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Trial registered on ANZCTR

Registration number
Ethics application status
Date submitted
Date registered
Date last updated
Type of registration
Prospectively registered

Titles & IDs
Public title
The effects of a single session of spinal manipulation on power, strength, and cortical drive in athletes
Scientific title
The effects of a single session of spinal manipulation on power, strength, and cortical drive in Taekwondo athletes
Secondary ID [1] 288376 0
Universal Trial Number (UTN)
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Functional performance, including strength, power, muscle fatigue and cortical drive in an athletic population 297374 0
Condition category
Condition code
Musculoskeletal 297557 297557 0 0
Normal musculoskeletal and cartilage development and function
Neurological 297558 297558 0 0
Studies of the normal brain and nervous system
Physical Medicine / Rehabilitation 297588 297588 0 0
Other physical medicine / rehabilitation

Study type
Description of intervention(s) / exposure
A single session of spinal manipulation as intervention performed by a registered chiropractor. The duration of the session is approximately 30 minutes. The study is a crossover trial with a one week washout period between each treatment. The entire spine and both sacroiliac joints will be assessed for segmental dysfunction, and treated where deemed necessary by a registered chiropractor. The clinical indicators that will be used to assess the function of the spine prior to and after each spinal manipulation intervention include assessing for tenderness to palpation of the relevant joints, manually palpating for restricted intersegmental range of motion, assessing for palpable asymmetric intervertebral muscle tension, and any abnormal or blocked joint play and end-feel of the joints. All of these biomechanical characteristics are used by the chiropractors as clinical indicators of spinal dysfunction. All of the spinal manipulations carried out in this study will be high-velocity, low-amplitude thrusts to the spine or pelvic joints. This is a standard manipulation technique used by chiropractors and is also sometimes referred to as spinal adjustments. The mechanical properties of this intervention have been investigated; and although the actual force applied to the subject's spine depends on the therapist, the patient, and the spinal location of the manipulation, the general shape of the force-time history of spinal manipulations is very consistent and the duration of the thrust is always less than 200 milliseconds. The high-velocity type of manipulation is chosen specifically because previous research has shown that reflex electromyographic activation observed after manipulations only occurred after high-velocity, low-amplitude manipulations (as compared with lower-velocity mobilizations). This manipulation technique has also been previously used in studies that have investigated the neurophysiological effects of spinal manipulation. The chiropractor providing the spinal manipulation will be recording a log of all manipulations performed to monitor adherence.
Intervention code [1] 293676 0
Treatment: Other
Comparator / control treatment
The subject’s head and/or spine will be moved in ways that include passive and active movements in flexion, extension, lateral flexion, rotation etc., similar to what is done by the chiropractor that provide actual chiropractic treatment during the spinal manipulation intervention. This is intended to act as a sham treatment.
Control group

Primary outcome [1] 297115 0
Change in absolute maximum force of contraction (strength/MVC).
Muscle force, including maximum isometric plantarflexion force, will be measured using an isometric strain gauge (Model MLP100 transducer Techniques Tennecula, California, USA) mounted on a custom-built platform. The athletes will perform three progressive maximum voluntary contractions (MVC) of the ankle plantar flexors of five seconds duration each, separated by two-minutes rest. During the procedure, the athletes will be verbally encouraged to produce maximal force. The highest plantar flexor EMG activity during MVC and absolute force measured in each intervention (spinal manipulation and control intervention) will be used for analysis and to compute the submaximal target contraction levels for H- and M-recruitment curve recordings.
Timepoint [1] 297115 0
Pre and post intervention (spinal manipulation) sessions and pre and post control sessions
Secondary outcome [1] 320049 0
The rate of change of force (power) is assessed using an isometric strain gauge during plantar flexion.
Explosive strength has been quantified as the contractile rate of force development (RFD), and the contractile impulse (CI), during a maximal isometric contraction. Contractile RFD is quantified from the slope of the force- (or torque) time curve. CI is identical to the kinetic impulse, (or angular momentum), reached during limb movement and CI directly determines the rotational angular velocity of the distal segment at a given time point. RFD and CI will be calculated based on the slope of force-time curve and integral of the force-time curve associated with the MVC’s that are performed during the strength assessment.
Timepoint [1] 320049 0
Pre and post intervention (spinal manipulation) sessions and pre and post control sessions
Secondary outcome [2] 320050 0
Change in median frequency of the power spectrum (fatigue) is assessed using an isometric strain gauge during plantar flexion.
Fatigue development of a muscle can be observed either by an amplitude and spectral analysis of EMG recordings or absolute force values. In this study, we will measure both. The time-dependent shift in mean power frequency (MPF) of electromyographic (EMG) signals to lower frequencies during the fatigue process is a well-established phenomenon. EMG will be recorded during MVC pre and post spinal manipulation or control intervention to measure fatigue. MVC data segments will be epoched offline and processed in Matlab using purpose-written scripts. A Fast Fourier Transformation (FFT) will be performed and the MPF calculated as the frequency (Hz) centre of the spectrum.
Timepoint [2] 320050 0
Pre and post intervention (spinal manipulation) sessions and pre and post control sessions
Secondary outcome [3] 320051 0
Change in h-reflex and m-wave (cortical drive).
This is a composite secondary outcome. The athlete will perform a low-level tonic contraction of the plantar flexors (10% MVC) while the direct motor response (M-wave) and H-reflex of the soleus muscle (SOL) will be elicited. To ensure the athletes are able to contract 10% of their MVC, they will be provided with online feedback of the contraction level exerted, which is displayed on a clearly visible computer monitor.
Timepoint [3] 320051 0
Pre and post intervention (spinal manipulation) sessions and pre and post control sessions
Secondary outcome [4] 320052 0
Change in v-wave (cortical drive).
Pre and post spinal manipulation or control sessions the athletes will perform seven MVC’s of five seconds duration with a two minutes rest period in between. During these contractions, five supramaximal stimuli (110% of the current needed to evoke maximal M wave; 1 ms square pulse) will be applied to the tibial nerve at the instant that the force exceeded 90% of the MVC.
Timepoint [4] 320052 0
Pre and post intervention (spinal manipulation) sessions and pre and post control sessions

Key inclusion criteria
Participants will be representative Taekwondo athletes who live in the Auckland area of New Zealand. To be eligible to participate volunteers must have represented their club at the senior premiership level during the previous 12 months, or represented their province or country within the previous 12 months. They must also have been actively engaged in resistance training at least twice per week on average over the previous six weeks.
Minimum age
18 Years
Maximum age
40 Years
Both males and females
Can healthy volunteers participate?
Key exclusion criteria
Subjects will be ineligible to participate if they exhibit no evidence of spinal dysfunctions, have absolute contraindications to spinal manipulation, have experienced previous significant adverse reactions to spinal manipulation, or if they are currently being treated for their subclinical pain symptoms.

Study design
Purpose of the study
Allocation to intervention
Randomised controlled trial
Procedure for enrolling a subject and allocating the treatment (allocation concealment procedures)
Participants will be randomised using a computer generated random number table to first receive spinal manipulation.
Participants and the chiropractors providing care during the study will not be blinded to group allocation. Outcomes assessors and data analysts will remain blinded to group allocation throughout the study period.
Methods used to generate the sequence in which subjects will be randomised (sequence generation)
Dynamic (adaptive) random allocation method (Minimizer)
Masking / blinding
Blinded (masking used)
Who is / are masked / blinded?

The people assessing the outcomes
The people analysing the results/data
Intervention assignment
Other design features
Not Applicable
Type of endpoint(s)
Statistical methods / analysis
Sample size calculations are based on detecting a difference in a continuous response variable from independent control and experimental participants with one control per experimental participant. Calculations are made based on the changes observed in our previous study that investigated changes in force in lower limb muscles pre and post a spinal manipulation session. If the true difference in mean MVC between the experimental session and the control session has an effect size of 0.5 we will need 11 participants to be able to reject the null hypothesis that the population means of the experimental and control groups are equal with probability (power) 0.8. The Type I error probability associated with the test of this null hypothesis is 0.05. To allow for attrition during the trial and relative uncertainty relating to power outcomes we will enrol 15 participants in this trial.

Statistical analysis:
A multifactorial repeated measures ANOVA will also be used to assess for within and between group differences. TIME (pre and post intervention measures) and INTERVENTION (spinal manipulation vs control) will be used as factors. A priori pairwise comparisons of the pre and post intervention data will be carried out when an interactive effect is significant. Significance will be set at P = .05.

Recruitment status
Date of first participant enrolment
Date of last participant enrolment
Date of last data collection
Sample size
Accrual to date
Recruitment outside Australia
Country [1] 7543 0
New Zealand
State/province [1] 7543 0

Funding & Sponsors
Funding source category [1] 292728 0
Name [1] 292728 0
Address [1] 292728 0
Dampfaergevej 22,
2100 Copenhagen,
Country [1] 292728 0
Funding source category [2] 292730 0
Name [2] 292730 0
Centre for Chiropractic Research, New Zealand College of Chiropractic
Address [2] 292730 0
6 Harrison Rd,
Mt Wellington,
Auckland 1060
Country [2] 292730 0
New Zealand
Primary sponsor type
Centre for Chiropractic Research, New Zealand College of Chiropractic
6 Harrison Rd,
Mt Wellington,
Auckland 1060
New Zealand
Secondary sponsor category [1] 291461 0
Name [1] 291461 0
University of Southern Denmark
Address [1] 291461 0
Campusvej 55,
5230 Odense M,
Country [1] 291461 0

Ethics approval
Ethics application status
Ethics committee name [1] 294216 0
Southern Health and Disability Ethics Committees
Ethics committee address [1] 294216 0
Ministry of health
PO box 5013
Wellington 6011
Ethics committee country [1] 294216 0
New Zealand
Date submitted for ethics approval [1] 294216 0
Approval date [1] 294216 0
Ethics approval number [1] 294216 0

Brief summary
Over the past ten years several research groups have demonstrated that spinal manipulation can change various aspects of nervous system function, including altered motor control, cognitive processing, reaction time, and the speed at which the brain processes information.Although motor control is altered after spinal manipulation, it is not yet clear if these alterations result in clinically significant changes to outcomes that are important for functional performance. Three aspects of motor function that are important for human performance are strength, power and muscle fatigue. However we recently published and presented three trials that demonstrated that a single session of spinal manipulation performed by a chiropractor increased muscle force and reduced fatigue in healthy young adults. This may have clinical implications for a variety of patient populations and in particular athletes are likely to benefit from gains in power and strength if they occur following spinal manipulation. Further research is now required to investigate whether similar findings are observed following spinal manipulation in athletes who already have high levels of power and strength before being treated. This proposed study will build on our previous work by investigating whether spinal manipulation influences muscle strength, power, fatigue and cortical drive in athletes. The study will involve a single pre and post manipulation assessment during each arm of this crossover trial. Study participants will be 15 high level athletes.
Trial website
Trial related presentations / publications
Public notes

Principal investigator
Name 62914 0
Dr Heidi Haavik
Address 62914 0
New Zealand College of Chiropractic
6 Harrison Road
Mount Wellington
Auckland 1060
Country 62914 0
New Zealand
Phone 62914 0
+64 95266789
Fax 62914 0
Email 62914 0
Contact person for public queries
Name 62915 0
Dr Kelly Holt
Address 62915 0
New Zealand College of Chiropractic
6 Harrison Road
Mount Wellington
Auckland 1060
Country 62915 0
New Zealand
Phone 62915 0
+64 95266789
Fax 62915 0
Email 62915 0
Contact person for scientific queries
Name 62916 0
Dr Kelly Holt
Address 62916 0
New Zealand College of Chiropractic
6 Harrison Road
Mount Wellington
Auckland 1060
Country 62916 0
New Zealand
Phone 62916 0
+64 95266789
Fax 62916 0
Email 62916 0

No information has been provided regarding IPD availability
Summary results
Have study results been published in a peer-reviewed journal?
Other publications
Have study results been made publicly available in another format?
Results – basic reporting
Results – plain English summary