Immediate Effects of Spinal Manipulative Therapy on the Performance of Elite Brazilian Soccer Players: A Pilot Randomized Controlled Trial With an Internally Validated Sham Treatment

Abstract

Objective

The purpose of this study was to assess the feasibility of the procedures’ routine, the recruiting rate, the presence of any significant detrimental impact on the players’ training routine, and the sham efficacy in achieving blinding.

Methods

A parallel randomized controlled clinical trial was performed with 20 elite soccer players who were randomly assigned to 1 of 2 groups: spinal manipulative therapy (SMT) and sham SMT. All players were from the same team, were injury free, and were naive to SMT. Measured outcome tests (30-m sprint run with a 10-m split and change of direction [COD] test) were performed at the same time by all participants immediately before and after interventions. Photocell devices were used for data acquisition.

Results

Twenty participants were analyzed (10 in each group). There were no changes to the sprint (10 m and 30 m) and COD test results immediately after either of the interventions. All participants in both groups (SMT and sham SMT) answered “yes” to a question after the intervention asking if they were treated by SMT. No adverse effects or training routine impairment were reported.

Conclusion

This pilot study protocol showed it was an appropriate design for a confirmatory clinical trial. The study had minimal effect on the team training routine, and the recruitment rate was excellent. The proposed sham SMT strategy was successful in blinding the players. In this sample, SMT did not have any immediate effect on the performance of these elite soccer players, as measured by 10- and 30-m sprint times and COD sprint times.

Introduction

An integral part of competitive sport for athletes is the pursuit of maximum performance.¹ Athletes will attempt to enhance performance from many different factors, including physiological, dietary, physical, social, and economic ones.1, 2, 3

It has been hypothesized that forms of spinal biomechanical dysfunction, which may be asymptomatic, could possibly generate impaired central nervous system proprioceptive input, and motor control and central processing deficits.^4,5 The thought is that this could result in performance loss.4, 5, 6, 7 Such vertebral, biomechanical dysfunctions are hypothesized to be responsible for maladaptive central nervous system neuroplasticity.^6,8 When addressed with spinal manipulative therapy (SMT), there may be improvement in joint proprioception and motor response.6, 7, 8, 9

It is thought that asymptomatic spinal biomechanical dysfunctions consist of an alteration of the normal vertebral biomechanical joint play, which does not cause pain or other clearly perceived symptoms. Assessment of this condition is made based on findings of static and dynamic physical examination, when performed by trained health professionals. These findings may include abnormal joint end play, restricted inter-segmental motion, soft tissue tenderness with palpation, or paraspinal asymmetric muscle tension.^10,11

SMT has no consistent definition in the literature.^10,11 For this study, we defined it as any manual technique that incorporates a controlled, high-velocity, low-amplitude dynamic thrust applied to a spinal joint, taking it beyond the passive range of motion but without exceeding anatomic limits at the paraphysiological space.^10,11 The choice of direction of the controlled thrust is based upon physical examination findings of specific joint dysfunctions.¹¹ This treatment method for spinal biomechanical functional disorders is most widely used by chiropractors^10,12, 13, 14 and sometimes by other health professionals, including orthopedists,¹⁵ physiotherapists,¹⁶ and osteopaths.¹⁷

Neurophysiological effects of SMT could theoretically influence sports performance. These include changes in surface electromyographic activity,^18,19 corticospinal20, 21, 22 and spinal cord22, 23, 24 excitability, increased muscle strength,^7,25,26 decreased muscle inhibition,^27,28 lower expression of proinflammatory cytokines,²⁹ decreased pain sensation,30, 31, 32, 33, 34, 35, 36, 37, 38 and prevention of muscle fatigue.³⁹

It has been proposed that SMT may influence and improve aspects of sports performance. These aspects include increased full-swing for golfers,⁴⁰ increased judoka grip strength,²⁵ and increased ball kicking speed for soccer players⁴¹; however, there are few studies in this field about the influence of SMT on sports performance from laboratory studies, field tests, and real events.⁴²

In soccer, athletic trainers and coaches use various field tests to assess the fitness and capacity of their players.^43,44 These include sprint (10 m and 30 m) and change of direction (COD) tests, which are widely used to evaluate ability to sprint and to change direction quickly.^45,46 Their usage ranges from guidance for individual training routines to decisions on collective competition tactics, as when used to choose the most suitable player for a particular position for a specific match.^45,46 Employing these test methods, individual training programs can be developed to improve a player's ability to accelerate (10 m), increase maximal velocity during sprints (30 m), and abruptly change direction while running at speed. Additionally, these tests can provide guidance on improved running technique and use of energy systems.^45,46

Up to this point, there has been no randomized controlled clinical trial to assess the effect of SMT on the performance of elite soccer players. Therefore, the aim of this pilot study was to assist designing a full randomized controlled clinical trial to assess whether such SMT may influence the performance of elite soccer players. Thus, the purpose of this study was to assess the feasibility of the procedures routine, the recruiting rate, the presence of any significant detrimental impact on the players training routine, and the sham SMT efficacy in achieving blinding.

Methods

Trial Design

A parallel randomized controlled clinical trial was performed with an allocation ratio of 1:1 between the 2 intervention groups (SMT or sham SMT).

Ethics

Ethics and research committee approval for the study was received from Instituto Mantenedor de Educação Superior, Brazil, and the study was registered in the institute's database (No. 3993). The study protocol was also registered in the ISRCTN registry under the identification number ISRCTN29691307. This trial adheres to CONSORT (Consolidated Standards Of Reporting Trials) reporting guidelines.

Participants

All team players in the under 20 years category were invited to participate and did so (population study). As a result, 20 elite professional soccer players were included. The players’ regular physical training schedule comprised 5 sessions per week, with the duration of each session typically being 120 to 180 minutes. Each session included soccer training, strength training, and conditioning. All participants completed a consent form.

Eligibility Criteria

All participants included were male, volunteers, and elite soccer players from the same team. Inclusion criteria were the ability to understand and sign the informed consent form, participation in training or competition at least 5 days a week, and no previous experience of SMT.

With respect to exclusion criteria, the athletes were assessed by a physician qualified in both medicine and chiropractic, and with postgraduate sports medicine qualifications in both disciplines. First, this assessment was for a number of common contraindications to SMT, any of which would lead to noninclusion in the study.⁴⁷ These included acute fracture, acute infections, neurological deficits, signs of joint instability or pathological ligament laxity, the absence of biomechanical spinal joint dysfunction amenable to SMT, and other contraindications to SMT given in guidelines from the World Health Organization.⁴⁷ Second, the assessment was for another noninclusion criterion, which was the presence of any acute musculoskeletal lesion that might prevent the patient from full participation in the study tests. A final noninclusion criterion was previous experience of SMT treatment.

Settings and Data Collection

Data were collected in the middle of a regular soccer season on the first day of the training week, with no changes in the athletes’ training routine on the previous or following days of the tested interventions. Tests and interventions were performed at the under-20 team training facilities in Brazil.

Interventions

All tests were conducted and data collected after participants performed a standard warm-up consisting of 15 minutes of low-intensity running and striding, followed by 3 submaximal sprints. Then, in a line, they performed the sprint test sequentially. After completion of this by all participants, they lined up again to perform the COD test sequentially. All participants then attended the intervention office. After the entire group completed the baseline tests and intervention stage, which took about 3 hours, the warm-up was performed again and the participants were retested. This flow of procedures is summarized in Figure 1.

Fig 1.

Flowchart of the study tests and interventions.

In the intervention office, participants visited 1 of the 2 treating physicians available, both being qualified as chiropractors and having ongoing postgraduate training in sports chiropractic and at least 3 years’ experience of chiropractic practice. At the office, the physician randomly assigned them to the SMT or sham SMT group based on a coin flip.

All participants in both groups had received the same general information about the treatment under investigation and its possible adverse effects. They spent a similar time in the treatment room with the treating physician, namely between 10 and 15 minutes. Each participant attended a single intervention session.

Spinal Manipulative Therapy

For those in the SMT group, correction of spinal biomechanical dysfunction was performed as needed, which was determined by dynamic and static evaluation of all spinal (cervical, thoracic, and lumbar) and pelvic (sacroiliac) joints. Physical examination findings used as indicators of joint dysfunction included abnormal or blocked joint play, restricted inter-segmental motion, soft-tissue tenderness over relevant joints, and paraspinal asymmetric muscle tension. These findings are commonly used by physicians as indicators of spinal biomechanical dysfunction.¹¹

Treatment was given employing high-velocity, low-amplitude Diversified Technique.¹¹ All participants in this SMT group received some treatment, though the number of treatments and spinal regions targeted varied because treatment was based upon clinical findings. Cervical SMT was performed with the participant lying supine, thoracic SMT with the participant lying prone, and lumbo-pelvic SMT with the participant in a side-lying position. Treatment was delivered using hands only, and on a Thuli Table (Thuli Table Inc, Dodgeville, Wisconsin).

Sham SMT

The same physicians who performed the SMT performed interventions in the sham group. They used a Thuli Table and its drop mechanisms, addressing 3 different areas: the cervical, thoracic, and lumbo-pelvic regions of the spine.

With the participant lying prone, the physician activated a mechanism that lifts a specific section of the table, either the cervical, thoracic, or lumbo-pelvic sections. The section dropped back to its neutral position on application of pressure to the margin of the elevated section by the physician, done without physical contact with the participant. When the raised section fell back to a neutral position its impact with the main body of the table generated a loud clap. This procedure was performed 3 times for each spine-related area (cervical, thoracic, and lumbo-pelvic), providing a total of 9 maneuvers for each participant in the sham SMT group. A similar sham intervention has been used in a previous study.²⁵

Outcomes

The outcome tests (30-m sprint run with a 10-m split, and the COD test) were performed after a standard and simultaneous warm-up by all participants. These were performed immediately before the interventions and immediately after all athletes finished the interventions stage, which could take up to approximately 3 hours for some athletes. The participants were placed in a line and consecutively performed the tests using the same track line. Timing was recorded by single-beamed photocell devices. Reliability of this measure for short-sprint studies is around 0.03 seconds of standard error and 2% of coefficient of variation.^48,49 All athletes’ clothing were the same typical soccer training gear. The researcher responsible for the testing was not aware of the group allocation of each participant. Only the 2 care providers were aware of group allocations. They had no access to each other during data acquisition.

The sprint test was carried out on a 30-m straight-line track, using a system containing 3 single-beamed photocell devices (Microgate, Bolzano, Italy). These devices were set with one at the beginning, one at 10 m (split time), and one at the 30-m mark (Fig 2). The starting position was with the preferred foot just before the starting line. Each participant decided when to start, meaning that data were not influenced by differences in reaction time.⁴⁹ The first device or barrier of photocells was located immediately after the starting line, and time was recorded when the participant's body crossed this and then the next 2 photocell barriers. During the entire execution of the test, athletes were verbally encouraged. This procedure was performed 2 times, with a rest interval of 5 minutes in between. The lowest value (faster time) was used for analysis.⁴⁴

Fig 2.

Sprint and change of direction tests.

The change of direction test was conducted over a length of 20 m. Participants were required to run in a zigzag pattern while crossing four 5-m distance barriers, each one located at a 100° internal angle from the next one (Fig 2).⁵⁰ Time was measured by a system of 2 single-beamed photocell barriers (Microgate, Bolzano, Italy), one at the beginning of the track and another at the end. Starting position was the same as used for the 30-m run. During the entire execution of the test participants were again verbally encouraged. The test was performed twice, with a rest interval of 5 minutes in between. The lowest value (faster time) was used for analysis. This test provides rapid acceleration and deceleration movements, similar to the real demands of a match.⁵⁰

Sample Size

All team players in the under 20 years category of the same team were invited to participate and did so. As a full population study, no sample size calculation was performed.

Allocation Concealment

Group allocation was performed just before the intervention, by means of a coin flip by the physician at the intervention office before physical examination. No one else had access to information on allocation. There was no contact between the physicians and those assessing the outcomes (sprint and COD).

Blinding

Those assessing outcomes and performing statistical analysis were blinded to each participant's group allocation. Care providers, given the nature of the interventions, could not be blinded. Participants were blinded to interventions. To assess the blindness of a participant, right after interventions all completed a form asking them to answer the question, “Have you been treated by spinal manipulative therapy procedures?”

Statistical Methods

The Shapiro-Wilk and Levene's tests were used to test the data for normality and homogeneity of variance. Two-way, mixed-model analysis of variance was used to assess for differences between the effects of a single session of SMT or sham SMT on sprint and COD test times. Intervention (SMT and sham SMT) and time (pre- and postintervention measures) were used as factors. The partial eta squared (η_p²) was calculated to determine the effect size for the interactions. Cohen d for the paired test was used to determine the effect size when there was a main time effect. The t test or χ² test assessed baseline characteristics. Alpha value was established as 5%. Statistical testing was carried out using SPSS Statistics version 20 (IBM, Armonk, NY).

Results

All team players (n = 20) were randomly assigned to 1 of the 2 groups (SMT or sham SMT). Asymptomatic spinal biomechanical dysfunctions were found in all participants from both groups, at cervical, thoracic, and lumbo-pelvic spine. Therefore, all participants were eligible and received the intended intervention. Data from all participants were included for analysis Figure 3. summarizes the study flow. Also, for the test and intervention sequence, participants progressed through the steps shown in Figure 1. All athletes performed these steps during the same time.

Fig 3.

Study enrollment flowchart.

After randomization, each of the SMT and sham SMT groups had 10 participants. There were no losses in either group. All individuals were analyzed for baseline characteristics, which are shown in Table 1. Comparisons between groups at 10 m and 30 m, and regarding the COD tests, are shown in Table 2.

Table 1.

Baseline Characteristics of 20 Male Participants

Characteristic	SMT	Sham SMT	P Value (t Test)
Height (m)	1.80	1.81	.748
Weight (kg)	73.00	69.57	.516
Age (y)	18.20	18.20	1.000
Experience (y)	9.40	7.70	.287
Practice levela	International (7)	International (6)	.627a

SMT, spinal manipulative therapy.

^aP value calculated via χ² test.

Table 2.

The Mean ± SD of Time (s), P Value, Effect Size, and 95% CI of Pre- and Post-SMT and Pre- and Post-Sham SMT Groups for 10-m Sprint, 30-m Sprint, and COD Test

Test	SMTMean + SD(95% CI)		Sham SMTMean + SD(95% CI)		Group	Time	Group X Time
	Pre	Post	Pre	Post	P Value (ES = ηp2)	P Value (ES = ηp2)	P Value (ES = ηp2)
10-m sprint	1.721 ± 0.087	1.731 ± 0.056	1.739 ± 0.065	1.791 ± 0.644	.096 (.079)	.186 (.051)	.370 (.024)
	(1.677-1.766)	(1.686-1.776)	(1.694-1.784)	(1.741-1.841)
30-m sprinta	4.050 ± 0.138	4.146 ± 0.171	4.116 ± 0.107	4.208 ± 0.092	.145 (.061)	.036 (.123)	.976 (.000)
	(3.965-4.135)	(4.060-4.231)	(4.031-4.201)	(4.113-4.304)
COD test	5.655 ± 0.101	5.702 ± 0.257	5.778 ± 0.144	5.779 ± 0.244	.121 (.067)	.711 (.004)	.722 (.004)
	(5529.7-5781.7)	(5575.7-5827.7)	(5652.3-5904.3)	(5646.4-5912.0)

CI, confidence interval; COD, change of direction; ES, effect size; SD, standard deviation; SMT, spinal manipulative therapy.

^aP value ≤.05.

No statistically significant changes were observed in either of the 2 groups according to sprint (10 m and 30 m) and COD test results measured immediately after the interventions.

Sham SMT Validity Internal Test

All participants in both groups (n = 20) answered “yes” to the question, “Have you been treated by spinal manipulative therapy procedures?” which was asked after the intervention by an independent researcher who was not aware of group allocations. Accordingly, the sham SMT intervention employed in the trial was effective in blinding these athletes, as shown in Table 3.

Table 3.

Frequency of Sham SMT Blindness Efficacy

Have you been treated by spinal manipulative therapy procedures?	SMT	Sham SMT
Yes	100%	100%
No	0	0

SMT, spinal manipulative therapy.

Adverse Effects

No adverse effects were reported. The team staff did not report any impairment on the athletes´ training routine.

Discussion

This is the first study to test the performance based on sprint and COD tests of elite soccer players after SMT. Team staff commonly use these tests to predict physical performance in professional soccer.^43,44 The present pilot study has had a high adherence among players and team staff, with no significant impairment on their training routine, and reports no change in sprint or COD outcomes after SMT.

Although there is a hypothesis that SMT addresses biomechanical dysfunction, which may have a positive influence on sports performance,⁴² there currently is a lack of compelling evidence. Other researchers, Shrier et al⁵¹ and Sandell et al,⁵² found no change in sprint times after SMT was given to sprint and middle-distance athletes. Shrier et al evaluated flying 40-m sprint times (40 m: run of 20-60 m) in a crossover study with 19 elite athletes from “sprint sports.” Sandell et al evaluated 30-m sprint times after 3 weekly SMT interventions in a group of 17 middle-distance runners. Although the protocols and participants were different in these 2 studies, their combined results suggest that SMT did not seem to influence sprint times in athletes.

On the other hand, the aforementioned studies had small sample sizes and low statistical power to detect differences. Also, there were other factors that may not have been properly controlled that may have influenced sprint timing. These include timing technology, different starts procedures and triggering devices, environmental characteristics and changes, and athletes’ clothing.⁴⁸ Another plausible explanation may include the complexity of sprinting, which is influenced by several variables that may mask potential benefits from SMT. Such variables include muscle activation patterns, motor control, movement coordination, and anaerobic resistance. One possibility is that there are positive effects of SMT, but that these do not have sufficient impact to overcome other factors involved in sprinting and be seen in the final outcomes measured, which is sprint time.

Similar SMT investigations to ours, though using different outcomes, have shown increased performance after SMT for biomechanical dysfunction. Costa et al⁴⁰ observed an increased full-swing driving distance for golfers (16.9-m increase, P < .05) after 4 combined interventions of full spine SMT and stretching performed weekly (stretch × stretch + SMT, n = 43). Botelho and Andrade²⁵ found increased grip strength immediately after 1 cervical SMT biomechanical correction and after 3 weekly interventions (10.53% right and 16.81% left hand, P < .05), in a study performed with 18 elite judokas. Christiansen et al⁷ observed an increased corticospinal excitability and muscle strength (7.58%, P < .05) of ankle plantar flexor muscles in 11 elite taekwondo athletes after a single SMT session in a crossover randomized controlled clinical trial.

Comparisons of other research studies with the present study are challenging, as the populations, protocols, interventions, and outcome measures in other studies are quite different. However physiological differences may be a relevant factor in explaining whether or not SMT produces a positive result in the studies. Deep cervical spine muscles have a higher concentration of proprioceptive afferents than other spinal muscles.^53,54 This could result in different neurophysiological responses to SMT in the upper and lower spine and limbs, and partly explain the conflicting results of the sprint and upper body studies being reviewed. In addition, the delayed time of postintervention assessment may have missed early transient effects. Christiansen et al reported ankle plantar flexor muscles increased strength after SMT lasted more than 30 but no longer than 60 minutes.⁷ Also, the range of motion and balance variables associated with the full-swing golfing movement may be influenced by SMT in a different way to the main variables in sprinting.

The one previous study that analyzed the effects of SMT on soccer players was a nonrandomized study performed by Deutschmann et al.⁴¹ They found an increased ball-kicking speed after lumbar or sacroiliac SMT or a combination of both (average increase of 3.52-6.57 km/h, depending on group allocation, P < .05). Data were acquired immediately before and after the interventions (SMT or sham). Their results, reporting a more positive response to SMT than in our study, may suggest that SMT has a different impact on tasks with different motor control, strength, and complexity. We could not find any other study where SMT effects were evaluated for a COD test.

Our pilot study is the first study of its type, and 2 critical methodological aspects are worth noting with some emphasis. One is that all participants were naive to the treatment being given (SMT), and the other is that the sham SMT intervention was internally validated. Despite the significant mechanical and physical differences between the chosen sham SMT maneuver and the SMT delivered in the study, participants in the sham SMT group believed that the intervention they were receiving was the active one being studied. This may have been because these participants were naive to SMT, and because of the combined effect of the drop mechanism moving their body segments and causing the loud sound described.

Also, regarding study design strengths and weaknesses, we believe collecting data from all athletes at the same time was noteworthy because it avoided between-participant interference from weather, such as effects of wind, sun exposure, and temperature. This is especially significant when collection of data is in an open field, as was the case in our study. All of the participants (n = 20) completed each test within 15 minutes (2 trials). On the other hand, this design did not allow assessment of the effects of SMT immediately after it was performed, as could be done with assessments on an individual basis.

Limitations

Conducting clinical investigations with high-performance athletes can be very challenging. This is especially true because of the inherent difficulties of having a large sample size and of conducting a trial while the athletes are training or competing, and with minimum or no impact on their routine.¹ In this study, all current players in the under 20 years category were invited and agreed to participate. However, the sample size was small (n = 20) and therefore generalization of the present results is limited. This study was conducted with male soccer players; therefore, it is unknown if similar results would be found in female soccer players.

Two different physicians treated the study participants, and the treatment provided was based upon their skills and clinical judgment to identify and correct biomechanical joint dysfunctions. This subjective aspect of the treatment may represent a limitation. It is worth noting that both of them had formal qualifications as chiropractors, were graduates of accredited chiropractic programs, and had at least 3 years of chiropractic clinical experience.

Also, the same physicians performed both the active and sham SMT interventions, which could generate bias as soccer players could have had different general information, recommendations, and time spent with the physician. To minimize its potential detrimental effects on participants’ blindness and possible placebo effects, both of the physicians underwent specific training before commencing the study. This training consisted of guidance for delivering the same general information about SMT and its possible adverse effects, and also to spend a similar time at the treatment room with every participant regardless of group allocation.

The players could see each other during the execution of the tested outcomes (sprint and COD), as they have performed these tests together and consecutively. Although the players could not view each other's test results, being allowed to view one another before test execution may have influenced players’ performance, and this should be taken into consideration.

Execution of the tests by the participants was done consecutively, but the order of execution before and after the interventions were not recorded or required to be the same. This means the interval between outcomes measurement (sprint and COD) performed after the interventions may have varied up to approximately 3 hours between participants. Although the participants were compared with themselves and it is thought that this limitation should not have influenced outcomes, this should be taken into consideration.

The research protocol did not address lifestyle factors that might lead to performance bias, such as nutrition and patterns of sleep, because it was judged that the potential influence of these was minimal to zero owing to the study design with its single treatment session and immediate pre-post measurements of participants. All participants were fed at the team facilities and offered the same meal times and food. All participants used their regular sports gear.

Although the participants were instructed not to discuss the treatment received with their teammates, some may have, and this was beyond our control. However, any such discussion is unlikely to have influenced the outcomes because, as shown by the internal sham SMT validation test, all participants believed they were treated by SMT.

Conclusion

Our pilot study showed that the proposed study protocol proved to be a feasible and adequate design for a confirmatory clinical trial. The study had minimal effect on the team training routine, and the recruitment rate was excellent. Also, the proposed sham SMT strategy was successful in blinding the players who were naive to SMT treatment. This seems to be an important strategy tool for future studies.

In this pilot study, spinal manipulative therapy did not have any immediate effect on the performance of these elite soccer players, as measured by 10- and 30-m sprint times and COD sprint times. This pilot study shows that further investigation with larger sample sizes and more outcomes are feasible.

Funding Sources and Conflicts of Interest

The CAPES Foundation (Ministry of Education, Brazil) granted the first author (M.B.B.) a PhD scholarship while this study was being conducted. No conflicts of interest were reported for this study.

Contributorship Information

Concept development (provided idea for the research): M.B.B., M.A.B., A.F.B.

Design (planned the methods to generate the results): M.B.B., M.A.B., A.F.B.

Supervision (provided oversight, responsible for organization and implementation, writing of the manuscript): M.B.B., M.A.B., C.S.J., J.P.R.L., A.M., A.F.B.

Data collection/processing (responsible for experiments, patient management, organization, or reporting data): M.B.B., M.A.B., C.S.J, J.P.R.L., A.M., A.F.B.

Analysis/interpretation (responsible for statistical analysis, evaluation, and presentation of the results): M.B.B., M.A.B., C.S.J., J.P.R.L., A.M., A.F.B.

Literature search (performed the literature search): M.B.B., M.A.B., C.S.J., J.P.R.L., A.M., A.F.B.

Writing (responsible for writing a substantive part of the manuscript): M.B.B., M.A.B., C.S.J., J.P.R.L., A.M., A.F.B.

Critical review (revised manuscript for intellectual content, this does not relate to spelling and grammar checking): M.B.B., M.A.B., C.S.J., J.P.R.L., A.M., A.F.B.

Practical Applications.

• •This is the first study to test the performance of elite soccer players, based on sprint and change of direction tests, after spinal manipulative therapy (SMT).
• •This pilot study showed that the study protocol was feasible for a confirmatory clinical trial.
• •The proposed sham SMT strategy was successful in blinding the players who were naive to SMT treatment.

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