Fascia Insights: The Third Rhythm in the Cranium

By Lina Amy Hack and Thomas Rosenkilde Rasmussen
March 2022

ABSTRACT For years the primary evidence of the third rhythm of the cranium was observation by palpation. In 2021 Dr. Thomas Rosenkilde Rasmussen and Dr. Karl Christian Meulengracht published their results of direct observation of the third rhythm using robotics and software analysis in their peer-reviewed publication, “Direct measurement of the rhythmic motions of the human head identifies a third rhythm” in the Journal of Bodywork and Movement Therapies. In this interview, Rasmussen discusses his background as medical researcher and craniosacral practitioner that led to building this measurement machine, doing this experiment, and the various questions his laboratory group are considering for the future. 


Lina Amy Hack: Thank you for meeting with me, where do I find you today for this interview?

Thomas Rosenkilde Rasmussen: I’m in Copenhagen, Denmark. And where are you now?

LAH: Ah, Saskatoon, Saskatchewan, Canada. Great to connect at such great distances. 

Today we’re going to talk about your 2021 peer-reviewed publication, “Direct measurement of the rhythmic motions of the human head identifies a third rhythm,” which was published in the Journal of Bodywork and Movement Therapies (Rasmussen and Meulengracht 2021). Can you tell me a little bit about your background, are you a researcher and a practitioner?

TRR: My background is, I have a PhD in medicine and I worked for fifteen years as a scientist in cancer research. I was a research leader for many years. And then, at one point I became an associate professor at a young age. I was thinking, what do I want to do now? And I decided that I really want to learn about manual therapy. Every time I asked questions about it, it was clear, we don’t have  the same kind of research in the field  of manual therapy as you have in cancer research. 

Then I spent some time learning craniosacral therapy from Upledger Institute International, then visceral manipulation and neural manipulation from the Barral Institute. Then I sent myself to osteopathic school in Europe and stepped back from my hard science work for some years, because I wanted to learn by hand and by experience. Coming into some of the topics, it was a fight between my left and right brain, because at one point I was a very experimental scientist, and here in manual therapy, people were just discussing their experiences. Especially the experiences people had with fascia. How can fascia react the way that fascia reacts? And it’s not controlled alone, in our view, by the central nervous system. I got triggered by that, as a lot of people didn’t know [the important details involved]. My inquiry became focused on the cranial rhythm – when I put my hands on the cranium – do I feel a rhythm because I imagine it? Because it is so gentle, I was really caught in my own head about this. 

At one point, I ended up in many left-brain discussions about it. I studied further with Upledger Institute International, then I became a teacher of craniosacral therapy, I taught a lot of classes and students frequently questioned the existence of a rhythm different from the respiratory and cardiac rhythms. We could only find one real study that was very clear about measuring the cranial movement by Viola Frymann, DO, FAAO (1921-2016). Back in the seventies, she built a machine to measure the rhythmic motions of the cranium in situ (Frymann 1971). 

With modern technology, we built a machine with sensors that could detect down to one micrometer of movement. So now we have a validated machine. 

All of us doing craniosacral therapy, we all had this view about what the craniosacral rhythm was, what we had been reading in the textbooks. And then we began to find out that a lot of it is actually not true. The third rhythm, it doesn’t change. It’s a very fundamental rhythm. And then, this was the beginning. 

We had to say, okay, we need to go back and do a very basic study to do very basic measurements. We had to stop thinking of the textbooks we have all read about the craniosacral rhythm. As a profession, manual therapists had become stuck in a logical circle, because everyone is quoting everyone else saying the same thing when they define the rate of the cranial rhythm. But where does this come from?

We measured hundreds of people just to learn. And also, to become aware of all the variables that move the cranium in the micrometer range. Now we have the clear knowledge that when you breathe, that will make your skull move. People say the skull can’t move. Now we know, the head is moving when we breathe, we measured it. And we could measure the arterial rhythm in the head (see Figure 1). Then we asked ourselves, how do we make a very clear distinguishing measurement between the different rhythms that move the cranium internally? To answer this, we did Fourier transformations to separate all the different rhythms of the skull from the raw data. This is the technology we have now. And it became a much longer project than we expected. We had to start at the beginning, looking at the data, we just called it a third rhythm to make clear the fact that the skull has a movement that is not respiratory breathing, and it is not the heartbeat. 

Figure 1: The three different rhythmic movements of the human skull, the average of each participant is reported by a data point, along the x-axis, n indicating participant number, and the y-axis is the cycles per minute of the movement observed. For each participant a circle indicates the average of their identified third rhythm, a diamond indicates their average respiratory rhythm, and a triangle indicates their average heart rate. Creative Commons license: CC BY-NC-ND 4.0.


We needed to define that first. In this study, we invited fifty people to be our participants. We made sure that the people didn’t know what craniosacral therapy was, many of them had never heard about it. And there was no therapist in the room. We programmed the machine to observe the participant lying supine, on their own. 

LAH: That is what struck me about your paper, in the body of knowledge of manual therapy, your 2021 article fills an important gap. You have begun to characterize the normal behavior of the third cranial rhythm that we believe to be the product of cerebrospinal fluid production and absorption in the central nervous system. This is a foundational piece and for my colleagues, structural integration practitioners specifically, we need this knowledge about what is actually happening in the skull. 

Let’s define a few terms for our readers, in your paper you write about the primary respiratory mechanism and the cranial rhythmic impulse. What are these two terms and how are they different?

TRR: We can say that the primary res–piratory mechanism was a concept made by William Sutherland, DO, (1873-1954) to define that there is a movement within the head different from the breathing of the lungs which also moves the head (1939). Sutherland never wrote anything about the rate of the rhythm. And in some of Sutherland’s texts, there are many different rhythms discussed, some are described more like tides. 

The cranial rhythmic impulse, sometimes called cranial rhythmic index, is central to craniosacral evaluation and is a manifestation of the primary respiratory mechanism that is in our body. Cranial rhythmic index became the term used in scientific papers because the primary respiratory mechanism is not clearly defined. 

Also, if you look in textbooks and different schools of craniosacral studies, they focus on different rhythms of Sutherland’s concept, like the mid-tide, long-tide, and breath of life. These are not clearly defined and they were not defined by Sutherland. So we can say that the Upledger craniosacral school and the other schools of craniosacral therapy, they call the cranial rhythm experienced by palpation the craniosacral rhythm or cranial rhythmic index often showing different range of rates. And we don’t know if that was what Sutherland experienced, because what Sutherland experienced, we cannot put hands on and say, "I have the same experience as Sutherland," we just don’t know that. In the paper we define a third rhythm experimentally, creating the foundation for further understanding and evidence of the cranial movements used in manual therapy for years. 

We asked, what head movements exist when a person is at rest and can we relate them to that palpatory experience that people have?

LAH: Yes, that is a brilliant question. You mentioned Dr. Frymann, she did some measurements of internal head movements in the 1960s and 1970s, but her methodology wasn’t conclusive and it is critiqued often. Why didn’t that work? What was the weakness of that methodology?

TRR: Number one, it was the software because Frymann’s measuring tool needed a very strong physical contact on the head. That pressure alone interfered with the normal movement of the head and it also often created a headache in the people lying down. 

LAH: Oh wow, that sounds intense. 

TRR: And the second issue was that there were different kinds of movements acting on the head and her methodology couldn’t separate them. They would have people hold their breath for a long time. In that Frymann study, there was one client that I think was conclusive. That was a man who was really proficient in holding his breath for a long time. And while he was doing that and not having a headache, you can actually see that there was a movement around seven to eight cycles per minute. And for me, that was conclusive, but I think the research struggled in the development of the machine and there wasn’t much follow up after that series of investigations. 

Reading the Frymann paper, I also saw that they had a lot of struggles with that kind of measurement because there are so many movements of the human body and it is possible to get confused if you cannot separate them (1971). This also became one of our biggest challenges, but our location in time allowed better technology.

LAH: Yes, let’s talk about your machine. You attached sensors to the mastoid process of the temporal bone on either side of the subject’s head and you recorded data about their relative movement away from each other and toward each other – were the sensors like calipers attached to each other? Can you describe the apparatus for us?

TRR: The sensors are not attached to each other, they are two independent sensors, it was the software and the computer that calculated their relative motion. The sensors we had on the participants’ heads are called servo actuators and you can program the amount of pressure they apply to the head. Even when the head was expanding, normally a machine would have an increase in pressure and the head would meet resistance, but here the machine is programmed to keep the same pressure on the participant’s skin, no matter where it moves. This is important, we had the same pressure regardless of movement. We programmed it to be ten grams of pressure. The machine had minimal interference with the participant’s head and they reported they didn’t really feel the machine on their head. The sensors, they are programmed to be on that spot, so no matter where the head moves around, the sensors will follow the head and keep a ten-gram contact. 

We found that there were asymmetries between the left- and right-side  movements of the bones. We are going to follow up on that finding and then see if cranial manipulation will change the asymmetry, and we want to investigate if craniosacral therapy will change the amplitude of skull movement. 

LAH: So many important avenues to investigate with this technology. The participants didn’t need to be strapped down or restrained because the computer could adapt to their regular movements?

TRR: Yes. Participants were lying down on a soft treatment table, they were invited to relax and they reported they didn’t feel the measurement tool. 

LAH: And you mentioned there was nobody else in the room, so it was just the participant’s biofield being measured by the instrumentation. 

TRR: Yes, and interestingly, when we had just built the machine and were starting to test it out, we could see that if a client was on the table and a therapist came into the room, it affected the measurement. Knowing this, we knew we had to be very strict so we could record the baseline movement, this study was the ground zero for a group of studies of this kind. Now that we have it published, in the future we can learn what kind of variance would be created by a therapist entering the space of the client and stuff like that. 

LAH: This baseline study of yours is essential. To summarize, you had fifty participants, men and women, and they had an age range of eighteen to ninety-two. This is the whole adult lifespan that you covered. And the participants had no knowledge of cranial work; they were fresh. 

TRR: Yes, and they were actually easier to measure. We have also found out in our pretests that if you have a therapist lying down on the table, in their head they are thinking about what will happen. If you are cognitively processing while being measured for cranial bone movement, you have a fascial reaction and that does create a lot of disturbance in the measurements. You actually see that in the data. 

LAH: When I first read your paper I thought, these researchers must be physicists because there is a lot of math and physics in how this investigation was done. You’re a medical researcher. You and your team, you built the machine for this type of investigation. 

TRR: We built it completely from scratch and the sensors are robot technology. When you have robots that need to do something, then you need to know the exact distance of movement for robotic arms. And the robot needs to know the exact pressure and it needs to control all movements. So, we took the sensors from robot technology and then integrated it with complex software to try to deal with all these variables. 

LAH: That’s so smart. You’re providing an important piece of the puzzle for us practitioners as we communicate with medical colleagues. It is hard to convey that the physical interventions manual therapists are doing are interacting with this third rhythm. That there is a third rhythm of the head and body, that it is something we can palpate, and it’s something that we are working with to alleviate discomfort. Up until now, I haven’t had a paper that I can point to with my physician clients and say, “Here it is, the third rhythm characterized and published.”

TRR: Yes, right, and it’s also been very helpful for educating therapists, because when I teach now, I am even more clear about what they have in their hands. I encourage them to distinguish between when they feel the third rhythm, from the breathing movements and arterial pulse. You can feel it everywhere in the body when your palpation skills are increasing, but in the beginning, we say, “Okay, you want to actually feel the two different rhythms,” meaning the difference between respiration in the thorax from the third rhythm. They are close together in their cycle frequency. 

We have done clinical explorations where we invited very experienced craniosacral therapists and we blindfolded them while they were palpating the cranium. And then we asked, “What do you feel?” We could see from our live data from the head sensors when they were reporting feeling the breathing cycle and we could confirm for them when they were differentiating that from the different rhythmic movement of the third rhythm. We gave them instant feedback while palpating.

LAH: So cool, what a great way to learn. Let’s talk about the results of this particular investigation. You reported your results as frequencies of cycles per minute (see Figure 1A). People breathe about fifteen to forty times a minute, where there is individual difference between people. You graphed the frequency of movement in relation to time on the x-axis and the amplitude of the movement on the y-axis, or range of excursion. So, we can see a cluster of movements between fifteen to forty cycles per minute clearly – that’s the head being moved by the person’s breathing. And slower than that, there is a second peak from four to thirteen cycles per minute. Am I seeing that correctly?

TRR: Yes.

LAH: And that slower rhythm is the third rhythm that was observed with each participant?

TRR: Yes, we had a second measuring device on the body detecting the respiration movements on top of the respiratory diaphragm (see Figure 1B), so the breathing movements in the head were detected (see Figure 1C) and confirmed with the thoracic breathing movements. We observed variation in people’s breathing, even when they were lying down. When we looked at head movement there was something else other than this. There was actually a rhythm that is slower than breathing (see Figure 1D). 

Figure 2: Measuring of cranial rhythmic movements and separating a third rhythm from the movements of thoracic respiration. (A) Frequency of cranial movement in relation to time on the x-axis and amplitude of the movement on the y-axis. Two clusters of movement observed, one averaged thirty-five cycles per minute and the second was observed at four to six cycles per minute. (B) Respiratory movement measured at the respiratory diaphragm for a single person over a period of sixty seconds. This individual’s respiration was sixteen cycles per minute. (C) Rhythmic movements of respiration measured in the cranium movements matches the sixteen cycles per minute. (D) The third rhythm. It is rhythmic movement in the narrow cluster of four to six cycles per minute identified in A. This third movement is a wave within a wave function with a ‘shoulder’ about halfway between maximum and minimum amplitude. Creative Commons license: CC BY-NC-ND 4.0.


The breathing rhythm is a beautiful sigmoid curve. When we looked at this third rhythm, it was slower and it could be recognized by a completely different movement pattern. 

LAH: Fascinating, such important information. I’m hanging on to the idea about differentiating palpating the breathing movement at the head compared to this third rhythm. They are close together in their cycles per minute, but the third rhythm is differentiated by both being slower and not being a simple sigmoid curve. 

What is the wave nature of the third rhythm?

TRR: It is a wave within a wave. 

LAH: The mastoid processes were measured to be moving away from each other, that was the peak of the high amplitude part of the graph. Then the mastoid processes start moving toward each other to a middle zone, where the movement turns around for a moment, and then the mastoid processes move away from each other again. They do this just for a little bit of time, that must be the smallest of spaces, and then the movement turns around again as it were, and the space between the mastoid processes decreases quite a bit to an inferior peak. These low peaks are the smallest distance measured between the mastoid processes. The movement amplitude then starts to increase. And again at the middle zone, the area on the mastoid processes neither at their widest, nor at their closest, do this second expand away and narrow together with a small amplitude, before then taking the long trip back up to the widest amplitude peak. 

How did you make sense of that?

TRR: We looked very closely at this detail because in cranial studies, especially from Sutherland, it is all based on this flexion/extension movement, with a neutral zone in the middle. As practitioners, when we are palpating, we feel this stopping or shift, in the middle as you said. With our hands we can feel that as distinct from the flexion to extension. We were very interested to actually measure this. Then we designed the software so we could try to really look in detail at this wave function. What we realized is that by laws of physics and looking at wave functions, this is a wave within a wave. Why is there a wave within a wave? We don’t know, but we are very interested, as this might give a clue as to where the wave is coming from. 

We compared this third rhythm wave form with the idea of understanding the waves on a cardiogram that have a very complex movement. We are at the beginning of this study; we are curious to find out. It is a part of physiology, and when we see this wave pattern, it is giving us a clue. That is what we are looking into now, how is the wave of this rhythm shaped. Perhaps there is a shifting where these waves are produced or something is interfering, one wave source on top of another wave. In theory, this third rhythm could be the product of two different things going on in the body, but they always follow each other. And so, they’re very close. Whatever generates it, this wave inside a wave is a clue and that is what we are trying to follow. 

LAH: That graph (Figure 1D) is interesting to look at, to see the wave on a wave shape you measured, I want to superimpose that knowledge on what I feel between my hands while working. Of course, I want to assign meaning to this, I want to say to myself, the choroid plexus is producing the cerebrospinal fluid and this expansion is perhaps the one aspect of this wave where the mastoid processes move away from each other. And then the downstream absorption of cerebrospinal fluid being the part of the wave where the mastoid processes are their closest, with that inner wave as the neutral zone. Is that what you, perhaps, think it is?

TRR: This comes down to a very core question, and that is, is it the cerebrospinal fluid, and the physiology of this liquid form, that creates the movement, or, do we have a mechanism that makes this movement in the liquid? Which one comes first or what is generating what?

And of course, we look into a lot of brain research regarding cerebrospinal spinal fluid circulation in the brain. What you can see from that is that even the production of cerebrospinal fluid by the choroid plexus is controlled by many mechanisms, including the higher sympathetic tone. Autonomic nervous system balance influences cerebrospinal fluid production. We have cilia that sit on the lining of the ventricles that can move cerebrospinal fluid in a certain direction when it wants to do that. The movement of the cerebrospinal fluid in the third ventricle is controlled largely by a hormone that generates cilia movement. 

Brain scientists have actually put a camera inside the third ventricle and there you can see the cilia are moving. And if you are blocking this hormone, you’re blocking the cilia movement, and then by extension, you are blocking the movement of cerebrospinal fluid. 

Movement in the fourth ventricle has also been measured where you can see in daytime, when people are walking and talking, the pulsing of the cerebrospinal fluid follows our breathing rhythm. But when people go into deep sleep, their brains shift to a different brainwave pattern, the cerebrospinal fluid falls to a very slow wave, but it creates more fluid movement. So that relates to how important deep sleep is for cerebrospinal fluid movement around the brain. How that relates to stress when there is a lack of deep sleep is something to think about, perhaps it plays a role in developing Alzheimer's disease. 

LAH: This is great information. Another finding that I thought was unexpected was that this third rhythm didn’t have a lot of variation between individuals compared to the variation of their breath. When it came to the cycles per minute, everyone was almost the same, in a small range (see Figure 3). Did I see that right?

Figure 3: The average (mean) rate of the third rhythm for each participant in the study (n=50). Range of third rhythm of the cranium is from four to seven cycles per minute. Creative Commons license: CC BY-NC-ND 4.0.


TRR: Yes. But also, look at this other graph (see Figure 4). You can see it is  measurements from three individuals while they are lying down for forty-two minutes. The person with the highest rate, they also had the bigger variation. The correlation between the variation in the rhythm and the rate of the rhythm was quite strong. It seems that these high-rhythm people had more superficial, fast breathing, but a fifty-person study was not large enough to determine that part. 

Figure 4: Dynamic nature of the third rhythm during rest of the three persons who represent the highest, lowest, and mid-range rhythm. Mean, max, min, and variance are given for each person. Creative Commons license: CC BY-NC-ND 4.0.


Our new study also looks at this to define the relationship on a larger scale, relating the third rhythm to breathing and to see if this relates to a basic autonomic nervous system setting. The third rhythm will not go quickly up and down; if you measure the average rhythm of a person and you do it next week and next week and next week again, it’ll be in the same range. And the mean measure [the average] would also be the same under the same conditions of measurement, relaxing awake. 

LAH: In the paradigm of Rolfing® Structural Integration, we tend to think about clients as on a spectrum of fascial tension, or tonality is a word we like to use, between hypertonus, where their fascia is generally tight and perhaps feels like shrink wrap to touch, versus hypotonality where people have a lot of fluidity, at the extreme it can even be too much. When I read that part in your article about the lower cycles per minute relating to less movement of the temporal bones, it made me think, perhaps that is their fascial system wholistically just really tightly wrapped? Perhaps hypertonality generally would be most related to the smaller amplitude of movement between the mastoid processes?

TRR: If you think of the fascia, then think of the amplitude of the skull. Think of the superficial fascia around the skull. If we think of that tightness, we can say it may be a clue to what we are going after here. What would be important for the clinical studies is the amplitude of the skull movement. If you look at the amplitude of the skull movement in Figure 5, that is where the big variation is between participants and that could be closely related to the hypertonus/hypotonus of fascia in the Rolfing paradigm. 

Figure 5: The amplitude of all three rhythmic head movements originating from the arterial pulsation, respiratory breathing, and the third rhythm were measured in micrometers. Grey bar on top = arterial pulse generated amplitude, black = respiratory breathing generated amplitude, and grey bar below = third rhythm generated amplitude. Creative Commons license: CC BY-NC-ND 4.0.


When we compare amplitude of the relaxed state between clients, then practitioners can feel the fascial system of the body and feel a very core part of the fascial system, and that’s going to be easiest with people with the big amplitude. Then a practitioner feels a tight fascial system, and their client has a very low head amplitude when palpated. As practitioners, we come across clients with this presentation, they can have asymmetry and a tight skull. If you try to move the fascia, it doesn’t really want to move. And that hypothetical client, say they have very low flexibility in the fascial system in general, this is how you mean that they have a low amplitude. 

LAH: Yes, you get my thinking. 

TRR: Yes, so the amplitude of the skull you can say from a clinical perspective is a very important part because that’s where you see the instant effect of a fascial reaction from manual therapy, because we know that cranial manipulation is a fascial treatment. When you do something with the fascia of the central nervous system, as you’re doing craniosacral work, you shift the amplitude very quickly. 

LAH: That is the meaning that Rolfers often make when we are making our fascial interventions. To have yourself and your lab group investigating it is very exciting. 

You mentioned that in the paper, the past research about the cranial rhythmic impulse was primarily done experientially based on investigations where practitioners were reporting their palpation findings, but this was not received well by the scientific community due to the variation of practitioner skill and the subjective nature of that type of inquiry. We already touched on this, that the palpation of the primary respiratory motion was often done by practitioners monitoring the sphenoid-occiput movement, and to quote your paper it said, “Palpating only for the expansion and retraction may often lead to palpation of respiratory-generated movements . . . As the visceral pharyngeal basilar fascia is attached on this sphenoid/occiput area, the degree of respiratory-transmitted movements to the head may depend on the tension in this visceral fascial system” (Rasmussen and Meulengracht 2021, 28). 

Are you saying there that this particular fascia transmits the breath movement to the sphenoid and the practitioner is not feeling a pure third rhythm at the sphenoid because of it? And, is that why you chose to put your sensors on the temporal bones, to bypass that?

TRR: No, because you can say the movement will reflect into all of the skull. So we did test if we move the sensors around the skull, will we have the same rhythm, and we investigated whether we would get different amplitudes. But the reason why we chose the mastoid was because it’s a very easy fix point for everyone to lock the sensors on. We could repeatedly lock them the same way between people. If you go up on the skull, you start to have differences in the skull, and it becomes more difficult to say we are on the same point. That was very important, not for the rate of the rhythm, but more for the studies of amplitude. 

The part that you bring up about the fascia is because we can say the whole Sutherland’s concept is based on the movement of the sphenoid. If you look at the fascia systems that affect the skull, the pharyngeal basilar fascia has a very strong attachment on the sphenoid, that is central in osteopathy and craniosacral work. And we say to ourselves, okay, we have a strong fascia sitting here that affects the whole head movement. I did a series of sessions with people with asthma. For people who have suffered real asthma for years, every time they breathe, everything on the head follows that movement because the fascial system is tight. Because you have a tight fascial system, it transmits respiratory breathing movement strongly into the skull; as a practitioner you really have to focus to bypass that breathing movement and feel the third rhythm, because the respiratory breathing can be such a strong movement in the asthmatic situation. 

This is our explanation, because some people have a very light fascial system that is very elastic, and then the biggest contribution to the movement of the head is the third rhythm. But if you have someone where their system is tight, then you can say the movement will be very influenced by respiratory breathing, and you’ll feel that readily on the skull. 

LAH: What great information. I really appreciate how you’re cautious in your language in the paper. You focus on the term: third rhythm. Is that because it isn’t yet known what the source of the third rhythm is? How do you teach practitioners to speak about this concept?

TRR: This is my recommendation when different schools are in contact with me, they want to take the conclusions one step ahead like you mentioned, and I turn it around and I say, “The reason why we call it the third rhythm is to keep it open for everyone. We have measured something. If your school wants to call it something, you are welcome to do that, but you need to define what you mean.” We can call it the craniosacral rhythm and if you say that the third rhythm is the craniosacral rhythm, then you need to define it from that. We don’t know what is moving here. Is it the fascia contraction? Bones moving? We don’t know. So, we have to be honest and say, we can conclude on what we have measured here, but we cannot draw the conclusion further than that. Everyone can look at this study and see we have something measured and it is different from respiration and heart rhythm. We have to be careful what we call it or we have to define clearly what we associate it with.

We need to think differently if we want our profession to develop and we want to be as clear as possible when we speak and when we teach. It becomes important when we want to speak between different schools or when we want to speak with the medical society. We can be clear in what we are saying, and I think fascia research in general is very interesting. For many schools, including yours, fascia research is very important for understanding the actual phenomena of the body, and fascia research informs how we develop what we do. 

LAH: So well said, it’s an exciting time to be doing this work because of the increasing volume of fascia research, now we have peer-reviewed work as our baseline of ‘normal’ function. As practitioners, we are able to learn from researchers, like you, and paying careful attention to our language is so important. The variable called the third rhythm is a new language for me and I’m going to use it liberally. It is important that we have a common language that’s agreeable between disciplines. 

You already mentioned a little bit about the relationship of the third rhythm and the autonomic nervous system, you related it to having changes between walking compared to sleeping. My own lens when I think about autonomic nervous system functioning, I think about sympathetic and parasympathetic arousal levels, as Rolfers we often think about fight, flight, and freeze. Do you think the third rhythm has variation around these kinds of arousal states?

TRR: I would believe so, but I don’t have the data. I have a sense that what we have seen in the data is that the third rhythm is more a long-term setting. Let’s say my brainstem, due to whatever I experience as trauma in my life, more easily goes into the red-alert trauma field. So, I will be running on a fight or flight responses very easily. Then my base setting in my autonomic system is high. We know that if you have a client and their base setting is very high, it will often be a long-term process to shift the brainstem setting to be in less frequently in the red zone. But maybe many sessions can support the baseline autonomic function to a more flexible setting. 

LAH: Exactly. 

TRR: I think that the third rhythm has some kind of relation to that and we will see a more long-term pattern. Breathing can do this in a clearly palpable and observable rate. The cardiac rhythm can do a quick response, but the third rhythm is a more long-term setting. When we see people with a more superficial breathing and that they are alert, they have a tendency to have a higher arousal rate. Whereas, the people who have deeper and more flexible breathing, they have a tendency toward a lower rate. It’s only a tendency that we see. Like all the other basic life rhythms, they have at least some part of their control from the brainstem. And we know that the cranial or third rhythm is out of our cognitive control. You cannot control it. 

LAH: Your article is just the big beginning of so many great questions. What kinds of things are your research team looking at next? 

TRR: We can say what’s coming out in 2022. We will look at physiological experiments where we are pressing the human body to its extremes while we are measuring the third rhythm. We are redesigning the equipment for that because you need to measure someone who is moving. So, we will look at what happens when people perform at their maximum output and what will happen when they go from that to deep relaxation. 

LAH: From running to stillness. 

TRR: Yes. And what happens when you force the breathing, if you hyperventilate to almost fainting states. So that’s one part of what we are looking at. Then we have done a very long-term clinical study to see the long-term effects of craniosacral therapy on the rhythm, on the amplitudes and the skull, because as a practitioner, as you said yourself, you feel that if you have this completely frozen fascia system, or you feel that tightness and tension in the fascia, will that actually change when you follow the person over time and will that change affect the amplitude of movement of the skull? And the major thing that we are interested in here is finding out if we can affect the cerebrospinal fluid circulation with manual interventions. For me, I see that as a very important part in the future, because of the exponential increase in neurodegenerative disorders like Alzheimer’s and all kinds of dementia. 

LAH: Yes, this is the heart of it. Your work is directly expanding the knowledge we have and it’s gratifying to think about this now clearly defined third rhythm and the relationships that may now be observed, the important questions to ask. Thank you so much for helping me and our readers get up-to-date with this current knowledge. Great research, thank you for explaining it to us. 

TRR: You’re welcome. Hopefully all the different aspects we have from fascia, physiology, and central nervous system research come together in manual therapy and we can be a major part of the future of health care. 

Thomas Rosenkilde Rasmussen, PhD, MSC, CST-D, is a Danish researcher and craniosacral therapy practitioner. He has a PhD in medicine from University of Copenhagen, a master’s of science degree in chemistry, a bachelor’s degree in biochemistry, and another bachelor’s degree in biology. For fifteen years Rasmussen worked as a scientist in cancer research, working in different parts of the world including Canada, United States, and Japan. Part of Rasmussen’s research was with hematological cancers. He also has a focus on the craniosacral system, as he is an instructor with the Upledger Institute International, and the Director of Research for Upledger Institute International. 

Lina Amy Hack, BS, BA, SEP, became a Rolfer in 2004 and is now a Certified Advanced Rolfer (2016) practicing in Saskatoon, Saskatchewan, Canada. She has an honors biochemistry degree from Simon Fraser University (2000) and an honors psychology degree from the University of Saskatchewan (2013), as well as a Somatic Experiencing® Practitioner (2015) certification. Hack is the Editor-in-Chief of Structure, Function, Integration. 


Frymann, Viola M. 1971. A study of the rhythmic motions of the living cranium. The Journal of the American Osteopathic Association 70(9): 928-945.  

Rasmussen, Thomas Rosenkilde, and Karl Christian Meulengracht. 2021. Direct measurement of the rhythmic motions of the human head identifies a third rhythm. Journal of Bodywork and Movement Therapies 26:24-29. 

Sutherland, W. G. 1939. The cranial bowl. Mankato, Minnesota: Free Press Co. ■ 

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