Page 36 - JSOM Winter 2021

population with chronic LBP during low impact tasks such as LBP. Ultimately a team approach is necessary to reduce injury
walking may further relate the importance of these strategies risk and optimize performance levels for MARSOC personnel.
9
in the military. This is notable in that the military popula-
tion is often subject to high external load during training and Limitations
deployments. This study was not without limitations. Self-reported injury
history was used to determine those with a history of LBP
While lower extremity strength and the activation of the rather than official medical records, in part because active
stretch shortening cycle is likely the driving force behind the military personnel suffering from chronic low back pain may
CTRL group jump height performance, this relationship does not seek treatment and the condition may go unreported. Ad-
not seem to be present in the LBP group. 19–22 This may mean ditionally, we have successfully used self-reported injury his-
that individuals suffering from LBP may use other strategies tory for analysis in previous studies. 4,35 Individuals who were
to achieve the levels of performance as healthy individuals. currently seeking treatment or reported experiencing pain that
The lack of relationship between lower extremity strength prohibited physical or tactical training were excluded from
and jump height in the LBP group, but also the lack of dif- this study. Though this information would have been valuable,
ference in isokinetic strength between the two groups, leads we believe that the alternative strategies employed by those
us to question if there are underlying muscular changes that with LBP are due to prolonged compensations from pain, as
are happening in the LBP group that contribute to the me- all had suffered from LBP for a minimum of 6 months and
chanics beyond strength. In other injured populations with have by this point become learned behaviors. Additionally, it is
well-documented strength deficits, it is theorized that muscle recognized that the plug-in gait marker set may not have been
mechanics and neurological dysfunction are driving strength ideal for this functional analysis. Due to the complexity of the
23
alterations. While LBP is commonly a nontraumatic injury, task, valid and reliable capture of the pelvis trajectories was
there are frequent neurological deficits among those with LBP, difficult and therefore removed the hip joint from the analysis.
even if individuals are not experiencing neurological or radic- Future biomechanical analyses using marker sets that allow
24
ular symptoms. These neurological deficits may be driving for accurate tracking of the hip, pelvis, and trunk, along with
the lack of relationship between strength and performance, reliable frontal plane mechanics, would provide significant in-
leading us to theorize that individuals suffering from LBP may sight into potential compensatory strategies that involve the
be experiencing similar muscular deficits. Further research entire body.
examining lower extremity muscle mechanics in an active
LBP population is necessary to understand and explain these
relationships. Conclusion
Chronic injury, such as LBP, has a significant impact on war-
Overuse injuries – including pain – are commonly reported in fighter readiness. Though this study demonstrates that active
25
military in the lower extremities and low back. Once an injury MARSOC personnel with a history of LBP may still perform
has occurred, the risk of sustaining another injury increases at similar levels to those without a history of LBP, they demon-
significantly. 26–28 Effective strategies to absorb shock and ulti- strate altered relationships to achieving similar levels of per-
mately reduce the cumulative effects of dynamic loading often formance from individuals without LBP. The asymmetrical
involve the knee. For example, reduced knee flexion has been VGRF impulse identified within the LBP group and the rela-
linked to increased peak VGRF during walking, running, and tionships between dominant limb knee and ankle work with
landing, and has been linked to the onset and progression of jump height suggest a potential dominant limb strategy used
a variety of different acute and chronic injuries. These inju- by the LBP group to achieve maximal jump height during a bi-
ries include LBP, anterior-cruciate ligament injuries, and knee lateral explosive task. This difference may help inform military
osteoarthritis. 10, 29–31 MARSOC personnel in the LBP group performance teams when working with individuals suffering
demonstrating asymmetrical loading patterns without corre- from LBP. The differences in relationships to jump height that
sponding asymmetries in strength may indicate the inability to we show here indicate further investigation is needed into the
adequately accommodate increased loading on the dominant compensatory strategies that military individuals with LBP
limb. In this study, asymmetries in VGRF impulse were present make to perform at similar levels as their healthy counterparts.
in LBP group. The impulse of the VGRF curve provides a more
holistic look at overall loading during a task, rather than as- Acknowledgments
sessing load at a single point in time, such as peak VGRF. This Opinions, interpretations, conclusions, and recommendations
provides more insight into which kinematic strategies would are those of the author/presenter and not necessarily endorsed
reduce overall load throughout the force, generating a compo- by the Department of Defense, Office of Naval Research, or
nent of a dynamic movement. The cumulative effects of these the United States Marine Corps Forces Special Operations
asymmetrical loading patterns within the LBP group, along Command.
with the fact that they have a chronic injury, may put them
at a substantially higher risk of developing future musculo- Funding
skeletal injuries. However, appropriate training strategies have Funding for this work was supported by the Office of Naval
been shown to improve balance and landing strategies, and Research (N00014-15-1-0069).
these benefits can be conferred independent of lower extremity
strength. 32–34 These findings suggest that these training strate- Author Contributions
gies could be a viable injury risk mitigation tactic. Many Spe- JW, JA, and NH conceived the study concept. JA obtained
cial Operations Commands have begun to incorporate athletic funding. SR, KP, RS, and JW recruited participants. AJ, SR, KP,
trainers, physical therapists, and performance specialists into RS, NH, JA, and JW coordinated and collected the data, and
their team. This allows for individualized training and reha- AJ, JR, KP, JA, and JW analyzed the data. AJ wrote the first
bilitation programs for servicemembers experiencing chronic draft, and all authors read and approved the final manuscript.

34 | JSOM Volume 21, Edition 4 / Winter 2021