The effectiveness of neuromuscular warm-up strategies, that require no additional equipment, for preventing lower limb injuries during sports participation: a systematic review (original) (raw)

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Published: 19 July 2012

BMC Medicine volume 10, Article number: 75 (2012)Cite this article

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Abstract

Background

Lower limb injuries in sport are increasingly prevalent and responsible for large economic as well as personal burdens. In this review we seek to determine which easily implemented functional neuromuscular warm-up strategies are effective in preventing lower limb injuries during sports participation and in which sporting groups they are effective.

Methods

Seven electronic databases were searched from inception to January 2012 for studies investigating neuromuscular warm-up strategies and injury prevention. The quality of each included study was evaluated using a modified version of the van Tulder scale. Data were extracted from each study and used to calculate the risk of injury following application of each evaluated strategy.

Results

Nine studies were identified including six randomized controlled trials (RCT) and three controlled clinical trials (CCT). Heterogeneity in study design and warm-up strategies prevented pooling of results. Two studies investigated male and female participants, while the remaining seven investigated women only. Risk Ratio (RR) statistics indicated 'The 11+' prevention strategy significantly reduces overall (RR 0.67, confidence interval (CI) 0.54 to 0.84) and overuse (RR 0.45, CI 0.28 to 0.71) lower limb injuries as well as knee (RR 0.48, CI 0.32 to 0.72) injuries among young amateur female footballers. The 'Knee Injury Prevention Program' (KIPP) significantly reduced the risk of noncontact lower limb (RR 0.5, CI 0.33 to 0.76) and overuse (RR 0.44, CI 0.22 to 0.86) injuries in young amateur female football and basketball players. The 'Prevent Injury and Enhance Performance' (PEP) strategy reduces the incidence of anterior cruciate ligament (ACL) injuries (RR 0.18, CI 0.08 to 0.42). The 'HarmoKnee' programme reduces the risk of knee injuries (RR 0.22, CI 0.06 to 0.76) in teenage female footballers. The 'Anterior Knee Pain Prevention Training Programme' (AKP PTP) significantly reduces the incidence of anterior knee pain (RR 0.27, CI 0.14 to 0.54) in military recruits.

Conclusions

Effective implementation of practical neuromuscular warm-up strategies can reduce lower extremity injury incidence in young, amateur, female athletes and male and female military recruits. This is typically a warm-up strategy that includes stretching, strengthening, balance exercises, sports-specific agility drills and landing techniques applied consistently for longer than three consecutive months. In order to optimize these strategies, the mechanisms for their effectiveness require further evaluation.

Peer Review reports

Background

Historically, stretching as part of a warm-up strategy before exercise has been strongly advocated to prevent injury [1]. However, current evidence suggests that stretching alone may confer no injury prevention benefit [2–5]. More recently, researchers and sports medicine practitioners have developed and investigated multi-factorial neuromuscular training strategies targeting injury prevention for a variety of sports and athletic levels. The importance of musculoskeletal injury prevention is highlighted by estimates that 22 million sports injuries occur in the UK each year [[6](/articles/10.1186/1741-7015-10-75#ref-CR6 "Barclays survey reveals sports injury rate in the UK. [ http://www.personal.barclays.co.uk/BRC1/jsp/brccontrol?task=popup1group&value=11147&target=_blank&site=pfs

            ]")\]. Furthermore, sixty to seventy percent of the population in the UK are considered to be physically inactive. Physical inactivity is currently estimated to cost the UK economy £8.3 billion per annum and is more prevalent than obesity, alcohol misuse and smoking combined \[[7](/articles/10.1186/1741-7015-10-75#ref-CR7 "Chief Medical Officer: 2009 Annual Report of the Chief Medical Officer. 2010, London: Department of Health")\]. It is more important than ever to encourage people to engage in some form of physical activity \[[8](/articles/10.1186/1741-7015-10-75#ref-CR8 "James PT, Rigby N, Leach R: The obesity epidemic, metabolic syndrome and future prevention strategies. Eur J Cardiovasc Prev Rehabil. 2004, 11: 3-8. 10.1097/01.hjr.0000114707.27531.48.")\] and the recent Chief Medical Officer report 2009 described physical activity as a 'wonder drug' or 'miracle cure' with huge potential benefits \[[6](/articles/10.1186/1741-7015-10-75#ref-CR6 "Barclays survey reveals sports injury rate in the UK. [
              http://www.personal.barclays.co.uk/BRC1/jsp/brccontrol?task=popup1group&value=11147&target=_blank&site=pfs
              
            ]")\]. However, an inevitable consequence of increasing physical activity is an increased incidence of musculoskeletal injury. To reduce the resultant personal and economic burden, there is a need for practical, time efficient and cost-effective injury prevention strategies.

Neuromuscular training programmes are hypothesized to improve joint position sense, enhance joint stability and develop protective joint reflexes, ultimately preventing lower limb injuries. Hübscher et al. [9] recently completed a high quality systematic review on neuromuscular training programmes for sports injury prevention. A meta-analysis indicated that multi-intervention programmes may reduce lower limb, acute knee and ankle injuries and that balance programmes may reduce ankle injuries [9]. However, the practicality of these findings for many individuals, teams and clubs may be limited due to the need for equipment purchases (for example, balance boards) and the requirement of additional training sessions to normal practice and competition. In these cases, a more practical solution would be to encompass neuromuscular training programmes which do not require additional equipment and which can be incorporated into warm-up or current routines. A number of neuromuscular warm-up strategies which fit these criteria have been proposed, evaluated and published in the literature. Just two of these programmes were included by the Hübscher et al. [9] systematic review. Therefore, an up-to-date systematic review of the literature related to neuromuscular warm-up strategies which can be easily incorporated into warm-up or current routines and do not require the acquisition of additional equipment is needed to further guide recommendations for effective lower limb injury prevention.

The aims of this systematic review were: (1) to evaluate the efficacy of functional neuromuscular warm-up strategies which do not require additional equipment in preventing lower limb injury in order to guide clinical and sporting practice; and (2) to identify the common elements of successful strategies in order to guide future research.

Methods

Search and evaluation strategy

Embase, SPORTDiscus, Google Scholar, PubMed, ISI Web of Knowledge, Scirus and PEDro were searched for articles from inception to June 2011 and updated in January 2012. Search terms included (movement training OR neuromuscular OR proprioceptive OR proprioception OR plyometric) AND (training OR program OR programme) AND prevent* AND (injury OR injuries). Limits included English language (due to the cost of translation) and human studies. The reference list of retrieved articles was manually checked for potentially relevant studies.

Inclusion and exclusion criteria

Inclusion/exclusion criteria are shown in Table 1.

Table 1 Study selection criteria.

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Quality Assessment

A modified version of the nine item van Tulder et al. [10] was used to assess the methodological quality of each study. The van Tulder et al. [10] criteria focus on the internal validity of clinical trials and recent evidence suggests it is reliable and has good face and content validity [11]. Two independent reviewers (KH and CB) scored each criterion. Any disagreement with scoring the methodological criteria was solved by consensus and a third reviewer (DM) was available if necessary, but was not needed.

Data extraction and analysis

Details of study design, participant characteristics, interventions, statistical analysis, results and study limitations were extracted and tabulated from each included study by one reviewer (KH). Additionally, two reviewers (KH and CB) extracted data related to participant numbers and injury incidence for the various types of lower limb injuries reported. Review Manager version 5.0 was used to calculate risk ratios (RR) and their 95% Confidence Intervals (CI) for all comparisons as well as to produce forest plots to represent this data visually. The number needed to treat (NNT) was calculated only for variables producing a statistically significant RR (that is, 95% confidence intervals did not cross 1.0). Sensitivity analysis was completed to identify if the use of equipment improved injury prevention. To complete this, the effectiveness of a selection of eight studies, five randomized controlled trials (RCTs) [12–16] and three cohort studies [17–19] which utilized equipment in their programmes and, hence, were excluded from the primary review were evaluated using the same analytical approach.

Results

Literature search

The initial search identified 766 articles (Figure 1). Duplicates were excluded. Many studies were excluded because they involved use of additional equipment not readily available at training or competition venues (see Table 2). Relevant titles and abstracts were selected based on the inclusion criteria, yielding 15 articles. Application of inclusion/exclusion criteria to the full text left nine articles and excluded six articles; five studies because injury prevention was not the primary outcome [20–24] and one study because it lacked a control [25].

Figure 1

Flowchart to demonstrate the literature search.

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Table 2 Reasons for exclusion of studies.

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Methodological quality

Table 3 shows the results of the methodological quality assessment for the nine included studies. All nine studies scored a minimum of five points on the scale indicating they were of reasonable quality [10]. The following study weaknesses were noted: failure to blind participants to the intervention [26–33], unacceptable, inadequate or absent randomization [26, 27, 29], failure to blind researchers to the intervention [26–28, 30], no intention to treat analysis [28, 30], different group values at baseline [30], high drop-out rate [32] and poor compliance [32].

Table 3 Assessment of methodological quality for each included study.

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Description of Studies

Details of each study are summarized in Table 4 including study design, participants, neuromuscular warm-up strategy evaluated, control intervention, and outcomes evaluated. Studies included an average of 1,500 participants (range 1,020 to 2,020). Two studies [33, 34] investigated male and female participants, while the remaining seven investigated females only [26–32]. The age range of participants was 13 to 26 years. Five studies evaluated amateur football players [26, 28, 29, 31, 32], two studies evaluated army recruits [33, 34], one study evaluated amateur football and basketball players [30] and one study evaluated amateur football, basketball and volleyball players [27]. Three studies evaluated primarily ACL injury [26–28], two studies assessed all lower extremity injury risk which included the foot, ankle, leg, knee, thigh, groin and hip [31, 32], one study assessed lower extremity injuries which included knee and ankle [30], one study evaluated injuries to the knee including collateral ligament, ACL, meniscal and patella injuries [29], one study measured general overuse injuries [34] and one specifically anterior knee pain (AKP)[33]. Studies quantified injury incidence per 1,000 player hours [29, 31, 32], per 1,000 athlete exposures [26–28, 30] and by cumulative incidence [33, 34].

Table 4 Summary of details regarding each included study.

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Undefined lower limb injuries

RRs for the effectiveness of neuromuscular warm-up strategies in preventing undefined lower limb injuries are shown in Figure 2. 'The 11+' [31] and 'KIPP' [30] were found to significantly reduce the risk of overall lower limb injuries (RR 0.67, CI 0.54 to 0.84, NNT 18; and RR 0.50, CI 0.33 to 0.76, NNT 24, respectively) and lower limb overuse injuries (RR 0.45, CI 0.28 to 0.71, NNT 31; and RR 0.44, CI 0.22 to 0.86, NNT 49, respectively). Similar to studies without equipment, the sensitivity analysis indicated a mixture of effective and ineffective warm-up programmes which used additional equipment.

Figure 2

Forest plot graph demonstrating risk ratios for the effectiveness of neuromuscular warm-up strategies in preventing undefined lower limb injuries.

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Hip and thigh injuries

None of the strategies evaluated were able to produce significant reductions in hip or thigh injuries, with calculated risk ratios shown in Figure 3. A strong trend was indicated for the 'The 11' programme [32] to reduce groin injuries (RR 0.39, CI 0.15 to 1.02, NNT 77). Similarly, the sensitivity analysis failed to identify any warm-up programmes using equipment which were able to reduce the risk of hip and thigh injuries.

Figure 3

Forest plot graph demonstrating risk ratios for the effectiveness of neuromuscular warm-up strategies in preventing hip and thigh injuries.

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Knee injuries

RRs for the effectiveness of neuromuscular warm-up strategies in preventing knee injuries are shown in Figure 4. The 'HarmoKnee' [29] and 'The 11+' [31] programmes significantly reduced the risk of knee injuries (RR 0.22, CI 0.06 to 0.76, NNT 72; and RR 0.48, CI 0.32 to 0.72, NNT 28). Additionally, the PEP [26] strategy was the most effective at reducing ACL injuries (RR 0.18, CI 0.08 to 0.42, NNT 70). The PEP [28] also significantly reduced the risk of recurrence in those with previous non-contact ACL injuries (P = 0.046). The AKP PTP [33] was able to reduce the incidence of anterior knee pain (RR 0.27, CI 0.14 to 0.54, NNT 28). Similar to studies without equipment, the sensitivity analysis indicated a mixture of effective and ineffective warm-up programmes which used additional equipment to prevent knee injuries.

Figure 4

Forest plot graph demonstrating risk ratios for the effectiveness of neuromuscular warm-up strategies in preventing knee injuries.

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Lower leg and ankle injuries

RRs for the effectiveness of neuromuscular warm-up strategies in preventing lower leg and ankle injuries are shown in Figure 5. A strong trend was indicated for the 'KIPP' [30] strategy to reduce non-contact ankle sprains (RR 0.42, CI 0.18 to 1.01, NNT 77). However, none of the neuromuscular warm-up programmes evaluated produced a significant reduction in lower leg or ankle injuries. Contrary to this, five of the eight programmes using equipment which were evaluated in the sensitivity analysis significantly reduced the risk of ankle injury. Additional equipment used in successful studies included balance boards [13–15, 17], sticks [16] and medicine balls [17].

Figure 5

Forest plot graph demonstrating risk ratios for the effectiveness of neuromuscular warm-up strategies in preventing lower leg and knee injuries.

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Discussion

This systematic review investigated the effectiveness of neuromuscular warm-up strategies for injury prevention. Based on available data a number of strategies appear to be effective in preventing lower limb injuries. Specifically, 'The 11+' [31] strategy may reduce overall and overuse lower limb injuries in young amateur female footballers; the 'KIPP' [30] strategy may reduce non-contact overall and overuse lower limb injuries in young amateur female basketball and volleyball players, the PEP strategy [26, 28] may reduce ACL injuries in young amateur female footballers; and the AKP PTP [33] may reduce the incidence of overuse anterior knee pain in young male and female military recruits.

Study Analysis

The quality assessment criteria revealed that the studies had various methodological weaknesses affecting their internal validity. Firstly, sample sizes were often too low to evaluate specific injuries (for example, ankle sprains). If evaluating the effectiveness of neuromuscular warm-up programmes on more specific injuries, sample size calculations prior to commencement and recruitment of larger samples are recommended. Additionally, future studies should ensure blinding of assessors, concealment of treatment allocation, intention to treat analysis and more adequate randomization procedures to reduce the impact of issues relating to internal validity. External validity was also limited, in particular the applicability of the findings to age groups other than between 13 and 26 years.

There is also a need to determine the mechanism of effectiveness of neuromuscular warm-up strategies and determine whether injury reduction is the result of each individual component or due to a combination of exercises. No studies were identified which compared two different components or combinations of neuromuscular warm-up strategies and, in general, programmes targeted varying risk factors associated with a variety of specific injuries. Addressing this through further research will enable more emphasis on effective components of injury-specific interventions and facilitate the development of more successful neuromuscular warm-up strategies for injury prevention, specifically in reference to specific lower limb injuries.

There is limited homogeneity between the prevention strategies and the methods of recording injury incidence, making data pooling for meta-analysis inappropriate. Injury incidence was reported by a certified athletic trainer [28], a coach [26, 27, 30–32], an author [29, 34] and participant self-reporting [33]. This may have led to a difference in the incidence of injury reporting due to the individuals' medical understanding of an injury. For example, the participants who are self-reporting may be less likely to complain of an injury perhaps due to a lack of medical insurance, compared to the author who, incidentally, is an orthopaedic consultant. The duration of the prevention strategies were 12 weeks [27, 28, 34], 14 weeks [33], eight months [31, 32], nine months [29], and one [30] and two years [26]. Currently, it is unclear how these differences may have impacted outcomes. Further research is needed to determine the minimum participation period needed to provide protection against injury. The prevention strategies were not performed before every training session in the studies by Steffen et al. [32], Gilchrist et al. [28], LaBella et al. [30], Kiani et al. [29] and Brushøj et al. [34]. This potentially allowed other warm up strategies to confound any benefits of the neuromuscular training exercises and conversely for optimal effects not to be realized.

Adverse effects were only noted in four studies [26, 28, 31, 33] and should be recorded more frequently in future studies. Those mentioned include muscle soreness at the introduction of the study [26], one minor hamstring strain [31] and one fractured tibia/fibula from falling over a ball while jumping over it [28]. It is important for studies to directly question participants about adverse effects so that safe, as well as effective, strategies are established.

Total incidence of lower limb injuries

The effectiveness of three neuromuscular warm-up strategies in preventing the total number of lower limb injuries was evaluated in studies included in this review. Of these, only 'The 11+' [31] and KIPP [30] were found to be effective, both reducing the risk of undefined lower limb and overuse lower limb injuries. The two strategies found to be ineffective were 'The 11' [32] and the PTP [34]. In the case of the 'The 11' [32] lack of effectiveness may be explained by poor compliance. 'The 11' [32] was only used in 52% of training sessions, most likely because of a seven-week summer break during the study. The training may have had an additive effect that was lost when detraining over this period and the number of teams using the strategy after this period dropped from 60% to 44%. The authors concluded that better compliance was needed for sufficient training effects to reduce injuries.

The PTP [34] may have been ineffective at reducing lower limb injuries in military recruits due to the sudden increase in intensity of participants' training, the low load of the participants' training and the lack of supervision/training of the soldiers. Additionally, the strategy was of a short duration (12 weeks) and used less technically demanding exercises (including no warm-up, agility or plyometric exercises).