top of page

A Scientific Look at the Physics of Leash Pulling and No-Pull Dog Equipment

Updated: Jan 2

By: Eileen Koval, CDBC, CBCC-KA, CPDT-KA, MSc

Pulling is not just a human problem, and not just a big dog/small owner problem.

No-pull equipment is a generic “catch-all” term to describe a wide assortment of products that reduce pulling by differing means. Who really needs no-pull equipment anyway? Let's take a comprehensive and scientific (not subjective) look at these issues.

Are they good? Bad? Effective? Cruel? Necessary?

The truth is that they are frequently lumped into a single category of tools considered controversial but in fact, they vary significantly in how they function depending on their design. But this should not be a surprise. Most of the controversy is attached specifically to head halters or head collars, but there is ample enough variety in the design and intended (and actual) functions of harnesses to extend the controversy to those as well. Without dogs being able to articulate how they feel as individuals about these tools, we need to take a comprehensive look from the standpoints of physics – more specifically, classical mechanics -- and then evaluate these findings through the lens of animal welfare. These harnesses and head halters are marketed to reduce pulling, but they do so in diverse ways that can affect dog’s health, happiness and well-being. Some are also more effective than others. The important details are with how and where the weight/mass is applied, and where the energy derived from motion (kinetic energy) is directed.

I am a bit of a science geek. In graduate school, I earned a Master’s of Science degree in Operations Management (an industrial engineering field mixed with some business topics) to complement the work I did with the military in planning and executing joint air and missile defense exercises and intelligence work with their associated science, technology, and flight operations. I am by no means a math or physics expert, but definitely interested! I later ended up switching career fields to working in animal behavior, but I did not lose my interest in the physical sciences. Thinking and pondering things leads to better understandings of how the world around us works…and solutions! This is how I began looking into the problem of pulling/lunging dogs and exploring possible safety solutions. As many people know, I had a dog coming off months of medical rest who was wild when we started getting off our property for short leashed walks. Past training went out the window as he lunged at smells, uninterested in any high value rewards. Nothing was remotely of interest compared to the environmental experiences he had largely been denied access over the past several months. A long line leash or off-leash walk was not an option as this dog would have been running, which was not yet allowed in his return-to-sport plan following rehabilitation.

Let’s explore walking harnesses:

There are harnesses that distribute the weight evenly throughout the chest (the center of gravity) and attach to a leash via a clip midway down a dog's back. There are other ones that clip behind the dog's neck. These usually are a great and safe option for owners and dogs if those dogs do not pull. However, they allow the application of weight/mass directly from the dog’s center of gravity (the chest) where a dog can generate the most energy and force, and allows them to apply that forward. As the dog’s body mass increases, so does the amount of kinetic energy -- meaning that a larger dog with more body mass can pull with a lot more force. Most of us know that (although I think a small subset of people are in denial of this).

It is important to note, too, that according to the laws of classical mechanics regarding kinetic energy, a small dog accelerating at high speed can have the same kinetic energy/force as a large dog moving at slower speed. Yes! It is true. Small dogs can hurt people too! There are a LOT of small dogs out there. A large dog who is not pulling hard can topple a person over since they require less velocity to generate large amounts of energy and force.

Kinetic energy (the energy or force generated from when a dog is in motion) = half of an object's mass (1/2*m) multiplied by the velocity squared

In fact, dog walking injuries have increased over the past two decades according to research released in 2023 by John Hopkins University. During the past 20 years, 422,000 Americans were seen in the emergency room due to injuries from walking their leashed dog. The most common injuries were fractures to the fingers, traumatic brain injuries, and shoulder sprains. Women and middle-aged adults were those most commonly seen for injuries. Despite conventional wisdom, injury to owners is not rare, and it is not only a problem with big dogs who lunge on leash and have small or elderly owners. Furthermore, it is not good for dogs’ legs and backs to be straining and lunging on leash either. I have seen plenty of dogs who were hurt over the years from this. Just because something hurts does not mean a dog will necessarily stop. Dogs coming off crate rest from injury or illness are at risk of re-injuring themselves if they get out into the world and are lunging and pulling to get to exciting things. They do not always have a sense of self-preservation if there is something exciting in the environment they want to get to. This is why we see seriously injured agility dogs excited to get to the course and run (don’t let them do this!). This is likely the same with people who also have painful health issues like back or knee injuries. We put on a tough face and meet up with our friends go have fun outdoors on the weekends, knowing that we will pay for it later. We all seek enjoyment in life, and sometimes to our own detriment. Lunging and pulling is NOT good for humans OR dogs and should always be addressed regardless of the size of the dog or human and regardless of the dog or human’s health status. There are serious risks to both parties. Let’s look at another type of safety restraint for comparison. Seat belts are not only for those people who drive big vehicles, or only those travel at high speeds on the interstates. We wear seatbelts any time we get in a car, no matter how fast or what vehicle we drive because there can be injury at both low and high velocities, and there is risk with vehicles regardless of whether they are small or large mass. The risks may vary based on weight and velocity, but there are risks. We do not just tell people to be better drivers to avoid risk. We take safety precautions with equipment. The same should be true with dogs because dogs WILL error in their training, even if it is rare, just as a human will make mistakes on the road that could lead to serious injury to themselves or others. Both physics and recent research shows us that there are significant impacts to BOTH ends of the leash beyond the rare “large, lunging dog and small or elderly owner” that is thrown out there as at high risk of injury.

While they may reduce pressure on the throat, from a physics standpoint they likely will not reduce pulling on their own (without training) unless the dog dislikes the pressure applied to the neck/chest area when they lunge/pull forward forcefully. There are other ones that clip the leash to a martingale loop on the dog's chest to apply torque (rotational movement) to a dog who is pulling so the force generated cannot be as easily applied in a forward motion. While these are helpful and safe for some dogs, they frequently chafe against the body and alter dogs’ natural gaits as the harness pulls to the side in its rotation of the dog. I have even seen dogs with atrophy in their hind leg and shoulder muscles from fighting the torque motion of the tool and more heavily utilizing one side of their body in order to get that forward motion. This is not a good thing!!! In my personal experience, they seem to work more effectively with less negative effects on dogs with deep and wide chests (like brachycephalic breeds that tend to be stocky), whereas the harness may slide more significantly on shallow chested dogs. Frightfully, there are even harnesses that tighten down on the rib cage when a dog pulls. Some do this through a martingale loop located on the back, while other have the ability to endlessly tighten down on the ribs. Yikes! These tightening harnesses stop pulling due to infliction of discomfort to slow the dog’s velocity rather than changing the center of gravity so they cannot as easily apply their body mass to generate kinetic energy. With tightening harnesses, dogs can physically pull, but they may choose not to due to discomfort. Harnesses are not all the same in fit or intended function but yet are lumped into the same category. No harness is “force free”. One of the laws of inertia states that an object that is in motion will stay in motion unless an outside force (such as a harness) stops it. Still, they are NOT all alike.

Let’s take a look at head collars/head halters:

If this diversity of design and intent is true for harnesses, then it should be no surprise that this same also applies to head halters. To the average person, the designs may all look very similar with the colorful fabric and straps that go around the neck and muzzle – just like many harnesses look remarkably similar even if they actually are not. The nitty gritty details of the designs affect how the tool works with (or against) dogs’ natural movements while reducing pulling. Some head halters intend to reduce pulling clearly by using constant aversive pressure on the dog's nose to slow their velocity/movement, and that pressure increases with pulling or lunging, forcing the muzzle and head in a downward motion. Other head halters take the energy from the dog’s motion and direct it into a rotational movement, forcing the dog’s head to turn sharply in a different direction. While this limits the force with which a dog can direct that energy to forward motion, this forced rotation of the head can increase the possibility of whiplash or other neck injuries. Some head halters, sadly, also rely on the addition of physical corrections from the owner.

The head halter I designed (the Gilly Halter, patent pending) goes against these traditional models. Like a normal walking harness, it does not exert any pressure unless a dog pulls. When they do pull, the pressure is distributed evenly across the muzzle instead of across the chest/neck. This is not to create a “physical correction” any more than a harness putting pressure on the chest is intended to create a correction. Rather, by moving the application of weight from the chest to the head we can decrease the ability to utilize body mass to generate kinetic energy. Speed and weight/mass affect how much kinetic energy a dog can generate, but where that energy is distributed matters. The pivot point where weight/mass is applied is moved away from the center of gravity to an area where they cannot direct their weight as easily – the head. Imagine sticking your arm out away from your body and trying to push a 50 lb rock forward with that hand. Now imagine standing with your arms in front of your chest and putting your body weight against that object to push it forward. See the difference?

The center of gravity, one’s mass/weight, and the velocity at which one is moving are all key to creation of kinetic energy and force. Once they are no longer pulling the halter goes back to its normal, loosened position, just like a regular walking harness. Obviously, dogs may (or may not) be bothered by the feeling of a harness pressing against their chest/neck or a strap pressing against the face/muzzle. That is not the intent of a standard Y-shaped harness or of the Gilly Halter. Some dogs hate their harnesses regardless of how we try to get them to like it. Dogs cannot verbally articulate how they are feeling. What is aversive may vary from one dog to another. The Gilly Halter seems to generally be well-accepted – and quickly -- by the vast majority of dogs who try it and have no prior head collar history. I believe this is likely due to the minimalistic and relaxed design, no forceful head turning, and because it allows bending down to sniff and normal movement. So, it likely is not seen as aversive by those wearing it. Still, it is important to remember that regardless of what tool one uses, the individual wearing it is the one who decides whether it is aversive or positive.

Looking Through the Lens of Welfare

I like to judge equipment based on how it affects a dog's Five Freedoms of Animal Welfare. Does it limit their ability to move and behave like a dog would in their environment? Does it cause fear, stress, or discomfort? Is it, in fact, designed with the intent to induce discomfort, pain, or fear? Any restraint equipment comes with some risks and those risks may vary from one dog to another. The same applies to management at home, such as if a dog is crated. There can be risks and impacts to welfare so it should only be done carefully. It is up to owners and their veterinarians to assess those risks and make the best choice of equipment for each dog as an individual but some carry more risks than others when they are forcefully turning a dog's head in different directions, reducing the ability to pant by tightening down on their muzzle, or tightening on a dog's body to cause discomfort and therefore suppress a behavior instead of teaching a new, more desirable behavior. It is important to evaluate tools carefully based on how they functionally work – not whether they are collar, harness, head halter or head collar, etc. How did it perform the intended function? Furthermore, look at how they are perceived by the individual wearing them and whether it helps them to “be a dog” or if it actually limits that. Most of all, do not discount the risk of injury to both ends of the leash if pulling occurs. Both parties may be hurt, and it is a greater risk than is currently acknowledged by and large if we look at the emergency room statistics cited above and the simple laws of motion. I hope that others continue to utilize science to innovate better safety solutions that are less aversive and preserve a dog's ability to "be a dog".


Interested in receiving notification of educational information, new classes, and new articles/posts? Click here to go to our homepage and add your email to our subscriber's list!


Eileen Koval, CDBC, CBCC-KA, CPDT-KA, MSc (in Operations Management) is a fully certified dog behavior consultant with the International Association of Animal Behavior Consultants (IAABC). She believes the foundation of a good cross-species relationship is understanding the needs and normal behavior patterns of each dog as an individual, as he/she was bred to be. She enjoys helping humans and dogs communicate more effectively to create brilliant relationships with joy, purpose, and fulfillment for all species involved. She offers private consulting for serious dog behavior issues, obedience/manners, and agility training. Eileen developed a unique online course to help pet parents and trainers develop reliable snake avoidance behavior off-leash through positive reinforcement techniques. These techniques have been applied by trainers worldwide to teach dogs reliable avoidance of dangerous environmental hazards and off-leash property boundaries. She lives on a small ranch in Las Vegas, Nevada with her husband and their Nederlandse Kooikerhondjes.



Bever, Lindsay. “Dog Walking Injuries May Be More Common Than You Think.” The Washington Post. 01 May 2023.

709 views0 comments

Recent Posts

See All


bottom of page