Review
Pain and motor control: From the laboratory to rehabilitation

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Abstract

Movement is changed in pain and is the target of clinical interventions. Yet the understanding of the physiological basis for movement adaptation in pain remains limited. Contemporary theories are relatively simplistic and fall short of providing an explanation for the variety of permutations of changes in movement control identified in clinical and experimental contexts. The link between current theories and rehabilitation is weak at best. New theories are required that both account for the breadth of changes in motor control in pain and provide direction for development and refinement of clinical interventions. This paper describes an expanded theory of the motor adaptation to pain to address these two issues. The new theory, based on clinical and experimental data argues that: activity is redistributed within and between muscles rather than stereotypical inhibition or excitation of muscles; modifies the mechanical behaviour in a variable manner with the objective to “protect” the tissues from further pain or injury, or threatened pain or injury; involves changes at multiple levels of the motor system that may be complementary, additive or competitive; and has short-term benefit, but with potential long-term consequences due to factors such as increased load, decreased movement, and decreased variability. This expanded theory provides guidance for rehabilitation directed at alleviating a mechanical contribution to the recurrence and persistence of pain that must be balanced with other aspects of a multifaceted intervention that includes management of psychosocial aspects of the pain experience.

Introduction

Rehabilitation of control of movement and muscle activity is a mainstay of management of many pain conditions related to the musculoskeletal system. This is based on the premise that pain and movement are intimately linked. In the acute phase, the motor system provides an opportunity for the nervous system to respond and remove or reduce a threatening noxious stimulus (mechanical, chemical or thermal) to the tissues. If the nervous system concludes that a situation is threatening (this may be in response to discharge of nociceptive afferents or the threat of a noxious input) it can move or change the mechanical behaviour of the body to remove the threat, and reduce the potential for further pain/injury to the tissues. In the chronic phase the motor response may be less meaningful, less accurate or unnecessary as the threat to the tissues may be less relevant as a result of the range of physiological and psychological issues that change the gain of the pain system. Thus, the pain that a person experiences does not necessarily match the input from the nociceptive afferents and pain may not reflect harm or potential harm to the tissues. Maintenance of a motor adaptation in chronic pain may not provide benefit to the system.

Many clinical interventions target changes in motor control that accompany pain. These include motor learning strategies (e.g. exercise with error correction, augmented feedback, part-practice), some psychological interventions (e.g. treatments to reduce threat value of pain), and hands-on techniques (e.g. manual therapy, muscle stretching, needling techniques). However, the mechanisms that underlie the motor adaptation to pain are surprisingly poorly understood and two primary theories have been proposed: “vicious cycle” (Roland, 1986) and “pain adaptation” (Lund et al., 1991). These theories explain some observations in clinical and experimental pain. However, there are two major limitations. First, many clinical and experimental observations are inconsistent with predictions made by these theories; and second, the link between these theories and rehabilitation is weak. The aim of this paper is to review the limitations of current theoretical models of the motor adaptation to pain, to review a new theory (Hodges and Tucker, in press) that accounts for many of the observations that cannot be explained by existing theories, and to consider the implications for rehabilitation.

Section snippets

Current theoretical models for the motor adaptation to pain and their relationship to rehabilitation

The “vicious cycle” theory proposes a stereotypical increase in activity of muscles that are painful or move the painful region. This muscle activity induces ischaemia from vascular compromise and becomes a source of further pain due to accumulation of pain metabolites (Roland, 1986). Various mechanisms have been proposed to explain the increase in muscle activity, including increased sensitivity of muscle spindles (Johansson and Sojka, 1991). Treatments based on this theory include the use of

New theory of the adaptation to pain

A new theory has been developed on the basis of data from micro (motoneuron discharge) to macro (whole muscle behaviour) levels of the motor system in order to reconcile the complex nature of the adaptation in motor control that accompanies pain (Hodges and Tucker, in press). This theory is a progression from the vicious cycle and pain adaptation theories and is inclusive of the observations associated with the basis for those theories. The key progression of the theory is that it aims to

Implications of the new theory of motor adaptation in pain for rehabilitation of musculoskeletal pain

How can the new theory inform rehabilitation for people with musculoskeletal pain? Although existing models of the adaptation to pain provide limited guidance for rehabilitation, the expanded theory of motor adaptation to pain provides a rich array of implications that can be used to shape interventions. Such interventions may include exercise (e.g. training of motor control or movement strategy), psychological interventions (e.g. treatments that change the threat value of pain), and physical

Can motor adaptation be changed with intervention and does it make a difference?

A variety of clinical interventions have been proposed to retrain motor control in musculoskeletal pain. These interventions vary in their approach and are based on a multitude of clinical theories such as aiming to modify loads on painful structures (Crossley et al., 2000) and enhance protection of a painful part (McGill, 2002, van Dieën et al., 2003). The common feature is the use of relearning strategies to change motor features considered to contribute to the perpetuation or recurrence of

Conclusion

The new theory of motor adaptation to pain provides a more comprehensive explanation of clinical and experimental observations. The theory also provides a range of principles that can be applied and trialed for the rehabilitation of musculoskeletal pain. Some of these implications are supported by data from clinical trials whereas others provide predictions that require testing to confirm the magnitude of potential clinical effects.

Acknowledgement

PH is supported by a Fellowship from the National Health and Medical Research Council of Australia.

Paul Hodges Ph.D. Med. Dr. D.Sc. B.Phty. (Hons.) FACP is the Director of the Centre for Clinical Research Excellence in Spinal Pain, Injury and Health (CCRE SPINE) funded by the National Health and Medical Research Council (NHMRC) of Australia and is an NHMRC Senior Principal Research Fellow. He has 3 doctorates; one in physiotherapy and two in neuroscience. His research blends these skills to understand pain and control of movement. The large multidisciplinary research centre that he leads

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    Paul Hodges Ph.D. Med. Dr. D.Sc. B.Phty. (Hons.) FACP is the Director of the Centre for Clinical Research Excellence in Spinal Pain, Injury and Health (CCRE SPINE) funded by the National Health and Medical Research Council (NHMRC) of Australia and is an NHMRC Senior Principal Research Fellow. He has 3 doctorates; one in physiotherapy and two in neuroscience. His research blends these skills to understand pain and control of movement. The large multidisciplinary research centre that he leads focuses on understanding pain physiology, and the development and testing of novel treatments. Recent work has led to the development of new understanding of the motor adaptation to pain. He has received numerous international research awards (including the 2006 ISSLS Prize for back pain research), published >200 scientific papers, presented >120 invited lectures at conferences in >30 countries, and received more than $AU22 million in research funds.

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