The Up And Down Of It – Shoulder Angle/Humerus Bone – Part 2

In part one I talked about the difference between shoulder slope and shoulder angle.  The important parts to remember are;

  • We want the horse’s shoulder slope to largely land between 45-55 degrees, the lower end for a Dressage horse and the upper end for a jumper, outside that range at either end is doable but comes with potential issues
  •  Anything less than 90 degrees is a closed shoulder angle and significantly affects potential stride length, and for most horses it should be a deal breaker
  •  A horse standing with its front legs too far under its body or too far out in front of its body will artificially change the shoulder angle

The above addresses the swing potential of the front leg, but there’s something else in the front end that determines all the rest, specifically the style of the horse’s movement; daisy cutter or high knee action and everything in between.  Even the horse’s front end lateral movement comes from this: the length and orientation to the horizon of the humerus bone.   The humerus is attached to the scapula at the point of shoulder by a ball and socket joint giving the humerus bone forward and back motion as well as side to side motion.  At the other end the humerus joins the radius-ulna (forearm) bone creating the elbow joint.


Here are the basic rules about the humerus bone:

  • The longer the humerus bone the more scope to the horse’s movement, forward and back as well as laterally – a long humerus bone must be at least 50% the length of the scapula
  • The shorter the humerus bone the more choppy the horse’s movement – a short humerus bone would be less than 50% the length of the scapula
  • The steeper (vertical) the humerus bone the higher the horse can lift its knees (think knees to ears in the jumping horse)
  • The more horizontal the humerus bone the less natural ability the horse has to lift its knees to create high action or fold it’s knee (think daisy cutter and a horse that hangs its knees over jumps)

(Note: The humerus bone along with the shoulder angle determines a short, choppy stride, not a short or upright pastern as is so often claimed.)

Gaited horses that are prized for their high knee action would thusly possess a long humerus bone orientated more vertically and likely also possess a quite open shoulder angle, well exceeding 90 degrees.  This would be the same for a Jumper that could put his knees to his ears with the exception of the placement of his knees being lower by having a shorter cannon bone; a requirement to stay sound from repeated landing concussion.

The Dressage horse will also possess a long humerus bone, but less vertical compared to the gaited or jumping horse and in most cases not as open a shoulder angle, but certainly still maintaining the minimum 90 degrees.  The shoulder slope of the Dressage horse will tend to be more laid back than the jumper.

The Hunter horse with a long, sweeping, and low daisy cutting action will also have a long humerus bone, but it will lie more horizontal limiting the ability of the knee to be raised.

The stilted front end gait of many Western horses is due to a closed shoulder angle and/or a shorter humerus bone set horizontally.

Horse #1 – QH Stallion


Our QH stallion has very good length to his humerus bone at approximately 64%.  This trait helps to minimize the effects of his slightly closed shoulder angle.  The humerus more on a horizontal orientation giving flat movement.


Horse #2 – QH Gelding


This QH gelding also has very good length to his humerus bone at about the same 64%.  Its orientation is identical to our stallion, except that we know this horse is not standing with his front legs properly underneath himself.  If he was, then his humerus would be a bit more vertical than our first horse.  However, paired with a slightly more laid back shoulder (and the same closed shoulder angle) these two horses should move in the same general manner with their front legs.


Horse #3 – 4yr old QH


This horse has the longest humerus bone of the group at 67%.  He also has the most vertical orientation of the lot and with the most open shoulder angle.  Coupled with his upright shoulder and surprisingly this horse has the potential to bring his knees up the most and fold his lower leg the tightest of this group, as well to have very good scope and potential for lateral movement.   Though he should have more expression to his gait than the first two QH’s, I’d bet my own money (again) that he moves in a typical QH fashion, flat and short.  I’ll talk about why in a future article.


Horse #4 – Arabian Stallion


Another long humerus bone at 60%, with a vertical orientation between that of the QH stallion and the grey QH, paired with an all-around shoulder slope of 50 degrees and adequate shoulder angle gives this horse middle of the road action (neither daisy cutter nor hackney) and scope.


Horse #5 – TB Gelding


We’ve won the lottery as here is another horse that still maintains a long humerus at 59%.  The orientation is identical to our Arabian, but with the more upright shoulder we should expect our TB to be able to lift the knee a bit higher, but the lower leg no tighter due to shoulder angle and humerus bones length being very much alike.  Both horses should possess similar scope and lateral potential.


Horse #6 – Paint Mare


Our Paint mare has the shortest humerus of the group at approximately 55.5%, which still makes it long enough but she will have the least scope and lateral movement of all of our horses.  Unfortunately it’s also the most horizontally placed on a quite upright shoulder.  Still she manages to keep a minimum 90 degree shoulder angle.

While it’s a desirable trait to have a long shoulder, this horse has too much shoulder length placing the point of shoulder too low.  This low placement puts a horse more over its shoulder and onto its front end.  Horses of this construction tend to be forever pigeon-breasted.  She’s a contradiction.  The upright shoulder says she can bring the knee up, but the horizontal humerus says she can’t.  The humerus bone wins every time and so a horse constructed like this will lead with its chest when it jumps and hang its knees all day long, every day.