The Yi Jin Jing, generally translated as the ‘Classic of the Transformation of Muscles and Tendons’, can be understood, in contemporary terms, as a progressive method for reconfiguring the musculo-tendinous, fascial, respiratory, postural and nervous systems, rather than simply as a set of stretching exercises. Where tradition speaks of ‘changing the tendons’, ‘loosening the muscles’, ‘circulating the breath’ and ‘strengthening the interior’, scientific vocabulary describes instead an improvement in active mobility, neuromuscular coordination, postural tone, proprioception, diaphragmatic breathing, autonomic regulation and the quality of connective tissues. It remains necessary, however, to exercise constant caution: modern science does not validate all the claims attributed to the Yi Jin Jing, but it does provide sufficient insights to understand why this practice can produce tangible effects on the body’s overall organisation.
From this perspective, the Yi Jin Jing cannot be reduced to a simple passive stretch. It involves a methodical interweaving of held postures, slow movements, active stretches, joint rotations, deep breathing, focused attention, gentle contractions, progressive releases and overall body coordination. Whereas conventional stretching primarily alters the perception of range of motion, the Yi Jin Jing offers controlled ranges of motion, guided by the breath, organised around an axis, sustained by intention and accompanied by light but constant muscular activation. From this perspective, it is closer to neuro-myo-fascial training than to a simple flexibility exercise, a view confirmed by recent research which describes it as a traditional method capable of improving flexibility, strength and physical performance, particularly in older adults, although the quality of the evidence varies from one study to another.
The term ‘Yi’ in the title refers to the idea of change and transformation, which can be rephrased, in scientific terms, as a process of gradual adaptation of the body-brain system. As the same movement is slowly repeated, the nervous system refines its ability to control muscles, joints and balance; motor circuits become more efficient, the perception of the body’s position in space becomes more precise, and movement becomes more refined, shedding unnecessary compensations. There is nothing magical about this: what tradition presents as transformation stems from neuroplasticity, that is, the nervous system’s ability to reshape its connections through repetition, attention and conscious bodily experience.
As for the word ‘Jin’, often translated as ‘muscles and tendons’, it now needs to be broadened: it also encompasses the fasciae, ligaments, joint capsules, aponeuroses, and the entire network of connective tissues and myofascial chains that organise the transmission of forces within the body. The Yi Jin Jing never works on an isolated muscle; when we stretch our arms, open our chest, rotate our spine, or shift our weight down into our legs whilst breathing deeply, it is continuous lines that stretch and readjust, from the feet to the legs, from the pelvis to the spine, from the shoulders to the hands. This view is very close to the modern concept of myofascial chains, where the body is seen as a network of interconnected tissues rather than as a collection of independent segments.
Within this network, the fasciae play a central role. These connective tissues envelop, connect and transmit tension between muscles and organs; they contribute to posture, the transmission of force, proprioception and the body’s internal sensitivity. The slow stretches, spiral twists, open postures and the interplay of opposing directions characteristic of the Yi Jin Jing seem particularly suited to fascial physiology, which responds well to progressive stress, multidirectional stretching, variations in pressure and slow movement, all of which are conditions conducive to tissue hydration and the maintenance of their elasticity. Contemporary research on the fascial system also highlights its ability to store and release elastic energy and to contribute to the overall efficiency of movement, which directly illuminates the logic of the ‘tendinous force’ sought in the internal arts.
The practice also has a profound effect on proprioception, the ability to sense the body’s position, the angle of the joints, the degree of muscle tension, balance and movement. The Yi Jin Jing constantly prompts implicit questions such as: where are my feet, my centre, my shoulders, my breath, my spine, my hands; am I pulling too hard, am I slumping, am I really breathing? This silent awareness refines the body’s internal map: the more precise the map, the clearer the movement and the less confused or hesitant it becomes. This is one of the reasons why this type of work can support balance and coordination, a fact confirmed by research into traditional Chinese exercises – including the Yi Jin Jing – which highlights positive effects on balance and walking in older people.
In terms of strength, the Yi Jin Jing is not like heavy weight training. It strengthens the body through slow contractions, fine postural control, holding specific positions, working against one’s body weight, and close coordination with breathing. When the arms remain raised, the legs bend gently, the spine lengthens, and the posture is maintained without tension, it is the deep muscles that take over: the stabilising muscles of the back,
the deep core, and the musculature around the hips, legs, shoulders and neck. The result is a subtle yet profound strengthening, which focuses less on visible muscle mass and more on the quality of support, joint stability and the ability to maintain a gentle, continuous and sustained tension. Recent analyses of the Yi Jin Jing in older adults support this view, suggesting potential benefits for muscle strength and physical performance, whilst noting that the evidence remains mixed.
Tendons, for their part, respond particularly well to progressive, repeated and well-measured stresses. From this perspective, the slow pace of the Yi Jin Jing becomes a protective factor: each posture establishes a moderate but continuous tension, which teaches the tendon to bear the load, to transmit force and to stabilise the joint without being subjected to traumatic jolts. Where traditional terminology refers to ‘making the tendons supple and strong’, modern physiology speaks of connective tissue remodelling, mechanical adaptation and improved force transmission along the myofascial chains. The joints benefit from the same approach: shoulders, wrists, spine, hips, knees, ankles and ribcage are mobilised slowly, through large, controlled ranges of motion. This mobilisation improves joint lubrication, the coordination of the muscles around each joint and the awareness of individual limits; it can reduce certain stiffnesses, provided a fundamental principle of the tradition is observed: a joint must never be pulled violently, the correct stretch being described as deep but comfortable, intense but not painful.
The spine occupies a central place. Flexion, extension, rotation, lengthening, opening of the back, relaxation of the neck, and fine adjustment of the pelvis: the Yi Jin Jing invites a segmental rediscovery of the spine, not as a rigid block but as a succession of coordinated segments. This work can improve segmental mobility, postural awareness, and coordination between the pelvis, spine, and ribcage. As many back pains are linked to a lack of movement, poor distribution of stress, excessive tension or weakness in the stabilising muscles, a slow, gradual, mindful practice that restores flexibility to the spine without straining can help to reorganise the system, though it does not promise an automatic cure for all lower back or upper back pain.
Diaphragmatic breathing is another essential pillar. The Yi Jin Jing generally employs slow, deep, regular breathing, synchronised with movement. Such breathing engages the diaphragm, ribs, abdomen and back; it alters intra-abdominal pressure, supports trunk stability, promotes venous return and influences emotional state as well as the balance of the autonomic nervous system. Slow breathing appears to encourage parasympathetic activity, associated with calm, recovery, digestion and internal regulation; recent studies on Qigong suggest that long-term training can not only deepen breathing but also improve the coupling between breathing and the autonomic nervous system, refining physiological responses during and after practice. In this context, the Yi Jin Jing can be understood as a method of modulating the autonomic nervous system: by moving slowly, breathing deeply, by relaxing the jaw, stretching gently and maintaining attention within the body, we send a signal of safety to the nervous system that reduces sympathetic hyperactivation – tension, hypervigilance, shallow breathing, defensive contractions – and creates more space for recovery.
Attention itself is not merely an accessory. The Yi Jin Jing requires precise presence, which alters the way the brain organises movement. A movement performed mechanically yields little in the way of learning; the same movement performed with attention becomes an opportunity for neurological remodelling. The brain refines its sensory maps, inhibits superfluous contractions, improves coordination and strengthens the coherence between intention and movement. What the tradition calls Yi – clear intention – corresponds, in contemporary terms, to processes of attentional control, sensorimotor integration and cortical regulation of movement. In this context, learned relaxation is far from being a state of flaccidity: it is an ‘active relaxation’, in which one reduces unnecessary contractions without losing basic postural tone. The body learns to maintain a posture with less energy expenditure; muscles that were working excessively calm down, whilst those that are truly necessary organise themselves more effectively. This neuromuscular optimisation paves the way for the emergence of a particular kind of strength, often described as ‘elastic’.
Metabolically speaking, Yi Jin Jing is generally of low to moderate intensity. It does not replace sustained cardiovascular training or intensive weight training, but it can make a significant contribution to overall physical activity, particularly for sedentary, elderly or frail individuals who struggle with strenuous exercise. Some studies combining Yi Jin Jing with other forms of exercise, such as the use of resistance bands, report effects on weight, body fat, muscle function or certain metabolic markers in middle-aged or older individuals with prediabetes. Here again, it remains necessary to distinguish between the effects attributable to Yi Jin Jing itself and those resulting from a broader combined programme.
Because it combines movement, attention, breathing and emotional regulation, Yi Jin Jing also influences brain dynamics. As a mind-body practice, it engages the neural networks involved in attention, mood and body perception.
A recent study examining a Yi Jin Jing intervention in patients suffering from post-stroke depression highlighted an improvement in mood correlated with changes in functional brain connectivity; this example illustrates the practice’s potential, although sample sizes, the specificity of the populations and the variety of protocols mean these results should be interpreted with caution. The slowness of the movements, at the heart of this training, plays a decisive role here: it gives the nervous system time to perceive errors and correct them in real time. In a rapid movement, compensations go unnoticed; in a slow movement, the raising of the shoulder, the buckling of the knee, the holding of the breath, the closing of the pelvis or the stiffness of the neck become visible and thus amenable to change. This slowness makes the Yi Jin Jing a veritable laboratory for the body, a space where the invisible becomes perceptible.
The hips, for their part, are worked through bends, rotations, lowering and weight transfers, which directly links the practice to issues of posture, walking, balance and back protection. Free hips allow the weight to drop and permit a holistic movement, whereas locked hips force the spine to compensate. Deep breathing, linked to the concept of intra-abdominal pressure, further helps to stabilise the whole system. It is not a matter of rigidly contracting the abdominals, but of gently establishing a dialogue between the diaphragm, pelvic floor, deep abdominal muscles and back muscles. The Yi Jin Jing cultivates this internal stability: from the outside, the body appears relaxed; from the inside, it is supported by a subtle architecture of pressure and tone.
The Yi Jin Jing can be seen as a form of training in bodily anti-fragility. With age, strength, mobility, speed, balance and bodily confidence diminish; this method addresses many of these losses through a gentle, progressive practice combining mobility, flexible strengthening, balance, breathing and mindfulness. It does not replace all other forms of exercise, but it occupies a unique place due to its ability to integrate, within a single movement, tissue work, training of the nervous system and the cultivation of a stable mental presence. This, moreover, explains the growing interest in contemporary research into the Yi Jin Jing in the context of ageing and chronic conditions.
The Xi Sui Jing, generally translated as the ‘Classic of Washing the Marrow’, lends itself less readily to a direct scientific explanation than the Yi Jin Jing, because studies focusing specifically on it are rare; yet, based on what we know today about qigong, slow breathing, bodily meditation, the autonomic nervous system, immunity, deep tissues, bone marrow, the brain-spinal cord axis and psychophysiological regulation, it is possible to offer a serious and coherent interpretation of it. It is important to clear up a misunderstanding from the outset: nothing in the available data allows us to assert that the Xi Sui Jing literally ‘washes’ the bone marrow; this image belongs to traditional language, but it can be understood as a metaphor for a profound transformation of internal regulation – the nervous system, the immune system, blood circulation, breathing, body awareness, stress, sleep, internal perception and the capacity for recovery.
In classical terminology, ‘Xi Sui’ does indeed mean ‘to wash’ or ‘to purify the marrow’, and this marrow is not limited to bone marrow in the modern sense: it refers to a complex system encompassing bones, the brain, the spine, deep vitality, Jing, longevity and clarity of mind. The Xi Sui Jing is often presented, within the tradition, as a more internal practice than the Yi Jin Jing: whereas the latter emphasises the transformation of muscles, tendons, fasciae and visible physical strength, the Xi Sui Jing focuses on the depths – marrow, brain, nerves, vital essence, consciousness – and thus operates at a more subtle level of practice. From a historical perspective, the exact origin of these two classics remains a matter of debate: some lineages link them to Bodhidharma and the Shaolin Monastery, but contemporary textual research suggests later processes of compilation and reconstruction, involving Buddhist, Taoist and martial influences, and highlights that direct attribution to Bodhidharma is difficult to sustain on strictly philological grounds.
If one attempts to translate the idea of ‘washing the marrow’ into contemporary language, one might say that the Xi Sui Jing aims at a profound regulation of the body’s internal state rather than a crude focus on the musculature alone. It is not simply a matter of loosening the tendons or strengthening the muscles, but of altering the way the entire organism functions: calming the nervous system, refining the breath, promoting circulation, reducing chronic stress, refining bodily awareness, supporting immune functions, improving recovery, and establishing a more stable coherence between body, breath and mind. Science therefore does not speak of ‘qi washing the marrow’, but of regulation of the autonomic nervous system, stress modulation, the influence of breathing on the heart and brain, deep proprioception, interoception, inflammatory balance, immunomodulation, brain plasticity, vagal tone, sleep quality and neuroendocrine coordination.
From a strictly biological perspective, bone marrow is a living tissue located at the centre of bones, responsible in particular for the production of most blood cells – red blood cells, white blood cells, platelets – and is therefore closely linked to oxygenation, immunity, tissue repair and general vitality. It would be misleading to claim that a qigong exercise ‘cleanses’ the marrow in the same way one cleanses a surface; however, it is reasonable to assume that regular practice which improves stress levels, sleep, circulation, autonomic regulation and certain inflammatory markers creates an environment more conducive to immune and haematological balance. From this perspective, the traditional metaphor of ‘washing the marrow’ becomes meaningful: it evokes the gradual release, deep within the body, of the cumulative effects of chronic stress.
The link with immunity emerges naturally here. As the bone marrow is central to the production of immune cells, any practice capable of modulating stress and inflammation may, indirectly, influence certain aspects of the immune response. However, qigong, taken as a whole, has already been studied for its potential effects on immunity and inflammation: systematic reviews published in 2012 highlighted occasionally favourable results regarding certain symptoms, inflammatory markers, quality of life, mood and certain blood parameters, whilst highlighting the varying quality of the trials and the presence of studies showing no significant differences, which necessitates maintaining methodological caution. A more recent review, published in 2020, focusing on tai chi and qigong, concludes that there may be a physiological impact on immune function and inflammatory responses, but emphasises the need for more rigorous and better-standardised studies. In this context, one cannot say that ‘Xi Sui Jing cleanses the marrow’, but rather that qigong-type practices appear capable of influencing certain immune and inflammatory parameters, without it yet being possible to precisely isolate the effect of a specific form such as Xi Sui Jing.
One of the key aspects of the modern explanation lies in the autonomic nervous system, which regulates breathing, heart rate, digestion, vascular tone, sweating, recovery and stress responses. Under the influence of chronic stress, the sympathetic branch tends to dominate: constant vigilance, diffuse tension, shallow breathing, fragmented sleep, increased inflammation, impaired digestion, and deep muscle tension. A slow, breath-focused, physical and meditative practice such as Xi Sui Jing can promote a rebalancing in favour of the parasympathetic branch, notably through the activation of the vagus nerve, and help the body move away from a state of constant defence to return more regularly to a state of deep recovery.
The term ‘marrow’ also refers to the spinal cord, the major nerve pathway connecting the brain to the rest of the body, even though this structure differs from bone marrow. Many approaches to Xi Sui Jing place great emphasis on the vertical axis: attention to the back, the skull, the sacrum, the alignment of the spine, and breathing that seems to rise and fall along a ‘central channel ’. In a contemporary interpretation, this corresponds to an improvement in awareness of the body’s axis, posture, deep muscle tone, coordination between breathing and alignment, and sensorimotor regulation; the more finely the practitioner senses their spine, the less they need unnecessary tension to stand upright. Thus, what the tradition refers to as ‘nourishing the marrow and the brain’ can be rephrased as an improvement in the relationship between posture, breathing, the central nervous system and internal perception.
The Xi Sui Jing is further characterised by a marked internalisation of attention. Less demonstrative than the Yi Jin Jing, it relies more on deep sensation, stable concentration, mental calm, intention and, at times, visualisation. This approach is very similar to what science calls interoception, that is, the ability to perceive the body’s internal state – breathing, heartbeat, visceral activity, temperature, deep tensions, energy fluctuations, fatigue and stress. Good interoception contributes to better emotional regulation, earlier detection of tension, more refined management of exertion and an increased ability to calm the nervous system; from this perspective, the Xi Sui Jing appears as a method for the systematic cultivation of bodily depth.
To fully grasp the value of this approach, Xi Sui Jing must be placed within the context of chronic stress. Stress is not merely a mental state: it permeates the muscles, fascia, viscera, sleep, immunity, hormones, digestion, breathing and the perception of pain. An organism subjected to high levels of stress over a long period accumulates somatic traces: a blocked diaphragm, clenched jaw, stiff neck, contracted abdomen, defensive pelvis, shallow and high-chested breathing, and disturbed sleep. Xi Sui Jing can therefore be seen as a method aimed at cleansing these deep layers of stress; the verb ‘to wash’ takes on its full meaning here, not as a physical act, but as a gradual release from patterns of tension entrenched deep within.
In addition to working on internal fluids, there are likely effects on blood and lymphatic circulation. Slow movements, moderate contractions, diaphragmatic breathing and variations in body pressure facilitate overall circulation, which is particularly important for the lymphatic system, which lacks a central pump and is largely dependent on movement, breathing and changes in pressure. In this sense, the Xi Sui Jing can be regarded as a form of gentle internal drainage: not medical drainage in the technical sense, but a harmonious stimulation of the circulation of bodily fluids, in keeping with the traditional view that associates ‘washing’ with the idea of fluidising, decongesting, clarifying and preventing stagnation.
In this context, bones are no longer perceived as inert structures, but as living organs—vascularised, innervated, constantly remodelling, and sensitive to mechanical stresses and hormonal, inflammatory and nutritional balances. The standing postures, grounding, gentle pressure, certain vibrations, deep breathing and slow movements of Xi Sui Jing can promote greater bone awareness and a more harmonious postural alignment around the skeleton. Nevertheless, it would be an exaggeration to claim that Xi Sui Jing directly increases bone mineral density; we can simply note that weight-bearing exercises, balance, posture and moderate physical exertion are, in general, beneficial for bone health.
Certain forms of Xi Sui Jing also incorporate gentle shaking, micro-vibrations, percussion, self-massage or vibrational breathing. From a scientific perspective, this type of stimulation can activate sensory receptors, alter muscle tone, enhance body awareness, promote relaxation and increase local circulation; however, these methods require great caution, particularly in frail individuals, those with osteoporosis, high blood pressure or neurological disorders, as improperly calibrated vibrations can be harmful. Where tradition speaks of allowing the breath to penetrate the bones, science describes phenomena of deep sensory stimulation and modulation of muscle tone.
In traditional medicine, the Kidneys govern the bones, produce marrow, nourish the brain, store Jing and determine longevity; modern physiology distributes these functions amongst the kidneys, gonads, endocrine glands, bone marrow, brain, nervous system and metabolism. We cannot naively superimpose these two maps, but we can see them as two ways of designating a set of profound functions: tradition groups together under the term ‘Kidneys’ a symbolic constellation of vital reserve, structure, reproduction, growth, bones and the brain, whilst science breaks it down into distinct systems. From this perspective, the Xi Sui Jing appears as a practice which, in modern terms, targets not a single organ, but a totality of fundamental neuro-endocrine-immune functions.
This is perhaps the most accurate interpretation: to regard the Xi Sui Jing as a practice of neuro-endocrine-immune regulation. ‘Neuro’ refers to the nervous system, the brain, the spinal cord, the vagus nerve and bodily perception; ‘endocrine’ denotes stress hormones, cortisol, melatonin, sex hormones and metabolic regulation; ‘immune’ covers inflammation, white blood cells, immune responses and repair processes. These three systems are in constant communication; stress disrupts them, sleep restores them, and breathing, movement and meditation can help rebalance their interactions; Xi Sui Jing seeks precisely this depth, not merely by moving the body, but by altering the quality of the internal state.
Xi Sui Jing is described as more meditative than muscular. Whilst the Yi Jin Jing works primarily on transforming the visible structure – muscles, tendons, fasciae, chains of force – the Xi Sui Jing focuses more on the silent depths: subtle breathing, the central axis, the symbolic marrow, the brain, essence, and the overall internal state.
From a scientific perspective, one might say that the Yi Jin Jing relates more directly to mobility, strength, connective tissues and posture, whilst the Xi Sui Jing relates more clearly to nervous, immune, hormonal, respiratory and psychological regulation. This is why it is generally practised after preparatory work: a body that is too tense, too agitated, too weakened or too scattered finds it difficult to engage in such a profound practice; one must first build the structure, then refine the interior.
The possible mechanisms of Xi Sui Jing can therefore be summarised as a constellation of converging processes: slow breathing acting on the autonomic nervous system; a reduction in stress altering inflammation and recovery; improved circulation through gentle movement and variations in pressure; proprioceptive and interoceptive stimulation refining internal perception; neuroendocrine regulation linked to calm, sleep and breathing; indirect immune modulation observed in certain studies on qigong; postural reorganisation centred on the spine and pelvis; gentle toning of the pelvic floor and deep core; neuroplasticity enhanced by mindful repetition; emotional regulation supported by the union of breath, body and attention.
Xi Sui Jing can be understood as a profound practice of maintenance and regulation, not as a universal miracle cure. In this context, the word ‘purify’ can be translated into very concrete terms: reducing chronic tension, improving sleep, calming hypervigilance, breathing more easily, improving circulation, releasing visceral tension, regulating inflammation, refining bodily awareness, lightening the emotional burden and restoring the ability to recover. ‘Washing the marrow’, in this sense, means releasing what, within the body, has become clogged by stress, stagnation, tension and nervous agitation.
A modern, cautious and consistent practice of Xi Sui Jing must therefore remain gentle and structured: a stable standing posture, slow breathing, attention to the spine, relaxation of the pelvis, awareness of the bones, perception of the skull and sacrum, very slow movements, moderate self-massage, light vibrations, internal meditation and periods of silent recovery. It must avoid excessive breath-holding, excessive pressure, violent contractions of the perineum, dangerous sexual methods, overly intense jolts, promises of radical ‘purification’ and training undertaken without adequate preparation.
This practice can be understood scientifically as a method of internal transformation based on breathing, attention, posture, deep relaxation and regulation of the nervous system; tradition says that it ‘washes the marrow’, nourishes the bones, clarifies the brain and refines the essence, whilst science, whilst unable to confirm these images in a literal sense, offers a coherent interpretation in which this practice likely acts upon the deepest regulatory systems – the nervous system, immunity, endocrinology, circulation, respiration, posture, sleep and internal perception.
One might say, in traditional terms, that after transforming the tendons with the Yi Jin Jing, one purifies the marrow with the Xi Sui Jing; in scientific terms, that after reorganising the musculo-fascial structure, one focuses on the deep neurophysiological regulation of the body.
