Borzoi breeders have been long time advocates of extensive, purposeful free running in order for young Borzoi to develop properly. By purposeful I don't mean forced running, I simply mean that for most sighthounds they will not self exercise if let out alone and they need to be out with their humans hiking/going somewhere or have other dogs to run with.
Dogs that have access to extensive free running develop differently. Again, there is a lack of research in dogs so I've never seen a formal study but I've talked to a lot of breeders and I've seen the difference in my own dogs. Sighthounds that get to free run are broader, have better rib during and general breadth.
In the picture below, left is Ash the Saluki at 8 months. I brought him home at 7 months. He came to me having had access to a modest yard, but limited reason to stretch out and run. He also had been severely malnourished as a young puppy and was suffering from intractable giardia when I brought him home. Still, he has some muscle tone in the picture. I was in an apartment when I added him and for awhile I was very diligent about finding fenced yards to run in. However, my health took a bad turn the year I brought Ash home, which eventually limited how often I could drive him to run and he had essentially no recall, so hiking off leash was an impossibility. Accordingly you can see how weedy and leggy he looks (even for a pediatric neuter which makes a dog more leggy than they would have been if they stayed intact through maturity).
Contrast that to Birdie at 8 months on the right. Birdie had been off leash hiking from five weeks old all the way through her puppyhood and adolescence. She grew up with other sighthounds to run and play with and push her in good ways. There is a clear difference in muscle ton, chest development, and overall breadth.
Is it essential that your pet dog develop to the absolute best of their potential? No necessarily. Just like a child who focuses on painting does not use their body in the same way that a child playing elite level soccer, a dog going on leashed walks and occasional hikes does not use their body in the same manner that a dog competing in elite level sports does. However, I will always support developing our dogs to the best of their abilities so they can be sound and well-rounded individuals and free running with other dogs of similar speed helps all dogs with coordination, versatility, and mental fortitude.
Let's discuss each of the benefits of lots of access to free running in young dogs. First, coordination. The below video attached is side by side of my two male Azawakh- Anubi top and Tabiri bottom. Anubi in that video was just under four years old, was #13 LGRA All Breed last year, his fastest FCAT speed was 31mph (in a breed that is not supposed to be quick off the line), and while certifying a Greyhound in lure coursing the judge came off the field very impressed by his speed. He's a very seasoned running dog and is hands down the fastest Azawakh I've ever met. Note how he coordinates his legs in an efficient fashion to maximize his speed.
On the bottom is Tabiri at 3.5 year old. He degloved himself on a fence and thanks to a fantastic surgeon is extremely lucky to be alive. He was a house pet the first 3+ years of his life and while he ran in the back yard had never had reason to stretch out and he'd never seen the lure before a month before that video. He was also a few pounds overweight still and out of condition. His gallop has smoothed out as he gained confidence and condition but he will always be a bit stiff and never have the coordination of my dogs that grew up with lots of room and competition to free run. In the video you can see why I wanted to do OFAs to insure his accident hadn't don't lasting orthopedic damage. I have had a rehab vet go over him and we suspect he does have a fused vertebra at his anticline (where the vertebra change directions and the spine "hinges" creating flexibility and extension). This happens often after trauma as a way to protect the body and Tabiri's largest scar is across his spine right over the anticline.
Notice the difference in both extension and limb coordination between Anubi and Tabiri. Anubi has good extension. This extension is less than you will see in Whippets and Greyhounds, largely because a shorter back and less up/down spinal flexibility, but Anubi still has good extension for the breed. Whereas, Tabiri lacks the level of extension that Anubi is able to reach.
This is due to Tabiri's inury yes, but it is also a difference in upbringing and experience.
Coordination can and should certainly be improved through practice. The below picture is exactly one year after the above picture and video.
Notice while he will never have the extension that Anubi has, his extension has notably improved both by practice and better conditioning. His head is down and he's driving hard with his rear.
So you can really get a feel for the difference in running form (and really just overall daily coordination), here are some images of my dogs that learn how to run hard, young.
The general themes? Head down, powering with the rear, the more experience the dog in these pictures, the better the extension. I did include a picture of Birdie at 3 months and Azhidar at 7 months as well as a couple pictures of Amalu and Birdie as young adults with still developing form, but even in those, the trends are still clear. Even in the picture where Anubi has lifted his head to check the lure, look at the extension.
Contrast that to my dogs who did not grow up competitively. I do want to note that Ash and Tabiri have been ranked nationally in various running organizations before, so they are not bad running dogs, but they do lack the advantage exposure young, brings.
The pictures above are organized into three sets- Ash, Tabiri, and Gem. They are posted in chronological order and you can start to see an evolution of running style in all three dogs. Now, I will say I could cherry-pick images of my other dogs caught at a bad point in their stride and find similar looking images. But what I want you to take away is that I have substantially more images of the other dogs fully extended, head down, and digging than I do of the three that came to competitive running (and free running conditioning) as adults.
There are a number of schools of thought of how to prepare young sighthounds for competitive running. That is a whole blog post (or series of blog posts) that I wont' get into at this moment. However, I believe the in order to have dogs that can run in all weather conditions and a wide variety of terrains and surfaces, it is absolutely vital for those dogs to experience all of those conditions before they are exposed to them in competition.
I have spoken to a number of people who hunt their sighthoudns who have testified that the only way for a sighthound to learn how to thread through derelict barbed wire at speed is to learn how to do so at a young age. And while I've never dealt with this directly, the few patches of derelict barbed wire I've seen at open field coursing make me nervous, because they aren't obstacles my dogs are used to though they have been exposed to all manner of terrain.
All of my dogs get extensive exposure to hiking in all weather and all manner of surfaces and terrains. From a young age they hike and run on sand, gravel, rocks, dirt, grass, mud, sand, snow and really anything I can find. We go out in all weather from downpours to high temperatures to fog to snow and temperatures well below freezing. We tackle flat ground, soft rolling hills, true elevation gain, and broken terrain. I let my puppies set their own pace, but also encourage them to tackle all obstacles as long as they are within their abilities.
The result? I feel comfortable running even my young, green dogs in all manner of weather and footing. Birdie debuted in LGRA and certified in ASFA in pouring rain. Azhidar ran his first coursing ability tests (to get him used to turns) in high temperatures (of course the the aid of lots of cooling aids). I have run my dogs on soft turf, harsh dirt, broken sage brush flats, and more. And my dogs are sound and comfortable tackling those challenges.
I do think the assertion that it is important to habituate your sighthounds to very varied terrain is going to be a potentially controversial statement. There are three main objections I can think of.
Some breeds simply aren't safe to run in some conditions. I absolutely concur. Truly, one of the reasons that I have Azawakh (and even the Saluki) over other breeds like Greyhounds or Whippets is because they are running sighthounds that keep their safety in mind, even while in drive. They won't take a turn on difficult terrain at full speed because they will weight the risk to their body and instead slow and tackle that turn at a more reasonable speed. That being said, I have scratched dogs because of dangerous course and dangerous terrain and will again and I will always acknowledge different breeds have different running styles for a reason and some breeds have more risks with some terrain than others. That being said, I have had the honor of running alongside Whippets and Greyhounds in challenging terrain and challenging weather and those individuals who are able to run in those circumstances are always those dogs that have practiced running hard noncompetitively on hard terrain. Practice can make all the difference.
But their growth plates aren't closed! This argument is a huge one because it has been pushed heavily in the pet dog sector, again for good reason. I absolutely have seen puppies walked too hard, too long, too young. And even if it doesn't have lasting physical damage, it can begin to make exercise aversive for a dog mentally. However, this obsession with "five minutes of exercise a day per months old" is...absurd to me, to use the most polite term I can bear. I grew up playing national level Volleyball (I attended nationals twice) and state level Soccer (my team finished second my senior year). I played hard, ran hard, and you can bet my exercise wasn't restricted. Yet, for some reason instead of focusing on building strong muscle that can help developing bones, pet owners are being encouraged to bubble wrap their puppies so they never learn how to use their bodies. All my puppies that I have allowed to run hard as young dogs have passing hips (3 Excellent, 1 Good) and passing elbows. This is a really nice article on exercise in young dogs.
My sighthound can't be off leash. I'm not going to tackle this here. I just don't have the time or patience. Instead I'll link my post about sighthounds off leash. Just remember, sighthounds have been used to hunt off leash for literally thousands of years and in my experience it is far more aversive for a sighthound to live on leash than to utilize low level e-collar to give them freedom.
Lastly in the benefit of free running to all dogs, whether the be athlete or couch potato- mental fortitude. There are a lot of things that running with other dogs teaches young dogs. It teaches body awareness and how to get out of the way. It teaches grit and the willingness to keep running with a dog even when they're being pushed. It teaches them when a situation is too difficult and they need to back off and take a different tact. Or to plop their butt down and rest. It is absolutely possible for adults to push young dogs too hard and that is something to keep in mind, but I have also found if you have adults that are good at knowing their limits, that is wisdom they can impart to young packmates. Essentially, I hate managing play and I want my young dogs to learn their limits early.
So what if you didn't start running your dog young? What if they had to grow up on leash or without a playmate that challenged them to be their best, for whatever reason. It's really not too late. Yes, structurally your dog will still have a different build than if they had more access to free running. But I'm truly impressed with the changes that conditioning an adult dog can bring.
The top picture is Ash at 8 months. He had access to moderate on leash hiking, but ultimately my health and abilities were limited and it shows in his physique.
Middle picture is Ash on his third birthday. He is fully an adult and has decent muscle tone and better chest depth that comes with maturity. He was hiking on leash regularly and in decent shape. He had not yet started lure coursing or racing.
The last picture is Ash just before his sixth birthday. At this point he had extensive access to free running and he was running extensively competitively. Notice his topline has firmed, his chest has filled out. He is still narrow, but there's more breadth and depth to him in general.
The second set of images is a less stark difference (partially because white dogs are really hard to see muscle tone). The left picture is again taken on Ash's third birthday. The right was taken the same day as the above picture slightly before his sixth birthday. Again, look at the difference in his topline and muscle. There is a noticeable difference and it is entirely due to more access to free running.
If all you have access to is leash walking or a small yard, if you don't have the recall to hike off leash, then do what you can. This isn't meant to make you feel bad. But there are many reasons why I prioritize off leash running for my dogs (not even including enrichment which I hardly touch on in this post). This is why I start my puppies on baby hikes before they leave. This is why I truly believe, apart from a major collision due to equipment failure that would have crippled any dog, my dogs have been sound when participating in running sports.