Pelvic balance is all important for the body to maintain. And we have spoken of this in several different articles based around lower back, abdominal and core strength and movement of the legs in general. As an adjunct to this information, let's look at a slightly different influence at the centre of the pelvic balance - the influence of the BIG 4 in the Anterior/Posterior plane of the pelvis.
In any joint space, there is a constant pull/push relationship being established by muscular and connective tissue 'tension'. A joint moves in a 2 or 3 dimensional fashion and some joints are more secure than others, with more muscular attachments or ligaments stabilising the movement. Joints are both inhibited and assisted by muscular tensions in order to maintain function and/or enhance it. In this way muscles play a huge role in how much a joint space allows the body's movement patterns to occur. How much can you arch, bend, flex and swing. We can train our bodies to be more agile, stronger, or flexible according to our movement habits and with our training. However there are certain relationships of tension that need to be maintained for ideal function.
The pelvis is an interesting and complex joint as it involves one of the largest bony girdles in the body. Human engineering and evolution has seen the pelvis develop from a prone, 4-legged, tail end, to a base of support for the upright biped. Not only that but a biped that moves with alarming speed and agility, leaping, dodging, jumping and balancing on a single leg. These evolutionary developments mean that the pelvis is now very much a key balance point in the body. It serves as the keystone to the central axis around which the body moves. This is why it is so important.
So there are 4 major groupings of muscles that act directly on the pelvis and need to be considered by any person involved with the efficiency of movement. The pelvis can be seen to be a block and tackle structure. A central axis around which 4 main cables pivot and operate. It has a certain amount of tilt and swing that it can tolerate before it becomes compromised. As with all joint spaces, there are pulls on the joint that must be essentially maintained to enable function.
The Big 4
Quadriceps - these strong powerful knee extensors and hip flexors are a powerhouse of the human biped. They really do allow us to leap, run, squat, lift and climb. Their attachment at the superior (upper) part of the pelvis via the Anterior Inferior Iliac Spine (AIIS) or what most people touch when they talk about 'hip bones', pull downward on the pelvis. Tension here can result in an increased arched lumbar and sway back position as the pelvis is drawn downwards (anterior tilt), throwing the centre of gravity forwards and leads to excessive use of the posterior chain (see below)
Iliopsoas - it's worth mentioning the primary hip flexor here as it technically crosses both the posterior and anterior aspects of the pelvis whilst actually not attaching to the pelvis at all. Originating at the lumbar spine and inserting on the tubercles of the femur (leg bone) the iliopsoas does cross the pelvis from front to back. It influences greatly the alignment of the pelvis and can dramatically change the anterior or posterior tilt of the pelvis along with the quads and lumbar back (see below). Depending on the contributing influence of other BIG 4 muscles, tension in this muscle pulls the pelvis into an anterior tilt and can very much result in a 'sway back' or 'bussle bum' which places excess curvature on the lumbar curve.
Abdominals - it's tricky to establish what the 'abdominals' actually are as many people do get slightly confused thinking that the abdominals are all about the core muscles. In this instance, we are speaking strictly about the rectus abdominals as it acts directly on the pelvis via its insertion at the pubic symphysis. These muscles act on the upward pull of the pelvis anteriorly (in the front). Whilst they do not directly influence the pelvis outright; their tension can influence the alignment of the pelvis in relation to it's other primary movers. If the rectus abdominus becomes too tight then the upward pull of the pelvis can result in an inability to extend the hips, arch backwards or stabilise the core.
Lumbar Muscles - this is not a technical term but I use it here to refer to the muscles that act on the posterior alignment of the pelvis and spine. It is primarily the Quadratus Lumborum (QL) but also includes the Erector Spinae group of muscles. These muscles attach to the superior lips of the iliac crest, the highest point of the girdle at the back. The Erector group attach more centrally via the transverse process' of the lumbar spine, but are connected via ligaments to the pelvis bone. Thus their pull is upward towards the back - almost like a skeletal wedgie! This results in an anterior tilt of the pelvis especially if combined with tightness in the iliopsoas. This can make forward flexing at the hips restricted or difficult.. It can also vaguely include the Latissimus Dorsi (Lats) muscles that do connect to the pelvis via the thoracolumbar fascia. Due to this attachment, the Lats can contribute to the pelvic alignment and the excessive pull upward.
Hamstrings - the other large primary movers of the legs. The hamstrings are large powerful muscles that are very much important to our development as a land animal and our ability to leap, run and climb. They attach to the Posterior Superior Iliac Spine (PSIS) and their influence draws the pelvis downwards at the back, which can flatten the lumbar spine.
Adductors - similarly to the mention of the iliopsoas, these large muscles on the inside thigh cross the anterior and posterior aspects of the leg. This influences the pelvis greatly as the pull on the adductors origin at the pubic symphysis will result in a downward rotation of the anterior pelvis, with the same result as the pull of the quadriceps group.
So you can see the complexity of the pelvis and how this is influenced by the pull of each group of muscles. IF you look at the picture attached, you can see that the pelvis is like a swinging pulley inside a group of cables. Each muscle group is pulling in different directions on the bony girdle to maintain it's position. If you have ever seen the skycam at work in large venues like the Rod Laver Arena, the same principle applies here. Essentially 4 main cables that each determine the location of the central camera or item. Maintaining a balance of these elements is important that allows the structure to move, fly, stabilise and hold in all different directions. It's an incredible balancing act that has been evolved by us (aren't we clever) to ensure we are one of the top tier animals of adaptive movement in the animal kingdom.
For this vital keystone of the human body, it's imperative that we keep the positioning intact and in the correct alignment, as inefficient movement here is magnified throughout our body and compensations in other articulations are a direct result. For an understanding of this is see the article on 'lower backs'. So with any issue of pelvic balance and stability, always remember the BIG 4. Each are as important as the other and need to be addressed to keep our keystones level and stable.
NB - this article deals with the anterior/posterior axis and does not address the issues involved with uneven lateral pull on the pelvis. That's a whole other article.