Recent scientific findings support what many students of Classical dressage principles have known all along: The shoulder-in exercise is not only good for the horse’s physical development but it also influences their mental state – and the benefits of practicing it apply whether the rider is very skilled or less experienced.
The history of shoulder-in
Since its ‘invention’ over 300 years ago, the shoulder-in has received much praise from the who’s who of the classical and modern dressage scene. Particularly in the classical dressage world, the shoulder-in is regarded as the foundation exercise when it comes to improving straightness and balance, preparing horses for higher degrees of collection and the other lateral movements such as travers.
The Duke of Newcastle, a 17th-century Englishmen and classical dressage master, performed the ‘predecessor’ of our contemporary shoulder-in on a circle on multiple tracks. However, he reported that riding this movement on a bent line is very difficult.
A few decades later, the Baroque Frenchman and riding master de la Guérinière further refined Newcastle’s embryonic shoulder-in by riding it on a straight line (on four tracks) instead. This marks the birth of the shoulder-in movement as it is known today with one ‘minor’ amendment: The track numbers it’s supposed to be ridden on in dressage competitions has shifted from de la Gueriniere’s original four to the FEI’s three tracks.
Shoulder-in is held in ‘high regard’ in the equestrian literature
De la Guérinière describes the shoulder-in as “(…) the most difficult and the most useful [exercise] (…) which must be used to supple the horse” [1; p.62]. It “(…) produces so many good results at once that I regard it as the first and the last of all those [exercises] which are given to the horse.” [1; p.66].
Steinbrecht, a 19th century German dressage master, often referred to as the father of ‘modern’ dressage, highlights the important role shoulder-in plays in suppling the shoulders, achieving the best longitudinal bend, and teaching the horse to bend his hind legs when stepping under the center of gravity .
Decarpentry, an early 20th-century French cavalry officer and international equestrian judge, emphasises the positive impact of shoulder-in on the horse’s balance, muscular system, and the quality of the gaits .
With all these great benefits linked to one single movement, the FEI defines the shoulder-in as an essential schooling movement as it “(…) helps to straighten and supple your horse as well as develop the ability to collect and carry more weight on the hocks and hind end.” 
Shoulder-in in competitive and contemporary dressage
Today’s shoulder-in, as defined by the FEI and national riding manuals, is ridden on three tracks.
The German National Equestrian Federation (FN), for instance, describes the shoulder-in as a movement where the horse’s forehand (shoulder) is brought to the inside whilst the hindquarters stay on the wall. It is performed on three tracks with the outside hind leg traveling on track one, the inside hind leg and outside front leg traveling on track two, and the inside front leg traveling on track three . The imaginary angle between the wall and the horse’s shoulder should be approximately 30 degrees.
Shoulder-in on three tracks, however, is a recent ‘innovation’, and dressage and horse training manuals of the first half of the 20th century still describe shoulder-in as an exercise ridden on four tracks, such as the German Heeresdiensvorschrift – a main work of its time on horse and rider training in the German cavalry .
New research backs the Classical masters
The claim that shoulder-in is beneficial for the physical and mental states of horses is supported by the findings of an interesting recent study.
Mendonca and colleagues  studied on a sample of 40 horses how being ridden in shoulder-in influences their behaviour and physiological responses. The horses were aged between 4 and 11 years and familiar with the shoulder-in movement.
Two FEI riders of different experience levels, one professional and one amateur, were asked to ride the horses during the experiment.
It was hypothesised that the lacking balance and precision of the amateur rider could impact the correct execution of the movement shoulder-in and therefore potentially affect the results.
In a first session, the horses were ridden on straight lines in walk, trot, and canter. In a second session, the riders were asked to ride the horses in shoulder-in (lateral exercise) in walk, trot, and canter.
Heart rate variability (HRV), used to measure stress, and horse behaviours indicative of lacking attention (“looking around frequency”) and relaxation (“playing with/chewing the bit”) were recorded in both sessions.
During the first session, horses were significantly less attentive and showed more ‘looking-around’ behaviours compared to session two where the horses displayed behaviours indicating relaxation/focus more frequently.
These behavioural observations are in line with the researchers’ measurements that showed increased activity of the sympathetic nervous system during session one (straight lines session) compared with a mainly parasympathetic nervous system activation during session two (shoulder-in session).
Based on their findings, it seems evident that riders, in general, have “(…) little if any influence on the horses’ behavioural parameters.” (e.g., looking around) (p.18)  [note: The riders were instructed to allow head movements in case the horses were looking around].
“The results concerning LAF [“looking around frequency”] and PCB [“playing with/chewing the bit”] between the two sessions suggest that lateral exercises, as performed in session two, may be useful to increase attention and decrease tension, independent of the rider.” (p.18) 
The researchers conclude that “(…) lateral exercises are an important tool that unexperienced riders could use to reduce stress-related events during training (…)” (p.20) 
It seems evident that lateral movements in general may reduce stress-related responses in horses. Therefore, besides their ‘gymnastisising’ effects, they may also be used to help lower a horse’s emotional level and re-focus their attention on your aids.
- De la Gueriniere, F. R. (1992). Ecole de Cavalerie, Part II. Cleveland Heights: Xenophon Press.
- Steinbrecht, G. (2004). Das Gymnasium des Pferdes. 3. Auflage. Brunsbek: Cadmos Verlag.
- Decarpentry, A. (2012). Academic Equitation. North Pomfret: Trafalgar Square.
- Federation Equestre Internationale (Fei) (2020). Dressage Movements 101 – Intermediate. [internet]. Available from: https://www.fei.org/stories/lifestyle/teach-me/dressage-movements-101-intermediate Accessed 22nd June, 2021.
- Deutsche Reiterliche Vereinigung (FN) (2008). Richtlinien Reiten und Fahren Band 2, Ausbildung für Fortgeschrittene. Warendorf: FN Verlag.
- Heeresdienstvorschrift H.Dv.12 (2007). Stuttgart: Frankh-Kosmos Verlag.
- Mendonça, T., Bienboire-Frosini, C., Sanchez, N., Kowalczyk, I., Teruel, E., Descout, E., & Pageat, P. (2020). de la Guérinière was right: shoulder-in is beneficial for the physical and mental states of horses. Journal of Veterinary Behavior 38, pp.14-20
The original study is published in the Journal of Veterinary Behavior and the abstract is available here.