Why should exercises be pain-free? Part 1 – pain and biomechanics

Introduction

The blog aims to take a look at exercise prescription for MSK pain. Why do we prescribe exercises the way we do? What does the evidence tell us? Does exercise work the way we think it does?

Let’s start by thinking about what pain is and why might we think exercise is helpful for it.

What is pain?

The International Association for the Study of Pain (IASP) defines pain as ‘an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage’ [1]. The traditional view of pain further summarises: 1) pain is viewed as a symptom and warning sign, the function of which is to avert the person from harm; 2) it provides a pivotal role in identifying underlying pathology; 3) ethically, medical and rehabilitation practice should aim to avoid or alleviate pain as much as possible [1,2].

In short – the traditional view of pain is that it is a direct sign of tissue damage that should be avoided.

No wonder cross-sectional online questionnaire surveys of practice that examined this aspect of exercise prescription have demonstrated that many physiotherapists suggest avoiding pain when prescribing exercises [3,4]. Many physiotherapists in these studies also recommend limiting all forms of physical activity in the presence of pain.

This biomedical model of pain typically attributes the sensing of harmful stimuli to nociception*. It fails to distinguish between sensation and the perception of pain. Pain was thought to be conveyed to the brain directly from nociceptors [5].

*Nociceptors are specialised primary sensory neurons situated in various body tissues, such as skin, muscles and tendons, which are involved in the transduction and transmission of information from the periphery to the central nervous system [6,7].

WHY EXERCISE?

It is often assumed that the primary mechanism by which exercise improves pain and disability in musculoskeletal pain is biomechanical, i.e. changes to the load distribution of the musculoskeletal system [8]. Improvements in joint range of movement, muscle strength and endurance and postural control after exercise programmes are thought to contribute to changes in loading at the painful site, thus reducing the painful stimuli. With a corresponding decrease in nociception and pain perception [9].

Does the evidence support this? Perhaps not…..[8,10]. Improvements in pain and function after exercise programmes often occur in the absence of any changes to joint position and movement in knees, shoulders and backs.

For example:

1. Rathleff’s 2014 systematic review looked at hip strength and patellofemoral pain. They included 27 articles and 1,971 participants [11]. The review demonstrated that while hip-strengthening exercises appear to improve pain and symptoms for people with patellofemoral pain, these improvements in pain they do not to change any kinematics and alignment dysfunction at the knee or patella [11].
2. A 2012 systematic review assessing changes in pain and, joint position and movement with exercise interventions for low back pain included 16 articles and 1,476 participants. They demonstrated that people with LBP gain some improvements with exercises, but that pain reductions were not attributable to changes in joint position or movement [9].
3. Similarly, a 12-week strengthening programme for patients with knee osteoarthritis (OA) improved pain and symptoms, without any changes in joint load [12]. In an RCT (n = 89), Bennell (2010) compared a therapist-supervised exercise program to no intervention in people with medial compartment tibiofemoral OA and varus malalignment [12]. It was hypothesised that strength improvements would reduce joint load (as measured by knee adduction moment) and improve pain and function, as cross-sectional research shows increased varus malalignment and higher peak knee adduction moment in patients with knee OA [13,14]. The study demonstrated a discrepancy between prospective and cross-sectional research findings, with improved symptoms and function occurring without altering medial compartment loading.
4. Finally Drew et al. (2014) conducted a systematic review to evaluate the relationship between observable structural change and clinical outcomes following therapeutic exercise [15]. They included trials that measured the structure of a tendon (US, MRI or CT) before and after a course of therapeutic exercises. They included 20 studies with 625 participants and concluded that on average patients improve over time in terms of pain and function; observable structural pathology did not change [15].

It is likely that changes in biomechanics, with subsequent changes in load distribution of the musculoskeletal system, do not fully explain the improvements in pain and symptoms seen with exercise interventions. The inconsistency demonstrated indicates how more complex and unexplored this topic is but does challenge the idea that exercises need to reduce tissue loading at painful body sites.

The second part of this blog will discuss the philosophy of pain and how that influences exercise prescription.

This was originally posted on Dr Ben Smith’s website. You can click here to read more blogs from them.