1 non-binary) with a mean age of 20.08 years old (SD = 4.46 years) took part. Prior to arriving at the site of the study, 26 participants were allocated to the Control Group, and 27 were allocated to the EAL Group. Age and gender were controlled for by ensuring a similar distribution in each group. This study was approved by Newcastle University’s Faculty of Medical Sciences ethics committee (reference code: 2624/35236) and participants were required to provide informed consent regarding the pain induction and potential interaction with horses. They also completed a medical history form that was required for emergency purposes for the equine-assisted sessions. Ten riding school ponies took part in the EAL sessions at a Riding Centre near Newcastle. They were all in work with riding lessons and were fit and well. Their sizes ranged from 12.0 hands to 15.1 hands. The youngest pony to take part was 9 years old and the oldest was 25 years old. While there was a mix of mares and geldings, they all took part in the EAL sessions in same sex friendship pairs. The study received Animal Welfare and Ethical Body approval Project ID: 1063. An inclusion/exclusion checklist (appendix 1) was applied each time a pony took part and any welfare/health issues discussed with the Riding Centre if they arose. Sessions for all groups were led by a qualified EAL practitioner/Development Psychologist (author GDS) who was present throughout each session for all participants. In addition, a group of three research assistants were responsible for collecting data from all participants, including the pain measurements. This study was a mixed methods design, using both a quantitative and qualitative approach. The experimental component used a 2 Time Points × 2 Groups mixed design. The two Time points were tested within-subject (pre-activity vs post-activity pain rating). The two Groups were between-subject (EAL Group vs Control Group), so participants were randomly allocated to one of two groups. The first group was the EAL Group, in which participants carried out activities with guidance from the EAL facilitator, in the presence of two ponies. The Control Group carried out activities in the horse arena without the ponies present. The EAL practitioner was present throughout all sessions for both groups. Some verbal interaction occurred in both groups between her and the participants during their group and individual activity. In addition participants interacted with one another during the group part of each session. For each time point, we measured the participants’ pain rating to moderate-pain induction. The qualitative portion of the study consisted of short individual interviews with each participant straight after their individual session. An epistemological approach, critical realism, 31 was taken so that each participant’s response was looked at independently, focussing on the individual as well as any differences between responses within as well as between groups. Thematic analysis based on Braun and Clarke’s six stage framework (2006) 33 was used to analyze and code each transcript. Materials, measures and procedure were all the same as Study 1 with the following exceptions. The calculated moderate-pain pressure for each group were as follows: EAL ( M = 156.9 mmHg, SE = 7.3 mmHg), and Control ( M = 167.7 mmHg, SE = 7.4 mmHg). The activities were carried out in a larger indoor arena (40 m × 22 m). It again had a viewing gallery and there were a few objects within the arena as in study 1 which participants sometimes used in their interactions with the ponies. The facilitator of the activity sessions was the EAL practitioner. The post-activity questionnaires were replaced by semi-structured interviews conducted immediately after the activity sessions. These consisted of four open questions: How did you feel during the session? What can you remember about the experience? Were there any moments that stood out? Did you observe any notable differences from pre-session to post-session? For each participant the average pain ratings for before (pre-activity) and after (post-activity) the test sessions were calculated. A 2 (Group: EAL, Control) × 2 (Time Point: pre-activity, post-activity) mixed analysis of variance (ANOVA) was conducted, with Group as the between-subjects variable, and Time Point as the within-subject variable. Given our hypothesis, we used planned paired t -tests to determine if there was a significant decrease in pain rating post-activity for the EAL and Control Groups and adopted a significance level of p = .05 for the statistical analyses reported, using a one-tailed approach. The interview transcripts for each participant were coded, and thematic analysis based on Braun and Clarke’s six stage framework (2006) 33 led to the emergence of four themes. Of the 53 participants whose quantitative data was collected, 45 were successfully interviewed (EAL Group, n = 24, Control Group, n = 21). The eight without interview data were due to insufficient time for them to be interviewed or because recording equipment failed. The participant’s interview number corresponded with their participant ID for the quantitative data collection and a letter was added depending on whether they participated in an EAL session (e.g. P1H) or were part of the Control Group (e.g. P6C). The descriptive statistics for pre-activity and post-activity pain ratings are shown in Table 3 . Table 3. Mean and standard deviations of pain ratings before and after session by experimental Group. EAL Control Mean SD Mean SD Pre-activity pain rating 6.45 1.62 6.28 1.93 Post-activity pain rating 5.05 1.35 6.54 1.83 Mean and standard deviations of pain ratings before and after session by experimental Group. The 2 × 2 ANOVA showed that there was a statistically significant main effects of Time Point, F (1, 51) = 20.04, p < .01. The average post-activity pain rating was significantly lower than the average pre-activity pain ratings, with a large effect ( η p 2 = 0.28). There was no main effect of Group. The interaction between Time Point and Group was statistically significant, F (1, 51) = 41.79, p < .01, with a large effect ( η p 2 = 0.45). Given the prior assumption that the pain rating would decrease across Time Point in the EAL Group but not in the Control Group, planned t -tests were used to explore the interaction. Pain rating was significantly lower in the post-activity compared to pre-activity measurement for the EAL Group, t (26) = 8.18, p < .01, and the effect size for this group ( d = 0.89 95% CI [1.00 – 2.14] was found to exceed Cohen’s (1988) 34 convention for a large effect ( d = 0.80). There was no significant difference between the pre-activity and post-activity pain rating for the Control Group, t (25) = −1.33, p = 0.20 (two-tailed test). Forty-five (Control Group: n = 21, EAL Group: n = 24) of the participants were interviewed post-session regarding their experience and an analysis of their responses is given in this section. Four themes were identified, two of which related to both the EAL and Control Groups, shown in the thematic map ( Figure 2 ). Figure 2. Thematic map of study 2 participant self-reported experiences of EAL and control. Thematic map of study 2 participant self-reported experiences of EAL and control. Each theme allowed us to dissect the experiences of those participating in our study allowing us to examine differences between individuals within and across conditions. ‘In-Session Feelings’ describes any feelings that the participants reported feeling during the group and individual sessions. ‘Horse Interaction’ describes any experiences related to the horses discussed by the EAL Group, such as their thoughts on their own interactions with the horses or how they felt observing the ways in which the horses interacted with one another and the environment. The theme ‘Attitude Toward Control Task’ applies to the Control Group’s insights into how their task impacted them, even though there were no horses present. ‘Post-Session Effects’ refers to any changes reported by the participants as a result of carrying out the activity. The most relevant quotes from the transcripts have been used to represent each theme. To begin the interview, the participants were asked how they felt during the experience. These could be divided into positive, neutral or negative experiences from a participant perspective. A total of 28 participants (EAL Group: n = 21, Control group: n = 7) described their experience as positive, including reports of feeling relaxed and happy, as well as some describing their experience as fun, enjoyable, exciting or interesting. Some participants expressed several different emotions and the incidence of each is discussed below. The experience of feeling calm, relaxed or chilled was reported by 18 participants. For example, P2H said: ‘[The experience made me feel] …quite relaxed and happy’. Moreover, P50H said: ‘The horses were really calm and made me feel calm’. And P34H said the experience was ‘quite calming and that [the ponies] were nice to be around’. There were also instances of these feelings reported by the Control Group such as P26C who felt ‘quite calm’ and P44C who felt ‘pretty normal and chill’. Twelve participants (EAL Group: n = 9, Control Group: n = 3) reported feeling happy or felt like they had a good or nice experience. Those in the EAL group often attributed their feelings of happiness to their interaction with the horses: ‘…the horses made me happy’ – P2H, ‘It was very nice to do’ – P18H. Those in the Control Group often noted feeling happy due to completing the activity objective and finding the treat: ‘I found [the treat] very quickly so I was very happy’ – P6C. There were also instances of EAL participants describing their experience as fun ( n = 3), enjoyable ( n = 3), exciting ( n = 2), and interesting ( n = 1). There were 8 participants who didn’t express feeling a strong emotional response within the session and described feeling fine or indifferent during the session (EAL Group: n = 2, Control Group: n = 6). Participants P7C and P10C also described feeling neutral about the experience but later noted feeling frustration, suggesting that some participants had a more nuanced grasp of their feelings and were able to separate their emotional state from negative cognitive feelings they were experiencing as a result of the task. A total of 13 participants (EAL Group: n = 3, Control Group: n = 10) experienced negative feelings during the session. One participant (P16H) described the experience as ‘a bit scary’ but also ‘kind of fun’ overlapping between having positive and negative in-session feelings. Including participant P16H, 3 participants noted feeling stressed or scared during the session (EAL Group: n = 2, Control group: n = 1). For example, participant P29C said they felt ‘a bit stressed because [they] couldn’t find the treat’. Two Control Group participants recalled feeling awkward or embarrassed during the session, while another 2 Control Group participants reported feeling bored. Six Control Group participants expressed negative cognitive feelings which included confusion ( n = 4) and frustration ( n = 2). Although the interview questions did not specifically ask the participants about their interactions with the horses, when asked what they could remember or if there were any moments which stood out to them, all those in the EAL condition ( n = 24) described their interactions or what they observed of the horses interacting with each other. It is useful to note that the interview began by asking the participants about their feelings which may have influenced them to answer subsequent questions in a way which centred around or justified their previous answer. Thirteen participants attributed their positive feelings to the horses: ‘The horse made me happy’ – P2H; ‘Definitely more relaxed when I’m petting them’ – P13H; ‘Horses were really calm and made me feel calm’ – P50H; ‘I feel like I really bonded with them when they walked with me’ – P38H, ‘When I got the horse to follow me I felt talented’ – P18H. Four participants mentioned slightly negative experiences in regard to their interactions with the horses: ‘I was nervous but then comfortable with the horses’ – P14H; ‘Bit wary of horses’ – P17H; ‘Not a massive fan of horses, I’ve just realised’ – P12H. The rest of the EAL participants ( n = 7) had more neutral answers simply describing what they did or how the horses acted, without going into detail about how this interaction made them feel. For example, P39H said: ‘When the horse followed me and stopped when I stopped’ and P41H talked about ‘Walking around with one of the smaller ponies around the cones’. Unlike the EAL Group, the horses were not present for the Control Group’s session which meant that when they were asked what they could remember or if there were any moments that stood out to them, 15 participants in the Control Group discussed their feelings and attitudes towards the activity. Five participants recalled having a positive experience completing the activity because of finding the treat. For example, finding the treat was described as ‘rewarding’ – P21C and P6C said they ‘found it very quickly’ and this made them ‘very happy’. The only positive attitudes towards the task were reported by those who found the treat suggesting that it was likely the sense of accomplishment from completing the task which elicited positive feelings rather than the motions of going through the task. This is unlike the majority of the EAL Group who regarded the whole process of their interactions with the horses as a pleasant experience. On the other hand, 10 Control Group participants who were not able to complete the task or were looking for the treat for a while (maximum 10 min), reported negative feelings towards the control task. Negative cognitive feelings previously mentioned as prominent in-session feelings experienced by the Control Group were discussed further in relation to the task specifically. One of these feelings was frustration ( n = 2): ‘Bit frustrated walking around not being able to find it’ – P7C, ‘Slight bit of frustration as I went everywhere and didn’t find it at first’ – P10C. Two participants reported feeling bored with the task and 4 participants said they felt confused regarding the point of the task or the task itself: ‘A bit confused at what I was doing’ – P42C. For participant P29C not being able to find the treat caused them to feel a ‘bit stressed’. In addition, 2 participants expressed that having to carry out the task while being observed made them feel ‘a bit awkward’ – P22C, and ‘a bit embarrassed’ – P9C. When asked if they noticed any differences from pre-session to post-session, 20 participants (EAL Group: n = 16, Control Group: n = 4) reported positive emotional changes. One positive emotional effect of the session reported by 15 participants (EAL Group: n = 14, Control group: n = 1) was feeling calmer, more relaxed or less stressed. For example, P36H said: ‘I feel like a lot of my stress is gone’ and P5H said they felt ‘more relaxed and calmer’. Seven participants (EAL Group: n = 4, Control Group: n = 3) reported feeling happier or in a better mood after the session: ‘Made me feel better’ – P38H, ‘I’d say I’m probably more relaxed and in a good mood’ – P11H. Those in the Control Group who reported feeling better after the session implied that this was due to the session being over or because they felt accomplished due to completing the task: ‘Now that it’s over I feel better’ – P23C, ‘I feel a lot better because I found the treat’ – P45C, ‘I feel better about myself because I found the treat’ – P46C. Three EAL Group participants noted that their participation in the session resulted in a physical change. Reduced pain perception was a physical change reported by two participants: ‘While they were measuring my pain response the horse was licking my hand, so I wasn’t paying as much attention to the pain’ – P5H, ‘I think the pain measurements felt less painful’ – P41H. One EAL participant reported feeling colder after the session but did not elaborate on this physical change. Only one EAL participant expressed feeling worse as a result of participating in the session. Participant P12H reported feeling more anxious after the session due to not being comfortable interacting with the horses: ‘I was more anxious after the session. I’m not a massive fan of horses, I’ve just realised’. It is useful to note that this was the only participant in the EAL Group whose pain perception did not decrease after the session. This may suggest that an anxious state may impact the efficacy of horse-interaction in reducing pain perception. Sixteen participants (EAL Group: n = 2, Control Group: n = 14) said they observed no difference in the way they felt before and after participating in the session. The studies reported here examined the effect of horse-interaction on acute pain perception. It was hypothesized that EAP, HI (without EAP) and EAL would serve as effective means of reducing an individual’s perception of acute pain. It was predicted that those who participated in the EAP, HI and EAL groups would experience a significant reduction in pain ratings after activities involving horses, and that this reduction would not be observed in the Control groups. The results supported the hypothesis with a significant reduction in pain ratings by participants in all three horse-interaction groups but not those in the control groups. It is reasonable to suggest that being around horses (whether there is psychological guidance or not) has a significant beneficial effect on pain perception. The potential mechanisms behind this reduction may include distraction, physiological changes, and positive emotion. The qualitative data regarding participants’ experiences of EAP, HI and EAL have similarities across the two studies. The horses and their behaviour are clearly salient to participants who readily report details of their experiences with the horses. In addition, the majority of participants report positive emotional experiences while interacting with the horses as well as feeling calmer, relaxed and happier after the sessions. It is noteworthy that participants from both studies report some nervousness before the sessions. While many then experienced a transition to enjoyment and happiness during the activity, at least one participant did not overcome her nervousness. A minority of participants from both studies were explicitly aware of their reduced pain perception following interacting with the horses and mentioned this in their accounts. Distraction involves a competition for attention, in this case between pain and a consciously directed focus on external stimuli, that is, a horse. While participating in the EAP, HI and EAL groups, participants were engaged in an attention-occupying active interaction between themselves and the two horses present with them. As mentioned previously, horses and ponies alike require a high level of attentiveness from their human counterpart due to their size and sensitivity to visual and auditory cues. In contrast although the Control Group participants did a similar task in the same environment, they did not have a horse/pony present. Rischer et al. (2020) 35 conducted a study looking at high and low demand tasks in relation to painful stimuli. They found that those in the high load condition experienced significantly reduced perceived pain intensity when compared to the low load condition, and that the size of the distraction correlated with pain perception. Post-session pain rating were taken while still in the arena and the horses were still present. One way to explain the reduced pain perceived while with horses in the current study is therefore perhaps that the horses provide sufficient distraction. The physiological changes that may have occurred during the experiment are suggested from previous research on AAT animal interaction. 36 Furthermore increased levels of endorphins, as neurotransmitters, have been found to inhibit pain in the body, while also inhibiting positive feelings when at reduced levels. 37 Hence, potential physiological changes may underlie some of the reduction in pain we see in our study. Future research could explore this. It is important to note that physiological changes, in particular endorphin release, also occur with any interesting or engaging activity, 38 so this may not be just a horse/pony effect, but simply an outcome of participants enjoying themselves when interacting with the horses/ponies. Looking at the current qualitative data, a transition from nervous and anxious feelings to calm and relaxed feelings was observed in the EAP, HI and EAL groups. Certainly horse-interaction provided participants with feelings of enjoyment and reward, with an overwhelmingly positive array of responses observed in those who participated in horse-interaction. These positive responses support research conducted by Braun et al. (2009) 39 suggesting that AAT leads to the release of endorphins which promote a feeling of well-being. Positive emotion can lead to pain reduction 40 giving a potential explanation that the significant reduction in pain perception observed in the horse-interaction groups ties in with the positive responses found in their qualitative descriptions. It remains to be seen whether the effect of such interactions is due to their novelty as well as whether the magnitude of pain perception reduction is or is not greater with horses in comparison to other inherently enjoyable experiences. The results have shown that interaction with horses reduces pain perception, potentially through the processes of distraction, physiological changes, increased positive emotions and reduction in anxiety/increased relaxation. The Dynamic Model of Affect (DMA 11 ), can aid the explanation of how these findings, on acute pain perception, can relate to the treatment of chronic pain. The DMA accounts for how positive states may influence adaptation to chronic pain. When applying the DMA to chronic pain populations, it was found that the ability to sustain positive states decreases vulnerability to negative pain and fosters adaptive recovery from pain. With horse-interaction possibly providing a positive outlet for emotion, it may be possible that horses could provide a positive state to those with chronic pain. It is also proposed that horse-interaction may provide a sufficient distraction to aid the relief from chronic pain to those who suffer from it. Indeed a participant in a horse condition commented that: ‘ as someone who suffers from endometriosis and PTSD, this study showed me that there is a chance for me to feel relief ’. Making horses available to patients has practical and monetary restrictions and it remains to be seen what the relative cost effectiveness of such interventions would be in comparison to other activities. Horses certainly command particular mindfulness when people are around them, partly because of their size, 41 which may enhance a therapeutic effect. Some of our participants expressed that their initial nervousness stemmed from the awareness of the large size of the horses. Interestingly we found similar effects when larger horses (Study 1) and smaller ponies (Study 2) took part. Frewin and Gardiner (2005) 42 stated that the horses’ size can be intimidating for people, which engenders increased attentiveness and self-awareness around them. An advantage of this size differential is the opportunity to face one’s fears and insecurities, which translates to improved self-esteem resulting from managing horse-oriented tasks effectively. 43 This is reflected in our findings, as many stated that successful interactions with the horses were a source of increased self-esteem and confidence. It is also well-documented in previous literature, being described as one of the most prominent benefits of EAP in many studies. 44 For example, Wilson et al. (2017) 45 interviewed eight EAP registered therapists offering EAP to adolescents diagnosed with depression and/or anxiety. When asked about the benefits they have observed in their patients, the most cited improvements were improved self-esteem and confidence. This was also the case in another sample of licensed therapists interviewed, with respondents claiming EAP facilitated increases in self-esteem and self-efficacy in depressed adolescents. 46 There are a number of limitations of the current study. First, while participants were randomly allocated to the different groups, which were matched on age, we could not match groups also on other potentially important variables including previous experience with horses. All groups included some participants with little or no experience and some with extensive experience. However we did not collect data on this or quantify it. This would be an important focus for future research as previous experience might impact how participants respond to the EAL sessions, for example, by affecting novelty of the experience as well as feelings of anxiety. Second while we attempted to have adequate control groups in both studies, controlling for physical environment and activity levels, on reflection these could have been improved considerably by changing the task that participants were asked to complete. Future research should attempt to have a task that is inherently enjoyable (perhaps social) whether it is accomplished with or without the horses. This would hopefully reduce the negative feelings felt by some of the participants in the control group which may have created a confounding factor. Future research can also investigate individual differences in responses to EAP. It has been well-documented that mental health conditions, such as depression, influence pain perception. 47 It remains to be seen if the reductions in pain perception we found here would also occur across different mental health conditions. Furthermore, there is a need for research to investigate pain perception and horse-interaction with individuals who present with chronic pain conditions. Lastly as discussed above, the majority of our participants reported feeling calmer, more relaxed and less nervous after the session, indicating a possible decrease in anxiety and stress. It would therefore be informative to include physiological measurements of anxiety and stress levels (e.g. heart rate, electrodermal activity) in future studies, in order to better understand the impact of human-horse interaction, and how this relates to changes in pain perception. Lastly, further research can examine whether more long-term participation in the EAP, HI and EAL groups would produce significant changes in pain tolerance over a sustained period of time.