This is a new one to me! Most horses can be ridden for many hours providing their backs are not damaged in anyway and time has been spent strengthening them. Think of the endurance riders. My only conclusion to this video is that the horse concerned either had an injured back prior to the riding or was a horse that hadn't been ridden for for some time so that it's back muscles had not been built up and strengthened for riding or that the saddle was poorly fitted or not suitable for the horse. I would be interested to know what others think.

Well, of course horses will feel pain in their backs - they are not, after all, made to be ridden. That is an entirely human idea.
Therefore it is essential that the equipment is fitted as well as it can possibly be and that the rider gives the horse plenty of good exercises to build up muscles in it's back since it's the muscles we sit on. When we sit on the unprotected bone, the risk of pain and inflammation increases greatly. There is no surprise in that.
.
Horses *needs* to be ridden in a correct shape, form and tempo to be able to work and develop without getting sore (barring the "good" muscle soreness that comes from correct exercise, of course)or prolonged pain etc.
Riders need to be well balanced and follow the rhythm of the horse without bouncing, sitting crooked, or distribute their weight unevenly.
.
Riding with a saddle, as opposed to bareback, is better because a saddle will distribute the weight much better.
.
A young or untrained horse should not carry a rider for longer than 10-15 min when you start riding it, or it will start getting fatigued and feel pain = not too happy with carrying a rider. Long lining exercises and climbing hills will help it develop muscles.
.
I watched part of the vid. I think it is important to note that the vid is inspired by the Russian trainer Alexander Nevzerov (sp?). He comes from a culture where riding takes little regard to the horse's well-fare and I think he needs to be very blunt in his information to get the message through. What we see in the vid is the really bad examples they show to wake people up. Unfortunately, it works too well some times, when more empathic people are horrified.
.
As pray animals, horses will mask their pain so they won't be targeted by the carnivores, or chased away from the herd. It is our job as their riders/owners to check their backs frequently and make sure they are OK. And have the sense to let them rest when they need it.
That way we will have horses who loves to work under their rider for years to come.

Sounds like an ill fitting saddle to me if the horse is hurting for that small amount of time.

Thanks Kicki for such a thorough explanation -mine was sadly lacking in many respects!

Add on - I am delighted that Cash the ex-race horse I helped quieten last year is now being ridden and that the woman who befriended him is now taking dressage lessons which will hopefully improve her position and balance. However I am fearful that his back muscles have not been strengthened effectively first and that the riding sessions could be a little long for him. Nothing I can do about it but he seems a bit stiff and sore in his paddock lately. As Kicki points out above it is so important to take time to strengthen a horse's back muscles prior to initially riding them and again after any long absence from riding. Short bursts of riding only, walking up and down slopes is good, lots of ground work and pole work etc.

MaggieF, I hope I didn't come across too much as a "know-it-all". That was (is!) never my intention, but I have a frightful problem with keeping things short. (Plus the vid agitated me a bit.)
Good to hear the relationship between Cash and his rider is moving forward. It's great that she is willing to become a better rider. Hopefully her trainer will help her with his back.

No it was fine Kicki - made me realize how lacking my response was so that was all good!

Thanks

for comments sorry i accidentally added the last comment early

on a related note, recently I was reminded of the importance of saddle fit and the need to check the fit over time since it can change. I have been riding my horse for some time with a decent saddle. recently, I noticed a rub mark where there had never been any indications. I thought it was a misplacement of the saddle and was extra careful the next time to be sure. Well the mark was there again. After talking with my trainer, I realized that the saddle no longer fit the horse. Now for the tie in, it was causing the horse to react as if he was going lame! I have retired that saddle, and am letting the horse rest and recover with only ground work for the moment. I have also brought out a new saddle with a higher gullet and more room that I can further adjust. lesson learned, check periodically and start with a proper fit or you will injure your horse.

Correct saddles etc are all fine and dandy. However, if your horse is not trained to "collect" when ridden, to the extent that they eventually naturally do so with a rider then they are going to experience back pain and some trauma. The studies that corroborate this are exhaustive, and, yes, the British Equine Society's studies agree as well.

I have also learnt in recent years that if your horse changes in weight or muscle level during the year it maybe necessary to check your saddle fit a couple of times during the year. Particularly so if your horse has had a past back injury and is prone to back problems.