This really takes a very meticulous look at the kinesiology of this pose in particular and discussion to clarify Can you really 'turn off' the glute in this pose? What does that mean exactly? And then, most important question: What does that mean to YOU?
Any time the head of the femur moves toward a 'hip extension' in Active movement, the glute is going to activate, meaning muscle spindles will turn ON. The head of the femur has to glide anteriorly with hip extension : Arthrokinematics 101. Muscle spindles are part of the contractile components of muscle physiology. There are also mechanoreceptors in the joint space that tell the brain, "hey, wake up, my femur bone is moving as related to my pelvic bone so tell Mr. Guteus he needs to help out!!!" This happens without our cognitive input , under conditioned movements like walking , etc. Now, this leads to another question: Can we learn to tell the muscle to not fire on when we move the femur through hip extension? Most definitely, yes with passive Range of motion but how about Active Range of motion?
Lots to discuss- whew. Oh, and then we have what is optimal versus normal. And, add to that, what YOUR body has been trained to do versus MY body and what our potentials are between the two of US!!!!
I am going to keep this one simple, it is important to know that you cannot turn off the glute completely in Half Locust if you do the pose to it's complete Posture. This means, if you are moving through the joint range of motion - there is no turning 'off' the glute completely, can you turn the volume Down? YES SIR. Can you train the glute to not fire at all when in a static position like laying on belly without trying to lift the legs- YOU BET!!! However, some of us, have trained our nervous system to be 'FIRED UP' all the freaking time. So, some of us, need to be reminded that we can control the 'on' switch when we are supposedly in a passive position. This is Freeing Stuff right here! Wow, to think we can actually control our nervous system in some very profound ways. With our cognitive brain, i.e. the frontal lobe communicating with that other part of our brain that sends motor messages to the spinal chord- we can in fact, say 'let's chill out , glutes so the internal rotators can take lead and our pelvic floor has a chance to get more hardwired here before we move further into the pose". Yippie! However, in Active movement, the glute will in fact, through muscle physiology- turn on to assist gliding the head of the femur into hip extension. However, it is also relevant to use verbal cues to guide the participants to 'sense in' (see above sentence) to which muscles you are trying to get them to turn on in ADDITION to the glute and to guide them with verbal cuing , into more Synergistic relationships between the muscles that would be required to perform this posture- therefore working towards a BALANCED foundation within the neuromuscular and arthrokinematic platforms.
This is the foundation to take regarding if you have a herniation in your back, if you have large glutes getting in the way, if you have a more powerful glute than your internal rotators of the hip, or if you want as an instructor to emphasize Mula Bandha and so much more. The the question should not be initially: "Do I turn the glutes on or off" The initial question should be: " What is my intention here?" "Where am I headed with this?' So, you see, there is no right or wrong for ALL people. There is only, What works for YOU? For some of us, like myself included, my intention is to create Balance between the front of my body and the back. Especially since I know that my Psoas muscle is the one constantly fired up and thinks she is in control, that over time from having a chronic compression load to the nerve that innervates both my psoas and glute, that my glute has started 'shutting down' without my conscious control. This means that my muscle fibers are not firing up in the numbers that I want them too to achieve a balance between my agonist and antagonist relationship. So, for me I see things like weakness in my glutes, pain in my front of hip, and inability to perform some poses, even as simple as altering my gait, due to this imbalance. Does that mean I ALWAYS want to try and 'turn on' my glute then in a back bend? Nope, not necessarily because it depends on the intensity, duration, and frequency that I am putting into balancing out my restorative modalities with my tearing down/thus muscle building activities. My nervous system needs to know how to adapt to change and restore - so sometimes, I have to practice this 'conscious awareness technique of turning off'.
In the what works for you category, it takes some real time, real tools, real self inquiry to come to a full awakening , intellectually and somatically what is the most Optimal considerations at that moment. We change, daily. This is why all of us have an opportunity to learn from one another. Sometimes, even the most astute teachers, have imbalances that they are not even aware - so to be shut down to listening and learning from others, is a disservice to self and in yogic terms, perhaps is quite egocentric. It is not about you are wrong and I am right. It is about, listening to self and others without the distractions of a Rigid perspective. That is so old school Western Conformity. It is time to start a Revolution. Be Free. They say some people are not capable of change, of evolving. I do not conform to that opinion. I believe we all are more capable than we know. I know that I am more capable and I want to know how to reach my highest potential.
Know yourself. Know truth. Know Freedom- to choose. Let's Fly Together. Namaste.