Eksentrik Egzersiz ve Fleksibilite

Department of Clinical
Therapies, University of
Limerick, Ireland
Correspondence to
Kieran O’Sullivan,
Department of Clinical
Therapies, University of
Limerick, Limerick, Ireland;
kieran.osullivan@ul.ie
Received 4 December 2011
Accepted 8 March 2012
The effects of eccentric training on lower limb
flexibility: a systematic review
Kieran O’Sullivan, Sean McAuliffe, Neasa DeBurca
ABSTRACT
Background Reduced flexibility has been documented
in athletes with lower limb injury, however, stretching
has limited evidence of effectiveness in preventing
injury or reducing the risk of recurrence. In contrast, it
has been proposed that eccentric training can improve
strength and reduce the risk of injury, and facilitate
increased muscle flexibility via sarcomerogenesis.
Objectives This systematic review was undertaken to
examine the evidence that eccentric training has demon-
strated effectiveness as a means of improving lower
limb flexibility.
Study appraisal and synthesis methods Six elec-
tronic databases were systematically searched by two
independent reviewers to identify randomised clinical
trials comparing the effectiveness of eccentric training
to either a different intervention, or a no-intervention
control group. Studies evaluating flexibility using both
joint range of motion (ROM) and muscle fascicle length
(FL) were included. Six studies met the inclusion/exclu-
sion criteria, and were appraised using the PEDro scale.
Differences in the muscles studied, and the outcome
measures used, did not allow for pooled analysis.
Results There was consistent, strong evidence from all
six trials in three different muscle groups that eccentric
training can improve lower limb flexibility, as assessed
using either joint ROM or muscle FL.
Conclusion The results support the hypothesis that
eccentric training is an effective method of increasing
lower limb flexibility. Further research is required to com-
pare the increased flexibility obtained after eccentric
training to that obtained with static stretching and other
exercise interventions.
INTRODUCTION
Lower limb injuries are very common among ath-
letes, with significant consequences for both ath-
letes and their teams.1 2 It is important therefore
to identify, and effectively manage, factors that
could reduce injury risk and the time until return
to sport.3–5 Several factors have been proposed as
contributing to the high incidence of lower limb
injuries, including non-modifiable factors such as
age,1 6 gender7 and previous injury.1 8 Modifiable
factors have also been implicated, including
altered neuromuscular control,9 reduced muscle
strength,10 11 altered muscle length-tension curve12
13 and reduced flexibility.14
There is some evidence that using an early
stretching programme to increase flexibility may
reduce the time until return to sport.4 15 However,
the main benefit of stretching seems to be an
increase in flexibility,16 with most studies sug-
gesting stretching is ineffective at reducing injury
risk,3 17–24 postexercise muscle soreness,25 or
improving performance.26 27 Increased flexibility
after a single bout of stretching only lasts approx-
imately 30 min.28–31 This short-term increase is
mainly due to temporary changes in viscoelastic
behaviour.32 A stretching programme performed
regularly for several weeks results in meaningful
improvements in range of motion (ROM),33–35
however, such increases in flexibility do not seem
to reduce injury risk.
Considering the existing evidence of reduced
flexibility in some lower limb injuries,29 36 37 the
limited evidence to support stretching appears
contradictory. However, it is possible that deficits
in flexibility which are observed clinically are sim-
ply one manifestation of an alteration in muscle
function. Athletes with less flexible hamstrings
display an altered muscle length-tension curve,
with changes in the angle of peak torque and
the torque produced at longer muscle lengths.38
Consequently, athletes with reduced flexibility
may be exposing their muscles to potentially
damaging lengthening forces. Eccentric training
results in the addition of sarcomeres in series (sar-
comerogenesis) in animal models.39 This increases
the joint angle at which peak torque is generated,40
and increases muscle fascicle length (FL).41 The
use of such eccentric training to increase flexibil-
ity would combine strengthening and ‘stretching’
of the muscle tissues, which may be important
considering the advantages for lower limb tissues
avoiding prolonged eccentric loading at length-
ened joint angles.42
Currently, in the absence of clear effectiveness of
many exercise interventions, training and rehabil-
itation of lower limb injuries commonly includes
strengthening, stretching and other components
including balance training.43 However, research
from animal models39 41 44 suggests that eccentric
training could increase flexibility via sarcomero-
genesis without the need for additional stretch-
ing exercises. This is significant considering the
additional benefits of eccentric training in terms of
power development and injury risk reduction.11 45 46
Furthermore, technological developments have
facilitated the imaging of intramuscular responses
to exercise, such as ultrasound imaging of muscle
FL.47 However, it is not clear if there is sufficient
data from human studies to support the hypoth-
esis that eccentric training is an effective stimulus
for increased flexibility. Therefore, the aim of this
systematic review was to appraise the evidence
Published Online First
20 April 2012
Review
838 Br J Sports Med 2012;46:838–845. doi:10.1136/bjsports-2011-090835
group.bmj.comon February 26, 2013 - Published bybjsm.bmj.comDownloaded from

from randomised clinical trials on whether eccentric training
results in meaningful increases in lower limb flexibility when
compared with another, or no, intervention.
METHODS
Overview
TheCochraneandMEDLINEdatabaseswereinitiallysearched,
revealing no systematic reviews regarding the effectiveness of
eccentric training on lower limb flexibility. Randomised clini-
cal trials which compared the effect of eccentric training on
lower limb flexibility to either no intervention, or a differ-
ent intervention, were included in this review. Studies using
a method of measuring actual muscle length (eg, ultrasound
imaging of FL) or joint ROM (eg, goniometry) were included.
Studies involving adults aged >18 years, with or without
a history of injury, were eligible. Studies focusing solely on
the effects of eccentric training on other factors such as peak
torque or injury incidence were excluded. Studies involving
eccentric training of <4 weeks duration, such as those examin-
ing muscle damage postexercise, were excluded. Only peer-re-
viewed articles were considered. Conference proceedings were
excluded because they are not consistently peer reviewed, and
often lack sufficient information to adequately assess method-
ological quality. The review was registered (CRD42011001659)
on the PROSPERO database,48 and has been reported in accor-
dance with the PRISMA statement.49
Search strategy and inclusion criteria
The following databases were searched; Academic Search
Complete, AMED, Biomedical Reference Collection, CINAHL,
MEDLINE and SPORTDiscus. Two authors (KOS, NDB) inde-
pendently searched these databases using the following agreed
range of keywords; eccentric (Abstract) AND flexib* OR range
of motion OR fascicle (Abstract) AND strength OR training
(full-text) (figure 1). Studies were limited to those involv-
ing humans, published in English, after 1999. The titles and
abstracts of these selected articles were then screened. When
no abstract was available, or when it was not clear if the study
should be included, full-text articles were retrieved. Studies
were excluded if they did not involve the lower limb, did not
examine flexibility or if eccentric training was only one of sev-
eral interventions. The reference lists of the selected articles
were also manually searched for any further relevant articles.
Data extraction
For each article the following information was extracted
by two authors (SMA, KOS), and cross-checked for accuracy;
(1) sample size (2) participant gender, (3) participant age, (4)
muscle group studied, (5) type of outcome measure used and
(6) inclusion/exclusion criteria (table 1).
Assessment of methodological quality
Two authors (NDB, SMA) independently rated the method-
ological quality of the included studies using the PEDro scale,
which has established reliability50 and validity.51 Neither
author was specifically trained in the use of the PEDro scale,
but clarifying information on several aspects of the scale was
sought from the designers of the scale in advance. Authors of
the original studies were emailed for clarification if necessary.
Thereafter, a consensus decision was reached with a third
author (KOS). Study quality was classified as ‘high’ (>6/10),
‘fair’ (4/10–5/10) or ‘poor’ (<4/10) according to PEDro scores.52
As this review only includes studies published in databases,
there is an overall risk of publication bias. Furthermore, the
reliability and validity of the methods used to analyse flex-
ibility were appraised.
Data Synthesis
Differences in the muscles studied, and the outcome measures
used, did not allow for pooled analysis. Instead, the data for
each muscle group were analysed together to identify consis-
tent effects of eccentric training on lower limb flexibility.
RESULTS
Identification of studies
The electronic search resulted in a total of 530 potentially
relevant papers, which was reduced to 285 after the removal
of duplicates. After screening the title and abstract of
each article, seven full-text articles were identified by both
reviewers independently. One study53 was excluded as it
compared two mixed concentric/eccentric training pro-
grammes of different intensities, rather than comparing eccen-
tric training to a different exercise intervention. Searching the
reference lists of these articles did not add any further articles.
Consequently, the final number of articles included in this
review was six.54–59 The selection procedure is outlined in
figure 2.
Description of included studies
A detailed description of the included studies, listed alpha-
betically, is presented in table 1. The number of participants
included ranged from 18 to 69. In five54–58 of the six studies,
the mean age of participants was 16 to 28 years, with one
study59 including much older participants (mean age of 71
years). Four54 56 58 59 of the six studies included both male and
female participants. ROM using goniometry,56–58 or FL using
ultrasound,54 55 58 59 were used as outcome measures, with one
study58 using both. Inclusion and exclusion criteria were very
similar between studies. No study included participants with
a current or previous lower limb injury. Only one study57
specifically included participants with muscle ‘tightness’.
Eccentric training characteristics
The eccentric training completed in each study is described in
table 2. There were significant variations in terms of the type
of eccentric training, the number of repetitions and sets per-
formed, the intensity of the training, the duration for which
the eccentric contraction was sustained, as well as the fre-
quency and duration of the training.Figure 1 Boolean logic of search terms used.
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Br J Sports Med 2012;46:838–845. doi:10.1136/bjsports-2011-090835 839

METHODOLOGICAL STUDY QUALITY
All six studies were rated as ‘high quality’ using the PEDro
scale (table 3). All six studies randomly allocated participants
and involved concealment of allocation. In three studies, par-
ticipants were not different at baseline in the main outcome
measure of interest to this review, either FL or ROM. However,
in the other three studies,54 58 59 baseline differences were pres-
ent, which could partly explain different responses between
groups, and this concern is addressed in detail later. Two stud-
ies did not state using an outcome assessor who was blinded to
group allocation.57 59 None of the trials blinded the therapists
or patients, which is almost unavoidable in studies of exercise
interventions. All six studies reported follow-up measures for
at least 85% of participants, although in three studies,54 56 57
all participants were not followed up and there was no use
of intention to-treat analysis, or detail on how dropouts were
handled. All six studies performed between-group analysis,
and provided information on both point measures and vari-
ability. Regarding other methodological issues not covered in
the PEDro scale, no study justified the sample size used based
on a power calculation, and there was a strong bias towards
male participants in three studies.55 57 58
DESCRIPTION OF RESULTS
All six studies showed consistent evidence that eccentric train-
ing increases ROM,56 57 or FL,54 55 59 or both,58 irrespective of
the joint or muscle group studied. At the ankle, Mahieu et al56
reported a significantly greater increase in dorsiflexion (mean
change=+6°) compared with a no-exercise control group (mean
change=+1°). Using ultrasound measurements of FL rather
than ankle joint ROM, Duclay et al55 reported similar results.
There was a significant increase in FL (mean change=+3.36
mm) at rest after eccentric training, compared to a control
group (mean change=+1.01 mm) which performed no exercise
intervention.55
Consistent increases in flexibility after eccentric training
were also reported for the hamstrings. Nelson and Bandy57 ran-
domised participants into one of three groups; static stretching,
eccentric training and control (no exercise). Both the eccentric
training (mean change=+12.79°) and static stretching (mean
change=+12.05°) groups reported significantly larger increases
in ROM at follow-up compared with the control group (mean
change=+1.67°). Potier et al58 also studied the hamstrings, and
was the only study to include both FL and ROM as outcome
measures. After the training period, there was a significantly
greater increase in ROM (mean change=+6.9°) in the eccen-
tric training group, compared to the non-exercise control
group (mean change=−1.8°). Furthermore, the increase in FL
was significantly larger for the eccentric training group (mean
change=+34%), being twice as large as the increase reported in
the control group (mean change=+17%).
Finally, two studies54 59 examined the effect of eccentric
training on quadriceps flexibility. Unlike the other four studies,
both of these studies used as the comparison another exercise
intervention which could increase muscle strength, similar to
eccentric training. Reeves et al59 observed a significant increase
in FL after eccentric training, which had not been evident dur-
ing a 14-week pretraining monitoring period. Furthermore,
Table 1 Description of included studies
Study Sample size Gender Mean age Muscle group Outcome measure Inclusion/exclusion criteria
Blazevich et al54 33 16 M/17 F 23 Quadriceps FL Recreationally active; No lower limb injury; No weight training;
No co-existing medical conditions; Not a manual occupation;
Not exercising vigorously >4 times/week
Duclay et al55 18 All male 23 Calf FL Healthy students; Recreationally active; No neurological injury/
disease; Not engaged in resistance training
Mahieu et al56 64 32 M/32 F 22 Calf ROM Recreationally active; No lower limb injury; Not elite athlete
Nelson and Bandy57 69 All male 16 Hamstring ROM Tight hamstrings; Not currently increasing their exercise
intensity; No lower limb injury; No low back pain
Potier et al58 22 16 M/6 F 28 Hamstring FL and ROM Not engaged in resistance training; No musculoskeletal injury;
No co-existing medical conditions
Reeves et al59 19 8 M/10 F 71 Quadriceps FL Recreationally active; No musculoskeletal injury; No co-existing
medical conditions; Living independently
F, female; FL, fascicle length; M, male; ROM, range of motion.
Figure 2 Flow chart of study identification procedure.
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while FL also increased from the baseline in a mixed concen-
tric/eccentric training group (mean change=+6 mm, or +8%),
the increase was significantly greater in the eccentric train-
ing group (mean change=+16 mm, or +22%). Blazevich et al54
included three groups in their study of the quadriceps; an
eccentric group, a concentric group and a non-exercise control
group. Both the eccentric (mean change=+3.1%) and concen-
tric (mean change=+6.3%) training groups demonstrated sig-
nificant increases in FL (mean change=+4.2%) after 10 weeks,
unlike the control group (mean change=−0.3%). However,
unlike Reeves et al,59 FL increased to a greater extent, albeit
non significantly, in the concentric training group.
DISCUSSION
Main findings
Consistent evidence in six high-quality studies supported the
hypothesis that eccentric training is effective at increasing
lower limb flexibility. This finding was consistent across dif-
ferent muscle groups, and using different outcome measures.
All four studies54 55 58 59 which examined muscle FL identified
significant gains in FL following eccentric training, indicating
structural adaptations within the muscle. Similarly, the find-
ings from all three studies56–58 examining ROM confirm that
increases in ROM occur after eccentric training, irrespective of
the muscle group studied.
Defining and analysing flexibility
Reviewing the literature in this area is complicated by attempts
to define flexibility. Flexibility has traditionally been examined
using indirect ROM measurements defined separately as ‘flex-
ibility’ and ‘stretch tolerance’,60 while recent technological
developments have allowed direct measurements of FL.58 In
this review, we considered studies which have evaluated any
of these measurements before and after eccentric training as
a measure of ‘flexibility’. The ROM measurements such as
those used in this study are relatively reliable29 61 and clini-
cally applicable. However, it must be acknowledged they may
not accurately represent underlying muscle length, especially
in biarticular muscles such as those included in these studies.
Obviously other factors can increase ROM, such as a simple
warm-up,29 and inconsistency across studies on the use of a
warm-up could influence the magnitude of change in ROM
observed, although this would not change the overall effec-
tiveness reported across all muscle groups. Furthermore, in
one study, the baseline differences in ROM between groups
(7.9°) actually exceeded the increase reported after eccentric
training (6.9°).
Analysing FL using ultrasound also involves a degree of
error, especially in those studies involving vastus lateralis54
59 and the hamstrings,58 where their relatively long FLs47 55
required FL to be estimated using linear extrapolation. This
may partly explain why there were baseline differences in
FL in two studies.54 59 While the use of a repeated baseline
with very little variation supports the measurement proto-
col in one of these studies,59 a large change in FL among the
control group in one study58 and after the intervention had
ended in another study,54 further question the between-day
reliability of FL measurement and the similarity of groups
Table 2 Eccentric training characteristics in each study
Study
Comparison
groups
Duration
(weeks)
Total
number of
sessions Reps/Sets per session
Duration
of each
exercise (s) Intensity Intervention
Blazevich et al54 1) Eccentric
2) Concentric
3) Control
10 30 Progressed from 6/4 6/5 6/6 3 s* 1) 50%-100%
E1RM
2) 50%–100%
C1RM
1) Eccentric
dynamometry
2) Concentric
dynamometry
Duclay et al55 1) Eccentric
2) Control
7 18 6/6 3 s
(two exercises)
120% C1RM Eccentric
dynamometry
Mahieu et al56 1) Eccentric
2) Control
6 42 15/3 6 s N/R Eccentric heel drops
Nelson and Bandy57 1) Eccentric
2) Stretching
3) Control
6 18 6/1 5 s N/R 1) Eccentric hip flexion
with knee extended
2) Static hamstring
stretching
Potier et al58 1) Eccentric
2) Control
8 24 8/3 5 s 100% E1RM Weights machine
Reeves et al59 1) Eccentric
2) Mixed conc/ecc
14 42 10/2 1) 3 s
2) 2/3 s (two exercises)
1) 80% E5RM
2) 80% C5RM
Weights machine for
both
C1RM, concentric one repetition maximum; E1RM, eccentric one repetition maximum; N/R, not reported.
*Approximation based on detail provided in the study.
Table 3 Methodological quality of included trials assessed using PEDro scale
Study Random Conceal Baseline
Blind
assessor
Blind
subject
Blind
therapist Follow-up ITTA BGA PMV Score
Blazevich et al54 X X X X 6 (High)
Duclay et al55 X X 8 (High)
Mahieu et al56 X X X 7 (High)
Nelson and Bandy57 X X X X 6 (High)
Potier et al58 X X X 7 (High)
Reeves et al59 X X X X 6 (High)
BGA, between-groups analysis; , meets criteria; X, does not meet criteria; ITTA, intention to-treat analysis; PMV, point measure and variability.
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at baseline. This highlights the need for estimates of reli-
ability or repeated baseline measurements when using this
approach.55 59 Furthermore, studying a portion of a muscle
group such as vastus lateralis may not necessarily reflect
accurately the rest of that muscle group.47 Interestingly,
the recent availability of extended field-of-view ultrasound
(EFOV-US), has confirmed that the estimation methods used
in three of the four included studies which examined FL are
likely to have underestimated FL, and the error involved is
not consistent across muscle lengths.62 The availability of
EFOV-US appears to be much more reliable and may address
these concerns.62 Notwithstanding these legitimate method-
ological concerns, the findings are remarkably consistent in
all studies.
Mechanism of increasing flexibility
Sarcomerogenesis remains the most likely mechanism by
which flexibility increases after eccentric training, as has
clearly been demonstrated after eccentric training in animal
studies.39 A prolonged shift in the muscle length-tension
curve consistently occurs after repeated bouts of eccentric
training,40 suggesting that muscles adapt to mildly damaging
eccentric training by sarcomerogenesis. This optimises gen-
eration of torque at more extended joint positions, to limit the
potential for muscle damage.44 63 The findings of this review
further support this hypothesis, with increases in ROM,56 57
FL,54 55 59 or both58 evident after eccentric training. The fact
that changes in both ROM60 and FL54 appear to be closely
related to changes in the muscle length-tension curve further
support this hypothesis.
Clinical implications
The magnitude of increase in flexibility after eccentric training
appears to be clinically relevant, and in line with the increases
observed after static stretching. For example, a recent review64
demonstrated mean changes of between +6°and +13° in passive
knee extension (PKE) ROM following static hamstring stretch-
ing, in line with the gains in PKE ROM reported after eccen-
tric hamstring training in this review.57 58 Considering ROM
deficits after hamstring injury are typically less than this,29 36
these increases appear to be clinically relevant, notwithstand-
ing the fact that all studies in this review involved painfree
participants. Similarly, the increase in dorsiflexion ROM (mean
change =+6°) reported by Mahieu et al56 is relatively large, and
at least matches the increases reported after static stretching.65
It is harder to interpret the clinical relevance of the increases
in FL seen after eccentric training, other than to note that FL
was significantly increased in each muscle group studied
to varying degrees. While it is likely that both measures of
flexibility (ROM and FL) correlate strongly, this has not
yet been clearly established, and the pennation angle of mus-
cle fibres may influence the relationship. Nevertheless, the
one study which examined both ROM and FL58 demonstrated
clear improvements in both FL and ROM after eccentric
training.
The exact timeframe for improving flexibility with eccen-
tric training is unclear, although sarcomerogenesis is thought
to occur within 10 days of starting eccentric training.63 In this
review, eccentric training as short as 6 weeks resulted in signif-
icant increases in flexibility.56 57 It is unclear if these increases
in flexibility are maintained after ceasing eccentric training,
although it is likely that some ongoing eccentric training
would be needed, similar to gains in flexibility achieved with
static stretching.33 35 66
It is not possible to conclusively establish how the gains
in flexibility observed after eccentric training compare with
those reported for static stretching. The only study in this
review which compared eccentric training and a static stretch-
ing programme observed no significant difference between
them, with both groups demonstrating large, clinically mean-
ingful increases in ROM.57 Given the additional benefits of
eccentric training in the development of power and injury
prevention,67 68 this questions the benefit of additional static
stretching. However, the increases in ROM after eccentric
training reported in the two studies of the hamstrings are
quite different.57 58 When the actual exercise programmes are
analysed, the eccentric training used by Nelson and Bandy57
was not related to maximal baseline strength, and appears
to be of relatively low load. Despite this, they report a larger
increase in ROM (12.79°) than reported by Potier et al58 (6.9°)
after longer duration, higher load eccentric training. Since the
eccentric training used by Nelson and Bandy57 incorporated
a static hold at end range, their ‘eccentric’ training could be
considered a mix of traditional eccentric training and static
stretching. Therefore, the improvements in flexibility after
more typical eccentric training in the other five studies may
not be as large as those obtained by static stretching. No
other study in this review analysed both ROM and FL. Nelson
and Bandy57 did not analyse injury rate or changes in torque
profile, such that it is not possible to determine if their pro-
gramme improved these other parameters as effectively as tra-
ditional eccentric training. There is considerable evidence that
eccentric training is associated with improvements in peak
torque,67 performance,67 muscle length-tension curves63 and
reduced pain and disability.69–72 As a result, even in the event
that eccentric training is not as effective as static stretching in
increasing flexibility, these other advantages of eccentric train-
ing over static stretching suggest an eccentric component to
training is very important.
The two studies to compare eccentric training with other
exercise interventions based on strengthening reported dif-
ferent findings, despite examining the same muscle (Vastus
Lateralis) and using the same outcome measure (FL). Both
studies reported that eccentric training increased FL. However,
while Reeves et al59 reported a greater increase in FL after
eccentric training, Blazevich et al54 observed no significant
difference between the two training groups, with a trend for
greater increases in FL among the concentric training group.
While the population in the Reeves et al study59 was much
older, which may influence muscular responses to eccentric
training,73 the results are very consistent with other studies in
this review. The effectiveness of the eccentric training stimu-
lus used by Blazevich et al54 is unclear. Typically, exercise gains
are magnified in the exercise mode which is trained, such that
concentric training increases concentric strength more than
eccentric training and vice-versa.59 74 In contrast, Blazevich
et al54 reported that while the concentric training group dem-
onstrated greater gains in concentric torque than the eccentric
training group, there were no between-group differences in
eccentric torque afterwards. This suggests that the eccentric
training may have been suboptimal, despite being designed
relative to one repetition maximum (1RM) ability. Another
concern relates to the baseline between-group differences in
FL,54 which may also explain why FL continued to increase
towards the values of the control group during the detraining
period. Furthermore, nearly all of the increase in FL occurred
in the first 5 weeks of the 10-week training programme, before
a further slight increase in FL after training ceased. This data
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for FL contrasts with data for concentric and eccentric torque
in the same subjects, which showed predictable, incremental
increases over the 10-week programme, with some rever-
sal after training ceased, in line with data from other stud-
ies. Blazevich et al54 proposed that the lack of superiority for
eccentric training suggests that the ROM through which the
muscle is exercised may be more critical than the mode of
exercise, which is consistent with the trend for greater fascicle
strain observed among their concentric training group. The
fact that muscle damage, and the subsequent adaptation, is
strongly linked to the length of the muscle while being exer-
cised supports this proposal.60 75 76 Furthermore, the changes
in FL reported were strongly related to changes in the torque-
angle relationship. However, considering the findings outlined
above in this study which are at odds with other studies, rep-
lication in other studies is required to support the contention
that concentric training is as effective a stimulus for increasing
FL as eccentric training.
LIMITATIONS AND RECOMMENDATIONS
Despite promising results, several limitations must be
acknowledged. Since all included studies involved only
uninjured participants, care must be taken when extrapolat-
ing the findings to people with lower limb injury. Eccentric
training is associated with significant postexercise sore-
ness77 and poor compliance,77 and these issues may be even
greater in injured participants if addition of eccentric load is
not managed carefully. However, since injured athletes are
more likely to display deficits in flexibility,29 there may be
greater scope for improving flexibility. As mentioned earlier,
the term ‘flexibility’ and what tissue properties this actually
reflects, is debatable. The authors who rated study quality
were not specifically trained in the use of the PEDro scale,
which could affect the reliability of the scoring.50 In contrast
to the approach typically taken in PEDro rating, we con-
tacted the study authors if further information was required,
although the authors of one study57 failed to reply with the
requested clarifying information.
Whether increases in flexibility after eccentric training
reduce the need for static stretching requires clarification, as
while the results of one study57 suggest this, their eccentric
training protocol contained a static stretch-type component.
Similarly, it is unclear if concentric training done at a suf-
ficiently high load, either through a large ROM or in a length-
ened position, is as effective as eccentric training since the
two studies54 59 comparing concentric and eccentric training
report contrasting findings. Therefore, further research is
needed to extrapolate which exercise parameters, including
mode, intensity and the ROM used, have the greatest influ-
ence on flexibility. Ideally, these studies would also evaluate
other parameters of muscle function including peak torque
and the muscle length-tension curve. Furthermore, while
eccentric training may be a useful component in the man-
agement of several lower limb disorders,69–72 the precise
eccentric training programme which is the most effective at
increasing lower limb flexibility, or indeed improving perfor-
mance and/or reducing injury risk, is debatable. For example,
despite considerable differences between the eccentric train-
ing programmes, all appear to have significantly increased
lower limb flexibility. Future studies will hopefully be able
to address the main limitations identified among the stud-
ies included in this review. Specifically, this would include
ensuring baseline comparability between groups, blinding
of the outcome assessor, using more accurate EFOV-US or
similar to measure FL, and cross-checking the effectiveness
of the training programmes used by also analysing related
measures such as peak torque, torque-angle relationships and
injury rate.
CONCLUSION
Based on six high-quality studies in different muscle groups,
this systematic review demonstrated consistent evidence that
eccentric training is an effective method of increasing lower
limb flexibility, measured using either joint ROM or muscle
FL in uninjured participants. Combined with evidence that
eccentric training is also associated with benefits including
reductions in pain, disability and injury recurrence, as well as
alterations in peak torque, muscle length-tension curves and
athletic performance, eccentric training is an important part
of lower limb rehabilitation. It remains unclear if the improve-
ments in flexibility with eccentric training reduce the need
for static stretching to increase flexibility, and whether the
improvements in flexibility are similar with other exercise
interventions.
Contributors KOS and SMA were involved in conception and design. KOS and NDB
independently reviewed the literature. KOS/SMA extracted the study data. SMA and
NDB were involved in rating the literature, with KOS acting to mediate disagreements
in ratings. All authors were involved in data analysis and interpretation, as well as
preparing the manuscript for publication.
Acknowledgements The first author (KOS) is currently on a research fellowship
funded by the Health Research Board of Ireland.
Funding One author (KOS) is supported by a Health Research Board of Ireland
research fellowship.
Competing interests None.
Provenance and peer review Not commissioned; externally peer reviewed.
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What is already known on this topic
▶ Flexibility is often reduced in athletes with lower limb
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▶ Static stretching increases flexibility, but has little impact
on injury risk or recurrence.
▶ Eccentric training has been shown in animal models to be
capable of increasing muscle fascicle length, suggesting it
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What this study adds
▶ Eccentric training is an effective means of improving lower
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▶ This effect is seen in all lower limb muscle groups studied,
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▶ This review has highlighted the need to clarify the effects
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Review

doi: 10.1136/bjsports-2011-090835
2012
2012 46: 838-845 originally published online April 20,Br J Sports Med
Kieran O'Sullivan, Sean McAuliffe and Neasa DeBurca
limb flexibility: a systematic review
The effects of eccentric training on lower
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