Increased participation in sports has led to more sports injuries. Evidence-based methods

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1 REVIEW ARTICLE Prevention of Sports Injuries Systematic Review of Randomized Controlled Trials Sari Aaltonen, PT; Heli Karjalainen, PT; Ari Heinonen, PT, PhD; Jari Parkkari, MD, PhD; Urho M. Kujala, MD, PhD Increased participation in sports has led to more sports. Evidence-based methods to prevent sports are needed. A systematic review was conducted of the effects of randomized controlled interventions to prevent sports. A systematic search was performed of various databases and the reference lists of articles and reviews. Two reviewers independently extracted the data and assessed the methodological quality of the included trials. Thirty-two trials ( participants) met the inclusion criteria. We found evidence of the preventive effect of 3 types of injury prevention interventions. In 5 trials including 6 different comparisons (2446 participants), custom-made or prefabricated insoles reduced lower limb compared with no insoles in military recruits (risk reduction 50% in 4 comparisons). All 7 studies investigating external joint supports ( participants) showed a tendency to prevent ankle, wrist, or knee (risk reduction 50% in 5 studies). All 6 multi-intervention training programs (2809 participants) were effective in preventing sports (risk reduction 50% in 5 studies). Various interventions may prevent sports. A decreased risk of sports was associated with the use of insoles, external joint supports, and multi-intervention training programs. More high-quality randomized controlled trials in different sports and populations are needed. Arch Intern Med. 2007;167(15): Aside from its well-known health benefits, leisure physical activity may cause sports. 1,2 Between 1997 and 1999, an estimated 7 million Americans received medical attention for sports and recreational, the incidence being 25.9 per 1000 population. 3 According to Gotsch et al, 4 the incidence of nonfatal sports- and recreation-related treated between July 2000 and June 2001 in hospital emergency departments in the United States was 15.4 per 1000 population. At present many different methods to prevent sports are recommended and practiced by sports participants. Several methods of sports injury prevention have been studied in randomized and nonrandomized studies, but the results Author Affiliations: Department of Health Sciences, University of Jyväskylä, Jyväskylä (Mss Aaltonen and Karjalainen and Drs Heinonen and Kujala), and UKK Institute, Tampere (Dr Parkkari), Finland. have often been inconclusive and sometimes conflicting. 5 Evidence from randomized controlled trials (RCTs) is needed because it seems that a substantial proportion of sports can be avoided by the use of effective preventive methods. 5,6 Some earlier systematic reviews 7-12 have summarized the effects of specific injury prevention methods based on RCTs, and a few of them have also included other controlled trials. To date, only 1 wider review 5 of RCTs of sports covering a variety of preventive methods has been published. This review did not, however, include quality assessment of the included trials, and since its publication many new trials have been published. The aim of this systematic review of published RCTs is to summarize the effects of interventions targeted at preventing sports. 1585

2 METHODS DATA SOURCES AND SEARCH STRATEGY We searched for relevant trials published in English through December 31, 2005, without a start date, using the following domain databases: MEDLINE (January 1, 1966, to December 31, 2005), PubMed, the Cochrane Central Register of Controlled Trials, SPORTDiscus, CINAHL (Cumulative Index to Nursing and Allied Health Literature) ( January 1, 1982, to December 31, 2005), and PEDro (the Physiotherapy Evidence Database). Key words in the search were sports injury/ies, athletic injury/ies, prevention, preventive, randomized, controlled trial, and randomized controlled trial. In addition, the manual archives of the senior authors (A.H., J.P., and U.M.K.) and the reference lists of retrieved articles and relevant reviews were hand searched for possible information on trials of interest. Two reviewers (S.A. and H.K.) assessed the eligibility criteria together. TRIAL SELECTION AND OUTCOMES To be selected for this review a trial had to investigate the effects of any preventive intervention on sports. On the basis of the abstract, we assessed whether the study had the potential to be included, and on the basis of the full article, we decided whether the study met the inclusion criteria. We included trials if they were randomized or quasirandomized, controlled, and published before January 1, Trials that in all likelihood had not been randomized and abstracts unaccompanied by a full article in a peer-reviewed journal were excluded. In addition, the study report had to contain the injury rate or the number of injured individuals as an outcome, and the intervention protocol and outcome measures of the studies had to be explicitly described. DATA EXTRACTION AND METHODOLOGICAL QUALITY ASSESSMENT Two reviewers (S.A. and H.K.) independently extracted data on the study design, intervention and characteristics of the study participants, injury criteria, and main outcomes from each article. In addition, to evaluate the methodological quality of the included studies, 2 independent reviewers (S.A. and H.K.) collected information as recommended by van Tulder et al. 13 Any disagreements were resolved by consensus between the reviewers. If disagreements were not resolved, 3 other reviewers (A.H., J.P., and U.M.K.) were consulted. The assessment list of methodological quality consists of 11 criteria: randomization, concealed allocation, baseline similarity of the study groups, blinding of participants, blinding of care providers, blinding of assessors, co-interventions, compliance, dropout rate, timing of outcome measures, and intention-to-treat analysis. Every criterion was assessed as yes, no, or don t know, with only a yes answer being scored with a point. The sum score ranged from 0 to 11. STATISTICAL ANALYSIS Except for 5 studies, we calculated odds ratios (ORs) and their 95% confidence intervals (CIs) on the basis of the reported data in independent studies (Table 1). We calculated the ORs using the number of injured individuals, except for 3 trials in which we used the number of because information about the number of injured individuals was missing. Subgroups were formed on the basis of similarity of preventive methods despite the fact that the preventive methods reported were not identical in all respects and that study designs were otherwise somewhat methodologically heterogeneous. In subgroups of studies, first, a qualitative assessment of results on primary outcome measures of studies was performed. Second, we quantified the results by counting how many people in the intervention group compared with the control group showed at least a 30% reduction in the occurrence of. Because there were differences between studies in the information available, this calculation was performed on the basis of an OR of 0.70 or less, a relative risk of 0.70 or less, or at least a 30% higher reduction in the occurrence of in the intervention group compared with the control group. A similar calculation was performed using a 50% cutoff point. We assessed heterogeneity between studies by using I 2 statistics. 46 A value greater than 50% may be considered substantial heterogeneity. For these analyses we used the fixed-effects model in Review Manager version (Cochrane Collaboration, Oxford, England). RESULTS LITERATURE SEARCH AND TRIAL QUALITY The search strategy yielded 48 potentially relevant trials, of which 32 with participants met the inclusion criteria and were accepted for inclusion in this review (Figure and Table 1). To gather more precise information about the specific intervention methods used the studies were classified into subgroups (Table 1). The scores for methodological quality of the 32 trials varied from 1 to 8 of 11 points (Table 1 and Table 2). The mean score was 3.8 points, which we deemed as poorto-moderate general methodological quality. In 21 trials, no clear description of the method of randomization was given. Only 5 of 32 trials provided convincing evidence that the allocation of treatment was adequately concealed. A true intention-to-treat analysis was performed in 12 trials. The full methodological quality assessment is given in Table 2. INSOLES Five trials including 6 different comparisons (2446 participants) assessed the effectiveness of different insoles to reduce lower extremity compared with no insoles (Table 1). There was variation in the types of insoles used, but all 6 comparisons showed a trend toward preventive effects among those who used insoles compared with controls. In 1 study 15 this trend was statistically nonsignificant. All 6 comparisons showed injury risk reduction of 30% or more, and in 4 of these trials the risk reduction was 50% or more. Statistical heterogeneity was rather low (I 2 =38.1%), although the number of individuals was lowest in the comparisons showing the highest effect size. 18 In all cases the participants were military recruits. The effectiveness of custommade and prefabricated (readymade) insoles was similar (Table 1). In 1 study 19 different types of orthoses were compared, and no statistically significant differences were found in injury incidence. EXTERNAL JOINT SUPPORTS On the basis of 4 studies, ankle orthoses, 20,21 ankle stabilizers, 22 and outside-the-boot braces 23 reduced ankle, with the result being statistically significant in 3 studies and the risk reduction being 30% or more in 1586

3 Table 1. Characteristics of Randomized Controlled Trials Included in the Review Source Intervention a (% Male) Participants Finestone et al, Larsen et al, Milgrom et al, Schwellnus et al, Smith et al, Finestone et al, Biomechanical shoe Infantry recruits orthoses (custom) (NR) Biomechanical shoe Military conscripts orthoses (custom) (99.3%) Shock-absorbing Military recruits orthotic devices (prefabricated) Neoprene insoles Military recruits (prefabricated) (NR) (1) Poron insoles Coast guard (prefabricated) recruits (NR) (2) Spenco insoles (prefabricated) (3) Control (1) Soft orthoses Infantry recruits (custom) (2) Soft orthoses (prefabricated) (3) Semirigid biomechanical orthoses (custom) (4) Semirigid orthoses (prefabricated) Age Range, y Participants, Intervention/ Control, No. Insoles Duration Outcomes Examined OR or RR (95% CI) Quality Score / wk Lower extremity stress fractures OR, 0.40 ( ) b /9 3 mo Back and lower RR, 0.70 ( ) 7 extremity problems NR 143/ wk Lower extremity OR, 0.48 ( ) c 2 stress fractures / wk Lower extremity overuse (1) 30 8 wk Lower extremity (2) 30 (3) (1) 227 (2) 224 (3) 215 (4) wk Lower extremity overuse OR, 0.63 ( ) b 3 (1) vs (3) OR, 0.21 ( ) c (2) vs (3) OR, 0.10 ( ) c NC; no group differences observed External Joint Supports Surve et al, 20 Sport-Stirrup ankle Senior soccer NR 244/260 1 Playing Ankle sprains OR, 0.60 ( ) c orthoses players season Tropp et al, 21 Ankle orthoses Senior soccer NR 124/180 6 mo Ankle sprains OR, 0.16 ( ) c d players Sitler et al, 22 Semirigid ankle Military academy /812 2 y Ankle OR, 0.31 ( ) c stabilizers cadets (NR) Amoroso et al, 23 Outside-the-boot Military paratrooper /376 1 wk Ankle OR, 0.50 ( ) c braces students Sitler et al, 24 Prophylactic knee Military academy /705 2 y Knee OR, 0.43 ( ) c braces cadets (NR) Machold et al, 25 Wrist protectors Students (60%) 14.8 (mean) 342/379 1 wk Wrist OR, 0.12 ( ) c Rønning et al, Wrist protectors Snowboarders (64.2%) / mo Wrist OR, 0.27 ( ) c 7 Tropp et al, d Ankle disk training Senior soccer players Emery et al, 27 Home-based balance Physical education 2005 d,e training program students (50%) Söderman Balance board training Soccer players et al, d program (0%) Verhagen Balance board training Volleyball players et al, program (42.9%) Wedderkopp et al, d Wedderkopp et al, d,e Ankle disk and functional warm-up training Ankle disk and functional strength training Training Programs; Balance Board NR 144/180 6 mo Ankle sprains OR, 0.24 ( ) c /61 6 mo Sports OR, 0.16 ( ) c /100 7 mo Lower extremity OR, 1.25 ( ) c / wk Ankle OR, 1.06 ( ) c 4 Training Programs; Multi-Interventions With Balance Board Handball players / mo Sports OR, 0.20 (0.10, 0.41) c 3 (0%) Handball players (0%) /77 9 mo Sports OR, 0.29 ( ) c 4 Prophylactic program Senior soccer Training Programs; Other Multi-Interventions Ekstrand et al, /90 6 mo Sports NC; result favors d players intervention Heidt et al, Preseason training program Soccer players (0%) / mo Sports OR, 0.33 ( ) c 3 Holme et al, 34 Rehabilitation program Recreational /46 12 mo Ankle sprain OR, 0.18 ( ) c athletes (62%) re- Olsen et al, 35 Structured warm-up Handball players /879 8 mo Ankle and knee OR, 0.53 ( ) c d,e program (13.7%) 1 4 (continued ) 1587

4 Table 1. Characteristics of Randomized Controlled Trials Included in the Review (cont) Source Intervention a (% Male) Participants Pope et al, 36 Preexercise calf 1998 d,f muscle stretching Pope et al, 37 Lower extremity 2000 d,f stretching program van Mechelen Warm-up, cooldown, et al, and stretching program Barbic et al, 39 Type II (boil-and-bite) 2005 d,e mouth guard Finch et al, 40 Custom-made mouth 2005 d,e guard Barrett et al, Finestone et al, Milgrom et al, Jørgensen et al, (1) High-top shoes (2) High-top shoes with air chambers (3) Low-top shoes Modified basketball shoes Modified basketball shoes Instructional ski video Army recruits Army recruits Recreational runners University students (81%) Australian football players College basketball players (91.7%) Infantry recruits (NR) Infantry recruits Downhill skiers (58%) Age Range, y Participants, Intervention/ Control, No. Outcomes Duration Examined Stretching and Warm-up Programs / wk Lower extremity / wk Lower extremity NR 210/ wk Lower extremity and back OR or RR (95% CI) Quality Score OR, 0.87 ( ) c 5 OR, 0.98 ( ) c 5 OR, 1.22 ( ) c 2 Mouth Guards 20.9 (Mean) 322/324 3 mo Concussions OR, 1.04 ( ) c /111 1 Playing season Modified Shoes 20.6 (Mean) (1) 227 (2) 212 (3) 183 Head/orofacial RR, 0.56 ( ) 5 2 mo Ankle sprains (1) vs (3) OR, 1.34 ( ) c (2) vs (3) OR, 0.77 ( ) c / wk Lower extremity overuse NR 187/ wk Lower extremity stress fractures NC; no group 2 differences observed OR, 1.28 ( ) c 3 Videos /520 1 wk Sports OR, 0.64 ( ) c 3 4 Arnason et al, d Video-based awareness program Soccer players NR 127/144 5 mo Sports OR, 1.42 ( ) b 3 Abbreviations: CI, confidence interval; NC, not calculated; NR, not reported; OR, odds ratio; RR, risk ratio. a Comparison is made with a control group that has not participated in any intervention (except for Finestone et al 19 and Barrett et al 41 ). b Calculated by us using the number of in the intervention vs control groups. c Calculated by us using the number of injured individuals. d Cluster randomized. e Cluster randomization was taken into account in the analyses of the original report. f Quasi-randomized Studies identified and screened for retrieval 48 Articles retrieved for detailed evaluation 32 Articles included in systematic review Figure. Literature review flow diagram. all 4 studies and 50% or more in 3 studies (Table 1). Knee supports worn by military cadets while playing football 24 also showed a preventive effect on knee. Wrist protectors 4755 Studies excluded on the basis of title or abstract (not randomized, no control group, reviews, comments, editorials, duplicates, or full articles not available) 16 Articles excluded after article screening with inclusion criteria (outcome other than sports, not adequately randomized, lack of control group or not published in peerreviewed journals) were tested during snowboarding in 2 studies. 25,26 These interventions showed a similar effect in preventing wrist (ORs, 0.12 and 0.27). Therefore, all 7 studies investigating the effects of external joint supports ( participants) showed a tendency to reduce the risk of injury in intervention groups compared with control groups. Injury risk was reduced by 30% or more in all the trials and by 50% or more in 6 of the 7 trials. Statistical heterogeneity was low (I 2 =25.4%). TRAINING PROGRAMS Four trials 21,27-29 (1799 participants) testing balance board training to prevent gave contradictory results (Table 1). In the studies by Tropp et al 21 and Emery et al, 27 the rate of sports was significantly reduced in the training participants, whereas this was not the case in the studies by Verhagen et al 29 and Söderman et al. 28 The results showed heterogeneity 1588

5 Table 2. Methodological Quality Assessment of Included Trials a Source A B C D E F G H I J K TOT Finestone et al, YES DK YES YES DK DK DK YES NO YES NO 5 Larsen et al, YES YES DK DK YES DK DK YES YES YES YES 7 Milgrom et al, DK DK DK DK DK DK DK DK YES YES NO 2 Schwellnus et al, DK DK DK DK DK DK DK YES YES YES DK 3 Smith et al, DK DK DK DK DK DK DK DK NO YES NO 1 Finestone et al, YES DK DK YES DK DK DK YES NO YES NO 4 Surve et al, DK DK DK DK DK DK DK YES DK YES YES 3 Tropp et al, DK DK DK DK DK DK DK DK YES YES NO 2 Sitler et al, DK DK YES DK DK DK DK YES DK YES DK 3 Amoroso et al, YES DK YES DK DK YES DK YES YES YES NO 6 Sitler et al, YES DK YES DK DK DK DK YES DK YES DK 4 Machold et al, YES DK YES DK DK DK DK YES DK YES YES 5 Rønning et al, YES DK YES DK DK YES DK YES YES YES YES 7 Emery et al, YES YES YES DK DK DK DK YES YES YES DK 6 Söderman et al, DK DK YES DK DK DK DK NO NO YES NO 2 Verhagen et al, DK DK YES DK DK YES DK YES NO YES DK 4 Wedderkopp et al, DK DK DK DK DK DK DK YES DK YES YES 3 Wedderkopp et al, DK DK DK DK DK DK DK YES YES YES YES 4 Ekstrand et al, DK DK DK DK DK DK DK YES DK YES DK 2 Heidt et al, DK DK DK DK DK YES DK DK DK YES YES 3 Holme et al, YES DK NO DK DK DK DK DK NO YES NO 2 Olsen et al, YES YES YES DK DK YES NO YES YES YES YES 8 Pope et al, DK YES DK YES DK DK DK YES YES YES DK 5 Pope et al, DK YES DK DK DK YES DK YES NO YES YES 5 van Mechelen et al, DK DK YES DK DK DK DK NO NO YES NO 2 Barbic et al, DK DK YES NO NO NO DK YES YES YES NO 4 Finch et al, DK DK YES NO NO NO DK YES YES YES YES 5 Barrett et al, YES DK YES DK DK DK DK DK YES YES NO 4 Finestone et al, DK DK DK DK DK DK DK YES DK YES DK 2 Milgrom et al, DK DK DK DK DK DK DK YES DK YES YES 3 Arnason et al, DK DK DK DK DK DK DK YES YES YES NO 3 Jørgensen et al, DK DK YES DK DK DK DK DK DK YES YES 3 Abbreviations: A, adequate randomization (yes = random assignment was made by using a computer-generated random number table, sealed opaque envelopes, or another clearly described and acceptable random assignment method); B, concealed allocation (yes = assignment was made by an independent person who had no information about study participants); C, similarity between groups at baseline (yes = study groups were similar or comparable at baseline regarding demographic factors and other important prognostic factors); D, study population blinding (yes = study population blinding was clearly described and acceptable); E, physician blinding (yes = medical staff or care providers (eg, physicians, research assistants, or trainers) involved in the study were blinded regarding group assignment); F, outcome assessor blinding (yes = physicians, radiologists, physiotherapists, and other nursing staff who evaluated the were blinded regarding group assignment); G, avoided or similar co-interventions (yes = all confounding co-interventions were either avoided or similar between study groups); H, acceptable compliance (yes = compliance was regularly checked or otherwise strictly supervised by someone other than study participants, and it was more than 70% in every study group); I, described and acceptable dropout rate (yes = dropout rate was 20% for short-term follow-up [0-3 months] and 30% for long-term follow-up [3-24 months]; dropout reasons were given); J, similar timing of the outcome assessment (yes = duration of the intervention was similar for all study groups); K, intention-to-treat analysis (yes = intention-to-treat analysis was acceptable if all randomly assigned study participants were included in the analysis); YES, criteria was described and acceptable (1 point); NO, criteria was not acceptable (0 points); DK, do not know, criterion was unclear or was not described (0 points); TOT, total points of quality assessment (maximum of 11 points). a For a detailed explanation of how the assessment was performed see the Literature Search and Trial Quality subsection of the Results section and van Tulder et al. 13 (I 2 =80.9%). The highest effect size was seen in the study with the fewest participants. 27 Two multi-intervention trials by Wedderkopp et al 30,31 that included balance board training (400 participants) showed a significant reduction in the number of in the training groups compared with the control groups. Multi-intervention programs without balance board training, including exercise and rehabilitation (2409 participants), were assessed as interventions in 4 trials (Table 1) All these trials favored the use of multi-intervention programs. In the study by Ekstrand et al, 32 it was not possible to calculate the OR. However, in the original study the authors reported a 75% reduction in sports, which also supports the preventive effect of multi-intervention programs. All 6 multi-intervention training programs (2809 participants) showed a reduction in the risk of injury in the intervention groups. Injury risk was reduced by 30% or more in all the trials and by 50% or more in 5 of the 6 trials. There was no high statistical heterogeneity between the trials (I 2 =46.2%). OTHER INTERVENTIONS None of the 3 trials on the effect of stretching and warm-up programs (3052 participants) on the rate of lower extremity showed preventive effects (Table 1). No statistical heterogeneity was observed (I 2 =0%). The effect of a special mouth guard was assessed in the study by Barbic et al 39 in 646 university football and rugby players. The number of concussions observed did not differ between the intervention and control groups. In the study by Finch et al 40 it was not possible to cal- 1589

6 culate the OR, but the use of custommade mouth guards seemed to prevent head (including orofacial) among 301 Australian football players. Modified basketball shoes did not display a preventive effect on ankle sprains or other lower extremity No statistical heterogeneity was observed (I 2 =0%). In the studies by Jørgensen et al 44 and Arnason et al, individuals watched an instructional injury prevention video. Jørgensen et al showed a reduction in the number of downhill skiing in the intervention group. The study by Arnason et al, which also included an awareness program, did not show the instructional video to have a preventive effect on soccer. COMMENT In 32 trials with 40 comparisons, a significant effect of different preventive methods in preventing sports was reported for 19 interventions. We grouped sports injury preventive methods into subgroups. The analysis showed that the use of insoles, external joint supports, and training programs, including different components, was effective in preventing, whereas other prevention methods did not show a consistent preventive effect. We did not perform a comprehensive meta-analysis because of many different limitations related to the clinical and methodological diversity of the studies. Other possible limitations include selection bias due to inadequate concealment of allocation in 27 trials; performance and detection bias because of inadequate blinding of participants, care providers (eg, physicians, research assistant, or trainer), or outcome assessors in all 32 trials; attrition bias because of the lack of intention-to-treat analysis in 20 trials; and heterogeneity of follow-up times. Because the number of specific types of trials was low, statistical evaluation of publication bias was limited. Overall, 3 trials showing high effect size had low numbers of participants. The best methodological quality score given in this review was 8 of 11 points. In most sports injury prevention interventions, it is almost impossible to attain the maximum score because it is difficult to blind participants, physicians, and outcome assessors at the same time and to avoid co-interventions. It is possible that in many cases the quality criteria were in fact met but that because of inadequate reporting the studies may have scored lower points. 47 In general, studies published more recently scored higher than older studies. According to all 6 comparisons evaluated in this systematic review, the use of shock-absorbing insoles tended to reduce lower extremity and stress fractures in military recruits. The present results are in line with the findings of Rome et al. 7 However, opposite results were found in a nonrandomized study by Gardner et al 48 and in a new randomized study by Withnall et al, 49 in which insoles did not prevent stress fractures in military recruits. Although recruits usually go through a high-intensity physical training period, the generalization of findings to athletes is not straightforward. Athletes may already have an optimal shock-absorbing mechanism in their shoes, and thus, additional insoles may not help in injury prevention. The findings among military recruits may, however, have clinical relevance for formerly inactive individuals who start training programs to prevent or treat chronic diseases. Note that on the basis of the studies available we did not see a difference in the effect size between studies evaluating the effect of custom-made vs prefabricated insoles. These types were directly compared with each other in only 1 study. 19 The effectiveness of external joint supports has been assessed mostly in high-risk sporting activities, such as soccer, American football, basketball, parachute jumping, and snowboarding. In all 4 of the trials assessed in this review, the use of external ankle supports provided beneficial protection against traumatic ankle. Similar findings were established in a review by Handoll et al, 8 who conducted a meta-analysis of the effects of interventions used in the prevention of ankle ligament. The nonpreventive effect of modified shoes found by Barrett et al 41 can probably be explained from a biomechanical point of view. It is understandable that shoes cannot support the structures of an ankle to the same extent as more rigid orthoses, braces, and stabilizers. The shoe may actually contribute to the twisting force during an ankle sprain, and in this situation it clearly does not support the ankle. Promising, but to some extent contradictory, findings were found using a balance board training program as a preventive strategy. Interventions were performed in home and in team practice, but the results did not show which of these strategies is more effective. A recent study by McGuine and Keene 50 gives further evidence for the preventive effect of balance training. Caraffa et al 51 conducted a prospective, controlled, nonrandomized study to assess the effect of a proprioceptive training program, including the use of a wobble board, in soccer players. This study showed a significantly lower incidence of anterior cruciate ligament in the training group compared with controls (0.15 vs 1.15 per team per season). Although balance board training seems to be effective in preventing ankle, there is some disagreement whether balance board training alone prevents ankle, and there is not enough evidence to date that it has a preventive effect on the risk of knee. 28,29 All 6 of the multi-intervention training trials assessed implied that sports-related could be prevented by using different prophylactic programs. It is likely that the preventive effect of these programs is the sum of several individual methods. Because of the complexity of study designs, it is almost impossible to clarify which component of the intervention program is effective and which part of the intervention is not. Such multifactorial approaches are also usually highly labor intensive. The finding on the stretching and warm-up interventions reviewed is consistent with the results of 3 other reviews However, definitive con- 1590

7 clusions regarding the true effect of stretching cannot be drawn in this review owing to lack of goodquality RCTs. The role of different stretching protocols should also be studied among populations other than military recruits and focusing on specific types of. The prospective nonrandomized controlled study by Jakobsen et al 52 investigated the preventive effect of an individual training program including stretching, warm-up, and cooldown in recreational longdistance runners. Again, in this study the rate of lower limb did not differ between the intervention and control groups. A few RCTs have investigated the effects of other interventions, such as the use of instructional videos 44,45 and modified shoes. 41,43 However, the limited number or clinical diversity of these interventions means that it is not yet possible to form strong conclusions about their effectiveness. Two studies 39,40 on mouth guards gave contradictory results, which could mainly be explained by the difference in injury outcomes, since mouth guards provide impact energy attenuation only during impacts to the mouth and therefore have limited function in preventing concussions. Because many sports participants have limited resources to devote to the issue of injury prevention, recommendations based on RCTs can focus their interest on timeand resource-efficient methods. This systematic review of 32 RCTs shows evidence that different interventions, such as shock-absorbing insoles, external joint supports, and training programs, seem to have a preventive effect on reducing sports. However, there continues to be insufficient evidence to allow firm conclusions to be drawn about the effects of these methods of preventing in different types of sports thus far. Note that many effective means of preventing sports may not been studied using randomized designs, such as rule changes and the use of protective equipment. The present review focused only on interventions studied in randomized trials. Future research should focus on commonly practiced and high-risk sports, including modern sporting trends. In addition, in future studies issues concerning the acceptability, compliance, cost-effectiveness, and long-term adherence of the preventive measures should be well evaluated. Accepted for Publication: March 26, Correspondence: Urho M. Kujala, MD, PhD, Department of Health Sciences, University of Jyväskylä, PO Box 35 (LL), FIN Jyväskylä, Finland (urho.kujala@sport.jyu.fi). Author Contributions: Ms Aaltonen and Dr Kujala had full access to all of the published data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Study concept and design: Aaltonen, Karjalainen, Heinonen, and Kujala. Acquisition of data: Aaltonen, Karjalainen, Heinonen, Parkkari, and Kujala. Analysis and interpretation of data: Aaltonen, Karjalainen, Heinonen, Parkkari, and Kujala. Drafting of the manuscript: Aaltonen, Karjalainen, Heinonen, and Kujala. Critical revision of the manuscript for important intellectual content: Aaltonen, Karjalainen, Heinonen, Parkkari, and Kujala. Statistical analysis: Aaltonen, Karjalainen, Heinonen, and Kujala. Administrative, technical, and material support: Heinonen, Parkkari, and Kujala. Study supervision: Kujala. Financial Disclosure: None reported. REFERENCES 1. Requa RK, DeAvilla LN, Garrick JG. Injuries in recreational adult fitness activities. Am J Sports Med. 1993;21(3): Uitenbroek DG. Sports, exercise and other causes of : results of a population survey. Res Q Exerc Sport. 1996;67(4): Conn JM, Annest JL, Gilchrist J. Sports and recreation related injury episodes in the US population, Inj Prev. 2003;9(2): Gotsch K, Annest JL, Holmgren P, Gilchrist J. 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