The powerhouse, or core, can be described as the area from the bottom of the rib cage to a line across the hip joints in the front and to the base of the buttocks in the back. Joseph Pilates placed great emphasis on the powerhouse, considering it a physical center of the body from which all Pilates movements should proceed. Many Pilates exercises are designed to strengthen the powerhouse, and there is a desire to keep the powerhouse working consistently throughout a given exercise. If the powerhouse is being used appropriately, the limbs should be able to move in a more coordinated and connected manner.
Some Pilates practitioners and many people in disciplines such as dance, fitness, and rehabilitation also refer to this area as the core and the desired maintenance of appropriate positioning and activation during movement as core stability. Core stability can be thought of as the ability to keep the pelvis and spine in the desired position while moving the limbs or the whole body through space without undesired distortions or compensations. Someone who is not maintaining desired control of this area in a given movement and who arches the lower back or moves the pelvis excessively is often said to have a weak core or demonstrate poor core stability or poor core control.
In Pilates terminology, the powerhouse consists of the abdomen, lower back, and pelvis. The abdominals and the lower spinal extensors are considered particularly key to the concept of the powerhouse. In addition, the concept of the powerhouse includes the pelvis and, in general, the primary muscles that influence the movement and stability of the pelvis.
Each hip bone (os coxae) is connected firmly in the back to one side of the sacrum at the paired sacroiliac joints. The hip bones are also connected to each other in the front via a joint called the pubic symphysis. These strong connections allow the hip bones along with the interposed sacrum and coccyx to act as a unit, referred to as the pelvic girdle. Each hip bone is actually made up of three bones—the ilium, ischium, and pubis. Each of these bones has landmarks commonly used for identifying body alignment.
Bones have distinct markings such as indentations, openings, lines, and protrusions that are collectively termed bony landmarks. The selected bony landmarks described here are helpful in identifying core alignment and stability.
- Iliac crest. The ilium is the large upper winglike portion of the hip bone. If you move your hands down from your waist, you will feel a large ridge of bone. This is the upper border of the ilium. This convex border is called the iliac crest.
- Anterior superior iliac spines (ASIS). If you slide your hands to the front of the iliac crests and then slightly down, you will feel a bony prominence on each side of the front of the pelvis. These paired prominences are called the anterior superior iliac spines (ASIS).
- Pubic symphysis (PS). The pubis forms the lower and front portion of each hip bone. The pubis of each hip bone join at the front to form the pubic symphysis, connected by a disc of cartilage. You can see the pubic symphysis by standing with your side to a mirror. The pubic symphysis is the portion of the lower pelvis that is the most forward.
- Ischial tuberosity. The ischium is a very strong bone in the lower and back portion of each hip bone. The lowest portion of each ischium has a roughened prominence, the forward portion on which we sit, termed the ischial tuberosity, or sit bone. You can palpate these tuberosities easily while sitting on the floor. Lean forward and place your fingertips under the bottom of the pelvis from behind. Slowly begin to rock your weight back to sit upright. The tuberosities will press down against your fingers.
- Greater trochanter. The hip joint is formed between the hollowed socket of the pelvis (acetabulum) and the rounded top (head) of the femur. A large projection toward the top of the femur faces outward. This projection is called the greater trochanter. When you are standing, the tip of the greater trochanter is at about the same level as the center of the head of the femur as it sits in the hip joint. Although not a part of the pelvis, this landmark is included because a line between the right and left greater trochanters can be used to mark the lower border of the powerhouse. You can palpate the greater trochanter by placing your thumb on the side of the crest of the ilium and reaching down the side of the thigh with the middle finger. When you internally and externally rotate the leg, you should feel the greater trochanter move beneath the middle finger.
Learning to identify a neutral pelvic position, an anterior pelvic tilt, and a posterior pelvic tilt and to achieve the positions desired in a given Pilates exercise are important goals of Pilates. Because the pelvis moves primarily as a unit, the large movements of the pelvis mostly occur at the lumbosacral joint, the junction of the lower back with the pelvis. Stand upright with your side to a mirror to observe the first set of movements of the pelvis and related changes in the lumbar spine. Place one index finger on each ASIS to aid in seeing the desired relationships.
When in a neutral pelvic alignment, each ASIS (the top projections of the front of the pelvis) is aligned vertically with the pubic symphysis (the front of the lower pelvis). If a piece of poster board were held vertically from the pubic symphysis, both the right and left ASIS would touch this poster board. In this neutral position of the pelvis, the lumbar spine is also generally in a neutral position, exhibiting its natural curve, not a diminished or exaggerated curve.
In contrast, if you rotate the top of the pelvis forward, each ASIS will be in front of the pubic symphysis; this is logically termed an anterior pelvic tilt. This anterior movement of the pelvis will tend to increase the arch of the lumbar spine (extension or hyperextension). Check to see if you can see a change in your lower back curvature.
Conversely, if you rotate the top of the pelvis backward, each ASIS will be behind the pubic symphysis. This is a posterior pelvic tilt. With a posterior pelvic tilt, the curve of the lower back is decreased, flattened, or even reversed to round in the other direction, depending on the mobility of your spine.
Although these are the most emphasized aspects of pelvic movement, the pelvis can also move in other planes. The pelvis can tilt from side to side. When the right ASIS is lower than the left ASIS, this is called a right lateral tilt of the pelvis. Conversely, when the left ASIS is lower than the right ASIS, this is a left lateral tilt. This is observed more easily from a front view, such as facing a mirror. Lastly, the pelvis can rotate. When the right ASIS is in front of the left ASIS, this is left pelvic rotation. When the left ASIS is in front of the right ASIS, this is right pelvic rotation.
Although classically these movements of the pelvis are described in a standing position, they apply to many other positions used in Pilates, such as lying on the back, lying facedown, sitting, kneeling, or being supported on the hands and feet. In Pilates starting positions or exercises requiring a neutral pelvis, ideally the ASIS would be aligned with each other so they are level versus laterally tilted and square instead of rotated, as well as being in the same plane as the pubic symphysis.
Many of the muscles of the spine attach to the pelvis as well as the spine or rib cage. There are times when these muscles act to move the pelvis in isolation or in conjunction with the spine. So when the rectus abdominis and obliques contract, they are capable of creating a posterior tilt of the pelvis as well as spinal flexion. The spinal extensors are capable of creating an anterior tilt of the pelvis as well as spinal extension. The iliopsoas is capable of creating an anterior tilt of the pelvis as well as extension of the lumbar spine. And the quadratus lumborum can produce a lateral tilt of the pelvis as well as lateral flexion of the spine. One of the benefits of the Pilates method is that it incorporates exercises that use the multiple potential actions of these important core muscles. For example, Chest Lift uses the abdominals to flex the spine, whereas Pelvic Curl emphasizes the use of the abdominals to create a posterior pelvic tilt.
In many instances, the potential actions of these pelvic muscles are used to prevent an undesired action and create core stability rather than actual visible movement. For example, when the iliopsoas contracts rigorously to support the weight of the legs in Hundred, the potential action of the abdominals to create a posterior tilt is used to prevent the undesired anterior tilt associated with the iliopsoas so that the pelvis can remain stable and protect the lower back. Another example is when the quadratus lumborum works in a postural manner to help determine the distance between the top of the pelvis and the rib cage, a function used frequently in Pilates to keep the pelvis level.
Many other muscles that attach to the pelvis are known more for their actions of moving the legs at the hip joint than moving the pelvis. However, two muscle groups that are commonly included in a discussion of the powerhouse, or core, are the gluteus maximus and pelvic floor muscles.
The gluteus maximus is a powerful muscle that is pulled into play with movements such as jumping, cycling, stair climbing, and uphill running. In these activities, the muscle works as an extensor of the hip, but it can also function in a postural role to create a posterior pelvic tilt and help maintain core stability. The original Pilates work emphasized gripping this muscle and encouraged squeezing the buttocks together as if to pinch a dime between them. This approach may have been adopted because of the common tendency to lose tone in these muscles with aging. As they age, people often give up the powerful activities that effectively challenge the gluteus maximus. While still acknowledging the importance of strengthening this muscle, many current schools of Pilates put less emphasis on continuously gripping the gluteus maximus throughout a given Pilates exercise in favor of strategies of stabilization that are more functional in regard to everyday activities. Examples of alternative strategies include emphasizing a less forceful or continuous contraction of the gluteus maximus as well as combining its use with other core muscles such as the abdominals.
The pelvic floor muscles, consisting of the levator ani and coccygeus, form the funnel-shaped floor of the pelvic cavity. This muscular sling stretches between the coccyx and the front of the pelvis as well as between the lateral walls of the pelvis. The pelvic floor muscles provide support for the terminal part of the rectum, the prostate, and the urethra in males and the rectum, the vagina, and the urethra in females. Balanced strength and activation of the pelvic floor muscles is considered by some to be another important element of core stability. Simultaneous contraction of the diaphragm and pelvic floor muscles will help maintain the abdominal contents within the abdominopelvic cavity, while the transversus abdominis functions to enhance stabilization of the spine. Research indicates a close association between the pelvic floor muscles and transversus abdominis and that contraction of the pelvic floor muscles can be used to facilitate contraction of the transversus abdominis, and vice versa.
Read more about Pilates Anatomy.