The Effects of Stretching on Strength Performance

Abstract

Strength and flexibility are common components of exercise programmes; however, it is not clear how best to include both of these elements in a single training programme. It is common practice among athletes, coaches and recreational exercisers to perform a stretching routine before a strength training session. Stretching exercises are regularly recommended, even in many textbooks, with the claimed purpose of preventing injury and muscle soreness, or even enhancing performance. However, as highlighted in recent review articles, this recommendation lacks scientific evidence. Thus, the purpose of the present review is to determine the acute and chronic effects of stretching on strength performance, together with the underlying mechanisms. Although most studies have found acute decreases in strength following stretching, and that such decreases seem to be more prominent the longer the stretching protocol, the number of exercises and sets, and the duration of each set have, in general, exceeded the ranges normally recommended in the literature. Consequently, the duration of the stimuli were excessively long compared with common practice, thus making evident the need for further studies. In addition, when recommending flexibility exercises, one should consider other underlying issues, such as the safety of the participants, possible increases in injury risks and the unnecessary time expenditure. Many mechanisms underlying stretching exercises still demand investigation so that links between the observed effects, their causes and the consequences may be constructed.

Full text

Sports Med 2007; 37 (3): 213-224
R
EVIEW
A
RTICLE
0112-1642/07/0003-0213/$44.95/0
 2007 Adis Data Information BV. All rights reserved.
The Effects of Stretching on
Strength Performance
Ercole C. Rubini,
1,2
Andr
´
e L.L. Costa
2
and Paulo S.C. Gomes
2
1 Universidade Est
´
acio de S
´
a, Rio de Janeiro, Brazil
2 Laboratory Crossbridges and Department of Physical Education from Universidade Gama
Filho, Center for Interdisciplinary Research in Health, Rio de Janeiro, Brazil
Contents
Abstract ....................................................................................213
1. Acute Effects of Stretching on Strength Performance ........................................214
1.1 Effects on Isotonic, Isometric and Isokinetic Strength Tests ................................214
1.2 Effects on Jumping Performance ......................................................215
2. Chronic Effects of Stretching on Strength Performance ......................................215
3. Adaptation Mechanisms..................................................................218
3.1 Neurological Adaptations ............................................................218
3.2 Structural Adaptations ...............................................................220
3.3 Cellular Adaptations .................................................................220
3.4 Hormonal Adaptations ...............................................................221
4. Conclusions .............................................................................221
Strength and flexibility are common components of exercise programmes;
Abstract
however, it is not clear how best to include both of these elements in a single
training programme. It is common practice among athletes, coaches and recrea-
tional exercisers to perform a stretching routine before a strength training session.
Stretching exercises are regularly recommended, even in many textbooks, with
the claimed purpose of preventing injury and muscle soreness, or even enhancing
performance. However, as highlighted in recent review articles, this recommenda-
tion lacks scientific evidence. Thus, the purpose of the present review is to
determine the acute and chronic effects of stretching on strength performance,
together with the underlying mechanisms. Although most studies have found
acute decreases in strength following stretching, and that such decreases seem to
be more prominent the longer the stretching protocol, the number of exercises and
sets, and the duration of each set have, in general, exceeded the ranges normally
recommended in the literature. Consequently, the duration of the stimuli were
excessively long compared with common practice, thus making evident the need
for further studies. In addition, when recommending flexibility exercises, one
should consider other underlying issues, such as the safety of the participants,
possible increases in injury risks and the unnecessary time expenditure. Many
mechanisms underlying stretching exercises still demand investigation so that

214 Rubini et al.
links between the observed effects, their causes and the consequences may be
constructed.
Exercise programmes often include strength and LINE (1966–2006), EMBASE (1974–2006), Coch-
flexibility training. Both components are considered rane Database of Systematic Reviews (1993–2006),
fundamental for those who wish to attain a healthy Lilacs (1982–2006) and SciELO (1997–2006). Ref-
physical fitness level.
[1]
However, the best way to erences listed on recent reviews
[5-9,31-34]
on the topic
include both components in a single training session were also retrieved. The computer search used the
is not yet clear. following keywords individually or combined:
‘flexibility’, ‘stretching’, ‘elasticity’, ‘range of
It is common practice among athletes, coaches
movement’, ‘range of motion’, ‘training’, ‘injury’
and recreational exercisers to perform a stretching
and ‘warm-up’. These keywords were further com-
routine before the main exercise session, such as
bined with ‘resistance exercise’, ‘resistance train-
strength training. In addition, stretching exercises
ing’, ‘strength training’ and/or ‘acute effects’ or
have been recommended in many textbooks for the
‘chronic effects’. Most studies retrieved were in
claimed purpose of preventing injury and muscle
English, although articles in Portuguese and Spanish
soreness, and even enhancing performance. Two
were also considered in this search. All studies
randomized studies
[2,3]
investigating the effect of
related to the acute effects of stretching on strength
stretching before the main exercise session conclud-
performance were considered, regardless of the
ed that this did not decrease injury risks. Regarding
methodological aspects; however, a critical assess-
the reduction of delayed onset muscular soreness
ment of the text was included when needed.
(DOMS), only one study observed reduction in sore-
ness;
[4]
however, this occurred 72 hours after maxi-
1. Acute Effects of Stretching on
mum eccentric knee flexion. Results from this study
Strength Performance
should be interpreted with caution because, not only
did it take a long time for the beneficial effects to be
noticed, but the sample size was also very small (ten
1.1 Effects on Isotonic, Isometric and
females). Recent reviews
[5-9]
have suggested that
Isokinetic Strength Tests
stretching exercises do not protect against injury,
Many authors have studied the acute effect of a
nor do they diminish DOMS or enhance perform-
stretching routine on strength performance, but the
ance.
results are often controversial. Various studies, with
Stretching routines appear to have a negative
total stimuli duration varying from 120 to 3600
acute effect on the subsequent main activity, partic-
seconds, found that stretching exercises preceding
ularly when this is predominantly strength-depen-
the main strength activity significantly decreased
dent.
[10-30]
As stretching exercises are traditionally
performance.
[10-30]
All of these studies used static
recommended before most physical activities, it is
stretching, except for one article that used ballistic
important to determine to what extent a stretching
exercises
[15]
and three that used proprioceptive neu-
routine may influence performance of the main ac-
romuscular facilitation (PNF) stretching.
[21,24,25]
De-
tivity.
creases in strength ranged from 4.5% to 28%, irre-
The present study had two purposes: (i) to review
spective of the testing mode (i.e. isometric, isotonic
the acute and chronic effects of stretching on
or isokinetic). Most studies used lower body exer-
strength performance; and (ii) to review the underly-
cises, except for Evetovich et al.,
[18]
who investigat-
ing mechanisms associated with these adaptations.
ed the biceps brachii. Tests were isotonic (one repe-
Scientific articles were obtained from an exten- tition maximum [RM]), isokinetic (peak torque) and
sive search on several databases, including MED- isometric (peak torque and maximum voluntary
 2007 Adis Data Information BV. All rights reserved. Sports Med 2007; 37 (3)

Effects of Stretching on Strength 215
contraction). In contrast to these results, other au- (15 or 30 seconds) did not influence the degree of
force loss following static stretching.
thors
[35-40]
did not observe any detrimental effects of
stretching on strength. The total stimuli duration in
1.2 Effects on Jumping Performance
these studies was shorter, ranging from 30 to 480
seconds. Bandeira et al.
[41]
did not observe decreases
Several studies have investigated the acute effect
in strength performance of ballet dancers when us-
of stretching exercises on vertical jump perform-
ing 15 seconds of static active stretching exercises,
ance. Church et al.
[48]
reported a significant decrease
with a total of 90 seconds stretching. On the other
in performance when this was preceded by PNF
hand, when using 60 seconds for each exercise (360
stretching, but not by static stretching. This confirms
seconds total stimuli), performance of the hip flex-
the findings of Power et al.
[22]
and Knudson et al.,
[49]
ors was decreased, but not that of the hip extensors
who investigated the effects of static stretching and
(table I).
also found no significant decreases in vertical jump
performance. On the other hand, two studies did not
Most studies showed decreases in strength per-
find decreases in vertical jump performance in
formance when preceded by stretching exercises.
trained women either after PNF stretching
[50]
and
However, it should be noted that these studies used
following static or ballistic stretching.
[51]
Other stud-
more than one stretching exercise for the same mus-
ies found decreases in vertical jump performance
cle group and/or the number of sets and the duration
after static stretching,
[52-55]
ranging from
–
4.5% to
of stretching were greater than the ranges normally
–
7.3% and
–
3.2% to
–
4.4% with and without
recommended in the literature and used in sporting
counter movement, respectively (table II).
activities. It has been recommended that four sets of
Muscular strength is one of the most important
stretching is performed for each muscle group,
[42]
factors in performing the vertical jump. If stretching
with 10–30 seconds duration in each stretched posi-
has the acute effect of reducing performance in
tion.
[42-46]
For individuals >65 years of age, a longer
strength, it would be expected to reduce that of
duration of 60 seconds should be used.
[47]
Therefore,
jumping as well. In practice, this information is
it is possible that the total stretching duration may
highly important for sporting events in which
have been excessively long in the studies showing
strength and jumping performance are fundamental,
decreases in strength performance.
since a decrease in performance may hinder the final
Data from our laboratory
[21,25]
showed 8.9% and
result. It is possible that conflicting results could be
12.3% reductions in hip adductor isometric strength
explained by the different methods used for stretch-
ing or by the absence of information regarding relia-
measured at 45°, and 10.4% and 10.9% at 30° fol-
bility and precision of these methods. Therefore, it is
lowing four 30-second sets of static or PNF (‘con-
clear that this subject deserves further investigation.
tract-relax’ technique) stretching, respectively. De-
In addition, studies investigating the chronic effect
creases in strength after static stretching in knee
of stretching on jump performance are also required.
flexion and extension were 9.9% and 2.3%, and
decreases after PNF were 11.4% and 4.8%, respec-
2. Chronic Effects of Stretching on
tively. These findings concur with the evidence that,
Strength Performance
even with a total stretching time following the litera-
ture recommendations and with only one exercise
Very few studies have looked into the chronic
for each muscle group, a significant decrease in
effects of stretching on strength performance. Wor-
strength performance may still take place. Interest-
rel et al.
[56]
used static and PNF ‘contract-relax’
ingly, the deleterious effect of stretching on strength
methods to train the flexibility of the hamstrings;
performance seems to occur even with experienced
exercises were performed five times a week, for 3
stretchers, as evidenced by Nelson et al.
[23]
Recent-
consecutive weeks, totaling 15 sessions with 20
ly,
[29]
it was shown that the duration of the stimuli minutes per method, per session. Handel et al.
[57]
 2007 Adis Data Information BV. All rights reserved. Sports Med 2007; 37 (3)

216 Rubini et al.
 2007 Adis Data Information BV. All rights reserved. Sports Med 2007; 37 (3)
Table I. Studies investigating the acute effect of stretching on strength performance
Reference Type of stretching Duration of Muscles stretched Muscles tested Total duration Type of action Results
(sample size) stretching (s)
Kokkonen et al.
[10]
Static 5 exercises Hamstrings, hip Hamstrings, 450 Isot ↓ 7.3% flexion
M (n = 15); (passive) [assis./ 3 × 15s adductors, plantar quadriceps 1RM ↓ 8.1% extension
F (n = 15) not assis.] 15s rest flexors,
quadriceps
Muir et al.
[35]
Static 1 exercise Plantar flexors Plantar flexors, 120 Isok No change in performance
M (n = 20) (active) 4 × 30s dorsi flexors
10s rest
Avela et al.
[11]
Static 1 exercise Plantar flexors Plantar flexors 3600 Isom ↓ 23.2% MVC
M (n = 20) (passive) 1 × 60 min
Fowles et al.
[12]
Static 1 exercise Plantar flexors Plantar flexors 1755 Isom ↓ 28% MVC
M (n = 6); (passive) 13 × 135s
F (n = 4)
Nelson et al.
[16]
Static 3 exercises Quadriceps Quadriceps 360 Isok ↓ 7.2% 60°/s PT
M (n = 10); (active and 4 × 30s ↓ 4.5% 90°/s PT
F (n = 5) passive) 20s rest
Nelson et al.
[14]
Static 2 exercises Quadriceps Quadriceps 240 Isom ↓ 7% PT, at angle of 162°
M (n = 25); (passive) 4 × 30s
F (n = 30) 20s rest
Behm et al.
[13]
Static 4 exercises Quadriceps Quadriceps 900 Isom ↓ 12.2% MVC
M (n = 12) (passive) 5 × 45s
15s rest
Nelson and Ballistic 5 exercises Hamstrings, thigh Hamstrings, 450 Isot ↓ 7.5% flexion
Kokkonen
[15]
adductors, plantar quadriceps 1RM ↓ 5.6% extension
M (n = 11); flexors,
F (n = 11) quadriceps
Tricoli and Static 6 exercises Quadriceps, Quadriceps, 540 Isot ↓ 13.8% maximum strength
Paulo
[17]
(active) 3 × 30s hamstrings hamstrings 1RM
M (n = 11) 30s rest
Garrison et al.
[37]
Static NA Quadriceps Quadriceps 480 Isok No change in performance
(n = 29)
Mello and Static 2 exercises Hamstrings, Hamstrings, 30 Isok No change in
Gomes
[36]
(passive) 2 × 15, 30 and quadriceps quadriceps 60 performance
M (n = 5); 60s 120
F (n = 3) 10s rest
Evetovich et al.
[18]
Static 3 exercises Biceps brachii Biceps brachii 360 Isok ↓ 30°/s PT
M (n = 10); (2 active; 1 4 × 30s ↓ 270°/s PT
F (n = 8) passive) 15s rest
Bandeira et al.
[41]
Static 6 exercises Hip flexors, hip Hip flexors, hip 90 or Isok ↓ Flexors 60°/s
F (n = 10) (active) 1 × 15s and 60s extensors extensors 360
Continued next pag
e

Effects of Stretching on Strength 217
 2007 Adis Data Information BV. All rights reserved. Sports Med 2007; 37 (3)
Table I. Contd
Reference Type of stretching Duration of Muscles stretched Muscles tested Total duration Type of action Results
(sample size) stretching (s)
Avela et al.
[19]
Static 2 exercises Plantar flexors Plantar flexors 360 Isom ↓ 13.8% MVC (1st measure)
M (n = 8) (passive) 60 min ↓ 13.2% MVC (2nd measure)
2 weeks between
exercises
Cramer et al.
[20]
Static 4 exercises Quadriceps Quadriceps 480 Isok ↓ 3.3% 60°/s PT
F (n = 14) (1 active; 4 × 30s ↓ 2.6% 240°/s PT
3 passive) 20s rest
Rubini et al.
[21]
Static 1 exercise Hip adductors Hip adductors 120 Isom 45°: ↓ 8.9% and ↓ 12.3%
M (n = 18) PNF 4 × 30s or 30°: ↓ 10.4% and ↓ 10.9%
(passive) 4 × (3 × 10s) (static and PNF, respectively)
Cramer et al.
[38]
Static 4 exercises Quadriceps Quadriceps NA Isok No change in performance
M (n = 15) (1 active;
3 passive)
Behm et al.
[39]
Static 3 exercises Quadriceps Quadriceps 405 Isom No change in performance
M (n = 16) (passive) 3 × 45s hamstrings,
15s rest plantar flexors
Power et al.
[22]
Static 6 exercises Quadriceps Quadriceps, 810 Isom ↓ 9.5% MVC quadriceps and no
M (n = 12) 3 × 45s hamstrings, plantar flexors (270 for each change in plantar flexors
15s rest plantar flexors muscle group)
Mello and Static 6 exercises Quadriceps, Quadriceps, 3600 Isok ↓ 9.9% and ↓ 2.3%
Gomes
[25]
PNF 30s or (3 × 10s) hamstrings hamstrings ↓ 11.4% and ↓ 4.8% (static and
F (n = 17) (passive) PNF; flexion and extension,
respectively)
Marek et al.
[24]
Static 4 exercises Quadriceps Quadriceps 120 (static) Isok ↓ 2.8%
M (n = 9); PNF 5 × 30s 120 (PNF) (static and PNF)
F (n = 10) (passive) 30s rest
Nelson et al.
[23]
Static 5 exercises Quadriceps, Quadriceps, 1200 Isot ↓ 3.2% extension
M (n = 13); (passive) [assis./ 3 × 15s hamstrings hamstrings 1RM ↓ 5.5% flexion
F (n = 18) not assis.] 15s rest
Cramer et al.
[26]
Static 4 exercises Quadriceps Quadriceps 966 Isok ↓ 60°/s and 240°/s PT (dominant)
M (n = 7); (passive) 4 × 30s (dominant) (dominant/not ↓ 60°/s PT (not dominant)
F (n = 14) 20s rest dominant)
Derek et al.
[27]
Static 1 exercise Plantar flexor Plantar flexor 600 Isom ↓ 7% MVC
M (n = 15) (passive) 5 × 120s
Behm et al.
[28]
Static 3 exercises Quadriceps, Quadriceps 270 Isom ↓ 6.5% MVC
(Pre) (passive) 3 × 30s hamstrings,
M (n = 9); 30s rest plantar flexors
F (n = 9)
Continued next pag
e

218 Rubini et al.
used the PNF ‘contract-relax’ method to train the
knee extensor and flexor muscles; exercises were
performed three times a week for 8 consecutive
weeks, with a total of 86 minutes 40 seconds in each
session. The study by Worrel et al.
[56]
showed no
significant gains in flexibility, but 8.5% and 13.5%
increases in eccentric peak torque measured at 60°/s
and 120°/s, respectively, and 11.2% increase in con-
centric peak torque at 120°/s. Significant increases
in flexibility (up to 6.3%), in knee flexor and exten-
sor muscle eccentric peak torque (18.2% and 23.0%,
respectively), knee flexor concentric peak torque
(9.4%) and knee flexor isometric peak torque
(11.3%) were found by Handel et al.
[57]
Despite the need for more studies, the enhance-
ment of strength following flexibility training may
be attributed to hypertrophy of the stretched mus-
cles. Muscle hypertrophy has been observed in ani-
mals that underwent stretching protocols lasting 24
hours per day, for 3–30 days.
[58-60]
Although these
studies were conducted with animals, researchers
used stretching methods and duration that differed
greatly from those recommended for humans for
gains in flexibility, thus limiting applicability of
these results. In the case of humans, gains in strength
seem to occur after 3 weeks of flexibility training,
without any specific training for strength develop-
ment.
[56,57]
Therefore, evidence suggests that, al-
though stretching exercises may have a negative
acute effect on strength, this may not be the case
after chronic stretching.
3. Adaptation Mechanisms
3.1 Neurological Adaptations
Although evidence is still lacking, some authors
have tried to explain the possible neural mechanisms
underlying the acute effects of stretching exercises
and their effects on muscle strength performance.
The literature is rather inconclusive and some of the
findings do not relate to one other.
Rosenbaum and Henning
[61]
observed a signifi-
cant 5% decrease in isometric peak torque following
3 minutes of static stretching of the triceps surae,
which was accompanied by an increase in muscular
 2007 Adis Data Information BV. All rights reserved. Sports Med 2007; 37 (3)
Table I. Contd
Reference Type of stretching Duration of Muscles stretched Muscles tested Total duration Type of action Results
(sample size) stretching (s)
Behm et al.
[28]
Static 3 exercises Quadriceps, Quadriceps 270 Isom ↓ 8.2% MVC
(Post) (passive) 3 × 30s hamstrings,
M (n = 12) 30s rest plantar flexors
Brandenburg
[29]
Static 2 exercises Hamstrings Hamstrings 90 or Isom ↓ 15s
M (n = 10); (assist./not 3 × 15s or 30s 180 Conc ↓ 30s
F (n = 6) assist.) 30s rest Exce NS difference between type of
actions
Egan et al.
[40]
Static 4 exercises Quadriceps Quadriceps 480 Isok NS 60°/s
F (n = 11) 4 × 30s NS 300°/s
20s rest 5 min after stretching
Yamaguchi et Static 6 exercises Quadriceps Quadriceps 720 Isom ↓ 5% MVC
al.
[30]
(3 assist.; 4 × 30s ↓ 30% MVC
M (n = 20) 3 not assist.) 20s rest ↓ 60% MVC
assis. = assisted; conc = concentric; exce = excentric; F = females; Isok = isokinetic; Isom = isometric; Isot = isotonic; M = males; MVC = maximum voluntary contraction; NA =
not available; NS = statistically not significant; PNF = proprioceptive neuromuscular facilitation; Post = after a 4-week training programme; Pre = before training programme; PT =
peak torque; RM = repetition maximum; ↓ indicates decrease.

Effects of Stretching on Strength 219
Table II. Studies investigating the acute effect of stretching on jumping performance
Reference Method Sets and exercises Muscles stretched Stimuli Test Results
(sample size) duration (s)
Church et al.
[48]
Static 3 sets Quadriceps, hamstrings NA VJ ↓ PNF
F (n = 40) PNF NS static
Cornwell et al.
[52]
Static 1 set Hip extensors, knee 90 VJ ↓ 4.4% (VJ)
M (n = 10) (passive) 3 exercises extensors ↓ 4.3% (VJCM)
Knudson et al.
[49]
Static 3 sets Quadriceps, hamstrings, 45 VJ NS (VJ)
M (n = 10); F (n = 10) 3 exercises plantar flexors
Cornwell et al.
[53]
Static 3 sets Triceps surae 180 VJ ↓ 7.3% (VJCM)
M (n = 10) (passive) 2 exercises NS (VJ)
Serzed
ˆ
elo Corr
ˆ
ea et al.
[50]
PNF 3 exercises Quadriceps, hamstrings, 240 VJ NS (VJ)
F (n = 10) (CR) calf, gluteus LJ ↑ 10.7% (LJ)
Young and Behm
[54]
Static 4 exercises Quadriceps, plantar 120 VJ ↓ 3.2% (VJ)
M (n = 13); F (n = 3) flexors
Power et al.
[22]
Static 2 sets Quadriceps, hamstrings, 270 VJ NS (VJ)
M (n = 12) 3 exercises plantar flexors
Unick et al.
[51]
Static 3 sets Quadriceps, hamstrings, 180 VJ NS (VJ)
F (n = 16) Ballistic 4 exercises plantar flexors Statistic/Ballistic
Wallmann et al.
[55]
Static 3 sets Gastrocnemius 90 VJ ↓ 5.6% (VJ)
M (n = 8); F (n = 6) (passive)
CR = contract/relax; F = females; LJ = long jump; M = males; NA = not available; NS = statistically not significant; PNF = proprioceptive
neuromuscular facilitation; VJ = vertical jump; VJCM = vertical jump with counter movement; ↑ indicates increase; ↓ indicates decrease.
compliance. Muscle offers less resistance to passive afferents and producing a smaller electromy-
ographic amplitude.
stretching and increases its capability of distending
when muscular compliance increases. This phenom-
In addition to these mechanisms, other neural
enon is know as ‘stress relaxation’, which is a loss in
systems may be involved, such as activation of
nociceptors and inhibition generated by Golgi ten-
tension occurring when the muscle is stretched with
don organs, which contribute to a decrease in excita-
a constant length and which occurs irrespective of
bility of the α motoneuron.
[13]
An increased inhibi-
observed electromyographic alterations, as suggest-
tory drive of the α motoneuron pool generated by
ed by McHugh et al.
[62]
Thus, muscle compliance
types III and IV joint receptors after stretching exer-
resulting from stretching is suggested as one of the
cise was also suggested by Avela et al.
[63]
mechanisms responsible for the decrease in muscu-
Halbertsma and G
¨
oeken,
[64]
investigated the ef-
lar performance.
fects of 10 minutes of static stretching on subjects
In another study, Fowles et al.
[12]
found that there
with shortened hamstring muscles. The authors con-
was a decrease in motor unit activation and in elec-
cluded that the effect of such exercises would not be
tromyographic activity immediately following pas-
due to alterations in muscle elasticity, but to a
sive stretching of the plantar flexors. In addition,
greater tolerance to stretching. The same conclu-
there was a 28% decrease in maximum voluntary
sions were reported by Magnusson et al.
[65]
in a
contraction, which was still depressed by 9% 1 hour
study of static stretching of the hamstrings over 3
after stretching cessation.
weeks and by Halbertsma et al.
[66]
after a 10-minute
In the study by Avela et al.,
[11]
maximum volun-
session of 30 seconds of static stretching of the
tary activation was decreased by 23.2% immediately hamstrings with rest intervals of 30 seconds.
following 1 hour of repeated passive stretching of
Therefore, there seems to be a reduction in sensi-
the triceps surae. The authors observed a reduction
bility of the muscle, tendon, joint receptors and
in sensitivity to repeated stretches of the muscle
nociceptors, which are fundamental mechanisms for
spindles, reducing the activity of the large-diameter the protection of structures involved in motion. In
 2007 Adis Data Information BV. All rights reserved. Sports Med 2007; 37 (3)

220 Rubini et al.
addition to these alterations, there is a period where lasting for 45 seconds, with 15 seconds of rest
neuromotor responses are delayed immediately fol- between exercises. The authors concluded from the
lowing stretching exercises. These acute neural al- latter two studies that training decreased the viscosi-
terations may be related to the observed decrease in ty of the tendinous structures, but did not alter
strength and may predispose to or increase the risks elasticity.
of injury, although this requires further investiga-
Still trying to understand muscle elasticity,
tion.
Edman and Tsuchiya
[72]
concluded that during
stretching exercises the most affected elastic struc-
3.2 Structural Adaptations
ture was the titin, and that compliance properties of
tendons and all the other elastic structures were less
One of the hypotheses suggested for the reduc-
than for this protein. This concurs with other studies
tion in strength performance following successive
that have shown titin to be the main structure re-
stretching is the alteration of viscoelastic properties
sponsible for muscular elasticity.
[73,74]
Further inves-
of the muscle, which, in turn, may alter the length-
tigating this question, Avela et al.
[63]
hypothesised
tension relationship. However, there seems to be no
that the increase in compliance caused by stretching
consensus on the subject.
would be responsible for the decrease in the re-
Toft et al.
[67]
investigated viscoelastic and plas-
sponse caused by muscle spindles and, subsequent-
ticity properties of the plantar flexor muscles. They
ly, a lower activity of α motoneurons. Rubini and
concluded that these muscles experienced no modi-
Gomes
[75]
provide a review of the role of titin in
fication when measured 90 minutes after a passive
muscular elasticity.
stretching programme, nor at 24 hours after 3 weeks
Therefore, stretching exercises seem to acutely
of training twice a day. On the other hand, Taylor et
produce a decrease in viscosity of the tendinous
al.
[42]
observed a capacity to alter the length of the
structures, allowing muscle fibres to slide with less
musculo-tendinous unit of rabbits following stretch-
resistance to movement. At the same time, stretch-
ing, thus decreasing passive tension. Toft et al.
[68]
ing exercises generate an increase in muscle compli-
found 36% decreases in passive tension of the plan-
ance that may limit more crossbridge coupling, thus
tar flexors after 3 weeks of ‘contract-relax’ flexibili-
decreasing the capacity of the muscle to produce
ty training, twice a day. Furthermore, these authors
force.
found no significant correlation between the initial
Chronic studies with stimuli of longer duration
flexibility level of the subjects and the effect of
may help to improve understanding of the structural
stretching on passive tension, which was equivalent
adaptations and their effects on strength perform-
for all levels.
ance resulting from stretching exercises.
In order to understand the viscoelastic alterations
resulting from stretching, the same group of authors,
3.3 Cellular Adaptations
in three different studies, used ultrasound to observe
the medial gastrocnemius tendon and aponeurosis De Deyne,
[76]
in an attempt to explain the perma-
before and after stretching. Kubo et al.
[69]
concluded nent increase in range of motion resulting from
that 10 minutes of static stretching decreased the flexibility training, suggested a chronic adaptation
viscosity of the tendinous structures and increased through cellular mechanisms, such as new serial
their elasticity. In a chronic study,
[70]
the same group sarcomere addition. Myofibrilogenesis has been ob-
combined resistance exercises with static stretching; served in animals
[77-80]
and occurs, basically, in the
exercise were performed for 45 seconds with insertion of muscles exposed to casting, with the
15-second intervals, two sessions a day, 7 days a muscle immobilised in a stretched position for 24
week for 8 weeks. In a third study,
[71]
the subjects hours a day, over several days. However, these
performed static stretching in 20 consecutive days, models are very different from the methods normal-
with two sessions a day of five stretching exercises, ly used in flexibility programmes for humans.
 2007 Adis Data Information BV. All rights reserved. Sports Med 2007; 37 (3)

Effects of Stretching on Strength 221
Significant increases in protein synthesis were rapid increase in the number of ribosomal RNA,
found in studies with mice
[81]
that were exposed to indicating that hypertrophy of the muscle fibers
casting immobilization in a stretched position for 7 occur during translation.
[84,86]
These findings
days. The author suggested that stretching was the showed that stretching is capable of promoting in-
stimulating factor for protein synthesis. creases in muscle strength or hypertrophy. Never-
theless, the experimental conditions of the studies
Whether the addition of new sarcomeres has a
discussed in section 3.4 are very different from the
beneficial or detrimental effect on strength is still
conditions normally recommended and applied to
not known. This is a question that requires further
humans.
investigation, despite the difficulty in conducting
long-term studies. Studies that observed the occur-
rence of myofibrilogenesis in animals did not inves-
4. Conclusions
tigate the effects on strength, and the very few
Flexibility and strength are fitness components
chronic studies that investigated the effects of
that are fundamental in many sports modalities and
stretching on strength did not investigate the occur-
even for common daily motor tasks. Training for
rence of myofibrilogenesis.
flexibility and strength is widely recommended for
those who wish to attain good fitness levels and a
3.4 Hormonal Adaptations
better quality of life. Many activities rely heavily on
strength, but strength performance may be dimin-
During the last two decades, several studies have
ished by a preceding stretching routine; therefore, it
been carried out with the aim of observing the
is important to understand this phenomenon when
hormonal changes due to stretching. Some studies
prescribing physical exercise programmes. There
were conducted with animals being immobilised in a
appears to be substantial evidence suggesting a de-
stretched position for various days by casting. Gold-
crease in strength following stretching. Studies used
spink et al.
[58]
observed that stretching increased
different stretching techniques, duration and
insulin-like growth factor (IGF)-1 messenger RNA
targeted different muscle groups, and were tested
(mRNA) levels in mice. Yang et al.,
[82]
analysing
with isotonic, isometric or isokinetic devices. How-
possible hormonal alterations in rabbits, observed
ever, the number of exercises, duration of each
that stretching generated an IGF-1 isoform (IGF-1
exercise and number of sets (i.e. the total duration of
Eb), corresponding to the human IGF-1 Ec isoform,
stretching) was much longer than the ranges normal-
which is related to muscular growth. In another
ly used in practice and what is recommended in the
study, Yang et al.
[60]
observed increases in IGF-1
literature. This makes evident the need for further
mRNA levels, which correlated with increases in
studies with designs that do not threaten their exter-
muscle mass in rabbits. IGF-1 Ec, also known as
nal validity. Training studies should also be con-
mechano growth factor (MGF), is an IGF splice
ducted in order to assess whether the decreases in
variant that has autocrine and paracrine functions
strength observed during the training session will
capable of stimulating protein synthesis and muscle
have long-term consequences (i.e. suboptimal gains
hypertrophy.
[83]
Its secretion is stimulated in re-
in strength when compared with training without
sponse to mechanical stimuli such as force genera-
prior stretching).
tion and stretching, with stretching being the main
mechanical stimulus.
[83,84]
MGF locally controls tis- Furthermore, the safety of the participants should
sue repair, maintenance and remodeling.
[83,85]
The be taken into consideration in the recommendation
discovery of MGF finally linked the mechanical of stretching exercises. When the possible effects of
stimulus and genetic expression, demonstrating that these exercises are analysed, it seems that many of
cellular phenotypes are not determined only in the the mechanisms responsible for maintaining the
genome.
[84,86]
A particular function of MGF is to myo-osteo-articular integrity, such as muscle, ten-
activate satellite muscle cells.
[83,85]
MGF generates a don and joint receptors, are inhibited following
 2007 Adis Data Information BV. All rights reserved. Sports Med 2007; 37 (3)

222 Rubini et al.
10. Kokkonen J, Nelson AG, Cornwell A. Acute muscle stretching
stretching. Tolerance to pain also seems to be in-
inhibits maximal strength performance. Res Q Exerc Sport
creased, allowing range of motion to be greater and
1998; 69 (4): 411-5
11. Avela J, Kyr
¨
ol
¨
ainen H, Komi PV. Altered reflex sensitivity after
closer to the maximal limit of the stretched struc-
repeated and prolonged passive muscle stretching. J Appl
tures, and consequently, closer to injury risk. The
Physiol 1999; 86 (4): 1283-91
hypothesis that flexibility exercises preceding other
12. Fowles JR, Sale DG, Macdougall JD. Reduced strength after
passive stretch of the human plantarflexors. J Appl Physiol
physical activities may lead to greater injury risks
2000; 89: 1179-88
should be considered and investigated in future stud-
13. Behm DG, Button DC, Butt JC. Factors affecting force loss with
ies.
prolonged stretching. Can J Appl Physiol 2001; 26: 262-72
Many mechanisms underlying stretching exer-
14. Nelson AG, Allen JD, Cornwell A, et al. Inhibition of maximal
voluntary isometric torque production by acute stretching is
cises still demand investigation so that links be-
joint-angle specific. Res Q Exerc Sport 2001; 72 (1): 68-70
tween the observed effects, their causes and conse-
15. Nelson AG, Kokkonen J. Acute ballistic muscle stretching
quences may be constructed.
inhibits maximal strength performance. Res Q Exerc Sport
2001; 72 (4): 415-9
16. Nelson AG, Guillory IK, Cornwell A, et al. Inhibition of maxi-
Acknowledgements
mal voluntary isokinetic torque production following stretch-
ing is velocity-specific. J Strength Cond Res 2001; 15: 241-6
17. Tricoli V, Paulo AP. Efeito agudo dos exerc
´
icios de alonga-
We would like to thank the Conselho Nacional de
mento sobre o desempenho de for¸ca m
´
axima. Atividade F
´
isica
Desenvolvimento Cient
´
ifico e Tecnol
´
ogico (CNPQ), Minis-
e Sa
´
ude 2002; 7 (1): 6-12
try of Education, Brazil, for their financial support to Ercole
18. Evetovich TK, Nauman NJ, Conley DS, et al. Effect of static
C Rubini. The authors would also like to thank Dr Marta Inez
stretching of the biceps brachii on torque, electromyography,
Rodrigues Pereira for the preparation of the English version
and mechanomyography during concentric isokinetic muscle
of the manuscript and Dr Ana Maria Miragaya for reviewing
actions. J Strength Cond Res 2003; 17 (3): 484-8
the English version. The authors have no conflicts of interest
19. Avela J, Finni T, Liikavainio T, et al. Neural and mechanical
directly relevant to the content of this review.
responses of the triceps surae muscle group after one hour
repeated fast passive stretches. J Appl Physiol 2004; 96:
2325-32
20. Cramer JT, Housh TJ, Johnson GO, et al. Acute effects of static
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E-mail: crossbridges@ugf.br
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