Neutral Spine is Ideal
Throughout our daily life, a neutral spine and pelvis is the optimum position to operate in, so it makes sense to strengthen the muscles and perform the exercises with a neutral spine. Most people are not strong enough in their abdominals to hold a neutral spine position when performing the more advanced Supine Abdominal Series exercises when both feet are elevated off the floor and unsupported. This is why it is a good idea to use an imprinted spine for these exercises. However once abdominal strength is good enough to stabilise the spine, a neutral spine should ideally be used for all exercises.
A neutral spine means that the normal curve of the lumbar spine is present. This should not be too large or forced, or too small and flattened out. Every person’s neutral spine may look a little different to the next due to different body shapes and sizes. A general rule to determine a neutral pelvis is that when lying supine (ie lying on your back with your face upward), if you draw an imaginary triangle between the pubic symphysis and the the hip bones on both sides, the triangle should be parallel to the floor. That is, the pubic bone should not be higher or lower than the hip bones when supine. No tension should be felt in the lower back muscles – if so, then move into an ever so slightly more flattened (imprinted) position. It is more important to make sure the abdominals can activate well and there is no tension in the lumbar area, than it is to have absolutely perfect alignment of the hip bones and pubic bone, as this will differ for each person anyway.
An imprinted spine refers to an ever so slight posterior pelvic tilt, Using the abdominals to draw the lower back slightly toward the floor. When supine, the pubic bone will sit slightly higher than the hip bones.
This does not mean posteriorly tilting the pelvis so far that the tailbone lifts off the floor – the tailbone must always maintain contact with the floor, otherwise the transversus abdominus will not work effectively. Every person’s imprinted spine will look different to the next, the distance between the lumbar spine and the floor will be different for each person – the spine does not have to be touching the floor.
General Rules of When to use Imprint Versus Neutral for Exercises
In Pilates exercises, as a general rule:
An imprinted spine is used in all Supine Abdominal Series exercises, when both feet are elevated off the floor and unsupported (ie legs are either in tabletop position or extended). This is because it is easier to activate the oblique muscles in this position, and the lower back is more supported.
A neutral spine is used in all other exercises.