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1
No effect of muscle stretching within a full, dynamic warm-up on
athletic performance
Short title: Stretching during sports warm-up
Authors:
Anthony J. Blazevich1, Nicholas D. Gill2, Thue Kvorning3, Anthony D. Kay4, Alvin M. Goh1,
Bradley Hilton1, Eric J. Drinkwater5, David G. Behm6.
1 School of Medical and Health Sciences and Centre for Exercise and Sports Science
Research, Edith Cowan University, Australia.
2 Faculty of Health, Sport and Human Performance, University of Waikato, Hamilton, New
Zealand
3 Team Danmark, Copenhagen, Denmark
4 School of Health, The University of Northampton, Northampton, United Kingdom
5 School of Exercise & Nutrition Science, Deakin University, Melbourne, Australia
6 School of Human Kinetics and Recreation, Memorial University of Newfoundland, St
John’s, Canada
Corresponding author:
Anthony J. Blazevich, School of Medical and Health Sciences and Centre for Exercise and
Sports Science Research, Edith Cowan University, 270 Joondalup Drive, Joondalup,
Australia 6027 (a.blazevich@ecu.edu.au; Phone: +61 8 6304 5472).
2
ABSTRACT
Purpose: To examine the effects of static and dynamic stretching routines performed as part
of a comprehensive warm-up on flexibility and sprint running, jumping and change of
direction tests in team sport athletes.
Methods: A randomized, controlled, cross-over study design with experimenter blinding was
conducted. On separate days, 20 male team sport athletes completed a comprehensive warm-
up routine. After a low-intensity warm-up a 5-s static stretch (5S), 30-s static stretch (30S;
310-s stretches), 5-repetition (per muscle group) dynamic stretch (DYN) or no stretch (NS)
protocol was completed; stretches were done on 7 lower body and 2 upper body regions. This
was followed by test-specific practice progressing to maximum intensity. A comprehensive
test battery assessing intervention effect expectations as well as flexibility, vertical jump,
sprint running and change of direction outcomes was then completed in a random order.
RESULTS: There were no effects of stretch condition on test performances. Before the
study, 18/20 participants nominated DYN as the most likely to improve performance and
15/20 nominated NS as least likely. Immediately before testing, NS was rated less ‘effective’
(4.0±2.2 on 10-point scale) than 5S, 30S and DYN (5.3-6.4). Nonetheless, these ratings were
not related to test performances.
CONCLUSION: Participants felt they were more likely to perform well when stretching was
performed as part of the warm-up, irrespective of stretch type. However, no effect of muscle
stretching was observed on flexibility and physical function compared to no stretching. Based
on the current evidence, the inclusion of short durations of either static or dynamic stretching
is unlikely to affect sprint running, jumping or change of direction performance when
performed as part of a comprehensive physical preparation routine.
3
Key words: athletic preparation, sprint performance, vertical jump, change of direction,
muscle power, stretch-induced force loss.
4
INTRODUCTION
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It is believed that the completion of a pre-exercise (or pre-sport) physical preparation
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routine is required to augment performance and reduce injury risk (1-3). One component of
3
this routine that has received much scrutiny is the inclusion of static (particularly passive)
4
muscle stretching (3-8). From an injury minimization perspective, studies have typically not
5
confirmed a clear effect of pre-exercise static stretching on all-cause injury risk in sports (9,
6
10), which has resulted in some researchers suggesting a limited role for the practice (6, 7,
7
10) or for the inclusion of dynamic forms of stretching (2). However, other authors conclude
8
that static stretching might specifically provide a small-to-moderate protective effect for
9
muscle-tendon injury risk, especially in running-based sports (e.g. the various football codes
10
and court sports) (3, 4, 8, 9), which attract by far the highest participation (11) and injury (12)
11
rates. By contrast, no detailed studies have examined the effects of dynamic stretching on
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injury risk. Therefore, current scientific evidence favors static over dynamic stretching from
13
an injury prevention perspective, even though the overall benefit may be small-to-moderate
14
and limited to a subset of sports.
15
Nonetheless, several recent reviews have also concluded that static stretching can
16
significantly and negatively impact high-intensity physical performance (4, 5, 13). Several
17
researchers and advocacy groups, including the European College of Sports Sciences (14)
18
and American College of Sports Medicine (15), do not recommend the inclusion of static
19
stretching in pre-exercise routines, or call for its replacement by dynamic forms of muscle
20
stretching (2). Indeed, in some cases the continued use of static stretching by sports
21
participants has been explicitly admonished (16). Nonetheless, the majority of studies
22
examining the effects of pre-exercise muscle stretching have not been designed to assess its
23
effects on sports performance (e.g. see Supplement G in ref. 4). Common threats to external
24
validity in previous studies include (a) total stretching durations being longer than those
25
5
typically performed by athletes (17, 18), (b) the stretching rarely being followed by other
26
important components of a sport-specific warm-up, including high-intensity and movement
27
pattern-specific exercises (1, 19), even though it may mitigate the negative effects of
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stretching (20), (c) participants being only minimally familiarized with the tests (athletes, on
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the other hand, are familiar with their sporting skills), (d) differences existing in the execution
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(movement pattern) of static versus dynamic stretches, and (e) the imposition of non-
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stretching rest periods in control conditions/groups, which would not be performed in sports
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(4). Also, studies have been susceptible to serious threats to internal validity, such as the
33
expectancy effects of knowledgeable participants (21) and lack of experimenter blinding (22).
34
Notwithstanding these threats to validity, the effects of static stretching on dynamic
35
movement performance (e.g. jumping, running, sprint cycling) have been found to be small
36
on average when stretches are performed for <60 s per muscle (weighted average = -1.1%),
37
and the performance benefits of dynamic stretching performance is also surprisingly small
38
(+1.3%)(4). The call for the removal of static stretching and possible replacement with
39
dynamic stretching (16), despite the limited evidence of impact on sports performance,
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creates a dilemma for medical practitioners, physiotherapists and physical trainers who may
41
be asked to provide their opinions on proper sports participation practices.
42
Given the above, the decision to advocate against the static stretching, particularly on
43
the grounds that it might reduce exercise performance, is questionable, especially given that
44
sports participants show a preference to stretch their muscles despite this advocacy (23) and
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there being a potential small-to-moderate musculotendinous injury risk minimization benefit.
46
In the present study, we have attempted to overcome some of the limitations of previous
47
studies to specifically answer the question of whether the inclusion of short- or moderate-
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duration static or dynamic muscle stretching completed as part of a comprehensive pre-
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exercise routine (i.e. warm-up) influences performances in common, high-intensity sporting
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tasks. Based on the available evidence, we hypothesized that the imposition of short or
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moderate durations of static or dynamic stretching would not meaningfully impact high-
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intensity physical performance when performed as part of a comprehensive pre-exercise
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routine.
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METHODS
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Twenty healthy males (age = 21.1 ± 3.1 years; body mass = 73.4 ± 6.8 kg; height = 1.79 ±
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0.70 m) volunteered for the study. Participants were recruited if they were: 18 - 25 years of
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age; without recent injury or illness that would preclude exercise performance; and
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competing in running-based sports or performing at least three running-based exercise
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sessions per week. The study was approved by the Human Research Ethics Committee of
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Edith Cowan University (STREAM11450/11541) and conducted in accordance with the
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Declaration of Helsinki. All participants read and signed an informed consent document.
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Study design
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This study used a randomized, cross-over (repeated measures) design with control condition,
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and was designed to assess the effect of dynamic vs. both shorter- (5 s) and longer- (30 s)
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duration static muscle stretching interventions on performances in tests that mimic common
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sporting tasks. There were three experimental (stretching) conditions and a non-stretching
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control condition (hereafter referred to as ‘pre-testing routines’) performed at the same time
68
of day over four testing sessions separated by a minimum of 72 h and each followed by a
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comprehensive test battery (see Figure 1). The order of conditions and order of tests within
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each condition were randomized between the participants without replication by the
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participants choosing a numbered card randomly from a pack that related to a test and stretch
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condition order. The card was not replaced in order to ensure that some test and stretch
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condition orders could not be allocated more often than others.
74
7
A pre-testing routine was completed before the test battery was administered. The
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pre-testing routine, including any muscle stretching, was monitored by a research coordinator
76
who ensured that procedures (described below) were followed correctly but who could not
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communicate with researchers overseeing the test battery (hereafter referred to as ‘testers’).
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After completion of the pre-testing routine, the coordinators relinquished participant
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responsibility to the testers, who were given no information as to the pre-testing stretch
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condition administered and were naïve to the time required to complete the pre-testing
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routine; this prevented the possibility of guessing the pre-testing routine type since each
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required a different time to complete. Thus, the testers were blinded to the pre-testing routine
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condition.
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Familiarization of muscle stretching and performance tests
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At least one familiarization session was completed by each participant prior to data
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collection to become accustomed with the stretching protocols, learn the correct testing
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procedures, and acquaint themselves with the equipment, laboratory facility and the verbal
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instructions issued by the coordinators and testers for the stretching exercises and tests. A
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video demonstration of each stretch was provided to the participants in order to ensure
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similarity in instruction of the stretches, then each participant received individual feedback to
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correct errors. The participants were then shown how to complete each test and given
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multiple untimed trials to become familiar. The movement patterns of the tests (described
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below) were similar to the movement patterns used by the participants in their sports. An
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additional familiarization session was provided to four participants who declared a lack of
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confidence in the performance of one or more testing protocols.
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Pre-study Participant Outcome Expectations
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8
At the end of the familiarization session, each participant completed an outcome
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expectation survey to determine which pre-exercise routine they believed would prove most
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beneficial to performance. The participants were asked to “List in descending order the
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stretch condition you believe will stimulate the best improvement in your performance
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(dynamic, 5 s static, 30 s static and no stretch)” when compared to the other conditions. They
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therefore nominated in order from 1 to 4 (best to worst) which routine they believed would
103
improve (or reduce) performance the most. Post hoc, these expectations were compared to the
104
outcomes of the testing to determine whether expectation was aligned with outcome.
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Testing Session Design
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Participants were required to wear the same sports shoes and athletic clothing at each
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session, refrain from intensive exercise in the 24-h period before testing, and abstain from
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caffeine or any form of stimulant/depressant 24 h prior to testing. As the participants were
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team sport athletes, other physical training completed by the participants outside of the study
110
was monitored (for type, volume and intensity) by the participants providing a log book
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record of their activities in the 48 h prior to testing as well as a rating of their muscle soreness
112
from 1 to 10 to ensure that significant (>2 units) changes in their performance of, or recovery
113
from, their programs did not occur. If the standard training programs of the participants were
114
not adhered to, the testing session was to be cancelled and completed at least 72 h later,
115
however no instances of this occurred.
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Each session commenced with a short pre-stretching warm-up consisting of a 3-min
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jog at 50% of perceived maximum exertion, then 5-s high knees (to ~90 hip angle) and 5-s
118
heel-to-butt (i.e. knee flexion) drills at 50% of maximum perceived exertion. Heart rate was
119
obtained immediately after the warm-up phase by manual palpation of the carotid artery for
120
post-hoc examination of the repeatability of efforts, i.e. repeatability of the physical
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intensities used (heart rate itself could not be used as a target for intensity because of its slow
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temporal response after exercise commencement).
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Participants then completed one of three experimental (stretching) conditions or
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progressed immediately to the test-specific (i.e. ‘sport-specific’) warm-up (described below);
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note that a rest condition of equal duration to the experimental conditions was not included in
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the no-stretch (control) session as this is not typical sports practice. The four conditions were
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a 5-s of static stretching (5S), 30 s of static stretching (30S; 3 10-s stretches), a 5-repetition
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(per muscle group) dynamic stretch (DYN), and a no-stretch condition (NS) (see Text,
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Supplemental Digital Content 1, detailing the instructions [with photo] for each stretch). The
130
5S, 30S and DYN stretching protocols each consisted of nine stretches that were close
131
replicates (in body position) of each other in order to minimize the effect of stretching
132
movement pattern on test outcomes. The static stretches were held at the point of
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‘discomfort’, and maximal ROM was achieved in the dynamic stretches by ensuring a
134
secondary pulling-motion with each repetition. The order of pre-exercise routines was
135
randomized without replication between participants to minimize order effects.
136
Following the stretches (or after progressing immediately from the low-intensity
137
warm-up in NS) a test-specific (i.e. ‘sport-specific’), higher intensity warm-up was
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completed. This started with a 2-min moderate-intensity jog at 60% of perceived effort, and
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5-s high knees and 5-s heel-to-butt kick drills at 60% of perceived maximum effort. The
140
participants then performed three circuits of the six performance tests, which were organized
141
into three activity groups: 1) running vertical jump, 2) squat jump, countermovement jump
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and drop jump, 3) T agility test, and 4) 20-m sprint run, and the participants completed them
143
in an order identical to that of the following testing session (see below). The intensity of each
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circuit increased from 60% to 80% and then 100% of perceived maximal exertion with a 30-s
145
10
walk recovery between each activity set. This second part of the pre-testing routine took
146
approximately 15 min to complete.
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In order to address the study design limitation relating to the time between completion
148
of the final stretch and the commencement of testing (4), a 7-min passive rest period was
149
imposed between the completion of the pre-testing routine and the start of testing. This was
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done to more closely simulate game- or match-day situations where a short pre-competition
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briefing or an individual-specific sport preparation period is completed before match or
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competition commencement and allowed a better determination of the likely effect of the
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different pre-exercise routines on game- or match-day performance.
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Participants were permitted to consume plain water ad libitum throughout the testing
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sessions, and all sessions were conducted in the biomechanics laboratory at Edith Cowan
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University under similar environmental conditions. The test battery was completed in a
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circuit at specified testing stations: 1) sit-and-reach flexibility test, 2) running vertical jump
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test, 3) squat (SJ), countermovement (CMJ) and drop jump (DJ; from 40-cm height) tests, 4)
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T agility test, 5) 20-m sprint running test. The order of tests was randomized between
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participants without replication and then repeated at each session; however, the sit-and-reach
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test was always completed first in order to determine the effect of the pre-testing routine on
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flexibility (maximum range of motion) without the potential influence of other tests. The
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performance of the sit-and-reach test was not expected to influence performances in
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subsequent tests because of the short-duration of the stretch procedure. For the testing, 4 min
165
was allocated to each test station so that constant test timing was achieved regardless of the
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order of tests. An audio signal prompted the commencement of each test.
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Post-warm-up Participant Outcome Expectations
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11
To address issues around expectancy bias (21), during the 7-min rest period prior to
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testing in each session the participants also provided a rating score ranging from 1 to 10 for
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“how effective you believe the warm-up will be on your performance”, where 1 = no effect/
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possibly harmful to performance, 2 = very small improvement to performance, 5 = noticeable
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improvement in performance, and 10 = performance will improve dramatically. Obtaining
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this information immediately after completion of each pre-testing routine was expected to
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yield different results to the outcome expectation survey completed in the study
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familiarization session, and thus to allow a better analysis of whether participant expectancy
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might influence study results. Equal ratings between conditions were allowed.
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Testing Procedures
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Sit-and-reach flexibility
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The sit-and-reach test was conducted using the Flex-Tester apparatus (Novel Products
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Inc., USA). A double-leg protocol was used as prescribed by the Canadian Society for
182
Exercise Physiology (24). Each participant was instructed to sit bare-footed with knees in
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maximal extension and with both feet together and flat against the device. The participant
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then exhaled and stretched forward with palms overlapping and fingertips aligned, holding
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the furthest end point for 2 s. The score was recorded to the nearest 0.1 cm and repeated after
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a 30-s rest, with the greatest touch distance used for analysis.
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3-m running vertical jump
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A jump-and-reach system (Vertec, Swift Performance Equipment, Australia) was
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used for the running vertical jump to directly measure jump height based on the difference
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between reach height and the jump height obtained. Reach height was obtained before each
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test with the participant standing in a static position underneath the Vertec device and
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reaching as high as possible with the arm touching their ear but with shoulders remaining
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parallel to the floor. The fingers displaced vanes (each 1 cm apart) within touching distance,
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and the maximum reach height was obtained. For jump testing, each participant’s take-off
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foot was pre-determined during the familiarization session, and a self-selected starting
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position was assumed 3 m from the device, which was kept consistent across all testing
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sessions. At their own volition, the participant executed a running, single-leg jump to displace
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the vanes with the opposite hand. The maximum jump-and-reach height was recorded as the
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number below the score reflected on the Vertec device, and the true jump height was then
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calculated as the difference between the maximum jump-and-reach height and the standing
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reach height. Each participant was given a maximum of five attempts; however the test was
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stopped when the participant failed to further improve jump scores on two successive
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attempts. A 30-s passive rest was imposed between each jump, and the best (i.e. final) true
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jump height score was used for analysis.
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Squat (SJ), countermovement (CMJ) and drop (DJ) jump
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A piezoelectric force platform (987B, Kistler Instrumente, Switzerland) was used to
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measure vertical jump height using the flight time method (height = ½ g (t/2)2, where g =
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9.81 m·s-2 and t = time in air). The analog signal from the force platform was converted to a
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digital signal using Bioware software (Kistler Instrumente, Switzerland) sampling at 1000
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Hz. Flight time was identified as the period between take-off and contact after flight and this
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was obtained in each jump via analysis of the force-time curve. A 15-s passive recovery was
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imposed between each jump, which allowed the tester to record vertical jump height and to
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reset the systems for recording of the next trial. Two attempts were allowed for each jump
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type, however a third trial was completed if jump heights varied >5%. The best score was
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used for analysis.
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13
SJ trials were performed from a squatted position with heels in contact with the
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platform and with a self-selected knee angle (~75°). Each participant’s hands were kept on
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their hips throughout the jump and a countermovement was not allowed. The participant was
219
instructed to hold the squat position for at least 2 s before jumping. Visual observation of
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both jumping technique and the force-time trace was made to ensure that there was no
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countermovement in the jump. Trials were repeated if a countermovement could be visually
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observed by the tester. CMJ trials were performed from a vertical standing position with
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hands on hips and knees about shoulder-width apart. The participants then executed a two-
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footed vertical jump immediately following an eccentric countermovement to a self-selected
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depth (although the thighs could not be lower than parallel to the floor (19)). In the DJ, the
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participant stepped horizontally off a 40-cm box onto the force platform and then
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immediately jumped vertically. The instruction was given to “jump with minimal ground
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contact time upon landing” and then to jump as high as possible. The starting position on the
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top of the box was identical to the CMJ start position.
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T agility test
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For the T agility (change of direction) test, participants started at their own volition
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from a standing start 0.4 m behind a start line, sprinted forwards to touch the base of a cone
233
located 10 m in front of them, shuffled 5 m to the left to touch a cone, shuffled 10 m to the
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right to touch a cone, shuffled 5 m left to touch the center cone once again, and then ran
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backwards past the start line. A dual-beam photocell timing gate (Swift Performance,
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Australia) positioned at the start line was triggered when the participant broke the light beam
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after the start and was stopped when the participant completed the course. Each athlete faced
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forwards at all times and could not cross their feet while shuffling. The participants were
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instructed to use a standing sprint start and were not allowed to build momentum by rocking
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back and forth at the start line. They performed the test twice with a 30-s passive rest between
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and the fastest time was used for analysis.
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20-m sprint run
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The 20-m sprint test was performed on an indoor synthetic 60-m sprint track. The
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participants used the same starting position as for the T agility test, and ran with maximum
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speed to a cone placed 1.5 m past a 20-m mark. This cone was included to prevent the
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participants from decelerating before crossing the 20-m mark. The tester counted down and
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then instructed the participants to sprint at their own volition, and timing gates placed at 0
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and 20 m measured running time. Two attempts were given with a 30-s walk-back recovery
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between attempts, and the fastest time was used for analysis.
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Statistical Analysis
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Using IBM SPSS statistical software (version 22; IBM, New York), repeated
252
measures multivariate analyses of variance (MANOVAs) were performed to compare test
253
performances between conditions (5S, 30S, DYN, and NS), whilst a repeated measures
254
ANOVA was used to compare the performances between conditions specifically for sit-and-
255
reach scores. The alpha level was set at 0.05, and significant main or interaction effects were
256
examined in further detail using ANOVA and univariate tests, as appropriate. Additionally,
257
magnitude-based inference tests were performed and the precision of estimation was
258
calculated. Qualitative descriptors of standardized effects used the criteria: trivial < 0.2, small
259
0.2-0.6, moderate 0.6-1.2, large >1.2. Effects where the 95% confidence limits substantially
260
overlapped the thresholds for small positive and negative effects (i.e. exceeding 0.2 of the SD
261
on both sides of zero) were defined as unclear. Clear small or larger effect sizes (i.e., those
262
with > 75% likelihood of being > 0.20), as calculated using the spread sheet developed by
263
Hopkins (25), were defined as definitive. Precision of estimates was indicated with 95%
264
15
confidence limits, which defined the range representing the uncertainty in the true value of
265
the (unknown) population mean (26). To better assess the similarity (or lack) of performances
266
between trials, both Pearson’s (r) and intra-class (ICC) correlations were calculated; no
267
corrections were required for outliers or non-uniformity of scatter. ICC values less < 0.5, 0.5
268
- 0.75, 0.75 - 0.9, and > 0.90 were considered indicative of poor, moderate, good, and
269
excellent reliability, respectively. 90% confidence intervals were also computed for ICC
270
values, but this is not possible for r values calculated from multiple repeated measurements.
271
Finally, the Bland-Altman method for calculating correlation coefficients for repeated
272
measurements (within subjects) was used to determine if higher participant expectation
273
scores were correlated with better performances (27).
274
RESULTS
275
Participant Bias
276
When assessed during the familiarization session (i.e. before the commencement of
277
the data collection period), 18 of the 20 participants nominated DYN as the most likely
278
beneficial pre-testing routine (i.e. they ranked it 1st out of the four conditions) whilst two
279
participants nominated 30S as the most likely beneficial. Additionally, 15 of the 20
280
participants nominated NS to be least likely beneficial (i.e. ranked it 4th out of the four
281
conditions) whilst five participants nominated 30S. The commonest ranking order among the
282
participants was DYN > 5S > 30S > NS. Thus, there was a clear a priori bias within the
283
participant group.
284
When asked upon completion of each pre-testing routine to rate (on a scale of 1 – 10)
285
how effective they believed the routine would be for their performance, NS was rated
286
consistently worst (4.0 ± 2.2), and 5S (5.7 ± 1.9) and DYN (6.4 ± 1.6) were rated statistically
287
higher (p<0.05) than NS; a tendency towards a greater rating for 30S (5.3 ± 2.3) did not reach
288
16
statistical significance. No statistical differences were observed between the three stretching
289
conditions and, using magnitude-based inference, it was found that all three stretch conditions
290
were rated definitively (>75%) higher by participants than the no-stretch condition, with
291
97%, 87% and 100% likelihoods of 5S, 30S and DYN, respectively, being perceived of
292
greater benefit than NS. Nonetheless, correlation coefficients computed for repeated
293
measurements (within subjects) were small, ranging -0.16 – 0.21 and with explained variance
294
(R2) ranging 0.1 – 4.5%, indicating a lack of relationship between ratings of perceived benefit
295
and performance outcomes.
296
Jumping, running, change of direction and flexibility
297
No statistical differences were detected between conditions for the 3-m running
298
vertical jump, SJ, CMJ, or DJ tests (p = 0.471 for condition time interaction; see Figure 2),
299
indicating a lack of effect of pre-testing routine on performance, and no statistical difference
300
was detected between sessions 1 – 4, indicating a lack of order effect (i.e. effect of session
301
number irrespective of condition). All three stretch conditions were definitively (>75%
302
likelihood) found to elicit trivial effects on running vertical jump (95%, 92% and 86%
303
likelihood of trivial effect for 5S, 30S and DYN, respectively) and CMJ (97%, 89% and 95%
304
likelihood of trivial effect) performances when compared to NS. The effects on SJ (44%,
305
65% and 74% likelihood of trivial effect) and DJ scores (72%, 38% and 50% likelihood of
306
trivial effect) were less clear in SJ (56%, 32%, and 22% likelihood of higher jump in 5S, 30S
307
and DYN, respectively) and DJ (7%, 62% and 50% likelihood of lower jump).
308
No statistical differences were detected between conditions for the 20-m sprint run (p
309
= 0.354 for condition time interaction) or T agility test (p = 0.996; see Figure 3), indicating
310
a lack of effect of pre-testing routine on performances. Furthermore, no differences were
311
detected between sessions 1 – 4, indicating a lack of order effect. All three stretch conditions
312
17
were found to definitively (>75%) elicit trivial effects on 20-m sprint run time (88%, 86%
313
and 91% likelihoods of trivial effect for 5S, 30S and DYN, respectively) and T agility time
314
(84%, 93% and 75% likelihood of trivial effect) when compared to NS.
315
No statistical differences were detected for sit-and-reach scores (p = 0.076 for
316
condition time interaction) between 5S (27.1 8.9 cm), 30S (27.8 8.8 cm), DYN (28.4
317
8.36 cm) and NS (28.9 9.2 cm). A definitively trivial effect of condition was observed for
318
DYN (98% likelihood of trivial effect) when compared to NS, but 45% and 31% likelihoods
319
of trivial effects for 5S and 30S, with 55% and 68% likelihoods of lower sit-and-reach scores,
320
were observed in these conditions when compared to NS.
321
Reliability Analysis
322
Both Pearson’s (r) and intra-class (ICC [90%CI]) correlation analyses completed on
323
the test data revealed a high between-session repeatability of performances for SJ (r = 0.87;
324
ICC = 0.84[0.73-0.92]), CMJ (r = 0.90; ICC = 0.92[0.83-0.95]), DJ (r = 0.88; ICC =
325
0.87[0.78-0.93]), 3-step jump (r = 0.92; ICC = 0.92[0.85-0.96]) and 20-m sprint running (r =
326
0.93; ICC = 0.92[0.87-0.96]) tests despite the different stretching interventions being
327
imposed. Reliability estimates were slightly lower, but still moderate, for the T agility test (r
328
= 0.70; ICC = 0.71[0.54-0.84]).
329
Pre-testing routine intensities
330
Heart rates measured immediately upon completion of the low-intensity jogging bouts
331
during the pre-testing routine were not different between conditions. The heart rates after the
332
3-min jog at 50% of perceived maximum exertion (before the stretching) and after the 2-min
333
jog at 60% of perceived exertion (after the stretching) were 125 4 bpm and 139 19 bpm,
334
respectively.
335
18
DISCUSSION
336
The main finding of the present study was that the inclusion of a period of either static
337
(passive) or dynamic stretching within a comprehensive pre-exercise physical preparation
338
routine (i.e. a ‘warm-up’) did not detectibly influence flexibility or maximal vertical jump,
339
sprint running acceleration or change of direction (T agility) test performances compared to a
340
no-stretching control condition. In fact, inter-session test reliability coefficients were good to
341
excellent for 3-m running, squat, countermovement and drop jump (ICC = 0.87 – 0.92) and
342
20-m sprint running (ICC = 0.93) tests, and moderate (ICC = 0.71) for the T agility test,
343
despite the stretching component of the warm-up differing between sessions. Based on these
344
results, athletic individuals who are well familiarized with the physical performance tasks and
345
who complete a properly-structured warm-up period (e.g. ref. 1) may not experience
346
alterations in performance when short- or moderate-duration muscle stretching interventions
347
are included within the warm-up period. The participants showed a clear bias in their beliefs
348
with regard to the effects of stretching in the warm-up routine, with 90% (18/20) of
349
participants expecting performances to be better after inclusion of a dynamic stretching
350
period when asked to “list in descending order the stretch condition you believe will stimulate
351
the best improvement in your performance”. This might result from participants having
352
knowledge of sports science research, either as a university-level student or as an interested
353
reader. It may also have influenced perceptions of preparedness for high-intensity physical
354
activity after the warm-up period, with participants scoring 6.4 1.6 on a 1 – 10 scale after a
355
warm-up incorporating dynamic stretching when asked to rate “how effective you believe the
356
warm-up will be on your performance” (1 = no effect/possibly harmful, 5 = noticeable
357
improvement in performance, 10 = performance will improve dramatically). Nonetheless, no
358
statistical difference was observed between ratings after any stretching condition, and warm-
359
up routines incorporating 5-s static, 30-s static or dynamic stretching were 97%, 87% and
360
19
100% were likely to be perceived of greater benefit than when no stretching was allowed.
361
Furthermore, correlation coefficients (computed for repeated measurements within subjects;
362
(27)) were small (R2 = 0.1 – 4.5%), indicating a lack of relationship. These data differ
363
slightly from those presented recently by Janes et al. (21), where improvements in knee
364
extensor, although not knee flexor, strength were observed after static stretching in
365
participants who were told that the stretching should improve performance (i.e. there was an
366
expectancy effect). We conclude that the participants felt as though the warm-up period
367
prepared them better for high-intensity exercise performance when stretching was performed,
368
irrespective of the type of stretching, than when no stretching was allowed. Whilst such
369
beliefs did not meaningfully influence test performances in the present study, participants
370
might theoretically perform better in a competitive sport environment when their perceptions
371
of preparedness are higher, and this might be examined in future studies.
372
The current results, that static (passive) muscle stretching did not compromise, and
373
dynamic stretching did not enhance, high-intensity exercise performance (Figures 2 and 3),
374
appear to contradict the consensus findings of previous research. However, several previous
375
studies have shown a lack of effect of muscle stretching on high-intensity exercise
376
performance when comprehensive warm-ups were performed. Taylor et al. (20) found no
377
differences in vertical jump and 20-m sprint performances after a progressive, skill-based
378
warm-up in high-level netball athletes despite performance decrements being observed
379
immediately after a preceding static stretch period (VJ = -4.2% and 20-m sprint = -1.4%). In
380
professional (English Premier League) soccer players, Little and Williams (28) observed no
381
differences in 20-m sprint time or CMJ height after static or dynamic stretching, although a
382
statistically faster zig-zag agility (change of direction) performance after dynamic stretching,
383
when the stretching was performed as part of a full warm-up session (notably, 20-m sprint
384
performance was improved in both static and dynamic stretch conditions). Also, Samson et
385
20
al. (19) found no differences in rapid kicking, CMJ or 20-m sprint test performances between
386
static and dynamic stretch conditions when performed alongside general and specific warm-
387
up activities in recreational and competitive athletes. Such outcomes are not always observed
388
when a warm-up opportunity is provided, however. Static stretching has resulted in
389
decrements in high-intensity exercise performances when the sport-specific warm-ups were
390
brief (e.g. 2 × 50-m sprints (29)) or of moderate duration and/or intensity (e.g. 10-m high
391
knees, side-stepping, carioca and skipping and 20-m zig-zag run; (30, 31)). When considered
392
together, the available evidence indicates that muscle stretching does not influence high-
393
intensity exercise test performances when they are followed by a warm-up period of
394
sufficient duration and incorporating exercises performed at high (or maximal) intensities.
395
Such warm-up periods have been endorsed for the improvement of sports performance and
396
reduction in musculoskeletal injury risk, even when static stretching is incorporated (3, 32).
397
It is of practical importance that static or dynamic stretching early in the warm-up did
398
not improve flexibility more than warm-up alone, as measured by a maximal sit-and-reach
399
test. Time constraints did not allow for the specific testing of ranges of motion at different
400
joints, however a single, multi-joint test was expected to reveal changes given that nine
401
different stretches were performed. The lack of change in sit-and-reach distance indicated
402
that any effect of a stretch condition within the warm-up on maximal range of motion was
403
negligible, which is in agreement with previous evidence (33). Thus, the dynamic warm-up
404
activities may have elicited improvements in maximal range of motion that were not
405
improved upon by the performance of further stretching, as has been observed previously (34,
406
35). Alternatively, changes may have occurred in muscles other than those in the lower back
407
and hamstrings and did not meaningfully impact sit-and-reach performance. While it cannot
408
be excluded that the addition of muscle stretching to a warm-up routine might improve
409
maximal range of motion at specific joints, especially if longer or more intense stretch
410
21
periods are practiced (36), the present results indicate that stretching provided negligible
411
flexibility benefit in addition to the low- and high-intensity dynamic activities (i.e. high
412
knees, butt kicks and test practice) of the warm-up. It would be of interest to determine
413
whether the stretching protocols evoked changes in muscle-tendon stiffness (extensibility) as
414
opposed to maximum length (range of motion), as these have been shown to be differentially
415
influenced by warm-up and stretching (36). Nonetheless, any possible effects in the current
416
study were clearly insufficient to affect physical performance.
417
Steps were taken in the current study to improve both the external and internal
418
validity of the results. With respect to external validity, we accepted only participants who
419
competed in running-based sports or performed at least three running-based exercise sessions
420
per week, and then allowed time for extensive familiarization of the tests. We also used
421
stretching durations that are common in athlete populations (17, 18), ensured that the static
422
and dynamic stretch movement patterns were identical, did not allow a passive rest condition
423
in the non-stretch condition, and imposed a 7-min no-activity period after the completion of
424
the full warm-up period. These steps were taken to replicate as closely as possible what might
425
occur in the sporting environment. With respect to internal validity, we ensured that the
426
researchers who conducted the tests were blinded to the warm-up conditions completed by
427
the participants (although these were closely supervised by another researcher) and all
428
instructions were scripted so that they were identical on each test occasion; the stretch
429
maneuvers were also shown by video with written instructions so that variations in
430
instruction were minimized. It was not possible to recruit participants who lacked prior
431
knowledge of the potential effects of stretching. However, by assessing participant beliefs
432
before the study as well as after the completion of each warm-up condition we were able to
433
examine relationships between participant expectation and study outcomes. Together, these
434
steps will have reduced both experimenter and participant bias, allowing us to more
435
22
confidently accept the study outcomes. It should be acknowledged, however, that the study
436
was not designed to examine the effects of prolonged periods of static (passive) stretching
437
performed immediately prior to a physical task, as might be reflective of practice in some
438
rehabilitation and resistance training settings.
439
One potential limitation of the current study design is that the tests were conducted in
440
a circuit, with 4 min being allowed for the completion of each test block (i.e. 3-m running
441
jump; SJ, CMJ, DJ; 20-m sprint run; T agility test). Therefore, the final test on any test day
442
may have commenced up to 12 min after the commencement of the test battery, and it will
443
have been performed after several other maximal-intensity tests. It can then be questioned
444
whether tests performed closer to the end of the warm-up period might have been more
445
strongly influenced by the interventions. However, our analysis did not reveal any evidence
446
of an order effect of the tests so performances achieved when a test was first in the circuit
447
(immediately after the 7-min imposed rest) were not different to those when the same test
448
was completed at another time point. Based on this evidence, it appears that the (lack of)
449
effect of the stretching is consistent when a full warm-up is completed and a short post-
450
warm-up rest is imposed regardless of the time elapsed or the number of other tests
451
performed in the intervening period.
452
CONCLUSIONS
453
The results of the present randomized, controlled, cross-over trial indicate that neither short-
454
or moderate-duration static (passive) nor dynamic muscle stretching influence flexibility or
455
high-intensity running, jumping or change of direction (agility) performances in young,
456
athletic individuals who perform a complete, progressive pre-exercise warm-up routine.
457
However, the incorporation of static (passive) or dynamic stretching into a warm-up routine
458
allowed for individuals to feel more confident of high performance in the ensuing sports-
459
23
related tests; i.e. there was a psychological effect. Based on the present results and previous
460
findings of small-to-moderate reductions in muscle injury risk in running based sports, we
461
conclude that short- or moderate-duration static stretching should be allowed, or even
462
promoted, as part of the warm-up routine prior to sports participation. According to our
463
results, dynamic stretching practices may also be incorporated into the warm-up routine,
464
although it should be reminded that no data currently exist documenting the influence of
465
dynamic stretching on injury risk.
466
467
24
468
Acknowledgements
469
We are grateful to athletes who took part in the study. The authors declare no conflicts of
470
interest. No external funding was received for this research.
471
472
The results of the present study do not constitute endorsement by the American College of
473
Sports Medicine. The authors declare that the results of the study are presented clearly,
474
honestly, and without fabrication, falsification, or inappropriate data manipulation.
475
476
477
25
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478
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35. O'Sullivan K, Murray E, Sainsbury D. The effect of warm-up, static stretching and dynamic
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stretching on hamstring flexibility in previously injured subjects. BMC Musculoskelet Disord.
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36. McNair PJ, Stanley SN. Effect of passive stretching and jogging on the series elastic muscle
563
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564
565
566
27
567
Figure 1. Study design. After completing a low-intensity warm-up including 3-min jog and
568
running drills, a randomly-assigned stretching (no no-stretch control) condition was
569
completed. This was followed by a high-intensity warm-up comprising further jogging and
570
running drills and then three circuits at increasing intensity (to maximum) comprised of the
571
performance tests. After a 7-min rest, during which time the participants rated their
572
confidence that the warm-up would improve their performance (see text for details), a sit-
573
and-reach flexibility test was completed before the high-intensity performance tests were
574
completed in a random order (order repeated at each session). 5-rep: 5-repetition.
575
576
28
577
Figure 2. Squat (SJ; A), countermovement (CMJ; B), drop (DJ; C) and 3-step running (3-step
578
Jump; D) heights recorded in 5S (5-s static stretch), 30S (30-s static stretch), DYN (dynamic
579
stretch) and NS (no-stretch, control) conditions. There were no differences in jump test
580
performances between the conditions. Shown are the mean SE (black column with error
581
bar) and 95% confidence intervals of the mean (separate gray bar) jump performances.
582
583
29
584
Figure 3. 20-m sprint run (bottom panel) and T agility (top panel) times recorded in 5S (5-s
585
static stretch), 30S (30-s static stretch), DYN (dynamic stretch) and NS (no-stretch, control)
586
conditions. There were no differences in test performances between the conditions. Shown
587
are the mean SE (black column with error bar) and 95% confidence intervals of the mean
588
(separate gray bar) jump performances.
589
590
591
30
Supplemental Digital Content 1. Stretch instructions and photo
592
593
A. Calves
594
Static
595
1. Assume push-up position, keeping knees and elbows straight.
596
2. Allow one knee to drop by rolling onto ball of foot.
597
3. Gently lower heel of planted foot down as low to the ground as possible until stretch
598
is felt at the calf.
599
4. Hold the stretch at point of discomfort (POD) for 5 or 10 seconds (depending on
600
instructions for the day) before switching legs.
601
602
Dynamic
603
1. Assume push-up position, keeping knees and
604
elbows straight.
605
2. Allow one knee to drop by rolling onto ball of
606
foot.
607
3. Gently lower heel of planted foot down as low to the ground as possible until stretch
608
is felt at the calf.
609
4. Hold at POD only briefly (0.5 s) before lifting the heel up again.
610
5. Repeat for 5 repetitions per leg in a down-pause-up motion.
611
612
Performance points
613
1. Point grounded foot straight ahead
614
2. Keep the back straight.
615
3. Lower the heel as close to the ground as possible to POD.
616
617
618
619
620
B. Quadriceps
621
Static
622
1. Grasp ankle and gently pull your heel up and back until you feel the
623
stretch in the front of your thigh.
624
2. Tighten your stomach muscles to prevent your stomach from sagging
625
outward, and keep your knees close together.
626
3. Hold at POD for 5 or 10 seconds.
627
4. Switch legs and repeat.
628
629
Dynamic
630
1. Grasp ankle and gently pull your heel up and back until you feel the
631
stretch in the front of your thigh.
632
2. Tighten your stomach muscles to prevent your stomach from sagging
633
outward, and keep your knees close together.
634
3. Add a secondary pulling/tugging motion (pull foot upwards along
635
your back) before releasing the ankle and switching legs.
636
4. Repeat for 10 repetitions per leg in an up-tug-down motion.
637
638
639
31
C. Hamstrings
640
Static
641
1. Lie on back and lift knee up, keeping knees straight as far as possible and maintaining
642
dorsiflexion.
643
2. Grasp behind thigh near knee with both hands
644
and pull knee close to chest.
645
3. Hold stretch for 5 or 10 seconds at POD.
646
4. Release and repeat with opposite leg.
647
648
Dynamic
649
1. Lie on back and lift knee up, keeping knees
650
straight as far as possible and foot maintaining
651
dorsiflexion.
652
2. Grasp behind thigh near knee with both hands and pull knee close to chest.
653
3. Add a secondary pulling/tugging motion before releasing leg.
654
4. Repeat with opposite leg, 5 repetitions per leg.
655
656
Performance points
657
1. Maintain foot dorsiflexion
658
2. Keep knee extended
659
660
661
662
663
D. Hip Flexors
664
Static
665
1. Stand with hands on hips and with one leg approximately a leg
666
length in front of the other, with the forward leg slightly bent at the
667
knees and rear leg maximally extended.
668
2. Slowly lunge forward by bending forward leg.
669
3. With chest high, straighten hip of rear leg by pushing hips forward.
670
4. Hold stretch at POD for 5 or 10 seconds and repeat with opposite
671
side.
672
673
Dynamic
674
1. Stand with hands on hips and with one leg approximately a leg
675
length in front of the other, with the forward leg slightly bent at the
676
knees and rear leg maximally extended.
677
2. Slowly lunge forward by bending forward leg.
678
3. With chest high, straighten hip of rear leg by pushing hips forward.
679
4. Hold stretch at POD for about a second before returning to starting position.
680
5. Repeat for 5 repetitions in a ‘forward-pause-back’ motion before switching to
681
opposite leg.
682
683
Performance points
684
1. Keep torso upright, close to vertical.
685
686
687
32
E. Hip Adductors
688
Static
689
1. Stand with feet facing forward and slightly more than shoulder
690
width apart
691
2. Lean to one side by dropping one knee, causing the muscles of the
692
other leg to go into tension
693
3. Hold the stretch for 5 or 10 seconds at POD
694
4. Switch legs and repeat.
695
696
Dynamic
697
1. Stand with feet facing forward and slightly more than shoulder
698
width apart
699
2. Lean to one side by dropping one knee, causing the muscles of the
700
other leg to go into tension
701
3. Pause and hold at stretch position at POD for about a second before leaning to the
702
other side
703
4. Repeat for 5 repetitions per side in a ‘lean-pause-back’ motion.
704
705
Performance points
706
1. Maintain vertical upper body
707
708
709
710
711
F. Ankles
712
Static
713
1. Stand with hands on hips and feet shoulder-width apart.
714
2. Supporting bodyweight on one leg, roll ankle of other leg
715
laterally until stretch is felt to POD.
716
3. Hold for 5 or 10 seconds.
717
4. Return and repeat with opposite ankle.
718
719
Dynamic
720
1. Stand with hands on hips and feet shoulder-width apart.
721
2. Supporting bodyweight on one leg, roll ankle of other leg
722
laterally until stretch is felt to POD.
723
3. Hold stretch position for about a second before returning to
724
starting position.
725
4. Repeat for 5 repetitions in a ‘roll-pause-back’ motion before
726
switching legs.
727
728
729
730
731
33
G. Gluteals
732
Static
733
1. Standing on one leg, grasp below the knee of the other leg
734
and pull it as close to your chest as possible.
735
2. Hold the stretch at POD for 5 or 10 seconds.
736
3. Release and repeat with other leg.
737
738
Dynamic
739
1. Standing on one leg, grasp below the knee of the other leg
740
and pull it as close to your chest as possible.
741
2. Add a secondary tugging motion before releasing and
742
switching legs.
743
3. Repeat for 5 repetitions per leg.
744
745
746
747
748
H. Upper chest and shoulder
749
Static
750
1. Interlock fingers of both hands behind your back, palms together,
751
and lift both arms up and back as high as possible while
752
maintaining full elbow extension.
753
2. Hold the stretch at POD for 5 or 10 seconds.
754
755
Dynamic
756
1. Interlock fingers of both hands behind your back, palms together,
757
and lift both arms up and back as high as possible while
758
maintaining full elbow extension.
759
2. Pause at stretch position for ~0.5 s before releasing.
760
3. Repeat for 5 repetitions in a stretch-pause-release motion.
761
762
Performance points
763
1. Minimize shoulder shrug
764
765
766
34
I. Upper back
767
768
Static
769
1. Interlock fingers of both hands in front of torso, palms together, and
770
lift both arms forward and up until it is directly above your head.
771
2. Hold the stretch at POD for 5 or 10 seconds, feeling the stretch
772
through the back muscles.
773
774
Dynamic
775
1. Interlock fingers of both hands in front of torso, palms together, and
776
lift both arms forward and up until it is directly above your head.
777
2. Pause at stretch position for ~0.5 s before releasing, feeling the stretch
778
through the back muscles.
779
3. Repeat for 5 repetitions in a ‘stretch-pause-release’ motion.
780
781
782
783
784
785
786
