How do you measure postural tone? In this essay, Tim Cacciatore and Korina Biggs describe Cacciatore et al’s 2011 study, “Increased dynamic regulation of postural tone through Alexander Technique training,” published in Human Movement Science. The researchers use a novel device, dubbed “Twister,” to detect marked differences in background postural town between healthy controls, Alexander teachers, and subjects with back pain. The study documents reductions in postural stiffness in subjects with back pain after Alexander technique lessons. The essay was original published in Stat News in 2011.
This piece of research was driven by an interest in studying how the Alexander Technique affects patterns of muscular tension in the body. The brain must regulate muscle tension in order to support the body against gravity. This type of long-lasting muscle activity is technically called postural tone, and is particularly important along the body axis to keep the spine from collapsing. Because it seems so basic, it is easy to suppose that postural tone is well studied and scientifically understood. Surprisingly, it is not. This is primarily because postural tone is difficult to measure. Its slight magnitude, ongoing nature, and broad distribution across the musculature make it difficult to quantify. In contrast, balance (how we keep our body mass above our feet), a very different phenomenon, is well studied and well understood. This is because the frequent forward and back movements that occur with balance are easy to measure, in contrast to the sustained forces that oppose gravity, which are not.
Several years ago Dr Cacciatore worked in collaboration with Victor Gurfinkel, in Portland Oregon, to help devise a method for measuring postural tone, referred to as ‘Twister.’ It is a machine which measures and analyses the force required to very slowly twist the neck, trunk or hips as a person stands upright.
Standing upright requires muscular activity to counteract gravitational forces, and twisting stretches these muscles so that the resistance we measure to twisting reflects the forces (i.e. tension) in these muscles to oppose gravity. Leaning against a support reduces the amount of muscular activity needed and would affect the measurement. Thus Twister is built in a way that twists you, but you can’t lean on it, so that the resistance measured reflects a subject’s unaided muscular opposition to gravity. This is achieved by Victor’s clever arrangement of hinges and springs.
To ensure that the measurement of resistance reflects muscular forces, the twist is small. This was to exclude forces from ligaments, which only begin to tighten at around 30 degrees of twisting, so keeping the twist well below that angle gives a measurement of postural tone. Twister can be configured to measure tone in the neck, trunk or hips. Measurements reflect the total integrated activity of all muscles within each region, as opposed to that of a particular muscle. To date this method has led to six publications that help to shed light on how postural tone is controlled, but this is the first one to involve the Alexander Technique. The subjects of the other papers included Parkinson’s disease, and how tactile information affects postural tone.
The first Twister study (Gurfinkel et al. 2006) revealed that postural tone differs substantially across individuals. Stiff people are much stiffer (3–4 times) than less stiff people. These differences in postural tone could be caused by two factors: the amount of muscle tension, or how this tension adapts dynamically to changes in posture or load. In other words, low stiffness could result from a person having low tension or by changing this dynamically during twisting—by ‘letting go’ (reducing activity) of those muscles lengthened by twisting and ‘taking up slack’ (increasing activity) of those shortened. This first Twister study found that the major difference between subjects was that stiff people tended to have fixed muscle activity, while those who were less stiff adapted tone dynamically.
The objective in the present study was to investigate the effects of the Alexander Technique on postural tone. While it is clear from subjective experience that such patterns change, it is not clear precisely how. The amount of tension, its distribution throughout the body, and its dynamic adaptability likely all change from lessons, in complex interrelated ways. This study began to examine these issues. From a scientific standpoint, the question of general importance was whether a person can make their tone more dynamically responsive through some kind of training.
This study consisted of two parts. First, the postural tone of Alexander teachers was compared with that of control subjects. Second, the postural tone of people with low back pain was examined over time—before and after lessons. These two approaches yield complementary information.
Postural tone was measured with Twister in the neck, trunk and hip. Each of these requires separate trials, with body attachments in appropriate places so that the respective region is rotated. In all cases, several ten degree rotations in each direction were used, which takes three minutes as rotation is very slow. In essence, a trial feels similar to having a teacher with very free hands turn your head, shoulders or pelvis very slowly. The device feels unusual because it is extremely stiff towards rotation (required to measure resistance) but extremely compliant for all other motions (so as not to provide postural support).
Study using Alexander teachers
Fourteen pain-free teachers and fifteen pain-free control subjects were recruited to match in age, weight, height and gender.
It was found that the Alexander teachers had much lower resistance to twisting than control subjects. The average stiffness of Alexander teachers was roughly half that of the controls for all regions (i.e. neck, trunk, and hips).
As described above, the lower stiffness in Alexander teachers could be due to having less tension or more adaptive tension. Three different methods were used to assess how adaptive their tone was: the variability of resistance, the shift in neutral position (also called phase advance), and electrical measurements of muscle activity. In general, adaptive tone is more variable, has a larger shift in neutral position, and muscle activity that changes with twisting.
This study found that all three measures were greater in Alexander teachers than in the controls, indicating that their postural tone was more adaptive. A correlational analysis supported that this increased dynamic adaption did indeed contribute to lower stiffness.
Study using the back pain subjects
Eight subjects with low back pain were used. All subjects were tested over a baseline period, after a placebo-control intervention, and after Alexander lessons. The interventions were both given two sessions per week for ten weeks. Intervention order was also randomised.
It was found that the back pain subjects decreased hip and trunk stiffness significantly (by 29%) following Alexander training but not the control intervention. Neck stiffness was not measured. Before lessons, back pain subjects had more variation in stiffness: some were very stiff while others had extremely low stiffness. The subjects with the highest stiffness had the biggest decrease from the Alexander Technique. There were not enough back pain subjects to determine whether their postural tone became more dynamic, however.
The significance of this study is that it found the Alexander Technique changes the muscle tension along the spine and hips that supports the body against gravity. Importantly, the part using Alexander teachers showed that the Technique changes this tone in an interesting way, by making it more dynamic (i.e. less fixed).
The study also found that both Alexander teacher training and a short course of lessons decrease stiffness along the spine and hips. The effect of teacher training appears to be considerably bigger, however. It is important to note that low stiffness is not necessarily a good thing (as was found in some back pain subjects). It can result from insufficient support as well as highly adaptable tension.
This study represents a first step towards understanding the Alexander Technique and postural tone. More research is needed to understand how the amount of tension and its distribution throughout the musculature change with the Technique, in addition to its adaptability. Future studies will examine these issues as well as how postural tone relates to movement co-ordination and pain.
Cacciatore, T.W., et al. (2011) Increased dynamic regulation of postural tone through Alexander Technique training. Human Movement Science. Vol 30, Issue 1. (pp. 74–89).