# New locomotor indicators of emotions in sport horses

Sophie Biau, Elena Pycik, Laetitia Boichot, Anais Ascione, Lea Lansade, Alice Ruet

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## ► To cite this version:

Sophie Biau, Elena Pycik, Laetitia Boichot, Anais Ascione, Lea Lansade, et al.. New locomotor indicators of emotions in sport horses. Multidisciplinary Biomechanics Journal, 2025, 50th congress of the., 10.46298/mbj.16180. hal-05191732v2

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Submitted on 23 Oct 2025

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# New locomotor indicators of emotions in sport horses

Sophie Biau<sup>a*</sup>, Elena Pycik<sup>a</sup>, Laetitia Boichot<sup>a</sup>, Anais Ascione<sup>b</sup>, Lea Lansade<sup>b</sup>, Alice Ruet<sup>a, b</sup>

Received date: 03/04/2025

Accepted date: 27/06/2025

Publication date: 27/10/2025

**Keywords:** jerk, fluidity, locomotion, welfare, riding

© 2025 The Authors

Licence CC-BY 4.0

Published by Société de Biomécanique

## 1. Introduction

From a societal point of view, there is a growing concern about animal welfare. The state of well-being varies according to the animal's perception of the situation. It reacts temporarily to an event, and this reaction or emotion involves behavioural, physiological and cognitive changes (Boissy et al. 2007). It's usually supposed that intense emotions can last from a few minutes to several hours, but no study provides precise measurements of the duration of an emotional state following an event.

Based on accelerations measured at the level of the sternum, a recent preliminary study demonstrated a physiological response and, more specifically, a change in locomotion that discriminates between a state of positive anticipation and a state of frustration (Phelipon et al. 2024). Additional information could be extracted from the acceleration signal, such as in humans, where the notion of fluidity based on the calculation of Jerk and Spark made it possible to detect emotional states. The main objective of this study was to define new locomotor indicators in sport horses that could identify the gait following exposure to a positive or negative situation compared with a neutral situation. The hypothesis was that emotional state affects the activation of muscular patterns required for smooth, efficient movement. This first approach presents results based on jerk calculation, to quantify the smoothness or fluidity of a horse at walk and trot in positive, negative and neutral emotional conditions.

## 2. Methods

### 2.1 Animals

Eleven sport horses (12,8 ± 2 years old) were tested. There were 9 geldings and two mares. The horses were familiar with the experimentator.

### 2.2 Data collection

The study was carried out in an indoor arena (round pen) familiar for all the horses, close to the stable. The tests were performed on three consecutive days. All horses were tested in left hand on the lunge.

After the three minutes warm-up, three minutes of induction were carried out by an experimenter (the same for the 3 conditions and for all horses), a positive C[+] induction, a C[-] induction and a neutral C[N] induction, in random order. The inductions were validated beforehand by analysing facial expressions and behaviour, according to the bibliography. After these three minutes, the lunger induced the horse to walk at stable speed for five minutes, minimising interaction as much as possible. At the end of these 5 min of walking, the horse was again induced for three minutes to perform the five minutes of trotting.

Horses fitted with one inertial measuring units (Shimmer3 IMU 91 Unit, Shimmer Sensing, Dublin, Ireland) attached to the surcingle against the sternum. Shimmer IMU data provide an estimate of the sensor orientation with quaternions 6DoF Low Noise. This orientation is the rotation from a global reference frame

<footnote><sup>a</sup> Institut Français du Cheval et de l'Equitation, Plateau technique de Saumur, Saumur, France</footnote>

<footnote><sup>b</sup> INRAe, CNRS, University of Tours, PRC, Nouzilly, France</footnote>

<footnote>* Corresponding author: sophie.biau@ifce.fr</footnote>
to a local reference frame (Horse reference frame). Accelerometric data were recorded at ± 16 g, sampled at 256 Hz.

## 2.3 Data analysis

The time-derivative of vertical acceleration (Jerk in m/s³) was calculated to quantify smoothness or fluidity in accordance with the recommendations of (Melendez-Calderon, Shirota, & Balasubramanian 2021) and (Hogan & Sternad 2009). This calculation avoids the integration of the reconstructed acceleration signal, and therefore the errors associated with the drift of the reconstructed velocity that we have with SPARC for example. The smoothest movements have the lowest jerk.

It was calculated for the whole five min signal per condition and for the signal split minute by minute per condition and was normalised over time to allow comparison of the 5 min sequences with the one min-ute sequences. All data were analyzed with the Matlab R2019b software (MathWorks®).

Friedman tests were used to objectivate a significant effect of condition on the jerk, for the walk and the trot. The tests were also carried out intra condition minute by minute.

## 3. Results and discussion

Results showed a significant difference of the fluidity at trot between Conditions [-] and [N] (7.55±0.12; 6.72±0.11; p=0.012). C[-] trot was significantly less fluid than the C[N] trot. Emotions are expressed as a function of valence and intensity. The intensity of the positive valence may not have been sufficient to trigger a change in fluidity, or a positive valence may not affect the fluidity of locomotion. The proposed indicator is perhaps inappropriate for positive valence. Other indicators need to be explored. According to (Kang & Gross 2016), increased movement fluency was associ-ated with high intensity emotions, both pleasant and unpleasant (joy and anger). In our study, the change in the fluidity of the trot following the C[-] may only be linked to the emotional intensity provoked by the stimulus and not to the valence.

Figure 1 shows a decrease in jerk, i.e. a significant increase in fluidity from the fourth minute onwards. The negative situation affected this group of horses for an average of 3 minutes.

<figure><img src="image_3.png" /><figcaption>Figure 1. Jerk value at each minute for the C[-].</figcaption></figure>

## 4. Conclusions

The results of this preliminary study are promising for the search for new locomotor indicators of emotional state. Evaluation of the fluidity of the trot using the jerk calculation made it possible to distinguish the impact of a negative valence situation or simply intense stim-ulation from a neutral situation. A return to a normal gait was found in the fourth minute following the event.

Further investigations are required to find indicators of a positive emotional state.

## Funding

Institut Français du Cheval et de l'Equitation.

## Contributor Roles

SB: Conceptualization, Methodology, Writing origi-nal draft; EP: Contributed data, Data curation, Writ-ing-review & editing; LB: Collected the data; AA: Methodology, Collected the data; LL: Conceptualization, Methodology; AR: Conceptualization, Methodology, Validation, Writing-review& editing

## References

* Boissy, A., Manteuffel, G., Jensen, M. B., Moe, R. O., Spruijt, B., Keeling, L. J., Winckler, C., Forkman, B., Dimitrov, I., Langbein, J., Bakken, M., Veissier, I., & Aubert, A. (2007). Assessment of positive emotions in animals to improve their welfare. *Physiology & Behavior, 92*(3), 375-397. https://doi.org/10.1016/j.physbeh.2007.02.003

* Hogan, N., & Sternad, D. (2009). Sensitivity of smoothness measures to movement duration, Amplitude
and Arrests. *Journal of motor behavior, 41*(6), 529–534.
https://doi.org/10.3200/35-09-004-RC

Kang, G. E., & Gross, M. M. (2016). The effect of emotion on movement smoothness during gait in healthy young adults. *J Biomech., 49*(16), 4022–4027.
https://doi.org/10.1016/j.jbiomech.2016.10.044

Melendez-Calderon, A., Shirota, C., & Balasubramanian, S. (2021). Estimating movement smoothness from inertial measurement units. *Frontiers in Bioengineering and Biotechnology, 8*. https://doi.org/10.3389/fbioe.2020.558771

Phelipon, R., Ascione, A., Ruet, A., Bertin, A., Biau, S., Arnould, C., Boichot, L., & Lansade, L. (2024). Differences in behaviour, facial expressions and locomotion between positive anticipation and frustration in horses. *Applied Animal Behaviour Science, 274*, 106262.
https://doi.org/10.1016/j.applanim.2024.106262