Muscle tone is a ubiquitous and foundational sensorimotor phenomenon, underlying muscular tension and postural support, which has been poorly understood (Ivanenko and Gurfinkel, 2018) and could contribute to pain. Muscle tone has passive and active components. The passive component originates from viscoelasticity of multiple tissues and has been discussed in detail elsewhere (Mense and Masi, 2010; Ivanenko and Gurfinkel, 2018). The active component arises from low-level, sustained muscle activation, which is regulated by complex central and peripheral neural circuits. Pathologies of tone such as hypertonia and hypotonia commonly result in pain (Alwardat et al., 2019; Ostojic et al., 2019; Miller, 2020), and active muscle tone is generally disrupted with musculoskeletal pain (Dankaerts et al., 2006; Mork and Westgaard, 2006; Park et al., 2013; Claus et al., 2018; Worman et al., 2023). Such disruptions in tone would affect joint loading. Active muscle tone is also closely related to excitability, which has been proposed to play a critical role in chronic pain (Hodges and Tucker, 2011; Jenkins et al., 2023). As with pain, pathological disruptions in tone can severely affect motor ability (Goo et al., 2018; Ha and Sung, 2023). Thus, the regulation of healthy tone may be an important target for chronic pain as well as movement coordination (Cacciatore et al., 2014; Chen et al., 2023; Worman et al., 2023; Wendt and Waszak, 2024).

The past several decades have led to increased understanding of muscle tone, in particular how it is centrally controlled. Active muscle tone is regulated by a complex, dynamically adaptive neural system that is interconnected across the body and highly sensitive to postural demands (Gurfinkel et al., 2006; Takakusaki et al., 2016; Ivanenko and Gurfinkel, 2018). It is closely connected with excitability of lower levels of the nervous system, which is tuned by tonic descending neural drive (Deliagina et al., 2014).

While many practices address tension as a means for improving pain and performance, they generally do so without reference to the complex adaptive brain systems that regulate muscle tone. Instead, interventions often involve isolated stretching and strengthening (Slade and Keating, 2006; Geusebroek et al., 2023), which emphasizes peripheral contributions, or focus on volitionally controlling posture (Harvard Medical School, 2017) or relaxing muscles (Conrad and Roth, 2007). None of these approaches address the complexities of the tone system, which is multifaced and involuntary, and it is not clear how to best address it. However, somatic practices have been found to alter muscle tone (Stephens et al., 2006; Masi and Hannon, 2008; Cacciatore et al., 2011a) and improve pain (Little et al., 2008; MacPherson et al., 2015; Kong et al., 2016; Berland et al., 2022) and motor control (Jones et al., 1959; Cacciatore et al., 2014; Yang et al., 2014; O'Neill et al., 2015; Berland et al., 2022). These methods may give insight into how to influence and improve tone regulation.

The aim of this paper is to convey a modern understanding of the regulation of active muscle tone, address how it may be related to pain and performance, and highlight practices that may yield insight into how to address it.

Two terms are used to refer to muscle tone: resting tone and postural tone, depending on the postural state of the subject. Both forms likely share passive and active mechanisms, although to different extents, and likely share neural circuitry (Figure 1A). Resting muscle tone refers to the tension when subjects are relaxed and fully supported; it is often assessed by passive resistance to movement (Foster and Rivers, 1892). Resting tension acts to prevent muscle slackness, although its function remains somewhat obscure. In the extremities, resting muscle tone is generally electrically silent (Masi and Hannon, 2008) but axial and proximal muscles are often active, even when subjects are supported and relaxed (Burke and Gandevia, 1993; Mense and Masi, 2010).

In contrast, postural muscle tone emphasizes the functional role of holding different parts of the skeleton in relation to each other (Gurfinkel, 2009); it is typically assessed during antigravity postural maintenance, where muscle activation is required to prevent collapse. Postural tone is typically < ~7% of maximal contraction (Gurfinkel et al., 2006) and is modulated by loading and by the mechanical demands to stabilize body posture. For instance, tonic activation of upper and lower body musculature is larger when standing than when lying down (Viir et al., 2007; Rubini et al., 2012), and it can disappear with the addition of external support (Masani et al., 2013). While the differences between resting and postural tone aren’t well understood, the main distinction may relate to the state of the subject during measurement. For instance, postural tone may involve increased activity in the same circuitry as resting tone. It is also possible that postural tone relies on somewhat different underlying circuitry.

Muscle tone is involuntary. It is behaviorally distinct from and engages different brain pathways than voluntary control (Guo et al., 2015; Teng et al., 2017; St George et al., 2018; Russell et al., 2022). Thus, the tonic leg extensor activation in stance constitutes tone but the sustained flexor activation when making a fist does not (Figure 1B). Muscle tone develops according to a genetically determined timescale, changing from flexor to extensor biased in early infancy, and sequentially developing postural support for the head and then body (Amiel-Tison, 2002; Lefèvre, 2002; Goo et al., 2018).

Various measures have been used to quantify muscle tone – all of which relate to muscle tension (Table 1). As it is difficult to noninvasively measure the series tension of a muscle, tone is often assessed by the resistance to passive joint motion though the change in force per unit length (Worman et al., 2023). This measure reflects the tensional changes in all muscles that cross the deformed region, including both lengthened and shortened muscles. However, mechanical measures do not identify the relative contributions of active vs. passive sources (Morin, 2016), which can be discriminated by EMG.

Muscle tone can be inferred through muscle hardness (Fischer, 1987) or myotonometry, that quantifies the dynamic response to muscle belly deformation (Hu et al., 2018). Another indirect measure of tone is the resonance frequency of body segments, assessed with an oscillating perturbation (Walsh, 1992). While tone can also be estimated from postural alignment (Worman et al., 2023), this is region dependent and problematic due to muscular redundancy and anatomical differences.

Clinically, muscle tone can be assessed through the resistance to passive movement, joint restrictions, the pendulum test (Wartenberg, 1951), traction test (Jabbour and Clark, 1965), abnormal posturing, and clinical scales (Amiel-Tison, 2002; Reinhold and West, 2014; Goo et al., 2018).

Difficulty characterizing this distributed, adaptive, low-level system has hindered the understanding of muscle tone and its relation to other phenomena, such as performance and pain. Many measures of tone are indirect, and most do not discriminate between active and passive contributions (Worman et al., 2023). The small magnitude, constant nature, and contribution of deep muscles to tone often render surface EMG unreliable (Van Houtte et al., 2013). Characterizing muscle tone also requires evaluating the dynamic adaptive responses to yield and resist as well as cross-body interactions. There are many ways tone can be distributed, adaptive and interconnected, which make it impractical to comprehensively assess with a fixed protocol.

Muscle tone is broadly distributed throughout the musculature. Because of mechanical redundancy, a given body configuration can be stabilized by many different distributions of activity (Latash, 2012). For instance, numerous combinations of superficial, deep, medial, lateral, and antagonistic muscles can be engaged to support the trunk. For this reason, body alignment alone does not reveal how tone is distributed across the muscles.

Muscle tone adapts dynamically to meet biomechanical requirements, varying across different postures to counteract changing static loads (O'Sullivan et al., 2006; Caneiro et al., 2010). While one maintains a posture, tonic activity increases to resist deformation to external loading (Marigold et al., 2004; van Drunen et al., 2013). The tone system is extremely sensitive to changes in position and force, allowing it to readily compensate for disturbances. Changes occur at extremely low displacements (<1 deg) and velocities (< 1 deg./s) (Gurfinkel et al., 1995a,b; Gurfinkel et al., 2006).

Muscle tone also adapts in the opposite way – to yield to a load, allowing posture to change, for instance when a barber turns your head, or a dance partner lifts your hand. This creates postural plasticity through “lengthening and shortening” reactions, which decrease tone during muscle lengthening and increase it during shortening (Sherrington, 1909; Walsh, 1992; Gurfinkel et al., 2006). Functionally, this allows muscles to change length while maintaining constant tension. Such compliant tonic reactions are prominent in healthy infants in the first year of life, and thus constitute an innate aspect of tonic control (Solopova et al., 2019; Dolinskaya et al., 2023).

While muscle tone can readily adapt to changing postural demands, it is also conservative. Muscle tone varies widely across people; several-fold differences in tone are commonly observed (Gurfinkel et al., 2006). Both the distribution of tone and its adaptivity at different body regions are highly individual. This manifests as marked individual preferences in tone and postural alignment that are stable over long time periods (Lestienne and Gurfinkel, 1988; Lacquaniti and Maioli, 1994; Gurfinkel et al., 2006; Cacciatore et al., 2011a; Wainio-Theberge and Armony, 2024). There is a tendency to drift back to one’s habitual posture over time (Duarte and Zatsiorsky, 2002), which presumably creates a consistent, stable platform for coordinating action.

Muscle tone is influenced by both neighboring and distant parts of the body, such as neck position affecting limb tone (Gurfinkel and Levick, 1991; Gurfinkel et al., 1995a,b; Bruijn et al., 2013). Many non-local influences on tone have been observed, including from the jaw to the neck and trunk (Lippold et al., 2006; Giannakopoulos et al., 2013; Julia-Sanchez et al., 2019), from the trunk to the neck and eyes (Bexander and Hodges, 2023), and from the limbs to the trunk (Kluzik et al., 2007). Interactions also occur within (Gurfinkel et al., 1989; Solopova et al., 2019; Dolinskaya et al., 2023) and across limbs (Zelenin et al., 2015; Solopova et al., 2019; Dolinskaya et al., 2023). In addition, haptic finger contact has been observed to affect hip tone (Franzén et al., 2011). Cross-body interactions can result from the mechanics of interconnected kinematic or myofacial chains (Loram et al., 2016; Wilke et al., 2016; Kellis et al., 2024) or can be mediatiated by neural circuits (Zelenin et al., 2015; Giannakopoulos et al., 2018).

Much of the feedback circuitry that regulates muscle tone is located within the spinal cord. These circuits have been characterized using tilts of the support surface in quadrupeds (for review see Deliagina et al., 2014), which results in phasic and tonic changes in muscle activity to stabilize the body. The underlying spinal cord circuits are complex, being comprised of hundreds of heterogeneous interneurons (Figure 2B) that are distributed across the spinal cord laminae and that act in different phases of tilt (Zelenin et al., 2015). These spinal circuits form distinct front-and hind-limb feedback controllers that integrate afferent information from ipsi-and contra-lateral limbs to adapt tone to different planes of surface tilt. This architecture differs fundamentally from the monosynaptic stretch reflex, to which tone is often misattributed (Davidoff, 1992; Masi and Hannon, 2008; Mense and Masi, 2010). Resistive and compliant tonic reactions also likely involve oligosynaptic feedback pathways within the spinal cord and possibly also the brainstem (Solopova et al., 2019; Dolinskaya et al., 2023).

Although feedback circuits are contained within the spinal cord, tonic excitation is essential for them to function (Deliagina et al., 2014). This tonic drive is usually provided by vestibulospinal, reticulospinal, and monoaminergic descending input (see Figure 2) and acts to provide an excitability bias that “switches on” the spinal circuits. Interrupting communication between the brainstem and spinal cord abolishes muscle tone and postural responses (Zelenin et al., 2013). However, various forms of excitatory input, such as constant epidural stimulation, vibration, or strong cutaneous input, can substitute for the intrinsic descending drive and activate spinal feedback circuits, even in the isolated spinal cord (Musienko et al., 2010; Lavrov et al., 2015; Takakusaki et al., 2016). Thus, descending systems provide an essential but unspecific tonic input that increases the excitability of spinal networks (Musienko et al., 2008; Deliagina et al., 2014).

Tonic drive may serve as an important mechanism for regulating muscle tone by modulating spinal excitability (Gurfinkel et al., 1999). The importance of excitability for muscle tone regulation is clear from many observations, including: changes in tonic muscle activity following vibration and post-contraction (Gurfinkel et al., 1989; Gurfinkel et al., 1995a; Gurfinkel et al., 1999; Gurfinkel et al., 2006); fluctuations in state following decerebration (Sherrington, 1909; Beritoff, 1915; Musienko et al., 2008; Zelenin et al., 2013); the influence of remote voluntary effort on tone (Walshe, 1923; Wolff et al., 1983; Yanagisawa and Hashimoto, 1995; Jiang et al., 2021); and excitability-related facilitation of lengthening and shortening reactions (Gurfinkel et al., 2006; Solopova et al., 2019; Dolinskaya et al., 2023). Tonic drive may act to switch on spinal circuits (Musienko et al., 2008; Ivanenko et al., 2017), set response levels (Musienko et al., 2008), and specify whether to resist or yield to loading (Gurfinkel et al., 1989; Gurfinkel et al., 2006). This is reminiscent of Bernstein’s (1940) statement that, “Tonus as an ongoing physiological adaptation and organization of the periphery is not a condition of elasticity but a condition of readiness.”

Because muscle tone is present after decerebration, it is predominately generated in the hindbrain and spinal cord. However, it is influenced by other brain structures, such as the cerebellum, basal ganglia, limbic system and cortex (Beloozerova et al., 2003a; Musienko et al., 2008).

Muscle tone is influenced by a heterogeneous assortment of afferent input. This sensory influence occurs through more than just simple feedback loops, but via a complex integration of sensory inputs suggestive of a “body scheme” (Gurfinkel and Levick, 1991; Gurfinkel et al., 1995a,b; Kluzik et al., 2007; Franzén et al., 2011). At the spinal level, feedback circuits receive input from 1a and 1b afferents (Deliagina et al., 2000), which both facilitate muscle tone (Pratt, 1995; Duysens et al., 2000; Van Doornik et al., 2011). Thus, spinal feedback circuits respond to information reflecting muscle state.

Sensory input also acts supraspinally, for instance through vestibular organs that affect vestibulospinal drive. The descending monoaminergic pathways respond to a variety of sensory stimulation, including vibration, cutaneous input, sound, and particularly deep pressure (Moolenaar et al., 1976; Lapole et al., 2023). This non-specific sensitivity of descending tonic drive could underlie the diversity of ways that afferent inputs, ranging from light touch to deep massage, can influence tone.

Perhaps surprisingly, it is not clear how habitual postural preferences are represented in the nervous system. While postural setpoints are affected by descending vestibulospinal drive (Hsu et al., 2012), this signal reflects “operative” changes that modulate setpoints according to current demands (Lestienne and Gurfinkel, 1988), as opposed to habitual postural preferences. Postural setpoints are also influenced by neural integrators (Shadmehr, 2017; Albert et al., 2020), which set postural tone based on the preceding movement command. These might underlie how “posture follows movement like a shadow” (Sherrington, 1906) as well as forms of cervical dystonia (Shaikh et al., 2016). Neural integrators have been identified for the eye and neck in the midbrain (Shadmehr, 2017) and have been demonstrated to exist for the limbs (Albert et al., 2020), but their anatomical location is not yet known. However, neural integrators are also likely operative, as they set tone levels based on recent movement. It is possible that long-term habitual setpoints are manifestations of the brainstem and associated descending tonic drives (Thiele et al., 2014), however they could also be encoded at higher levels, such as the body scheme (Lestienne and Gurfinkel, 1988; Romano et al., 2021). Another possibility is that habitual postures are stored in a distributed fashion, through long-term stable properties across multiple levels of the nervous system.

Evidence from multiple sources suggests that tone and voluntary movement constitute distinct forms of behavior. (1) Cortical inhibition suppresses voluntary reaching but does not affect muscle tone (Guo et al., 2015). (2) Axial tone is impaired in idiopathic camptocormia in the absence of attention, but the trunk can be held upright voluntarily (St George et al., 2018). (3) Muscle tone and movement commands are adapted independently via separate cerebellar loops (Shadmehr, 2017). (4) Postural tone and voluntary contraction differentially activate brainstem and corticospinal tracts, respectively (Teng et al., 2017; Russell et al., 2022).

Despite the behavioral distinction between muscle tone and movement, they share some overlapping circuitry. For instance, neurons in the brainstem participate in both movement and tone regulation (Schepens and Drew, 2004; Schepens et al., 2008; Gibson et al., 2023), and descending monoaminergic gain control pathways affect muscle recruitment during voluntary actions (Heckman et al., 2003; Wei et al., 2014). In addition, gait coordination is affected by vestibulospinal projections that also influence tone (Gottschall and Nichols, 2007; Gottschall and Nichols, 2011).

The Gurfinkel et al.’s (1999) “Lock with Two Keys” framework provides a conceptual basis for the involvement of both tonic and phasic commands in movement. Tonic commands set excitability levels to prepare lower circuits for action while phasic commands initiate and coordinate the movement. Consistent with this view, tonic drive from the various descending brainstem projections configures the spinal cord, while outputs from cortical motor and premotor regions and central pattern generators coordinate the phasic mechanisms. Evidence supporting the role of tonic commands in movement control includes findings that increasing excitability of spinal circuits can invoke gait rhythms (Solopova et al., 2015; Ivanenko et al., 2017).

Movement is also associated with anticipatory postural adjustments (APAs), which provide targeted stabilization for predictable movement-related disturbances before movement onset. However, it is currently unclear whether APAs involve changes to muscle tone. As tone represents ongoing activity, it is difficult to determine whether movement-related changes result from anticipatory feedforward processes or from sensory feedback that occurs later as a result of the movement. Evidence for the idea that anticipation affects muscle tone includes findings that reticulospinal neurons are activated before voluntary limb movement (Schepens and Drew, 2004; Schepens et al., 2008), mechanical disturbance is decreased to changes in sustained postural load when subjects trigger the unloading themselves (Viallet et al., 1992), and that humans adjust their neck posture in preparation for walking (Baer et al., 2019). Evidence against the idea that APAs affect muscle tone include findings that predictable platform tilts do not cause anticipatory changes in tone (Beloozerova et al., 2005) and observations that APAs tend to be phasic (Belen'kii et al., 1967; Cordo and Nashner, 1982; Viallet et al., 1992; McIlroy and Maki, 1999; Caronni and Cavallari, 2009; Lee et al., 2009; Cohen et al., 2017). For example, tapping a finger induces transient anticipatory changes in arm and back muscles to counteract movement-related interaction torques (Caronni and Cavallari, 2009), which are too brief to represent muscle tone. One way that postural tone does “anticipate” movement is through a general increase in tone beforehand, for example prior to gait initiation, which provides general mechanical stiffness that resists movement related perturbations (Mori, 1987).

Muscle tone can affect movement. For instance, the flexed posture present in newborns prevents locomotion, even in the presence of weight support, until extensor tone is predominant (Amiel-Tison, 2002; Wilson et al., 2022). Movement coordination is degraded with tone pathologies; both hyper-and hypotonia alter sit-to-stand coordination (Ha and Sung, 2023) and hinder overall motor performance (Goo et al., 2018). Muscle tone is necessary for locomotion and closely integrated with the underlying neural circuitry. Stimulating excitatory and inhibitory brainstem tone regions can initiate and terminate gait, respectively (Mori, 1987; Takakusaki et al., 2016).

Axial muscle tone appears to be particularly important for motor function. Atypical axial tone is a major sign of disease or disability in infancy and its evaluation features centrally in early neurological assessments (Haataja et al., 1999; Amiel-Tison, 2002; Leyenaar et al., 2005; Romeo et al., 2016). Axial tone also affects gait coordination (Martin, 1967; Ivanenko and Gurfinkel, 2018) and is correlated with rolling and turning impairment in Parkinson’s disease (Franzen et al., 2009). In addition, providing head support to newborns results in the expression of movements that are typically seen in much older infants (Amiel-Tison and Grenier, 1983), and providing trunk support to six-month-old infants leads to much smoother reaching movements (Hopkins and Rönnqvist, 2002). The importance of axial tone may stem from its essential role in stabilizing the spine (Lucas and Bresler, 1960). Moreover, the complexity and redundancy of axial musculature allows many possible distributions, including ones that may interfere with movement, for example through altered mechanical interactions between limbs (Gurfinkel et al., 2006). However, axial tone may be primarily important for neurological reasons. For instance, poor axial tone could degrade coordination by disrupting muscular recruitment.

In neurologically healthy subjects, muscle tone affects various movements including scapular kinematics in swimmers (Chen et al., 2023), speech production after spaceflight (Shamei et al., 2023), and vocal coordination in vocal tension dysphonia (Hocevar-Boltezar et al., 1998; Kooijman et al., 2005; Tomlinson and Archer, 2015). Alterations to muscle tone can also affect pelvic function (Worman et al., 2023) and respiration (Austin and Ausubel, 1992). Tone may also affect the smoothness of whole body movements (Cacciatore et al., 2014). The general effects of tone on movement coordination suggest that muscle tone may be an important determinant of motor performance, consistent with Bernstein’s theory that tone forms the foundational level of the motor system (Latash et al., 1996; Profeta and Turvey, 2018).

While pain is multifaceted and complex, muscle tone and pain are interrelated. Altered tone has been reported for many chronic musculoskeletal pain conditions including neck (Falla et al., 2004), back (van Dieen et al., 2003), and pelvic pain (Worman et al., 2023). Changes associated with pain include increased muscular stiffness (Alcaraz-Clariana et al., 2021a; Alcaraz-Clariana et al., 2021b; Li et al., 2022; Kurashina et al., 2023; Proulx et al., 2023; Vatovec and Voglar, 2024) and altered distribution of tonic EMG (van Dieen et al., 2003; Dankaerts et al., 2006; Mork and Westgaard, 2006; Planken et al., 2010; Park et al., 2013; Claus et al., 2018). Further links between muscle tone and pain are implied by coincident changes in tone and pain following intervention (Wong et al., 2015; Buttagat et al., 2016). Notably, tone is altered during deep sleep in people with chronic neck pain (Mork and Westgaard, 2004; Aldabbas et al., 2024), reflecting the automatic and subcortical origin of disruptions in tone.

Despite the sophistication of tone regulation, it is often addressed simplistically, without reference to the nature of the underlying system. While muscle tone is dynamic, interconnected across the body, and closely related to excitability, it is often addressed locally through stretching and strengthening. Sometimes the main aim is only to “relax” (Conrad and Roth, 2007). In contrast, postural advice is commonly volitional, effortful, and positional (e.g., “stand up straight”; Harvard Medical School, 2017). However, volitional control (Teng et al., 2017; Russell et al., 2022) and even postural biofeedback (Baer et al., 2022) involve different brain circuitry from the brainstem structures that are engaged during postural support. Moreover, addressing posture positionally does not take into account the dynamic nature of tone. In general, current mainstream approaches to muscle tone are unlikely to fundamentally and optimally address its regulation.

Another obstacle to improving muscle tone concerns what constitutes “ideal” tone regulation. Healthy adults exhibit a range of tone properties, and it is unclear how muscle tone is optimally distributed, modulated and interconnected across the body. However, features can be identified which correlate with performance and pain. For instance, research showing that both hyper-and hypotonia lead to pain and motor impairment supports the idea that there is an ideal range for the level of tone. Axial tone also appears to be especially important for both performance and pain (Amiel-Tison and Grenier, 1983; Amiel-Tison, 2002), in particular through the engagement of deep muscles (Falla et al., 2004; Hodges and Danneels, 2019). Both the reduced modulation of tonic activity with pain (Claus et al., 2018; Gouteron et al., 2022) and the correlation of “suppleness” with recovery (Wernli et al., 2022) suggest that adaptability of muscle tone is beneficial. Theoretically, it might be important for tone to be both supportive and adaptable.

It may also be possible to gain insight into addressing muscle tone through disciplines that have empirically developed ways to influence it. In particular, many complementary and integrative somatic practices address muscle tension, and the implicit knowledge manifested in their ways of working might offer practical insight into tone regulation. Somatic practices aim to enhance performance and body–mind integration through awareness; they include the Alexander Technique, Feldenkrais Method, Tai Chi and Qigong. These disciplines also share a focus on tension and may reflect sophisticated ways of working with tone (Schmalzl et al., 2014). Of these, muscle tone has been studied most in the Alexander Technique, which has been found to increase adaptivity of axial tone (Cacciatore et al., 2011a; Cohen et al., 2015), but alterations in tone are also implicated in the Feldenkrais Method (Stephens et al., 2006). Changes in muscle tone may explain improvements in performance and pain resulting from these practices (Stephens et al., 2006; Little et al., 2008; MacPherson et al., 2013; Preece et al., 2016; Becker et al., 2021; Berland et al., 2022; Little et al., 2022; Hodges et al., 2024). While contextual factors such as expectations of improvement generally contribute to clinical benefit (Rossettini et al., 2018), pain reduction and alterations to tone and coordination from the Alexander Technique and Feldenkrais Method have exceeded that for control interventions (Little et al., 2008; Cacciatore et al., 2011a; MacPherson et al., 2013; Berland et al., 2022), suggesting a non-placebo mechanism. Many other complementary and integrative practices are consistent with addressing tension, but their effects on tone are not well studied, including Craniosacral Therapy, Hanna Somatics, Rolf Movement, Contact Improv, Total Motion Release for pediatrics (TMRTots), Somatic Experiencing and Jin Shin Jyusu. While somatic practices are distinct from one another and may alter muscle tone in different ways, similarities relevant to tone regulation include:

Differentiation between subtle tensional states: Distinctions are often made between states such as relaxed, released, engaged, tense, and responsive (Feldenkrais, 1964; de Alcantara, 1999; Cacciatore et al., 2005; Schmalzl et al., 2014; Osypiuk et al., 2018). It might be important to identify subtle aspects of tone in order to promote certain qualities. These different states may relate to the diversity of pathways that affect tone, and they may affect both excitability and tension.

Mental attention to the body and space: Somatic practices include attention and awareness on the body and space when addressing tension (Jones, 1976; Cacciatore et al., 2005; Schmalzl et al., 2014). These practices can also include subtle intentions regarding desired relations between body parts (de Alcantara, 1999), imagery (Cohen et al., 2015), as well as awareness of internal sensation (Mehling et al., 2011; Schmalzl et al., 2014). Verbal instructions based on the Alexander Technique influence axial tone and adaptability (Cohen et al., 2015), supporting the importance of high-level, attentional influences on muscle tone. Bodily and spatial attention in itself is salient for pain (Moseley et al., 2009; Torta et al., 2013; Lotze and Moseley, 2022) and may overlap with circuitry that influences tone (Gurfinkel and Levick, 1991; Gurfinkel et al., 1995a,b).

Haptic touch: Some somatic practices such as Feldenkrais, Craniosacral Therapy, TMRTots and the Alexander Technique incorporate light touch that aims to alter tone (Feldenkrais, 1964; Cacciatore et al., 2005; Brough et al., 2015). This may act by drawing attention to a body region or tensional relationship or might directly interact with the tone regulating circuitry at a lower level of the nervous system.

Emphasis on involuntary regulation: Many disciplines aim to prevent volitionally micromanaging and anticipating motor behavior (Bigé and Godard, 2019; Woods et al., 2020). This concept is described as “wu wei” in Tai Chi and “non-dong” in the Alexander Technique (de Alcantara, 1999). Thus, change originates from non-judgmental attention, awareness, intention and imagery, rather than from voluntary effort (Tang et al., 2022). For example, postural instructions based on the Alexander Technique are perceived as effortless in comparison with typical effortful modification of posture (Cohen et al., 2015). As tone pathways are largely distinct from those controlling voluntary action, such non-doing principles may be a way of targeting the relevant pathways to address the involuntary regulation of muscle tone.

Whole body interactions: The influence from one body region to another is widely acknowledged among complementary and integrative practices, and tension is often addressed remotely (Feldenkrais, 1964; de Alcantara, 1999; Schmalzl et al., 2014). This is consistent with tonic cross body interactions and may reflect overall organizing principles. Many somatic practices focus on axial tone including Qigong, Craniosacral Therapy, Feldenkrais and the Alexander Technique (Feldenkrais, 1964; de Alcantara, 1999; Brough et al., 2015).

Resistance and compliance activities: Activities involving resistance and compliance are ubiquitous in somatic practices. Examples include push hands and immovable arm in Tai Chi and Qigong (Chen et al., 2010), as well as many activities in Feldenkrais and the Alexander Technique. The desired resistance and compliance is described as “latent, automatic resistance and mobility” (de Alcantara, 1999), and is supported by measurements of increased compliance and resistance (Cacciatore et al., 2011a; Cacciatore et al., 2020). The involuntary nature of this resistance and compliance is consistent with an underlying state of “readiness” that facilitates adaptable tone, and may be closely related to excitability (Gurfinkel et al., 2006; Cacciatore et al., 2011a).

Smooth, quasistatic movement: Somatic practices often involve movement. However, the aim is not to perfect a particular movement trajectory but pertains to movement quality. Tai Chi, Qigong, Feldenkrais and the Alexander Technique all emphasize slow, smooth and reversible movement (de Alcantara, 1999; Liu and Frank, 2010; Russell, 2020). Slow movement decreases momentum and therefore may constrain postural support to be adaptive. For example, Alexander Technique teachers exhibit a prolonged and extremely smooth weight shift in sit-to-stand that is difficult to mimic (Cacciatore et al., 2011b; Cacciatore et al., 2014). The continuous shifting of weight to the feet may arise from increased adaptability that sensitively adjusts extensor muscle activity throughout the action (Cacciatore et al., 2020). Thus, the quasistatic nature of movement performed in somatic practices may act to increase the adaptability of muscle tone.