Motor Control Changes and Pain

Original Editor - Tarina van der Stockt

Top Contributors - Tarina van der Stockt, Kim Jackson, Lucinda hampton and Rachael Lowe  

Introduction

Motor control is the "ability to regulate or direct the mechanisms essential for movement". Previous motor control theories explained that pain leads either to muscle inhibition or muscle spasm. Older theories postulated a vicious cycle of pain where muscles become hyperactive Movement is played out in an interaction between the person, environment and the task. Newer theories describe pain as more individualised and that it will depend on the person, the task, and the environment. Movement in itself is an interaction of different body systems like "sensory/perceptual, cognitive, and motor/action"

A person's functional capacity is determined by the individual's capacity to meet the demands of the environment and the task.

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.

People move differently due to the influence of pain, either the threat, the presence, resolution, or precursor of pain. Changes could be beneficial or problematic:

• 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
• Problematic: an increase in muscle activation is also a predictor of recurrent low back pain
• Beneficial and problematic: 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 can lead to persistent ankle stiffness.

There are 4 main ways motor control changes happen with regards to pain, nociception, injury or even the anticipation of them. Hodges (2016) summarised the finding of different authors as follows:

1. Suboptimal movement/motor control as a precursor to injury and pain

2. Impaired movement/motor control as a consequence of interference by actual or threatened injury and/or pain

3. Modification of movement/motor control for the protection of the painful/injured/threatened region

4. 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.

Different theories exist to explain changes in motor control:

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
  • the person may have optimal movement or motor control but load exceeded the tissue capacity
• Repetition
  • examples: poor posture, poor joint alignment during movement, poor coordination or control between different segments of the body
  • empirical evidence is limited
  • different schools of thought
    1. continued repetition of suboptimal movement could be a precursor to pain or injury or be a risk factor for recurrence. The (tissue) threshold will be reached with sufficient exposure to suboptimal movement or loading and lead to pain or injury. This threshold can even be reached by a low load or force over time. This is complex because each person's threshold and capacity is different.
    2. many people have suboptimal movement or posture without pain on injury so this leads to questioning the relationship to pain
  • Multiple factors need to be reached to exceed the tissue threshold for load tolerance

There are different reasons people have suboptimal loading strategies. Hodges (2016) summarises the different factors as follows:

• 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 - stand or run with hip adduction due to ITB tightness.
• Previous exposure to pain or injury - the motor changes remain even after the pain or injury resolves. This can also become a risk factor for pain recurrence.

Aspect 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, it does not mean it is the cause of continued pain
• If the nociceptors are continually activated by suboptimal tissue loading then changing a person's movement might be indicated to resolve the symptoms
• The relationship between pain and loading is non-linear and thus the 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 (like with the ankle sprain) or it may interfere or change motor behaviour in a way that is not protective
• These effects happen at different levels of the nervous system. One explanation is how nociceptive and non-nociceptive afferent input can excite or inhibit motor neurons. Also, when the peripheral sensory function is disrupted interferes with motor control by altering the position of movement or muscle spindle sensitivity. There is also evidence for acute and subacute muscle changes like atrophy, muscle fibre-type changes, fatty infiltration, and changes in connective tissue that are associated with pain or injury
• It does not matter what the mechanism is, 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), you need to address either or 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 like bed rest or participation like work
• 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.

Movement may initially be provocative

of symptoms because of nociceptor activation due to tissue loading (with or without

sensitization). Over time, via a process of classical conditioning, pain (the conditioned

response) may be experienced in association with movement (the conditioned stimulus), in the

absence of nociceptive discharge (the unconditioned stimulus). An individual may continue to