'The One Hundred' exercise is the 'bread and butter' of the Pilates world and every Instructor will incorporate this basic exercise in their repertoire, after the Pilates Fundamentals and a warm up.
Start by lying flat on the mat and try to create a slight curve at the base of the spine to protect the lower back, then bring the legs up into a 'table top' position, one at a time to keep hip stability. The knees should bent at a 90 degree angle with the ankles and shins in line with the knees and hips. Keep the arms are down by the sides of the body and the legs, knees and ankles hip width apart.
Breathe out and curl the head and shoulders off the mat from the breastbone and then breathe in whilst keeping the lower abdominals hollowed and scooped. Reach away with the hands in a straight line, just off the mat. Focus the eyes on the pelvic area and start breathing in and out as you beat your arms up and down together, slowly. Check to make sure your rib cage is flat and the area above the pubic bone is not 'doming'.
This exercise is called the 'the 100' is because you breathe in and out whilst beating the arms up and down 5 times and, as you improve, you work up to beating 100 times, breathing in for 5 beats and out for 5 beats. The hands move and up and down over a distance of approximately 15 cms so think of using the backs of the arms and keep reaching away past the hips.
Try to keep the pelvis in neutral but also try to remember to press the spine right down from the tail bone into the mat. Try to keep a very small gap between the spine and the mat just above the crest of the hips, keeping the shoulders down and try not to push your head forwards but more upwards.
When you feel comfortable with this try moving your legs from the bent position to an extended position towards the ceiling. If your neck or back start to complain then you know it is too soon progress, yet.
For those who find either of these positions tough on the neck but your back is coping well, you can try bringing one hand behind the head to take the pressure off the neck or using a block under the head.
The advanced level is lying flat on the mat and bringing the head and shoulders up whilst extending the legs just off the mat in a straight line and counting 20 breaths (100 beats).
This exercise is excellent for improving posture by strengthening the TVA (Transversus Abdominus) which the muscles just above the pubic bone and the external obliques which are situated in either side of the body just under the ribs as well as the Latissimus Dorsi and Teres Major which are the muscles of the upper back.
Finish with a full body stretch.