A point to ponder - top line vs bottom line

[JLav]

Ok I see what your saying however to me if the horse hollows/raises its head/comes above the bit, call it what you will, he can only do this by contracting the muscles above the vertebrae and so wouldn't this action cause them to become stronger and more developed? How else can the horse carry his head too high/inverted without using and therefore developing them? The rider is not holding the head up with the bit. If the inverting has occured because the horse is fighting the bit then the action of the bit is downwards so surely the horse uses the topline muscles to lift the head higher to resist the bits action. Would not the opposing muscles on the underside tend to be stretched rather than contracted at this point. If the muscles on the underside of the neck were also to contract then surely if they became over developed and therefore stronger they would over-ride the action of the top muscles and the horses head would lower, wouldn't it?
Does what I'm saying make sense?

This is just the genuine interest of someone with a functional rather than professional knowledge of anatomy and biomechanics as it relates to training and particularly dressage.

 

[puddicat]

Yes I'm interested in it from a training angle too - here is what I think but feel free to disagree.


...if the horse hollows/raises its head/comes above the bit, call it what you will, he can only do this by contracting the muscles above the vertebrae...

yes definitely


...and so wouldn't this action cause them to become stronger and more developed? How else can the horse carry his head too high/inverted without using and therefore developing them?

No not necessarily there are 3 main factors involved in developing muscle size (1) the length of time/number of times the muscle used (2) whether is it shortening, staying the same length or lengthening (3) the amount of force being produced by the muscle. (This is the same for humans, if you want to get big muscles you work against heavy weights, lots of times). So argument goes like this. If the horse is in an outline, the top line muscles are working constantly at reasonably high force to support the neck. With a high head carriage the top line muscles work hard to get the head above the bit but don't need to generate much force to keep it there (ladder analogy) so the time spent using the muscles at high force is low. Muscles develop to the size required to do the work that's asked of them so certainly they won't atrophy because as you say some force is required to keep the head above the bit. The point is the force isn't enough to develop what we'd think of as a top line. "you can lift a tin of beans for as long and as often as you like but you're muscles won't develop past the size needed to lift a tin of beans".


The rider is not holding the head up with the bit.

Agreed. I was really just pointing out that when the horse (with head in the air) pulls, the force exceeds the force that would be required to keep the neck in that position so the top line muscles could potentially relax. So the horse could support its head carriage by leaning on the bit. Again, because of leverage the rein force required is less that one might imagine.


If the inverting has occured because the horse is fighting the bit then the action of the bit is downwards so surely the horse uses the topline muscles to lift the head higher to resist the bits action.

Ahhhh no although I agree that's what common sense suggests. This is where it gets complicated but I think its fascinating and relevant so here goes. Take the scenario where the horse sticks its head in the air and the rider drops their hands so the bit action is down and back. If we ignore the aiding effect (ie that resulting from sensory input) of this action and just concentrate on the mechanical effect - the mechanical effect, paradoxically, is to keep the head in the air or raise it, not lower it. So you aren't working against top line muscles, you are working with them! The reason is that even though your hands are lowered they are still above the height of the vertebra at the base of the neck so the rein is acting like a muscle above the neck vertebrae (even though it goes below the front few vertebrae). This is unintuitive because the rider sees the rein coming downwards from the mouth and naturally assumes that means pulling downwards will force the head down. But if you think about it, the top line muscles pull downwards to get the head in the air because the neck slopes upwards from the whithers!


Would not the opposing muscles on the underside tend to be stretched rather than contracted at this point.

Certainly they would be stretched ie they would be longer than their resting length, but they wouldn't be relaxed, they would still be contracting. The punchline of the explanation above is to say that the hands and the top line muscles work against the bottom line muscles so if you pull, regardless of direction, the top line muslces can relax a bit and the bottom line muscles need to do more work!


If the muscles on the underside of the neck were also to contract then surely if they became over developed and therefore stronger they would over-ride the action of the top muscles and the horses head would lower, wouldn't it?

Not necessarily it comes back to leverage and the significance of the arch-shape of vertebrae. The muscles above the vertebrae have a mechanical advantage so the muscles below have to be relatively bigger to balance the force produced by muscles above the vertebrae. The rein has an even bigger mechanical advantage so what you might consider to be not a particularly strong puller still needs a lot of bottom line muscle.