sentences:  While a surcingle and side reins are considered classical training tools, the use of the full bitting rig is controversial in some circles.The basic debate is whether the use of the overcheck or any other rein setup other than the classic side rein is unnatural and develops incorrect musculature in the neck, back, and hindquarters.Like any tool, a bitting rig can be overused, leading to soreness and fatigue in the horse, and in some cases, improper use may teach a horse to lean on the bit and develop a hard mouth rather than relaxing and giving to it.