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RESEARCH ARTICLE Open Access
The effectiveness of neuromuscular warm-up
strategies, that require no additional equipment,
for preventing lower limb injuries during sports
participation: a systematic review
Katherine Herman, Christian Barton, Peter Malliaras and Dylan Morrissey
*
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.
Keywords: neuromuscular training, lower limb, injuries, prevention
* Correspondence: d.morrissey@qmul.ac.uk
Centre for Sports and Exercise Medicine, William Harvey Research Institute,
Bart’s and the London School of Medicine and Dentistry, Queen Mary
University of London, Mile End Hospital, Bancroft road, London, E1 4DG, UK
Herman et al.BMC Medicine 2012, 10:75
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© 2012 Herman et al; licensee BioMed Centra l Ltd. This is an Open Access article distributed under the terms of the Creative Commons
Attribution License (http://creative commons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in
any medium, pro vided the original work is properly cited.
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 preven-
tion is highlighted by estimates that 22 million sports
injuries occur in the UK each year [6]. 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]. It is more important
than ever to encourage people to engage in some form
of physical activity [8] and the recent Chief Medical
Officer report 2009 described physical activity as a ‘won-
der drug’or ‘miracle cure’with huge potential benefits
[6]. However, an inevitable consequence of increasing
physical activity is an increased incidence of musculos-
keletal injury. To reduce the resultant personal and eco-
nomic 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 prevent-
ing lower limb injuries. Hübscher et al. [9] recently com-
pleted a high quality systematic review on neuromuscular
training programmes for sports injury prevention. A
meta-analysis indicated that multi-intervention pro-
grammes 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 train-
ing 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 incorpo-
rated into warm-up or current routines. A number of
neuromuscular warm-up strategies which fit these cri-
teria 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 evalu-
ate 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 Jan-
uary 2012. Search terms included (movement training
OR neuromuscular OR proprioceptive OR propriocep-
tion 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.
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
suggestsitisreliableandhasgoodfaceandcontent
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, inter-
ventions, 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% con-
fidence intervals did not cross 1.0). Sensitivity analysis
was completed to identify if the use of equipment
improved injury prevention. To complete this, the effec-
tiveness of a selection of eight studies, five randomized
controlled trials (RCTs) [12-16] and three cohort studies
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[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 stu-
dies because injury prevention was not the primary out-
come [20-24] and one study because it lacked a control
[25].
Methodological quality
Table 3 shows the results of the methodological quality
assessment for the nine included studies. All nine stu-
dies scored a minimum of five points on the scale indi-
cating 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 com-
pliance [32].
Table 1 Study selection criteria.
Inclusion Criteria
Those studies:
•Which investigated neuromuscular warm-up strategies without the need for additional equipment other than that readily available at training
or competition venues
•for the prevention of any lower limb injury (hip, thigh, knee, ankle, leg)
•using functional training
•could be performed anywhere (for example, on-pitch)
•without the use of specialist apparatus
•easily incorporated into regular activity
•Which are detailed enough for replication
•Where injury incidence was an outcome
Exclusion Criteria
Those studies:
•Where the intervention is not part of a warm-up program
•Using home-based exercises due to the poor uptake and regular commitment
•Using equipment (for example, wobble board training) due to cost and availability
•Where the intervention included training outside of sporting participation sessions
•Where participants had an ongoing injury
•Using no control or comparison group
•Which were non-peer reviewed articles
•Of single participant study design
Literature Search (June 2011):
Embase, SPORTDiscus, Google Scholar, PubMed, ISI Web
of Knowledge, Scirus and PEDro
766 articles
Duplicates were excluded, relevant titles and abstracts were
selected yielding 15 articles
A modified version of the nine item van Tulder et al10 was
used to assess the studies.
Applied inclusion/exclusion criteria left nine articles
Figure 1 Flowchart to demonstrate the literature search.
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Description of Studies
Details of each study are summarized in Table 4 includ-
ing study design, participants, neuromuscular warm-up
strategy evaluated, control intervention, and outcomes
evaluated. Studies included an average of 1,500 partici-
pants (range 1,020 to 2,020). Two studies [33,34] investi-
gated male and female participants, while the remaining
seven investigated females only [26-32]. The age range
Table 2 Reasons for exclusion of studies.
Study Reason for study exclusion
Tropp et al. 1985 Ankle discs, orthoses used
Caraffa et al. 1996 Balance boards used
Bahr et al. 1997 Balance boards used
Hewett et al. 1999 Wobble boards used
Wedderkopp et al. 1999 Ankle discs used
Heidt et al. 2000 Treadmill sessions implemented
Söderman et al. 2000 Wobble boards used
Junge et al. 2002 Not detailed enough for replication
Kaminski et al. 2003 Injury prevention not the primary outcome
Stasinopoulos et al. 2004 Orthoses, balance boards used
Verhagen et al. 2004 Wobble boards used
Olsen et al. 2005 Wobble boards used
Garrick et al. 2005 Wobble boards used
Peterson et al. 2005 Balance boards used
Verhagen et al. 2005 Injury prevention not the primary outcome
McKuine et al. 2006 Wobble boards used
Mykleburst et al. 2007 Lack of control group, mats and balance boards used
Mohammadi et al. 2007 Orthoses, ankle weights, resistance bands, wobble boards used
McHugh et al. 2007 Foam stability pad used
Emery et al. 2007 Wobble boards used
Pasanen et al. 2008 Wobble boards used
Hupperets et al. 2008 Wobble boards used
Steffen et al. 2008 Injury prevention not the primary outcome
Hupperets et al. 2009 Balance boards used
Kraemer et al. 2009 Balance boards used
Lim et al. 2009 Injury prevention not the primary outcome
Eils et al. 2010 Wobble boards used
Eisen et al. 2010 Injury prevention not the primary outcome
Emery et al. 2010 Wobble boards used
Parkkari et al. 2011 Sticks used as part of a training approach
Table 3 Assessment of methodological quality for each included study.
Methodological Quality Criteria
Study Quality Score A B C D E F G H I
Mandelbaum et al. [1] 5 N N Y N Y Y Y Y N
Pfeiffer et al. [1] 5 N N Y N Y Y Y Y NR
Gilchrist et al. [1] 5 NR N Y N Y Y Y Y N
Kiani et al. [1] 6 N N Y Y Y Y Y Y NR
LaBella et al. [1] 6 Y NNNYY Y Y Y
Soligard et al. [1] 7 NR N Y Y Y Y Y Y Y
Steffen et al. [1] 7 Y N Y Y Y N Y Y Y
Coppack et al. [1] 8 Y N Y Y Y Y Y Y Y
Brushøj et al. [1] 9 Y Y Y Y Y Y Y Y Y
A = acceptable method of randomization, B = concealed treatment allocation, C = similar group values at baseline, D = blinded assessor, E = no or similar co-
interventions, F = acceptable compliance (≥75%), G = acceptable dropout rate (≤30%), H = similar timing of the outcome assessment in all groups, I = intention
to treat analysis. Y, yes; N, no; NR, not reported.
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Table 4 Summary of details regarding each included study.
Study Design Participants Neuromuscular warm-up program Control Group Outcome
Mandelbaum
et al. [26]
CCT 1,041 female soccer
players, aged 14 to
18 years
Prevent Injury and Enhance Performance
Programme: three basic warm-up
exercises, five stretching exercises for the
trunk and lower extremities, three
strengthening exercises, five plyometric
exercises and three soccer-specific agility
drills. Performed before matches and
training, 20 minutes, for two years
Normal warm-up
strategy
ACL injuries
Pfeiffer et al.
[27]
CCT 1,439 female soccer,
basketball and
volleyball players,
aged 14 to 18 years
Knee Ligament Injury Prevention
Programme: four progressive phases of
jumping and landing forwards and
backwards, two- and one-footed drills,
plyometric and agility training. Performed
either before or after training sessions
twice a week, 20 minutes, for two
consecutive seasons
Normal warm-up
strategy
ACL injuries
Gilchrist et al.
[28]
RCT 1,435 female football
players, average age
19.9 years
Prevent Injury and Enhance Performance
Program: Three basic warm-up exercises,
five stretching exercises for the trunk and
lower extremities, three strengthening
exercises, five plyometric exercises and
three soccer-specific agility drills. Before
training, 20 minutes three times a week
for 12 weeks
Normal warm-up
strategy
Undefined knee and ACL injuries
Kiani et al.
[29]
CCT 1,506 female football
players, aged 13 to
19 years
The ‘HarmoKnee’program: warm-up,
muscle activation, balance, strength, core
stability exercises. Performed twice a
week preseason (three months), once a
week during in-season training session
(six months), total duration 20 to 25
minutes
Normal warm-up
strategy
All new knee injuries
LaBella et al.
[30]
RCT 1,558 female football
and basketball
players, average age
16 years
Knee Injury Prevention Program:
combining progressive strengthening,
plyometric, balance and agility exercises.
In season for one year. Total duration 20
minutes before team practices, an
abbreviated version with dynamic motion
exercises only before games
Normal warm-up
strategy
Gradual-onset lower extremity
injuries, acute-onset non-contact
lower extremity injuries, non-contact
knee, ACL and ankle sprains
Soligard et al.
[31]
RCT 1,982 female football
players, aged 13 to
17 years
The ‘11+’:10 exercises including slow
running, active stretching, controlled
contact, exercises for strength, balance,
jumping and soccer-specific agility drills.
Before training, 20 minutes, only running
exercises before match, for eight months
Normal warm-up
strategy
Overall and overuse lower limb
injuries, groin, posterior and anterior
thigh injuries, undefined knee, MTSS
and undefined ankle injuries
Steffen et al.
[32]
RCT 2,020 female football
players, aged 13 to
17 years
The ‘11’: 10 exercises for core stability,
balance, dynamic stabilization and
eccentric hamstring strength. Two
months preseason, six months in-season
before training, 20 minutes for 15
consecutive training sessions then once a
week thereafter
Normal warm-up
strategy
Overall lower limb injuries, groin and
thigh injuries, undefined knee and
ACL injuries, and undefined ankle
injuries
Coppack et
al. [33]
RCT 1,502 male and
female army recruits,
aged 17 to 25 years
Anterior Knee Pain Prevention Training
Programme: warm-up consisted of eight
exercises closed chain strengthening
exercises, 10 to 14 repetitions each;
warm-down involved four stretching
exercises, three repetitions. Performed at
each training session (mean = seven per
week), 15 minutes, for 14 weeks
Normal warm-up
strategy (running,
stretching,
strengthening)
AKP
Brushøj et al.
[34]
RCT 1,020 female and
male army recruits
aged 19 to 26 years
Prevention Training Programme: Five
exercises for strengthening, balance,
stretching performed in three sets of five
to 25 repetitions. Before military training,
15 minutes, three times a week for 12
weeks
Strategy for the
upper body
Overall and overuse lower limb
injuries, AKP, patella tendinopathy,
ITBFS, MTSS, ankle sprain and Achilles
injuries.
ACL, anterior cruciate ligament; AKP, anterior knee pain; CCT, controlled clinical trial; ITBFS, iliotibial band friction syndrome; MTSS, medial tibial stress syndrome;
RCT, randomized controlled trial.
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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 volley-
ball 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 collat-
eral 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].
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, respec-
tively). Similar to studies without equipment, the sensi-
tivity analysis indicated a mixture of effective and
ineffective warm-up programmes which used additional
equipment.
Hip and thigh injuries
None of the strategies evaluated were able to produce
significant reductions in hip or thigh injuries, with cal-
culated 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.
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] pro-
grammes 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 signif-
icantly reduced the risk of recurrence in those with pre-
vious 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 indi-
cated a mixture of effective and ineffective warm-up
programmes which used additional equipment to pre-
vent knee injuries.
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 pro-
duced a significant reduction in lower leg or ankle inju-
ries. 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 med-
icine balls [17].
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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Figure 3 Forest plot graph demonstrating risk ratios for the effectiveness of neuromuscular warm-up strategies in preventing hip and
thigh 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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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. Specifi-
cally, ‘The 11+’[31] strategy may reduce overall and
overuse lower limb injuries in young amateur female
footballers; the ‘KIPP’[30] strategy may reduce non-con-
tact 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 exer-
cises. No studies were identified which compared two
different components or combinations of neuromuscular
warm-up strategies and, in general, programmes tar-
geted varying risk factors associated with a variety of
specific injuries. Addressing this through further
research will enable more emphasis on effective compo-
nents of injury-specific interventions and facilitate the
development of more successful neuromuscular warm-
up strategies for injury prevention, specifically in refer-
ence to specific lower limb injuries.
There is limited homogeneity between the prevention
strategies and the methods of recording injury inci-
dence, making data pooling for meta-analysis inap-
propriate. 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 con-
sultant. 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 strate-
gies 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
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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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 sore-
nessattheintroductionofthestudy[26],oneminor
hamstring strain [31] and one fractured tibia/fibula from
falling over a ball while jumping over it [28]. It is impor-
tant 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 stra-
tegies in preventing the total number of lower limb inju-
ries was evaluated in studies included in this review. Of
these, only ‘The 11+’[31]andKIPP[30]werefoundto
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 num-
ber 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.
ThePTP[34]mayhavebeenineffectiveatreducing
lower limb injuries in military recruits due to the sud-
den 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).
Hip and thigh injuries
Hip and thigh injuries were recorded during the evalua-
tion of two neuromuscular warm-up strategies, ‘The 11
+’[31] and ‘The 11’[32]. Neither strategy significantly
reduced hip or thigh injury rates, most likely because
they were not powered to do so. Highlighting this, ‘The
11’[32] programme indicated a strong trend toward
reduced risk of groin injuries. This would likely have
been a significant finding had more participants been
recruited. In addition to study power, the components
of the strategies may not have been adequate to reveal
protection against hip and thigh injuries. A recent
review of hamstring injury prevention demonstrates that
isometric warm-up exercises, hamstring flexibility and
concentric and eccentric strength training may be pro-
tective against hamstring injuries [35]. Additionally, core
strength is a recognized factor in reducing the risk of
injury. Evidence suggests that core muscle weakness
may increase the risk of groin strain injuries [36]. Both
‘The 11+’[31] and ‘The 11’[32] incorporated Nordic
hamstring curls for hamstring strength training and
plank exercises for core stability. However, the number
of repetitions or the frequency of these exercises may
have been inadequate to reduce injury rate.
Knee injuries
Knee injury rates were recorded in all of the nine stu-
dies, with six of these recording ACL injuries. Based on
available data, four neuromuscular warm-up strategies
were found to be effective in preventing knee injuries.
These included individual studies showing ‘The 11+’
[31] and ‘HarmoKnee’[29] programmes to reduce the
risk of undefined knee injuries, the PEP to reduce signif-
icantly the risk of both ACL injuries [26] and their
recurrence [28] and the AKP PTP [33] to reduce the
risk of anterior knee pain development.
Success of the AKP PTP [33] may relate to strategy fre-
quency as it was performed an average of seven times per
week, totalling 105 minutes, a higher frequency compared
to other studies. In comparison, the PTP [34] demon-
strated no reductions in anterior knee pain, and this was
used only three times a week totalling 45 minutes.
Despite investigating the same warm-up strategy (that
is, the PEP strategy), Mandelbaum et al. [26] demon-
strated a highly significant reduction in ACL injuries
while Gilchrist et al. [28] showed only a trend toward
risk reduction; a significant risk reduction in ACL inju-
ries during practice, but the overall risk remaining
unchanged. Reasons for this are likely to be the result of
the study design and methodology. The study underta-
ken by Mandelbaum et al. [26] was a CCT with inherent
methodological limitations, while Gilchrist et al. [28]
performed a RCT providing gold standard evidence. In
the study by Mandelbaum et al. [26] there was no blind-
ing or randomization which introduced the potential for
subject and allocation bias, respectively. Additionally,
the authors in the study by Mandelbaum et al. [26]
informed the intervention football clubs that they would
be receiving a strategy to reduce injury and enhance
performance. Participants and trainers were, therefore,
not blinded and were likely to have been influenced by
motivational bias. Of those remaining, one study
informed participants of its purpose but did not disclose
to which group they had been randomly allocated [27]
while the others informed subjects of the purpose in a
similar way to Mandelbaum et al. [26,28-34].
The PTP [34], and KLIPP [27] programmes did not
convey any significant protection against knee injuries.
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As previously discussed, this may relate to lack of
advice, sudden increase in training and less demanding
exercises in the PTP programme [34]. Additionally, the
strategy components did not include any running or agi-
lity drills, which provide a comprehensive warm-up, and
have been included in successful strategies such as ‘The
11+’[31]. The KLIPP [27] did incorporate such exercises
but their study had inherent methodological limitations.
This strategy had the lowest frequency (two times per
week) and this may partly explain its lack of effective-
ness. The most successful strategies (’The 11+’[31], PEP
[26,28] KIPP [30] and AKP PTP [33]) were performed
at every training/match session suggesting that the effec-
tiveness of neuromuscular warm-up strategies may
depend on a dose-response relationship.
The ‘HarmoKnee’[29] programme significantly
reduced the risk of knee injuries. However, findings did
not indicate a significant reduction in the risk of specific
injuries including ACL, MCL, LCL or medial meniscus
injuries, despite the intervention group injury numbers
being zero for each. This is due to the very low number
of injuries identified in the control group, with the num-
ber being five or below for each of these specific injuries
and NNTs ranging from 146 (ACL injuries) to 729
(medial meniscus injuries). Until larger studies are com-
pleted evaluating the ‘HarmoKnee’[29] programme,
these results must be interpreted with caution. Consid-
ering the high costs associated with surgery and rehabi-
litation following injuries such as an ACL tear, these
reduced rates may still be clinically meaningful.
Lower leg and ankle injuries
The effectiveness of four neuromuscular warm-up stra-
tegies which did not require additional equipment in
preventing lower leg and ankle injuries were evaluated
in studies from this review. Based on the results, no
neuromuscular warm-up programme was able to reduce
lower limb injury risk significantly. However, it should
be considered that the KIPP [30] indicated a strong
trend toward reduction of the incidence of ankle
sprains, with an NNT of 77. Reasons for the prevention
of ankle sprain injuries in the KIPP [30] strategy rather
than the PTP [34] include the more comprehensive neu-
romuscular warm-up programme which took longer to
perform and included lower repetitions of many more
elements as well as dynamic exercises. Additionally, the
studybyBrushøjet al. [34] which evaluated the PTP
programme had fundamental methodological flaws as
mentioned earlier. No other strategies report significant
reductions in lower leg or undefined ankle injuries. The
‘11+’[31] results showed a trend towards reduced risk
of MTSS and undefined ankle injury; however, these
were not convincing enough to conclude their effective-
ness in injury prevention.
A previous systematic review comparing balance work
(using balance boards) and neuromuscular exercises
(without balance boards) revealed that ankle sprains
were reduced by 36% and 50%, respectively [17]. Addi-
tionally, the sensitivity analysis completed in this review
indicated that the addition of equipment, in particular
balance boards, to warm-up programmes may be effec-
tive in reducing ankle injuries. This provides evidence
that neuromuscular strategies can reduce ankle injuries.
However, the practicality of these programmes may be
questioned due to the need for acquisition of additional
equipment requiring funding, maintenance and storage.
Therefore, many sporting clubs and individuals, particu-
larly in an amateur setting where most sports participa-
tion occurs, may consider that implementing such a
programme is not worth the effort. In fact, this is the
reason studies in our review were excluded if additional
equipment were required. To impact on ankle injury
prevention across all sports participation to a greater
extent, design and evaluation of warm-up programmes
which focus on dynamic balance and strengthening
without the need for equipment such as balance boards
is needed. If successful, this may provide a more practi-
cal and cost-effective alternative to using balance boards.
Examples may include single leg balance exercises
including throwing a ball with a partner and resisting a
push from partners, hopping, and squat exercises
including with heels raised and one leg squats.
Recommendations
According to the present systematic review, several
practical neuromuscular warm-up strategies which do
not require additional equipment that is not readily
available at the usual amateur competition or training
venues are effective to varying degrees at preventing
lower limb injuries. However, in some instances a large
number of participants would need to undertake a strat-
egy before one injury is prevented. This is the case with
the PEP [26] strategy requiring 70 participants to pre-
vent one injury. ‘The 11+’[31], ‘KIPP’[30] and ‘AKP
PTP’[33] appear to provide more reasonable NNT
values, requiring less than 35 participants to undertake
the neuromuscular warm-up strategy to prevent one
injury. Of these strategies, the KIPP [30] and ‘11+’[31]
strategies prevent the most injuries with NNTs for over-
all lower limb injuries being just 18 and 24, respectively.
Importantly, this systematic review highlights several
areas that may account for significantly better injury
prevention when incorporating neuromuscular warm-up
strategies. These include: (1) incorporation of stretching,
strengthening and balance exercises, sports-specific agi-
lity drills and landing techniques; (2) completing the
strategy for longer than three consecutive months; and
(3) completing of the strategy at all training sessions. In
Herman et al.BMC Medicine 2012, 10:75
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Page 10 of 12
addition to these programme specifics, further evalua-
tion of the ‘11+’[31] programme has highlighted the
importance of compliance, with high compliance being
linked significantly to reduced lower limb injury risk
[37].
Directions for Future Research
Further studies need to determine whether ‘The 11+’
[31], KIPP [30], ‘HarmoKnee’[29], AKP PTP [33] and
PEP [26,28] programmes are also effective in men, other
age groups, and other sports as our review incorporated
mainly women and involved only football, basketball,
volleyball and military training. It is important to deter-
mine whether injury prevention programmes would also
be effective if taught to older players who might possess
more engrained poor motion patterns. In addition,
healthcare professionals are encouraging middle-aged
individuals to engage in sports and so research needs to
include older individuals who are at a higher risk of sus-
taining an injury due to changed activity levels. It would
also be beneficial to see if ‘The 11+’[31], ‘KIPP’[30],
‘HarmoKnee’[29], PEP [26,28] strategy and AKP PTP
[33] could be successfully combined to ultimately
recommendasingleinjurypreventionstrategy.Finally,
we need to know more about the mechanisms of injury
prevention of neuromuscular warm-up strategies in
order to optimize their effectiveness.
Conclusions
The current systematic review identified five practical
neuromuscular warm-up strategies which do not require
additional equipment and which may effectively reduce
the risk of lower limb injuries. Specifically ‘The 11+’
reduced overall and overuse lower limb injuries and
knee injuries in young amateur female football players,
the ‘KIPP’reduced non-contact overall and overuse
lower limb injuries in young amateur female football
and basketball players, the ‘HarmoKnee’[29] programme
reduced the risk of knee injuries, the ‘PEP’strategy
reduced the risk of non-contact ACL injury in young
amateur female football players and the ‘AKPPTP’
reduced the risk of anterior knee pain in male and
female military recruits. Further research evaluating the
effectiveness of these strategies in more varied popula-
tions, particularly men and older individuals is now
needed. To provide the greatest potential for reduced
lower limb injury rates, it is recommended that neuro-
muscular warm-up strategies incorporate stretching,
strengthening and balance exercises, sports-specific agi-
lity drills and landing techniques, and are completed for
adurationoflongerthanthreeconsecutivemonthsat
all training sessions. Identification of which neuromus-
cular warm-up strategy components are most beneficial
and the mechanisms behind their effectiveness is needed
to further reduce lower limb injury risks.
Authors’contributions
KH and CB were the primary initiators of the study while all authors made
substantial contributions to data analysis and interpretation. All authors were
involved in drafting and revising the manuscript and approved the
penultimate version. The final version was approved and submitted by DM.
Competing interests
The authors declare that they have no competing interests.
Received: 17 February 2012 Accepted: 19 July 2012
Published: 19 July 2012
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Pre-publication history
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http://www.biomedcentral.com/1741-7015/10/75/prepub
doi:10.1186/1741-7015-10-75
Cite this article as: Herman et al.: The effectiveness of neuromuscular
warm-up strategies, that require no additional equipment, for
preventing lower limb injuries during sports participation: a systematic
review. BMC Medicine 2012 10:75.
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