Page 35 - JSOM Winter 2021

TABLE 2 Means and 95% Confidence Intervals of Jump Height, of the stop jump, compared to their nondominant limb. This
Strength, and Biomechanical Variables in Both Limbs and Groups asymmetrical difference was not present in the CTRL group.
CTRL LBP Though the VGRF impulse between limbs was not large
Mean CI Mean CI (0.01% BW/s), this asymmetry may be of clinical importance
Jump height (m) 0.41 0.38–0.44 0.44 0.40–0.47 as it had a moderate effect size of 0.512, and this asymme-
DOM HAM (% BW) 1.38 1.26–1.49 1.34 1.25–1.43 try was not present in the CTRL group. Further, in the CTRL
NDOM HAM (% BW) 1.40 1.28–1.52 1.36 1.28–1.44 group, increased strength significantly correlated with higher
DOM QD (% BW) 2.62 2.41–2.84 2.57 2.41–2.74 jump height, though these relationships were not present in the
LBP group, in which dominant limb knee and ankle work ex-
NDOM QD (% BW) 2.65 2.43–2.87 2.60 2.46–2.74 hibited a relationship to jump height (Table 3). Although the
TE (% BW) 4.03 3.70–4.36 4.14 3.71–4.56 LBP group had similar levels of strength and achieved similar
TF (% BW) 2.40 2.22–2.59 2.46 2.26–2.66 jump height as the CTRL group, it appears that the LBP group
DOM KW (J) 1.49 1.33–1.64 1.44 1.31–1.58 may have used different movement strategies to achieve these
NDOM KW (J) 1.43 1.26–1.60 1.48 1.36–1.59 jump heights. The moderate correlations between jump height
DOM AW (J) 0.73 0.65–0.82 0.80 0.73–0.87 and dominant limb knee (r = 0.467, p = .03) and ankle (r =
NDOM AW (J) 0.77 0.69–0.85 0.77 0.71–0.83 0.447, p = .03) work within LBP suggests a consistent move-
DOM VGRF impulse 0.26 0.24–0.28 0.26 0.24–0.27 ment strategy that relied more on the dominant limb to achieve
(% BW/s)* maximal jump height. This concept agrees with previous lit-
NDOM VGRF impulse 0.26 0.23–0.29 0.25 0.23–0.26 erature assessing joint coordination in individuals with LBP,
(% BW/s)* indicating that those suffering from low back pain tend to use
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SD = standard deviation, % BW = percentage of body weight in kilo- a more consistent strategy than those without low back pain.
grams, DOM = dominant leg, NDOM = nondominant leg, HAM = In the military, where training volumes are large and the train-
hamstring strength, QD = quadriceps strength, TE = trunk exten- ing intensity is high, a less variable compensatory movement
sion strength, TF = trunk flexion strength, KW = knee work, AW = strategy may lead to overloading or an increased risk of injury.
ankle work, VGRF = vertical ground reaction force, LBP = low
back pain group, CTRL = control group, CI = confidence interval.
*Indicates a significant difference between the dominant and nondom- The dominant limb dependent strategy exhibited by the LBP
inant limb in the LBP group. group has been reported previously in individuals with chronic
LBP during low impact tasks, such as walking. This dominant
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TABLE 3 Correlations Between Strength and Biomechanical limb strategy is a compensatory mechanism, in which indi-
Variables to Jump Height viduals with chronic LBP rely more heavily on one limb to
CTRL LBP complete a task in an effort to potentially unload one side of
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DOM QD r = 0.436, p = .043* r = –0.075, p = .748 the body. The significant correlations between jump height
NDOM QD r = 0.571, p = .006* r = 0.073, p = .753 and dominant limb knee and ankle work within the LBP group
DOM HAM r = 0.575, p = .005* r = –0.056, p = .811 further substantiates the idea that the LBP group consistently
relies on the dominant limb during performance. Previous
NDOM HAM r = 0.654, p = .001* r = 0.310, p = .171 literature assessing joint coordination during running has
TES r = 0.663, p = .001* r = 0.310, p = .160 indicated that individuals with LBP move with less variable
TFS r = 0.501, p = .015* r = –0.152, p = .499 movement patterns compared to those who are not experi-
DOM KW r = 0.007, p = .974 r = 0.470, p = .027* encing low back pain. Though compensatory strategies may
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NDOM KW r = 0.064, p = .770 r = 0.345, p = .115 present themselves in a multitude of fashions depending on
DOM AW r = 0.254, p = .242 r = 0.447, p = .037* the specific task at hand, the variability within each specific
NDOM AW r = 0.193, p = .378 r = 0.179, p = .425 compensatory strategy appears to translate across a variety of
DOM VGRF r = –0.320, p = .136 r = 0.138, p = .540 different dynamic tasks. This less variable movement may lead
Impulse to asymmetrical movement patterns and muscle firing tech-
NDOM VGRF r = –0.320, p = .137 r = 0.126, p = .577 niques. Over long and grueling missions, this consistency may
Impulse be repeated numerous times, affecting the muscle response and
r = correlation coefficient; DOM = dominant side; NDOM = nondom- magnitude of load experienced by specific joints or locations
inant side; QD = quadriceps strength; HAM = hamstring strength; within joints, which cumulate over time. Though the overall
TES = trunk extension strength; TFS = trunk flexion strength; KW = load may not be different between LBP and CTRL groups,
knee work; AW = ankle work; VGRF = vertical ground reaction force. if the LBP group experiences consistent asymmetrical loading
*Designates significance (alpha < .05).
patterns more often than CTRL group, this may put them at
an increased risk for the development of secondary chronic
the different biomechanical strategies used to complete a injuries or an increased progression of chronic disabilities.
double-limb stop jump task. There were no group differences
in strength or jump height between LBP and CTRL groups. Individuals experiencing chronic pain may compensate and
Therefore, our primary hypothesis – anticipating reduced per- eventually develop learned behaviors and lasting musculo-
formance in the LBP group compared to healthy controls – skeletal damages. If the asymmetrical loading patterns (VGRF
was not supported. There were also no group differences in impulse) identified in the LBP group during the take-off phase
the biomechanical variables of interest between LBP and the translate to other dynamic tasks, and the LBP group is con-
CTRL group. In partial support of our secondary hypothesis, sistently loading their dominant limb more, it could be hy-
there were inter-limb asymmetries within the LBP group that pothesized that the cumulative effects of such mechanics could
were not present in the CTRL group. MARSOC personnel lead to an increased risk of injury or chronic disability, such
suffering from LBP demonstrated an increased load (VGRF as osteoarthritis in the dominant limb. The fact that dominant
impulse) on their dominant limb during the take-off phase limb dependent strategies have been identified in the general

Loading Patterns in Military Personnel With Back Pain | 33