The use of intermittent trunk flexion to alleviate low back pain during prolonged standing

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Abstract

The current study examined of the effect of intermittent, short-term periods of full trunk flexion on the development of low back pain (LBP) during two hours of standing. Sixteen participants completed two 2-h standing protocols, separated by one week. On one day, participants stood statically for 2 h (control day); on the other day participants bent forward to full spine flexion (termed flexion trials) to elicit the flexion relaxation (FR) phenomenon for 5 s every 15 min (experimental day). The order of the control and experimental day was randomized. During both protocols, participants reported LBP using a 100 mm visual analogue scale every 15 min. During the flexion trials, lumbar spine posture, erector spinae and gluteus medius muscle activation was monitored. Ultimately, intermittent trunk flexion reduced LBP by 36% (10 mm) at the end of a 2-h period of standing. Further, erector spinae and gluteus medius muscle quietening during FR was observed in 91% and 65% of the flexion trials respectively, indicating that periods of rest did occurred possibly contributing to the reduction in LBP observed. Since flexion periods do not require any aids, they can be performed in most workplaces thereby increasing applicability.

Introduction

Low back pain (LBP) is a common, chronic and recurrent condition that affects approximately eighty-five percent of Canadians (Cassidy et al., 2005) with the highest incidence occurring between the ages of 30–50 years old (Hoy et al., 2010). Further, LBP has been found to be strongly associated with static postures related to a sedentary lifestyle such as standing (Janwantanakul et al., 2011, Mohseni-Bandpei et al., 2011). Occupations such as assembly-line workers, bank tellers and grocery store cashiers along with various other professions, require workers to stand for extended periods of time, increasing the incidence of LBP.

Despite minimal compressive loading of the low back during prolonged standing (Nachemson, 1981), LBP persists. It is hypothesized that individual differences in how a person stands impacts the severity of LBP development during prolonged standing (Gregory and Callaghan, 2008). Further, neuromuscular activity varies between acute LBP developers and non-pain developers during prolonged standing. Greater co-contractions of the gluteus medius (Nelson-Wong et al., 2008) and trunk musculature (Nelson-Wong and Callaghan, 2010a) are found in people who develop acute LBP in comparison to non-pain counterparts. Alterations in muscle recruitment strategies are also found between these two cohorts (Nelson-Wong et al., 2012). Additionally, postural control strategies during standing reflect differences in people who experience LBP and those who do not (Gregory and Callaghan, 2008). Knowledge of neuromuscular and postural control strategies may be helpful in early identification of at-risk LBP populations.

In 1951 Floyd and Silverman identified the flexion relaxation phenomenon (FRP), characterized by back extensor muscle quiescence near peak lumbar flexion. It is theorized that passive tissues (the intervertebral disc and posterior ligaments) take over for the trunk extensor musculature to support the increased moment about the spine during peak flexion. While silencing of the extensor muscles occurs, small amounts of force are still theoretically generated elastically through passive stretching (McGill and Kippers, 1994).

Myoelectric silencing of the back musculature is often absent or reduced in individuals with chronic LBP (Sánchez-Zuriaga et al., 2015, Maroufi et al., 2013, McGorry and Lin, 2012, Mak et al., 2010, Neblett et al., 2003, Mannion et al., 2001, Kaigle et al., 1998, Shirado et al., 1995). Kaigle et al. (1998) identified only a 13% silencing of the lumbar erector spinae muscles in chronic LBP individuals as compared to 78% silencing shown by healthy controls. The authors proposed that continuous myoelectric activity in chronic LBP individuals restricts intervertebral motion as a means to stabilize the injured or diseased spine. Likewise, Shirado et al. (1995) found that FRP occurred in 100% of a sample of healthy controls; in contrast, 0% of chronic LBP patients examined experienced FRP at any point during the study (Shirado et al., 1995).

Differing from chronic LBP patients, FRP has been shown to occur in acute LBP participants (Horn and Bishop, 2013, Nelson-Wong et al., 2010). Interestingly, acute pain developers, after prolonged standing, report the desire to flex forward in an attempt to alleviate their pain (Gregory and Callaghan, 2008) despite known findings that flexion can be a risk factor for LBP (Solomonow et al., 2003). Similarly, Dolan et al. (1988) found that individuals tended to commonly adopt postures that result in a flexed spine. It is possible that desired reports to flex forward after prolonged standing may reduce LBP through the onset of FRP, inducing periods of muscle rest. Additional studies have further examined the impact of spine flexion to alleviate/prevent LBP. Nelson-Wong and Callaghan (2010b) found that standing on a sloped surface (eQ Almond, Alberta, Canada) decreased reports of LBP by 59.4%, which has been shown to induce flattening the lumbar spine through posterior rotation of the pelvis and flexion of the lumbar spine and trunk (Gallagher et al., 2013).

It is important to develop methods that alleviate and potentially prevent LBP in order to increase quality of life and the productivity of workers in occupations that demand prolonged standing postures. Therefore, the purpose of this study was to determine if transient trunk flexion would mitigate LBP development induced by prolonged standing in previously asymptomatic individuals (i.e. no pain at the start of a two-hour standing period and no previous history of chronic LBP in the past 12 months). It was expected that the FRP would occur in acute LBP populations, and that FRP would provide transient muscle rests throughout two hours of prolonged standing, in turn decreasing LBP development.

Section snippets

Participants

A sample population of young adults between 18 and 30 years of age (8 males and 8 females; N = 16; university population) were recruited for this study (Table 1). All participants reported having to stand for prolonged periods of time in either previous or current employment opportunities. Participants were excluded from the study if they had experienced chronic LBP in the past 12 months that required them to visit a doctor and/or take time off work. Participants were also asked to refrain from the

LBP development and the effect of transient trunk flexion

As the 2-h protocol progressed, LBP ratings during the control day significantly increased (p < 0.0001), most notably at 75 min (Fig. 1). Of the sixteen participants, twelve participants were considered acute LBP developers based on control day low back VAS scores exceeding 8 mm at any time point during the two hours of standing. The average VAS score for non-LBP developers was 1.64 mm (SE 0.4) and 16.19 mm (SE 1.78) for LBP developers over the two-hour control protocol. The average VAS scores at the

Discussion

The purpose of this study was to determine if trunk flexion would mitigate LBP development induced by prolonged standing in previously asymptomatic individuals. For LBP developers, intermittent short duration trunk flexion was found to alleviate pain after 75 min of standing (an average reduction of 10 mm on a 100 mm visual analogue scale). At every time point beyond 75 min of standing, a significant difference was identified between the control day LBP ratings and post-flexion ratings. As time

Conflicts of interest

None.

Acknowledgment

The authors wish to acknowledge the Natural Sciences and Engineering Council of Canada for funding.

Danielle M. Stewart received her BA (2013) and her MSc (2015) from Wilfrid Laurier University in Kinesiology with an emphasis in biomechanics and ergonomics. Her primary research focus is in occupational biomechanics and ergonomics, more specifically using in-vivo and in-vitro approaches to understanding spine and trunk biomechanics.

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    Danielle M. Stewart received her BA (2013) and her MSc (2015) from Wilfrid Laurier University in Kinesiology with an emphasis in biomechanics and ergonomics. Her primary research focus is in occupational biomechanics and ergonomics, more specifically using in-vivo and in-vitro approaches to understanding spine and trunk biomechanics.

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