Learn to ride a circle: how to get a round figure rather than an egg, with aids, bend and orientation in the arena, plus what studies show about circles.
Why do my circles turn into eggs? The honest answer: because horse and rider naturally work unevenly on a circle and you have to plan the shape in your head. The circle is the big round figure in the dressage arena. The arena is 20 metres wide and 60 metres long [1]. A circle across the full width has a diameter of 20 metres. Smaller circles of 6, 8 or 10 metres are called voltes, larger ones stay circles [2].
The horse itself changes on a circle: measurements on 12 horses without a rider showed that back and neck bend inward on the circle, the thoracolumbar spine by about 4 degrees and the neck by about 5 degrees more than on the straight [3]. So bend is partly a result of the shape you ride, not an extra feat of strength. This is a small study without a rider; it says nothing about ideal bend under saddle.
The legs also work unevenly: on circles of 10 and 15 metres the inside forelimb had a longer stance phase than the outside one at walk, trot and canter [4]. At walk the outside hind limb showed a greater range of motion than the inside one [5]. A round circle is therefore harder than it looks.
A 20-metre circle, for example around point X in the middle, touches both long sides and crosses the centre line twice. Those are your four orientation points (practice, not from the study). Plan them before you start. Milestone: You can name the touch points without thinking.
Ride the circle in a calm, even rhythm. According to the FEI the horse should adjust its bend to the line at changes of direction without resistance or change of pace, rhythm or speed [6]. Milestone: The four-beat at the walk stays the same along the whole line.
Flex the inside hand slightly, the inside leg lies at the girth and the outside one contains behind it. Your horse should follow the line, not tip toward the centre. The bend of the spine partly arises from the circle shape by itself [3]; you do not have to force it. Milestone: The horse follows the line without drifting in or out with the shoulder.
A typical mistake is flattening on the long sides. Plan the way to the next touch of the boards before the corner. Your gaze always goes ahead. The circle should have the same curvature at the front and the back, not look like an egg. Milestone: You see the circle shape from above in front of you before you ride it.
Release the aids evenly and ride straight along the line. On a figure of eight you make your horse straight for a moment before changing direction [2]. Milestone: Your horse stays in rhythm when the bend falls away.
The circle does not replace supervised training. As a beginner practise it at the walk and with an instructor. Small circles load unevenly: on the 10-metre circle the stance phase was longest at walk and canter [4]. How strongly small circles load joints and back over the long run, the studies I read do not show. So start with big circles, change hands often and give the horse breaks on the straight. If your horse shows lameness, tension or resistance on one rein, that is a case for the vet and instructor, not for "more circle".
Place four cones at the touch points and ride circles without knocking them over. A round circle becomes visible when your eye "jumps" from cone to cone. This is a training idea from practice; I found no studies on it. Note also that every rider has an individual pelvis motion that hardly changes across horses and exercises [8].
In the dressage arena (20 by 60 metres) the large circle is 20 metres in diameter [1]. Smaller circles of 6 to 10 metres are called voltes [2].
Because the shape demands it: measurements show a bend of the thoracolumbar spine (about 4°) and neck (about 5°) on the circle, even without a rider [3]. You guide it by setting the shape.
A volte has a diameter of 6, 8 or 10 metres, a larger circle is a circle [2]. The volte is harder for balance and bend.
Plan the touch points beforehand, look ahead and keep the rhythm even. Counting and cones help. Have your instructor show you the shape from outside.
Often. Horses are usually better on one rein than the other, and circles load inside and outside unevenly [4]. A fixed time value is pure practice.
Riding a Volte: The Small 10-Metre Circle