- Email: [email protected]
Does warming up prevent injury in sport?
Journal of Science and Medicine in Sport (2006) 9, 214—220
REVIEW
Does warming up prevent injury in sport? The evidence from randomised controlled trials? A.J. Fradkin, B.J. Gabbe ∗, P.A. Cameron Department of Epidemiology and Preventive Medicine, Monash University, Central and Eastern Clinical School, Alfred Hospital, Commercial Road, Melbourne, Vic. 3004, Australia Accepted 22 March 2006 KEYWORDS Review of evidence; Warm-up; Injury prevention; Physical activity
∗
Summary Background: The practice of warming up prior to exercise is advocated in injury prevention programs, but this is based on limited clinical evidence. It is hypothesised that warming up will reduce the number of injuries sustained during physical activity. Methods: A systematic review was undertaken. Relevant studies were identified by searching Medline (1966—April 2005), SPORTDiscus (1966—April 2005) and PubMed (1966—April 2005). This review included randomised controlled trials that investigated the effects of warming up on injury risk. Studies were included only if the subjects were human, and only if they utilised other activities than simply stretching. Studies reported in languages other than English were not included. The quality of included studies was assessed independently by two assessors. Results: Five studies, all of high quality (7—9 (mean = 8) out of 11) reported sufficient data (quality score >7) on the effects of warming up on reducing injury risk in humans. Three of the studies found that performing a warm-up prior to performance significantly reduced the injury risk, and the other two studies found that warming up was not effective in significantly reducing the number of injuries. Conclusions: There is insufficient evidence to endorse or discontinue routine warmup prior to physical activity to prevent injury among sports participants. However, the weight of evidence is in favour of a decreased risk of injury. Further wellconducted randomised controlled trials are needed to determine the role of warming up prior to exercise in relation to injury prevention. © 2006 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.
Corresponding author. Tel.: +61 3 9903 0951; fax: +61 3 9903 0576. E-mail address: [email protected] (B.J. Gabbe).
1440-2440/$ — see front matter © 2006 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.jsams.2006.03.026
Warm-up...Does it reduce the risk of injury?
215
Contents Introduction ................................................................................................ Methods..................................................................................................... Inclusion and exclusion criteria......................................................................... Search strategy......................................................................................... Assessment of study quality ............................................................................ Results...................................................................................................... Search results .......................................................................................... Methodological quality of included studies ............................................................. Effect of warm-up on risk of injury ..................................................................... Discussion................................................................................................... Conclusions ................................................................................................. Practical implications ....................................................................................... Acknowledgments ......................................................................................... References ................................................................................................
Introduction Sports injury is a collective name for all types of injury that can occur in relation to physical activity. Injury has been identified as a significant barrier to physical activity participation.1—3 The treatment of sports-related injuries can be time-consuming, difficult and expensive, thus making preventive strategies justified, not just from a medical perspective but an economic one also.4,5 Preventive measures, also termed countermeasures, are one method for controlling injury risk and are introduced with the intention of reducing the incidence and severity of injury.6 One of the most commonly recommended countermeasures for sports injury is performing an appropriate warm-up.7 The term warm-up in sport is defined as a period of preparatory exercise in order to enhance subsequent competition or training performance.7 For the purpose of this review, an appropriate warmup consists of the three different factors recommended by Safran et al.8 These three factors are the components of a warm-up that are most commonly cited in the warm-up literature and include: 1. a period of aerobic exercise to increase body temperature; 2. a period of sport-specific stretching to stretch the muscles to be used in the subsequent performance; 3. a period of activity incorporating movements similar to those to be used in the subsequent performance. Although three components are recommended, no study has investigated the effects of all three components of a warm-up in relation to injury prevention. The injury prevention benefits of stretching prior to sporting activity have been investigated
215 215 215 215 216 216 216 216 216 218 219 219 219 219
recently, with all authors concluding that stretching alone does not prevent injuries.9—12 Three of these papers were review articles,10—12 while the remaining study evaluated the effects of stretching before exercise on the risk of injury in new military recruits undergoing 12 weeks of initial training.9 In that study, the effects of supervised stretching of the calf muscles before exercising on the risk of six specific leg injuries were investigated. Recruits were considered to have sustained an injury if they were unable to return to full duties without signs or symptoms in 3 days.9 It should be noted that stretching is only one component of a warm-up, and thus it may be possible that different results will occur when a more comprehensive warm-up is undertaken prior to activity. This review synthesises research findings of the effects of a multi-component warming up on risk of injury in physical activity.
Methods Inclusion and exclusion criteria This review included randomised controlled trials that investigated the effects of warming up on injury risk in physical activity. Studies were included only if the subjects were human (not animals), and only if they utilised at least two components of a warm-up, not simply stretching. Studies reported in languages other than English were not included as translations were not available.
Search strategy Relevant studies were identified by searching Medline (1966—April 2005), SPORTDiscus (1966—
216 April 2005) and PubMed (1966—April 2005). The databases were searched for the terms ‘‘warmup’’, ‘‘warm up’’, ‘‘warmup’’, ‘‘warming-up’’, ‘‘warming up’’, ‘‘exercise’’, ‘‘prior exercise’’, ‘‘injury’’ and ‘‘injury prevention’’. The reference lists of the studies identified by these electronic searches were then searched recursively until no further studies were identified.
Assessment of study quality Methodological quality was assessed with the PEDro scale, which is based on the Delphi list. This scale was used because its items were chosen by a panel of experts, its reliability is supported empirically and its utility has been demonstrated in recent systematic reviews.13,14 A total score out of 11 is derived for each study from the number of criteria that are satisfied (see footnote in Table 2 for a brief description of criteria). The higher the score obtained, the greater the quality of evidence. The quality of included studies was assessed independently by two assessors.
Results Search results A total of 39 studies were identified in the initial search. Five studies were excluded because they were studies performed on animals, another five studies were excluded because they were review articles and a further 24 studies were excluded because they were not related to this particular topic or did not investigate two or more components of a warm-up. Table 1 shows the characteristics of the five studies identified that investigated the effects of warming up in humans on injury risk in physical activity.
Methodological quality of included studies The methodological quality of the studies was high (Table 2). The range of quality scores was 7—9 (mean = 8) out of 11. Not all criteria on the PEDro scale were satisfied in these studies. If the study did not clearly state that a criterion was met, it was scored as not satisfying the criterion. This was a way of ensuring that the methodological quality was conservative and would not be overestimated, and so the conclusions may actually be stronger.
Effect of warm-up on risk of injury Five studies investigated the effects of warmup on the risk of injury. Although injury defini-
A.J. Fradkin et al. tions were different in all papers, the injury outcomes were similar. Three of the studies found that performing a warm-up prior to physical activity significantly reduced the risk of injury,15,16,17 while the remaining studies found that the warmup did not significantly reduce the number of injuries.18,19 The studies were heterogeneous with respect to interventions, participants’ characteristics and performance activities. In three of the studies the participants were teenagers,15,16,17 while the participants in the other two studies were older.18,19 Three of the five studies involved only male participants15,18,19 and one study involved only female participants.16 The total warm-up time varied from 3 to 40 min. All five studies, however, included activities from the three types of exercise recommended for inclusion in a warm-up routine. The studies that found that warming up prior to physical activity reduced the risk of injury investigated handball16,17 and American football.15 One handball study found that by warming up, the number of both traumatic and overuse injuries in the intervention group was significantly lower than that in the control group.16 The difference in the proportion of injured players between the groups was 80% during games and 71% during practice. In addition, after adjusting for exposure, the players in the control group were 5.9 times more likely to sustain an injury than the players in the warm-up group. The remaining handball study investigated the effectiveness of warm-up for preventing knee and ankle injuries.17 They found that the intervention group sustained a significantly lower rate of 0.5 injuries per 1000 player/h, than the control group (0.9 injuries per 1000 player/h). The authors concluded that a structured warm-up program reduced the incidence of knee and ankle injuries by at least 50%. Bixler and co-workers,15 in their study of American football players, found that by performing a warm-up at half-time, the number of sprains and strains that occurred in the third quarter was significantly lower (p < 0.05) than the control group even after adjustment for multiple comparisons.15 However, no difference was found between the intervention and control groups for the other injury outcomes such as the overall number of injuries. Relative risk was not calculated because of a lack of exposure information. The studies that found that warming up was not effective for reducing the number of injuries investigated recreational runners18 and military recruits undergoing 12-weeks of military training.19 In the running study, over the 16-week period there were 23 injuries in the control group and 26 injuries in the warm-up group. Injury incidence for control and
Summary of the methodology of studies investigating warm-up as an injury prevention measure for physical activity
Study and country
Design
Participants
Adopted warm-up practices
Outcome measurement
Bixler and Jones15 USA
Controlled trial
5 high school American football teams
Number of injuries, types and location of all injuries, quarter injury occurred
Van Mechelen et al.18 The Netherlands
Randomised controlled trial
421 male recreational runners: 167 in control group; 159 in intervention group
Wedderkopp et al.16 Denmark
Cluster randomised controlled trial
Pope et al.19 Australia
Randomised controlled trial
237 female European team handball players aged 16—18 years: 126 in control group; 111 in intervention group 1279 male army recruits: 656 in control group; 623 in intervention group
Olsen et al.17 Norway
Cluster randomised controlled trial
3 min warm-up including: 30 s light running in place, 30 s moderate running in place, 30 s jumping jacks, 15 s trunk twists, 25 s hamstring stretch, 25 s groin stretch, 25 s quadriceps stretcha,b 19 min warm-up including: 6 min running exercises, 3 min loosening exercises, 10 min stretching iliopsoas, quadriceps, hamstrings, soleus and gastrocnemiusa,b 10—15 min use of an ankle disk, as well as 2 or more functional activities for all major muscle groupsa,c One 20 s stretch for gastrocnemius, soleus, hamstring, quadriceps, hip adductor, and hip flexor, interspersed with 4 min of jogging and side-steppinga,b 4—5 min exercises on ball, 4—5 min using wobble board, 4—5 min using balance mat, 4—5 min other unspecified exercisea,c
a b c
1837 handball players aged 15—17 years: 879 in control group; 958 in intervention
Number of injuries, types and location of all injuries, compliance with warm-up program
Warm-up...Does it reduce the risk of injury?
Table 1
Number of injuries, types and location of all injuries, injury severity, injury incidence per 1000 h of match and practice Number of lower limb injuries, types and location of all lower limb injuries
Rate of acute injury to knee or ankle, number of lower limb injuries
Aerobic exercise. Stretching. Activity similar to actual event (from description in the paper methods).
217
218 Table 2
A.J. Fradkin et al. Criteria list and quality scores for a methodological assessment of trials of warm-up for preventing injury
Study Bixler and Jones15 Van Mechelen et al.18 Wedderkopp et al.16 Pope et al.19 Olsen et al.17
Scores on PEDro scalea
Total scoreb
1
2
3
4
5
6
7
8
9
10
11
− + + + +
+ + − + +
+ − + − +
− − − − −
+ + + + +
+ + + + +
+ + + − −
+ − + + +
+ + + + +
− − + − −
+ + + + +
8/11 7/11 9/11 7/11 8/11
(+) Indicates that the criterion was clearly satisfied and (−) indicates that the criterion was not clearly satisfied. a Column numbers correspond to the following criteria on the PEDro scale: 1, description of inclusion and exclusion criteria; 2, subjects randomly allocated to groups; 3, appropriate subjects; groups similar at baseline; same data collection methods for each group; 4, researcher and subjects were blinded; 5, control group utilised; 6, appropriate statistics used and measures of variability provided; 7, warm-ups described in enough detail, i.e. able to copy it; 8, all biases were addressed and discussed; 9, relevance of outcome measures; occurrence and type of injury, etc.; 10, measures of key outcomes obtained for more than 85% of subjects and 11, addressed possible confounders. b The total score is determined by counting the number of criteria that are satisfied.
warm-up groups was 4.9 and 5.5 running injuries per 1000 h, respectively.18 However, the attrition rate was high (22.3%), and compliance with the prescribed warm-up program was low (46.6%).18 Results were further complicated by differences in data collection methods between control and intervention groups, for example, differences in the questionnaires administered between the two groups. The military study recorded 333 lower limb injuries during the training period, including 214 soft tissue injuries.19 There were 158 injuries in the intervention group and 175 in the control group, a non-significant difference. Furthermore, the authors concluded that there was not a clinically worthwhile reduction in the risk of lower limb injury19 related to warm-up, although no justification was given for this statement.
Discussion This systematic review evaluated five high quality studies investigating whether or not undertaking a warm-up prior to physical activity reduced the risk of injuries in humans. All of the studies focused on warm-up behaviours in isolation and no other concurrent safety practices. Three of the studies found that performing a warm-up prior to physical activity significantly reduced the risk of injury, while the remaining two studies found that the warm-up was not effective in reducing the number of injuries. Due to the heterogeneity of the studies reviewed, no meta-analysis was undertaken. Interventions in the three studies which found that warm-up significantly reduced the risk of injury had a greater focus on exercise to increase body temperature than the remaining two studies.
The studies that found warm-up to be ineffective focused heavily on the stretching aspect. Furthermore, the studies that found reductions were quite specific and focused with relation to the participants’ age and physical activity, whereas the two studies which found no reduction in injury risk had heterogeneous samples in relation to age and the type of physical activity undertaken. In the military recruit study by Pope et al.19 statistical power was sufficient to rule out a clinically useful reduction in injury risk, although the authors reduced the stretching duration to one 20 s stretch per muscle group. This was despite a previous study which found no significant reduction in injury risk with greater total stretch stimulus.11 However, there was a reduction in soft tissue injuries between the intervention group compared to the control group, though this was not significant. Whether or not the study was sufficiently powered to find a difference for this injury subgroup was not stated. The study by Van Mechelen et al.18 found that there was no injury prevention benefit to runners by participating in a warm-up prior to performance. However, they had a very poor compliance rate within the warm-up group, with only 68.4% of the participants complying with the warm-up.18 Analysis of this study was done on an intention-to-treat analysis, which is appropriate for this type of study. The low compliance could have contributed to the non-significant finding. Additionally, a power calculation was not provided. It is therefore unclear whether or not the sample size was sufficient to meet the aims of the study. None of the included studies reported the intensity level of the warm-up, which may be a crucial factor in determining whether or not warmup is effective for reducing the risk of injury.
Warm-up...Does it reduce the risk of injury? Optimal combinations of intensity and duration of warm-up may be needed to bring about the desired warm-up effect. The main goal for a participant is to undertake enough activity for an effective warm-up without causing fatigue.20 Too little warm-up activity does not achieve optimal levels of temperature21—23 and too much warm-up can result in impaired performance due to fatigue.24 The reviewed studies did not address this issue but it warrants consideration for inclusion in further investigations. Specific injury types could be more conducive to prevention through warm-up than others. The injury definition of each evaluated study varied, making comparisons difficult. Definitions included: participants had to stop activity immediately and required medical attention18 ; participant could not resume physical activity after 3 days19 ; injury caused participant to miss next training or game16 ; participant’s performance was altered15 or no injury definition was given.17 Experimental research on animals suggests that warming up is likely to reduce the number of injuries.8,23 There are ethical problems associated with inducing injury in humans and consequently there has been little direct evidence regarding the protective effect of a warm-up. Investigators cannot intentionally allow subjects to perform an activity that has the potential to cause an injury, and therefore most of the available evidence is related to animal studies. Conversely, it should be noted that investigators cannot ethically stop their control group from performing a warm-up if they decide they wish to. Only three of the five studies15,16,17 included in this review specified that the control groups continued to undertake their ‘‘normal’’ or ‘‘usual’’ warm-up routines throughout the study. No detail was provided as to what this entailed, however. The remaining studies18,19 did not provide any details about the activity of the control group. The potential for participation in warm-up activities by controls to confound the study findings cannot be excluded. As each sport has its own unique qualities, it is also possible that warming up may be a useful injury prevention tool for some sporting activities and not others. This, however, needs further research to confirm or deny.
Conclusions Due to the paucity, heterogeneity and limitations of published studies, definitive conclusions cannot be drawn as to the role of warm-up for reducing the risk of exercise-related injury. In three of
219 five studies reviewed there were significant injury prevention benefits from participating in warm-up. There is little evidence to suggest that warming up is harmful to sports participants. Well-conducted randomised controlled trials are needed to evaluate further the role of warming up prior to physical activity in relation to injury prevention.
Practical implications • The weight of evidence is in favour of warming up decreasing the risk of injury. • The studies demonstrating a protective effect of warm-up focused on specific sports and homogeneous populations. • As each sport has its own unique qualities, it is possible that warming up may be a useful injury prevention tool for some sporting activities and not others.
Acknowledgments Andrea Fradkin was supported by a Public Health Postgraduate Scholarship from the National Health and Medical Research Council (NHMRC) of Australia whilst Belinda Gabbe was supported by an NHMRC Public Health Research Fellowship during the preparation of this manuscript.
References 1. Bauman A, Owen N. Physical activity of adult Australians: epidemiological evidence and potential strategies for health gains. J Sci Med Sport 1999;2(1):30—41. 2. Bauman A, Bellow B, Vita P, et al. Getting Australia active: towards better practice for the promotion of physical activity. Melbourne: National Public Health Partnership; 2002. 3. Finch CF, Owen N. Injury prevention and the promotion of physical activity: what is the nexus? J Sci Med Sport 2001;4(1):77—87. 4. Egger G. Sports injuries in Australia: causes, costs and prevention. Health Promot J Aust 1991;1(2):28—33. 5. Parkkari J, Kujala UM, Kannus P. Is it possible to prevent sports injuries? Review of controlled clinical trials and recommendations for future work. Sports Med 2001;31(14):985—95. 6. Hrysomallis C, Morrison W. Sports injury surveillance and protective equipment. Sports Med 1997;24(3):181—3. 7. Hedrick A. Physiological responses to warm-up. Natl Strength Cond Assoc J 1992;14(5):25—7. 8. Safran MR, Seaber AV, Garrett WE. Warm-up and muscular injury prevention — an update. Sports Med 1989;8(4):239—49. 9. Pope RP, Herbert RD, Kirwin JD. Effects of ankle dorsiflexion range and pre-exercise calf muscle stretching on injury risk in army recruits. Aust J Physiol 1998;44:165—77.
220 10. Herbert RD, Gabriel M. Effects of stretching before and after exercising on muscle soreness and risk of injury: systematic review. BMJ 2002;325:468—72. 11. Shrier I. Pre-exercise stretching may not be helpful. Clin J Sport Med 2004;14:267—73. 12. Thacker SB, Gilchrist J, Stroup DF, et al. The impact of stretching on sports injury risk: a systematic review of the literature. Med Sci Sport Exerc 2004;36(3):371—8. 13. Moseley AM, Maher C, Herbert RD, et al. Reliability of a scale for measuring the methodological quality of clinical trials. In: Proceedings of the Cochrane Colloquium, vol. 39. 1999. 14. Verhagen AP, de Vet HC, de Bie RA, et al. The Delphi list: a criteria list for quality assessment of randomised clinical trials for conducting systematic reviews developed by Delphi consensus. J Clin Epidemiol 1998;51:1235—41. 15. Bixler B, Jones RL. High-school football injuries: effects of a post-halftime warm-up and stretching routine. Fam Pract 1992;12(2):134—9. 16. Wedderkopp N, Kaltoft M, Lundgaard B, et al. Prevention of injuries in young female players in European team handball. A prospective intervention study. Scan J Med Sci Sports 1999;9:41—7.
A.J. Fradkin et al. 17. Olsen OE, Myklebust G, Engebretsen L, et al. Exercises to prevent lower limb injuries in youth sports: cluster randomised controlled trial. BMJ 2005;330:449—52. 18. Van Mechelen W, Hlobil H, Kemper HCG, et al. Prevention of running injuries by warm-up, cool-down, and stretching exercises. Am J Sports Med 1993;21(5):711—9. 19. Pope RP, Herbert RD, Kirwin JD, et al. A randomised trial of pre-exercise stretching for prevention of lower-limb injury. Med Sci Sport Exerc 2000;32:271—7. 20. Martin BJ, Robinson S, Wiegman A, et al. Effect of warm-up on the metabolic responses to strenuous exercise. J Sci Med Sport 1975;7:146—9. 21. Richards DK. A two-factor theory of the warm-up effect in jumping performance. Res Q Exerc Sport 1968;39:668— 73. 22. Bergh U. Human power at subnormal body temperatures. J Appl Physiol 1980;48:1—9. 23. Safran MR, Garrett WE, Seaber AV, et al. The role of warm-up in muscular injury prevention. Am J Sports Med 1988;16(2):123—9. 24. Gleim GW, McHugh MP. Flexibility and its effects on sports injury and performance. Sports Med 1997;24(5):289— 99.
REVIEW
Does warming up prevent injury in sport? The evidence from randomised controlled trials? A.J. Fradkin, B.J. Gabbe ∗, P.A. Cameron Department of Epidemiology and Preventive Medicine, Monash University, Central and Eastern Clinical School, Alfred Hospital, Commercial Road, Melbourne, Vic. 3004, Australia Accepted 22 March 2006 KEYWORDS Review of evidence; Warm-up; Injury prevention; Physical activity
∗
Summary Background: The practice of warming up prior to exercise is advocated in injury prevention programs, but this is based on limited clinical evidence. It is hypothesised that warming up will reduce the number of injuries sustained during physical activity. Methods: A systematic review was undertaken. Relevant studies were identified by searching Medline (1966—April 2005), SPORTDiscus (1966—April 2005) and PubMed (1966—April 2005). This review included randomised controlled trials that investigated the effects of warming up on injury risk. Studies were included only if the subjects were human, and only if they utilised other activities than simply stretching. Studies reported in languages other than English were not included. The quality of included studies was assessed independently by two assessors. Results: Five studies, all of high quality (7—9 (mean = 8) out of 11) reported sufficient data (quality score >7) on the effects of warming up on reducing injury risk in humans. Three of the studies found that performing a warm-up prior to performance significantly reduced the injury risk, and the other two studies found that warming up was not effective in significantly reducing the number of injuries. Conclusions: There is insufficient evidence to endorse or discontinue routine warmup prior to physical activity to prevent injury among sports participants. However, the weight of evidence is in favour of a decreased risk of injury. Further wellconducted randomised controlled trials are needed to determine the role of warming up prior to exercise in relation to injury prevention. © 2006 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.
Corresponding author. Tel.: +61 3 9903 0951; fax: +61 3 9903 0576. E-mail address: [email protected] (B.J. Gabbe).
1440-2440/$ — see front matter © 2006 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.jsams.2006.03.026
Warm-up...Does it reduce the risk of injury?
215
Contents Introduction ................................................................................................ Methods..................................................................................................... Inclusion and exclusion criteria......................................................................... Search strategy......................................................................................... Assessment of study quality ............................................................................ Results...................................................................................................... Search results .......................................................................................... Methodological quality of included studies ............................................................. Effect of warm-up on risk of injury ..................................................................... Discussion................................................................................................... Conclusions ................................................................................................. Practical implications ....................................................................................... Acknowledgments ......................................................................................... References ................................................................................................
Introduction Sports injury is a collective name for all types of injury that can occur in relation to physical activity. Injury has been identified as a significant barrier to physical activity participation.1—3 The treatment of sports-related injuries can be time-consuming, difficult and expensive, thus making preventive strategies justified, not just from a medical perspective but an economic one also.4,5 Preventive measures, also termed countermeasures, are one method for controlling injury risk and are introduced with the intention of reducing the incidence and severity of injury.6 One of the most commonly recommended countermeasures for sports injury is performing an appropriate warm-up.7 The term warm-up in sport is defined as a period of preparatory exercise in order to enhance subsequent competition or training performance.7 For the purpose of this review, an appropriate warmup consists of the three different factors recommended by Safran et al.8 These three factors are the components of a warm-up that are most commonly cited in the warm-up literature and include: 1. a period of aerobic exercise to increase body temperature; 2. a period of sport-specific stretching to stretch the muscles to be used in the subsequent performance; 3. a period of activity incorporating movements similar to those to be used in the subsequent performance. Although three components are recommended, no study has investigated the effects of all three components of a warm-up in relation to injury prevention. The injury prevention benefits of stretching prior to sporting activity have been investigated
215 215 215 215 216 216 216 216 216 218 219 219 219 219
recently, with all authors concluding that stretching alone does not prevent injuries.9—12 Three of these papers were review articles,10—12 while the remaining study evaluated the effects of stretching before exercise on the risk of injury in new military recruits undergoing 12 weeks of initial training.9 In that study, the effects of supervised stretching of the calf muscles before exercising on the risk of six specific leg injuries were investigated. Recruits were considered to have sustained an injury if they were unable to return to full duties without signs or symptoms in 3 days.9 It should be noted that stretching is only one component of a warm-up, and thus it may be possible that different results will occur when a more comprehensive warm-up is undertaken prior to activity. This review synthesises research findings of the effects of a multi-component warming up on risk of injury in physical activity.
Methods Inclusion and exclusion criteria This review included randomised controlled trials that investigated the effects of warming up on injury risk in physical activity. Studies were included only if the subjects were human (not animals), and only if they utilised at least two components of a warm-up, not simply stretching. Studies reported in languages other than English were not included as translations were not available.
Search strategy Relevant studies were identified by searching Medline (1966—April 2005), SPORTDiscus (1966—
216 April 2005) and PubMed (1966—April 2005). The databases were searched for the terms ‘‘warmup’’, ‘‘warm up’’, ‘‘warmup’’, ‘‘warming-up’’, ‘‘warming up’’, ‘‘exercise’’, ‘‘prior exercise’’, ‘‘injury’’ and ‘‘injury prevention’’. The reference lists of the studies identified by these electronic searches were then searched recursively until no further studies were identified.
Assessment of study quality Methodological quality was assessed with the PEDro scale, which is based on the Delphi list. This scale was used because its items were chosen by a panel of experts, its reliability is supported empirically and its utility has been demonstrated in recent systematic reviews.13,14 A total score out of 11 is derived for each study from the number of criteria that are satisfied (see footnote in Table 2 for a brief description of criteria). The higher the score obtained, the greater the quality of evidence. The quality of included studies was assessed independently by two assessors.
Results Search results A total of 39 studies were identified in the initial search. Five studies were excluded because they were studies performed on animals, another five studies were excluded because they were review articles and a further 24 studies were excluded because they were not related to this particular topic or did not investigate two or more components of a warm-up. Table 1 shows the characteristics of the five studies identified that investigated the effects of warming up in humans on injury risk in physical activity.
Methodological quality of included studies The methodological quality of the studies was high (Table 2). The range of quality scores was 7—9 (mean = 8) out of 11. Not all criteria on the PEDro scale were satisfied in these studies. If the study did not clearly state that a criterion was met, it was scored as not satisfying the criterion. This was a way of ensuring that the methodological quality was conservative and would not be overestimated, and so the conclusions may actually be stronger.
Effect of warm-up on risk of injury Five studies investigated the effects of warmup on the risk of injury. Although injury defini-
A.J. Fradkin et al. tions were different in all papers, the injury outcomes were similar. Three of the studies found that performing a warm-up prior to physical activity significantly reduced the risk of injury,15,16,17 while the remaining studies found that the warmup did not significantly reduce the number of injuries.18,19 The studies were heterogeneous with respect to interventions, participants’ characteristics and performance activities. In three of the studies the participants were teenagers,15,16,17 while the participants in the other two studies were older.18,19 Three of the five studies involved only male participants15,18,19 and one study involved only female participants.16 The total warm-up time varied from 3 to 40 min. All five studies, however, included activities from the three types of exercise recommended for inclusion in a warm-up routine. The studies that found that warming up prior to physical activity reduced the risk of injury investigated handball16,17 and American football.15 One handball study found that by warming up, the number of both traumatic and overuse injuries in the intervention group was significantly lower than that in the control group.16 The difference in the proportion of injured players between the groups was 80% during games and 71% during practice. In addition, after adjusting for exposure, the players in the control group were 5.9 times more likely to sustain an injury than the players in the warm-up group. The remaining handball study investigated the effectiveness of warm-up for preventing knee and ankle injuries.17 They found that the intervention group sustained a significantly lower rate of 0.5 injuries per 1000 player/h, than the control group (0.9 injuries per 1000 player/h). The authors concluded that a structured warm-up program reduced the incidence of knee and ankle injuries by at least 50%. Bixler and co-workers,15 in their study of American football players, found that by performing a warm-up at half-time, the number of sprains and strains that occurred in the third quarter was significantly lower (p < 0.05) than the control group even after adjustment for multiple comparisons.15 However, no difference was found between the intervention and control groups for the other injury outcomes such as the overall number of injuries. Relative risk was not calculated because of a lack of exposure information. The studies that found that warming up was not effective for reducing the number of injuries investigated recreational runners18 and military recruits undergoing 12-weeks of military training.19 In the running study, over the 16-week period there were 23 injuries in the control group and 26 injuries in the warm-up group. Injury incidence for control and
Summary of the methodology of studies investigating warm-up as an injury prevention measure for physical activity
Study and country
Design
Participants
Adopted warm-up practices
Outcome measurement
Bixler and Jones15 USA
Controlled trial
5 high school American football teams
Number of injuries, types and location of all injuries, quarter injury occurred
Van Mechelen et al.18 The Netherlands
Randomised controlled trial
421 male recreational runners: 167 in control group; 159 in intervention group
Wedderkopp et al.16 Denmark
Cluster randomised controlled trial
Pope et al.19 Australia
Randomised controlled trial
237 female European team handball players aged 16—18 years: 126 in control group; 111 in intervention group 1279 male army recruits: 656 in control group; 623 in intervention group
Olsen et al.17 Norway
Cluster randomised controlled trial
3 min warm-up including: 30 s light running in place, 30 s moderate running in place, 30 s jumping jacks, 15 s trunk twists, 25 s hamstring stretch, 25 s groin stretch, 25 s quadriceps stretcha,b 19 min warm-up including: 6 min running exercises, 3 min loosening exercises, 10 min stretching iliopsoas, quadriceps, hamstrings, soleus and gastrocnemiusa,b 10—15 min use of an ankle disk, as well as 2 or more functional activities for all major muscle groupsa,c One 20 s stretch for gastrocnemius, soleus, hamstring, quadriceps, hip adductor, and hip flexor, interspersed with 4 min of jogging and side-steppinga,b 4—5 min exercises on ball, 4—5 min using wobble board, 4—5 min using balance mat, 4—5 min other unspecified exercisea,c
a b c
1837 handball players aged 15—17 years: 879 in control group; 958 in intervention
Number of injuries, types and location of all injuries, compliance with warm-up program
Warm-up...Does it reduce the risk of injury?
Table 1
Number of injuries, types and location of all injuries, injury severity, injury incidence per 1000 h of match and practice Number of lower limb injuries, types and location of all lower limb injuries
Rate of acute injury to knee or ankle, number of lower limb injuries
Aerobic exercise. Stretching. Activity similar to actual event (from description in the paper methods).
217
218 Table 2
A.J. Fradkin et al. Criteria list and quality scores for a methodological assessment of trials of warm-up for preventing injury
Study Bixler and Jones15 Van Mechelen et al.18 Wedderkopp et al.16 Pope et al.19 Olsen et al.17
Scores on PEDro scalea
Total scoreb
1
2
3
4
5
6
7
8
9
10
11
− + + + +
+ + − + +
+ − + − +
− − − − −
+ + + + +
+ + + + +
+ + + − −
+ − + + +
+ + + + +
− − + − −
+ + + + +
8/11 7/11 9/11 7/11 8/11
(+) Indicates that the criterion was clearly satisfied and (−) indicates that the criterion was not clearly satisfied. a Column numbers correspond to the following criteria on the PEDro scale: 1, description of inclusion and exclusion criteria; 2, subjects randomly allocated to groups; 3, appropriate subjects; groups similar at baseline; same data collection methods for each group; 4, researcher and subjects were blinded; 5, control group utilised; 6, appropriate statistics used and measures of variability provided; 7, warm-ups described in enough detail, i.e. able to copy it; 8, all biases were addressed and discussed; 9, relevance of outcome measures; occurrence and type of injury, etc.; 10, measures of key outcomes obtained for more than 85% of subjects and 11, addressed possible confounders. b The total score is determined by counting the number of criteria that are satisfied.
warm-up groups was 4.9 and 5.5 running injuries per 1000 h, respectively.18 However, the attrition rate was high (22.3%), and compliance with the prescribed warm-up program was low (46.6%).18 Results were further complicated by differences in data collection methods between control and intervention groups, for example, differences in the questionnaires administered between the two groups. The military study recorded 333 lower limb injuries during the training period, including 214 soft tissue injuries.19 There were 158 injuries in the intervention group and 175 in the control group, a non-significant difference. Furthermore, the authors concluded that there was not a clinically worthwhile reduction in the risk of lower limb injury19 related to warm-up, although no justification was given for this statement.
Discussion This systematic review evaluated five high quality studies investigating whether or not undertaking a warm-up prior to physical activity reduced the risk of injuries in humans. All of the studies focused on warm-up behaviours in isolation and no other concurrent safety practices. Three of the studies found that performing a warm-up prior to physical activity significantly reduced the risk of injury, while the remaining two studies found that the warm-up was not effective in reducing the number of injuries. Due to the heterogeneity of the studies reviewed, no meta-analysis was undertaken. Interventions in the three studies which found that warm-up significantly reduced the risk of injury had a greater focus on exercise to increase body temperature than the remaining two studies.
The studies that found warm-up to be ineffective focused heavily on the stretching aspect. Furthermore, the studies that found reductions were quite specific and focused with relation to the participants’ age and physical activity, whereas the two studies which found no reduction in injury risk had heterogeneous samples in relation to age and the type of physical activity undertaken. In the military recruit study by Pope et al.19 statistical power was sufficient to rule out a clinically useful reduction in injury risk, although the authors reduced the stretching duration to one 20 s stretch per muscle group. This was despite a previous study which found no significant reduction in injury risk with greater total stretch stimulus.11 However, there was a reduction in soft tissue injuries between the intervention group compared to the control group, though this was not significant. Whether or not the study was sufficiently powered to find a difference for this injury subgroup was not stated. The study by Van Mechelen et al.18 found that there was no injury prevention benefit to runners by participating in a warm-up prior to performance. However, they had a very poor compliance rate within the warm-up group, with only 68.4% of the participants complying with the warm-up.18 Analysis of this study was done on an intention-to-treat analysis, which is appropriate for this type of study. The low compliance could have contributed to the non-significant finding. Additionally, a power calculation was not provided. It is therefore unclear whether or not the sample size was sufficient to meet the aims of the study. None of the included studies reported the intensity level of the warm-up, which may be a crucial factor in determining whether or not warmup is effective for reducing the risk of injury.
Warm-up...Does it reduce the risk of injury? Optimal combinations of intensity and duration of warm-up may be needed to bring about the desired warm-up effect. The main goal for a participant is to undertake enough activity for an effective warm-up without causing fatigue.20 Too little warm-up activity does not achieve optimal levels of temperature21—23 and too much warm-up can result in impaired performance due to fatigue.24 The reviewed studies did not address this issue but it warrants consideration for inclusion in further investigations. Specific injury types could be more conducive to prevention through warm-up than others. The injury definition of each evaluated study varied, making comparisons difficult. Definitions included: participants had to stop activity immediately and required medical attention18 ; participant could not resume physical activity after 3 days19 ; injury caused participant to miss next training or game16 ; participant’s performance was altered15 or no injury definition was given.17 Experimental research on animals suggests that warming up is likely to reduce the number of injuries.8,23 There are ethical problems associated with inducing injury in humans and consequently there has been little direct evidence regarding the protective effect of a warm-up. Investigators cannot intentionally allow subjects to perform an activity that has the potential to cause an injury, and therefore most of the available evidence is related to animal studies. Conversely, it should be noted that investigators cannot ethically stop their control group from performing a warm-up if they decide they wish to. Only three of the five studies15,16,17 included in this review specified that the control groups continued to undertake their ‘‘normal’’ or ‘‘usual’’ warm-up routines throughout the study. No detail was provided as to what this entailed, however. The remaining studies18,19 did not provide any details about the activity of the control group. The potential for participation in warm-up activities by controls to confound the study findings cannot be excluded. As each sport has its own unique qualities, it is also possible that warming up may be a useful injury prevention tool for some sporting activities and not others. This, however, needs further research to confirm or deny.
Conclusions Due to the paucity, heterogeneity and limitations of published studies, definitive conclusions cannot be drawn as to the role of warm-up for reducing the risk of exercise-related injury. In three of
219 five studies reviewed there were significant injury prevention benefits from participating in warm-up. There is little evidence to suggest that warming up is harmful to sports participants. Well-conducted randomised controlled trials are needed to evaluate further the role of warming up prior to physical activity in relation to injury prevention.
Practical implications • The weight of evidence is in favour of warming up decreasing the risk of injury. • The studies demonstrating a protective effect of warm-up focused on specific sports and homogeneous populations. • As each sport has its own unique qualities, it is possible that warming up may be a useful injury prevention tool for some sporting activities and not others.
Acknowledgments Andrea Fradkin was supported by a Public Health Postgraduate Scholarship from the National Health and Medical Research Council (NHMRC) of Australia whilst Belinda Gabbe was supported by an NHMRC Public Health Research Fellowship during the preparation of this manuscript.
References 1. Bauman A, Owen N. Physical activity of adult Australians: epidemiological evidence and potential strategies for health gains. J Sci Med Sport 1999;2(1):30—41. 2. Bauman A, Bellow B, Vita P, et al. Getting Australia active: towards better practice for the promotion of physical activity. Melbourne: National Public Health Partnership; 2002. 3. Finch CF, Owen N. Injury prevention and the promotion of physical activity: what is the nexus? J Sci Med Sport 2001;4(1):77—87. 4. Egger G. Sports injuries in Australia: causes, costs and prevention. Health Promot J Aust 1991;1(2):28—33. 5. Parkkari J, Kujala UM, Kannus P. Is it possible to prevent sports injuries? Review of controlled clinical trials and recommendations for future work. Sports Med 2001;31(14):985—95. 6. Hrysomallis C, Morrison W. Sports injury surveillance and protective equipment. Sports Med 1997;24(3):181—3. 7. Hedrick A. Physiological responses to warm-up. Natl Strength Cond Assoc J 1992;14(5):25—7. 8. Safran MR, Seaber AV, Garrett WE. Warm-up and muscular injury prevention — an update. Sports Med 1989;8(4):239—49. 9. Pope RP, Herbert RD, Kirwin JD. Effects of ankle dorsiflexion range and pre-exercise calf muscle stretching on injury risk in army recruits. Aust J Physiol 1998;44:165—77.
220 10. Herbert RD, Gabriel M. Effects of stretching before and after exercising on muscle soreness and risk of injury: systematic review. BMJ 2002;325:468—72. 11. Shrier I. Pre-exercise stretching may not be helpful. Clin J Sport Med 2004;14:267—73. 12. Thacker SB, Gilchrist J, Stroup DF, et al. The impact of stretching on sports injury risk: a systematic review of the literature. Med Sci Sport Exerc 2004;36(3):371—8. 13. Moseley AM, Maher C, Herbert RD, et al. Reliability of a scale for measuring the methodological quality of clinical trials. In: Proceedings of the Cochrane Colloquium, vol. 39. 1999. 14. Verhagen AP, de Vet HC, de Bie RA, et al. The Delphi list: a criteria list for quality assessment of randomised clinical trials for conducting systematic reviews developed by Delphi consensus. J Clin Epidemiol 1998;51:1235—41. 15. Bixler B, Jones RL. High-school football injuries: effects of a post-halftime warm-up and stretching routine. Fam Pract 1992;12(2):134—9. 16. Wedderkopp N, Kaltoft M, Lundgaard B, et al. Prevention of injuries in young female players in European team handball. A prospective intervention study. Scan J Med Sci Sports 1999;9:41—7.
A.J. Fradkin et al. 17. Olsen OE, Myklebust G, Engebretsen L, et al. Exercises to prevent lower limb injuries in youth sports: cluster randomised controlled trial. BMJ 2005;330:449—52. 18. Van Mechelen W, Hlobil H, Kemper HCG, et al. Prevention of running injuries by warm-up, cool-down, and stretching exercises. Am J Sports Med 1993;21(5):711—9. 19. Pope RP, Herbert RD, Kirwin JD, et al. A randomised trial of pre-exercise stretching for prevention of lower-limb injury. Med Sci Sport Exerc 2000;32:271—7. 20. Martin BJ, Robinson S, Wiegman A, et al. Effect of warm-up on the metabolic responses to strenuous exercise. J Sci Med Sport 1975;7:146—9. 21. Richards DK. A two-factor theory of the warm-up effect in jumping performance. Res Q Exerc Sport 1968;39:668— 73. 22. Bergh U. Human power at subnormal body temperatures. J Appl Physiol 1980;48:1—9. 23. Safran MR, Garrett WE, Seaber AV, et al. The role of warm-up in muscular injury prevention. Am J Sports Med 1988;16(2):123—9. 24. Gleim GW, McHugh MP. Flexibility and its effects on sports injury and performance. Sports Med 1997;24(5):289— 99.