Been using since February, and the concept of involuntaries is still as foreign as ever. I've probably read a small novel's worth on this phenomenon, but still have so much trouble understanding it. The anus literally begins contracting on its own? Does it just do this out of nowhere? Does it need a trigger? How hard are the contractions? Can you stop them, or is it more like a muscle twitch?
The most common thing I see is to try and fatigue the muscles, but that has never worked. I've been doing kegels (when I remember) and even exercising a bit to work all the muscles in my lower body. I've spent entire sessions trying to wear myself out, just contracting and relaxing for three hours straight, only stopping a few times to empty my bladder. My muscles absolutely do not tire. It's just not happening.
I've also tried several "do nothing" sessions, but no movement. My experience with sessions like that has been thus: do nothing = feel nothing.
It's such a strange idea to begin with, that my body could just start moving the Helix of its own accord. Is that really the way it works?
It is indeed comparable to a muscle twitch. Your ass Will start to contract on its own. Don't expect huge movement: the contractions are subtle and so is the movement (although this may evolve in episodes of stronger movement and contractions, where the aneros Will move in and out - so called autofuck). It is like a spasm in your muscles. Compare it to a twitch in the muscle surrounding your eye when you are tired (of you ever experienced that), except it is caused by arousal rather than being tired. For me, i can induce Them by tiring my muscles, but the do nothing' approach works best for me. Make sure you are very aroused when starting your sessions. Oh and it make take a while before you experience Them - rook me a year!
It takes some time. In the beginning it is ok to play around with contractions. Just to feel different sensations. It is true that in the end your body, muscles know what to do. I call it rewired.
it took me some 2 yrs to reach a so called super o. The journey was great too. And still getting better. Now it is possible for me to have orgasms even without aneros inside. Enjoy the journey! And as you will have read before... drop all expectations. Just observe. Relax. Breath.
@CollectingSmiles, fully agreeing with the recent comments, I'd only like to add, that it worked best for me to try some contractions to move the Aneros ever so slightly that they stay nearly not sensible.
Thus you train your perception for the fine inducements coming from your gland. You can, too, try to clench your whole lower body like you would do when you suddenly were scared by something. Then again I would do nothing.
I just now, trying this myself, feel some increasing blood flow down there. And some vibes begin to spread out all through my body.
I hope this can help you over the next hurdle. But as said in the recent comments, this Aneros way is a journey of patience.
Most of all, drop your expectations, especially because, what comes is so different to all what you already know. Thus your expectation would hinder you to discover the new.
Good luck and take it easy.
@CollectingSmiles, the above posters have given you sound advice.
The anus literally begins contracting on its own?
Yes and No, the anal sphincters respond to both the Somatic nervous system and the
Automatic nervous system.
Does it just do this out of nowhere?
I don't think so, there is much we don't know about the workings of our nervous system but totally random firing of nerve cells (while not impossible) is unlikely.
Does it need a trigger?
I believe it does. I think this trigger exists in the realm of interaction between the somatic and autonomic nervous systems. Here is where one's intent can influence the effect.
How hard are the contractions?
The inducing contractions may be minimal while the reactionary contractions can vary from very slight to quite hard.
Can you stop them, or is it more like a muscle twitch?
The muscle twitch is an apt description but if you remove the triggering stimulus (Aneros device and conscious focus) the muscular response abates.
It's such a strange idea to begin with, that my body could just start moving the Helix of its own accord. Is that really the way it works?
Yes, the presence of the Helix has a physically stimulating effect which engages the autonomic nervous system to respond. The process of rewiring associates this response with the somatic nervous system making Anerosless sessions possible due to a mirroring of neurons in the brain.
Your ability to perform alternating contraction/relaxation exercises for up to three hours is impressive so I'd surmise your sphincter muscles are well toned. I hope you are also receiving some P-waves with each contraction sequence. In regards to the "do nothing" method please read the thread - "Do Nothing" What does that mean?. I suggest you try a hybrid technique between the do nothing and the active (contraction/relaxation) method, namely try holding a 25% level contraction indefinitely to see if this triggers some involuntary contractions. I suggest you also read Aneros guru 'B Mayfield's thread B's Best of the BEE-Line in regards to contractions.
Good Vibes to You ! 
Thanks to everyone for your responses. This helps a lot.
Your ability to perform alternating contraction/relaxation exercises for up to three hours is impressive so I'd surmise your sphincter muscles are well toned.
I can't imagine why. It's probably been a decade since I last experimented with anal play, and it was rare even then. I tend to hold myself in a non-relaxed state throughout the day, so maybe I've been inadvertently exercising those muscles my whole life. But if that were the case, shouldn't this journey be a little easier?
I hope you are also receiving some P-waves with each contraction sequence.
I...think so? There are times when I think I could be onto something - bouts of pleasure. It feels very, very good, but nowhere near orgasmic, and it never lasts long. I'm still not sure whether those random pleasure periods relate to my contractions. If there's a pattern, I haven't been able to detect it since a large percentage of my sessions yield little to no sensation. I feel like I could contract/relax far, far longer than three hours if I didn't eventually get bored of it.
...maybe I've been inadvertently exercising those muscles my whole life. But if that were the case, shouldn't this journey be a little easier?
I had to chuckle a bit about your comment. Perhaps it might be a little easier for some men and it does appear that some men enter the Aneros journey somewhat 'pre-wired' for the experience but for most of us it is a about learning a new thought paradigm.
IMHO, far too many newbies get hung up on concentrating on their physical techniques. Differing physical techniques do have differing effects with differing individuals which is why there is NO unique formula for success. As I and many others have often stated, the Aneros journey is more than 90% a mental exercise (see the threads Aneros: The Essential Mind State & Whole Body/Whole Mind - the mental side). Your attitude and mood have far more effect on the outcome of any particular Anerosession than the physical technique you employ. Part of this rewiring journey involves a paradigm shift in thinking about What's an orgasm?. For most of us men we grow up equating orgasm with ejaculation from years of penile masturbation practice, this is one of the major obstacles in our thought processes. Breaking free from this old train of thought can prove to be quite daunting despite one's ability to practice multiple physical techniques. Once you can break free from the old thought paradigms and become more attuned to what your body is capable of producing for you, your Anerosessions will become more pleasurable.
"All that we are is the result of what we have thought. The mind is everything. What we think, we become." - Buddha. Become the orgasm, Anerosessions as erotic meditations can lead us into an altered state of consciousness (orgasm) and perhaps give us a taste of Nirvana.
Good Vibes to You ! 
try holding a 25% level contraction indefinitely
So, I just got through a long session where I tried this. At times, I did get a little twitching, but it was fast and very irregular. Felt a bit like essential tremor. (I get that in my arms sometimes when they're fatigued, something I inherited from my mother.) Did it feel good? I suppose. Not among my best sessions, but yeah, it was nice. Am I on the right track?
So, I just got through a long session where I tried this. At times, I did get a little twitching, but it was fast and very irregular. Did it feel good? I suppose. Not among my best sessions, but yeah, it was nice. Am I on the right track?
OK, I'm glad you did get some involuntaries and YES, I think you are on the right track. The fact that they were fast and irregular is not of any particular significance, sometimes they may be that way at other times they maybe slower and more rhythmic. The important thing is to focus on the pleasure received and not try to force more from your session. Please read @Clenchy 's wonderfully succinct recent post in regards to the mental aspect and following the pleasure.
Good Vibes to You ! 