The position adopted by a player on a horse is of utmost importance, as we shall see. The weight of a “;;;;;stationary” horse is distributed between its front and back limbs: 60% of weight is placed on its front legs, while the other 40% is placed on its back legs.
In this manner the horse is balanced; the 20% weight difference is down to the weight of the horse’s head and neck on the front legs. The position adopted by a rider will therefore constantly alter this distribution of weight.
The weight varies greatly, but the balance does not - the closer we get to the horse’s point of equilibrium the more stable the horse will become. The half seat position, in its different forms, is the position that most favours the horse’s balance.
A clear example of this occurs when a jockey races a thoroughbred; here, moving forward favours the horse’s natural movement. In polo, the stirrups are placed in line with the horse’s central point of gravity, or balance; simply placing our weight towards the stirrups favours the horse’s balance and comfort.
With the horse in play, we can aid its movements with a half seat position; if we check, we gain support from the stirrups and by gripping the knees, thus favouring action from the horse’s back legs. The position of the horse’s head and neck will also be a comfortable one.
A bad distribution of weight by the player on the horse will force the player to look for support in the bridle. This will make the horse rigid and jumpy, and prone to shake its head. A good riding position will achieve the correct balance necessary for the horse to perform to its greatest ability.