GENERAL REVIEW

Core Stability Exercises for Low Back Pain in Athletes: A Systematic Review of the Literature Kent J. Stuber, DC, MSc,* Paul Bruno, DC, PhD,† Sandy Sajko, DC, MSc,‡ and Jill A. Hayden, DC, PhD§

Objective: The aim of this study was to systematically review the evidence for the effectiveness of core stability exercises for treating athletes with low back pain (LBP).

Data Sources: We searched several databases (Medline, AMED, CINAHL, SportDiscus, and EMBASE). Our eligibility criteria consisted of articles published in a peer-reviewed journal in English, using any prospective clinical study design, where athletes with nonspecific LBP were treated with core stability exercises in at least 1 study arm, and back pain intensity and/or disability were used as outcome measures. All included randomized controlled trials (RCTs) were assessed for risk of bias using the Cochrane Risk of Bias tool, whereas non-RCT studies were assessed for quality using the Downs and Black checklist. Main Results: Five studies including 151 participants met the inclusion criteria, including 2 RCTs. The quality of the literature on this topic was deemed to be low overall, with only 1 non-RCT having a moderate quality score, and 1 RCT having a lower risk of bias. Four studies reported statistically significant decreases in back pain intensity in their core stability intervention group.

Conclusions: The quantity and quality of literature on the use of core stability exercises for treating LBP in athletes is low. The existing evidence has been conducted on small and heterogeneous study populations using interventions that vary drastically with only mixed results and short-term follow-up. This precludes the formulation of strong conclusions, and additional high quality research is clearly needed.

Submitted for publication January 3, 2013; accepted December 23, 2013. From the *Division of Graduate Education & Research, Canadian Memorial Chiropractic College, Toronto, Ontario, Canada; †Faculty of Kinesiology and Health Studies, University of Regina, Regina, Saskatchewan, Canada; ‡Sports Clinic, University of Toronto Mississauga, Mississauga, Ontario, Canada; and §Department of Community Health and Epidemiology, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada. Dr. K. J. Stuber helped conceive and design the review, conducted the searches and article retrieval, and participated in the analysis and interpretation of the data. Dr. P. Bruno and Dr. S. Sajko helped conceive the review and participated in the analysis and interpretation of the data. Dr. J. A. Hayden helped conceive and design the review and participated in the analysis and interpretation of the data. Dr. K. J. Stuber, Dr. P. Bruno, Dr. S. Sajko, and Dr. J. A. Hayden participated in drafting and revising the article and provided final approval of the version to be published. The authors report no conflicts of interest. Corresponding Author: Kent J. Stuber, DC, MSc, 19-8 Weston Drive SW, Calgary, AB T3H 5P2, Canada ([email protected]). Copyright © 2014 by Lippincott Williams & Wilkins

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Key Words: low back pain, athletes, exercise therapy, core stability (Clin J Sport Med 2014;0:1–9)

INTRODUCTION Low back pain (LBP) is common in athletes. The 1-year prevalence of LBP has been reported to be 68% among top athletes from multiple sports1; studies on specific sports have reported 1-year prevalence of 49% in orienteering,2 54% in wrestlers,1 86% in gymnasts,3 and 94% in hockey players.1 Comparatively, the reported 1-year prevalence of LBP in the general population varies from 22% to 65%.4 Although the results of 2 studies suggest that the prevalence of LBP in athletes is similar to that of the general population,2,5 1 study investigating the prevalence of LBP among Australian Rules football players indicated that it was higher than in a nonathletic control group.6 Depending on the sport, athletes require their lower backs to have the capacity to tolerate high loads and perform complex repetitive movements.7–9 It is well documented that certain forms of spinal injury are more common in athletes than in the general population. For example, 33% of elite American football linemen were found to have hyperconcavity of the vertebral endplates with expansion of the disk space compared with 8% of age-matched controls,10 although this does not seem to have an effect on lumbosacral spine symptoms or duration of playing career.11 Degenerative disc disease is more common in elite athletes than nonathletes.12–14 Spondylolytic injuries seem to be more common in some sports than others (eg, American football, rowing, diving, gymnastics, martial arts, rugby), with throwing sports, in particular, having higher rates of spondylolytic injuries.7,14–18 American football linemen produce nearly 7 times their body weight in compressive force and 2.6 times their body weight in shear force on the L4–L5 segment when blocking; with repetition, these forces may increase the risk for fatigue failure and injury.7 Cricket bowlers place high compressive loads on their spines during the power phase of the throw because of the frequent repetition of high velocity lumbar movements in a very specific sequence.9,18 Gymnasts also place large vertical and lateral impact forces on their spines,19 and overuse has been implicated as a potential risk factor for back injury in this population.18 There are many possible treatment options for LBP in athletes including medications, biopsychosocial interventions, physical and electrical modalities, manual therapies, and exercise therapies.20 Among exercise therapies, there are www.cjsportmed.com |

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different forms of exercise that can be prescribed for LBP, including stretching or mobility exercises, cardiovascular endurance or aerobic exercises, and strengthening exercises.21 One form of strengthening exercise that has received increasing attention in the literature and popular media is “core stability exercise.” This type of exercise is variably defined, as any exercises that strengthen spinal musculature or specifically as those that emphasize the deep lumbopelvic musculature (eg, transversus abdominis, multifidus).22 There is some evidence that exercises thought to target these deep muscles are effective in treating chronic LBP in the general population.23,24 However, it has also been argued that focusing on 1 or 2 deep muscles in core stability exercise programs is misguided because both deep and superficial muscles contribute to spinal stability.25–29 McGill et al28 state that “any exercise that grooves motor patterns, that ensure a stable spine, through repetition, constitutes a ‘stabilization’ exercise.” A recent meta-analysis that defined core stability exercise broadly as “the reinforcement of the ability to insure stability of the neutral spine position” reported that such exercises are more effective than general exercise in treating chronic LBP in the general population.30 Differences in the athlete compared with the general population (eg, higher physical demands, repetitive motions, and higher baseline fitness level) warrant assessment of treatment evidence specifically for this population. The aim of this study was to systematically review the available evidence for the effectiveness of core stability exercises for athletes with LBP.

studies were assessed for quality using the Downs and Black checklist.34 Non-RCT studies were deemed to be high quality for scores of $21 on the checklist, moderate quality for scores between 11 and 20, and low quality if they scored #10.35 Statistical significance (set at P , 0.05) for between-group differences and within-group differences over time was used to interpret positive results. To determine whether minimal clinically important differences were achieved between groups in the included studies, we considered a 20-point (out of 100) or 2-point (out of 10) improvement in pain intensity and a 10-point (out of 100) improvement in functional measures to be clinically important.36 We also considered a minimum average of 30% improvement within groups from baseline to be clinically important.36 Two of the authors (K.J.S. and P.B.) independently applied the GRADE criteria37 for interpreting the overall quality of the available evidence. Using this framework, high quality evidence indicates that further research is very unlikely to change our confidence in the estimate of effect, moderate quality evidence indicates that further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate, low quality evidence indicates that further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate, and very low quality evidence indicates that any estimate of effect is very uncertain.

RESULTS Search Results and Study Designs

METHODS We conducted and reported this systematic review according to the PRISMA guidelines,31 with a protocol defined a priori. We searched 5 online databases (Medline, AMED, CINAHL, SportDiscus, and EMBASE) from the start date of the respective database through the last week of June 2012 with no language restrictions, using a comprehensive set of MeSH and key word terms referring to athletes, LBP, and core stability exercises (Appendix 1 for the Medline search strategy). Two reviewers (K.J.S. and S.S.) independently screened the titles and abstracts for potentially applicable studies, and full-text reports of potentially eligible citations were retrieved for final selection. Any disagreement on inclusion was discussed and mediated by a third author (J.A.H.) when necessary. We searched reference lists of all included studies to identify other potentially relevant studies. Included studies had to meet specific criteria (Table 1). Two of the authors (P.B. and S.S.) independently extracted data from the included studies into a prespecified electronic data extraction form, which was subsequently reviewed by a third author (J.A.H.). Critical appraisal of included studies was conducted independently by 2 authors (K.J.S. and P.B.) with a third author (J.A.H.) resolving any differences. All included randomized controlled trials (RCTs) were evaluated using the Cochrane Back Review Group modification of the Cochrane risk of bias tool.32 Randomized controlled trials were deemed to have a low risk of bias, if they had $6 of the 12 risk of bias criteria scored as low risk.33 Non-RCT

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We identified 677 potential citations and screened 9 full-text articles (Figure). Four of the 9 articles were excluded because of poor reporting of the LBP subgroup and a lack of pain intensity reporting38 or because the intervention did not specifically include core stability exercises.38–41 Five studies met all selection criteria and were included in the review: 3 observational studies42–44 and 2 RCTs.45,46 Table 2 presents a description of included studies.

Participants Sample sizes of included studies ranged from 744 to 50 (25 participants per group).42 All of the participants in 1 study were women,43 whereas only men participated in the remaining studies. In 2 studies, the participants were middle-aged and older.42,46 The participants were adolescents in 1 study,43 whereas in the remaining 2 studies, the average age of the patients was in their early twenties.44,45 Sports involved included cricket,44 field hockey,45 ice hockey,46 teamgym gymnastics,43 and a variety of sports.42 The participants had either acute,43 chronic LBP,42,46 or a mixture of subacute and chronic LBP.45

Outcome Measures Used For all included studies, outcomes were assessed during and/or after intervention only, between 3 and 12 weeks after baseline.42,43,46 None of the studies performed long-term follow-up assessments after their postintervention assessments. Four studies used the visual analog scale ! 2014 Lippincott Williams & Wilkins

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TABLE 1. Study Criteria for Inclusion in the Review Published in a Peer-Reviewed Journal in the English Language Any prospective clinical study design, including RCTs, controlled clinical trials, and observational studies. Single case reports, case series, qualitative studies, and review articles were excluded Participants were adult and youth athletes (.10 y of age) from any sport, at any competitive level (recreational, competitive amateur, or professional) with nonspecific LBP (acute, subacute, or chronic). At least 50% of the participants in the study were required to be athletes participating regularly in some sporting activity At least 1 treatment arm incorporated core stability exercise (exclusively or in combination with other interventions), which was defined as any exercise(s) designed to improve the strength and/or endurance and/or activation of the lumbopelvic and/or abdominal musculature. Participants’ use of medications, supplements, and/or other cointerventions was acceptable In comparative studies, the comparison group(s) could consist of no treatment, placebo, or a different type of treatment Outcome measures included at least an assessment of pain intensity and/or disability due to pain (primary outcomes). Additional outcome measures could include return to sport, global health measures (such as the SF-12 or SF-36), physical function measures (such as ranges of motion or core strength), or a global rating of change (secondary outcomes). Short (,3 mo), medium (3 mo-1 y), and long-term (.1 y) outcomes were all considered SF-12, short-form 12 questionnaire; SF-36, short-form 36 questionnaire.

(VAS) to measure pain intensity42,44–46; the remaining study used the Borg Category Ratio Scale.43 One study46 used the Oswestry Disability Index (ODI) and short-form 36 questionnaire (SF-36) in addition to the VAS. Three studies used some form of physical function outcome measure.42,45,46

Intervention Type The core stability exercises evaluated in the included studies varied. One study used machine-based strengthening exercises for the low back and abdomen,42 whereas another used a full-body strengthening program that combined machines, free weights, and body-weight exercises targeting

the abdominal and lower back muscles (eg, crunches performed using a Swiss ball, prone “Supermans,” traditional abdominal crunches).46 Two of the studies involved exercises where participants cocontracted the transversus abdominis and multifidus muscles and progressed from easier to more complex positioning and the use of unstable surfaces.43,44 The remaining study45 used “dynamic muscular stabilization technique,” which also involves a progression of resistance and more difficult positioning through different stages. Control/comparison group interventions also varied widely between the studies—for example therapeutic

FIGURE. Selection process of included articles. ! 2014 Lippincott Williams & Wilkins

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TABLE 2. Summary of Included Studies First Author, Year of Publication

Population and Sample Size

Study Design

Outcome Measures

Ganzit et al,42 1998

Adult males with chronic LBP involved in a variety of sports, n = 25 per group

Prospective comparative trial

VAS, isokinetic strength of lumbar flexors and extensors. Assessment at 12 wk

Harringe et al,43 2007

Youth female gymnasts with acute LBP, n = 19 after baseline, 15 in the intervention group and 4 in the control group

Prospective controlled intervention trial

Borg category-ratio scale. Assessment at 9-12 wk

Hides et al,44 2008

Adult and youth male elite cricket players with LBP, n=7

Single blinded pretreatment, posttreatment assessment

VAS, cross-sectional area of the multifidus muscles. Assessment at 6 wk

Kumar et al,45 2009

Adult male field hockey players with subacute and chronic LBP, n = 15 per group

RCT

VAS, walking distance, stand-ups, stair climbing. Assessments at 3 and 5 wk

Jackson et al,46 2011

Middle-aged and older adult male ice hockey players with chronic LBP, n = 15 per group

RCT with 3 groups in total: middle-aged experimental, old-aged experimental, and control (which had both middle-aged and old-aged participants)

VAS, ODI, SF-36, 5 repetition maximum leg press, bench press, and lat pulldown. Assessments at 8 and 12 wk

Interventions Stability group—machine-based resistance exercises (extension, abdominal, and rotatory torso machines), 3-5 sets of 25 repetitions, 2 or 3 times per wk Comparison group—Souchard postural exercises, stretching, and unweighted abdominal and back muscle strength exercises for 1 h, 2 or 3 times per wk Stability group—group exercises performed during warm-up 3-4 times per wk and consisting of abdominal hollowing through isometric cocontraction of the transverse abdominis and lumbar multifidus with progressive positions (prone to 4 point to prone with opposite arm/leg raising to standing on balance board to a trampette) Control group—regular training Stability group—15-30 min of daily stabilization training consisting of cocontraction of the multifidus, transversus abdominis, and anterior pelvic floor muscles, using real-time ultrasound imaging feedback. Participants progressed from supine hook-lying to upright (sitting/standing) positions Stability group—DMST performed in 4 progressive stages over 5 wk Comparison group—conventional treatment (ultrasound, shortwave diathermy, and lumbar strengthening) with 18 sessions over 5 wk Stability group—full-body progressive PRT including abdominal crunches, swiss ball crunches, and prone “Supermans” performed 4 times per wk Control group—regular recreational activity (ice hockey) twice per wk for .60 min

DMST, dynamic muscular stabilization technique; n, number; PRT, periodized resistance training.

ultrasound, short-wave diathermy, and floor-based lumbar strengthening exercises (which could also be considered a form of core stability exercise) 45; Souchard postural exercises with stretching and unweighted abdominal and back muscle strengthening exercises (potentially another form of core stability exercise)42; and regular training and recreational activities.43,46 One observational study did not include a control or comparison intervention.44

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Primary Study Outcomes: Back Pain and Disability Table 3 depicts the results of the included studies. Two RCTs (45 participants) and 3 nonrandomized studies (47 participants) provided information on the effect of core stability exercises on pain and disability outcomes. Four of the 5 studies reported a statistically significant improvement in average pain intensity for their core stability intervention groups,42,44–46 and ! 2014 Lippincott Williams & Wilkins

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TABLE 3. Summary of Results

First Author, Year of Publication

Critical Appraisal of Study (Cochrane ROB Tool for RCTs and Downs and Black Checklist for Nonrandomized Studies)

Within-Group Results

Between-Group Results

Ganzit et al,42 1998

6/27 items satisfied on Downs and Black checklist—low quality

Postural exercise group mean VAS No significant differences in score went from 4.5/10 to 2.5/10. pain intensity were noted Strengthening group mean VAS between groups score went from 5.0/10 to 2.5/10. Both groups demonstrated statistically significant improvements (P , 0.01)

Harringe et al,43 2007

11/27 items satisfied on Downs and Black checklist—moderate quality

Median pain intensity in the intervention group with LBP went from 2/10 to 0/10, whereas in the control group with LBP, the median pain intensity went from 1.25/10 to 0.5/10. No significant differences in either control or intervention group in terms of maximum or median pain intensity between baseline and after intervention. The intervention group showed a significant difference (P = 0.02) for fewer days with LBP, whereas in the control group, there was a trend toward increased number of days with LBP (P = 0.06) Stabilization exercise significantly reduced pain (after intervention compared with baseline) in the intervention group from a mean of 4.3/10 to 2.3/10 (P , 0.05) VAS scores in conventional treatment group went from an average of 7/10 to 5.8/10 (day 21) to 4.3/10 (day 35). VAS scores in the DMST group went from an average of 7.1/10 to 4.9/10 (day 21) to 1.5/10 (day 35). In both the treatments, the mean levels of all variables between days (within subjects) differed significantly either at P , 0.05 or P , 0.01, except walking in (the) conventional (group) (day 0 and day 21) Control group VAS went from 4.2/10 to 4.6/10 (8 wk) to 4.5/10 (12 wk). ME group VAS went from 4.3/10 to 3.7/10 (8 wk) to 3.2/10 (12 wk). OE group VAS went from 4.5/10 to 3.9/10 (8 wk) to 3.3/10 (12 wk). Both the ME and OE groups showed statistically significant (P , 0.05) improvements in pain intensity, disability, and QoL scores from baseline to week 8, baseline to week 12, and week 8 to week 12

Hides et al,44 2008 10/27 items satisfied on Downs and Black checklist—low quality Kumar et al,45 2009

7/11 items with low risk of bias on Cochrane ROB tool

Jackson et al,46 2011

2/11 items with low risk of bias on Cochrane ROB tool

No significant differences between groups in terms of maximum or median pain intensity. Significant difference (P = 0.005) in terms of number of days of pain favoring the exercise intervention group

NA

Reviewers’ Conclusions A statistically significant and clinically important improvement in pain intensity was noted over time in the core stability exercise group. No statistically significant or clinically important differences in pain intensity were noted between groups Neither statistically significant nor clinically important differences in pain intensity were noted between groups or within the core stability exercise group over time

A statistically significant and clinically important improvement in pain intensity was noted over time

The mean levels of all variables DMST group had statistically differed significantly (P , significant and clinically 0.01) between treatments important improvements in pain (between subjects) except on intensity over time and when day 0. The levels of all compared with the conventional variables on both day 21 and treatment group after intervention day 35 were significantly high(er) (P , 0.01) in DMST than in conventional, except pain, which was similar (P , 0.05) at day 21

At weeks 8 and 12, the ME and A statistically significant but not OE groups both showed clinically important improvement significant (P , 0.05) in pain intensity was noted in improvements in pain, both the ME and OE groups over disability, and QoL measures time and when compared with the as compared with the control control group after intervention. group. There were no Disability due to LBP showed significant (P , 0.05) statistically significant and differences between the ME clinically important improvement and OE groups at weeks 8 in both core stability groups over and 12 in pain, disability, and time and when compared with QoL control after intervention

DMST, dynamic muscular stabilization technique; ME, middle-aged experimental; NA, not applicable; OE, old-aged experimental; QoL, quality of life; PRT, periodized resistance training; ROB, risk of bias.

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clinically meaningful differences in average pain intensity were observed in 3 of the 5 studies.42,44,45 Average pain intensity in both core stability intervention groups in the study by Jackson et al46 demonstrated statistically significant but not clinically important improvement over time, whereas the average pain intensity in their control group increased by the end of the trial. Two studies42,45 reported statistically significant improvement in pain intensity in their comparison treatment groups over time. Two RCTs (75 participants) and 2 nonrandomized trials (69 participants) provided information on the effect of core stability exercises compared with other treatments. One study45 noted statistically significant and clinically important improvements in pain intensity, favoring the core stability intervention group over their conventional treatment group (which included lumbar strengthening). Jackson et al46 noted statistically significant but not clinically important improvements in pain intensity in both of their core stability intervention groups compared with the control group, with no statistically or clinically significant differences noted between the 2 intervention groups. The remaining studies42,43 did not find statistically significant or clinically important differences in pain intensity between their intervention and comparison groups. Jackson et al46 found that disability due to LBP (ODI) showed statistically significant and clinically important improvement in both of their intervention groups compared with the control group, with no statistically significant or clinically important differences noted between the 2 intervention groups.

Secondary Study Outcomes: Functional Testing and Global Health Findings Jackson et al46 found statistically significant increases in strength for all of the functional measures assessed (bench press, leg press, lat pulldown) in both of their intervention groups compared with the control group. One study42 found statistically significant increases in peak isokinetic torque at 60 degrees per second for the lumbar flexors and extensions in the intervention group, whereas the comparison group demonstrated a statistically significant increase in peak isokinetic torque at both 60 degrees per second and 120 degrees per second. Another study45 found statistically significant improvements in all functional measures assessed (walking, stand-ups, and climbing) in their intervention and comparison groups, with statistically significant differences favoring the intervention group. Jackson et al46 further found that quality of life (SF-36) was significantly improved in both of their intervention groups compared with the control group in both the physical and mental composite scores, with no statistically significant differences noted between the 2 intervention groups. None of the included studies reported any adverse events occurring during the trials. However, only one of the studies45 specifically indicated an absence of adverse events.

Methodological Quality One of the non-RCTs43 was found to have moderate quality, and one of the RCTs45 was found to have a low risk of bias. The remaining studies could be considered low

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quality or at a high risk of bias. Downs and Black checklist scores of the 3 non-RCTs ranged from 6 to 11. The critical items missing from all 3 non-RCTs were: adequate descriptions of the representativeness of participants, treatments, and settings; a lack of participant and provider blinding; a description of study compliance or adverse events; and adequate power calculations. The 2 included RCTs had 246 and 745 items with low risk of bias; common potential biases were a lack of blinding of participants and providers and nonreporting of treatment compliance. The overall quality of the available evidence was rated as low, as we judged future research to be highly likely to change our estimate of the effect.

DISCUSSION We found only a small number of studies focusing on the use of core stability exercise as a treatment for athletes with LBP, including only 2 RCTs. There was important heterogeneity among included studies and an overall low quality of evidence available. Most of the included studies reported statistically significant and clinically important improvements in pain intensity over time in the groups performing core stability exercises. Two RCTs, 1 with a low risk of bias, demonstrated statistically significant and clinically important differences in pain intensity and functional outcomes, favoring core stability exercise over conventional treatment45 and regular training.46 Differences in the studies included the ages of the athletes involved, the sports in which they participated, and the different forms of “core stability exercise” used as an intervention. This heterogeneity precluded meta-analysis. Furthermore, none of the studies reported long-term follow-up, and sample sizes were small. Core stability exercises have received increasing scrutiny recently.29,47 One survey indicated that core stability exercises are the most frequently recommended form of exercise by Irish physical therapists.48 Previous systematic reviews and meta-analyses have demonstrated that core stability exercise programs can be effective for specific populations with LBP, particularly those with chronic LBP.21,23,24,30 The limited findings provided by the current review of athletes with LBP undergoing core stability exercise programs demonstrates conflicting findings in both within-group and between-group differences, particularly when considering clinically important differences in pain intensity and functional outcomes. That being said, the 3 studies that included athletes with chronic LBP42,45,46 generally reported statistically significant and clinically important within-group and/ or between-group improvements in pain intensity for their core stability groups. However, only one of those studies45 on patients with chronic LBP was found to have a low risk of bias. The one study that specifically included athletes with acute LBP43 did not report statistically significant improvements in pain intensity over time for their core stability group. These findings are similar to what has been found for the general population. Issues with muscular weakness, imbalance, and recruitment specific to the hip and/or core musculature have been implicated among many potential sources of LBP in ! 2014 Lippincott Williams & Wilkins

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athletes.49–53 Athletes with a history of LBP are also at increased risk for future LBP.54 Therefore, it seems plausible that core stability exercises would be a potentially suitable intervention to consider for athletes with LBP. Although core stability exercises may be useful in treating athletes with chronic LBP, it cannot be conclusively stated which form(s) of core stability exercise are most effective because the included studies varied.

as an outcome measure is advocated for future research, as well as some form of functional outcome, and a measure of disability due to back pain (eg, ODI). The use of standardized exercise protocols and outcome measurement in future research would be beneficial in allowing for meta-analyses to be performed.

Strengths and Weaknesses

The quantity and quality of the evidence available on the use of core stability exercise as an intervention for athletes with LBP is low. The types of exercises evaluated in the included studies varied considerably as did study populations, which were small and saw only mixed results in terms of short-term pain intensity and disability. Pooling of data was not possible and the state of the evidence precludes conclusions from being drawn at this point. Further research on this topic is clearly needed and should include consistent definitions of both study populations and interventions.

Among the strengths of this review were the searching of multiple databases and using reference searching, along with authors independently evaluating database search results and assessing the literature for quality and risk of bias, with a third author resolving differences. However, the relatively small number of studies that met the inclusion criteria and the overall low quality of included studies could lead to bias in the conclusions. In addition, the inclusion of nonrandomized comparative studies and uncontrolled studies in this review could potentially be a source of bias. Another limitation was that only articles in English were retrieved. However, as the search strategy was conducted in all languages, such cases should have been identified. It is also possible that there is publication bias with respect to the use of core stability exercises in athletes with LBP, particularly given the popularity of core stability exercises in the lay media and their use among the general population. The heterogeneity of the included studies (eg, athlete characteristics, nature of the “core stability exercise” interventions) limits the interpretation of the findings of this review and their applicability in clinical practice. It is also acknowledged that some participants in studies evaluating core stability exercises for LBP in the general population may be athletes from different sports and at different levels of competition. However, such studies also include nonathletes and do not specifically analyze the results of athletes versus nonathletes.

Future Research Directions Further research is clearly needed on this topic. Researchers and clinicians need to determine whether core stability exercises should be used to treat low back injuries, prevent low back injuries and possible recurrences, or if they should be used for performance enhancement. Perhaps, the role of core stability exercises is a combination of the above. A consistent definition of what comprises a core stability exercise must be used in future research. This could be determined through a consensus study. Higher-quality adequately-powered RCTs are needed to determine which interventions have the greatest effect on athletes with LBP and should compare different forms of core stability exercise, both alone and in combination with other treatments (eg, manual therapies, biopsychosocial interventions, different forms of exercise therapy). The effects of core stability exercises in athletes with LBP of different durations (ie, acute, subacute, or chronic) across different age groups (youths, adults, seniors), from different sports, and at different levels of competition (recreational, amateur, professional), each need to be further evaluated. Continued use of the VAS ! 2014 Lippincott Williams & Wilkins

CONCLUSIONS

ACKNOWLEDGMENTS The authors thank and acknowledge Anne TaylorVaisey of the Canadian Memorial Chiropractic College and Mary Chipanshi of the University of Regina for their assistance with formulating the search strategy and conducting the literature search. REFERENCES 1. Jonasson P, Halldin K, Karlsson J, et al. Prevalence of joint-related pain in the extremities and spine in five groups of top athletes. Knee Surg Sports Traumatol Arthrosc. 2011;19:1540–1546. 2. Foss IS, Holme I, Bahr R. The prevalence of low back pain among former elite cross-country skiers, rowers, orienteerers, and nonathletes: a 10-year cohort study. Am J Sports Med. 2012;40:2610–2616. 3. Durall CJ, Udermann BE, Johansen DR, et al. The effects of preseason trunk muscle training on low-back pain occurrence in women collegiate gymnasts. J Strength Cond Res. 2009;23:86–92. 4. Walker BF. The prevalence of low back pain: a systematic review of the literature from 1966 to 1998. J Spinal Disord. 2000;13:205–217. 5. Mogensen AM, Gausel AM, Wedderkopp N, et al. Is active participation in specific sport activities linked with back pain? Scand J Med Sci Sports. 2007;17:680–686. 6. Hoskins W, Pollard H, Daff C, et al. Low back pain status in elite and semi-elite Australian football codes: a cross-sectional survey of football (soccer), Australian rules, rugby league, rugby union and non-athletic controls. BMC Musculoskel Disord. 2009;10:38. 7. Gatt CJ, Hosea TM, Palumbo RC, et al. Impact loading of the lumbar spine during football blocking. Am J Sports Med. 1993;25:317–321. 8. Reed JJ, Wadsworth LT. Lower back pain in golf: a review. Curr Sports Med Rep. 2010;9:57–59. 9. Ferdinands RED, Kersting U, Marshall RN. Three-dimensional lumbar segment kinetics of fast bowling in cricket. J Biomech. 2009;42:1616–1621. 10. Moorman CT, Johnson DC, Pavlov H, et al. Hyperconcavity of the lumbar vertebral endplates in the elite football lineman. Am J Sports Med. 2004;32:1434–1439. 11. Paxton ES, Moorman CT, Chehab EL, et al. Effect of hyperconcavity of the lumbar vertebral endplates on the playing careers of professional american football linemen. Am J Sports Med. 2010;38:2255–2258. 12. Ong A, Anderson J, Roche J. A pilot study of the prevalence of lumbar disc degeneration in elite athletes with lower back pain at the Sydney 2000 Olympic Games. Br J Sports Med. 2003;37:263–266. 13. Hangai M, Kaneoka K, Hinotsu S, et al. Lumbar intervertebral disk degeneration in athletes. Am J Sports Med. 2009;37:149–155.

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Appendix 1: Medline Search Strategy 1. Athlete. 2. Athletic performance. 3. Athletic injuries. 4. Sports. 5. Sports injuries. 6. 1 or 2 or 3 or 4 or 5. 7. Low back pain. 8. Lumbar vertebrae. 9. Lumbosacral. 10. Spine. 11. Low back pain. 12. Lower back pain. 13. Lumbar pain. 14. Backache. 15. 7 or 8 or 9 or 10 or 11 or 12 or 13 or 14. 16. Exercise therapy. 17. Resistance training. 18. Physical therapy modalities. 19. Isometric contraction. 20. Abdominal muscles. 21. Dynamic muscular stabilization techniques. ! 2014 Lippincott Williams & Wilkins

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Clin J Sport Med ! Volume 0, Number 0, Month 2014

22. 23. 24. 25. 26. 27. 28. 29.

Periodized resistance training. Periodized musculoskeletal rehabilitation. Trunk muscle strength. Resistance exercise. Segmental muscle control exercise. Lumbar extensor strengthening. Back strengthening. Lumbar strengthening.

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Stability Exercises for Back Pain in Athletes

30. 31. 32. 33. 34. 35.

Spine rehabilitation. Core exercise. Core strength. Core stabilization. Isometric core exercise. 16 or 17 or 18 or 19 or 20 or 21 or 22 or 23 or 24 or 25 or 26 or 27 or 28 or 29 or 30 or 31 or 32 or 33 or 34. 36. 6 and 15 and 35.

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