|FRAME ONE: This is the 1st hoofbeat (bold black outline of legs) of the stride, with the outside hind landing out of suspension.||FRAME TWO: Hoofbeat Two is the nearly simultaneous landing of the inside hind-outside fore diagonal pair (RH-LF for right canter). The horse is midway through pulling himself forward on three stance phase (grounded) legs.|
|FRAME THREE: Balance on Right Hind - Left Fore diagonal pair.||FRAME FOUR: Hoofbeat Three is the landing of the inside foreleg (RF for right canter). This is the other time of the canter when three legs are grounded. The horse begins the rock forward and its viscera push against the diaphragm and lungs, assisting the exhalation of air.|
|FRAME FIVE: Preparation for take-off into suspension. This is also a critical moment for giving the aid for flying changes. Three legs are in swing phase and can be repositioned for the next lead.||FRAME SIX: Suspension or Time Four of the canter, where all four legs are off the ground. The canter has three hoofbeats plus the "silent" time which must be counted in the tempo of the stride.|
Summary of color code: darker colors show a higher relative degree of contraction. Muscles are:
BLUE shades = serratus (ventral and cervical) or hamstring group
PINK shades = latissimus dorsi (forelimbs) and medial gluteal (hindlimbs)
GREEN shades = brachiocephalicus (point of shoulder to top of neck) and tensor fascia latae (hindquarters)
This animation shows clearly the importance of the relationship among the ribcage, front legs and base of the neck. A crucial link among these body parts is provided by the serratus muscle. The serratus is a huge fan-shaped muscular connection between ribcage and the base of the neck. Note that the dark blue wave of contraction in the serratus moves in the OPPOSITE direction from the front leg. As an example of torque, or force that acts through an angle of rotation. It parallels the physics of helicopters (for example), where the force is applied in the opposite direction from the motion. The serratus muscle has a dual role. When sleeping standing up, the horse uses it as part of its "sleep locks" or stay apparatus.
IMPORTANCE OF KNOWING MUSCLE LOCATIONS & ACTIONS TO THE RIDER:
1) A saddle should be set so that its front edge does not interefere with the cartilage cap at the top of the shoulder blade. The saddle should be checked frequently to make sure it does not have any shape that interferes with the horse's back. To check this, walk the horse unsaddled while you place a hand at the top of its shoulder. You will feel the top of the scapula move as the leg goes through its cycle.
2) You are sitting on the union of 'lats' and 'glutes' when the saddle is accurately placed. Each gait has a unique pattern (repeated sequence) of contractions and relaxations of the whole back. If your seat is relaxed, your pelvis will lift and fall gently with each back cycle in a gait. Riding with your pelvis slightly angled across the horse's back (inside leg about 4" ahead of the outside leg) allows your seat movements to passively match those of the horse. As you learn these gait-specific sequences, you can learn to enhance the horse's movement without interfering.
3) Your lower leg can reach parts of the serratus. This allows you to influence a series of muscles directly connected to the tongue via the HYOID APPARATUS.
4) A biomechanically effective seat is one where a rider's RELAXED seat matches motions of appropriate motions of the horse's whole back while maintaining a receiving elastic connection with the reins.