I recently found a new respect for a simple 3-loop serpentine exercise through mine and a few of my students experience. 3-loop serpentine as described in dressage manuals can be ridden in walk, trot and canter. It is 20 m half-circles connected to each other in a continuous bending line. There is only 1-2 straight steps between the loops while changing direction and bend. The challenge is to make it look easy :) This means correct lines, evenly sized loops, very smooth, regular, balanced and round gaits - same tempo, rhythm and frame during changes of bend/direction. This is proof of the horse's suppleness, obedience and throughness. Mistakes would be speeding, stiffening, raising head up, drifting, falling in/out in turns, etc. In trot I use 3-loop serpentine in my warm up to check on my horse's readiness for further more advanced work.
If a ring is shorter than 60 m in length the loops will be smaller in diameter and there will be a short straight line in between. Also, 4-loop serpentine in 60 m ring will have same characteristics. 3-loop serpentine is asymmetrical movement and must be ridden on both reins. 4-loop serpentine is symmetrical and can be used as a fancy way to change direction :)

There are numerous variations a rider can create while riding a 3-loop serpentine. Variations help to improve the qualities we are looking for in the correct execution of the movement. Instead of drilling the serpentine over and over again trying to ride it better it is more efficient and practical to purposefully add changes such as:

• Add a circle on a stiff side. For example, the horse is not changing bend from right to left smoothly and quickly enough. Add a 10 m circle to the left in the middle of the ring between changes of bend
• Make loops uneven in diameter. Make a loop bigger if the horse falls in or smaller is the horse falls out
• Purposefully do not reach the wall one or two meters and make sure you do it throughout the whole exercise not just during one loop.
• Add couple steps of a leg-yield with the purpose of teaching the horse to yield his side and stand up through the ribcage
• Riding all three loops in the same bend is a great suppling exercise that challenges horse's coordination, balance and perception
• Shallow loop is a variation of 3-loop serpentine and a great suppling exercise in all gaits. Adding a small circle in the corners and at the apex adds variety and focuses the horse especially one that wants to rush his trot.
• Transitions over centerline of all sorts - walk-halt, trot-walk, trot-halt, canter-trot, canter-walk, canter-halt, reinback. You can add them to improve your horse's obedience and throughness by teaching your horse not to rush the change of bend, to collect, to respond to half-halt, etc
• Canter offers enormous amount of variations. For example, you can do just one loop in canter and other two in trot as a simplest version. This one offers variations in itself because a canter loop can be any loop, or there can be two canter loops first and last and they both on the same lead. My students love this one because it makes them stay focused and purposeful during transitions. They like schooling trot-canter transitions this way :)
• Advanced versions are canter the whole exercise on the same lead, or change leads through simple lead changes or flying changes

For the rider it is important to stay centered and quiet. There is a lot of multitasking happening during 3-loop serpentine. For example, changing bending aids and at the same time watching the line, balance of your horse and commitment to the bit. During learning process it is advisable to change bending aids one set at a time not all at once. Later it will all blend in one continuous and smooth action.
For example, approaching centerline from the left loop:

1. Change legs positions (new inside right one moves to the girth position, new outside left one moves behind the girth). This action should not disturb any other aids.
2. Then change flexion from left to right without losing contact on either rein or letting the horse drift with the shoulders.
3. The last change is in your seat as new inside leg asks for the ribcage and new inside hind to yield and engage, the seat conforms to it and monitors the change in the horse.

Last but not least, do not forget to tell your horse how awesome he or she is :). Always remember the horse owes you nothing, never take their willingness and effort for granted.

Happy riding...