The Side Reins are used while lunging. Used with a training surcingle or saddle while lunging, it attaches to the girth with either a snap or girth loop. Reins run up through the bit and hook onto the rings of the surcingle or saddle.
This martingale differs from other training devices because the rider doesn't pull the horse's head into position, but allows the horse to adjust it's head to the position that is set by the ring that the running fork is attached to.
