Achieving a balanced, supple position on your horse will make you a more effective rider.
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Maintaining a well balanced position allows you to ride without gripping too tightly or using great strength. This ability allows you to use your legs, arms and hands more effectively and therefore being able to transmit your aids clearly. Consistent balance, solidly on the seat bones, should be easily held in walk, trot, and canter with or without stirrups.   
The rider's position in the saddle affects your riding ability. Sitting equally on the seat bones without tucking the pelvis in or arching your back will develop into a neutral alignment of your spine, allowing your joints and muscles to be in the most efficient position to contract and relax. Personal exercise off the horse is the key to improve your posture and core strength, this will the help you maintain a good shape without any tension in your body. 

Jane dressage dixon
Your legs, seat and hands should all be in harmony with the horse's movement. Being able to feel the horse without any rigidity in you or your horse will help your working partnership. Lacks of harmony produces an inconsistent seat, leg and rein contacts therefore confusing the horse. Physical flexibility and supple joints will help you achieve this, so again personal fitness is recommended.
Combined good balance, harmony and keeping a consistent lower leg position will all improve your security in the saddle. Toned muscles and general fitness will allow you to hold a good position and will help you maintain a secure seat along with an even rein contact.
Watch and listen to your horse, appreciate the horse's natural instincts and learn to understand the horse's reactions to different situations. A horse may see or hear things that we can not, understand messages your horse is telling you through their body language such as a shortening stride, flicking ears, nostril flaring or whinnying. 
Being in tune with your horse will help both the rider and the horse enjoy the task with confidence. 
Practical experience gained from riding different horses in different activities will develop feel and it takes time. The beginning is being able to know which diagonal in trot you are on and recognising the canter lead leg. A natural instinctive 'feel' to the horse's movement and mind will develop the harmony and partnership.
Language is not the only communicative tool; the messages received through the rider's aids are the direct link for the horse. Achieve independent use of the seat and legs and co-ordinate the hands to hold the horse within those aids. Always remember that is something goes wrong or the horse does not respond immediately it is probably your fault not the horses. Clear exact communication will help in developing you as arider and the training of the horse. The voice is a powerful tool, it can convey praise and encouragement and also nervousness or anger, use it wisely.
Progressive exercises in training your horse and competition will demand a higher level of personal fitness in order to maintain your ability and sharpness of mind. 
A good posture, balance, strength and stamina help your security in the saddle and eliminate bad habits forming such as rounded shoulders, leaning forward and hanging onto the reins and horses mouth. Take your fitness as seriously as your horses to achieve your full potential. Read more riding tips and exercises
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