Motor Control Changes and Pain
Original Editor - Tarina van der Stockt
- 1 Introduction
- 2 Issues surrounding rehabilitation of movement disorders
- 3 Theories explaining motor control changes
- 4 Application
- 5 Clinical Significance
- 6 References
Pain serves as a protective mechanism that leads to changes in movement. Altered movement may be appropriate in early protective phases, but, if maintained, this altered movement can contribute to poor recovery, continued disability, and decreased quality of life.
Motor control is the "ability to regulate or direct the mechanisms essential for movement". Movement is played out in an interaction between the person, environment and the task. Movement in itself is an interaction of different body systems like "sensory/perceptual, cognitive, and motor/action"
Muscle control and Pain theories (older theories listed first)
- Pain produces a vicious cycle of pain where muscles become hyperactive
- Pain leads either to muscle inhibition or muscle spasm.
- Pain is more individualised and that it will depend on the person, the task, and the environment. A person's functional capacity is determined by the individual's capacity to meet the demands of the environment and the task.
Issues surrounding rehabilitation of movement disorders
In the rehabilitation of movement disorders, the individual will practice different tasks, but it is not always clear which tasks, in what order and when it should be practised.
- Beneficial: after an acute ankle sprain, a person will be partial or non-weight bearing and avoid dorsiflexion
- Beneficial: during back pain, the trunk muscles co-contract to limit movement and pain, but also Problematic, an increase in muscle activation is a predictor of recurrent low back pain
- Beneficial and problematic: beneficial in the acute phase after an ankle sprain a person might avoid load on the injured ligament, and might walk with the leg externally rotated, but this increases the demand on the proximal joints and is problematic if leads to persistent ankle stiffness.
Theories explaining motor control changes
There are 4 main ways motor control changes happen with regards to pain, nociception, injury or even the anticipation of them. Hodges (2016) summarised them thus:
- Suboptimal movement/motor control as a precursor to injury and pain
- Impaired movement/motor control as a consequence of interference by actual or threatened injury and/or pain
- Modification of movement/motor control for the protection of the painful/injured/threatened region
- Modified movement/motor control explained by a conditioned association with pain
Each one of these ways will look different in every individual and will influence them in different ways. They may also overlap and the order might be different. These differences in individuals need to be considered when doing an assessment and planning rehabilitation.
1. Suboptimal tissue-loading theory
This is where alignment or movement load tissues suboptimally. This can happen as a single event of repetitively:Single loading events that lead to nociception, tissue injury, or pain. Examples -a slip or a fall, unexpected force or high load in a suboptimal position, optimal movement or motor control but load exceeded the tissue capacity
- Multiple factors need to be reached to exceed the tissue threshold for load tolerance
- examples: poor posture (see image), poor joint alignment during movement, poor coordination or control between different segments of the body
- different schools of thought
- continued repetition of suboptimal movement could lead to pain/injury/a risk factor for recurrence. The (tissue) threshold will be reached with sufficient exposure to suboptimal movement or loading leading to pain or injury (threshold can even be reached by a low load or force over time however each person's threshold and capacity is different).
- many people have suboptimal movement or posture without pain on injury so this leads to questioning the relationship to pain
Different reasons people having suboptimal loading strategies. (summarised below): 
- Habit - posture or specific muscle activation
- Environmental - bad posture due to ergonomics (chair, computer), changed in hip mobility because of sitting with a posterior tilt for long durations
- Functional - asymmetrical tasks/sports
- Presumed benefit - overcorrecting posture in standing or sitting because the person thinks it is the ideal posture
- Minimising energy - resistance in the muscles or tendons leads to a change in posture or movement - Jogging with hip adduction because of ITB tightness.
- Previous exposure to pain or injury - the motor changes remain even after the pain or injury resolves (a risk factor for pain recurrence). 
Aspects to consider
- Pain does not mean there is abnormal loading or nociception
- Pain intensity is not reflective of the amount of suboptimal tissue loading
- A change in movement and loading might have initiated the experience of pain, may not be the cause of continued pain
- If the nociceptors are continually activated by suboptimal tissue loading changing a person's movement may resolve the symptoms
- The relationship between pain and loading is non-linear and rehabilitation of movement may not always resolve the symptoms, or it may resolve but not for the reasons the therapist thinks. 
2. Pain/injury interference/inaccuracy hypothesis
- Pain and injury is also responsible for changes in motor control
- This can be seen as protective (eg ankle sprain) or it may interfere/change motor behaviour in a way that is not protective
- Effects happen at different levels of the nervous system. Proposed mechanisms: nociceptive and non-nociceptive afferent input can excite or inhibit motor neurons and the peripheral sensory function is disrupted interfering with motor control by altering the position of movement or muscle spindle sensitivity; injury/pain induced acute and subacute muscle changes like atrophy, muscle fibre-type changes, fatty infiltration, and changes in connective tissue leading to changed in motor control.
- The maladaptive motor changes due to pain and injury will affect function and may lead to additional pain and injury and to counteract this effect (called interference/inaccuracy), physiotherapists should address either/both the stimulus for the effect like joint swelling and the consequence of the interference (reflex inhibition).
3. Protective response hypothesis
The natural response to pain or injury is to protect. This is different between people and tasks. If this response is continued it can lead to more pain in injury in the same area or even in other areas due to suboptimal loading. 
This protective response can happen in different ways: 
- limitation in movement due to increased stiffness (spine movement is limited due to splinting of back muscles)
- change in the amount of force (limping to reduce the force on the sprained ankle)
- change in the force direction (change in knee position because of pain in the infra-patellar fat pad)
- change the activity of muscles to decrease stress
- avoid movement or function eg take to bed/avoid participation eg work, sport.
- fear-avoidance can lead to changes in motor control
There is a short term advantage to this protection but possible long term consequences due to suboptimal tissue loading. If this response is maintained past what is necessary then the protective response needs to be addressed before symptom resolution. 
4. Conditioned response hypothesis
This is where an individual associates movement with pain, thus movement will lead to pain without nociception. This is also called pain memory. Initially, the pain was linked to movement that produced symptoms as a result of nociceptor activation in tissue loading.
Integration of hypotheses
These 4 hypotheses cannot be separated from each other and it is possible that we can only understand the motor control changes as it relates to pain and injury by looking at how these hypotheses interact with one another. Every individual's response to pain and injury is different, and different mechanisms play a role at different times and might change with time. To have a successful intervention you need to be able to identify the mechanism behind the change in motor control and be specific with your treatment to target that. 
The treatment intervention for each individual will depend on the mechanism involved and might need a combination strategy. 
- Suboptimal tissue loading as a result of an impaired motor strategy - change the movement strategy
- Movement interference due to pain or injury - treat the interference and prevent/reverse the consequences of the interference
- Protective motor changes that are sustained or continued longer than needed - training should aim to reduce or resolve the motor changes in order to have a more normal tissue loading, and help restore participation and activity
- Conditioned response to pain - focussed interventions to extinguish/resolve the conditioning
The American Physical Therapy Association Vision Statement describes physical therapists as health care professionals who are “transforming society by optimizing movement to improve the human experience.” Understanding the interplay among pain-related nervous system processing, movement impairments, and recovery is important for physical therapists, the movement experts.
- Butera KA, Fox EJ, George SZ. Toward a transformed understanding: from pain and movement to pain with movement. Physical therapy. 2016 Oct 1;96(10):1503-7. Available from:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5046190/ (last accessed 20.2.2020)
- Shumway-Cook, A., & Woollacott, M. H. (2007). Motor control: translating research into clinical practice. Lippincott Williams & Wilkins
- Lund JP, Donga R, Widmer CG, Stohler CS. The pain-adaptation model: a discussion of the relationship between chronic musculoskeletal pain and motor activity. Can J Physiol Pharmacol 1991;69(5):683–94.
- Hodges, PW. Chapter 4. Motor Control and Pain. Sluka KA. Mechanisms and management of pain for the physical therapist. Lippincott Williams & Wilkins; 2016 Feb 2.
- Motor Impairment. Prof Paul Hodges talks about pain and altered movement. 2018. Available from: https://youtu.be/mDw_HTCgxc4
- Healing Chronic Pain- The Pain PT. Chronic Pain: A Learned Habit- Pavlov's Dog- TMS- Dr. Sarno. 2019. Available from: https://youtu.be/s49GP71caY0