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  • Writer's pictureAdele Shaw

What and Why? // Fear Thresholds

Updated: Mar 1, 2021

I spent many many years working with horses that had different amounts of anxiety and fear, never understanding what a fear threshold was and why it mattered. In fact I think the majority of horse people out there can't tell you what a fear threshold is. Fast forward to now and I honestly have no idea how I ever got away with not understanding this concept. I believe this bit of information is so critical to successfully and humanely training and handling a horse that it should absolutely be information that every horse person understands. Whether you are a trainer, a horse owner, or just taking occasional lessons you should be able to recognize fear levels in your horse and know how to handle them. It's absolutely vital for the well-being of your horse, the success of your training program, and your own personal safety.

What Is A Stimulus?



noun: stimulus; plural noun: stimuli

  1. something that rouses or incites to activity

  2. an object or event that is apprehended by the senses

  3. something that stimulates or acts as an incentive

  4. any drug, agent, electrical impulse, or other factor able to cause a response in an organism

A stimulus can be anything from something the handler is doing to an environmental event or even physical pain. For example, when a rider applies leg to get a horse to move forward the rider is applying a stimulus. If a saddle is poorly fitting and causing pain, the saddle is applying stimulus. If you're walking your horse down the road and a plastic bag flies across the street the plastic bag's movement or even presence is a stimulus. Anything that causes a reaction in a horse, or could cause a reaction in a horse can be considered a stimulus.

What Is Fear?




  1. an unpleasant emotion caused by the belief that someone or something is dangerous, likely to cause pain, or a threat.

  2. be afraid of (someone or something) as likely to be dangerous, painful, or threatening.

This one I think most people will understand, as humans also experience different levels of fear in different situations. But, for the sake of clarity, fear is when an animal or human experiences an undesirable reaction to a stimulus. This stimulus can be either emotional or physical. Usually with animals it's environment, while with humans it can be both environment or mental/emotional. Often physical reactions to fear include an elevated heart rate, quickened shallow breathing, release of the adrenaline hormone, sweating, muscle tremors, and powerful lasting implications on the brain and memories (we will discuss this more later.). Fear usually triggers a fight or flight response.

Explain Fight Or Flight (also called hyperarousal, or the acute stress response)

Humans and animals alike usually choose between one of two responses when confronted with a fear inducing stimuli, . Wikipedia explains it as

"The fight-or-flight response is a physiological reaction that occurs in response to a perceived harmful event, attack, or threat to survival. It was first described by Walter Bradford Cannon."

So, for example, some people are afraid of rats or snakes. When a rat runs out unexpectedly across the floor often the person will scream and run away. But in some cases when a human is frightened they will choose to fight back, especially when they feel trapped and their only option to rid themselves of this fear inducing stimuli (the rat) is through physically attacking it. This is the same for animals, except some animals (particularly predators) will be more likely to fight back than a prey animal, such as a horse.

There is some research showing that perhaps for animals such as the horse (a prey animal) the label should be more along the lines of "freeze or flight", where as the "fight" response would be linked to an emotional response of rage. However, I believe for the point of this article we will go continue with the more traditional phrase "fight or flight".

What Is A Fear Threshold?


noun thresh·old \ˈthresh-ˌhōld, ˈthre-ˌshōld\

  1. the point at which a physiological or psychological effect begins to be produced "has a high threshold for pain"

  2. a level, point, or value above which something is true or will take place and below which it is not or will not

So when we add in the word "fear" .... The definition of "fear threshold" is the point at which a stimulus is at a strong enough intensity to cause a negative and fearful reaction. There are also other thresholds, such as an emotional threshold (anger, sorrow, joy, depression etc.), stress threshold, pain threshold, stimulus threshold (the point at which you recognize a stimulus. such as temperature change etc), and so many more. However when dealing with animals that are instinctively very fearful creatures, fear is the most common threshold we need to be aware of and need to understand in order to be effective trainers and handlers.

Understanding Threshold Stages

There are three different stages of a "threshold". Under, At, and Over. These three stages are important to understand when it comes to training or working with fear. A lot of natural horsemen/women instinctively know when a horse is reaching threshold and are able to successfully work off of instinct alone, but I still think it's important (vital even) to understand and be able to explain what it is we are looking for when working with horses.

Understanding these levels will give you a better understanding of how to be effective with your training, how to manage your horse's emotional and mental state, and how to keep both you and your horse safer. Think of it as like a scale.

When a horse is "under" threshold they are showing no fear or anxiety towards the stimulus presented. They will remain completely calm and relaxed, they are experiencing no fear. Consider this the "safe zone". This is ideally where you want your horse to remain at all times.

It's important to note that this is NOT to be confused with learned helplessness .. the state at which the horse no longer responds to the stimulus because it has learned it can't get away from it so it might as well give up and accept it's fate. This is the same mental state that a prey animal being chased down by predators assumes when it no longer is able to try escaping, usually do to exhaustion or injury.

When a horse is "at" threshold they have reached the point where they will go from showing no fear or anxiety to showing some awareness of the stimulus. This is the "be cautious zone", the zone at which your horse can escalate dangerously or could cool back down into the "safe zone".

When a horse is "over" threshold they are showing apparent signs of distress, anxiety, and fear towards the stimulus. This is the point at which your horse's fight or flight response has been triggered. This is the "danger zone".

How Does A Horse Communicate It's Fear Threshold?

Unlike humans, horses can not just simply open their mouth and tell you they are afraid. They can't admit that they are afraid of the dark, or that they have a fear of heights. Instead, as responsible horse people, we need to listen to how our horses do tell us what they are afraid of. Which is through body language.

I'm going to talk about each level and show you relevant pictures of horses expressing the level of body language you'll be looking for. At the end of this article I will be linking a full video that will show you live examples of horses displaying different levels of reactivity along the threshold scale. I'm going to try and use the same horses so you can get a feel of how each horse expresses it's fear threshold physically.

Staying "under" threshold can be easier for some horses than for others. Genetics, training, and environment have a lot to do with this. Either way the signs of a horse under threshold are pretty straight across the board for all horses. Relaxed and calm is what a horse under threshold looks like. Natural or low head carriage, relaxed muscles, steady breathing, relaxed facial features, relaxed happy ears, soft eyes, and so on. Other signs might be a nice relaxed sigh, steady breathing and heart rate, and a willingness to engage with handler.

Recognizing when a horse is "at" threshold may be a little harder, it can also vary from horse to horse. This is where getting to know the individual horse you are working with is very critical, but general signs might include being hesitant to move (freezing), muscles beginning to tense, a cocked back leg, elevated head, ridged forward ears/rapid ear movement, hesitation to eat, slightly uneven or increasing breath rate, slight heart rate increase, muscle twitches, shortened gaits/movement, lack of awareness for handler and more. When a horse has reached this stage it's often up to the handler whether the situation escalates or deescalates.

When a horse has reached an escalated state of anxiety or fear, and is "over" threshold, it's usually pretty obvious to the educated horse person. Common behaviors being bolting, bucking, biting, kicking, rearing, frantic whinnying, circling, whites of the eyes, flared nostrils, elevated head, high tail carriage, trembling, sweating, heavy breathing, loud snorting, increased heart rate, refusal to eat, and overall body tension.

Under Threshold, relaxed and attentive. Her muscles are relaxed. Mouth is soft. Eyes are soft. Her ears are perked forward because she's watching something going on, but it doesn't alarm her in the least. If she were to elevate her head, and harden her facial features she would show me that whatever she was looking at was beginning to alarm her.

At Threshold, rapidly approaching Over Threshold. Her eyes are wide open and hard. Muscles tensed. Muzzle/Chin tight and hard. Ears abruptly forward. This is the point where she will continue to escalate or will calm back down.

Over Threshold, "flight or fight" hasn't kicked in as she's trying very hard to follow my lead. She's however about a fraction of a second away from hitting the red zone and becoming dangerously reactive. Tight, hard, wide open eyes. Ridged forward ears. Tense body. Snorting/Flared nostrils. Tight mouth. Preparing for flight most likely.

Under Threshold, relaxed and attentive. Her muscles are relaxed and everything in general is relaxed. Her ears are perked forward because she's watching something going on, but it doesn't alarm her in the least.

At Threshold, Her eyes are wide open and hard. Muscles tensed. Muzzle/Chin tight and hard. Ears abruptly forward. She's also leaning forward and dumping weight onto her forehand. My guess is because she's wanting to actually approach the stimulus, which might arguably put this more on the "approaching threshold" level. However, this could all change in a split second and she could change her mind and escalate rapidly into "flight" mode (which is over threshold) where she would probably sit back or shy to the side. So I'm putting this in the "at threshold" category because the horse is still not calm and relaxed and I would definitely consider this a "caution zone"

Under Threshold, relaxed and attentive. Her muscles are relaxed even though she's working under saddle. Head/neck is relaxed, happy attentive facial expression.

Over Threshold, "flight or fight" has kicked in. Body is tense, back hollowed, tail up, head elevated, and her face is expressing uncertainty.

Under Threshold, relaxed and attentive. Her muscles are relaxed even though she's working under saddle. Head/neck is relaxed, happy attentive facial expression.

At Threshold, rapidly approaching Over Threshold. Her eyes are wide open and hard. Muscles tensed. Muzzle/Chin tight and hard. Ears abruptly forward. This is the point where she will continue to escalate or will calm back down. You'll notice her hind leg is 'cocked' too, which is often a sign of preparation to flee and a stress sign. She is not obviously not in a resting state here.

Another way a horse can express anxiety/stress or the moments following stress is through what's called a displacement behavior. A displacement behavior is when "the horse is motivated to perform two behaviors that are in conflict with each other. Instead of engaging in either behavior, the horse engages in a third behavior that is unrelated to the context of the dilemma". source

Some examples of this kind of behavior would be wood chewing, pawing, licking/chewing, and more. Or in an example given by Dr. Paul McGreevy "With a ridden horse that desires to move forward but is restricted for more than it can readily tolerate, it may start bending it's neck laterally in an apparent attempt to groom its flank even though self grooming is not the most appropriate response to restraint mediated through the bit." source

Why Does It Matter?

Other than the facts that a frightened 1,000lb animal is not necessarily safe to be on or around, a horse's mental state (whether it's relaxed or afraid) has a strong impact on it's ability to learn or how it learns. To be effective and humane trainers we must be very aware of the mental state our horses are in. I'll explain further, but you're going to have to bear with me and process through some scientific jargon to really understand how critical it is to grasp the importance of fear thresholds.

If you don't want to read the research and just want to hear my translations of it, skip the italicized paragraphs. But of course I recommend you read the research for yourself.

"When an individual is confronted with a threat, stress systems are activated and elevate the levels of several different stress chemicals that are circulating throughout the body. An increase in one of those chemicals, cortisol (stress hormone), can have a dramatic impact on how memories are processed and stored. The production of cortisol and adrenalin (as well as noradrenaline in the brain) in a normal stress response leads to memory formation for events and places that generate danger. More specifically, elevated cortisol levels (stress) can strengthen the formation of memories of emotional events, block the ability to unlearn fear memories, and enhance the formation of memories of the surrounding context in which the fearful event occurred. Interestingly, too much cortisol (stress) can also have the opposite effect and actually impair memory and learning in non-threatening contexts. Thus, the biological response to stress is intimately involved in both fear learning and unlearning." source

Basically, when a horse is confronted with a situation or stimulus they instinctively respond to as dangerous, their bodies start dumping hormones that allow them to respond effectively to the threat. One of those hormones is the stress hormone (cortisol). Cortisol can both help commit a scene, action, or event to memory (helping the animal learn to stay alive through what's called "fear learning") or an excessive amount of it can actually prevent memory retention and the ability to learn. This excessive level of cortisol can prevent the unlearning of fear reaction to a stimulus (aka desensitizing), or the process of learning anything new at all.

To put this simply, when a horse is presented with something we don't want them to fear (lets say... a blanket) and they go above threshold when we present this stimulus (the blanket), they are far more likely to respond fearfully to the stimulus in the future than they ever were before because their body is designed to work this way to keep them alive. Also, the fear response is likely to get stronger and happen quicker each time they go above threshold for the same stimulus in the future.

On the flip side, lets say you just bought a new horse that already has a terrible fear of blankets and you want to undo this negative association with the blanket, if you only work with the blanket at a level that puts the horse above it's fear threshold it will be almost impossible to undo the fear reaction. The stress hormones being dumped into the horse's system will be blocking "unlearning", preventing successful re-training or desensitizing.

"Fear learning can form emotional memories that are extremely powerful and long lasting.... Behavioral neuroscience research with animals has shown that chronic elevation of cortisol can have a number of detrimental effects, including increased damage to brain cells in areas that support learning, thereby leading to increased impairment in subsequent memory formation." source

In other words, if we work with our horses in a chronic state of fear or stress we are actually causing long term damage to the horses ability to learn new information, retain lessons learned, and to learn how not to be afraid.

"A large and growing body of research, including animal studies as well as recent neuroimaging studies of human adults, has revealed groundbreaking insights into the brain circuitry that underlies how we learn to be afraid and how we come to associate a specific event or experience with negative outcomes. Two extensively studied structures located deep in the brain—the amygdala (which is actually enlarged in the horse's brain) and the hippocampus— are involved in fear conditioning (learning when to be afraid). The amygdala detects whether a stimulus, person, or event is threatening and the hippocampus links the fear response to the context in which the aversive stimulus or threatening event occurred. Studies also show that both the amygdala and the hippocampus play an important role in how the body then responds to this threat. Elevated stress hormones such as cortisol have been shown to affect the growth and performance of the hippocampus and the activity of the amygdala in rodents and nonhuman primates, and early and persistent activation of the stress response system adversely affects brain architecture in these critical regions. Beyond its impact on these two brain structures, heightened stress has also been shown in animals to impair the development of the prefrontal cortex, the brain region that, in humans, is critical for the emergence of executive functions—a cluster of abilities such as making, following, and altering plans; controlling and focusing attention; inhibiting impulsive behaviors; and developing the ability to hold and incorporate new information in decision-making.....Behavioral neuroscience research in animals tells us that the prefrontal cortex is highly sensitive to the detrimental effects of excessive stress exposure and that its developing architecture is vulnerable to the negative effects of chronic fear." source

Further research showing that working with a horse in a state of fear or stress, especially when it's excessive, inhibits and even damages the horse's ability to retain and learn new information. It also effects the horse's ability to stay focused during a training session, and could potentially cause the development of chronic impulsive behaviors . I would have to do further research but this leads me to believe behaviors such as cribbing could be due to chronic stress or damage to the prefrontal cortex from chronic stress.

"The brain region in animals that appears highly vulnerable to adversity in this regard is the prefrontal cortex, which is the critical area for regulating thought, emotions, and actions as well as for keeping information readily accessible during the process of active learning. For example, researchers have found that elevations in brain chemicals like noradrenline, an important neurotransmitter, can impair functions that are controlled by the prefrontal region by altering the activity of neurons in that area of the brain. In a related fashion, humans experiencing chronic stress have been shown to perform poorly on tasks related to prefrontal cortex functioning (such as working memory or shifting attention), and their ability to control their emotions is typically impaired." source

This is explaining how when a horse is in a heightened state of stress or fear that they will be unable to control their emotions, to remain focused on their handler, and activate working memory (desired learned behaviors already taught to them.) Which is really showing why we don't want to ever put them intentionally into a state of fight or flight response. It doesn't help anyone. By the time they have reached a point of such reactivity they become dangerously unpredictable and their emotions/instinct kick into over drive.

I urge you also to keep this all in mind when you consider a horse to be acting in a "disrespectful way". Could your horse actually just be responding in the way it's body was designed and it has no cognitive power to control?

Not all problems that arise from stress and fear are brain related though, stress and fear can be detrimental to other functions in the body such as the immune system and the digestive system too.

"In the early 1980s, psychologist Janice Kiecolt-Glaser, PhD, and immunologist Ronald Glaser, PhD, of the Ohio State University College of Medicine, were intrigued by animal studies that linked stress and infection. From 1982 through 1992, these pioneer researchers studied medical students. Among other things, they found that the students' immunity went down every year under the simple stress of the three-day exam period. Test takers had fewer natural killer cells, which fight tumors and viral infections. They almost stopped producing immunity-boosting gamma interferon and infection-fighting T-cells responded only weakly to test-tube stimulation.

Those findings opened the floodgates of research. By 2004, Suzanne Segerstrom, PhD, of the University of Kentucky, and Gregory Miller, PhD, of the University of British Columbia, had nearly 300 studies on stress and health to review. Their meta-analysis discerned intriguing patterns. Lab studies that stressed people for a few minutes found a burst of one type of "first responder" activity mixed with other signs of weakening. For stress of any significant duration - from a few days to a few months or years, as happens in real life - all aspects of immunity went downhill. Thus long-term or chronic stress, through too much wear and tear, can ravage the immune system." source

"Life-sustaining functions, such as breathing, heartbeat, blood pressure, and body temperature, are regulated through the autonomic nervous system. This complex network of nerves extends from the brain to all the major organs of the body and has two major divisions. The sympathetic nervous system triggers the "fight or flight" response. The parasympathetic nervous system calms the body down after the danger has passed. Both the sympathetic and parasympathetic nervous systems interact with another, less well-known component of the autonomic nervous system — the enteric nervous system, which helps regulate digestion.

The enteric nervous system is sometimes referred to as a "second brain" because it relies on the same types of neurons and neurotransmitters that are found in the central nervous system (brain and spinal cord). After sensing that food has entered the gut, neurons lining the digestive tract signal muscle cells to initiate a series of intestinal contractions that propel the food farther along, breaking it down into nutrients and waste. At the same time, the enteric nervous system uses neurotransmitters such as serotonin to communicate and interact with the central nervous system.

This "brain-gut axis" helps explain why researchers are interested in understanding how psychological or social stress might cause digestive problems. When a person becomes stressed enough to trigger the fight-or-flight response, for example, digestion slows or even stops so that the body can divert all its internal energy to facing a perceived threat. In response to less severe stress, such as public speaking, the digestive process may slow or be temporarily disrupted, causing abdominal pain and other symptoms of functional gastrointestinal disorders. Of course, it can work the other way as well: persistent gastrointestinal problems can heighten anxiety and stress." source

So... What Now?

So here we are after reading all that information and left a little dazed and confused as to how this very simply and directly affects horse training. To put it very directly... The closer a horse is to approaching it's fear threshold the more likely the horse will be to experiencing stress. Once the horse reaches it's fear threshold level it will be experiencing stress, and the stress level will continue to increase the more over threshold the horse goes. Once a horse is experiencing stress it's body will begin preparing to fight or flee and will be producing hormones that inhibit and even damage the horse's ability to learn, increase it's future fear responses, and will be negatively impacting the horse's immunity and digestive health.

So you can see, being very attentive to your horse's mental and emotional state is critical to humane and effective horse training. We should always be striving to create minimal stress with our training to optimize learning and to avoid long term negative impacts on our horses.

Can I Change My Horse's Fear Threshold?

Yes! Absolutely! Whether you realize it or not you've been gradually (and sometimes not so gradually) increasing or decreasing your horse's fear threshold since day one. This type of training is also commonly referred to as "desensitizing", though often people choose to work with a horse that is well over threshold versus the low stress and highly effective way of working with a horse always under threshold. Here it the point where you might ask me "why would anyone choose the higher stress route then though? How do they ever get results?" That is such an excellent question.

I'm going to go into more detail about the various ways of handling fear responses in horses in the next article and how to help your horse be less fearful in an effective and positive way. We will discuss the different forms of desensitizing, how to use them, and how they can positively and/or negatively impact your horse. Until then, watch this video of me you through recognizing when my horse's are under, at, and over threshold and comment your thoughts!

- Adele

#training #science #theory

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