Page 33 - JSOM Winter 2021

This is especially true during high performance tasks, such Three-dimensional motion capture was used to capture lower
as a double-limb stop jump in which side-to-side movement extremity mechanics during the landing phase of the double-
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asymmetries have been previously observed. For example, limb stop jump. Lower extremity segments were defined and
a stop jump type of task translates easily to military opera- tracked using the plug-in-gait marker set. Retro-reflective
tions, such as scaling walls and jumping across and over ter- markers were placed at the following anatomical landmarks:
rain. Therefore, the purpose of this project was to determine bilateral anterior superior iliac spine, posterior superior iliac
if military personnel with chronic low back pain have reduced spine, lateral thigh, lateral femoral epicondyle, lateral shank,
performance, and if they use a different strategy to complete a lateral malleolus, posterior heel, and head of second metatarsal.
functional performance task as compared to healthy military Anthropometric calipers and a tape measure were used to col-
personnel. We hypothesize that those with chronic low back lect lower extremity leg length, knee diameter, and ankle inter-
pain will have reduced performance and asymmetrical lower malleolar distance for the plug-in-gait model. Kinematics were
extremity mechanics compared to healthy individuals. collected at 200 Hz with an eight-camera three- dimensional
motion capture system (Vicon, https://www.vicon.com/) and
marker trajectories were filtered using a fourth-order lowpass
Methods
Butterworth filter with a cutoff of 6 Hz. Ground reaction
United States Marines were recruited from the United forces captured on two in-ground force plates (Type 9286BA,
States Marines Corps Forces Special Operations Command Kistler Instrument Corp., https://www.kistler.com/en/) and
( MARSOC) individual training program classes as part of a raw vertical ground reaction forces (VGRF) were sampled at
larger surveillance study. Those who reported they had suffered 1200 Hz. These were filtered using a fourth order low-pass
from chronic low back pain for a minimum of 6 months were Butterworth filter with a cutoff of 50 Hz. All biomechanical
included in this study. Inclusion in the low back pain group data were processed using Visual 3D (C-Motion, https://www
included individuals who (1) indicated they were experiencing .c-motion.com/). Jump height was calculated from the posi-
low back pain but were also currently cleared for full and un- tion of the posterior superior iliac spine makers from the point
restricted participation in physical and tactical training despite of takeoff, as determined by the force plates, to peak vertical
pain, (2) reported no history of other lower extremity injuries trajectory. Knee and ankle joint work were calculated as the
within the past year that led to the cessation of training, and integral of the joint power curves during the take-off the stop-
(3) had no history of lower extremity surgery. Individuals were jump (Figure 2). For the take-off phase, VGRF impulse was
excluded from the low back pain group if they were experienc- calculated as the area under the curve of the VGRF.
ing radicular low back pain, had been previously diagnosed
with a musculoskeletal deformity (such as scoliosis), or had a FIGURE 2 Double limb stop jump knee power curve in which joint
diagnosis that represented arthritis of the back. Additionally, work is calculated from, with the highlighted portion representing
the area under the curve of the power generation phase, indicated as
a subset of healthy controls was identified. Those included in positive knee work.
the healthy control group (CTRL) did not report any lower ex-
tremity injuries within the past year, history of lower extremity
surgery, or history of back pain, injury, or surgery. Individuals
were asked to limit any strenuous physical training, avoid caf-
feine, nicotine, and alcoholic beverages for 24 hours prior to
testing. The study was approved by the University of Kentucky
Institutional Review Board with all individuals having signed
a written informed consent prior to their participation.

All individuals completed a double-limb stop jump perfor-
mance task. The stop jump task was performed with the indi-
vidual positioned with both feet, at a distance of 40% of their
height away, from the edge of the force platform. They were
instructed to perform a double-limb broad jump to the force
platforms, land with one foot on each platform, and immedi-
ately perform a maximal vertical jump. The stop-jump has two
phases, a landing phase (ground contact to peak knee flexion)
and a take-off phase (peak knee flexion to toe-off). For the
purpose of this study, we focused on performance measures.
Thus, we only included variables from the take-off phase of
the stop jump (Figure 1, Supplementary Media File). Maximal voluntary isokinetic quadriceps and hamstring
strength (Figure 3), and trunk extension and flexion strength
FIGURE 1 Skeleton animation of double limb stop jump, (Figure 4) were assessed using the Biodex System 4 isokinetic
highlighting the take-off phase, in which outcome variables are dynamometer (Biodex Medical Systems, https://www.biodex
extracted from. .com/), during a standard concentric/concentric protocol at
60°/s. 15,16 Each individual completed two practice trials at a
50% effort and one practice trial at 100% effort before com-
pleting five recorded maximal effort trials. Two minutes of rest
was provided between each trial. Consistent verbal encourage-
ment was provided throughout the testing protocol. Strength
was determined by the average of five repetitions and normal-
ized to body weight (% BW).

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