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biomechanics와 관련된 review논문이라면 그저 흥분된다.
인체의 움직임에 관한 이렇게 세밀하고 엄밀한 연구들이 진행되고, 그 결과가 최신의 스포츠 과학, 최신의 치료적 운동의 기초가 되고 있다.
trunk motion에 따른 trunk strength와 척추에 가해지는 부하에 관한 연구를 review한 논문이다.
결론은 간단하다.
trunk strengthe, IAP(intra-abdominal pressure, 복압), muscle activity, imposed trunk moment
The e?cts of motion on trunk biomechanics.pdf
Abstract
Objective. To review the literature that evaluates the influence of trunk motion on trunk strength and structural loading.
Background. In recent years, trunk dynamics have been identified as potential risk factors for developing low-back disorders. Consequently, a better understanding of the underlying mechanisms involved in trunk motion is needed.
Methods. This review summarizes the results of 53 studies that have evaluated trunk motion and its impact on several biomechanical outcome measures. The biomechanical measures consisted of trunk strength, intra-abdominal pressure, muscle activity, imposed trunk moments, and spinal loads. Each of these biomechanical measures was discussed in relation to the existing knowledge within each plane of motion (extension, flexion, lateral flexion, twisting, and asymmetric extension).
Results. Trunk strength was drastically reduced as dynamic motion increased, and males were impacted more than females. Intra-abdominal pressure seemed to only be a?fected by trunk dynamics at high levels of force. Trunk moments were found to increase monotonically with increased trunk motion. Both agonistic and antagonistic muscle activities were greater as dynamic characteristics increased. As a result, the three-dimensional spinal loads increase significantly for dynamic exertions as compared to isometric conditions.
Conclusions. Trunk motion has a dramatic a?fect on the muscle coactivity, which seems to be the underlying source for the decrease strength capability as well as the increased muscle force, IAP, and spinal loads. This review suggests that the ability of the individual to perform a task ``safely'' might be significantly compromised by the muscle coactivity that accompanies dynamic exertions. It is also important to consider various workplace and individual factors when attempting to reduce the impact of trunk motions during dynamic exertions.
Relevance
This review provides insight as to why trunk motions are important risk factors to consider when attempting to control low-back disorders in the workplace. It is apparent that trunk motion increases the risk of low-back disorders. To better control low-back disorders in industry, more comprehensive knowledge about the impact of trunk motion is needed. A better understanding of muscle coactivity may ultimately lead to reducing the risk associated with dynamic exertions.
1. Introduction
Despite mechanization increases in the workplace, manual material handling has remained a vital component
of work. As electronic commerce becomes more prevalent, more frequent lifting (often with lower force) must occur to process on-line orders. More frequent lifting often is associated with more rapid movements [1,2]. Hence, modernization has impacted the work by making lifts more dynamic. Similarly, in the manufacturing environment, better methods and faster machines have increased output, requiring the worker to keep pace with the process. Thus, a better understanding of how trunk dynamics may impact the worker is becoming more important.
Trunk motion has recently been identified as a potential risk factor for low-back disorders (LBD). Three-dimensional trunk velocity has been found to significantly increase LBD risk [1±3]. Marras and associates [1,2] reported odds ratios (comparing ``high risk'' to ``low risk'') for sagittal, lateral, and twisting trunk velocity on the job between 1.34 and 3.3, 1.04 and 1.73, and 1.09±1.66, respectively. Norman et al. [3] found an odd ratio of 1.9 for peak sagittal trunk velocity when comparing cases to randomly selected controls. In all three of these studies, trunk velocity variables were included
in the multivariate models, indicating that these motion characteristics may play an important role in the development of LBD. In addition, high values of combined trunk velocities (e.g. simultaneous lateral flexion and twisting velocities) were found to occur more frequently in high and ``medium'' risk jobs than low risk jobs [4]. Thus, dynamic motion plays a dominant role in development of LBD, particularly when the motion occurs in multiple planes simultaneously. However, our knowledge of the underlying injury mechanisms associated with dynamic trunk motion is limited.
1.1. Potential mechanisms leading to LBD
Many factors may contribute to the relationship between dynamic motion and LBD risk. Two major categories of such factors include: trunk strength and spine structural loading. While both factors may potentially cause LBD, each typically is thought to be associated with different mechanisms of LBD. LBDs that result from lack of strength would exceed muscular tolerance while structural loading LBDs would result from forces being placed on the spinal structures exceeding the tolerance limits. In either case, LBD risk is viewed in a load-tolerance perspective, regardless of whether it is muscular or skeletal in nature.
Dynamic strength of the trunk has typically been measured with sophisticated dynamometers that control the motion while measuring the force being exerted. Typically, the motion has been isolated to one plane of motion (e.g. sagittal, lateral, or twisting). The premise behind strength capacity is that the closer the required strength (load) is to the strength capacity (tolerance), the greater the risk of injury [5,6].
Structural loading factors would include the biomechanical factors that contribute to loading on the spinal structures such as intra-abdominal pressure (IAP), muscle activity, and the imposed trunk moment, as well as the actual loads on the structures of the spine. IAP has traditionally been thought of as a mechanism that assists in generating an extensor moment, thus, reducing the loading on the spine [7]. Others have suggested that IAP assists in maintaining the integrity of the abdominal muscles [8] and vertebral motion segments [9], as well as stability of the vertebral column [10,11].
Muscle activity has traditionally been used as an indirect indicator of the level of force generated by a particular muscle [12]. However, it should be noted that these measurements are not an indicator of muscle tension but rather the
degree of muscular activation solicited from the muscle. In order to estimate the tension in the muscle, the signal
must be adjusted (modulated) to account for the length and velocity of the muscle [12]. The trunk moment imposed
on the spine (external load) needs to be o?et by the trunk muscles (internal load) [13,14]. Thus, as the imposed trunk moment increases, there would be a corresponding increase in muscle activity.
As a result of the muscle activity and, potentially, IAP, loads on the spine are generated in the form of compression, anterior ±posterior (A±P) shear (front-to-back shear forces), and lateral shear (side-to-side shear forces) forces.
This review investigated the impact of trunk dynamics on trunk strength and structural loading variables and attempted to provide insight into how these factors may be the underlying causes for trunk motions that may be associated with risk of LBD. The literature was summarized across the all planes of motion providing a comprehensive evaluation for each of the potentially contributing factors. This provided opportunity to draw conclusions as well as identify major voids in the literature.
방법
Typically, there have been five groups of biomechanical measures that have been commonly investigated in literature: strength, IAP, trunk moments, spinal loads, and muscle activity (agonistic and antagonistic).
결과
3.2. Trunk strength
Dynamic motion generally decreased trunk strength in all directions by approximately 10~30%. Most of the high quality studies (14 studies) evaluating extension strength (Table 1) reported diminished strength of 10~30% for dynamic exertions compared to static conditions with only a few studies finding some postures having increased strength. The dynamic exertions with increased strength occurred during more awkward postures (e.g. load placed at a full reach away from the body) [38] or in an upright posture (as indicated by the upward pointing arrows in Table 1) [31,49].
It appears that some of the variability in the strength results for extension may be attributable to whether the exertion was isolated to the L5/S1 joint (e.g. lower body was constrained) or was a whole body assessment (e.g. able to move legs during exertion).
Flexion strength decreased for dynamic exertions by 5~80% for all but two studies (Table 2). Smith et al. [57] reported that flexion strength increased by 34~75% as compared to the isometric exertion. Khalaf et al. [31] found similar results for males but not for the females.
The three studies that investigated dynamic lateral flexion strength reported a decrease of 11~88% for dynamic lifts (Table 3). Dynamic twisting strength was found to be 15~80% lower than for isometric twisting for the high quality studies (Table 4). Only two twisting studies reported an increase in strength for the dynamic lifts, one study reported increases for females only [57]while the other included only one condition [66]. The only two studies that evaluated asymmetric extension exertions found mix results ranging from a decrease of 63% to an increase of 91% (Table 5).
For the studies that evaluated both genders, an interesting trend in the impact of dynamics of the strength of the individuals emerged. Strength for the males decreased with dynamic exertions by about 30% while the femalesO decrease in capacity was about 15±20%. This would mean that trunk motion had more an impact on the male strength than the females by about 10%. This gender finding was relatively consistent across all exertion directions.
In summary, an individualOs strength is reduced by 10±30% when exertions are performed dynamically as compared to isometric strength. In other words, given the same exertion level, a dynamic exertion would be closer to the tolerance of the muscle than during a static exertion, resulting in more risk of a muscular injury. Trunk motion appears to have a greater impact on the malesO strength than on the females.
3.3. Intra-abdominal pressure
The studies evaluating IAP provided very inconclusive
results when comparing dynamic trunk motion to
isometric exertions. In the high quality studies that
evaluated extension exertions (Table 1), IAP was found
to decrease in four studies, no di?rence in one, and
increased in one when dynamic motion was involved.
No studies have evaluated IAP while performing dynamic
¯exion, lateral ¯exion, or twisting exertions.
Marras and Mirka [11] combined the results of four
individual studies evaluating IAP and concluded that
IAP increased monotonically with trunk velocity.
However, this increase in IAP appeared to be only at
high levels of exerted force. To date, there has been no
comparison of the impact of dynamics on IAP between
males and females.
In summary, the results for IAP were inconclusive.
The impact of dynamics on IAP seems to be greatest at
high exertion levels. There is a need for a better understanding
of the in¯uence of trunk dynamics on IAP,
particularly di?rences between genders, as well as an
improved appreciation of the biomechanical role of
IAP.
3.4. Trunk moments
Overall, the moments imposed on the trunk have
been observed to increase by 15±70% during the dynamic
exertions. The majority of the studies that evaluated
trunk moments were not considered to be in the
high quality category since most of them did not control
velocity. For extension exertions (Table 1), studies that
used subjective motions found increases ranging from 3±
227% while controlled motion exertions actually saw the
trunk moments decrease with the introduction of dynamics
(by 12±69%). In the study that found a decrease
in trunk moment, the lower torso was restricted which
may have in¯uenced how the exertions were performed
(e.g. subject pulled the weight closer to the body during
the dynamic conditions). No di?rence between trunk
moments was found in one study [29] but there was no
di?rence in the actual trunk velocity between the two
subjective velocity categories (preferred and faster than
preferred). Similarly, McIntyre et al. [68] reported that
individuals gravitated towards a preferred trunk velocity
when exerting below 25% of their maximum e?rt,
which may provide insight into the results of Granata et
al. [29]. Similar increases in trunk moment were reported
for asymmetric extension exertions (Table 5). No studies
evaluated the imposed trunk moments for ¯exion and
lateral ¯exion. The only study to evaluate imposed
twisting moments was Marras and associates [63] who
found the trunk moments to increase 15±25% in most
conditions. To date, di?rences in the impact of trunk
motion between males and females have yet to be explored.
In summary, imposed trunk moments during dynamic
exertions were found to be greater than during isometric
exertions, monotonically increasing with faster motions.
Since much of the research evaluating dynamic trunk
moments have relied upon uncontrolled velocities, there
is a need for further investigation of how imposed trunk
moments are a?cted by trunk motion under more
controlled conditions, especially in the non-extension
exertions.
3.5. Muscle activity
In general, both agonistic and antagonistic muscle
activity increased with increased dynamic trunk motion.
Agonistic activity increased by approximately 10±40%
while antagonistic activity increased by as much as
450%. There have been no studies that have evaluated
muscle activity while performing dynamic ¯exion exertions
and few evaluating twisting or lateral ¯exion. For
the 10 high quality extension studies (Table 1) evaluating
agonistic muscle activity, most (all but four) found
an increase in activity with dynamic motion (range of 4±
109% increase). Gallagher [25] reported decreases in the
activity of the Latissimus Dorsi, which accompanied
small (non-signi?cant) increases in erector spinae muscle
activity. Decreases in agonistic activity were also found
for very fast extensions (e.g. 90°/s) [48]. The only study
that evaluated lateral ¯exion and satis?ed the inclusion
criteria found agonistic muscle activity to increase by
46±116% with dynamic motion [61]. Two of three
studies found increases in agonistic activity in twisting
(6±157%) (Table 4). Four studies found decreases in
agonistic activity with trunk motion [25,44,45,65]. The
exerted force for dynamic condition velocities also decreased
as compared to the isometric exertions, thus, the
decrease in activity may be more re¯ective of the force
exerted. Marras et al. [63] reported a decrease in agonistic
activity when the subjects twisted in awkward
postures only.
Few studies (9) have investigated the impact of trunk
dynamics on the antagonistic muscle activity. Since
these muscles are not required for force generation, increased
activity indicates more coactivity of the trunk
musculature system and less eciently but probably
related to stability requirements. Results from the high
quality studies indicated that antagonistic activity might
be a?cted more by dynamics than the agonistic muscles.
For the extension exertions (Table 1), dynamic
motion increased antagonistic activity by about 50±
450% while dynamic lateral ¯exion exertions (Table 3)
increased the antagonistic activity by 20±133%. Although
McGill [69] did not directly compare the antagonistic
muscle activity during dynamic lateral ¯exion
to static, he noted that dynamic exertion resulted in moderate levels of co-contraction, in other words,
presence of activity in the antagonistic muscles. Dynamic
antagonistic muscle activity increased in two of
the three twisting studies (by 6±252%) (Table 4).
In summary, trunk dynamics dramatically in¯uenced
both the agonistic and antagonistic muscle activity.
Since the antagonistic muscle activity was impacted
more, the overall coactivity of the trunk musculature
was signi?cantly increased without resulting in any additional
force generating capability. Few studies have
evaluated the muscle activity while performing ¯exion,
lateral ¯exion, and twisting exertions. Future studies are
also needed to investigate how trunk dynamics might
in¯uence muscle activity for males and females di?rently.
3.6. Spinal loading
In general, trunk dynamics was found to increase the
three-dimensional spinal loads with increases of 10±50 %
for compression, 50±325% for lateral shear, and 10±30%
for A±P shear. The high quality extension studies (Table
1) reported an increase of 3±120% in compression force
when dynamic trunk motion was compared to isometric
exertions. Two of these studies reported increased A±P
shear forces during dynamic exertions (by 23±57%).
Reilly andMarras [55] (the only other study to report on
A±P shear force), found a decrease in shear for the
slowest velocities (less than 30°/s). Only two of the
studies evaluating extension exertions (Table 1) evaluated
lateral shear forces with one reporting a decrease
and one reporting an increase with the dynamic conditions.
This apparent con¯ict in results may be a direct
re¯ection of the low levels of expected lateral shear force
during sagittally symmetric exertions. In the one study
that reported lateral shears in asymmetric extensions
(Table 5), the lateral shears increased by 1±333%.
However, this study was not considered to be in the high
quality study group.
Only one study found in the literature [61] investigated
spinal loads during lateral ¯exion (Table 3). These
authors reported an increase in compression, lateral
shear, and A±P shear force by 10±33%, 50%, and 100±
325%, respectively. The only study included in the present
review to evaluate spinal loads during twisting exertions
reported a 50% increase in compression and a
15±45% increase in the lateral shear forces during the
dynamic exertions [62]. Combining the results of these
studies with the one asymmetric exertion study, nonsagittal
trunk motions had a large impact on the lateral
shear forces. No studies could be located that evaluated
spinal loads during ¯exion exertions.
In summary, trunk dynamics had a signi?cant impact
on three-dimensional spinal loads. Dynamic sagittally
symmetric exertions a?ct spinal compression and A±P
shear forces while non-sagittal (lateral ¯exion and
twisting) exertions result in higher compression and
lateral shear forces. The impact of trunk dynamics on
spinal loads for females has yet to be investigated. Since
females would be expected to have di?rent trunk
anatomies [70±75], the impact of trunk dynamics on
spinal loads may be di?rent for females as compared to
males. More studies are needed to evaluate the spinal
loads during dynamic ¯exion, lateral ¯exion, twisting,
and asymmetric extension exertions.
4. Discussion
Based on this review, it is clear that trunk dynamics
has a signi?cant impact on how the individual performs
an exertion and how the trunk musculoskeletal system
behaves. Trunk motion severely reduces the individualOs
ability to generate force. This would mean that when a
task requires a certain level of force to be employed,
more dynamic motions would hinder the ability of the
worker to meet the demands of the job. Potentially, the
mismatch between the individualOs strength capability
and the job demands may result in increase risk of the
LBD in industry, speci?cally, muscular injuries.
One factor that is highly dependent upon dynamic
strength is the dynamic functional capability of the individual.
Several studies have attempted to quantify the
functional capacity of an individual without an LBD
[76±84]. In general, these studies report the dynamic
functional capability for sagittal, lateral, and twisting
motion to be 40±140°/s, 70±120°/s, and 65±170°/s, respectively,
which was dependent upon the force exerted.
This indicates that high risk jobs found in the Marras
studies [1,2] and the cases in the Norman study [3] would
have velocities that were much closer to their expected
dynamic capabilities as compared to the corresponding
low risk and control jobs.
In addition, trunk strength would also be directly
linked to muscle coactivity. Decreases in strength capacity
during dynamic exertions suggest that more
muscle force would be required to respond to the external
load demands. In most cases, the activity of the
agonistic muscles as well as the antagonistic muscles
increased during dynamic motions. This indicates that
there is not only more activity in the primary force
generating muscles present, but also more overall coactivity
of the trunk musculature in general.
Higher levels of coactivity have a signi?cant impact
on the spinal loads since increased antagonistic muscle
activity must be o?et by the agonistic forces. In other
words, the muscle activity from the antagonistic muscles
produces more loading on the spinal structures without
contributing to the ability to o?et the external moment
imposed on the spine. In the studies that evaluated
spinal loads, trunk dynamics were found to signi?cantly
increase the compressive forces on the spine and seemed
K.G. Davis, W.S. Marras / Clinical Biomechanics 15 (2000) 703±717 711
to be independent of the type of motion used during the
exertion. However, the impact of dynamics on the shear
forces was much more dependent on the exertion type.
Dynamic sagittally symmetric extensions increased the
A±P shear forces while non-sagittal motions impacted
the lateral shear forces. In all types of dynamic exertions,
there was more three-dimensional or complex
loading on the spine.
The spine tolerance literature suggests that disc strain
and vertebral segment failure increases signi?cantly
when loading occurs in multiple directions simultaneously
[85±89]. This indicates that trunk dynamics
places the spinal structures at increased risk of failure
since spinal loads increased in multiple directions for all
types of motions. Fathallah et al. [24] found that the
load rate for compression and A±P shear increased with
trunk motion during sagittally symmetric motion and
for all three directions (compression, A±P shear, and
lateral shear) for asymmetric lifting. The rate at which
the load is applied to the spine also in¯uences the mechanical
properties of the disc [90±95]. Wang et al.
[94,95] predicted that the stresses in the annulus ?bers
increased with load rates using a ?nite-element model.
However, Yingling and associates [96,97] found that the
ultimate strength of the spinal motion segments increased
with faster load rates. These authors also indicated
that while the magnitude of the loads a?cts the
tolerance of the spine, the rate of the load actually in-
¯uences the site of the failure. Thus, both the magnitude
of the loads as well as the rate of the loads has the potential
of being the underlying mechanisms that explains
the relationship between trunk motion and LBD risk [1±
3]. Both of these factors have been found to be predictive
of high-risk of LBD [98]. These indices provide a
measure of how likely a task resembles a high risk job.
The load imposed on the spine may also have had an
impact on the resulting muscle activities and subsequent
spinal loads. Some of the increase in muscle activity
(especially for the agonistic muscles) and spinal loads
may have resulted from the higher imposed trunk moments
that accompany dynamic motions. When trunk
moments are increased, the trunk muscles have to increase
their output to o?et the moment, which result in
the higher spinal loads.
The importance of IAP in the reduction of the trunk
moment was not substantiated entirely with many
studies ?nding con¯icting results. The relationship between
IAP and trunk motion is poorly understood since
most of the studies were con?ned to the extension exertions
(either sagittally symmetric or asymmetric). With
no clear relationship between trunk motion and IAP, it
appears that IAP may be a by-product of the muscle
activity rather than an active contributor to o?etting of
the imposed trunk moments [11].
Trunk motion impacts the musculoskeletal system by
altering the recruiting patterns of the trunk muscles.
Muscle coactivity appears to be the driving force behind
the diminished strength and functional capability that
accompanies trunk dynamics as well as the increase
spine structural loading (IAP, trunk moments, and spinal
loads). The increased co-activation of the trunk
musculature associated with increases in trunk motion
may have resulted from programming of the neurological
pathways that control the muscles and are ?netuned
through experience [99]. McIntyre et al. [100]
provides evidence of motor recruitment programs by
reporting that individuals adopt a preferred trunk velocity
when performing an exertion. In other words, an
individual will adopt a certain motion pro?le that is
accompanied by a speci?c co-activation pattern based
on previous exposure to similar motions and these motor
recruitment programs are constantly updated.
Based on this premise, trunk dynamics provides a
concise representation of the current status of the trunk
musculoskeletal system. Many studies have found trunk
velocity and acceleration to be better discriminators
between individuals with and without LBD than range
of motion measurements (Table 6). When an individual
becomes injured, the musculoskeletal control program
must be adjusted to compensate for limitations related
to diminished muscle functioning, structural restrictions,
and guarding behavior [81,99]. These adaptations to the
motor control program are manifested in the high-order
motion pro?les (velocity and acceleration) for the individual
with LBD. Although the recruitment pattern will
be changed as a result of the injury, the pattern would be
expected to be consistent. Marras and associates [99]
reported that impairment magni?cation (insincere
e?rt) resulted in more variability in the motion pro?le,
providing further evidence of a central motor recruitment
program that guides trunk motion. Collectively,
these studies point toward trunk motion as a biomarker
of the status of the lumbar spine.
4.1. Other factors that in¯uence trunk motion
Several other factors may in¯uence the trunk motions
of the individual as well as the corresponding biomechanical
outcomes. One factor that may impact how the
exertions are performed is gender. The only studies in
the current review that have evaluated gender di?rences
were limited to strength assessments. These studies
found males to be impacted more by trunk dynamics
than females, that is, males had larger decreases in
strength for dynamic exertions. Males have also been
reported to have higher levels of functional capability to
perform dynamic motions, that is, males are able to
move up to 40% faster than females [79,80]. It may be
this discrepancy in functional capability (strength) that
results in trunk dynamics impacting males more. It
would also be possible that the muscle activity patterns and subsequent spinal loads would be di?rent between
genders, and thus, the impact of trunk motion on the
loads may also be a?cted. Di?rences in muscle activity
and spinal loads may result from strength di?rences as
well as muscle anatomy variations [70±75]. Strength
capability di?rences between the genders may also in-
¯uence the dynamic trunk moments imposed on the
spine.
Trunk dynamics has also been in¯uenced by several
workplace factors such as box weight, task asymmetry,
handles on the box as well as how the lifting task was
performed (e.g. mode of lift). Typically, when the
amount of box weight increased, the trunk motion was
found to decrease by 1±27% in the sagittal plane [110±
115]. Allread et al. [116] found that increased box
weight resulted in larger lateral trunk velocities during
asymmetric lifting. Task asymmetry has a major e?ct
on the trunk motions with more asymmetric tasks
having greater three-dimensional trunk velocities. The
sagittal and lateral trunk motions were found to increase
by 20±50% while a much greater impact was
seen for twisting velocities (100±300% increase in motion)
[110,116,117]. Conversely, one study found no
e?ct of asymmetry of the trunk motions [29]. Sagittal
trunk velocity was found to be higher when handles
were not present on the box by about 3°/s [118]. Thus,
workplace factors have the potential to alter the motions
of the worker, ultimately in¯uencing the spinal
loads and subsequent risk of LBD.
The mode in which the exertion is performed impacts
the trunk motion adopted. Gagnon and Smyth [113]
found that individuals lifted faster as compared to
lowering exertions. The biomechanics during lifting and
lowering were also found to be di?rent with lowering
having greater strength, lower muscle activities, and
higher spinal loading [18,50,119±122]. Marras and
Mirka [49] found strength to increase with lowering
exertions (up to 14%). The number of hands used
during lifting has also been found to in¯uence the trunk
motions with two-handed lifts having more sagittal
motion (10±30% more) and one-hand lifts having more
lateral motion (about 50%) [116,117]. There would appear
to be the potential for the lifting technique adopted
to in¯uence the trunk motion, although the current
results are con¯icting [123,124]. While the results to
date are less than conclusive, the way the exertions are
performed has an impact on the motion within the
trunk.
Individual factors such as anthropometry or LBD
status also can in¯uence trunk motions. Many studies
found the functional capacity of individuals with a LBD
to be diminished by as much as 70% [76,79±81] and had
lower dynamic strengths of about 20±40% [34,40,53,56,
60,64]. The impact of trunk motion on the strength for
these individuals was less than for asymptomatic individuals
[40,60]. Dynamic strength decreased by 27% for
extension, 5% for lateral ¯exion, and 15% for twisting
exertions. On the other hand, Lagrana et al. [40] actually
found increased strength in ¯exion for the dynamic exertions
(about 45%). Body compositions may also have
a role in how an individual performs a certain exertion.
Factors such as body weight and height may alter the
trunk motions. For example, taller individuals may have
to bend farther forward when lifting, possibly causing
Table 6
Summary of studies evaluating the impact of trunk motion on the ability to discriminate between LBP and non-LBP individuals
Study Range of motion Velocity Acceleration
Bishop et al. [100]
Esola et al. [101] NSa
Ferguson et al. [76]
Gomez [102]
Kaigle et al. [103]
Klein et al. [104]
Langrana et al. [40]b
Mandell et al. [43] NSa
Marras et al. [79]
Marras et al. [80]
Marras et al. [81]
Marras and Wongsam [105]
Masset et al. [82] NSa
Mayer et al. [106]
McClure et al. [107] NSa
McIntyre et al. [108]
Pope et al. [109]
* Indicates either mixed results or weaker LBP and non-LBP discrimination ability (e.g. P-values below 0.05 or error rates above 40%).
** Indicates stronger LBP and non-LBP discrimination ability (e.g. P-values below 0.01 or error rates below 25%).
a Indicates no signi?cant LBP and non-LBP discrimination ability (e.g. P-values >0.05 or error rates above 50%.
bNo statistical test performed.
K.G. Davis, W.S. Marras / Clinical Biomechanics 15 (2000) 703±717 713
them to move faster during the exertion. However, research
indicating how body dimensions in¯uence trunk
motions is very limited.
Finally, fatigue of the musculature has also been
found to in¯uence the trunk motions, muscle activities,
and subsequent spinal loading. Several authors have
reported that trunk motion in the primary plane (e.g.
¯exion and extension) decreases as an individual becomes
fatigued while motion in the o?planes (e.g. lateral
¯exion and twisting) increased [125,126]. Sparto
et al. [127,128] found dynamic strength to decrease and a
more stoop lifting style was adopted as the subject fatigued.
Marras and Granata [129] have also reported
that lifting motion changed over a 5-h lifting session,
resulting in decreases in trunk motion but increase in hip
motion. While these studies have provided insight into
how fatigue in¯uence trunk motion, our review failed to
yield any studies that compared the e?ct of fatigue
during dynamic and static exertions, simultaneously. A
better understanding of the impact of fatigue during
dynamic and isometric on trunk strength, muscle coactivity,
and spinal loads is needed.
4.2. Future research
As can be seen from the Tables 1±5, evaluation of
trunk motion has predominantly been performed for
extension exertions or assessing trunk strength. A
complete understanding of the in¯uence of trunk dynamics
will require more studies evaluating the other
biomechanical measures, especially for the non-extension
exertions. More complex motions will also need to
be evaluated. Some of the best insight may come from
assessments that include all directions of exertion within
the same study. There is also a need for additional epidemiological
studies to further establish trunk motion as
a risk factor for LBD since few of these types of studies
exist currently.
Additionally, the development of more easy-to-use
techniques for the quanti?cation of the trunk motion
and the corresponding biomechanical measure needs to
be undertaken. Many of the techniques employed for
the studies in this review require elaborate measurement
devices such dynamometers, motion analysis
systems, and electromyography. While it is important
to have sophisticated measurements to gain an in-depth
understanding, simpler measurement tools will allow
assessment of trunk motion in the actual workplace.
Through improved ability to provide quicker and more
versatile assessment of the workplace, a better understanding
regarding links between trunk dynamics and
risk of LBD may be obtained. Future research needs to
focus on the pathways in which trunk motion may lead
to LBD, particularly linking it to actual incidences of
LBD.
4.3. Potential limitations
Many of the summaries for the various biomechanical
outcomes were based on few studies. While this review
is the ?rst attempt to understand the impact of
trunk motion on common biomechanical measures, the
actual number of high-quality studies was particularly
limited for the non-extension exertions. In several cases,
there were not any studies under a given biomechanical
factor. However, these recommendations do represent
the state of the literature and what is currently known.
With any review, the conclusions drawn are only as
strong as the studies being evaluated. Since di?rent
researchers adopt vastly di?rent measurement techniques
(e.g. di?rent strength assessment devices, controlled
the exertion di?rently, various processing and
testing procedures, etc.) as well as di?rent experimental
conditions, total consensus within the results becomes
dicult. With this in mind, the review attempted to
address this issue by only including studies that control
the trunk motion and have an isometric reference.
However, more rigorous experimental methods may
provide a more de?nitive account of the impact of trunk
motion on the musculoskeletal system.
5. Conclusion
Trunk motion had a dramatic a?ct on the muscle
coactivity, which may dictate other biomechanical outcomes.
It appears the increased muscle coactivation that
accompanies increased trunk motion may be the underlying
source for the decrease strength capability as
well as the increased muscle force, IAP, and spinal
loads. Muscle coactivity may also in¯uence the physical
capability of the individual. Based on the results in the
current review, the ability to perform a task without risk
may be signi?cantly compromised by the muscle coactivity
that accompanies more dynamic exertions. In
addition, many workplace and individual factors have
been found to in¯uence the trunk motions during dynamic
exertions. It is apparent that trunk motion increases
the risk of LBD and to better control LBDs in
industry, more attention to trunk kinematics due to the
job is needed.
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