For many riders the half-halt is elusive even though they understand that if done correctly it will rebalance the horse, increasing engagement of his hind end and readying him for the next move. Your seat during the half-halt must be ready to receive the engagement of the hindquarters and increase of energy created by your legs, otherwise you'll lose your balance and be tempted to hold onto the reins or grab with your legs because the change in balance and energy has left you behind the motion of the horse.
There are many ways to ride a half-halt and many definitions for it. The FEI says: The half-halt is a hardly visible, almost simultaneous coordinated action of the seat, the legs and the hand of the rider, with the object of increasing the the attention and balance of the horse before the execution of several movements or transitions to lesser or higher paces. In shifting slightly more weight onto the horse's quarters, the engagement of the hind legs and the balance on the haunches are facilitated, for the benefit of the lightness of the forehand and the horse's balance as a whole.
This of course says something about the effect but not how to accomplish it and especially not the particulars of that coordinated action of seat, legs and hand.
When asking the horse to rebalance and increase engagement your legs go on to get more engagement and more activity from the hind legs. The half-halt rebalances the horse onto his hind end so you should feel the same amount of power from the hind legs as you would feel from a lengthening but you contain it, both with your seat and with your receiving hands. This energy comes over the horse's back and your seat must be ready to receive--buttocks soft, hip joints ready, pelvis movable and lumbar spine supple and supported by bracing the muscles of the lower torso to receive the energy. This is why the seat is listed first in the definition--prepare with your seat first (and the well trained horse will need little more than this to change his posture and energy).
As your legs close, and your horse responds he can lengthen his stride or become more compact and collected. Either way your seat must be ready and your shoulders elastic so the outside hand,acting independently of what the pelvis or chest are doing, can close to contain and steady the horse, helping to rebalance--and then soften or release to complete the circle of energy. The inside rein retains the flexion and bend to the inside with softness.
Your seat during the half-halt must be ready to receive the engagement of the hindquarters and resulting surge of energy created by your legs, otherwise you'll lose your balance and be tempted to hold onto the reins or grab with your legs because the change in balance and energy has left you behind the motion of the horse. The stiff seat stops the surge at horse's back, and the horse either rushes forward onto the forehand or slows--feeling the clunk in his back as the rider loses balance and stiffens in the back or chest or both. When the rider stiffens and comes behind the motion it's as if the horse hit a brick wall with the energy from his back legs and the circle of aids is interrupted. Your hands, if pulling, will rob you and your horse of the surge from the hind legs. The horse learns to ignore your punishing half-halts.
How do you as a rider prepare for the re-balancing and burst of energy, whether it's for lengthening or collecting or some other change?
First: Your spine and pelvis must oscillate around a neutral position--neither flexed or extended excessively. The horse moves your the sides of your pelvis alternately which impacts your spine and through this movement of your pelvis your lumbar spine will alternately flex and extend around the middle or neutral place. By remaining centered around a neutral spine you never go to the end range of motion and risk damage to soft tissues and disks under the stresses of riding.
Second: You must "catch" the first bounce of the surge or the nervous system will react to it with stiffening up and blocking the surge your horse has so graciously given you. It's like slipping on ice, if you are ready and your spine is stabilized and legs springy you can slide across it with glee--if it catches you off guard you're likely to slip, stiffen up, and perhaps fall. Correct spinal stabilization by bracing the layers of muscles encircling the lower torso will allow you to catch the surge without being caught off guard. This is abdominal bracing--or tummy out! -- not zipping-up or hollowing the abdomen which actually destabilizes the rider. Tummy-out with engaged abs and extensor muscles protects your spine while allowing it to move. Abdominal bracing also allows you to breathe in your lower abdomen, further increasing the well-coordinated and powerful use of your lower torso.
Third: Your hip joints will stay loose and your legs like wet towels when you move with and support your horse's change of balance. After giving the leg aid you let go again and let your hips remain mobile so your legs are springy and ready to absorb the loftier stride you've been given.
Fourth: Your hands are the last part of the half halt and their independence is dependent on your shoulders remaining relaxed. In the momentary closing of seat, legs, and hands your hands close and then soften and give so the horse's front-end isn't blocked. For this your well-coordinated lower torso will support the freedom of movement in your shoulders so your independently acting outside hand can close and then give to receive the horse's power. Your hands should feel like you could juggle a ball as you ride. Stiffened shoulders from a protective response to the horse's surge means the joints of the elbows will lose their elasticity and the hands will lose connection or clunk the horse in the mouth. Your stabilized but mobile pelvis and tummy-out posture will allow your back muscles to remain long, your head to remain balanced on your spine and your shoulders to hang.
Fifth: You'll enjoy the harmony you feel as your horse rebalances and gives you more power, happy to let you--with your receiving seat and giving hands--direct the dance.
I love to help riders move in harmony with the motion of their horse and I love the response of the horse as he is more comfortable and better able to give the rider the best performance. Contact me for clinics or video lessons utilizing the Feldenkrais work, Centered Riding, and total fitness training to teach all riders to ride in harmony. Video lessons are a great alternative to a clinic--you'll receive a program of awareness lessons and movement/fitness exercises to empower you to improve your riding. Visit SitTheTrot.com and Email me.