No one setting is appropriate for all horses; conformational differences between breeds as well as differences in size mean you'll need to adjust carefully. (Always begin your session with the side reins not attached; if you snap them on in the barn, your horse could snag them on something - or, when he takes those first steps off the crossties or out of the stall and feels his head restricted, he could panic.)
Side reins are an effective way to keep your horse's body straight (especially his outside shouilder) while he's working on the circle as you longe him. Or, if he's already straight, side reins adjusted a hole or two shorter on the inside encourage an inside bend on the circle. As a starting point, adjust both reins to the same length. If your horse is stiff on one side, that rein will be very taut; if he's hollow on one side, that rein will be loose. You may have to shorten one side or the other by a hole or two for him to feel the pressure evenly on both sides; if you're not sure about the adjustment, have someone else longe him while you stand back and watch him move. If he's going evenly and straight, he'll carry his tail evenly and his back will look relaxed and round.
Other uses of side reins include working your horse in hand (for upper-level movements such as piaffe) or long-lining, but this is advanced training.
For more on the basics of longeing with side reins, see Lendon Gray's "Create a Good Longe Partner" (Practical Horseman, February 1997) and Holly Hugo-Vidal's "Longe Safely, Longe Well" (Practical Horseman, December 2000). And be sure to end your longeing session by unsnapping the side reins and letting your horse stretch.
Lisa Zinger competes in dressage at FEI level and is an East Coast clinician. She is based in New Jersey.
Updated from Practical Horseman magazine, August 1998.
