Is there a role for the Yerkes-Dodson-Law in horse training?

Frauke Musial & Celina Skogan

Many of us have probably made that experience, at the latest in school or at university: Even if you think you are perfectly well prepared, it might be awfully difficult to come up with just the right answer during the exam. And this effect might be worse, if it is a teacher that you fear, a topic that you don’t’ like or that is particularly complicated, or if you are simply stressed out and afraid to the bones!

At the same time, a task that you find particularly boring, even though it may be at the same time complicated and intellectually challenging, may require an unusual amount of coffee to be able to perform it at all.

This relationship between a certain level of activation (called “arousal” in psychophysiology) and the performance in a task has been originally described by the psychologists Robert M. Yerkes and John Dillingham Dodson in 1908 [1]. It is since understood as a fundamental principle of learning, memory, and performance (Figure 1). 

Figure 1: The “upside down bathtub” curve of the relationship between performance (effectiveness, learning capacity, etc.) and arousal (tension level, activation level, stress level) according to Yerkes & Dodson [1].

As figure 1 illustrates, learning capacity, effectiveness or performance of a task increases with increasing activation or arousal. However, this is only true up to a certain point: If the activation increases and turns into a higher stress level, the effectiveness of problem solving as well as learning capacity decreases which means, that the resulting performance curve decreases. Consequently, the overall curve representing the relationship between performance and arousal looks like an “upside down bathtub”. 

Even though the Yerkes-Dodson-Law is widely accepted and applied in learning psychology as well as in occupational psychology and many other fields of research and application, it is important to notice, that the curve may be very different for different tasks, different individuals, as well as different situations. As a general rule, difficult or intellectually demanding tasks may require a lower level of arousal (in order to facilitate concentration), whereas tasks demanding persistence may be performed better with higher levels of arousal (in order to increase motivation). For some, very simple and overlearned tasks, the performance may even increase constantly with increasing arousal so that the curve actually never turns. Nonetheless, for most tasks and learning situations, the upside down U-shaped curve is applicable and thus the upward part of the curve represents the energizing and activating effects of arousal while the downward part represents the deleterious effects of stress on learning, memory, task performance, and problem solving (remember the “tunnel vision” in highly stressful situations). 

Over the last decades, the understanding of the underlying central nervous system mechanisms and here especially the brain mechanisms of how stress affects learning and memory has dramatically improved [2,3]. To date, it is well established that a group of stress hormones, the glucocorticoids, is responsible for this particular relationship of arousal and problem solving. In lower blood concentrations, glucocorticoids facilitate cognition, problem solving, as well as access to and forming of memories, while increasing blood levels of glucocorticoids lead to memory disturbances and reduced intellectual capacity [2,3].

Now, one could ask the question: “Ok, well, interesting! But why should this be relevant for horse training?” Figure 2 shows, where we would like our horse to be positioned “on” the upside down bathtub curve: Right on top or, maybe, just a little bit to the left.

Figure 2: An optimal activation level and as such a motivated horse will result in optimal performance and lead to optimal training results. 

For optimal training conditions, we would like to have a horse with just the right level of activation and thus motivation for the task. A horse that is too stressed or too bored, will not be able to show the best of his performance. Figure 3 describes a situation, where the horse is too little activated to perform optimally: 

Figure 3: A “bored” horse. The activation level is too low and the horse too unmotivated in order to achieve good training results.

In a situation like this, it may be necessary to adjust the task. Try something new or add a new and interesting component to it. It may be enough to change the order of the task elements, or to perform the sequence outside on a field instead of inside the riding hall. Why is this important? A horse that is “undertaxed” and bored, will most likely not solve the task to the satisfaction of his trainer or rider. Such a situation may lead to frustration and in turn to negative emotions and stress on both sides. A situation, which may lead to exactly the opposite situation, a stressed horse with a frustrated rider/trainer (see also our blog on how emotions transfer between humans and horses). As a result, the horse-human couple may in fact end up on the right side of the curve, which is in many ways, the most deleterious training situation (see Figure 4):

Figure 4: The horse is stressed and thus highly activated. Learning and performance levels will be low under these conditions.

In a situation like this, with a horse experiencing a high stress or tension level, basically no successful training or performance is possible. Since horses are a social species, emotions play a major role for the communication with our four legged friends and in addition, their memory is strongly connected to emotions (see our blog on the “elephant memory of horses”) . Frustration and bad feelings on the side of the trainer and/or rider will transfer to the horse and will most likely reduce performance even more for both of you and thus increase the stress level of the horse. A situation, which is unfavorable, not only with regard to the training situation, but even more so with regard to animal welfare and ethics. 

There are many different possibilities why horses maybe stressed, fortunately, there are quite a few options how we can influence their stress level (see Figure 5). The most obvious thing is to have a closer look at the husbandry conditions: Does your horse have enough opportunity to move? How is the feeding regimen? How harmonious is the heard? How is the health status? Is there a pain issue? (see our blog on the equine pain face). Beyond that, many other factors may influence the basic stress level of the horse. At the same time, we have several possibilities and options to increase the wellbeing level that reach far beyond the obvious issue of husbandry and animal welfare. A training concept, which takes the horses’ abilities and nature into account, is one of them. Massage has been shown to be a valuable instrument to increase the horses’ wellbeing AND performance (see our blog on equine massage “Scratch me if you can”). In addition, massage will increase the bonding and connection between you and your horse. All these measures are suitable to reduce the stress level of a horse and thus increase his learning and performance abilities (see Figure 5).

Figure 5: There are several reasons, which may account for a high basic stress level in horses. Resolving the obvious ones e.g. related to husbandry and/or health status will increase well-being and thus reduce the stress level. These measures are able to “move” the horse to the left along the curve resulting in better performance. Some additional measures, such as e.g. massage and/or ground work, are also suitable to reduce the stress level. They are particularly useful in situations, where the reduction in tension/stress level that can be achieved through medical treatment or change in husbandry may be limited, such as e.g. during rehabilitation after a pain syndrome. 

To date, most horses live in “our” world, it is us humans who determine and control basically every single aspect of their living conditions. With this understanding comes the responsibility to provide our four-legged companions with more than just their basic needs: Increased well-being will as immediate effect improve the performance of our horses, a goal that is probably desirable for all riders independently of their aims and ambitions. Beyond that, and especially because we as humans are in total control of our horses lives, we find it a fundamental, ethical obligation to ensure the best possible welfare for our equine friends. 


  1. Yerkes RM, Dodson JD (1908). “The relation of strength of stimulus to rapidity of habit-formation”. Journal of Comparative Neurology and Psychology. 18 (5): 459–482. doi:10.1002/cne.920180503.
  2. Sapolsky RM. Why stress is bad for your brain. Science. 1996;273(5276):749-750. doi:10.1126/science.273.5276.749
  3. Lupien SJ, Maheu F, Tu M, Fiocco A, Schramek TE (2007). “The effects of stress and stress hormones on human cognition: Implications for the field of brain and cognition”. Brain and Cognition. 65 (3): 209–237. CiteSeerX doi:10.1016/j.bandc.2007.02.007. PMID 17466428.