Trials. 2019 (Jan 3); 20 (1): 5 ~ FULL TEXT
James W. DeVocht, Robert Vining, Dean L. Smith, Cynthia R. Long, Thomas M. Jones and Christine M. Goertz
Palmer Center for Chiropractic Research,
741 Brady St,
Davenport, IA, 52803, USA.
BACKGROUND: Chiropractic manipulative therapy (CMT) has been shown to improve reaction time in some clinical studies. Slight changes in reaction time can be critical for military personnel, such as special operation forces (SOF). This trial was conducted to test whether CMT could lead to improved reaction and response time in combat-ready SOF-qualified personnel reporting little or no pain.
METHODS: This prospective, randomized controlled trial was conducted at Blanchfield Army Community Hospital, Fort Campbell, KY, USA. Active-duty US military participants over the age of 19 years carrying an SOF designation were eligible. Participants were randomly allocated to CMT or wait-list control. One group received four CMT treatments while the other received no treatment within the 2-week trial period. Assessment included simple hand/foot reaction time, choice reaction time, and Fitts' Law and whole-body response time. On visits 1 and 5, the same five assessments were conducted immediately pre- and post-treatment for the CMT group and before and after a 10-min wait period for the wait-list group. Primary outcomes included between-group differences for the pre-CMT/wait-list period at visit 1 and visit 5 for each test. Secondary outcomes included between-group differences in immediate pre- and post-(within visit) changes. Analysis of covariance was used for all data analysis.
RESULTS: One hundred and seventy-five SOF-qualified personnel were screened for eligibility; 120 participants were enrolled, with 60 randomly allocated to each group. Due to technical problems resulting in inconsistent data collection, data from 77 participants were analyzed for simple hand/foot reaction time. The mean ± standard deviation (SD) age was 33.0 ± 5.6 years and all participants were male. No between-group statistically significant differences were found for any of the five biomechanical tests, except immediate pre- and post-changes in favor of the CMT group in whole-body response time at both assessment visits. There were four adverse events, none related to trial participation.
CONCLUSIONS: A single session of CMT was shown to have an immediate effect of reducing the time required for asymptomatic SOF qualified personnel to complete a complex whole-body motor response task. However, sustained reduction in reaction or response time from five tests compared with a wait-list control group was not observed following three sessions of CMT.
TRIAL REGISTRATION: ClinicalTrials.gov,
NCT02168153 Read the original proposal here
KEYWORDS: Chiropractic; Military; Reaction time; Response time; Special Operations Forces; Spinal manipulative therapy
From the FULL TEXT Article:
United States military special operation forces (SOF)
personnel are required to maintain high levels of physical
fitness and the ability to perform activities requiring quick
reactions to diverse situations, including those that can be
life-threatening. Therefore, a high level of neurological
function is one necessary component of maintaining the
combat readiness of SOF personnel.
Efficient conscious and unconscious processing of sensory
information resulting in coordinated motor responses
are necessary for activities requiring prompt reactions to
different sensory stimuli. Compromised sensory stimulus
transmission, interpretation of such stimulus, or improper
synchronization of responses can result in delayed,
inaccurate, or uncoordinated reactions. Theoretically, any
dysfunction within these complex neurological pathways,
which may not be observable via symptoms, could lead to
aberrant reactions or delayed reaction and/or response
Spinal manipulation, the primary treatment delivered
by doctors of chiropractic is thought to impart some of
its therapeutic benefit through several complex neurological
mechanisms involving both spinal and cortical regions
of the central nervous system. Research indicates
that spinal manipulation causes plastic changes in sensorimotor
integration within the central nervous system
in human participants, particularly within the prefrontal
cortex. [2, 3] Spinal manipulation appears to alter the
net excitability of low-threshold motor units, increase
cortical drive, and prevent fatigue.  These neurological
mechanisms may explain improved reaction time , movement time [6, 7], motor control , and muscular
strength  following spinal manipulation. Kelly et
al. found a significant improvement in a complex reaction
time task after receiving spinal manipulation. 
Both Smith et al.  and Passmore et al.  reported
that hand and head movements in response to visual
stimuli were completed more quickly after participants
received spinal manipulation. Daligadu et al.  reported
results from 10 volunteers with subclinical neck pain who
completed specified keypad input sequences more quickly
after receiving spinal manipulation. No adverse events
(AEs) were reported in any of these studies.
Although prior studies suggest that spinal manipulation
can positively influence reaction and response time in the
short-term, it is unknown if performance can be optimized
in persons with little or no pain and with high-level motor
control and coordination skills. If changes do occur, it is
not yet known if multiple applications convey a cumulative
effect, or if longer-term changes occur. Optimizing reaction
and response time in SOF military personnel has the
potential to improve performance in activities requiring
rapid and accurate hand-eye coordination and instantaneous
decision making leading to physical movement of the
hands, arms, or legs. Improved and coordinated reactions
and responses to specific stimuli can be vital during combat
military operations and other activities by reducing
cognitive processing time. Understanding whether spinal
manipulation has such an effect in persons with high-level
physical capability also sheds more light on potential
mechanisms influenced by spinal manipulation. This
randomized controlled trial (RCT) was conducted to
answer the question: does chiropractic manipulative
therapy (CMT) lead to improved reaction and response
time in combat-ready SOF personnel reporting little or
Setting and participants
A protocol describing detailed trial methods has been
previously published.  This prospective RCT was
conducted at Blanchfield Army Community Hospital, Fort
Campbell, KY, USA. Active-duty US military participants
over the age of 19 years carrying the designation of SOF
were eligible. The trial was approved by the following
institutional review boards: Rand Corporation, Palmer
College of Chiropractic, and Dwight D. Eisenhower Army
Medical Center. Oversight also occurred by an independent
data and safety monitoring committee. All participants
provided written informed consent. Participants were not
compensated for participation.
Exclusion criteria included: average pain intensity over
the past week anywhere in the body rated ≥ 4 on a 0 (no
pain) to 10 (worst possible pain) numerical rating scale;
bone or joint pathology that constituted contraindication to
receiving CMT; requiring additional diagnostic procedures;
being currently treated for traumatic brain injury; pending
deployment or other situations that would prevent clinic
visits during the 2–4 weeks of the trial participation period;
or having received CMT within the previous 30 days.
Initially, the upper age limit was restricted to 45 years
and SOF personnel did not include women due to technical
subclassifications of SOF personnel. After 41 participants
were enrolled, eligibility criteria were changed to remove
the upper age limit and to allow women and those who
otherwise qualified for SOF.
Potential participants attended an initial visit with a project
manager, which comprised a consent process when all
aspects of trial participation were explained. If eligible
and interested in joining, participants signed an institutional
review board-approved informed consent document. Following
the informed consent process, participants reported
demographic information and a numerical rating scale of
pain intensity. The project manager then screened for nonclinical
eligibility criteria. Eligible participants received an
examination by one of the trial doctors of chiropractic to
screen for contraindications to chiropractic care. Participants
were eligible for enrollment when no contraindications
were identified. At the end of the first visit,
eligible participants were randomly allocated to one of
two groups: CMT or wait-list control. Enrolled participants
also practiced each of the five biomechanical tests
(see Biomechanical tests section below).
Group assignment was performed using concealed allocation
in a 1:1 ratio by a predetermined, computer-generated,
restricted randomization scheme with random block sizes.
The project manager, who had no knowledge of details of
the randomization process, accessed a secure, web-based
computer allocation module designed for this trial. Once
allocated, the project manager notified participants of their
During visit 2, all participants performed the first assessment
consisting of five biomechanical tests. At the beginning
of visit 2, all participants performed each of the five
tests twice. Participants in the CMT group performed all
five tests prior to the first treatment. After treatment, all
five tests were again completed. Those in the wait-list control
group did not receive CMT. Instead, wait-list group
participants performed all five tests followed by a 10-min
wait period before again performing each test. Participants
in the CMT group received three more treatments for a
total of four treatments over a 2-week period. Those in
the wait-list control group did not have visits between
biomechanical assessments. The testing protocol was
repeated during the final visit (visit 5) and concurrent
with the fourth CMT session for those in the CMT
The final assessment visit (visit 5) was held approximately
10 days after visit 2. Therefore, the two assessment
visits for participants in both groups were separated by
the same time frame. Following the final visit, those in the
wait-list control group were offered the opportunity to
receive four sessions of CMT over 2 weeks, just as those
in the CMT group received during trial participation.
CMT for this trial was provided by two doctors of chiropractic
serving as providers within the military treatment
facility, each with more than 9 years of experience. The
specific treatment given at each visit was determined
individually by information obtained from clinical evaluation,
which included standard orthopedic tests, range-ofmotion
assessments, and spinal palpatory examination.
The CMT provided was composed of high-velocity,
low-amplitude (HVLA) spinal manipulation procedures  consisting of manually applied thrusts to cervical,
thoracic, or lumbo-pelvic areas when indicated by analyzing
factors such as comorbid or complicating diagnoses, prior
response to care (if known), local tenderness, hypertonicity,
hypomobility, positions of relief and provocation, and other
individual factors. 
Five tests measured reaction or response time. Reaction
time was defined as the length of time occurring between
a prompt and the first body movement in response to the
prompt. Reaction time tests were modeled after those
reported by Luoto et al.  Response time was defined
as the duration of time occurring between a prompt and
accomplishment of a task involving both reaction and
movement time. 
Simple reaction time of the dominant hand
Participants sat in front of a computer screen holding
an electronic switch in their dominant hand. When a
prompt appeared on the screen, participants pressed a
switch with the thumb of their dominant hand. The test
consisted of a series of 11 prompts, with the results from
the first prompt being discarded. The time between a
button press for one prompt and the appearance of the
next prompt randomly varied from 0.5 to 4 s.
Simple reaction time of the dominant foot
This test was conducted in the same manner as the reaction
time test for the dominant hand except participants
pressed an electronic pedal switch with the dominant
foot upon recognizing the computer screen prompt.
Choice reaction time
Participants again sat before a computer screen holding
an electronic thumb switch in each hand. Each foot rested
on an electronic pedal switch. Prompts appeared on the
screen specifying which button or pedal to press. For this
test, a constant 1-s delay separated the press of a button
or pedal and the appearance of the next prompt. This test
consisted of a series of 41 prompts. Response to the first
prompt was not included in the results.
Fitts’ Law was used with methods drawn from Smith et
al.  Participants again sat in front of a computer
screen. This test consisted of a series of pairs of circles.
Each time a pair of circles appeared on the screen, one
circle included the letter X while the other contained the
computer cursor (Figure 1). Participants, using the mouse,
moved the cursor from one circle to the circle with the X.
Once inside, the mouse was clicked. Immediately upon
the click, the X disappeared from that circle, appearing instead
in the circle where the cursor was originally located.
Participants then moved the cursor back to the original
circle and clicked the mouse, completing the sequence.
When ready to continue, participants clicked anywhere on
the blank screen, which caused the next pair of circles to
appear and reactivated the electronic timer. Timing for
the test was recorded only when circles were visible on
the computer screen. Participants took as much time as
needed between each sequence. The test consisted of a
series of 32 circle pair sequences. Circles within each pair
were identical in size, but different pairs were oriented differently
with variably sized circles. The distance between
all circle centers for each test pair was identical.
Response time (whole body)
The t-wall® (Motion Fitness, Rolling Meadows, IL, USA)
is a commercially available device consisting of a panel
of 32 touch pad lights (Figure 2). Each panel is 8 × 8 inches
arranged in a 4 × 8 foot array. Participants stand in front
of the wall with one touch pad lit. The test begins when
the pad that is hit lightly with the hand, which turns off
the light and immediately lights another panel. The test
consists of hitting a series of 100 consecutively lit touch
pads in random sequence. Timing for this test begins when
the participant hits the first lit touch pad and ends when
the last panel in the sequence is hit. Participants were
encouraged to complete each test as quickly as possible.
Two random sequences were used for each test to prevent
anticipation and a learning effect. Each of the five tests used
in this trial are described in greater detail in the trial
protocol . Data management personnel responsible
for processing raw data were blinded to group assignment.
An intention-to-treat approach was used in which participants
were analyzed according to their original treatment
allocation. Data analyses were performed using SAS (version
9.4, Cary, NC). Because age eligibility changed mid-way
through the trial, age was controlled for in the data analyses.
The primary analyses compared the mean changes in
reaction and response time from sequence A, performed
before the CMT/break at visit 2, to sequence A
performed before the CMT/break at the final visit (visit
5) between the treatment and wait-list control groups,
using an analysis of covariance controlling for age for
each of the five biomechanical tests. We did not control
for analyzing multiple outcomes. Between-group mean
differences from the analysis of covariance were reported,
adjusted for age, with 95% confidence intervals. The level
of significance was set at 0.05. The secondary analyses
compared the immediate changes in sequence A before
the CMT/break to sequence A after the CMT/break at
both visit 2 and the final visit using the same methods
The sample size for this trial was based on a power
analysis that used the standard deviations (SDs) of
mean changes in reaction and response times over a
1-week period for each of the five biomechanical variables
obtained in a pilot study. The calculations were
based on an estimated effect size of a 10% change after
CMT of the mean reaction or response time as measured
in the first assessment for each variable with the
assumption that the wait-list control group would have
no change. Fifty participants per group would have at
least 85% power to detect a 10% or larger difference at
a 0.05 level of significance in mean change between
groups. To account for the possibility of a 15% loss to
follow-up, we increased the total sample size to 120,
with 60 per group.
During the enrollment period, 175 SOF-qualified individuals
were screened for eligibility as shown in the trial
flow diagram (Figure 3). Of those, 55 were excluded, resulting
in 120 participants. The first participant was enrolled
on 30 September 2014 and data collection was completed
on 7 June 2016. The two most common reasons
for exclusion were not being SOF qualified and scheduling
conflicts. Participants were primarily referred to the
project manager from physical therapists (49) and other
healthcare providers.  The remainder of the participants
were recruited from informational presentations by
the site project manager (24), informational emails (6), and
the SOF newsletter (3). Adverse events were defined as any
unexpected or unusual medical occurrence during the
conduct of the trial that may or may not have a causal
relationship with trial procedures. 
Four adverse events were reported during the course
of this trial. None were related to trial procedures. Two
participants suffered minor knee injuries, one while running
down stairs (meniscal inflammation) and another during a
military training exercise (patellar bruise). One participant
reported upper back pain while exercising at a gym.
Another reported aggravation of a pre-existing umbilical
hernia while exercising at a gym. No adverse event was
severe enough to restrict participation in the trial. All
adverse events were evaluated and managed by nontrialrelated
military healthcare providers.
Table 1 displays baseline characteristics. The mean ± SD
age of participants was 33.0 ± 5.6 years and all participants
were male. Characteristics were similar between groups.
Table 2 contains the results of the five biomechanical
outcome measures obtained from the two different assessment
sessions. Reaction time tests are displayed as mean
duration for participants reacting to a single prompt. The
response times shown (Fitts’ Law and t-wall®) represent
the total time needed to complete the entire sequence of
prompts for each test. There are additional missing data
for the simple hand and simple foot reaction tests due to a
problem in early data collection. The connection between
the computer software program (Paradigm software package,
Perception Research Systems, Inc.) and the MP150
Data Acquisition System (BIOPAC Systems, Inc.) was
reset inconsistently after each response resulting in inaccurate
reaction time computation. Once identified,
the problem was corrected. Because data collected before
the technical issue was corrected were unreliable and
likely inaccurate, they were not included in the analysis
for these two measures. There were no statistically significant
between-group differences during this time period
for any of the five tests.
Tables 3 and 4 display immediate changes in the five
biomechanical tests performed prior to receiving CMT or
the 10-min wait period during the first assessment and
second assessment, respectively. The CMT group experienced
a larger reduction in t-wall® response time following
treatment than the wait-list group at both assessments
(P = 0.03). No statistically significant between-group differences
were observed for any of the other tests in either
To our knowledge this trial is the first to explore reaction
and response time in US military SOF personnel following
a short course of CMT. We found no statistically significant
differences in reaction or response time over
the trial period, which lasted approximately 2 weeks.
Response time measured with the t-wall® showed a significant
difference in immediate (pre- and post-) changes
between groups, observed during both assessments. There
were no statistically significant between-group differences
in immediate pre- and post-measures for the other four
In general, findings are inconsistent with the research
literature that reports improved reaction and response
time following spinal manipulation. [5–8] This apparent
inconsistency may be due to the high-level physical conditioning
characteristic of SOF personnel. In such individuals,
neuromuscular systems already function at optimum or
near-optimum levels and further improvement in reaction
or response time may not be possible, regardless of
intervention. This trial did not assess whether reaction
or response time for non-SOF-qualified individuals or
those with musculoskeletal symptoms are influenced by
CMT. The trial is limited by the loss of data due to
inaccurately computed simple hand and foot reaction
times for a subset of participants. Although results could
possibly be different if data from the entire sample were
consistently collected and analyzed, findings are consistent
with results from the other three assessments in this trial.
Therefore, it seems unlikely that the lower number of participants
analyzed for these two tests had much influence
on overall findings.
Of the five tests used in this trial, the t-wall® test measured
the longest continuous response time, lasting approximately
1 min. The immediate performance improvement in the
CMT group at both visits observed in this trial suggests
that CMT may influence complex tasks that require
longer continuous periods of time to complete, suggesting
the need for further research in this area to understand
the underlying neuromuscular mechanism(s) at work.
Similarly, it is possible that conducting Fitts’ Law tests
with more trials, or possibly trials with smaller circles
making it more difficult, might enable discernment of
differences between groups.
A single session of CMT was shown to have an immediate
effect of reducing the time required for asymptomatic
SOF-qualified personnel to complete a complex motor
response task. However, three sessions of CMT did not
induce sustained reduction in reaction or response time
associated with five different biomechanical tests compared
with a wait-list control group.
The RCT discussed in this article was registered on ClinicalTrials.gov with the NCT02168153.
The initial version sent to ClinicalTrials.gov was received on 12 June 2014.
The authors acknowledge Darla Freehardt, Chiropractic Clinic, Blanchfield Army
Community Hospital, Fort Campbell, KY, USA, for her day-to-day contributions
to trial procedures, Qian Li, Palmer Center for Chiropractic Research, Davenport,
IA, USA, for his assistance with statistical analysis of data, and Dr. Lynn Giarrizzo
who served as the medical monitor.
This trial was funded by the Department of Defense Office of
Congressionally Directed Medical Research Programs, Defense Health
Program Chiropractic Clinical Trial Award (W81XWH-11-2-0107). Part of this
project was conducted in a facility constructed with support from Research
Facilities Improvement grant number C06 RR015433 from the National
Center for Research Resources, National Institutes of Health. The
identification of specific products or scientific instrumentation does not
constitute endorsement or implied endorsement on the part of the authors,
the Department of Defense, or any component agency.
CG was responsible for obtaining funding and provided global oversight for
initiation and development of the trial. JWD and DLS developed the
biomechanical assessments and processed outcome measure data. CL
performed the statistical analysis. TJ developed the treatment protocol and
served as the site principal investigator. RV developed and oversaw the
eligibility determination process, and monitored and graded adverse events.
JWD, DLS, CL, and RV developed the manuscript. All authors read and
approved the final manuscript.
The authors declare that they have no competing interests.
AE: = Adverse event;
CMT: = Chiropractic manipulative therapy;
HVLA: = High-velocity, low-amplitude;
RCT: = Randomized controlled trial;
SD: = Standard deviation;
SOF: = Special operations forces
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