The usual way of explaining hip joint anatomy is to focus on muscles according to region and/or function. I thought it would be helpful in this article to offer a slightly different point of view of the muscles of the hip.
The spokes of a bicycle wheel center the hub relative to the rim and help to keep this relationship stable, even during the stresses of being ridden.
With hip joint anatomy it may be helpful to compare the hip to a bicycle wheel with the understanding that the muscles of the hip work on the hip joint from different angles to centralize the hip, stabilize it (and to help keep it lubricated).
With balanced tension among the hip muscles the ball of the hip joint is centered in the socket of the hip bone and the hip joint is kept stable.
During changes in orientation of the pelvis relative to the leg or the leg relative to the pelvis, or changes to whether the leg is acting as a foundation or not, the muscles of the hip can maintain this balanced tension.
Hip muscle tension may directly affect tension of the joint capsule envelope.
With balanced tension throughout the tissue of the joint capsule, the synovial fluid within the joint capsule may be pressurized enough to prevent mating surfaces of the hip joint from rubbing against each other.
Viewing the hip joint as being like a bicycle wheel we can liken muscles to spokes. We can study each muscle individually and understand their function as tensioning devices, but we can then get a better idea of how hip joint as a whole works when we view them all in situe, as part of a fully functioning hip joint.
In this case, no single spoke or muscle is more important than any of the others, at least not for a fully functional and flexible hip joint.
(That being said it is handy to know which muscles do what.)
As a bike is ridden and the wheels roll, the spokes at the top of the wheel have more tension and the spokes at the bottom less.
However, the spokes at the bottom don't completely relax. They experience a lessening of tension. Then as the wheel rolls, those spokes experience a gradual increase in tension which probably peaks when a spoke is at 12 o'clock (or somewhere in the region since that riders' weight is actually in front of or behind the wheel depending on whether we are looking at the front wheel or back wheel.)
Once passed the peak point, tension lessens and then the cycle continues.
However, at all times, all spokes have tension, it's just that some have more tension and others have less. (At least that's my understanding of it. )
The hip joint could be viewed similiarly. Standing upright the muscles in a position to pull the pelvis upwards with respect to the thigh will have more tension. Tilting the pelvis forwards or backwards then the muscles best positioned to suspend the pelvis will then have the greater amount of tension. In each case the tension is enough to balance the weight that it is working against.
To better understand the hip joint, we can imagine a slightly modified bicycle wheel.Instead of spokes the wheel will have fabric attaching the hub to the rim. This fabric will attach, like spokes, to specific points on the wheel and rim. The fabric is like connective tissue.
And to add tension, there will be muscles which act like spokes, embedded within the fabric of the wheel. When the muscles of the hip are completely relaxed, the connective tissue loses tension so that thigh and pelvis can move freely with respect to each other.
By tensing muscles in particular ways the hip can be made stable in various positions or moved into various positions.
The muscles in our bicycle wheel hip joint can not only be used to create hip stability and movement but they can also be used as feedback mechanisms to help know the position the hip is in.
Effort exerted by muscles can help us figure out the disposition of the hip joint. In addition tension in the connective tissue can also give us clues as to the disposition of the hip joint.
Normal bicycle wheels don't change shape, unless you hit a bump or get stuck in a sewer grate! In comparing a hip joint to a bicycle wheel, how might the relationship of the hub with the rim be varied? By varying spoke tension.
On a real bicycle wheel spokes can be tightened or loosened. I've had experience of this trying to fix a bent rim.
By changing spoke tension it's possible to use the tension of the spokes to straightent the rim. A possible consequence is that the rim might be less round or the hub shifted slightly relative to the rim. It could be possible to vary spoke tension to shift the rim relative to the hub, rotate one relative to the other or even tilt one relative to the other.
The interesting thing about tightening spoke (or loosening them) is that when you turn the key you get an idea of how much tension the spoke already has. This is the same when tuning a guitar. The amount of effort required to turn the tuning pegs tells you how much tension the string already has.
Note that you can also tell tension by plucking a spoke or guitar string.
Replacing spokes with muscle tissue, muscles could then be used to maintain the relationship, make the relationship super stable, or change the relationship. Muscle tension and some indicator or muscle length could then be used to help us figure out what the current relationship is between hub and rim.
I'd suggest that while controlling the hip muscles in isolation is a helpful exercise, particularly when you are trying to figure out problems with your hips, (and I go over some simple isolation exercises in the hip control guide) another approach is simply to "balance tension" in and around the hip joint.
For hip control with respect to improving hip joint flexiblity in forward bends and backward bends, I've included step by step exercises in Active Stretching.