1 INTRODUCTION

A multidisciplinary, biopsychosocial approach is recommended to manage complex conditions of chronic pain/fatigue, including chronic low back pain, chronic widespread pain, fibromyalgia and chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME) (British Pain Society, 2013; Kamper et al., 2015; National Institute for Health and Care Excellence, 2007). Such conditions may be classified as somatic symptom disorders owing to the presence of physical symptoms (for example, pain and weakness) that disrupt daily functioning and are associated with altered thoughts, feelings or behaviours (American Psychiatric Association, 2013). In keeping with this classification, the impact of chronic pain/fatigue includes disability, anxiety, depression and altered behaviours such as fear avoidance, excessive persistence and overactivity–underactivity cycling (Abonie, Sandercock, Heesterbeek, & Hettinga, 2018; Kindermans et al., 2011; National Institute for Health and Care Excellence, 2007; van Koulil et al., 2010).

Patients may present with one or more somatic disorders due to overlapping symptoms (Davis, Kroenke, Monahan, Kean, & Stump, 2016; Tavel, 2015). Consequently, conditions of chronic pain/fatigue may be treated together, using holistic interventions that include physical and psychological therapies (American Psychiatric Association, 2013; Tavel, 2015). Specifically, rehabilitation programmes involve graded exercise, cognitive behavioural therapy (CBT), acceptance and commitment therapy (ACT) and mindfulness (British Pain Society, 2013; Goudsmit, Ho‐Yen, & Dancey, 2009; Larun, Brurberg, Odgaard‐Jensen, & Price, 2017; National Institute for Health and Care Excellence, 2007, 2016). Activity pacing is considered an important component of such strategies, and a core element of rehabilitation programmes (Beissner et al., 2009; Birkholtz, Aylwin, & Harman, 2004a; Booth et al., 2017; Nielson, Jensen, Karsdorp, & Vlaeyen, 2013; Torrance et al., 2011; Wallman, Morton, Goodman, Grove, & Guilfoyle, 2004).

Activity pacing aims to modify behaviours of avoidance, excessive persistence and overactivity–underactivity/boom–bust cycling. Boom‐bust cycling involves fluctuations between high activity levels (excessive persistence) which leads to increased symptoms and consequential days of low activity levels (Birkholtz et al., 2004a). Pacing encourages more consistent engagement in regular and meaningful activities, while reducing flare‐ups (Beissner et al., 2009; Birkholtz et al., 2004a; Nielson et al., 2013).

Pacing has been labelled using varying terminology—for example, activity modification, tailored pacing and activity scheduling. It has been described as adaptive pacing therapy (activities are undertaken within limited amounts of energy) (White et al., 2011) and the envelope theory (energy expenditure matches perceived energy levels) (Goudsmit & Howes, 2017). Such principles align with symptom contingency, in which activities are driven by perceived symptom levels, with the aim of avoiding symptoms/conserving energy (Racine, Jensen, Harth, Morley‐Forster, & Nielson, 2018). However, there have been minimal measurable improvements in function when pacing is described in these terms (Goudsmit et al., 2009; White et al., 2011). Alternatively, pacing has been described as Fordyce's operant approach (Fordyce, 1976). This quota‐contingent approach involves undertaking activities according to an amount/distance/goal with the aim of improving function (Nielson et al., 2013). The aim of pacing, to increase function or reduce the severity of symptoms, plays an important role in the efficacy of the strategy (Esteve et al., 2017; Hadzic, Sharpe, & Wood, 2017).

The individual facets of pacing may also influence whether patients benefit from it. Commonly cited facets of pacing include going slow and steady, breaking down tasks and using rest breaks (Cane, Nielson, McCarthy, & Mazmanian, 2013; McCracken & Samuel, 2007; White et al., 2007). As such facets may involve reductions in activities, it is perhaps unsurprising that pacing has been significantly associated with inactivity, avoidance and disability (Cuperus, Hoogeboom, Neijland, van den Ende, & Keijsers, 2012; Hadzic et al., 2017; McCracken & Samuel, 2007). Other facets of pacing include planning, consistency, setting goals and gradually increasing activities (Antcliff, Campbell, Woby, & Keeley, 2015; Birkholtz, Aylwin, & Harman, 2004b; Nielson et al., 2013). The effects of these facets have been less widely investigated.

To date, there is no consensus on the use and effects of different types of pacing. Adaptive pacing therapy for CFS/ME has been found to be ineffective (White et al., 2011); energy conservation for CFS/ME has improved fatigue, anxiety and self‐efficacy but not functional impairment (Goudsmit et al., 2009); pacing for chronic pain (breaking down tasks/using rest breaks) has been associated with improved psychological function, without improving disability or avoidance (Cane et al., 2013; McCracken & Samuel, 2007). Therefore, there is no widely used method of pacing that has consistently improved psychological and physical function among patients with chronic pain/fatigue.

Within the context of chronic pain/fatigue, there remains much debate into the types/uses of pacing, the aims, facets and clinical effects. In the absence of a strong evidence base or standardized framework, it follows that healthcare professionals, patients and researchers may interpret/implement pacing differently (Gill & Brown, 2009; Nielson et al., 2013). Here, we describe the first stage in the development of a comprehensive activity pacing framework which has wider clinical utility through its relevance for chronic pain and fatigue.