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Getting out of neutral: the risks and rewards of lumbar spine flexion during lifting exercises

Authors:

Abstract

Lifting exercises are essential for the development of strength qualities in the lower extremity. Traditionally, coaches encourage a neutral lumbar spine posture during these exercises in order to reduce injury risk and maximise performance. However, evidence suggests that significant amounts of lumbar spine flexion occur during lifting exercises, and appears to be unavoidable even when coached. It is the aim of this article to discuss the potential risks and advantages for allowing moderate amounts of lumbar spine flexion during lifting exercises.
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Title: Getting out of Neutral: The Risks and Rewards of Lumbar Spine Flexion During
Lifting Exercises
Authors and affiliations:
Louis Howe1, Greg Lehman2
1 Department of Sport and Physical Activity, Edge Hill University, Ormskirk, UK.
2 Private practice.
Corresponding author: howel@edgehill.ac.uk
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OVERVIEW
Lifting exercises are essential for the development of strength qualities in the lower
extremity. Traditionally, coaches encourage a neutral lumbar spine posture during these
exercises in order to reduce injury risk and maximise performance. However, evidence
suggests that significant amounts of lumbar spine flexion occur during lifting exercises, and
appears to be unavoidable even when coached. It is the aim of this article to discuss the
potential risks and advantages for allowing moderate amounts of lumbar spine flexion during
lifting exercises.
INTRODUCTION
Lifting exercises, such as squatting and deadlifting, are commonly prescribed as part of
strength and conditioning (S&C) programmes in an attempt to develop a variety of physical
qualities for the lower extremity. When coaching such movements, the role of the S&C coach
requires a continual analysis of performance by comparing technique against known technical
models to determine safety. For the technical models of most lifting exercises, a universal
inclusion is the maintenance of a neutral spine position (24, 33, 41, 88, 120, 121). This is
unanimously prescribed in the belief that: a) a neutral spine can be maintained while lifting
during strength training exercises, and b) a neutral spine alignment is protective against the
development of spinal pathologies. As a result of these assumptions, spinal flexion during
lifting exercises is commonly discouraged in an attempt to minimise injury risk. However,
biomechanical evidence comparing lifting strategies associated with varying lumbar spine
postures, do not support the use of a single technique over another when lifting loads during
occupational tasks (102, 114). Therefore, evidence to support the adoption of a neutral spine
during lifting requires review in the context of the S&C coaches’ practice. Therefore, the aim
of this article is to present key considerations when deciding whether the maintenance of a
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neutral spine and the avoidance of spinal flexion should be included in the technical model of
all lifting exercises.
WHAT IS NEUTRAL SPINE?
Neutral spine has been defined as the range of motion, or zone, where minimal restraint to
movement is offered by the surrounding passive structures (83). While sometimes viewed as
a single position, in the sagittal plane, a neutral spine exists within a range or zone (83). Both
in vivo and in vitro, the neutral zone is measured by calculating the load-deformation curve
of the spine during passive movement. In the neutral zone, laxity is high as the passive
structures that resist motion ‘uncrimp’ (i.e. the toe region of the load-deformation curve)
prior to being tensioned as they enter the elastic region of the load-deformation curve (50). In
the elastic region, ligaments and capsular tissues, the apophyseal joints and the intervertebral
disc potentially restrict movement (84, 95, 99). When the forces the spine experiences are
high such as they are during lifting, deviations into the elastic zone cause strain on such
passive structures that has the potential to cause tissue damage (69). However, when the
spine is in a neutral position, the stress placed on the passive structures is minimised (119)
and the spinal muscles are predominantly responsible for controlling spinal alignment (36).
It is important to note that the neutral zone is significantly less than the total available range
of motion (50, 94, 109). For example, Gay et al. (50) found the neutral zone of cadaveric
adult lumbar spine motion segments with intact posterior ligaments, intervertebral discs and
apophyseal joint capsules, averaged approximately 1-2° of the total flexion range of motion.
Similarly, Busscher et al. (27) showed that when examining six human cadavers sectioned
between L1-L4, neutral zone averaged approximately 2° in the sagittal plane for each motion
segment, while the total range of motion averaged approximately 5°. When measuring the
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lumbar spine from L1 to S1, Yamamoto et al. (124) found human cadavers possessed 9° of
lumbar flexion in the neutral zone.
Ranges of motion for the neutral zone found in cadaver studies appear to agree with
investigations that have established the neutral zone in vivo. Scannell and McGill (95) found
that the neutral zone in healthy adults was approximately 20° of the total lumbar spine range
of motion in the sagittal plane. Similarly, Toosizadeh et al. (111) found that the initial 11 ± 6°
of flexion between L1 and S1 occurred in the neutral zone in healthy young adults with no
history of low back pain. As the participants demonstrated a flexion-relaxation angle (defined
as the lumbar spine flexion angle at near end of the range of motion where electromyography
activity of the longissimus and rectus abdominus muscles is minimal) of 58 ± 12°, flexion in
the neutral zone contributed only 18% to this value. This would almost certainly be lower if
the end range of motion flexion angle were used instead of the flexion-relaxation angle to
calculate the percentage of total flexion that occurs in the neutral zone, as the flexion-
relaxation phenomenon occurs prior to maximum flexion (126). These findings indicate that
the neutral zone accounts for only a modest proportion of the available sagittal plane range of
motion at the lumbar spine (95, 111).
DOES THE SPINE REMAIN NEUTRAL DURING LIFTING EXERCISES?
Whilst maintaining a neutral spine is consistently included in the technical models for lifting
exercises performed in the weight room (24, 33, 41, 88, 120, 121), evidence suggests the
spine flexes beyond the neutral zone during the performance of strength training exercises.
For example, in the start position for a deadlift, competitive weightlifters and powerlifters
flexed their lumbar spine approximately 25 ± 11°, relative to standing (43). These findings
are similar to Aasa et al. (1), where the upper (T12-L2) and lower lumbar spine (L2-S2) of 24
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competitive powerlifters and weightlifters demonstrated 12 ± 7° and 22 ± 6° flexion-
extension range of motion, respectively, during the deadlift with 70% 1RM. Likewise, during
the back squat with the same relative load, flexion-extension range of motion at the upper and
lower lumbar spine were 10 ± 3° and 18° ± 5°, respectively (1). When determining the effect
of a heel raise on back squat technique with a barbell load equivalent to 50% of body mass,
Sayers et al. (94) found the lumbar spine (L1 to L5) flexed 13 ± 7° in resistance trained
athletes (1RM high-bar back squat = 1.56 ± 0.32 kg/body mass), with no difference observed
when a 5° heel elevation was added. Similar to the deadlift and squat exercises, Vigotsky et
al. (117) found that 15 healthy males with 8.6 ± 5.5 years of weightlifting experience flexed
at the lumbar spine 28° at the moment of peak hip flexion (95% CI = 26–29°) during the
good morning exercise with a load equivalent to 50% 1RM. Additionally, when the load was
increased by 10% increments up to 90% 1RM, no significant differences were reported for
lumbar flexion angles.
Comparisons of absolute values for lumbar spine flexion during lifting exercises from
different investigations should be interpreted with caution, due to differences in measurement
techniques and maximal lumbar flexion rarely being accounted for. When normalised to full
lumbar flexion (determined during the standing trunk flexion test), 17 competitive CrossFit
athletes, weightlifters and powerlifters were found to flex their lumbar spine approximately
76.8 ± 16.1% and 64.2 ± 19.8% of maximum during the deadlift and back squat with 85%
1RM, respectively (42). Collectively, these findings suggest that experienced lifters use a
movement strategy incorporating considerable lumbar spine flexion during the performance
of traditional strength training lifting exercises. Although the aforementioned investigations
did not identify the neutral zone for each participant, based on the contribution of flexion in
the neutral zone to total flexion range of motion reported in healthy individuals (95, 111), it is
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highly likely that a neutral spine is not maintained by experienced lifters during the deadlift,
squat and good morning exercises.
Strongman events unsurprisingly also require considerable amounts of spinal flexion likely
beyond a neutral position. McGill et al. (74) found that relative to standing posture,
strongman competitors demonstrated peak flexion angles for the lumbar spine of 33° (± 11°)
during the performance of both the log lift (75 ± 15 kg) and tire flip (309 kg). This
represented 97.5 ± 46% of the total available lumbar spine flexion when normalised to each
competitor’s maximum range of motion during the standing trunk flexion test. Additionally,
when participants performed the atlas stone lift (110 kg), peak spine flexion was 50 ± 7°,
equating to 146 ± 32% of the participants maximal spine flexion range of motion. Therefore,
a neutral spine position does not appear to be adopted when lifting awkward loads during
traditional strongman events. Instead, strongmen competitions seem to exhaust their lumbar
spine flexion capacity in order to lift the heavy and awkward loads associated with their
sport.
Exercises to develop explosive strength show a similar trend in lumbar spine kinematics.
McGill and Marshall (73) found that during performance of a kettlebell swing with a 16 kg
load, the lumbar spine flexed 26° at the bottom of the swing and extended 6° at the top of the
swing, equating to an angular displacement of 32°. Interestingly, the participants in this study
were cued to maintain a neutral spine, yet still demonstrated significant flexion-extension
motion at the lumbar spine. These values are similar to what has been reported during the
countermovement jump, with the angular displacement of the lumbar spine far exceeding
what likely represent the neutral zone (42 ± 12°) (102). As such, it appears that movements
performed at a faster velocity with reduced range of motion in the lower extremity relative to
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full squatting and deadlifting from the floor, still requires large amounts of lumbar spine
flexion. These findings indicate that the spine may provide some contribution, either directly
or indirectly, to explosive movement tasks that should not be necessarily regarded as a fault
in technique.
The findings presented in this section indicate that some spinal flexion during lifting is
inevitable. Accordingly, investigations that cue participants to maintain a lordotic lumbar
spine posture during lifting tasks still record considerable spinal flexion. For example, when
healthy young adults were trained to maintain a maximal lordotic posture during a maximal
static lifting task with the knees flexed to 45° (similar to the start position in the deadlift
(43)), the lumbar spine flexed 22° and approximately a third of the full flexion demonstrated
during the standing trunk flexion test (58). Similarly, Khoddam-Khorasani et al. (63) found
only a marginal decrease in lumbar spine flexion occurred when individuals were cued to
maintain a lordotic posture (mean lumbar flexion = 30°) versus a kyphotic posture (mean
lumbar flexion angle = 40°) during the performance of an isometric lifting task involving
holding a load equivalent to 180 N in the hands with a 65° forward trunk lean. Therefore,
while coaching resources may describe the maintenance of a neutral spine to be desirable
during lifting exercises (24, 33, 41, 88, 120, 121), it appears lumbar spine flexion is
unavoidable and only partially modifiable.
IS A NEUTRAL SPINE PROTECTIVE?
As lumbar flexion out of the neutral zone is likely inevitable during lifting exercises, it may
be that S&C coaches who select such exercises expose athletes to increased risk of spinal
pathology. However, this would only be the case if maintaining the spine in a neutral position
reduces injury risk when lifting. The purported benefit of maintaining a neutral spine during
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lifting is that it is protective against the injuries associated with lifting. This suggestion is
built on the premise that by ‘locking’ the spine in its neutral zone, stress on the
osteoligamentous structures is minimised. However, epidemiology and biomechanical
evidence to support this suggestion appears to be limited (93).
In athlete populations where sport performance depends on lifting capability (i.e.,
weightlifting, powerlifting, strongman training and CrossFit), a lack of prospective evidence
exists to indicate whether spinal flexion during lifting is a risk factor for the development of
low back pain. Additionally, while numerous epidemiological studies have identified risk
factors associated with low back pain for occupations involving repetitive lifting (118), few
have attempted to isolate the role of lumbar spine flexion. For example, Hoogendoorn et al.
(60) found that the percentage of time spent with the trunk flexed > 60° was a risk factor for
low back pain among 861 manual labors workers, office workers and caring professionals in
a three-year prospective cohort study. However, this investigation did not differentiate the
contribution of lumbar spine flexion from that of the hip joint or thoracic spine to the total
trunk flexion. Consequently, it is unclear whether lumbar spine posture, or the greater load on
spinal tissues associated with bending further forward during lifting (63) was the cause of the
elevated injury risk. Among studies that have measured lumbar spine flexion directly during
lifting tasks, little evidence supports the notion that greater flexion during lifting elevates
injury risk (93). Mitchell et al. (76) investigated the association between peak flexion-
extension angles in 117 female nurses during a range of functional tasks in a 12-month
prospective study. While 31 nurses reported at least one episode of significant low back pain
on follow-up, no difference was found for the upper (T12 to L3) or lower (L3 to S1) lumbar
spine flexion angles during bodyweight squatting (odds ratio = 1.02-1.03) or when picking up
a 5 kg box from the ground (odds ratio = 1.02-1.04). In line with these findings, a recent
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meta-analysis showed flexion at the lumbar spine during lifting tasks was not a risk factor for
low back pain (93). Although these results are limited when informing decisions as to
whether to allow spinal flexion during bilateral lifting exercises where loads are likely to be
much greater, it does question the relationship between lumbar spine flexion during lifting
and the occurrence of low back pain.
For sports that require repetitive lumbar spine flexion-extension with relatively high loads
(e.g., rowing), there is some suggestion that the prevalence of low back pain is greater than
for athletes competing in sports without. Bahr et al. (17) found rowers (63%) and cross-
country skiers (65%), sports associated with high forces and flexion-extension movements of
the lumbar spine (28, 59, 101), had a higher prevalence of low back pain compared to
orienteers (57%), a sport with limited spinal loading and sagittal plane displacement.
However, in a 10-year follow-up with the same cohort, no difference in prevalence was found
between the athletic groups, indicating years of repeated spinal flexion failed to result in
more low back pain (46). Future research should seek to establish whether the magnitude of
loaded spine flexion beyond the neutral zone elevates injury risk in sports associated with
high incidence rates for low back pain.
Loaded spinal flexion has been identified as a mechanism for intervertebral disc herniation,
as the posterior fibres of the anulus stretch and thins with flexion, while the hydrostatic
pressure simultaneously increases within the nucleus (7). As such, several cadaver studies
have identified repetitive flexion under low to moderate load as a mechanism for disc
herniation (29, 48, 70, 84, 107). For example, Callaghan and McGill (29) showed that in
porcine C3/C4 motion segments, posterior and posterior-lateral disc herniations occurred
following repetitive cycles of flexion (70,550 ± 29,477) with a modest compressive (relative
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to the ultimate compressive strength of the motion segment) load of 867 N. In the same
investigation, when compressive forces were increased to 1,472 N, representing
approximately 14-22% of the maximum compressive strength of a porcine cervical vertebrae
(107), significantly less flexion was required to cause disc herniation (34,974 ± 9,549).
Importantly, the angular rotation equated to only 35% of the maximum range of motion,
maintaining the angular rotation close to the toe region of the load-deformation curve (29).
These findings suggest that when a high number of repetitive cycles of flexion under
relatively low loads occur around the margins of the neutral zone, disc herniations will likely
result. As lifting exercises demand lumbar flexion towards and likely beyond the boundaries
of a neutral spine position, it appears little can be done to avoid disc pathology. Based on
these findings, if athletes are to perform lifting exercises, S&C coaches appear to have little
control over managing this risk factor.
The addition of extension beyond the resting position of a motion segment appears to
compound the damage observed in the anulus fibrosus when the intervertebral discs are
repetitively displaced in the sagittal plane under load. Balkovec and McGill (18) either flexed
or flexed and extended porcine C3/C4 motion segments 10,000 times under 1,500 N of
compressive forces. Each motion segment was then dissected, with the posterior migration of
nuclear material tracked in order to establish annular damage, defined as the area of the
anulus fibrosus infiltrated by nuclear material relative to its total area. Following the
repetitive cycles applied to each intervertebral disc, the flexion only and the flexion-extension
group demonstrated 5.9% and 12.4% annular damage, respectively. Greater damage to the
posterior wall of the anulus with repetitive flexion-extension cycles may occur as the
compressive loads placed on the posterior aspect of the disc during extension weakens the
posterior anulus, diminishing its capacity to restrict posterior movement of the nucleus (10).
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Consequently, the nuclear material migrates further with combined flexion and extension
than when flexion occurs exclusively in a loaded condition (18).
Whether it is the disc or other anatomical structures that are damaged during lifting may be
influenced by the compressive forces experienced. During the performance of lifting
exercises with heavy loads in the weight room, it could be that the disc is not the weakest link
in the chain when moderate amounts of lumbar spine flexion are present. Parkinson and
Callaghan (84) found that when applying compressive forces to 50 porcine C3/C4 and C5/C6
motion segments with loads equivalent to 10%, 30%, 50%, 70% and 90% of its compressive
tolerance, intervertebral disc herniation did not occur with loads > 30%. Instead, vertebral
bone and endplate fractures were identified when motion segments were subjected to higher
compressive forces. The authors concluded that the risk of disc herniation diminishes when
loads are increased, with the vertebral body and endplate becoming the limiting factor in
tolerating the forces associated with heavy lifting (84). Therefore, with extremely high forces
present during bilateral lifting exercises (30, 35, 44), the integrity of the osseous structures
may be a stronger determinant of injury risk.
The degree of lumbar spine flexion occurring during lifting may also influence how many
cycles of loading the spine can tolerate. Gallagher et al. (48) loaded 36 lumbar spine motion
segments from human cadavers in a flexed position that simulated 0°, 22.5°, or 45° of lumbar
spine (L5-S1) flexion. Each motion segment was subjected to compressive forces that
simulated the repetitive lifting of a 9kg weight until failure was identified. The number of
cycles required to cause failure were 8,253 ± 2,895, 3,257 ± 4,443 and 263 ± 646 for the 0°,
22.5° and 45° flexion conditions, respectively. Across the samples, damage was observed at
the vertebral bodies, endplates and apophyseal joints. Therefore, it appears that repetitively
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flexing the lumbar spine, even under moderate amounts on flexion, decreases the cycles
required to achieve fatigue failure relative to a neutral position.
As bilateral lifting exercises require significant sagittal plane angular displacement of the
lumbar spine into flexion (43, 73, 74, 94, 117) and extension (73, 122), cadaver studies
appear to suggest that performing these movements will inevitably result in structural
pathology. Furthermore, squatting (30), deadlifting (35) and variants of the Olympic lifts (44)
have all been shown to result in compressive forces that potentially far exceed the reported
compressive tolerance of a healthy lumbar vertebrae and intervertebral disc (89). It is
therefore challenging to appreciate how a weightlifter, performing approximately 20,000–
25,000 repetitions of multi-joint lifting exercises each year (104), does not incur a lumbar
disc herniation, vertebral body fracture, endplate fracture, or damage to the neural arch.
A likely explanation may be that tissue adaptation is not accounted for in studies relying on
in vitro designs to identify lumbar spine injury mechanisms. To support the adaptative
capacity of the lumbar spine, the vertebrae appear to significantly strengthen following long-
term resistance training. Granhed et al. (52) noted high bone mineral content at L3 among
international powerlifters (7.06 ± 0.87 gcm2) compared to matched controls (5.18 ± 0.88
gcm2) using dual-photon absorptiometry. Interestingly, the same investigation found a
significant correlation (r2 = 0.82) between bone mineral content and the lifters annual training
volumes (52). A similar relationship was also reported between sports performance and bone
mineral content using dual energy x-ray absorptiometry at L2L4 in elite junior Olympic
weightlifters (37). Among the 25 male adolescent lifters, a significant positive association
was found between bone mineral content of the lumbar spine and 1RM load in the squat (r =
0.64), snatch (r = 0.73) and clean and jerk (r = 0.72), suggesting adaptation in the vertebrae
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occurs following the consistent performance of heavy lifting exercises (37). While correlation
does not imply causation, and these findings could suggest certain individuals have a genetic
predisposition to strength sports, intervention studies have shown strength training increases
bone mineral content and density (23, 66, 77). Therefore, it is highly likely that years of
performing lifting exercises results in an axial skeleton with a high tolerance for loading.
While findings for increased bone mineral content following strength training do not directly
support the occurrence for adaptation in the disc, the tensile strength of the surrounding
ligaments (81) and outer wall of the anulus fibrosus (98) is significantly associated with the
bone mineral content of the adjacent vertebrae. It is, therefore, highly probable that the
intervertebral disc adapts to the repetitive loading associated with bilateral lifting exercises.
While much of the intervertebral disc is avascular (12, 113) and the re-modelling process is
slower relative to neighboring tissues (22, 97), adaptation to mechanical loading does occur
when rest follows activity (68). As such, like other anatomical structures around the spine,
the intervertebral disc is subject to Wolff’s Law, where anabolic cellular adaptations follow
increased strain and result in increased proteoglycan and collagen production (4, 26, 98, 123).
Consequently, the disc becomes stiffer following an optimal level of stress, resulting in a
greater tolerance level when next presented with a loading bout (4).
In vitro studies have shown an anabolic response within the intervertebral disc following
dynamic compressive loading (32, 45). Additionally, the tensile strain experienced by the
posterior wall of the anulus fibrosus can also trigger an anabolic cellular response. When
subjecting bovine coccygeal discs to tensile loading equating to 10% strain cyclically (1Hz)
for 60 minutes, Li et al. (67) showed increased type I collagen mRNA expression in the
cultured cells of the outer anulus fibrosus. As lifting tasks with 41º of lumbar flexion have
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been estimated to result in < 13% strain of the intervertebral disc at L4/L5 and L5/S1 in vivo
(63), an anabolic response may be present following a bout of lifting with lumbar flexion. Of
note, when attempting to maintain a lordotic posture during lifting, estimated disc strain in
the posterior wall of the anulus fibrosus is not significantly different to when adopting a
kyphotic posture (63). These findings indicate, regardless of whether an athlete attempts to
maintain a lordotic posture during lifting exercises, the strain on the intervertebral disc may
be a catalyst for adaptation in the preparation for subsequent loading.
In human cadavers, the compressive strength of the intervertebral disc has been related to
regular physical activity levels prior to death in nine young male lumbar spines (age ranging
between 16-32 years) (89). In vivo, a positive association between physical activity level and
apparent diffusion coefficient values (a surrogate measure of disc matrix composition and
structural integrity (14)) at L5/S1 in healthy adults has also been reported using magnetic
resonance imaging (25). Likewise, Owen et al. (82) found athletes who competed in ballistic
and high-impact sports (e.g., basketball and soccer), displayed signs of intervertebral disc
hypertrophy (calculated as the ratio of disc height to vertebral body height) and greater
nucleus hydration on sagittal T2-weighted magnetic resonance imaging when compared to
matched controls. Therefore, the available evidence suggests the intervertebral disc has
adaptive qualities. While the rate of adaptation is unclear following lifting exercises, a well-
designed strength training programme that allows for sufficient recovery following loading
would likely increase the discs resiliency against injury.
Lastly, an additional consideration for why intervertebral disc herniation isn’t a consistent
outcome when regularly performing lifting exercises is the role genetics may have on lumbar
spine disc degeneration. While performing repetitive spinal flexion and extension under load
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may be the primary mechanism for intervertebral disc herniation (12), heredity factors in
adult population explain 74% of the variance (19). Additionally, environmental factors
appear to have only a modest effect on intervertebral disc health (20), with physical activity
explaining the variance for disc degeneration in upper and lower lumbar spine by only 7%
and 2%, respectively (21). When identifying the relative risk of lumbar disc herniation in
young adults (< 21 years), individuals with a positive family history, defined as a parent or
sibling with history of low back pain, disc herniation or sciatica, have a five times greater risk
(115). Therefore, an athlete’s genetic profile seems to provide the primary influence on long-
term intervertebral disc health (20), while the adherence to a strength training programme
does not appear to increase the risk of disc herniation beyond that of sedentary individuals
(78).
DOES MAXIMAL SPINAL FLEXION DURING LIFTING INCREASE INJURY
RISK?
It is important to note that while it is recognised that a neutral spine is unlikely attainable
during most lifting exercises and not necessary to reduce injury risk during lifting exercises,
there is some suggestion that a fully flexed spine may be problematic. Cholewicki and
McGill (34) investigated lumbar spine kinematics during near maximal deadlifts (barbell load
ranging between 183.7–210.9 kg) in four competitive powerlifters using videofluoroscopy
(radiological investigation allowing for a dynamic assessment of spine motion). Relative to
their performance of the standing trunk flexion test, the experienced lifters flexed their
lumbar spine on average 4.6° less than their maximum capacity when performing the
deadlift. However, during one trial, a lifter exceeded their capacity to actively flex their
lumbar spine by 1° at L4/L5, reporting low back ‘discomfort’ during the movement. This led
the authors to later suggest that full lumbar spine flexion may be particularly injurious during
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lifting (71).
The compressive strength of the spine has been shown to diminish significantly when loaded
in a fully flexed posture. Gunning et al. (54) found that porcine cervical spines loaded in full
flexion, had a 43-63% lower compressive strength (defined as the load required to cause
damage) compared to motion segments held in a neutral position. Additionally, flexing the
lumbar spine beyond 100% of maximum under high compressive loads may increase the risk
of sudden intervertebral disc herniation (6). This occurs as the hydrostatic pressure in the
nucleus rises considerably due to the posterior ligaments of the neural arch (9, 34) and the
outer posterior wall of the anulus being stretched (6). As these tissues reside close to the
center of rotation of the interbody joints, the modest internal extensor moments generated
result in a high compressive penalty (5). This rise in compression loads may result in a
situation that is particularly hazardous for the vertebral body, endplate and disc (4, 54).
The posterior ligaments of the lumbar spine provide support to the intervertebral disc when
exposed to lifting heavy loads in a flexed posture (91). In particular, the supraspinous and
interspinous ligaments have been shown to damage prior to the intervertebral disc when
flexion at end range of motion is loaded (9). However, lifting with a flexed posture that is 1-
2° less than maximal flexion can provide a significant decrease in the tension of the posterior
ligaments (34). As lifting heavy loads with a fully flexed spine provides little additional
support from the posterior ligaments to overcoming the external flexion moments (34, 75),
the advantage of this strategy is questionable for maximising lifting performance. Therefore,
avoiding a fully flexed spine during heavy lifting exercises may provide the athlete with a
safety window that helps to minimise the risk of posterior ligament sprain (8). An alternative
perspective may be that lifting with a fully flexed spine provides the posterior ligaments with
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a stimulus for adaptation, that may be viewed as desirable. However, it is important to note
that the posterior ligaments are stressed with submaximal levels of lumbar spine flexion (63)
that may also induce positive adaptations. It is therefore suggested that while the evidence for
adaptation of the posterior ligaments to lifting is inconclusive at this time, S&C coaches
consider both the risks and benefits to lifting with a fully flexed lumbar spine before deciding
on the technical model they will adhere to when coaching.
Importantly, the compressive strength of the lumbar spine does not appear to diminish when
submaximal levels of flexion is present. When investigating the effect of posture on the
lumbar spine’s tolerance to compressive forces in human cadavers, Adams et al. (11) found
no difference between a position of 75% of maximum flexion and a neutral spine alignment.
While these findings support the suggestion that submaximal flexion of the lumbar spine does
not compromise the spines tolerance to load, the location of the failure provides an interesting
consideration. When analysing each motion segment, structural failure caused when held in a
position of neutral resulted in central vertebral endplate fractures, while failure occurring
when the spine was flexed to 75% of maximum led to failure closer to the anterior margin
(11). This likely happens from change to the axis of rotation altering the location of stress
concentrations. As tissue adaptation is localised to regions where stress is accentuated (53,
65), this may indicate that athletes who routinely lift with modest amounts of spinal flexion
may be more compromised when adopting a strategy incorporating additional flexion.
Likewise, athletes that have lifted for years with significant lumbar flexion may be at greater
risk of injury when suddenly coached to maintain a more lordotic posture at high loads. For
long-term development, S&C coaches may choose to develop a lifters robustness by
consistently exposing the athlete to a variety of lifting postures. This could be achieved by
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programming a range of lifting exercises, as the magnitude of lumbar flexion appears to
differ between exercise such as squatting and deadlifting (42).
Performing heavy lifting exercises can also expose the spine to shear forces that are
potentially injurious (35, 44). Shear forces exceeding the tolerance of the spine may lead to
damage of the pars interarticularis (125), pedicles (47) or vertebral endplate (48). Due to the
oblique sagittal plane orientation in a posterior-caudal direction, the lumbar division (pars
lumborum) of the iliocostalis lumborum and longissimus thoracic muscles provide resistance
to anterior shear forces. However, the line of action has been shown to significantly reduce
from 28° in a neutral lumbar position, to 11° when the spine is fully flexed (72). Such change
to alignment would diminish the capacity of the iliocostalis lumborum pars lumborum and
longissimus thoracic pars lumborum to resist the shear forces observed during heavy lifting
(90, 91). Consequently, avoiding full spine flexion has been suggested to help minimise
injury risk when performing lifts in the weight room (71). However, anterior shear forces
appear to be reduced at L4/L5 and L5/S1 when lifting with greater lumbar spine flexion (13,
62, 63), indicating that shear forces imposed by gravity decrease as trunk inclination reduces
with a flexed spine relative to a lordotic posture (13). Additionally, while the lumbar portion
of the iliocostalis lumborum and longissimus thoracic may buttress anterior shear forces at
the upper lumbar spine when a lordotic spine is cued during a lifting task, these muscles
actually impose an anterior shear force at L5/S1 that is greater than the values observed with
a flexed posture (13). Furthermore, the anterior shear forces observed during heavy lifting
exercises (35, 43) can be resisted by the apophyseal joint (38). These findings suggest that
evidence for the magnitude of shear forces with different postures does not provide
conclusive evidence to support the adoption of a single lifting strategy that minimises injury
risk for all athletes.
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Whether the function of the iliocostalis lumborum pars lumborum and longissimus thoracic
pars lumborum and anterior shear forces associated with lifting, should play a primary role in
deciding on an appropriate technique for lifting heavy loads is currently unclear.
While the evidence presented in this section partially supports avoiding full lumbar spine
flexion during lifting exercises, this suggestion has been developed predominantly from
cadaver studies and biomechanical models, with longitudinal evidence lacking. Prospective
studies identifying the effects of lifting with a fully flexed lumbar spine on the development
of low back pain would be needed to strengthen this common recommendation. At this time,
it remains unclear how athletes such as strongman competitors are able to flex their spine far
beyond their unloaded maximum against incredibly high resistances without incurring
catastrophic damage. While the answer may be in the development of an exceptional skeletal
architecture built over years of training (39), their ability to skillfully coordinate their
movements so that time points where spinal loads are greatest do not coincide simultaneously
with the spine being fully flexed (74), or selection bias (1), more evidence is required to
understand the effect of lifting maximum loads with a fully flexed spine. At present, when
attempting to minimise injury risk during lifting, it appears the literature is open to the
coach’s interpretation, with many of the commonly held beliefs for avoiding injury lacking
the support of conclusive evidence.
ADVANTAGES OF LIFTING WITH A FLEXED LUMBAR SPINE
As lumbar spine flexion appears to be consistently employed during lifting exercises, it may
be that this coordinative strategy provides the lifter with a performance advantage. This
logical assumption is supported by evidence showing powerlifters display large amounts of
20
spinal flexion when performing maximal lifts in competition (55). Mechanically, this strategy
has the potential to maximise performance during lifting exercises where the objective is to
lift as much external weight as possible. By flexing at both the thoracic and lumbar spine, the
barbell can be positioned closer to the lumbosacral region and hip joint, decreasing the
moment arm of the barbell and the resultant external flexion moment both joint complexes
must overcome (56).
Increased spine flexion would additionally decrease the hip joints sagittal plane contribution
to lowering the centre of mass during lifting (87). As the gluteus maximus and hamstring
muscles are the primary hip extensors during bilateral lifting exercises (57, 80), their capacity
to produce a high internal extensor moment is vital to performance. However, when hip
flexion angle increases beyond 35° as it does during most full range of motion lifting
exercises (105, 106), the hip extensor muscle moment arm length decreases significantly (15,
79). As such, some lumbar flexion during lifting may preserve the effectiveness of the hip
extensor muscles for generating high internal extensor moments at the hip joint by reducing
peak hip flexion angles. As a consequence, greater load could be lifted during maximal
attempts and is another likely explanation for why competitive weightlifters and powerlifters
perform heavy lifting exercises with a flexed lumbar spine posture (1, 34, 43).
Another advantage to lifting with a moderate amount of lumbar spine flexion is also the
change in length of the spinal extensor muscles altering their ability to produce torque.
Lumbar spine posture appears to have a considerable influence on spine extensor strength,
with greater force generation displayed in flexed postures (85, 51, 58, 108), whilst lordotic
postures are associated with decreased extension torque (99). These findings are mainly due
to muscle force generation being greatest when optimal overlap occurs between the actin and
21
myosin protein filaments (86). This generally happens at muscle lengths approximating 110%
of resting length and at the lumbar spine, corresponds with a flexed posture (2). The lumbar
spine is also able to access the stiffness generated in the passive structures of the muscle
when lengthened (92), resulting in a higher internal extensor moment being developed (5).
When the lumbar spine is flexed, the lumbodorsal fascia has the potential to assist the spinal
extensor muscles in generating the necessary extensor moments to lift exception loads (5).
This would provide the spine with a significant advantage, as the lumbodorsal fascia resides a
considerable distance posterior to each motion segments axis of rotation and consequently,
possesses a substantial moment arm (112). Furthermore, the lumbodorsal fascia has a very
high resiliency to loading (109) that would, in combination with its moment arm, support a
large internal extensor moment (5). However, in order to take advantage of the lumbodorsal
fascia, Dolan et al. (40) showed that lumbar flexion was required. Following the performance
of a static lifting task with postures varying from < 40% to > 100% of full lumbar flexion,
peak extensor moments were greatest when the lumbar spine was flexed between 78-97%.
Importantly, Dolan et al. (40) noted that at 80% of full flexion, an internal extensor moment
generated from passive structures was present that was not at lower ranges of lumbar spine
flexion. While only a small amount of this passive support can be attributed to the posterior
ligaments and intervertebral discs (3), Dolan et al. (40) suggested the lumbodorsal fascia has
a significant role in supporting the spine during the successful execution of a lifting task
where spinal flexion is accessed. As experienced lifters demonstrate lumbar flexion that is
slightly less than their full capacity (34, 42, 43), it may be that this strategy offers an ideal
compromise between optimising the length of the extensor muscles and facilitating the
contribution of the lumbodorsal fascia.
22
Lifting with some lumbar spine flexion may also present as an optimal strategy for some
individuals if considering the load sharing patterns between passive structures of the spine.
When attempting to maintain a lordotic posture during lifting, apophyseal joint compression
increases significantly at L5/S1, which is diminished with flexion (63). Relative to a neutral
position, the compressive stress placed on posterior wall of the anulus fibrosus also decreases
with a moderately flexed alignment compared to a neutral position (7). Additionally, the
dimensions of the intervertebral foramen are larger when spinal flexion increases (61).
Therefore, it may be that for individuals presenting with a history of apophyseal joint
irritation, a compromised posterior wall of the intervertebral disc, disc degeneration leading
to narrowing of the disc height, or stenotic changes in the lumbar spine, some lumbar flexion
during lifting would offer an ideal strategy for offloading sensitive structures (5).
At the hip joint, lumbar flexion has the potential to decrease hip flexion during lifting (87). If
lumbar spine flexion is accessed during lifting, end range of motion hip flexion may be
avoided (16, 87) that would result in reduced contact forces between the superior acetabulum
rim and the head-neck junction of the femur (31, 64). Avoiding end range of motion hip
flexion has the potential to increase stress placed on the passive structures of the hip joint
(49). Allowing some lumbar flexion to occur during lifting exercises may, therefore, reduce
stress on passive structures at the hip and provide the athlete with a movement strategy that
preserves the health of the hip joint (16).
SUMMARY
A neutral spine alignment is commonly included in the technical model for lifting exercises
prescribed as part of a S&C programme. The rationale for this inclusion is to diminish injury
risk (1) by minimising stress on osteoligamentous structures that limit end range of motion
23
(4, 34) However, it appears that some level of flexion during lifting exercises is unavoidable
(1, 43, 73, 74, 94, 117), even when cued (40, 58, 63). Whether the lumbar spine flexion that
occurs during lifting exercises is beyond the neutral zone is yet to be established. However,
based on the low values of flexion reported to occur in the neutral zone (27, 95, 111, 124), it
appears highly probable that exercises such as the squat and deadlift requires lumbar flexion
past the neutral zone.
While it is suggested that lifting with less lumbar spine is protective against injury, research
to support this is lacking (93). Cadaver models have shown that a neutral spine alignment has
a greater capacity to tolerate cycles of repetitive lifting when compared to a flexed spine (48).
However, potential adaptations of the spine to loading are not accounted for in these models.
Such adaptations are likely why many powerlifters, weightlifters and strongman competitors,
are able to accumulate very large volumes of heavy lifting without incurring spinal injury. As
such, it may be that when appropriately programmed, the lumbar spine adapts to the loading
imposed upon it when executing lifting exercises with a flexed spine. It is therefore suggested
that S&C coaches focus on the meticulous prescription of lifting exercises to develop the
structural properties of an individual’s spine and in turn, build its load bearing capacity.
Whilst maintaining a neutral spine does not appear to be attainable during lifting exercises,
avoiding a fully flexed posture is achievable for many athletes, potentially reducing injury
risk. This is due to the compressive strength of the spine being diminished (54), increased
strain on posterior ligaments of the neural arch (9, 34), and decreased contribution from the
lumbar erector spinae muscles to buttress the anterior shear forces associated with lifting (72,
90). However, evidence for injury risk being significantly greater when lifting with a
maximally flexed spine is not conclusive. Yet, as lifting with full lumbar spine flexion would
24
unlikely offer any additional performance benefits, it is suggested that S&C coaches
encourage their athletes to adopt a lifting strategy that does not fully exhaust their flexion
capacity. Future investigations should attempt to determine whether lifting with a fully flexed
spine directly elevates injury risk.
There may be performance benefits to lifting with moderate amounts of lumbar spine flexion.
Manipulation of the external flexion moment can be achieved by allowing some thoracic and
lumbar spine flexion, which serves to bring the load closer in the horizontal distance to the
lumbosacral joint and hip joints. This would also benefit the hip extensor musculature by
increasing their moment arm at the hip joint. Likewise, lumbar spine flexion may also
optimise the torque generation capabilities of the erector spinae muscles. Lumbar spine
flexion approximating 80% of maximum, similar to the values reported during squatting and
deadlifting among competitive powerlifters and weightlifters (42), also facilitates the
lumbodorsal fascia in contributing to the internal extensor moment (40). Lastly, encouraging
some lumbar spine flexion during lifting may be a useful strategy for certain athletes to
decrease stress concentrations on sensitised tissues. Collectively, it appears that a moderate
amount of lumbar spine flexion may benefit performance during lifting exercises. As the
injury risk for lifting with a moderately flexed spine is yet to be found to be significantly
more hazardous than a neutral alignment, S&C coaches should see lumbar spine flexion and
another “road to Rome” in their approach to optimising performance in the weight room.
25
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... Since one objective of this study was to develop a tool that may serve to improve sport performance and prevent injuries, the authors analyzed the recorded motions seeking to identify the most relevant parameters for a good and safe lifting execution. Although the neutral zone of the whole lumbar region in healthy adults was approximately 20° in the sagittal plane [30], based on results showed in [2] the accepted neutral spine deviation was fixed to 30°. Sensors at L5 and T8 offered the required information for spine deviation and the additional markers on the legs were used to observe the squat amplitude and the possible relation with poor spine posture. ...
... The results showed that more than 50% of common athletes have a poor spine posture during lifting exercises (during at least one of the two exercises captured), exceeding 30° of deviation from the neutral configuration, and presenting a high risk of lower back injury. Disc herniations will likely occur when doing a high number of repetitive cycles of flexion under relatively low loads around the limits of the neutral zone [2], and increasing the load will increase the likelihood of herniation development [32]. The mean spine deviation during deadlifts was 25.76° for the 39 subjects. ...
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... L'ACSM propose qu'une augmentation de deux à dix pour cent de la charge de travail se fasse lorsque le patient dépasse le nombre de répétitions maximales souhaitées avec la charge de travail actuelle (Kraemer et al., 2002). De plus, il n'existe pas de preuve que le port de charge avec une flexion lombaire maximale comme le "Jefferson curl" augmente le risque de blessure (Howe & Lehman, 2021). Par ailleurs, une étude rapporte que même certains professionnels de la santé véhiculent généralement des fausses croyances sur la compréhension de la lombalgie et les effets du mouvement sur celle-ci (Nolan et al., 2018;Rialet-Micoulau et al., 2022). ...
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There is evidence in animal populations that loading and exercise can positively impact the intervertebral disc (IVD). However, there is a paucity of information in humans. We examined the lumbar IVDs in 308 young athletes across six sporting groups (baseball, swimming, basketball, kendo, soccer and running; mean age 19yrs) and 71 non‐athletic controls. IVD status was quantified via the ratio of IVD to vertebral body height (IVD hypertrophy) and ratio of signal intensity in the nucleus to that in the annulus signal (IVD nucleus hydration) on sagittal T2‐weighted MRI. P‐values were adjusted via the false discovery rate method to mitigate false positives. In examining the whole collective, compared to referents, there was evidence of IVD hypertrophy in basketball (P≤0.029), swimming (P≤0.010), soccer (P=0.036) and baseball (P=0.011) with greater IVD nucleus hydration in soccer (P=0.007). After matching participants based on back‐pain status and body height, basketball players showed evidence of IVD hypertrophy (P≤0.043) and soccer players greater IVD nucleus hydration (P=0.001) than referents. Greater career duration and training volume correlated with less (i.e. worse) IVD nucleus hydration, but explained less than 1% of the variance in this parameter. In this young collective, increasing age was associated with increased IVD height. The findings suggest that basketball and soccer may be associated with beneficial adaptations in the IVDs in young athletes. In line with evidence on other tissues, such as muscle and bone, the current study adds to evidence that specific loading types may beneficially modulate lumbar IVD properties. This article is protected by copyright. All rights reserved.
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Background: The purpose of this study was to compare muscle forces and hip contact forces (HCFs) during squatting in patients with cam-type femoroacetabular impingement (cam-FAI) before and after hip corrective surgery and with healthy control participants. Methods: Ten symptomatic male patients with cam-FAI performed deep squatting preoperatively and at 2 years postoperatively. Patients were matched by age and body mass index to 10 male control participants. Full-body kinematics and kinetics were computed, and muscle forces and HCFs were estimated using a musculoskeletal model and static optimization. Normalized squat cycle (%SC) trials were compared using statistical nonparametric mapping (SnPM). Results: Postoperatively, patients with cam-FAI squatted down with higher anterior pelvic tilt, higher hip flexion, and greater hip extension moments than preoperatively. Preoperative patients demonstrated lower anterior pelvic tilt and lower hip flexion compared with the participants in the control group. Postoperative patients showed increased semimembranosus force compared with their preoperative values. Preoperative forces were lower than the control group for the adductor magnus, the psoas major, and the semimembranosus; however, the preoperative patients showed greater inferior gluteus maximus forces than the patients in the control group, whereas the postoperative patients did not differ from the control patients. Higher posterior, superior, and resultant HCF magnitudes were identified postoperatively in comparison with the preoperative values. Preoperative posterior HCF was lower than in the control group, whereas the postoperative posterior HCF did not differ from those in the control group. Conclusions: Higher postoperative anterior pelvic tilt was associated with an indication of return to closer to normal pelvic motion, which resembled data from the control group. Lower preoperative anterior pelvic tilt was associated with muscle force imbalance, indicated by decreased semimembranosus and increased gluteus maximus forces. The overall increased postoperative muscle forces were associated with improved pelvic mobility and increased HCFs that were comparable with the control-group standards. Clinical Relevance: Muscle forces and HCFs may be indicative of postoperative joint health restoration and alleviated symptoms.
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Irrespective of the lifting technique (squat or stoop), the lumbar spine posture (more kyphotic versus more lordotic) adopted during lifting activities is an important parameter affecting the active-passive spinal load distribution. The advantages in either posture while lifting remains, however, a matter of debate. To comprehensively investigate the role on the trunk biomechanics of changes in the lumbar posture (lordotic, free or kyphotic) during forward trunk flexion, validated musculoskeletal and finite element models, driven by in vivo kinematics data, were used to estimate detailed internal tissue stresses-forces in and load-sharing among various joint active-passive tissues. Findings indicated that the lordotic posture, as compared to the kyphotic one, resulted in marked increases in back global muscle activities (∼14-19%), overall segmental compression (∼7.5-46.1%) and shear (∼5.4-47.5%) forces, and L5-S1 facet joint forces (by up to 80 N). At the L5-S1 level, the lordotic lumbar posture caused considerable decreases in the moment resisted by passive structures (spine and musculature, ∼14-27%), negligible reductions in the maximum disc fiber strains (by ∼0.4-4.7%) and small increases in intradiscal pressure (∼1.8-3.4%). Collectively and with due consideration of the risk of fatigue and viscoelastic creep especially under repetitive lifts, current results support a free posture (in between the extreme kyphotic and lordotic postures) with moderate contributions from both active and passive structures during lifting activities involving trunk forward flexion.
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Quantifying lumbar back motion during functional activities in real-life environments may contribute to a better understanding of common pathologies such as spinal disorders. The current study therefore aimed at the comparative evaluation of the Epionics SPINE system, a portable device for measuring sagittal lumbar back motion during functional activities. Twenty healthy participants were therefore evaluated with the Epionics SPINE and a Vicon motion capture system in two identical separate research visits. They performed the following activities: standing, sitting, chair rising, box lifting, walking, running and a counter movement jump (CMJ). Lumbar lordosis angles were extracted as continuous values as well as average and range of motion (ROM) parameters. Agreement between the systems was evaluated using Bland-Altman analyses, whereas within- and between-session reliability were assessed using intraclass correlation coefficients (ICC) and minimal detectable changes (MDC). The analysis showed excellent agreement between the systems for chair rising, box lifting and CMJ with a systematic underestimation of lumbar lordosis angles during walking and running. Reliability was moderate to high for all continuous and discrete parameters (ICC ≥ 0.62), except for ROM during running (ICC = 0.29). MDC values were generally below 15°, except for CMJ (peak values up to 20° within and 25° between the sessions). The Epionics SPINE system performed similarly to a Vicon motion capture system for measuring lumbar lordosis angles during functional activities and showed high consistency within and between measurement sessions. These findings can serve researchers and clinicians as a bench mark for future investigations using the system in populations with spinal pathologies.
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Study design: Prognosis systematic review with meta-analysis. Objective: To evaluate whether lumbar spine flexion during lifting is a risk factor for low back pain (LBP) onset/persistence, or a differentiator of people with and without LBP. Literature search: Database search of Proquest, CINAHL, Medline and EMBASE until August 2018. Study selection criteria: We included peer-reviewed articles, investigating lumbar spine position during lifting as a risk factor for LBP onset or persistence, or as a differentiator of people with and without LBP. Data synthesis: Lifting task comparison data were tabulated and summarised. For meta-analysis, we calculated an n-weighted pooled mean (SD) of the results for each of the LBP and no LBP groups. Where a study contained multiple comparisons (i.e. different lifting tasks that used various weights or directions), only one result for each study was included in the meta-analysis. Results: Four studies (one longitudinal study and three cross-sectional studies) measured lumbar flexion with intra-lumbar angles and found no differences in peak lumbar spine flexion when lifting (longitudinal 1.5 degree (95%CI -0.7 to 3.7), p=0.19 and cross-sectional -0.9 (95%CI -2.5 to 0.7), p=0.29). Seven cross-sectional studies measured lumbar flexion with thoraco-pelvic angles and found people with LBP lifted with 6.0 degrees less lumbar flexion than people without LBP (95%CI -11.2 to -.89, p<0.01). Most (9 of 11) studies reported no between-group differences in lumbar flexion during lifting. The included studies were low quality. Conclusion: There was low quality evidence that greater lumbar spine flexion during lifting was not a risk factor for LBP onset/persistence, nor a differentiator of people with and without LBP. J Orthop Sports Phys Ther, Epub 28 Nov 2019. doi:10.2519/jospt.2020.9218.