Low back pain (LBP) is a leading cause of disability worldwide , . There is a pervasive belief in western society that the lower back is easy to injure and hard to heal , , , , and that bending and lifting (especially with a round-back posture) are dangerous , . This view likely originated from interpreting the results of early in vitro studies using direct measures to investigate the effect of load on cadaveric spines , , , , and historical in vivo studies on lumbar disc pressure, in which lifting with a round-back was reported as generating greater intradiscal pressure than lifting with a straight back , , ; thus conferring a greater risk of disc injury with the round-back lifting technique. Since then, straight-back lifting has been recommended as the safe lifting strategy , , , , , . Perceiving the back as vulnerable during bending and lifting  may influence a person’s behaviour while performing these tasks , , . It has been proposed that decisions about task behaviours adopted in daily life may occur as part of a dual-process, in which explicit (deliberate, analytical) and implicit (automatic) processes are involved in the appraisal of risk versus benefit associated with the task , . The influence of each process on task behaviour may vary depending on context, time and motivation , , . Therefore, assessment of beliefs related to the bending and lifting back posture is important. Specifically, evaluating these processes in people who are not experiencing pain provides a framework un-confounded by recent experience of LBP to understand the relationship between explicit and implicit beliefs.
Self-reported questionnaires are widely used to assess back beliefs (explicit measures) , . However, these are vulnerable to self-presentational bias and might only capture what the individual is aware of, or willing to disclose , . In addition, these do not assess beliefs about specific postures, being more generic evaluations of back beliefs , , . Implicit attitudes however, are better evaluated in a spontaneous context in which time for introspection and motivation is reduced . The Implicit Association Test (IAT) is commonly used to measure implicit associations in social , , health psychology , , , and pain , ,  research, but to date the IAT has not been used to investigate perceptions of safety in relation to specific back postures during bending and lifting in pain-free people.
A recent study evaluating implicit associations between back posture (straight-back vs. round-back) and safety related to bending and lifting in people experiencing back pain found that irrespective of self-reported fear of bending/lifting with a round-back, people were faster to associate images of round-back bending and lifting with words representing danger, rather than safety . Inferring from previous studies involving asymptomatic individuals , , , , the authors proposed this may reflect a pre-existing pervasive societal schema or belief , that is informed by media, healthcare providers, family, friends, and past experiences , . Nevertheless, that study did not evaluate a pain-free group. Based on our previous work , we hypothesised that (i) pain-free people would display an implicit bias towards evaluating bending and lifting with a round-back as dangerous, (ii) this bias would correlate only moderately with their explicit beliefs, and (iii) pain-free people would qualitatively appraise straight-back lifting as safest.
Therefore, the aims of this study were:
- to evaluate implicit associations (IAT) between back posture (straight-back vs. round-back) and safety (safe vs. danger) related to bending and lifting in pain-free people;
- to explore correlations between implicit (IAT) and explicit measures of beliefs towards vulnerability of the back (bending safety beliefs, back beliefs, and fear of movement);
- to investigate participants’ qualitative appraisal of safe lifting.
2.1 Study design
An exploratory cross-sectional study.
2.2 Participants and recruitment
Participant recruitment and data collection commenced in August 2017 and was completed by September 2017. Participants were recruited through social media, flyers and posters on Curtin University campus as well as approached in person.
Adults over 18 years of age, who had no low back pain (LBP) within the past 12 months were included (indicated by no pain, or pain ≤3/10 on average for less than a week, on a Numerical Rating Scale – NRS – anchored on 0=no pain, 10=worst pain ). Participants were excluded if they had difficulty to read and understand English, or if they were trained physiotherapists or currently studying physiotherapy (as this population has already been studied ).
Participants were screened over the phone or in person to check if they fulfiled the inclusion criteria. An information sheet clearly explaining the study was sent via email. This study was approved by Curtin University’s Human Research Ethics Committee prior to study commencement (HRE2017-0500). All participants provided informed consent, and were informed that they could withdraw from the study at any time.
Data collection occurred in two stages: (1) Online: completion of a survey online (using Curtin University’s Qualtrics online platform); (2) Experiment: completion of a computer-based task (IAT) measuring implicit attitudes related to bending and lifting back posture and perceived safety to the spine. This was followed by completion of the BSB questionnaire (measuring explicit attitudes related to bending and lifting back posture and perceived safety to the spine). Participants were required to meet with investigators at the research laboratory in the School of Physiotherapy and Exercise Science (Curtin University), or at an agreed upon external location to complete this stage. A flow chart of the study recruitment and procedure is displayed in Fig. 1.
2.4 Demographic data
Participants completed an online demographic questionnaire including age, gender, occupation, previous and current history of back pain, and information related to previous manual handling instructions received about lifting and bending. Participants also provided a subjective description of their understanding of “safe lifting” – this is described later in this section.
2.5 Outcome measures
The outcome measures assessed in this study were measures of fear of movement beliefs, back beliefs, explicit and implicit beliefs about bending/lifting posture and safety of the spine.
2.6 Implicit Association Test (IAT)
The IAT  is a well-established measure, which was adapted to assess associations between bending/lifting posture and safety in a group of people with back pain . The IAT is a computer based test comprising seven phases, separated by pauses for the instructions in between phases . This IAT is the same used in our previous work , which had five stimuli representing each target (“Round-back” and “Straight-back”) and attribute category (“Safe” and “Danger”). Twelve side view images of males and females standing, bending and lifting with an extended (“Straight-back”) and flexed lumbar spine (“Round-back”), were developed for this experiment after piloting with people with persistent LBP to confirm their suitability. The category “Danger” was represented by five words frequently used to describe danger associated with movement (selected from interviews with people with persistent LBP and high-fear , ). Words matching in length, frequency, and emotionality represented the category “Safe” . The category “Danger” consisted of words such as damaging, vulnerable, threatening, alarming and risky. The category “Safe” consisted of works such as harmless, confident, secure, protecting and certainty.
Participants were instructed to assign each stimulus displayed in the centre of the screen to its suitable category (displayed at the upper corners of the screen), by pressing the left or right “Shift” keys, as fast as possible while avoiding mistakes. On each trial the participant was given feedback (“correct” or “wrong”). The words were presented in bold, 20-point Arial font in white lower case on a black background. The images were presented embedded in a white square image of 800×800 pixels on a black background. In the first phase (20 trials), participants sorted each of the 10 images twice, into the categories “Round-back” and “Straight-back”. In the second phase (20 trials), participants sorted the 10 words twice into the categories “Safe” and “Danger”. In phases, three and four (20 and 40 trials each) participants sorted words and images into the combined categories (e.g. Danger/Round-back and Safe/Straight-back or Danger/Straight-back and Safe/Round-back). In phase five (20 trials) participants sorted images with the location of the categories switched. Phases six and seven (30 and 40 trials) reversed category combinations of phases three and four (e.g. Danger/Straight-back and Safe/Round-back or Danger/Round-back and Safe/Straight-back). As per recommendations , the sequence of congruent and incongruent matches during phases three and four, and six and seven were counterbalanced across participants.
2.6.2 Data processing
Each trial started with the display of a fixation cross for 1,000 ms followed by a word or image for 1,000 ms and an inter-trial interval of 1,000 ms. Response time was defined as the time elapsed from the presentation of the stimulus to when the shift key was pressed. This time was recorded and incorrect responses, responses shorter than 100 ms or longer than 1,000 ms were considered as errors. Presentation of the tasks and reaction time recording was controlled by DMDX . The performance is faster when highly associated categories share a response . The phases of the IAT being used in this study have been included in Online Appendix (Table 1).
A bias score (IATD-score) was calculated using the improved scoring algorithm recommended by Greenwald et al.  with an error penalty of two standard deviations. This was calculated as the difference between each individual’s mean response speeds on the two tasks where danger is paired with round back versus the two tasks where danger is paired with a straight back. The IATD-score could therefore be either positive or negative, with zero indicating no implicit bias in either direction, a positive score indicating implicit bias towards a round-back posture as dangerous and a negative score indicating implicit bias towards a straight-back posture as dangerous. The IAT exhibits adequate reliability and internal, construct and predictive validity , , .
2.7 Bending Safety Belief (BSB)
In order to assess specific beliefs related to back posture and safety of the spine during bending and lifting, the BSB was developed and used in a previous study  (Fig. 2). The BSB consists of a pictorial scale containing two images of a person bending forward and lifting a light object – one with a round-back and one with a straight-back. The participants were asked “how would you rate the level of risk to this person’s back?” for each image using a Likert scale (anchored on 0 meaning safe, and 10 meaning danger). These questions are clinically relevant when assessing people’s beliefs around bending, the way they bend and whether there is a perception of danger in relation to the way they bend (i.e. safe or dangerous). A thermometer score (BSBThermometer) was derived to determine the participant’s belief about safety of bending forward and lifting a light object. The danger rating of the picture illustrating bending with a “straight-back” was subtracted from the danger rating of the picture illustrating bending with a “round-back”. In line with the implicit IATD-score, a positive value therefore indicated a higher danger rating for round-back than a straight-back and a negative score indicated higher danger rating for straight-back than a round-back.
2.8 Tampa Scale of Kinesiophobia – General (TSK-G)
The TSK was specifically designed to measure pain related fear/or fear of movement in people with pain. It has been adapted (TSK-G), to measure fear of movement beliefs in the general population and people who do not have back pain . The TSK-G consists of 17 items that the participants rate on a four-point Likert scale, which ranges from “totally agree” to “totally disagree”. Scores range from 17 to 68 and as the original TSK scale, higher scores on the TSK-G indicate higher levels of fear of movement, even without the presence of pain . Cronbach’s alpha for TSK-G was found to be 0.78 for people without low back pain, which is acceptable internal consistency .
2.9 Back Pain Attitudes Questionnaire (BackPAQ)
The BackPAQ was designed to assess attitudes and underlying beliefs about back pain among the general population, people with back pain and health professionals . The questionnaire consists of 34 items representing five belief themes; the participant’s own back, looking after their back, back pain in general, what should be done if back pain develops, and recovery of back pain. The participants answered the items on a five-point Likert scale from “false” to “true” (intermediate labels: “Possibly False”, “Unsure”, “Possibly True”) and 11 items are reversed scored. The “True” response option normally represents beliefs that are unhelpful for recovery from back pain. Scores range from 34 to 170, with higher scores indicating more unhelpful beliefs about the back. For the purpose of this study, a subscale called “danger scale” (BackPAQDanger) was formed by using 14 items from the questionnaire. These items are questions 1–12, 14 and 21 as they are representative of “vulnerability” and “protection” themes. These themes emerged from the qualitative study which the BackPAQ originated from . Scores range from 14 to 70, with higher scores indicating greater perception that the back is danger, for example, that the back needs protection as it is easily injured. The total score of the “danger scale” was used to find its correlation with other explicit and implicit scores. The 34-item long form of the questionnaire has been shown to have acceptable internal consistency (α=0.70; 95% CI 0.66 to 0.73), construct validity and test-retest reliability , .
2.9.1 Statistical analysis
Descriptive statistics were used to describe the sample. A one-sample t-test was used to assess the degree and direction of deviation of the IATD-score and BSBThermometer score from zero. Additionally, Cohen’s d was calculated to provide a standardised effect size to assist in the interpretation of the size of the estimated bias. Pearson’s correlation coefficients, with associated 95% confidence interval estimates, were used to assess the correlation between implicit and explicit beliefs. Linearity of associations and absence of influential outliers were confirmed by visual assessment of scatterplots. SPSS version 24 statistical software was used for statistical analysis (IBM SPSS Statistics for Windows, version 24, IBM Corp., Armonk, N.Y., USA). An a priori power calculation estimated a sample of 60 participants would have 80% power to detect a standardised IATD-score difference from 0 of at least ±0.35 and correlations between implicit and explicit measures of ±0.35 or greater (two-sided tests, α=0.05).
2.10 Qualitative appraisal of “safe lifting”
A qualitative appraisal of participants’ views regarding “safe lifting” was evaluated by subjective descriptions of how safe lifting should be performed. Participant’s qualitative description of their understanding of a “safe” lifting technique (n=52/67) were analysed by two independent investigators and grouped into common themes, and the frequency of these themes were compared.
Sixty-eight pain-free participants were included in the study. One participant was excluded due to a computer error during the experiment, becoming unable to complete the IAT as required, therefore 67 participants were included in final analysis (52% male). The mean (SD) age was 29 years (9.44; range 18–60). The participants reported their occupation as office workers (54%), students (19%), manual workers (11%), or other (16%). Eleven participants (16%) stated a previous episode of lower back pain, with the remaining 56 participants (84%) having no history of back pain. Sixty participants (90%) stated receiving previous manual handling instruction and 52 participants (78%) provided subjective information of their understanding of “safe” lifting technique.
3.2.1 Implicit measure
The mean IATD-score was 0.65 (SD=0.45; 95% CI [0.54, 0.76] range −0.88 to 1.50), which was significantly greater than zero (t(67)=11.76, p<0.001). The magnitude of this estimated effect size as measured by Cohen’s d was 1.44. This indicates a strong implicit bias of the sample towards the association between images of “round-back” bending/lifting, rather than “straight-back”, with words representing “danger”, rather than “safety”.
3.2.2 Explicit measures
The mean level of fear of movement (TSK-G) was 36.5 (SD=5.6; range 21–49). The mean level of back pain beliefs (BackPAQ) was 105.5 (SD=13.8; range 63–139) and the mean of the subscale BackPAQDanger was 48.5 (SD=6.5; range 22–61). The mean of beliefs related to back posture and safety (BSB Thermometer) was 5.2 (SD=3.8; 95% CI [4.26, 6.13] range −10 to 10). The BSBThermometer was significantly greater than zero (t(67)=11.09, p<0.001), with the positive value indicating a higher danger ratings for round-back bending and lifting, rather than straight-back.
3.2.3 Associations between implicit and explicit measures
There was a moderate correlation between IATD-score and BSB Thermometer (r=0.38, 95% CI [0.16, 0.62]). There were weaker and non-statistically significant correlations between IATD-score and TSK-G (r=0.28, 95% CI [−0.02, 0.47]), between IATD-score and BackPAQ (r=0.21, 95% CI [−0.03, 0.45]), and between IATD-score and BackPAQDanger (r=0.22, 95% CI [−0.02, 0.46]).
3.3 Subjective description of “safe” lifting
Fifty-two participants (n=52/67, 77.6%) described their understanding of a “safe” lifting technique. The most common theme with respect to back posture was keeping a straight back, which included phrases such as “keep back straight”, “keep a flat back”, “don’t bend back” or “chest up” (n=27/52, 52%). Two participants were classified to the neutral back theme as they mentioned “neutral spine” (n=2/52, 4%), whilst one participant mentioned “bending over naturally” (n=1/52, 2%) potentially indicating using a flexed spine and therefore was classified as round back. If there was uncertainty regarding what back posture participants were describing, such as “good back position”, then they were not classified into the aforementioned themes but were included in the table (Online Appendix – Table 2).
Another common theme was related to squatting, which included “bend knees”/“squat” (n=35/52, 67%) and “use legs” (n=22/52, 42%). In combination 88.5% (n=46/52) of the participants mentioned either or both phrases. Twenty-two participants only described the legs, without a mention of spinal postures (22/52, 42%).
It was common for descriptions to include both keeping a straight back and squatting, for example: “Lifting from the legs rather than the back. Keep the back as straight as possible, bend your knees and lift through the legs” (P09, male, 22yo, office worker), “Keep your back straight and bend at the knees” (P55, male, 27yo, manual worker), and “Back straight, chest up, weight close to body and wide base of support” (P59, male 22yo, exercise physiologist).
The one participant who mentioned “bending over naturally” had the following response: “Many years ago (at least 30) I was instructed to bend at the knees and keep back straight, using the strength of my legs to do the lifting. In recent years I have been instructed to bend over naturally and pick up the object” (P31, female, 53yo, office worker). See Online Appendix (Table 2) for detailed table outlining all subjective descriptions of “safe” lifting technique grouped into themes.
The primary aim of this study was to test a hypothesis generated in our previous work  by evaluating implicit associations between images of bending and lifting with a round-back posture (vs. straight-back) and words meaning safety (vs. danger) in pain-free people. Results from the implicit task (IAT), indicate that participants were faster to associate images of bending and lifting with a “round-back” with words representing “danger”, rather than with words representing “safety”. This means the sample displayed an implicit bias towards bending and lifting with a “round-back” as dangerous. These results support our previous hypothesis, which proposed that pain-free people have a pervasive pre-existing belief . Critically, our results indicate this belief appears to be specifically related to “how” a person performs bending and lifting (i.e. back posture adopted during task).
Our results are consistent with a previous study. Goubert et al.  investigated implicit attitudes of pain-free people and found that they have a negative implicit attitude towards back-stressing activities. The authors used a variety of tasks (e.g. driving a car, hanging up a coat and, digging in the garden) and negative words (e.g. war, AIDS), making their research question more generic, and not specific to back posture during bending and lifting tasks. Notwithstanding, their results support the notion that pain-free people perceive the back as vulnerable both explicitly and implicitly . They also assessed people with persistent LBP, and found no implicit bias. The authors therefore suggested, the experience of pain was not the driver of this bias . Leeuw et al.  also assessed implicit attitudes in people with and without persistent LBP. Whilst the groups differed in self-reported fear of movement, the study did not find an implicit association between words representing back-stressing movements (e.g. falling, bending, pushing, lifting, running) and threat-related words (e.g. fatal, warning, terrible, dangerous, horrible) in either group . In addition, people with and without pain did not differ in their level of implicit fear of movement .
Recently, our group investigated implicit attitudes of people with back pain, specifically evaluating beliefs about back posture during bending and lifting . This study found that irrespective of their self-reported fear of bending/lifting with a round-back, all participants had a similar implicit bias towards bending and lifting with a “round-back” as dangerous . Additionally, a study investigating the implicit and explicit beliefs of physiotherapists (pain-free in the year of the experiment), also found an implicit danger bias towards bending and lifting with a round-back . The results of these studies support the hypothesis that this implicit “danger bias” to round-back bending and lifting may be pervasive in people with LBP and in health care workers, however this implicit bias had not been specifically investigated in a pain-free population. Collectively, these results support the idea that pain-free people may have a pre-existing schema. The results of the current study expand on this knowledge, providing evidence that this schema may be specifically biased to bending and lifting with round-back postures, supporting the idea of a “round-back danger” schema.
A secondary aim was to explore if implicit measures (IAT) correlated with explicit measures of back beliefs (BackPAQDanger), fear of movement (TSK-G) and safety of bending (BSB). Sample profiling indicated that participants generally displayed negative beliefs about the back, high levels of pain-related fear, and perceived danger related to bending and lifting with a round-back posture. There was a moderate statistically significant correlation between the implicit measure and the explicit measure specifically assessing beliefs related to back posture and safety of the spine during bending and lifting (BSB). There were only weak, non-statistically significant correlations with more explicit beliefs related to fear of movement (TSK-G) and beliefs about back (BackPAQDanger), which are less specific to back posture. This is in line with research of implicit measures, which reports that correlations are likely to be higher when the specific constructs assessed by both measures (implicit and explicit) have conceptual correspondence . This was the case in the current study, with both the IAT and the BSB assessing back posture and safety.
Finally, a qualitative appraisal of subjective descriptions of ‘safe’ lifting was performed. This revealed that descriptions related to a “straight back” and “squatting” were the most common, with considerably fewer participants describing a “neutral” or a “round-back” posture. This supports our findings that pain-free people perceived round-back lifting as dangerous in both the implicit (IAT) and the more specific explicit measure (BSB). Furthermore, a recent study by Nolan et al.  investigated the beliefs of manual handling advisors and physiotherapists regarding “safe” lifting technique. In this study, the participants were presented with images of four different lifting techniques, and asked to choose the one perceived as the safest and justify their choice. The results align with the current study, with the majority of the participants preferring a straight-back lifting posture . These straight-back postures were preferred on the basis that they avoided rounding the back, indicating a perception that “round-back” is dangerous. Additionally, the participants who preferred a straight-back posture, tended to have more negative back beliefs . This provides further support for the idea that beliefs about the danger of “round-back” postures are common in western society.
This pervasive belief about back posture and danger makes sense when considered in context of the information available in the public domain. As illustrated by the subjective descriptions in this study (Online Appendix – Table 2), people are commonly presented with “safety” regulations about the back and which posture to adopt when bending and lifting. A “straight-back” during bending and lifting is often advocated as ergonomically safe, whilst a “round-back” is often viewed as dangerous , , , , . This belief likely stem from extrapolations from the results of earlier in vitro  and in vivo , ,  studies, which suggest that flexion of the lumbar spine (i.e. round-back posture) is dangerous and should be avoided. The early seminal in vivo studies reported that lifting with a round-back generated greater intradiscal pressure than lifting with a straight back , , . Greater intradiscal pressure was rationalised as meaning a greater risk of disc injury with the round-back lifting technique , , . Later in vitro studies reinforced this view, suggesting the cadaveric spine has a limited number of bends (flexion cycles) before disc failure occurs . Since then, straight-back lifting has been recommended as the safe lifting strategy , . However, later in his career Nachemson (1981), the author of the original in vivo studies published a summary on several studies on intradiscal pressure, concluding that the difference between the two lifting techniques were only minor ,  and provided no basis for ergonomic interventions to be advocating straight-back lifting , . Furthermore, recent studies indicate there is a lack of in vivo evidence , , , ,  that support the notion of using a “straight-back” in preference to a “round-back” to reduce risk of LBP. Biomechanical studies have found no significant differences in spinal loads and compression forces between the two postures , , , . Studies have also been unable to establish a link between lifting and causation of low back pain , , , . Additionally, it has been shown that squat lifting (straight-back with deeper knee bend) is a less efficient lifting technique, when compared to adopting a more round-back posture during lifting heavier loads . In fact, pain-free forest workers were reported to change their lifting strategies from squat lifting to round-back lifting in order to save energy during a physically strenuous day involving repetitive lifting . This change in strategy was not accompanied with changes in lumbar load moments . Further, a recent systematic review reported no clear evidence supporting manual handling training in the prevention and treatment of LBP in nurses .
Together, the results of this study and others suggest that pain-free people may have a common belief that the back is vulnerable and that bending and lifting with a “round-back” is dangerous , , , , . The common-sense model of self-regulation ,  suggests that a person’s pre-existing schema influences their behavioural response when they experience pain. While speculative, our previous study investigating implicit beliefs in people experiencing back pain proposed that if pain-free people did in fact hold a similar implicit danger bias, as it was reported in the current study (“round-back danger”), then an experience of pain during bending/lifting may activate a “protect the back” schema . Protective behaviour demonstrated by people in pain would therefore not be irrational, but rather a common-sense response given their underlying implicit danger bias. However, it is not known if this implicit bias influence bending and lifting behaviour. This relationship is worth investigating because if implicit bias does influence behaviour, then investigating if it is amenable to change in both pain-free and pain populations, will also be of value.
This study was unique in that it investigated a group of people without current pain or pain in the last year, with the majority of participants reporting having never experienced back pain. The results therefore provide an insight into “general population” beliefs. However, a limitation of this study is that only a small sample of participants from an Australian city was investigated. Investigating a larger and more diverse population across different geographical areas and cultures (western vs. eastern), may provide a more complete understanding of general population beliefs and the influence of culture on beliefs and behaviour , .
The results of this study provide insight in beliefs of people without low back pain. Pain-free participants displayed an implicit association between images of “round-back” bending and lifting postures and words representing “danger”. Importantly, our findings support the idea that pain-free people may have a pre-existing belief that the back is in danger when rounded during bending and lifting. To understand the behavioural implications of these findings, further research evaluating the influence of implicit bias on behaviour in both pain-free and people in pain, may be worth pursuing.
The findings of this study may have implications for ergonomic guidelines and public health information related to bending and lifting back postures. Additionally, clinicians may need to be aware of this common belief in society, as this pre-existing schema may be reflected in how a person responds when they experience pain and present for treatment. Future research is warranted to evaluate the relationship between implicit attitudes and task behaviour in people both with and without pain.
Research funding: JP. Caneiro is supported by an Australian Postgraduate Award (APA) and Curtin University Postgraduate (CUPS) Scholarships.
Conflict of interest: Peter O’Sullivan receives speaker fees for workshops on pain management. All the other authors declare no conflicts of interest.
Informed consent: All participants provided informed consent, and were informed that they could withdraw from the study at any time.
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The online version of this article offers supplementary material (https://doi.org/10.1515/sjpain-2018-0056).