Research Review By Dr. Brynne Stainsby©


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Date Posted:

April 2019

Study Title:

Effect of chiropractic manipulative therapy on reaction time in special operations forces military personnel: a randomized controlled trial


DeVocht JW, Vining R, Smith DL et al.

Author's Affiliations:

Palmer Center for Chiropractic Research, Palmer College of Chiropractic, Davenport, IA, USA; Department of Kinesiology and Health, Miami University, Oxford, OH, USA; Chiropractic Clinic, Blanchfield Army Community Hospital, Fort Campbell, KY, USA; The Spine Institute for Quality (Spine IQ), Davenport, IA, USA.

Publication Information:

BMC Trials 2019; 20(5): published online.

Background Information:

Special operation forces (SOF) are required to maintain high levels of fitness and reaction time in order to respond to diverse and potentially life-threatening situations, both in training and real-world environments. Efficient, high-level neurological function and the ability to integrate sensory information for coordinated motor responses are necessary components of maintaining combat readiness. Theoretically, any dysfunction in the neurological system could lead to delayed reaction/response time, even if it does not result in clinical or observable symptoms (1).

Spinal manipulation may impart some of its therapeutic benefit through spinal and cortical responses in the central nervous system. Spinal manipulation (SM) has been demonstrated to cause plastic changes in sensorimotor integration, particularly within the prefrontal cortex, and appears to alter the net excitability of low-threshold motor units, increase cortical drive and prevent fatigue (2-4). Studies have also demonstrated improved reaction time (5), movement time (6, 7), motor control (8) and muscular strength (9) following spinal manipulation. It is also important to note that no adverse events were reported through these studies (5-9).

While these studies demonstrated short-term improvement, it is unknown if performance can be optimized in a pain-free population with a high level of baseline motor control and coordination skills (like SOF personnel). It is also unknown if multiple applications of SM have a cumulative effect or impart long-term changes. If this is possible, optimizing reaction and response times in SOF military personnel may be able to improve coordination, instantaneous decision-making and overall performance.

The aim of this randomized controlled trial was to determine whether chiropractic manipulative therapy (CMT) can lead to improved reaction and response time in combat-ready SOF personnel with little or no pain.

Pertinent Results:

  • A total of 175 SOF-qualified individuals were screened for eligibility, 55 were excluded and 120 participants were accepted into the trial. Baseline characteristics were similar between the two study groups (chiropractic manipulation and control). The average age of included subjects was 33.
  • Four adverse events were reported during the trial and none were related to trial procedures or participation in the trial.
  • There were no statistically significant between-group differences for any of the five tests, with one exception – the CMT group experienced a larger reduction in the response time (whole body) test at both assessments (p = 0.03). No statistically significant between group differences were observed for any other test.

Clinical Application & Conclusions:

Although this study did not demonstrate statistically significant differences in reaction or response time over a short trial period, this was the first study to explore these variables in healthy, pain-free SOF personnel. Although previous studies have demonstrated improvements in neurological variables following CMT, it must be noted that the population in the current study was exceptionally trained, so it is likely their neuromuscular systems were already functioning optimally (or at least at a better level than average, non-trained people!).

It should be noted that this study did demonstrate a significant difference in whole body response time (pre/post changes) between groups at both assessments, and of note, this test measured the longest total time duration. It remains possible that CMT may influence neurological function in complex and longer-lasting tasks. Future research may examine a potential role of CMT in improving performance of complex motor response tasks in highly trained, asymptomatic SOF personnel.

Although not examined in this study, it is also possible that CMT may positively impact neurological performance in less highly trained individuals or those in pain. For many clinicians, it is likely that patient populations are not as well trained (or as asymptomatic) as this study population, and after screening for contraindications of treatment, a trial of CMT may be indicated. We need more research in this area!

Study Methods:

This prospective RCT was conducted at Blanchfield Army Community Hospital (Fort Campbell, KY, USA). Eligible participants were active duty US military personnel over the age of 19 with the designation of special operation forces (SOF). Exclusion criteria included: average pain intensity in the past week anywhere in the body ≥ 4 (on a 0-10 numerical pain rating scale); bone or joint pathology that constituted a contraindication to CMT; requiring additional diagnostic procedures; being currently treated for traumatic brain injury; pending deployment or other situations that would prevent clinic visits during the trial participation period; or having received CMT within the previous 30 days.

Potential participants attended an initial visit with a project manager and if eligible and interested in participating, they were consented and provided demographic information and their numerical rating of pain intensity. During this first visit, participants then received an examination by one of the trial doctors to screen for contraindications to CMT. If eligible for enrolment, participants were randomly allocated to CMT or wait-list control using concealed allocation in 1:1 ratio by a predetermined, computer-generated randomization scheme. Participants practiced the biomechanical tests below but were not tested during visit one.

During the second visit, participants performed an assessment of five biomechanical tests to assess reaction time (time between the prompt and first body movement) (10) or response time (duration of time occurring between prompt and accomplishment of task) (7):
  1. Simple reaction time of the dominant hand: Participants sat in front of a computer screen holding an electronic switch in their dominant hand, and when a prompt appeared on screen, pressed a switch with their thumb. The test consisted of 11 tests, with the first being discarded and delay between prompts randomly varied from 0.5 to 4s.
  2. Simple reaction time of the dominant foot: Participants sat in front of a computer screen with an electronic pedal switch under their dominant foot, and when a prompt appeared on screen, pressed a switch with their foot. The test consisted of 11 tests, with the first being discarded and delay between prompts randomly varied from 0.5 to 4s.
  3. Choice reaction time: Participants sat in front of a computer screen holding an electronic switch in each hand, and each foot resting on an electronic pedal switch. Prompts appeared on the screen specifying which button or pedal to press. A constant delay of 1s separated each prompt. The test consisted of 41 tests, with the first being discarded.
  4. Response time: Participants sat in front of a computer screen, and a pair of circles appeared on the screen, one contained a computer cursor and one contained the letter X. Once the mouse was clicked, the X disappeared from that circle, appearing in the other circle. The participant moved the cursor back to the original circle and clicked the mouse, completing the sequence. When ready, the participant clicked anywhere on the blank screen and a new pair of circles appeared and the task restarted. The test consisted of 32 circle pair sequences.
  5. Response time (whole body): Participants stood in front of a commercially available device (t-wall) consisting of a panel of 32 touch pad lights, with one pad lit. The test began when the lit pad was hit lightly with the hand, which turned off the light and immediately lit another panel. The test consisted of hitting a series of 100 consecutively lit touch pads. Random sequences were used to prevent anticipation and learning effects.
Following this biomechanical test assessment, participants in the CMT group received a specific, individualized treatment based on clinical evaluation (orthopaedic tests, range of motion testing and spinal palpation). The CMT provided by a doctor of chiropractic with greater than nine years of experience, was high-velocity, low-amplitude (HVLA) and could have been delivered to the cervical, thoracic, or lumbopelvic spinal regions, as appropriate. Following intervention, the biomechanical tests were repeated. The wait-list control group waited 10 minutes between testing. The CMT group received three more treatments (a total of four treatments) over a two-week period. The testing protocol was repeated during visit 5 (the fourth treatment). The wait-list control group simply returned at the same timeframe (approximately 10 days after visit 2).

Sample size was calculated based on power analysis that used the standard deviations of mean changes in reaction and response times over a one-week period for each of the five biomechanical tests in a pilot study. Fifty participants per group would have at least 85% power to detect a 10% or larger difference at a 0.05 level of significance. To account for 15% loss, the sample size was increased to 60 per group (120 subjects). An intention-to-treat approach was used in this trial (participants were analyzed according to their original treatment allocation). The primary analyses compared mean changes in reaction and response time from visit 2 to the final visit between the treatment and waitlist control. The level of significance was set at 0.05. The secondary analyses compared the immediate changes before the CMT to after the CMT at both visit 2 and the final visit using the same methods.

Study Strengths / Weaknesses:

  • This study featured a high-quality, randomized controlled design, assessor blinding, appropriate concealment and subject allocation.
  • They employed a pragmatic design for the intervention (chiropractic spinal manipulation) to increase the external validity (generalizability) of the trial.
  • Calculation of sample size.
  • Intention to treat analysis.
  • The description of the biomechanical tests.
  • The primary limitation of this study (despite being interesting) is the lack of direct clinical applicability for many clinicians, given the highly trained and asymptomatic study population.
  • Given the specific population studied, it is possible the biomechanical tests were too simple, and thus significant differences could not be observed.
  • While the frequency of visits may replicate clinical practice, it is unknown if frequent “treatments” would be required for asymptomatic patients. While this may be considered a strength or a weakness, it is important to consider nevertheless.
  • The generalizability of the results is limited by the strict inclusion/exclusion criteria in this trial.

Additional References:

  1. Leach RA. Neuroimmune hypothesis. In: The chiropractic theories: a textbook of scientific research. 4th ed. Baltimore: Lippincott Williams & Wilkins; 2004: p. 339–61.
  2. Haavik H, Murphy B. The role of spinal manipulation in addressing disordered sensorimotor integration and altered motor control. J Electromyogr Kinesiol 2012; 22: 768–76.
  3. Lelic D, Niazi IK, Holt K et al. Manipulation of dysfunctional spinal joints affects sensorimotor integration in the prefrontal cortex: a brain source localization study. Neural Plast 2016; 2016: 3704964.
  4. Niazi IK, Turker KS, Flavel S et al. Changes in H-reflex and V-waves following spinal manipulation. Exp Brain Res 2015; 233: 1165–73.
  5. Kelly DD, Murphy BA, Backhouse DP. Use of a mental rotation reaction-time paradigm to measure the effects of upper cervical adjustments on cortical processing: a pilot study. J Manip Physiol Ther 2000; 23: 246–51.
  6. Passmore SR, Burke JR, Good C et al. Spinal manipulation impacts cervical spine movement and Fitts' task performance: a single-blind randomized before-after trial. J Manip Physiol Ther 2010; 33: 189–92.
  7. Smith DL, Dainoff MJ, Smith JP. The effect of chiropractic adjustments on movement time: a pilot study using Fitts Law. J Manip Physiol Ther 2006; 29: 257–66.
  8. Marshall P, Murphy B. The effect of sacroiliac joint manipulation on feed-forward activation times of the deep abdominal musculature. J Manip Physiol Ther 2006; 29: 196–202.
  9. Botelho MB, Andrade BB. Effect of cervical spine manipulative therapy on judo athletes' grip strength. J Manip Physiol Ther 2012; 35: 38–44.
  10. Luoto S, Taimela S, Hurri H et al. Mechanisms explaining the association between low back trouble and deficits in information processing. A controlled study with follow-up. Spine 1999; 24: 255–61.