Kay and Blazevich systemati- cally examined research that showed the effects of static stretching on mus- cle strength and other performance measures by separating the studies into total stretch durations of ,30 seconds, 30 to 45 seconds, 1 to 2 minutes, or .2 minutes. Some practical and tech- nical considerations may be helpful in considering their conclusion that static stretching only impairs muscle function with longer stretches.

1. SPORT MEDICINE JOURNAL CLUB
Journal Club Editor: Lawrence Hart, MBBCh, MSc, FRCPC
Editorial Associate: Ann Lotter, BA
Journal Club highlights recent studies in sport medicine that meet criteria for
methodological rigor and clinical relevance. Selected articles are formatted as
structured abstracts and published with accompanying expert commentaries.
Sponsorship for the Journal Club is provided by an unrestricted educational grant
from Genzyme Canada.
Does Static Stretching
Reduce Maximal Muscle
Performance? A Review
Kay AD, Blazevich AJ. Effect of
acute static stretch on maximal muscle
performance: a systematic review. Med
Sci Sports Exerc. 2012;44:154–164.
Objective: To examine the acute effects
of static stretching and its duration on
maximal muscular performance.
Data Sources: PRISMA guidelines for
reviews were followed. MetaLib was used
to search 4 databases (MEDLINE, Scien-
ceDirect, SPORTDiscus, and Zetocup) to
February 2011, for article titles containing
words including static and acute stretch
(exploded), and its effects on force,
power, and speed. Further searches were
conducted on the first authors and refer-
ence lists of relevant articles.
Study Selection: Inclusion criteria were
original peer-reviewed studies evaluating
a stretching intervention, in humans, on
maximal voluntary muscular performance
in strength-, power-, and speed-dependent
tasks. Studies were required to compare
$2 interventions or prestretch and post-
stretch data. One reviewer excluded
articles by title and then abstract, which
were then verified by a second reviewer.
The remaining full-text articles were
assessed by 2 reviewers, and consensus
on exclusions was reached. Study meth-
ods were evaluated on the 11-point
PEDro scale by 2 reviewers. From 4559
titles identified, 123 full-text articles were
screened and 106 were included.
Data Extraction: The extracted data
included stretch duration (,30 seconds,
30-45 seconds, 1-2 minutes, and
.2 minutes), muscle group stretched,
and maximal muscular performance
recorded and its relation to the stretching
intervention. One analysis included all
studies, and the second included only
studies with appropriate control or reli-
ability statistics. Because the interventions
and outcome measures were heteroge-
neous, the authors provided pooled sum-
mary effects in subgroups categorized by
duration of stretches.
Main Results: Examining the 149 find-
ings within the 106 articles, 44% showed
significant reductions in strength-, power-,
and speed-dependent tasks after acute
stretching (pooled estimate of reductions,
23.7% 6 4.9%). Among the 104 findings
in the 74 studies with appropriate controls,
50% showed significant reductions in per-
formance (pooled estimate of reductions,
24.5% 6 5.2%). Ten studies examined
the effects of stretches of ,30 seconds
duration on tests of 20-m sprint time, ver-
tical jump, medicine-ball throw; isomet-
ric hand and knee strength, jump
distance, and peak cycling power. Over-
all, ,30 seconds of stretching resulted in
a pooled estimate of 21.1% 6 1.8%
reduction. Fifteen studies examined the
effects of stretches of 30-seconds to 45-
seconds duration on tests of vertical jump
height, 10-m or 30-m sprint time, throw-
ing velocity, bench press, overhead
throws, or leg extension power. Overall,
30 to 45 seconds of stretching resulted in
a pooled estimate of 20.6% 6 3.1%
reduction in speed-dependent or power-
dependent tasks. Eleven studies exam-
ined the effects of 30 to 45 seconds of
stretching on handgrip strength, concen-
tric knee flexor muscular voluntary con-
traction (MVC), isometric and concentric
knee extensor strength, concentric plantar
flexor MVC. chest press strength, and
isometric knee flexor MVC. The pooled
estimate of the effect of 30-second to
45-second stretches on strength was a
reduction of 24.2% 6 2.7%. When
stretch durations were .60 seconds, the
mean reduction across tests of perfor-
mance was 24.2% 6 5.0%. Study qual-
ity was moderate (range, 3–7/11 points;
mean, 5.4) with infrequent blinding; 11
studies had no control group or reliability
analyses and 21 studies used the control
condition inappropriately.
Conclusions: Short durations of acute
static stretch did not result in a meaning-
ful reduction in muscular performance.
Stretches of 30 to 45 seconds may reduce
strength but not power, and stretches
longer than 60 seconds reduced maxi-
mal performance on strength-, power-,
and speed-dependent tasks.
COMMENTARY
Kay and Blazevich systemati-
cally examined research that showed
the effects of static stretching on mus-
cle strength and other performance
measures by separating the studies into
total stretch durations of ,30 seconds,
30 to 45 seconds, 1 to 2 minutes, or
.2 minutes. Some practical and tech-
nical considerations may be helpful in
considering their conclusion that static
stretching only impairs muscle function
with longer stretches.
Technically, pooled effects are pro-
vided in meta-analyses when the original
studies lack statistical power to detect
small but clinically meaningful effects.
Therefore, readers should focus on the
pooled results and ignore results that are
presented in a form such as “44% of stud-
ies showed significant effects” (as the
results were reported in this article)
because that just restates that most studies
were underpowered.
The authors were surprised to find
only 10 studies investigating total stretch
durations of ,30 seconds. We were sur-
prised that there were any studies exam-
ining the effect of ,30 seconds of
Source of funding for the original study: No
external funding.
Correspondence about the original article: Anthony
D. Kay, PhD, Sport, Exercise & Life Sciences,
The University of Northampton, Boughton
Green Rd, Northampton NN2 7AL, United
Kingdom (tony.kay@northampton.ac.uk).
450 | www.cjsportmed.com Clin J Sport Med Volume 22, Number 5, September 2012

2. stretching. First, the only references cited
that described stretching for ,30 seconds
as a common practice are a textbook and
a study on rabbits. Second, stretches of
such a short duration do not impart mean-
ingful changes in the mechanical proper-
ties of muscle, and the effects are not
sustained beyond a few minutes. For
example, Ryan et al1
described the dose
response of the plantar flexors with
respect to retention of the stretch-induced
decreases in passive resistance to stretch.
The effects of a total stretch duration of
2 minutes lasted ,10 minutes, whereas
the effects of stretch durations of
4 minutes lasted .10 minutes. The
effect of a stretch duration of 8 minutes
lasted at least 30 minutes.
Kay and Blazevich concluded,
“Static muscle stretches totaling ,45 s
can be used in preexercise routines
without risk of significant decreases in
strength-, power-, or speed-dependent
task performances.” If there is no clin-
ically meaningful change in range of
motion, our question is, “Why stretch?”
Would one prescribe a very low dose of
a drug to avoid known side effects with-
out considering the dose required to have
the desired effects?
The larger clinically meaningful
question is whether a stretching interven-
tion, sufficient to result in a prolonged
decrease in passive muscle stiffness, con-
fers any benefit with respect to injury
prevention (or other desirable effects) that
might outweigh the potential impairments
in muscle function shown in this review.
One of us (M.M.) believes yes, and the
other (I.S.) believes no; we both believe
that researchers and authors should focus
on relevant clinical questions that have
not yet been adequately addressed. For
injury prevention, we believe this
includes whether injury risk is decreased
with regular stretching and/or warm-up
and whether these effects are dependent
on the type of activity (eg, high vs low
intensity or extent of range of motion).
Ian Shrier, MD, PhD*
Malachy McHugh, PhD†
*Centre for Clinical Epidemiology
Jewish General Hospital
Montreal, Quebec, Canada
†Nicholas Institute of Sports Medicine
and Athletic Trauma
Lenox Hill Hospital
New York, New York
REFERENCE
1. Ryan ED, Beck TW, Herda TJ, et al. The time
course of musculotendinous stiffness responses
following different durations of passive stretching.
J Orthop Sports Phys Ther. 2008;38:632–639.
Two-Year Follow-up of
Injection With Platelet-Rich
Plasma Versus
Corticosteroid for Lateral
Epicondylitis
Peerbooms JC, Sluimer J, Bruijn DJ,
Gosens T. Positive effect of an
autologous platelet concentrate in
lateral epicondylitis in a double-blind
randomized controlled trial: platelet-
rich plasma versus corticosteroid
injection with a 1-year follow-up.
Am J Sports Med. 2010;38:255–262.
Gosens T, Peerbooms JC, van Laar W,
den Oudsten BL. Ongoing positive
effect of platelet-rich plasma versus
corticosteroid injection in lateral
epicondylitis: a double-blind
randomized controlled trial with
2-year follow-up. Am J Sports Med.
2011;39:1200–1208.
Objective: To compare the 2-year effec-
tiveness of concentrated autologous
platelet-rich plasma (PRP) injection with
corticosteroid injection in patients with
chronic lateral epicondylitis.
Design: Randomized, controlled, double-
blinded trial, with participants followed
for 2 years. Analysis was primarily by
intention to treat. Bonferroni corrections
were made for multiple comparisons.
Setting: Two hospitals in the Netherlands,
with recruitment between May 2006 and
January 2008.
Participants: Consecutive patients sched-
uled for injection therapy were screened.
Inclusion criteria were lateral epicondylitis
(pain over the lateral epicondyle on palpa-
tion and during resisted wrist extension)
for $6 months and pain of $50/100 on
a visual analog scale (VAS). Exclusion
criteria were age ,18 years; history of
carpal tunnel syndrome or cervical radicul-
opathy; systemic disorders; and treatment
for the condition with surgery or cortico-
steroid injection in the previous 6 months.
The patients had all failed previous treat-
ments (mean age, 47 years; 52% women;
65% dominant side involvement).
Intervention: For the 51 patients ran-
domized to PRP, the platelets were
centrifuged from a 27-mL blood sample
with the Recover System (Biomet Bio-
logics, Warsaw, Indiana), producing
about 3 mL of PRP. The buffered PRP
was then injected into the area of maxi-
mum tenderness and peppered into
the common extensor tendon. The 49
patients randomized to corticosteroid
injection (kenacort 40 mg/mL triamcin-
olone acetonide) were treated by the
same protocol. Bupivacaine hydrochlo-
ride 0.5% with epinephrine was added to
both types of injection. Patients were to
rest for 24 hours and could take acet-
aminophen for pain. After 4 weeks of
supervised progressive exercises, the
patient could return to normal sporting
activities as tolerated.
Main Outcome Measures: The main
outcome measures were differences in suc-
cessful outcomes (.25% reduction in pain
VAS scores or in disabilities of the arm,
shoulder, and hand [DASH] scores)
between the groups at the 1- and 2-year
follow-ups. Patients who needed a reinter-
vention were scored unsuccessful. Eight
patients (8%) were temporarily or perma-
nently lost to follow-up.
Main Results: After 1 year, there was
a greater proportion of successful out-
comes in the PRP group than in the cor-
ticosteroid group by the pain score
criterion (73% vs 49%; P , 0.001)
and by the DASH score criterion (73%
vs 51%; P = 0.005). After 2 years, the
differences in mean improvement in
VAS scores and DASH scores between
the groups continued to favor the PRP
group (P , 0.001), but pain scores had
deteriorated from baseline in 9 patients
in the corticosteroid group and in 2 in
the PRP group (P for difference =
0.017). There was deterioration in
DASH scores in 23 patients in the corti-
costeroid group and in 7 in the PRP
group (P for difference = 0.001). Rein-
terventions during the follow-up were
needed in 20 patients. In the PRP group,
3 patients had surgery and 3 required
a corticosteroid injection. In the cortico-
steroid group, there were 6 surgeries, 1
Source of funding for the original study: partly
sponsored by Biomet, Dordrecht, the Netherlands.
Correspondence about the original articles: Taco
Gosens, MD, PhD, Department of Orthopaedic
Surgery, St. Elisabeth Hospital, Tilburg, the
Netherlands (t.gosens@elisabeth.nl).
Clin J Sport Med Volume 22, Number 5, September 2012 Sport Medicine Journal Club
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