Background and aim Musculoskeletal disorders in athletes, including spinal biomechanical dysfunctions, are believed to negatively influence symmetry. Spinal manipulative therapy (SMT) is recognised as a safe and effective treatment for musculoskeletal disorders, but there is little evidence about whether it can be beneficial in symmetry. Therefore, this study aimed to measure the effects of lumbar SMT in symmetry.
Methods Forty asymptomatic athletes participated in the study. The randomisation procedure was performed according to the following group allocation: group 1 (SMT) and group 2 (SHAM). Each participant completed a physical activity questionnaire, and also underwent clinical and physical evaluation for inclusion according to eligibility criteria. Statistical significance (P<0.05) between groups and types of therapy were calculated by physical performance tests symmetry (static position, squat and counter movement jump (CMJ), pre- and post-SMT and SHAM. There were 14 trials of three symmetry tests for each participant, for a total of 560 trials.
Results Lumbar SMT produced immediate effects in symmetry in the static position; however, the same effects were not found in squat and CMJ on symmetry 1. Therefore, our results showed a significant difference in pre- (mean 16.3%) and post-lumbar SMT (mean 3.7%) in static symmetry. However, symmetry 2 showed no statistical significant differences for any of the tests and intervention groups. No statistically significant effects in symmetry pre- to post-SHAM were found in any of the tests.
Conclusions Statistically significant differences were found in lumbar SMT, but only for static symmetry. These findings suggest that SMT was effective in producing immediate effects in symmetry in the static position, but none in dynamic tests. Future studies could address our study's limitations.
Clinical trials register number NCT03361592.
- lumbar spine
- exercise testing
- randomised controlled trial
- symmetry index
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What are the new findings
Asymptomatic athlete participants presented static bilateral asymmetry before the interventions, from pre- 16.3% and after interventions, reducing significantly to 3.7%, immediately post-lumbar spinal manipulative therapy (SMT) intervention.
The lumbar (SMT) intervention produced immediate effects on static symmetry, but the same effects were not found in dynamic tests (squat and counter movement jump).
No statistically significant effects were found in symmetry, pre-to-post SHAM, in any of the physical performance tests.
How might it impact on clinical practice in the near future
In our randomised controlled study, lumbar SMT produced immediate effects on symmetry in the static standing position when applied therapeutically, but not in dynamic actions. Thus, this study expects to demonstrate that the single-session strategy of correcting the lumbar vertebral dysfunctions through lumbar SMT can effectively produce immediate effects in static symmetry.
Adding new information regarding the static symmetry influenced by lumbar SMT intervention, these findings seem to be useful for clinical context in rehabilitation programmes of athletes.
Asymmetric athletes may thus show decreased physical performance or have an increased risk for injury as a result of favouring the bilateral asymmetry of the body.10 11 Tomkinson et al10 12 suggested that athletes who are symmetric also have improved physical performance.
Bilateral asymmetry has been shown to be indicative of spinal abnormalities,5 13 and in clinical and sporting contexts, the ability to detect abnormal biomechanical parameters is extremely important when focusing on restoring normal function through the treatment strategies of these abnormalities.14–17 In this sense, we hypothesise that a therapeutic strategy for correcting spinal biomechanical dysfunctions through a lumbar spinal manipulative therapy intervention could produce immediate effects on symmetry.
Spinal Manipulative Therapy (SMT) is a safe and effective therapy for musculoskeletal disorders that has been increasingly utilised in sport.4 18–20 The purpose of SMT is to correct the biomechanical dysfunctions of spinal joints using a high-velocity low-amplitude movement, applied at the paraphysiological space, beyond the passive joint range of motion.19 21–23
A recent systematic review of the literature18 showed several studies that associate SMT with sporting performance, but none of them has been focused on physical performance tests, namely in symmetry.
Nevertheless, several gaps in knowledge as well as a low level of evidence were found in the related scientific literature.3 5 18 24 Therefore, to address these gaps, this randomised controlled study aimed to quantitatively measure the immediate effects of lumbar SMT on symmetry through physical performance tests: static standing position, squat movement, and counter movement jump (CMJ) in asymptomatic athletes.
A single-blinded, single-session, randomised controlled study was conducted.
Sample size calculations
Based on prior sample size25 calculations, 40 athletes (20 females and 20 males) from different fields of sport participated in this study.
According to the relevant literature, this number of participants performing in multiple trials was sufficient and viable for application to this type of study, to ensure good statistical viability with regards to the parameters in question.25 26
The participants were recruited through public advertisements at the Centre of High Performance, Faculty of Human Kinetics (FMH), University of Lisbon, Portugal, according to the triage process.
Ethical standards were applied according to the Helsinki Declarations, and the research protocol was approved by the Ethics Research Committee of the FMH University of Lisbon.
The CONSORT flow diagram, which is highly recommended for randomised clinical trials,27 was used as described in figure 1, which spans the time from enrolment, allocation and data collection procedures through the analysis of the data gathered from all the volunteer participants in this study.
All selected participants were asked to fulfil the eligibility criteria.
Each participant underwent a clinical and physical evaluation, performed by an experienced physiotherapist and a chiropractitioner, to verify suitability for inclusion. The participants were athletes of any gender, aged between 18 and 35 years, and were asymptomatic and had a normal clinical evaluation.
The participants were physically active according to the “International Physical Activity Questionnaire” (IPAQ); short-form28 scores to standardise the sample including only active participants; medium-to-high level of physical practice, to ensure homogeneity.
Athletes who did not have the characteristics of an active person were excluded. Participants who experienced any changes in their training routine or competition during the study, and participants who had a history of spinal surgery and who were treated with manual therapy at any time during the study, were excluded.29
After the eligibility criteria were fulfilled and the consent form was signed, participants were informed that the study protocol consisted of “therapeutic interventions” between physical tests.
The athlete participants were randomly divided into two groups by drawing from a black envelope containing the group assignment. All selected participants were asked to draw out one small ticket containing either the number 1 or 2, referring respectively to group 1 (n=20), who received the lumbar SMT intervention, and group 2 (n=20), who received the SHAM intervention.
Single-blinded: intervention mask procedure
The intervention mask procedure was performed only for group assignment (SMT and SHAM interventions), thus establishing the single-blinded construct of the study.30 In fact, the participants were not made aware of whether a therapeutic intervention would reach a “mechanical effect” or whether it would have no effect, independent of the type of interventions. Although it is reasonable to suggest that participants may notice a physical difference after intervention, participants did not know to which intervention their group was allocated; participants only knew that they received one therapeutic intervention, as was initially explained.
The biomechanical model31–33 was created for use in static, dynamic and explosive actions. A total set of 49 reflective markers and five clusters were used during the data collection based on the calibrated anatomical system technique (CAST).32
The motion capture system was equipped with an optoelectronic system of 15 cameras at 179 Hz, and two force platforms (Kistler, Winterthur, Switzerland), operating at 500 Hz, were utilised to collect the biomechanical parameters. 34 Additionally, two symmetry indexes (%) were used. The data were captured, processed and analysed using Qualisys QTM software (Gothenburg, Sweden) and Visual3D software (Version 5.01.18, C-Motion, Inc, Germantown, USA).
Physical performance tests symmetry (static position, free squat and CMJ) sequence, pre- and post-SMT and SHAM interventions, is presented in figure 2.
There were 14 trials of three physical performance tests symmetry (static position, free squat and CMJ) for each participant, for a total of 560 trials for all the athletes participating (n=40).
The study interventions SMT and SHAM were performed by a chiropractitioner, as shown in figure 3A, B.
Spinal manipulative therapy
The lumbar SMT intervention was performed on the participants by a chiropractitioner using diversified techniques35 that aim to correct the lumbar vertebral dysfunctional segments identified in the clinical assessments before the intervention. The participants were instructed to lay down prone for the spinal motion palpation analysis, to evaluate the presence of dysfunction in the vertebral segments of the lumbar spine. The SMT was subsequently performed with the athlete laying sideways while a correction was performed contacting the lumbar, namely on the transverse process (mammillary) of the lumbar vertebrae, performing the lumbar roll technique as described by Liekens-Gillet and Bergmann35 (figure 3A).
SHAM control intervention
The SHAM procedure (pre-load SMT positioning) was performed with the participant in the lateral recumbent position, as described in the lumbar SMT intervention. The researcher guided the participant through the same motion as that in the SMT using the maintenance of the set-up position; however, no manipulative thrust was delivered. The chiropractitioner applied minimal pressure, and the position was maintained for approximately 1 min in total for both sides (figure 3B).
The SMT and SHAM interventions were both performed by a researcher with expertise in physiotherapy and chiropractice and more than 15 years of experience in clinical and sporting physical rehabilitation.
Symmetry 1 (symmetry index, SI)
The SI index (%) is the method most commonly used and cited in publication to report bilateral asymmetries in physical performance tests.7
The symmetry measurement is the difference between two sides, known as SI, where XR is a measurement from the right side and XL is a homologous measurement from the left side (see equation below).
The SI (%), expressed as a percentage—with 0% representing perfect symmetry, indicating a more symmetrical pattern, and 100% representing complete asymmetry—was used to assess differences in the bilateral symmetry.
Symmetry 2 (linear global symmetry index, LGSI)
To calculate symmetry LGSI (%) was used to measure the left and right sides in each performance test. Through this index, we were able to calculate the 3D components of the Euclidean distances from the “joint centres” to the pelvis origin, as illustrated in figure 4.
The index was calculated as described by Cabral et al,36 adapted from the LGGA (linear global gait asymmetry) index, and is indicated in the following equation:
The 3D components of each vector are the input v in this index’s equation, where v represents the angular variables (all three components of the hip, knee and ankle joint angles, the absolute pelvis angle, and the trunk angle in relation to the pelvis), and xl (t) and xr (t) are the values obtained for the left and right sides, respectively, at t (each percentage of the time-normalised performance test cycle).36 37
Statistical calculations were performed using SPSS (version 24:IBM, IL), and Matlab software (MathWorks, Inc, USA).
Kolmogorov-Smirnov tests were conducted before the statistical analysis, and they confirmed that the data were normally distributed. The significance of the differences between the means of the participant characteristic groups (age, weight and height) was determined by one-tailed, unpaired Student’s t-test. The mean, SD and range (minimum and maximum) values of the selected variables were analysed. Differences between groups and pre- to post- instances of therapy were analysed using two-way analysis of variance (ANOVA). For all analyses P<0.05 was considered statistically significant.
Baseline participants’ characteristics
Based on the baseline participant characteristics, all participants were similar in regard to asymptomatic conditions, level of physical activity, and anthropometric characteristics.
The IPAQ classification values for all participants (n=40) were calculated and demonstrated a high level of physical activity, with a mean score of 3.342 MET/kg/min and SD of 233 MET/kg/min.
Participants’ anthropometric data were calculated and presented with a mean±SD for age of 23.8±5.3 years, body mass of 63±7.5 kg and height of 1.68±0.06 m, respectively.
All participants completed the study and none of them reported any complaints during their participation.
Symmetry: outcome measures
Group 1 (lumbar SMT)
Static standing position: The pre-phase (mean±SD) was 16.30±11.43%, with a post-phase of 3.77±4.13%. There were statistically significant differences in static symmetry (P=0.01) immediately after lumbar SMT.
Free squat: The pre-phase was 9.37±6.9%, with a post-phase of 10.27±7.70%. There were no statistically significant differences.
CMJ : The pre-phase was 12.8±8.6%, with a post-phase of 13.3±8.1%. There were no statistically significant differences.
Group 1 (lumbar SMT)
Static standing position: The pre-phase was 1.48±0.48%, with a post-phase measurement of 1.40±0.47%. There were no statistically significant differences.
Free squat: The pre-phase was 1.86±0.51%, with a post-phase of 1.82±0.61%. There were no statistically significant differences.
CMJ: The pre-phase was 1.96±0.55%, with a post-phase of 1.83±0.49%. There were no statistically significant differences.
Group 2 (SHAM)
Static standing position: The pre-phase (mean±SD) was 10.75±10.50%, with a post-phase of 9.02±6.18%. There were no statistically significant differences.
Free squat: The pre-phase was 11.73±9.55%, with a post-phase of 12.45±9.57%. There were no statistically significant differences.
CMJ: The pre-phase was 13.99±8.76%, with a post-phase of 12.40±8.59%. There were no statistically significant differences.
Group 2 (SHAM)
Static standing position: The pre-phase was 1.30±0.40%, with a post-phase of 1.46±0.52%. There were no statistically significant differences.
Free squat: The pre-phase was 1.90±0.52%, with a post-phase of 2.03±0.57%. There were no statistically significant differences.
CMJ: The pre-phase was 2.04±0.66%, with a post-phase of 1.99±0.49%. There were no statistically significant differences.
The symmetry 1 and symmetry 2 outcome measures from both groups (SMT and SHAM) are visually presented by the box-plot diagram in figure 5.
Statistically significance differences between pre- to post-SMT and between groups were found, and are presented in table 1A; table 1B shows the range of symmetry values, pre- to post-SMT and SHAM interventions.
Summary of main findings
In our study, our participants presented bilateral asymmetry values initially in the static position, and post-SMT intervention these values reduced significantly.
The lumbar (SMT) intervention produced immediate effects in static symmetry; however, the same effects were not found in the dynamic tests (squat and CMJ). Statistically significant differences were found between pre- and post-SMT intervention measurements, and between groups (SMT and SHAM), only for static symmetry. The symmetry 2 showed no statistical significant differences for any of tests, and in any of the groups.
The SHAM group showed no statistical significant differences between pre-and post-intervention measurements.
Strengths and limitations
Little evidence was found in the literature related to possible effects of SMT on symmetry in athletes. Surpassing this limitation, this study quantitatively measured physical performance test symmetry before and after lumbar SMT intervention to verify whether this intervention could effectively produce statistically significant effects.
The main limitation of this study relates to the blinding of the therapist to the intervention procedures performed on the participants. The double-blind procedure was not performed because it was incompatible with the protocol due to the inherent difficulty in blinding the therapist in this type of study. However, instrumental SMT, such as Activator, seems practical to perform these procedures and further investigations involving SHAM versus true interventions could consider incorporating the Activator instrument.
Another limitation was related to posture control variables that were not analysed because of the incompatibility of our protocol.
Comparison and discussion of findings with respect to previous research
Due to the little evidence found in the literature related to SMT on symmetry, our study was unable to compare results and discuss findings with other studies. Nevertheless, all our results in relation to those of other studies are discussed below.
Based on baseline group characteristics, both interventional groups of athletes were similar relative to asymmetry values, according to the literature.38–41
Before interventions, the participants presented asymmetry values in the SMT group with mean values of 16.3%, and the SHAM group presented mean values of 10.7%, indicating that some participants had considerable asymmetry.
Several authors who calculated symmetry based on performance tests40 42 43 determined the percentage of bilateral asymmetry with values of approximately 10–15%. Differences >15% are considered clinically significant.39–41
Despite some agreement in the literature regarding the asymmetry values of athletes in performance test-based assessments, Noyes et al44 stated that a symmetry index of 85% or higher is acceptable as a normal range for both genders, and sport activity levels.
Nevertheless, our participants presented initially considerable bilateral asymmetry values in symmetry 1 (table 1), and post-SMT intervention these values reduced significantly to what several authors, such as Herzog et al,7 consider to be the minimum level of bilateral asymmetry, with asymmetry values ranging from 4–13%.
Clinical relevance and future directions
By adding new information regarding the symmetry influenced by SMT intervention, this study expects to demonstrate that lumbar SMT can effectively produce immediate effects on symmetry in the static position, but not in dynamic actions, such as squat and CMJ. These findings seem to be useful in the clinical context of rehabilitative programmes for asymptomatic athletes.
Unfortunately, in order to be more relevant in terms of physical and sporting performance, our study would need to address other variables not found in this present study.
Future studies could be conducted, incorporating more variables, with short-term follow-up, and two or more groups crossed.
In our randomised controlled study, statistically significant differences were found between pre- and post-SMT, and between groups, for static symmetry only.
Lumbar SMT was shown to produce effects in bilateral symmetry in the static position when applied therapeutically. Therefore, our findings suggest that a single-session strategy of correcting lumbar vertebral dysfunction through SMT intervention was effective in producing immediate effects on symmetry in the static standing position. However, in dynamic tests (squat and CMJ), pre- to post-lumbar SMT and SHAM were not statistically significantly different in terms of symmetry.
Future studies could address our study's limitations.
The authors thank all the participants for their contributions to this study. The authors also thank the laboratory team for their assistance during the data collection and analysis process.
Contributors The randomised controlled study was completed, and all authors authorised the final version of the manuscript. The concept development; design; international clinical trial registration; local ethics council submissions; participant recruitment and allocation; clinical examinations; selection; experimental and control interventions, SMT and SHAM; data capture, collection and processing; biomechanics parameter and statistical calculations; analysis/interpretation; and writing of the report were performed by BAPA. The concept development, design, supervision, statistical analysis/interpretation and writing were performed by BAPA, RF, FJ, JPRL and APV. All other contributions to this work (critical review and writing a substantive part of the manuscript) were equally distributed among the authors.
Funding Doctorate Scholarship Funds to Bruno Alvarenga from Minister of Education Brazil – CAPES.
Competing interests None declared.
Patient consent Obtained.
Ethics approval FMH - Ethic Committee Register number: 31/2017.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement All participants submitted a signed informed consent form of Faculty of Human Kinetics - FMH institutional consent that included information about the purpose of thestudy, its procedures, the participants’ rights and welfare, participants’ protections and the collection of data for publication. All data generated or analysed in this study were included in this material. The dataset used and/or analysed during the current study will be shared upon previous communication to the corresponding author, B.A.P.A, on reasonable request. The datasets analysed are available from the Biomechanics and Functional Morphology Laboratory FMH, upon request and authorization. Faculty of Human Kinetics, University of Lisbon (Estrada da Costa, Dafundo. Lisbon, 1499-002, Portugal).
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