Levator Costalis can be used to "lift your back ribs."
Actually, your whole ribs will lift, but the back of your ribs will lift more. More importantly, it is an action you can learn to feel and deliberately do.
The advantages of lifting your back ribs are that it can make it easier to bend your spine backwards when doing back bending yoga poses. You may also find that you can use them in such a way to create deeper inhales.
A set of muscles that is closely related to the spinal erectors in terms of position is the levator costalis. They can be use to lift the back ribs. These muscles reach down from each thoracic vertebrae to the first and second set of ribs directly below the relative vertebrae. The muscle bodies are located in a space about two to three inches either side of the center line of the spine.
If you can feel your spinal erectors activating in this region, then in may be relatively easy to then use a similar feeling to cause the back of the ribs to lift.
You can use the spinal erectors to cause the ribcage to expand. Use them to bend your thoracic spine backwards. You can also use the intercostals. Now the focus is on using the levator costalis.
The purpose of learning to control and feel any one set of muscles isn't to say that one set of muscles is better than the other, rather it is to learn to use them all so that they can all act freely when required, or so thatyouwe can choose which muscle to focus on given what your are trying to do.
If you can already feel and control your spinal erectors, especially in the area of the back of the ribcage, then the levator costalis may be easier to feel since the feeling of the muscles contracting is quite similar although the effect is different.
When contracting the spinal erectors, they try to bend the vertebral column backwards.
When contracting the levator costalis they try to cause the back ribs move away from the pelvis, or towards the head.
Start with slow rhythmic backbending of the spine using the spinal erectors to cause the spine to bend backwards as you inhale. Relax slowly each exhale.
Once you are comfortable with this action focus on reaching the back ribs upwards each time you inhale. Lengthen your neck first, pull your chin to your chest and then move your back ribs towards your head. If you have a friend handy, you can have them place the palms of their hands on your back ribs. Have them slowly and slightly lift their hands as you inhale and try to move your ribs with their hands. Have them move their hands down while you exhale. And then you can switch.
You may notice that by lifting your back ribs, your entire ribcage lifts as a result. So that you know that you are using you levator costalis to cause this action, focus on pulling upwards on the back of the ribs (to either side of the spine.) The feeling is very similar to that of activating the erector spinae.
You may find that if you bend your thoracic spine forwards first, then try to lift your back ribs, the action is easier. You can then bend your thoracic spine backwards. To do this, follow the following steps:
Once you can lift your back ribs, play with the amount that you lift them. You may find tht you only have to lift them a little in order to bend your thoracic spine backwards. By becoming more sensitive, more aware, you'll find exactly how much you need to engage each set of muscles to get a desired result.
The nice thing about using the levator costalis is that they help to create space in the back of the ribcage. They also help in opening the space either side of the lumbar spine by drawing the back ribs away from the pelvis. And they make it easier to bend the spine backwards because of the change in angle between the ribs and the spine.
This action can also cause some of the spinal erectors to lengthen, particularly those fibers that attach the pelvis to the back of the ribs, making it then easier to contract these same muscles.Try doing wheel pose with or without the spinal erectors, but in either case while using the levator costalis. See for yourself whether this helps to deepen your backbend or at least make it more comfortable.
Because of all of these factors, it can often be helpful to use the levator costalis and spinal erectors together. The former create room so that we can bend the spine backwards while the latter cause the spine to bend backwards. But even in back bending postures where you aren't using the spinal erectors, using the levator costalis can still be beneficial, creating room for the thoracic spine to bend backwards passively.
Apart from in backbends, where else might the spinal erectors and levator costalis be useful? In forward bends for the hips. For beginners especially, and for anyone with tight hamstrings, the tendency in a standing or seated forward bend is to focus on bending the spine forwards in an effort to get the head to the knees. However, if you learn to feel you spinal erectors and when they are active, you can focus on keeping this feeling while at the same time tilting your pelvis forwards. In addition, if you keep your hands on the floor and slowly bend their elbows, you can use the weight of your upper body to slowly help to lengthen your hamstrings.
If you do try engaging your spinal erectors while in a forward bend (or some variation of a forwards bend) I would strong recommend pulling your head back and up (relative to your ribcage) and you chin in towards your chest so that the back of your neck lengthens. You may find that this action helps to further accentuate opening your chest.
As a final note, when using the spinal erectors to bend the spine backwards while forward bending at the hips, you may find it helpful to engage the side glutes to widen the thighs slightly. Or you may find that this happens naturally when you bend your spine backwards.
If you do try this action, try reaching your thighs forwards at the same time, as if pulling your thigh bones our of your hip socket. Take some time to feel both the action and the result of the action. See if forward bending happens easier as a result.