Are there differences in lifting technique between those with and without low back pain? A systematic review

David Nolan; Kieran O’Sullivan; Chris Newton; Gurpreet Singh; Benjamin E. Smith

doi:10.1515/sjpain-2019-0089

Article Publicly Available

Are there differences in lifting technique between those with and without low back pain? A systematic review

David Nolan , Kieran O’Sullivan , Chris Newton , Gurpreet Singh and Benjamin E. Smith

Published/Copyright: November 14, 2019

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From the journal Scandinavian Journal of Pain Volume 20 Issue 2

Abstract

Background and aims

To systemically review the literature to compare freestyle lifting technique, by muscle activity and kinematics, between people with and without low back pain (LBP).

Methods

Five databases were searched along with manual searches of retrieved articles by a single reviewer. Studies were included if they compared a freestyle lifting activity between participants with and without LBP. Data were extracted by two reviewers, and studies were appraised using the CASP tool for case-control studies.

Results

Nine studies were eligible. Heterogeneity did not allow for meta-analysis. Most studies (n = 8 studies) reported that people with LBP lift differently to pain-free controls. Specifically, people with LBP lift more slowly (n = 6 studies), use their legs more than their back especially when initiating lifting (n = 3 studies), and jerk less during lifting (n = 1 studies). Furthermore, the four larger studies involving people with more severe LBP also showed that people with LBP lift with less spinal range of motion and greater trunk muscle activity for a longer period.

Conclusions

People with LBP move slower, stiffer, and with a deeper knee bend than pain-free people during freestyle lifting tasks. Interestingly, such a lifting style mirrors how people, with and without LBP, are often told how to lift during manual handling training. The cross-sectional nature of the comparisons does not allow for causation to be determined.

Implications

The changes described may show embodiment of cautious movement, and the drive to protect the back. There may be value in exploring whether adopting a lifting style closer to that of pain-free people could help reduce LBP.

Keywords: lifting; back pain; manual handling; kinematics; electromyography

1 Introduction

Low back pain (LBP) is a common and costly health condition. Globally, between 1990 and 2015 the prevalence of LBP increased by 54% [1], and LBP continues to be the leading cause of years lived with disability [2]. Consequently, LBP bears a significant financial burden comparable to that of cardiovascular disease, cancer and mental health conditions [2], [3]. The majority of LBP costs are attributed to persistent LBP and its secondary consequences, including work productivity loss, work absenteeism and welfare/disability payments [3].

Lifting is commonly cited as being provocative in those with LBP [4], [5]. With this in mind, manual handling training often focuses on lifting to try to minimise the risk of LBP. This typically includes advice to lift loads close to the body whilst keeping the back straight [6], [7], [8]. This advice emanates from early in vitro modelling of cadaveric spinal intervertebral discs showing herniation following low-load repetitive flexion and extension moments [9]. Later, in vivo studies reported increased intradiscal pressures during lifting with a round back when compared to straight-back lifting [6], [10]. This message has been widely accepted by the physiotherapy (PT) and manual handling advisor (MHA) community: the vast majority of PTs and MHAs believe straight back lifting is safer than lifting with a more round back [11], and justify this belief in terms of the mechanics of load distribution. It is not clear, however, whether lifting advice based on this premise has been useful, as summarised in a recent editorial [12]. These beliefs are further challenged by evidence that shows that time spent bending the back is not associated with more LBP [13]. Furthermore, people with heavy manual activities often prefer to stoop rather than squat when lifting [14], due to stooping being less physically demanding [15] with there being no evidence that this strategy leads to more LBP. This may explain why there is no evidence that teaching lifting techniques prevents LBP [16]. The associations between heavy manual work and LBP are conflicting. While there are studies that show modest associations in between the two [17], there are also studies showing that a reduction in the physical nature of work did not reduce the incidence of LBP [18]. It is hard to explain the increasing rates of disabling LBP in modern societies at the same time as heavy manual jobs are reducing if load is a strong causative factor in LBP. Indeed, load has not been shown to be an independent risk factor in the development of LBP [19].

While it is not clear why advising on lifting technique does not appear to reduce the risk of LBP, the available research on how people with LBP move and bend offers some suggestions. People with LBP move and bend differently to those without LBP. A systematic review [20] of lumbopelvic kinematics confirmed that people with LBP move slower, through a smaller range of motion and with more muscle activity of the trunk than people without LBP. These changes would appear to reflect a guarded, cautious manner of moving [20]. These changes, interestingly, are associated with lower self-efficacy and higher fear [21]. No causal relationship can be drawn, but it is possible that people with more fear and lower self-efficacy excessively protect their back, resulting in kinematic and muscle activity changes. This suggests that how we think and relate to our pain influences how we move.

To our knowledge, no previous systematic review has evaluated kinematics and muscle activity during lifting tasks in people with LBP and pain-free controls. In order to get a better understanding of how to advise people regarding lifting, it is important to determine how people with and without LBP move during lifting tasks. Therefore, this systematic review aimed to compare kinematics and muscle activity of the trunk and lower limbs in people with and without LBP during freestyle lifting tasks.

2 Methods

2.1 Protocol and registration

This review has been registered in the PROSPERO database (CRD42015026425). The Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) statement for systematic reviews was used to guide the format and reporting of this review.

2.2 Eligibility criteria

The study design was limited to case control comparisons. Studies were included if participants reported LBP, if participants performed freestyle lifting activity, if the study had a pain-free control group as a comparison, and if participants were free to choose their preferred lifting technique (no postural or technique instructions). Included studies had to have participants with LBP with no red flags (fracture, inflammatory in nature, infected, malignancy or specific pathology such as acute disc prolapse with weakness or sensory changes), participants with leg pan were included as long as LBP was the dominant feature. Studies needed to use participants with clinical back pain, not experimentally induced back pain, and it needed to have been present for at least 6 weeks. Studies were required to compare kinematics and/or electromyography (EMG) between those with and without LBP while performing a freestyle lifting activity. Differences in kinematics or muscle activity had to be reported. Kinematics could include the lower limb or lumbar spine. Muscle activity could include trunk (back or abdominal) or lower limb muscles.

2.3 Information sources

The following databases were searched from inception to August 2018 by one reviewer (BS): CINAHL, EMBASE, Pubmed, AMED, and SPORTDiscus.

2.4 Search

The strategy used a combination of keywords that related to three components (lifting; LBP; kinematics and muscle activity), see Fig. 1.

Fig. 1:

Search terms.

2.5 Study selection

Once duplicates were removed, titles and abstracts of the studies were screened for eligibility by one reviewer (DN) who produced a list of studies for full text review if eligibility could not be decided based on the abstract alone. The final studies were then independently selected by two reviewers (DN and GS). Disagreements were resolved by a consensus meeting between two authors (DN and GS).

2.6 Data collection process and data items

Data for each study were extracted independently and cross-checked by two authors (DN and KOS). The following data were extracted: Study population, sex, age, eligibility criteria, pain/disability measure, lift task, weight lifted, experimental measures, and key findings. The data extracted from all studies are shown in Table 1. Results from the studies were combined and described separately for kinematics (total spinal range of motion, speed of spinal motion, coordination of spinal motion) and muscle activation (paraspinal activation and activation of other trunk muscles).

Table 1:

Results table.

Study	Study population, where they were recruited from and pain duration (PD)	Mean (SD) Pain duration	Sample size, sex (m/f)	Mean (SD) age	Eligibility criteria	Pain Disability measure: mean (SD) unless stated	Lifting task	Weight lifted	Experimental measures	Key findings
Boston [22]	LBP: Pain treatment centre at university HC: community volunteers	Not reported	LBP: 10 (5m; 5f) HC: 10 (5m; 5f)	LBP: 42.6 (13.9) HC: 43.1 (12.2)	Able to complete a minimum of 30 lifts during a standard isodynamic assessment	Not reported	Lift from 33 cm from the floor to waist every 15 s. Continue for 20 min, or until unable to continue. Resistance only to upward phase of lift	40% of maximum static lift strength	Kinematics of hip and knee angles derived from markers on the shoulder, hip knee and ankle	Among LBP patients, hip extension starts after knee extension, with the knees finishing first, and the lift is completed by the back
Commissaris [23]	LBP: women with back pain after birth attending exercise group HC: women in same group without LBP	Unclear, but at least several months	LBP: 7 (7f) HC: 9 (9f)	LBP: 33.4 (3.6) HC: 34 (3.4)	Within 12/12 of birth; back or pelvic pain. No other information reported	Pain: VAS median 27/100 range 2–98 Disability: DRI median 29/100 range 10–69	Lifting box from floor to chest and back to floor. 7 lifts recorded	8.3 kg, same for both groups	Kinematics of lumbo-sacral, hip, knee and ankle joints	LBP patients lifted slower No difference in lumbar ROM between groups Among LBP patients, hip extension starts after knee extension. LBP patients spent less time in with a maximally flexed lumbar spine while lifting During the downward phase, LBP patients on initially used ankle flexion more than lumbosacral flexion
Courbalay [24]	LBP: university chiropractic clinic HC: university community	9.4(11.6) years Minimum of >6 months	LBP:17 (10m; 7f) HC: 18 (10m; 8f)	LBP: 34.2 (14.1) HC: 32.5 (11.75)	Hx LBP>6/12 Excluded red flags (cancer, hypertension, neuromuscular disease), specific diagnoses (stenosis, disc herniation, surgery or recent trauma), women who were pregnancy, breastfeeding and use of psychotropic medication Not severe and disabling LBP – must be able to complete lifting procedure	Pain: VAS (/10) 3.52 (1.72) Disability: ODI (/100) 17.43 (5.9)	Box lift on the ground to waist height. 4 lifts of each of 3 weights were measured. Only the data from when the subjects knew the weight of the box used	5lb, 12.5lb and 20lb	EMG activity: lumbar ES and vastus lateralis Kinematics of knee, hip, lumbar and thoracic segments	LBP group had reduced VL activity LBP group had higher ES activity, but only during the lifting/lowering of the heaviest (20lb) weight No significant kinematic differences between groups
Ferguson [25]	LBP: several medical practices HC: not reported	Mean=10.2 months	LBP: 62 (32m; 30f) HC: 61 (31m; 30f)	LBP: 36.8 (10.1) HC: 38.4 (9.9)	LBP with leg pain included. 87% predominantly LBP. 13% LBP and leg pain equal intensity. Excluded people with neurological deficits or hypereflexia	Pain: VAS (/10) 5 (1.9) Disability: SF-36: Physical Functioning 20.7 (5.5)	Five lift origins (shoulder, waist, knee, waist-far and knee-far) to an upright position with elbow at 90°. Lifts were also done 45°and 90° clockwise and anticlockwise	4.5 kg, 6.8 kg, 9.1 kg, 11.4 kg	EMG timing (start and peak) and activation duration of ES, LD, RA, EO and IO Kinematic timing of peak position, velocity, acceleration and deceleration in the sagittal, coronal and transverse planes of the low back and pelvis	LBP group displayed significantly earlier activation of ES bilaterally, but no other muscles No differences in timing of peak activation between groups Activation duration was longer in LBP patients for all muscles, and reaching statistical significance for LD, right ES, right EO, left EO left ES LBP group moved more slowly on kinematic analysis, taking longer to reach peak trunk and pelvic angles
Lariviere [26]	Recruitment strategy not reported	>3 months	LBP: 15 (15m, 0f) HC: 18 (18m, 0f)	LBP: 40 (4) HC: 39 (3)	Both groups aged 35–45 years, with BMI lower than 28 kg/m² LBP: Daily or almost daily back pain +/− leg pain for >3 months HC: no LBP for 1 year, no prior back pain >1 week, never consulted for back pain	Pain: measured during task 2.6 (2.5) Disability: not reported	Box lifted from floor to waist in front or at 90° to the right and lowered back Number of lifts performed not reported	12 kg	EMG activity of LES, TES and BF Kinematics: ankle, knee, hip and lumbar vertebral angles	LBP group had less LES activity during lowering, but more TES activity lifting and lowering. No other significant differences No primary kinematic differences between groups. However, some inertial variables highlighted differences in how both groups lifted and lowered
Marras, 2001 [27]	LBP: orthopaedic practice HC: not reported	Mean 35 weeks (range 6 – 240 weeks)	LBP: 22 (12m; 10f) HC: 22 (12m; 10f)	LBP: 39 (10.1) HC: 36.4 (11.1)	LBP>6 weeks. 90% predominantly back pain, 10% back and leg pain equal	Pain: VAS 4.8 (1.7) Disability: not reported	Six lift origins: shoulder, waist, knee, mid shin, far-waist, far-knee. Lift ended with body upright and weight located at elbow. Each weight and each lift completed twice	4.5 kg, 6.8 kg, 9.1 kg, 11.4 kg	EMG activity of ES, LD, RA, EO, IO Sagittal plane kinematics of trunk and hip	LBP group flexed trunk and hips less and moved slower LBP patients had increased muscle activity in all muscle groups measured, and more co-activation of trunk muscle groups
Marras, 2004 [28]	LBP: several medical practices HC: not reported	median 5.5 months	LBP: 62 (32m; 30f) HC: 61 (31m; 30f)	LBP: 38.3 (9.88) HC: 36.9 (10.1)	LBP: pain of muscular origin (MD diagnosis); Pain 87% predominantly back pain, 13%. Excluded people with neurological deficits or hyperreflexia	Pain: Vas 5 (1.9) Disability: SF-36: 20.7(5.5)	Each weight lifted from six origins: Shoulder, waist, knee, mid shin, far waist, far knee. Lift ended with body upright and weight at elbow height. Then same lifts repeated from 45° and 90° left and right	4.5 kg, 6.8 kg, 9.1 kg, 11.4 kg	EMG activity of ES, LD, RA, EO, IO Kinematics of hip and trunk in the sagittal, coronal and transverse planes	LBP group demonstrated more activity in all muscles except ES LBP group moved more slowly, and with less range of motion
Rudy [29]	LBP: pain treatment centre HC: community volunteers	median 4.7 years (range 6 months – 19 years)	LBP: 53 (25m; 28f) HC: 53 (25m; 28)	LBP: 37.7 (10.1) HC: 35.2 (11.2)	LBP>6 months Had to be able to complete a minimum of 10 lifts in an assessment protocol HC: Could not be a ccompetitive athlete, or someone with a history of chronic pain or physical disability	Pain: not reported Disability: not reported	A handle 33 cm from the floor to waist. Resistance only to upwards phase. Lifted for 20 min with 15 s rest between. Stopped early if could not keep pace, or examiner deemed it unsafe	40% of maximum isometric lift strength	Kinematics: hip and knee angles	LBP group lifted slower than controls LBP group use more squat lift (deep knee flexion) rather than hip flexion, both at the beginning of the lft and throughout until the end of the lift – such that controls finished lift more vertically
Slaboda [30]	LBP: medical pain evaluation centre HC: community (athletes and students excluded)	LBP group overall: 4.1(5.4) years	LBP: 81 (38m; 43 f) HC: 53 (sex not reported)	Overall range 36 to 63 years LBP: 37.8 (10.1) HC: not reported	LBP every day, or almost every day for >3 months that was moderate or greater intensity Control subjects were recruited from the community, and athletes and college students were excluded They must have reported no pain and no history of back pain. The control subjects were	Pain: PSS (/6) guarded lifters 4.89 (0.86), non-guarded 4.47 (0.71) Pain Intensity(/10) guarded 6.66 (1.56) non guarded 5.57 (1.72) Disability: ODI (/100) 51.01(14.43)	A handle 33 cm from the floor to waist. Resistance only to up phase. Lifted for 20 min with 15 s rest between. Stopped early if could not keep pace, or felt unable to continue	40% of maximum isometric lift strength	Kinematics: hip and knee angles	LBP subjects appeared to adopt one of two strategies when lifting; 35 adopted a strategy similar to pain free group, whereas 46 lifted more slowly with low jerk

N=Number of participants; M=male; F=female; LBP=low back pain; HC=healthy control; VAS=visual analogue scale; DRI=disability rating index; Hx=History; PCS=Pain Catastrophising Scale; ODI=Oswestry Disability Index; TSK=Tampa Scale of Kinesiophobia; SF-36=Short Form Health Survey; ES=erector spinae; LD=latissimus dorsi; RA=rectus abdominus; EO=eternal oblique; IO=internal oblique; LES=lumbar erector spinae; TES=thoracic erector spinae; PSS=Pain Severity Scale; MPI=Multidimensional Pain Inventory; PES=Pain Experience Scale; TSSEQ=Task Specific Self Efficacy Questionnaire; PD=Pain duration.

We assessed clinical heterogeneity through examination of the data extraction table, in relation to participant characteristics and study design. Based on this assessment, the reviewers judged there to be high clinical heterogeneity, along with variation in outcome measures used and lifting tasks. Accordingly, it was not appropriate to pool data into a meta-analysis, and a narrative synthesis was conducted.

2.7 Risk of bias in individual studies

The Critical Appraisals Skills Program (CASP) checklist [31] for case-control studies was used to assess quality, as presented in Table 2. The checklist contains 12 questions; (Q1) Did the study address a clearly focused issue? (Q2) Did the authors use appropriate methods to address their question? (Q3) Were cases recruited in an acceptable way? (Q4) Were the controls recruited in an acceptable way? (Q5) Was the exposure accurately measured to minimise bias? (Q6) Aside from the experimental intervention, were the groups treated equally? (Q7) Have the authors takes account of potential confounding factors in their designs and/or analysis? (Q8) How large was the treatment effect? (Q9) How precise was the estimate of the treatment effect? (Q10) Do you believe the results? (Q11) Can the results be applied to the local population? (Q12) Do the results of this study fit with other evidence in the area? Since the CASP has many considerations for each question, consistency is key when reviewing studies. Therefore, a list of criteria for each question to be considered when appraising the quality of the included studies was drawn up and agreed between the authors. Two authors (DN and KOS) scored the studies independently using agreed criteria for each question, with any disagreements resolved using consensus, and discussion with another author (BS). Rather than using CASP to provide an overall quality score, the strengths and weaknesses of each study were noted based on these criteria.

Table 2:

Risk of bias assessment of included studies.

Study	Q1	Q2	Q3	Q4	Q5	Q6	Q7	Q8	Q9	Q10	Q11	Q12
Boston	✓	✓	✓	✓	✓	✓	✗	✓	✗	✓	?	✓
Commissaris	✓	✓	✓	✓	✓	✓	✗	✗	✗	✓	✗	✓
Courbala	✓	✓	✓	✓	✗	✓	✓	✗	✗	✓	✓	✓
Ferguso	✓	✓	✓	✗	✓	✓	✓	✗	✗	✓	✓	✓
Lariviere	✓	✓	✗	✗	✓	✓	✗	✗	✗	✓	?	✗
Marras 01	✓	✓	✓	✗	✓	✓	✗	✓	✗	✓	✓	✓
Marras 04	✓	✓	✓	✓	✓	✓	✓	✗	✗	✓	✓	✓
Rudy	✓	✓	✓	✓	✗	✓	✗	✓	✓	✓	✓	✓
Slaboda	✓	✓	✓	✓	✓	✓	✓	✓	✗	✓	✓	✓

✓=yes; ✗=no; ?=can’t tell.

3 Results

3.1 Study selection

The electronic search yielded a total of 10,262 potentially relevant studies (Fig. 2). Thirty-two full-text studies were identified [22], [23], [24], [25], [26], [27], [28], [29], [30], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45], [46], [47], [48], [49], [50], [51], [52], [53], [54] as potentially relevant after screening titles and abstracts. Twenty-three studies were removed after screening the full text [32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45], [46], [47], [48], [49], [50], [51], [52], [53], [54] of the identified studies. Searching the reference lists of these full-text studies led to two additional potentially relevant studies [55], [56]. Both were excluded after full text review, leaving nine eligible studies [22], [23], [24], [25], [26], [27], [28], [29], [30].

Fig. 2:

literature search flow chart.

3.2 Study characteristics

Table 2 provides a detailed description of the included studies. The mean ages across the studies were similar (mean age 37.4, range of means 33.4–43.1). All participants had red flags excluded and were predominantly LBP, although four studies [25], [26], [27], [28] did allow up to 50% of the pain to be “leg pain”, but without hard neurological signs (e.g. altered reflexes and weakness). The length of time participants had back pain varied across studies from 6 weeks to 19 years. Participants were not given any instructions on how to lift. Two studies [25], [28] used the same 62 patients, however they reported different variables, described in Table 2.

Three studies [22], [29], [30] got participants to lift for 20 min and analysed multiple lift cycles. In these studies participants lifted a handle 33 cm from the floor, and resistance was applied to the lifting phase only, with no data recorded while lowering without resistance. The other six studies lifted and lowered a weighted box and analysed the data from both phases. These six studies also compared a defined number of lifts, rather than a defined time of lifting. One study [25] used five different lift locations to lift the load, all from low down and at waist height. Two studies [27], [28] used these same five lift locations and also a lift from shoulder height. Two studies [25], [28] also added in lifts to and from the floor but the load was placed so participants had to twist 45° and 90° left and right while keeping the feet straight. One study [24] manipulated the load in the box so participants were expecting lighter or heavier load; however, in this review only the data where participants knew the weight in the box was extracted, as the effect of manipulating load expectancies was not our focus. The load of the lift varied between studies; six studies [23], [24], [25], [26], [27], [28] used the same weight for both groups. In contrast, three studies [22], [29], [30] used a lift equal to 40% of participant’s maximum isometric strength, such that people with LBP lifted a heavier actual load during testing. A full list of the weights used when lifting is illustrated in Table 2.

3.3 Outcome measures

Four studies [22], [23], [29], [30] only assessed kinematics of the trunk and lower limb.

Four of the other five studies [25], [26], [27], [28] measured kinematics and muscle activity of the trunk muscles, and one study also measures quadriceps activity [24]. Of the five studies that measured activity via EMG, four studies reported data regarding the magnitude of the contraction, while one study [25] reported the timing and duration of muscle activity. Kinematic data was collected in a similar way across all studies, but data were analysed using a variety of methods such as total range of motion (e.g. maximal lumbar, hip or knee flexion angle) speed of movement, or coordination patterns (e.g. whether movement was initiated with the knees, hips or spine first).

3.4 Results of individual studies

3.4.1 Kinematics

3.4.1.1 Total spinal range of motion

Four studies provided data comparing spinal range of motion (ROM) between those with and without LBP [23], [26], [27], [28]. Two studies [27], [28] (n=84) found that LBP patients flexed the lumbar spine less than pain-free controls when lifting: one study [27] found a 30% difference while the other study [28] stated a significant difference existed, but did not quantify it. However, the other two studies [22], [26] (n=17) did not report any ROM differences between groups.

3.4.1.2 Speed of spinal motion

Six studies (n=287) [23], [25], [27], [28], [29], [30] provided data comparing the speed of spinal ROM between those with and without LBP. However, two studies [25], [28] used the same participants, so these six studies used 225 different participants. All six studies reported that people with LBP lifted slower, or reached peak acceleration later when lifting.

3.4.1.3 Coordination patterns

Four studies [22], [23], [29], [30] (n=151) provided data comparing the coordination of movement between those with and without LBP. Two of the studies [22], [23] found changes in coordination, with LBP patients leading the movement through initially straightening their legs, and finishing the lift using their back. One study [29] found that LBP patients started with a deeper knee bend and finished more vertically than pain-free controls. Consistent with this, one study [30] reported that LBP participants used a deeper squat style of lifting compared to pain-free controls. This study also reported that 46 out of 81 LBP participants lifted with a “low jerk style”.

3.4.2 Muscle activation

3.4.2.1 Paraspinal activation

Five studies (n=177) provided data comparing the EMG activity (magnitude, duration or timing) of the erector spinae (ES) between those with and without LBP. Two studies [24], [28] found no change in lumbar spine ES activity between groups. One study [24] measured lifts from the floor to the waist with three differing weights, whereas the other study [28] measured both lifting and lowering with differing weights and locations of the load. In contrast, the three other studies [25], [26], [27] reported differences between those with and without LBP, but with variation in the type of differences reported. One study [27] consistently found higher lumbar ES EMG activity in LBP patients through various lifts from various locations and weights. Furthermore, one study [27] found lumbar ES activated earlier, and for longer, in LBP patients than controls during the lifting task. In contrast, one study [26] found lumbar ES activation was lower in LBP patients when lowering a weight from the waist to the floor, but not while lifting the load from the floor to the waist. However, this study found higher thoracic ES EMG while lifting and lowering the load.

3.4.2.2 Activation of other trunk muscles

Three studies (n=84, as two of the studies [25], [28] used same participants) provided data comparing EMG activity (magnitude, duration and timing) of other trunk muscles between those with and without LBP. Two studies [27], [28] found that the abdominal muscles and latissimus dorsi (LD) were more active in LBP patients. One study [25] found that right LD, but not the left, and external oblique (EO) were activated for longer in LBP patients. There were inconsistent changes in abdominal (IO and EO) and LD timing, with either there being no differences, or the LBP group being active earlier in the lift [25].

3.5 Risk of bias within studies

The critical appraisal findings are shown in Table 1. Sample size varied considerably, with five smaller studies ranging from seven to 22 participants [22], [23], [24], [26], [27], and four larger studies ranging from 53 to 81 participants [25], [26], [27], [28], [29], [30]. Two studies did not report where they recruited their participants from, and one did not state how the control group were recruited. In one study [29], participants were stopped if the lift was deemed “unsafe”, without a clear definition of “unsafe”, or clarity on how many were stopped prematurely due to “unsafe technique”. Two of the nine studies [22], [29] did not describe pain intensity among those with LBP, while four of the nine studies [22], [26], [27], [29] did not report a disability measure among those with LBP. Furthermore, there was large variation in how disability was measured. Only one study [30] compared the lifting technique of LBP participants with different disability profiles (pain and self-efficacy).

4 Discussion

Most studies in this systematic review reported that people with LBP lift differently to pain-free controls. Specifically, people with LBP lifted more slowly, use their legs more than their back especially when initiating lifting, and jerk less during lifting. There were inconsistencies in whether differences exist in overall spinal ROM or muscle activation, but generally the larger studies involving people with more severe LBP show people with LBP lift with less spinal ROM and greater muscle activity. This study is broadly consistent with a previous review that found people with LBP demonstrated reduced range of motion, slower movements [20], and increased muscle activity [57] while bending.

In general, the studies that showed minimal differences between the groups, either did not report pain or disability, or the pain score was low. The studies that used participants with higher levels of pain (NRS 4.8 and over) [25], [27], [28], [30] found more marked differences between the groups.

Recruitment methodology could explain why some studies showed no significant effects between groups. For example, one study [23] recruited women in the 12 months after birth with back pain, from an exercise group – they were wanting to exercise, had low pain scores and not seeking care for their back pain, which suggests that they were not significantly disabled.

The same critique can be made looking at muscle activity with lower pain scores associated with less difference between groups. However, three studies [25], [27], [28] found that participants with higher levels of back pain contracted their muscles earlier, with more activity and for longer than pain-free controls. However, there are limitations to the results of this review, mainly due to the heterogeneity of the results reported. For example, range of motion differences was only measured in one study; six of nine studies reported the speed but it was not clear from the methodologies how it was measured; coordination using more knee bend was reported in four of nine studies and EMG differences only reported in two of the nine studies. Further limitations are that disability was only reported in four of nine studies and parameters such as fear avoidance were not measured at all.

4.1 Why do people with LBP move differently?

There could be a number of explanations why people with pain lift differently, and these studies show associations only. The three most obvious explanations are: they move differently to protect the spine from excessive loading; they move like this as part of a pain behaviour; or there is a cultural acceptance that lifting “squat” style lifting is safest.

The theory that lifting slowly and through less ROM protects the spine from excessive load is largely extrapolated from in vitro studies that have shown repeated flexion movements can cause disc injury [9], [58], and other in vitro models showing the spine is harder to injure in neutral [59]. The in vitro models, however, often used differing methodologies and are not consistent, with contradictions in whether more spine flexion increases the load [60]. Furthermore, it is not clear how to extrapolate these theoretical studies from the laboratory into humans with LBP. Also, these studies have not been confirmed in vivo, where studies show no clear relationship between spine load and lumbar posture [61], [62].

In contrast, viewing this lifting strategy as a pain behaviour can be supported by the literature. Multiple studies have shown that those with LBP have less ROM and increased muscle activity during movement [20]. Furthermore, it has been found that higher levels of fear and lower self-efficacy are associated with less ROM [63], more muscle activity [21] and more spinal load [28] in participants with LBP. Moreover, those with specific fear of bending and lifting have less ROM with those tasks [64]. These studies do not prove causation, but could indicate that how people with LBP make sense of their experience influences their movement behaviours – guarded, stiff lifters trying to stay safe from pain and the “dangers” of lifting. Interestingly, it has been shown that both the pain [65] and pain-free [66] population implicitly associate lifting with danger. If this movement pattern is part of a safety/avoidance behaviour, it could be viewed as maladaptive and a target for treatment, with significant clinical implications for the ergonomic industry.

Studies that treat this guarded movement behaviour in people with chronic LBP as a maladaptive behaviour have shown reductions in pain and disability [67], [68]. Furthermore, studies have shown that teaching people with severe back pain to trust their back, use it and bend it have showed large reductions in disability, fear avoidance and improvements in muscle strength [69], [70], and these improvements were maintained at long term follow up [71]. However, kinematic studies have not confirmed whether improvements are associated with altered kinematics, and this would be an interesting area of further research.

4.2 Implications for training and education regarding lifting

Common beliefs among physiotherapists and MHAs are that you need to lift with a straight back [11], and that a squat style lift is safer. Furthermore, MHAs commonly believe that the back needs to be protected and is vulnerable [72]. This review shows that those with LBP are more likely to lift in a way the majority of physiotherapists and MHAs advise and deem safest. However, there is a reasoned argument, presented above, that these changes may be unhelpful, and the cautious, slow, guarded lifting style is a behavioural target for treatment. This may help explain why there is no evidence that teaching people how to lift “safely” prevents LBP [16], [73]. Teaching people to move, lift and bend the back less cautiously has been shown to help people with severe back pain [69], [70]; how these messages are integrated into workplace training while fulfilling legal requirements of a risk assessment require wider consultation with key stakeholders.

4.3 Limitations

These studies often used small sample sizes with low levels of pain and disability. There was some incomplete reporting and the studies were cross-sectional in nature. Due to the differing methods of collecting the data we were unable to conduct a meta-analysis. We only used one reviewer to screen titles and abstracts, and no attempt was made to obtain unpublished data.

4.4 Conclusion

This systematic review found evidence that people with LBP move differently (slower, stiffer, with a deeper knee bend) to pain-free people during freestyle lifting tasks. This pattern is most pronounced amongst those with more severe LBP. Interestingly, such a lifting style mirrors how people, with and without LBP, are often told how to lift. The cross-sectional nature of the comparisons does not allow for causation to be determined. However, there may be value in exploring whether adopting a lifting style closer to that of pain-free people could help reduce LBP.

Authors’ statements
Research funding: Authors state no funding involved.
Conflict of interest: KOS receives income from workshops promoting the biopsychosocial management of low back pain.
Informed consent: Not required for this systematic review.
Ethical approval: No ethical approval was required.

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Received: 2019-06-26

Revised: 2019-10-11

Accepted: 2019-10-17

Published Online: 2019-11-14

Published in Print: 2020-04-28

Articles in the same Issue

https://doi.org/10.1515/sjpain-2019-0089

Keywords for this article

lifting; back pain; manual handling; kinematics; electromyography