Defining proprioception, physiological pathways involved in joint sensation, planning and control: Part 1

One of the difficulties for proprioception is defining it, or rather the differing opinions on what it constitutes among researchers and clinicians. Whilst there is a plethora of definitions offered up, I liked the pragmatic definition offered by Susan Hillier in her 2015 paper. She suggests proprioception is “based on an ensemble of sensory inputs that serve sensing, producing, predicting, and simulating joint position, joint motion (velocity and direction), and force specification”

We can split proprioception into four main subcategories.

Joint position detection (performed 1. active or 2. passive) and was most routinely measured via joint angle error of contralateral limb. Number (3) is passive motion detection threshold and (4) passive motion detection discrimination (what direction; positive or negative)

The definition by Hillier fits nicely within another great framework by Kathryn Sibley et al., published in 2015, this time of postural control. They consider the 6 domains for postural control of which the scoping review established 9 operational components. These are seen in Table 1 below (taken from Sibley et al., 2015)

Table 1
Domains of Systems Framework Postural Control	Scoping Review Adaption
Biomechanical constraints	Functional Stability limits, underlying motor systems and static stability
Orientation in space	Verticality
Movement strategies (reactive, voluntary, anticipatory)	Reactive postural control, anticipatory postural control
Control of dynamics: gait and proactive control	Dynamic stability
Sensory strategies: integrations, reweighting	Sensory integration (including reweighting)
Cognitive processing (attention, learning)	Cognitive influences

At its fundamental level this view of proprioception is the sensing, production and prediction of movement involving both the local (tissue and peripheral nervous system) and central nervous system.  Notice how the aspects of proprioception each have inroads into many other aspects of human movement; it is not a stand-alone entity but rather proprioception is embodied within all aspects of movement (including the output).

Consequently, there is an entirely different view of proprioception, one I will expand on shortly.

Proprioception relies on populations of mechanosensory neurons distributed throughout the body, which are collectively referred to as proprioceptors. The below information is taken from a fantastic PRIMER review by Johnathan Tuthill and Eiman Azim from 2018.

Deep within mammalian skeletal muscles are muscle spindles. They are positioned in parallel with the extrafusal muscle fibres innervated by alpha motor neurons. Group Ia neurons encode both muscle length and the rate of change (velocity) of muscle length.

Load on a limb is detected by Golgi tendon organs; these are proprioceptors that lie at the interface between muscles and tendons. Group Ib afferents innervate tendon organs and encode muscle force — they are silent at rest and increase their firing frequency as tension in the muscle rises.

Joint threshold detectors are our Ruffini endings and Pacinian corpuscles and are divided by functional properties into 3 subcategories (types I=III) consisting of fast and slow adapting receptors at differing levels of depth in the joints.

The first site of gain for proprioceptors occurs peripherally via altering the sensitivity of the receptors in the joints, this is important as we can train the rate of gain in these receptors with resistance training or other modalities.

Redefining proprioception through embodied movement and proprioceptive-kinaesthesia coupling.

We have the prevailing view of proprioception as described above but there are arguments that this fails to address key areas.

As you or I interact with our environment, whether that be my typing of this article, or your eye-rolling, fidgeting and increasing desire to cease reading, we are perceiving and enacting (taking behavioural action) in a relational manner to different possibilities for actions with ourselves, our environment (ecological) or other people (social). This has previously been defined as affordances (Newell et al., 1989; González-Grandón et al., 2021). Because the ecological and social aspects of both perceiving and possibilities for action cannot be separated from the “feeling” aspect of both the perception and action in these conditions, there are calls that proprioception is better understood from an embodied proprioception-kinaesthetic coupling perspective (González-Grandón et al., 2021).

The authors suggest that a perceptual system arises from an active and ongoing coupling between feeling and possibilities for action and that these are dynamical relations i.e. they change as they interact with each other and the real world. Importantly, there are three dimensions of this proprioceptive-kinaesthetic coupling as described by González-Grandón et al., (2021):

The PK-coupling contingencies in relation to the self. This is related to the persons own spatial-temporal self-orientation of one part of the body to all other parts and the possible contingencies for action at any time.

The PK-coupling contingencies of the ecological-self describes the activity of the person with their environment and the possible contingencies for action. We consider here that the self extends into the environment and that the two are coupled intimately; to perceive we must move, to move we must perceive. On this premise, the agent is embodied within their environment.

The self-other which describes the ongoing PK coupling in relation to the persons activity when interacting with others and again, contingencies for action. I stress here that there is still the element of the ecological-self as we interact with each other in the real-world environment. Perhaps it would be more accurate to consider this dimension as the self-ecological-other, recognising we interact with others through our environment as an extension of our self-i.e. the embodied experience.

Woven within this embodied experience of PK is an emotional appraisal of the situation. It is a judgment of how oneself feels to be in that situation and experienced through bodily resonance. This is local or generalised sensations such as feelings of warmth or coldness; rich feelings of bodily resonance are examples such as a lump in the throat or tightening across the chest (Fuchs & Koch, 2014).

Because of its embodied nature, it is said we experience through our bodily resonance the emotional appraisal (anxiousness, anger etc.) of oneself in the situation. To borrow from Fuchs & Koch (2014) a tired, fatigued person will experience a familiar hill as being steeper than the same person who was fresh; the ‘hill is too high’ is perceived in this way through the tired body. Hence, our feeling body is the way we are emotionally tied to the world.

As mentioned above, the emotional appraisal of oneself in the situation is intimately related to the possibilities for action and the tension between possible and actual movement. Here Fuchs & Koch (2014) argue bodily resonance has two components: the affective dimension of how an event makes us feel (e.g. the anger of injustice) and the emotive (e-motive) component being bodily readiness for movement tendencies and directedness. In simple terms, it is impression (affective) and expression (emotive) and these always share a circular relationship.

Putting it all together.

Hopefully we can now see that movement (including PK-coupling) is embodied within the dynamical self-ecological-other and influenced by the affordances for action in the environment based on the task we are trying to achieve. This movement outcome is intimately influenced by affective and emotive components of bodily resonance in a bidirectional, dynamical relationship. This is largely based on the biomechanical constraints and action theory posited by Newell in 1986 (as cited in Newell et al., 1989) which suggests movement and coordination is emergent rather than prescribed and observable at the behavioural level.

We organise our action in response to the affordances of the environment and the nature of the task, and that following injury and with persistent pain, the possibilities for action are restricted and with this our ability to meaningfully engage with valued activities (Vaz et al., 2023).

Perhaps then, we reject the dualistic views of proprioception previously described.

They fall short of accounting for the embodied-embedded view of human movement; our thoughts, feelings (including kinaesthesia) and emotions are intertwined with our surrounding environment that is ever dynamical, and affordances depend on our perception possibilities relative to our task. This is not to say the neurophysiological aspects of proprioception are irrelevant, much the opposite! Such evolutionary adaptations are relied up on no end in our interactions with our environment and navigating the boundaries for possibilities of action, but they cannot be separated from all other aspects talked about above.

Thus, the ramifications for addressing human movement from the perspective of joint instability under this new prevailing paradigm are large and will be discussed in part two of the article.

The terms and concepts above may be new to you, if they are, I would recommend reading the papers referenced above as a good starting point.

References

Hillier, S., Immink, M., & Thewlis, D. (2015). Assessing proprioception: a systematic review of possibilities. Neurorehabilitation and neural repair, 29(10), 933-949.

Sibley, K. M., Beauchamp, M. K., Van Ooteghem, K., Straus, S. E., & Jaglal, S. B. (2015). Using the systems framework for postural control to analyze the components of balance evaluated in standardized balance measures: a scoping review. Archives of physical medicine and rehabilitation, 96(1), 122-132.

Stergiou, N., & Decker, L. M. (2011). Human movement variability, nonlinear dynamics, and pathology: is there a connection?. Human movement science, 30(5), 869-888.

Oranchuk, D. J., Storey, A. G., Nelson, A. R., & Cronin, J. B. (2019). Isometric training and long‐term adaptations: Effects of muscle length, intensity, and intent: A systematic review. Scandinavian journal of medicine & science in sports, 29(4), 484-503.

Jarvis, P., Turner, A., Read, P., & Bishop, C. (2022). Reactive strength index and its associations with measures of physical and sports performance: A systematic review with meta-analysis. Sports medicine, 52(2), 301-330.

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Tuthill, J. C., & Azim, E. (2018). Proprioception. Current Biology, 28(5), R194-R203.

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González-Grandón, X., Falcón-Cortés, A., & Ramos-Fernández, G. (2021). Proprioception in action: a matter of ecological and social interaction. Frontiers in Psychology, 11, 569403.

Li, R., Du, J., Yang, K., Wang, X., & Wang, W. (2022). Effectiveness of motor imagery for improving functional performance after total knee arthroplasty: A systematic review with meta-analysis. Journal of Orthopaedic Surgery and Research, 17(1), 65.

Araya-Quintanilla, F., Gutiérrez-Espinoza, H., Jesús Muñoz-Yanez, M., Rubio-Oyarzún, D., Cavero-Redondo, I., Martínez-Vizcaino, V., & Álvarez-Bueno, C. (2020). The short-term effect of graded motor imagery on the affective components of pain in subjects with chronic shoulder pain syndrome: open-label single-arm prospective study. Pain Medicine, 21(10), 2496-2501.

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