Of sagging backs and tickling tummies
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Way back when I started this blog I wrote a couple of posts about a study (1) done where they showed that a horse's back sags under the weight of the rider, not only standing still but at all gaits. I want to revisit that idea with an update of another couple studies and some other ideas that are commonly taught.
Studies done on ridden versus weighted horses
The study was very clear in its findings - dead weight causes the horse's back to sag, but it didn't affect the overall range of motion of the back. The back still flexed and extended the same amount, but it was moving around a more extended (hollowed) average. But is this the whole story? Is carrying lead weight the same thing as carrying a rider who is asking a horse to move differently than he does on his own?
The authors of this study said "we feel confident than the 'saddle with weight' condition sufficiently simulated a saddle with rider." They based this on a couple of other studies. In one study (2), which checked the amount of force on each leg of a horse going over a force-plate (a device built to measure such forces when a foot lands on it), they did find a slight shift of weight to the hind limbs compared to the front limbs when ridden as opposed to carrying dead weight. Their interpretation was that the rider could cause the horse to transfer more weight to the hind end. However, they also tested an experienced rider and an inexperienced rider on the same horses - 13 of them - and found no real differences in how the horses moved with the two different riders. Since I have problems seeing all 13 horses collecting just as well for the inexperienced rider as for the experienced rider, I wonder if it had more to do with where the weight distribution on the saddle really was between riders and the sand bags. They did suggest that more work should be done with more specific testing, but since that study was done in 1991, and it was quoted in the 2004 paper, I don't think it has ever been followed up. (I found a 2009 study that confirms the extended/sagged back under the rider and talked about it here.)
The other study (3), on which the authors of this study based their statement that weight and riding were similar, looked at riders on horses versus dead weight on horses working on a treadmill. In that study they didn't find any statistically significant differences between the two, though there were differences between these situations and the unloaded horse. However, they were only looking at angles of the lower limbs. With weight, there was more extension of the fetlocks, and that makes perfect sense when you think about it logically. But they weren't checking back conformation. So while the researchers in the main study felt this was good enough information to say that dead weight and riders have the same effect on the horse, they haven't proven that a rider doesn't affect back shape compared to dead weight.
"Fit saddles only after doing a belly lift"
On the other hand, if you read information on the internet or in the best selling book on saddle fit, you will learn that you are supposed to get your horse to do a "belly lift" before measuring his back so will "imitate its potential movement during exercise". Then you are to get a saddle to fit that shape. (4) A "belly lift" entails stimulating the horse's belly, getting him to contract his stomach muscles and thus lift the center of his back. It works. A horse will definitely raise his back if you do this (unless his muscles are so damaged he can't any longer), the same way you change shape if someone pokes you in the belly. But is this the shape of the horse's back under saddle? This author (and others) state that it is but they don't back up their statements with any experimental data. It is strictly their opinion that this is what happens. Yet this idea is regarded as "fact" in certain segments of the equine industry.
Why this is important anyway?
Because as tree makers, we are trying to fit the shape of the horse's back, and if the shape changes between what it is when the horse is standing there when we put a tree on and when the horse is being ridden, then what shape are we really aiming to fit? Is it the standing horse? A back with a slight sag compared to when he is just standing there? Or a back shape taken with a belly lift happening? With the conflicting information I have stated above, how do we really know?
Some principles to consider
As far as the back rounding up under a rider asking him to collect: If this happens (and I wish someone would do a study that would really confirm or deny that it can or not!), then the thing to remember is that the horse's back with a rider on it is not starting at the same place as an unweighted horse is. His back is sagged under your weight when you mount. Then, if you ask him to lift, how much can he do? Can his back even get back to the same level it was before you mounted? Or might he actually be able to raise it higher than that? And, most importantly, what is the shape of the lifted back under weight - the sagged and then lifted back. We don't have answers to any of these questions.
What percentage of time is a horse's back "rounded up"? Even dressage riders who ask for constant collection while doing their patterns have relatively long warm up and cool down periods where they don't ask their horses to collect. What about the working cowboy who has his horse very collected at times to do the work he needs to do? How much of his riding time is in that frame, and how much time is he far more extended, either getting out to where the work is, or going hard after a cow who doesn't like the idea of getting doctored?
And what percentage of riders have their horses in any stage of collection at all, really? Not a lot. Those horses will be "sagged" for sure. So who are you building for?
Saddle and tree makers don't agree
If you talk to tree and saddle makers and ask them the question, "If you had to have a little too much or a little too little rock in the bars, which would you choose?" you will get both answers. (The key here is "a little". Everyone agrees that too much the wrong way is a bad thing. It is the subtle differences we are discussing here.) This tells me that a little too much either direction doesn't hurt the horse because if it did, everyone would answer the question the same way. The horses would tell us which way was wrong if one was. We know there is a lot of change in the amount of rock in each side of the back during the different phases of every stride at every gait, so trees on both sides of this question will fit the rock really well at some point in the stride. But which one fits well for a higher percentage of the time? We don't know.
So what's a treemaker to do?
Rod has always felt that a little too much rock is better than a little too little. The thinking behind this is that with a little too much rock, the back of the tree will lift up a bit from the horse, but the majority of the bar will still be on the back to distribute the weight. With too little rock, the center of the tree won't carry weight and the chances of Poking in on the ends is greater, depending on horse conformation and tree design. After reading the studies, we are still happy with falling on this side of the question because having a little too much rock will fit a sagged back better anyway.
But do we plan on adding rock compared to the horse's standing back? Nope. We fit the standing back. Why? Because we don't have the full academic information to know how to build them differently, and because we know what we currently do (and have done for 16 years now) works! We have lots of testimonials to that effect. So... if it ain't broke, don't fix it!!
(1) Effects of girth, saddle and weight on movements of the horse. de Cocq, P., van Weeren, P.R., Back, W., (2004) Equine Veterinary Journal #36 (8) pg 758-763.
(2) Ground reaction force analysis of horses ridden at the walk and the trot. Schamhardt, H.C., Merkens, H.W. and vac Osch, G.J.V.M, (1991) in Equine Exercise Physiology, Eds: S.G.B.Persson, A. Lindholm and L.B. Jeffcott, ICEEP Publications, Davis, California. pg. 120-127
(3) Effects of weight and riding on workload and locomotion during treadmill exercise. Sloet van Oldruitenborgh-Oosterbaan, M.M., Barneveld, A., Schamhardt, H.C. (1995) Equine Veterinary Journal Supplement #18, pg. 413-417
(4) The western horse's pain-free back and saddle-fit book. Harman, Joyce, (2008) pg 170.