Literature Review

Stretching and injury prevention - An obscure relationship

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Abstract
It is generally accepted that increasing the flexibility of a muscle-tendon unit promotes better performances and decreases the number of injuries. Stretching exercises are regularly included in warm-up and cooling-down exercises; however, contradictory findings have been reported in the literature. Several authors have suggested that stretching has a beneficial effect on injury prevention. In contrast, clinical evidence suggesting that stretching before exercise does not prevent injuries has also been reported. Apparently, no scientifically based prescription for stretching exercises exists and no conclusive statements can be made about the relationship of stretching and athletic injuries. Stretching recommendations are clouded by misconceptions and conflicting research reports. We believe that part of these contradictions can be explained by considering the type of sports activity in which an individual is participating. Sports involving bouncing and jumping activities with a high intensity of stretch-shortening cycles (SSCs) [e.g. soccer and football] require a muscle-tendon unit that is compliant enough to store and release the high amount of elastic energy that benefits performance in such sports. If the participants of these sports have an insufficient compliant muscle-tendon unit, the demands in energy absorption and release may rapidly exceed the capacity of the muscle-tendon unit. This may lead to an increased risk for injury of this structure. Consequently, the rationale for injury prevention in these sports is to increase the compliance of the muscle-tendon unit. Recent studies have shown that stretching programmes can significantly influence the viscosity of the tendon and make it significantly more compliant, and when a sport demands SSCs of high intensity, stretching may be important for injury prevention. This conjecture is in agreement with the available scientific clinical evidence from these types of sports activities. In contrast, when the type of sports activity contains low-intensity, or limited SSCs (e.g. jogging, cycling and swimming) there is no need for a very compliant muscle-tendon unit since most of its power generation is a consequence of active (contractile) muscle work that needs to be directly transferred (by the tendon) to the articular system to generate motion. Therefore, stretching (and thus making the tendon more compliant) may not be advantageous. This conjecture is supported by the literature, where strong evidence exists that stretching has no beneficial effect on injury prevention in these sports. If this point of view is used when examining research findings concerning stretching and injuries, the reasons for the contrasting findings in the literature are in many instances resolved.
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Sports Med 2004; 34 (7): 443-449
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2004 Adis Data Information BV. All rights reserved.
Stretching and Injury Prevention
An Obscure Relationship
Erik Witvrouw,
1
Nele Mahieu,
1
Lieven Danneels
1
and Peter McNair
2
1 Department of Rehabilitation Sciences and Physical Therapy, Faculty of Medicine and Health
Sciences, Ghent University, Ghent, Belgium
2 School of Physiotherapy, Physical Rehabilitation Research Centre, Auckland University of
Technology, Auckland, New Zealand
Contents
Abstract ....................................................................................443
1. Working Mechanism of the Musculotendinous Unit during Movement .........................444
2. How Can Stretching Reduce the Risk of Injuries? ............................................445
3. Stretching and Injuries in Sports with High Stretch-Shortening Cycle (SSC) Movements ...........446
4. Stretching and Injuries in Sports with No or Low SSC Movements ..............................447
5. Conclusions .............................................................................448
It is generally accepted that increasing the flexibility of a muscle-tendon unit
Abstract
promotes better performances and decreases the number of injuries. Stretching
exercises are regularly included in warm-up and cooling-down exercises; howev-
er, contradictory findings have been reported in the literature. Several authors
have suggested that stretching has a beneficial effect on injury prevention. In
contrast, clinical evidence suggesting that stretching before exercise does not
prevent injuries has also been reported. Apparently, no scientifically based
prescription for stretching exercises exists and no conclusive statements can be
made about the relationship of stretching and athletic injuries. Stretching recom-
mendations are clouded by misconceptions and conflicting research reports. We
believe that part of these contradictions can be explained by considering the type
of sports activity in which an individual is participating. Sports involving bounc-
ing and jumping activities with a high intensity of stretch-shortening cycles
(SSCs) [e.g. soccer and football] require a muscle-tendon unit that is compliant
enough to store and release the high amount of elastic energy that benefits
performance in such sports. If the participants of these sports have an insufficient
compliant muscle-tendon unit, the demands in energy absorption and release may
rapidly exceed the capacity of the muscle-tendon unit. This may lead to an
increased risk for injury of this structure. Consequently, the rationale for injury
prevention in these sports is to increase the compliance of the muscle-tendon unit.
Recent studies have shown that stretching programmes can significantly
influence the viscosity of the tendon and make it significantly more compliant,
and when a sport demands SSCs of high intensity, stretching may be important for
injury prevention. This conjecture is in agreement with the available scientific
clinical evidence from these types of sports activities. In contrast, when the type of
444 Witvrouw et al.
sports activity contains low-intensity, or limited SSCs (e.g. jogging, cycling and
swimming) there is no need for a very compliant muscle-tendon unit since most of
its power generation is a consequence of active (contractile) muscle work that
needs to be directly transferred (by the tendon) to the articular system to generate
motion. Therefore, stretching (and thus making the tendon more compliant) may
not be advantageous. This conjecture is supported by the literature, where strong
evidence exists that stretching has no beneficial effect on injury prevention in
these sports. If this point of view is used when examining research findings
concerning stretching and injuries, the reasons for the contrasting findings in the
literature are in many instances resolved.
Traditionally, it is generally accepted that such as in cycling, jogging and swimming. In the
stretching promotes better performances and de- former role, an eccentric muscle action is immedi-
creases the number of injuries.
[1-6]
Consequently, ately followed by a concentric action. It is well
stretching exercises are regularly included in warm- known that if an activated muscle is stretched before
-up and cooling-down exercises. However, today shortening, its performance is enhanced during the
the scientific evidence concerning the preventive concentric phase. Consequently, jumping, hopping
effect of stretching on injuries seems unclear. In the and leaping movements are improved by making a
literature, prospective studies are lacking and con- counter-movement. Many previous studies have in-
tradictory findings have been reported concerning dicated that this phenomenon is the result of strain
the relationship between stretching and injury pre- energy stored in the tendon structures.
[9-18]
Muscle-
vention. The purpose of this article is to review the tendon units can store mechanical work as elastic
pertinent literature and to advance a new theory to energy during eccentric contractions. The storage
explain the relationship between stretching and inju- and subsequent release of elastic energy during
ry prevention. stretch-shortening cycles (SSCs) have generally
been considered as an ‘energy-saving’ mechanism.
Before looking at the available literature on
However, the effect of the re-utilisation of elastic
stretching and athletic injuries, it seems essential to
energy on the efficiency of movement has been
examine how the muscle-tendon unit works during
recently debated.
[19]
movements and how stretching would be able to
reduce the risk of athletic injuries. We believe that When a muscle has a less compliant muscle-
the contrasting results in the literature concerning tendon unit, more work is directly converted into
the relationship between stretching and injuries can external work. Activities like cycling, flying, skat-
be explained by taking into account the type of ing and swimming use predominantly positive
sports activity in which the individual participates. work-loops and little opportunity exists for absorb-
ing amounts of energy during the task or skill.
[8,20,21]
A more compliant muscle-tendon unit allows for the
1. Working Mechanism of the
effective storage and release of series elastic energy,
Musculotendinous Unit
but seems to be less suited for a task with a predomi-
during Movement
nantly positive work-loop. Wilson et al.
[22]
conclud-
Muscle-tendon systems may generate forces in ed that musculotendinous stiffness was significantly
two distinctly different ways: (i) as an elastic-like related to isometric and concentric performance but
spring in stretch-shortening motion
[7]
that occurs, not to eccentric performance. In their study, they
for example, during jumping-type activities; and (ii) found that the stiffer subjects performed significant-
as converters of metabolic energy into mechanical ly better than the more compliant subjects on both
work in predominantly concentric contractions,
[8]
the isometric tests and on the majority of the concen-
2004 Adis Data Information BV. All rights reserved. Sports Med 2004; 34 (7)
Stretching and Injury Prevention 445
tric tests, since the stiff muscles immediately trans- tion and hence compliance can be modified to suit
fer force to the muscle-bone junction. In contrast, different tasks. As such, Bach et al.,
[25]
and more
compliant muscles generated less power due to the recently Wilson et al.,
[26]
have noted that when the
delayed transfer of energy through the musculo- mechanical properties of the unit are optimised then
tendinous unit. Wilson et al.
[23]
observed in another maximal performance (e.g. for rapid force produc-
study that increasing the compliance of the mus- tion or economy) is obtained.
culotendinous unit through stretching, increased the
contribution of elastic strain energy to movement,
2. How Can Stretching Reduce the Risk
facilitating performance in an SSC movement.
of Injuries?
Therefore, it seems that different types of sports
need different levels of musculo-tendinous compli-
Before looking at the available literature where
ance. Many physical pursuits such as cycling, swim-
the relationship between stretching and injury pre-
ming, skating, wrestling and boxing involve the
vention is examined, we need to understand how
rapid development of force in an isometric or con-
stretching would be able to reduce the risk of athletic
centric muscular contraction, and it would appear
injuries. Firstly, consideration of the compliance of
that such performances could be enhanced through
the muscle-tendon unit is essential. To fully under-
an increase in musculotendinous stiffness. The stif-
stand the effect of compliance, we need to appreci-
fer the muscle-tendon unit, the faster the force is
ate differences between the active contractile (mus-
transferred to the bones, and the resulting movement
cle) component and the passive (tendon tissue) com-
of the joint is quicker. Therefore, looking only at
ponent of the muscle-tendon unit. According to
performance, it might be possible that in these sport
Safran et al.,
[27]
the ability of a muscle to absorb
activities there is no need for a highly elastic mus-
energy is dependent on both components. In a com-
cle-tendon that acts like a spring. The aim of sports
pliant system when the contractile elements are ac-
with a high amount of positive work-loops is to
tive to a high level, more energy can be absorbed by
convert metabolic energy as fast as possible into
the tendon tissue, thereby reducing trauma to muscle
mechanical work.
fibres. However, in case of a low compliance of the
Conversely, in sports with a high-intensity SSC,
tendon, forces will be transferred to the contractile
a more compliant muscle-tendon unit may be re-
apparatus with little energy absorption in the tendon.
quired for the storage and release of elastic energy.
This provides a mechanism to explain the noted
A muscle-tendon unit involved in such SSCs, needs
association between reduced flexibility and occur-
a high storage capacity for potential energy and
rence of muscle injury during SSC motion. Evi-
must, therefore, be sufficiently compliant. For en-
dence for this conjecture is found in the in vivo work
hanced performance, it seems that for these kinds of
by McHugh et al.,
[28]
who found increased evidence
sports there is a great need for a more compliant
of muscle damage following eccentric exercise in
muscle-tendon unit.
subjects with greater passive stiffness. In addition,
It should be considered that there may be an ideal this is consistent with other research,
[29]
which
level of compliance for a musculo-tendinous unit showed that in the outer ranges of movement, as
during a task. This level can be influenced by struc- tendon stiffness increases, greater passive forces are
tural characteristics of the unit. For instance, generated within the muscle. In people with stiff
Shadwick
[24]
has shown that compared with mature tendons, even greater passive muscle forces would
tendons, those of younger animals have a lower be expected to develop during SSC, which would
capacity to store and release strain energy as a result therefore increase the risk of muscle injury. In con-
of higher compliance levels and greater amounts of trast, a more compliant tendon, with greater energy-
hysteresis. The level of overall muscle compliance absorbing capabilities, would therefore seem to re-
can also be influenced by contractile element activa- duce the risk of muscle injury during SSC motion.
2004 Adis Data Information BV. All rights reserved. Sports Med 2004; 34 (7)
446 Witvrouw et al.
On the basis of these findings, the rationale for Nevertheless, transient or chronic increase in ten-
don compliance as an acute or chronic adaptation of
stretching as part of an injury prevention programme
stretching will theoretically lead to a higher ability
is to increase the compliance of the tendon unit, and
of the tendon to absorb energy. In the case of a high-
consequently more energy can be absorbed for a
intensity SSC movement (when a large amount of
given SSC performance.
[30]
Can stretching influence
energy needs to be absorbed), the greater energy
the compliance of the tendon structure? Recently,
absorbing capacity of the stretched tendon will theo-
Kubo et al.
[31]
investigated this question and looked
retically lead to a lower injury risk in the tendon and
for the acute and long-term effects of stretching on
the muscle structures: since (i) the tendon is able to
human tendons in vivo. They showed, using ultraso-
absorb more energy, the high stresses on the tendon
nography, that it was possible to quantify the visco-
(typically coming from the high SSC movements)
elastic properties of human tendon in vivo. Their
will less likely reach the maximal energy-absorbing
results on seven healthy men showed that immedi-
capacity of the tendon, and thus will less likely lead
ately after the execution of static stretching exer-
to injury to the tendon; and (ii) since the stretched
cises the tendon stiffness was transiently de-
tendon is able to absorb more energy, less energy is
creased.
[31]
In a more recent study,
[32]
the same au-
transferred to the contractile apparatus, therefore
thors investigated whether resistance and stretching
reducing the risk of injury within this component of
training programmes altered the viscoelastic proper-
the muscle.
ties of human tendon structures. In that study on
Does this theoretical background for stretching in
eight healthy males they showed that an 8-week
injury prevention in sports with a high SSC compo-
stretching programme (two stretching sessions dai-
nent, as described in the paragraph above, stand-up
ly, 7 days per week) made the tendon structures
when examined with the available literature in
significantly more compliant.
[32]
Their findings are
sports with high SSC movements?
in agreement with previous animal studies that re-
ported an increase in tendon compliance as a result
3. Stretching and Injuries in Sports with
of a stretching regime.
[33-35]
Kubo et al.
[32]
speculat-
High Stretch-Shortening Cycle
ed that stretching may be an effective means to
(SSC) Movements
increase the elastic energy to be utilised during
Ekstrand et al.
[3]
found that a group of elite soccer
exercise involving a SSC, by reducing the viscosity
teams randomised to a routine of warm-up and
of tendon structures.
stretching before exercise, leg guards, special shoes,
Concerning the relationship between stretching
ankle taping, controlled rehabilitation, education
and injury prevention, stretching and the subsequent
and close supervision had 75% fewer injuries than
decrease in tendon stiffness may lessen the imposed
the control group, which received no intervention.
load across the muscle-tendon unit during SSC
They concluded that the proposed prophylactic pro-
movements.
[31]
The mechanism by which the de-
gramme, including close supervision and correction
crease in stiffness occurs immediately after stretch-
by doctors and physiotherapists, significantly
ing and on the long term cannot be determined from
reduces soccer injuries. The same authors
[2]
hy-
the available research. However, McNair et al.
[36]
pothesised that a redesign of the warm-up with more
states that immediately after stretching, the mecha-
emphasis on stretching and the addition of cooling-
nism could involve the movement of the mobile
down exercises reduces injuries. According to Bix-
components/elements within the tissues. That is,
ler and Jones
[1]
high-school football injuries are very
liquid and polysaccharides may be redistributed
frequent each year in the US. In a randomised inter-
within the collagen matrixes.
[36]
After a periodic
vention study, they investigated whether completing
stretching programme, the changes are more likely
a warm-up and stretching routine after halftime re-
to involve structural changes to collagen.
duced the incidence of third-quarter injuries. The
2004 Adis Data Information BV. All rights reserved. Sports Med 2004; 34 (7)
Stretching and Injury Prevention 447
results of their study showed a reduction in injuries crease the risk of injuries by instituting a stretching
with the warm-up and stretching exercises.
programme. Furthermore, stretching in these ath-
letes will probably not lead to an increase of inju-
Witvrouw et al.
[5]
determined the intrinsic risk
factors for the development of patellar tendinopathy
ries. Subsequently, why shouldn’t they stretch if it
in an athletic population. Before the study, 138 male
doesn’t harm? The answer is related to performance.
and female physical education students had been
If these athletes stretch a lot and make their tendons
evaluated for anthropometric variables, leg align-
more compliant, they may be less adapted for their
ment characteristics, muscle tightness and strength
sports activities and consequently be less efficient
parameters. The study revealed that the only signifi-
during movement. In some sporting activities, stiff
cant determining factor was muscular flexibility,
tendons are advantageous for performing brisk, ac-
with the patellar tendinosis group being less compli-
curate movements because they allow rapid tension
ant in quadriceps and hamstring muscle-tendon unit.
changes and hence faster joint motion responses,
Lower flexibility of the quadriceps and hamstring
and perhaps provide more sensitive feedback to the
muscles may contribute to the development of patel-
central nervous system concerning muscle length
lar tendinosis in an athletic population. Therefore,
and tension.
[11,12,37]
Looking at the literature con-
the authors concluded that a stiff quadriceps and
cerning the effect of stretching on low SSC sports
hamstring muscle-tendon unit was a risk factor for
there seems to be some evidence for the above-
the development of patellar tendinopathy. The same
stated concept.
authors published a similar prospective study of 146
In 1993, van Mechelen et al.
[38]
studied the effect
professional soccer players.
[6]
Players with a ham-
of a health-education intervention on jogging inju-
string or quadriceps lesion were found to have a
ries. The intervention consisted of information/edu-
statistically lower compliance of these muscle-ten-
cation and the subsequent performance of
don units prior to their injury compared with non-
standardised warm-up, cooling-down and stretching
injured soccer players. On the basis of these find-
exercises. Male recreational joggers (n = 421) were
ings, they suggested that stretching might play an
randomly split into an intervention and a control
important role in the prevention of this condition.
group. During the 16-week study, both groups kept a
daily diary of their jogging distance and time, and
4. Stretching and Injuries in Sports with
reported all injuries. The results of this study did not
No or Low SSC Movements
identify any evidence of a reduction in soft tissue
injuries in the intervention group. The authors con-
If one participates in a sport with a low or no
cluded that the intervention was not effective in
frequency of SSC movements (e.g. cycling, swim-
reducing the number of jogging injuries. Recently,
ming), or a sport with a high frequency of SSC
Yeung and Yeung
[39]
assessed in their review the
movements but always at a low percentage of the
available evidence for preventive strategies for low-
maximum (e.g. jogging), these movements utilise
er limb soft tissue injuries caused by jogging. Their
little of the energy-absorbing capacity of the mus-
review identified five eligible trials (1944 partici-
cle-tendon unit. For optimal performance in such
pants in intervention groups, 3159 controls) that
activity, the tendons do not need to function as good
examined the effect of a stretching regimen on lower
energy-absorbing structures. Since the maximal en-
limb injuries caused by jogging.
[4,38,40-42]
Two stud-
ergy-absorbing capacity of these unstretched (stiff)
ies evaluated the effect of stretching outside the
tendons is less likely to be exceeded during these
training sessions.
[4,40]
The remaining three studies
sporting activities, the risk of tendon or muscle
examined the effectiveness of stretching immediate-
damage will be relatively low. A stiff tendon will
ly before training.
[38,41,42]
Their exploratory analysis
theoretically be sufficient to deal with the loads
of these five studies showed that in only one study
[4]
imposed on the musculo-tendinous structures during
a significant effect of stretching on the incidence of
these sports, and hence one cannot expect to de-
2004 Adis Data Information BV. All rights reserved. Sports Med 2004; 34 (7)
448 Witvrouw et al.
injuries could be found. The authors concluded on energy, which may lead to tendon and/or muscle
the basis of these findings that insufficient evidence damage. When the sports activity contains no, or
exists to suggest that stretching is effective in only low SSC movements (cycling, jogging), all or
preventing lower limb injuries in joggers.
[39]
most of the work is directly converted to external
work. In these cases, there is no need for a compliant
Looking in the literature concerning swimming
tendon since the amount of energy absorption re-
and cycling, no prospective studies could be found
mains low. Hence, additional stretching exercises to
examining the effect of stretching on the incidence
improve the compliance of the tendon may have no
of injuries. However, looking at the injury incidence
beneficial effect on injury prevention.
in these sports,
[43,44]
the rather low incidence of
musculo-tendinous injuries is interesting and sup-
It must be acknowledged that the aetiology of
ports our model. Looking at the regular training
injuries can be multifactorial. Taking out only one
schedule of professional cyclists in Europe, it is
aspect (e.g. stretching) and examining its effect on
surprising to see how little stretching is performed in
the incidence of injuries is a rather narrow outlook
most teams. In contrast, swimmers tend to devote
on this problem. For example, fatigue is widely
considerable time to stretching. However, recent
believed to be predisposing factor in muscle inju-
literature
[45]
advises to minimise stretching, particu-
ry.
[38]
In addition, other problems remain. Even
larly at the shoulders where hyper-mobility is often
within the same sport, the demands on different
apparent.
players (position on the field) may be different.
However, we believe that far greater attention
should be given to an examination of the type of
5. Conclusions
activity in which the athlete participates when one
In summary, stretching is perhaps the most com-
considers the merits of stretching to reduce injury.
mon routine advocated by sports coaches and sports-
medicine professionals. However, in the literature,
Acknowledgements
conflicting data have been reported concerning the
The authors have provided no information on sources of
relationship between flexibility and athletic injury.
funding or on conflicts of interest directly relevant to the
Stretching recommendations are clouded by mis-
content of this review.
conceptions and conflicting research reports. The
literature reports opposing findings from different
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2004 Adis Data Information BV. All rights reserved. Sports Med 2004; 34 (7)
  • ... These authors observed no negative effects of short-duration StS on power performance. Accordingly, and with reference to previous findings (Witvrouw et al., 2004;Woods et al., 2007;McHugh and Cosgrave, 2010;Behm et al., 2016) of small-to-moderate reductions in muscle injury rate in running-and change of directionbased sports, Blazevich et al. (2018) recommended the use of short-duration StS as an integral part of a pre-exercise warm-up routine that includes aerobic activity, dynamic activities, and sport-specific activities. Furthermore, participants in the Blazevich et al. (2018) study experienced positive psychological benefits expressing that they were more likely to perform well when stretching was performed as part of the warm-up, irrespective of the stretch type. ...
    ... The general belief that dominated the last two decades is that StS does not only contribute to the prevention of injuries (Thacker et al., 2004;Witvrouw et al., 2004) but also impairs athletic performance (Pope et al., 2000;Shrier, 2004b;Shrier, 2004a;McHugh and Cosgrave, 2010;Simic et al., 2013). Accordingly, it has been recommended not to apply StS in a pre-exercise warm-up routine, especially if strength-and power-related activities are performed subsequently (Magnusson and Renström, 2006;Garber et al., 2011;Simic et al., 2013). ...
    ... In addition, recent evidence suggests that when considered within a full warm-up routine, short-duration StS may even contribute to lower the risk of sustaining musculotendinous injuries (Small et al., 2008;Blazevich et al., 2018;Reid et al., 2018). In fact, Witvrouw et al. (2004) suggested that a sufficient level of MTU compliance is needed for sports conducted in the SSC to effectively store and release a high amount of elastic energy. In case of insufficient MTU compliance, the demands in energy absorption and release may rapidly exceed the capacity of the MTU, which may cause a higher risk of injuries (Witvrouw et al., 2004). ...
    Article
    Full-text available
    The effects of static-stretching (StS) on subsequent strength and power activities has been one of the most debated topics in sport science over the past decades. The aim of this review is i) to summarize previous and current findings on the acute effects of StS on muscle strength and power performances ii) to update readers’ knowledge related to previous caveats and iii) to discuss the underlying physiological mechanisms of short-duration StS when performed as single-mode treatment or when integrated into a full warm-up routine. Over the last two decades, StS has been considered harmful to subsequent strength and power performances. Accordingly, it has been recommended not to apply StS before strength and power-related activities. Recent evidence suggests that when performed as a single-mode treatment or when integrated within a full warm-up routine including aerobic activity, dynamic-stretching, and sport-specific-activities, short-duration StS (≤60s per-muscle group) trivially impairs subsequent strength and power activities (∆1-2%). Yet, longer-durations StS (>60s per-muscle group) appear to induce substantial and practically relevant declines in strength and power performances (∆4.0-7.5%). Moreover, recent evidence suggests that when included in a full warm-up routine, short-duration StS may even contribute to lower the risk of sustaining musculotendinous injuries especially with high-intensity activities (e.g., sprint running and change of direction speed). It seems that during short-duration StS, neuromuscular activation and musculotendinous stiffness appear not to be affected compared with long-duration StS. Amongst other factors, this could be due to an elevated muscle temperature induced by a dynamic warm-up program. More specifically, elevated muscle temperature leads to increased muscle fiber conduction-velocity and improved binding of contractile proteins (actin, myosin). Therefore, our previous understanding of harmful StS effects on subsequent strength and power activities have to be updated. In fact, short-duration StS should be included as an important warm-up component before the uptake of recreational sports activities due to its potential positive effect on flexibility and musculotendinous injury prevention. However, in high-performance athletes, short-duration StS has to be applied with caution due to its negligible but still prevalent negative effects on subsequent strength and power performances, which could have an impact on performance during competition.
  • ... These authors observed no negative effects of short-duration StS on power performance. Accordingly, and with reference to previous findings (Witvrouw et al., 2004;Woods et al., 2007;McHugh and Cosgrave, 2010;Behm et al., 2016) of small-to-moderate reductions in muscle injury rate in running-and change of direction-based sports, Blazevich et al. (2018) recommended the use of short-duration StS as an integral part of a pre-exercise warm-up routine that includes aerobic activity, dynamic activities, and sport-specific activities. Furthermore, participants in the Blazevich et al. (2018) study experienced positive psychological benefits expressing that they were more likely to perform well when stretching was performed as part of the warm-up, irrespective of the stretch type. ...
    ... The literature on StS has been subject to controversial debate over the past decades (Figure 1). The general belief that dominated the last two decades is that StS not only contributes to the prevention of injuries (Thacker et al., 2004;Witvrouw et al., 2004) but also impairs athletic performance (Pope et al., 2000;Shrier, 2004a,b;McHugh and Cosgrave, 2010;Simic et al., 2013). Accordingly, it has been recommended not to apply StS in a pre-exercise warm-up routine, especially if strength-and powerrelated activities are performed subsequently (Magnusson and Renström, 2006;Garber et al., 2011;Simic et al., 2013). ...
    ... In addition, recent evidence suggests that when considered within a full warm-up routine, short-duration StS may even contribute to lower the risk of sustaining musculotendinous injuries (Small et al., 2008;Blazevich et al., 2018;Reid et al., 2018). In fact, Witvrouw et al. (2004) suggested that a sufficient level of MTU compliance is needed for sports conducted in the SSC to effectively store and release a high amount of elastic energy. In case of insufficient MTU compliance, the demands in energy absorption and release may rapidly exceed the capacity of the MTU, which may cause a higher risk of injuries (Witvrouw et al., 2004). ...
    Article
    Full-text available
    The effects of static stretching (StS) on subsequent strength and power activities has been one of the most debated topics in sport science literature over the past decades. The aim of this review is (1) to summarize previous and current findings on the acute effects of StS on muscle strength and power performances; (2) to update readers’ knowledge related to previous caveats; and (3) to discuss the underlying physiological mechanisms of short-duration StS when performed as single-mode treatment or when integrated into a full warm-up routine. Over the last two decades, StS has been considered harmful to subsequent strength and power performances. Accordingly, it has been recommended not to apply StS before strength- and power-related activities. More recent evidence suggests that when performed as a single-mode treatment or when integrated within a full warm-up routine including aerobic activity, dynamic-stretching, and sport-specific activities, short-duration StS (≤60 s per muscle group) trivially impairs subsequent strength and power activities (∆1–2%). Yet, longer StS durations (>60 s per muscle group) appear to induce substantial and practically relevant declines in strength and power performances (∆4.0–7.5%). Moreover, recent evidence suggests that when included in a full warm-up routine, short-duration StS may even contribute to lower the risk of sustaining musculotendinous injuries especially with high-intensity activities (e.g., sprint running and change of direction speed). It seems that during short-duration StS, neuromuscular activation and musculotendinous stiffness appear not to be affected compared with long-duration StS. Among other factors, this could be due to an elevated muscle temperature induced by a dynamic warm-up program. More specifically, elevated muscle temperature leads to increased muscle fiber conduction-velocity and improved binding of contractile proteins (actin, myosin). Therefore, our previous understanding of harmful StS effects on subsequent strength and power activities has to be updated. In fact, short-duration StS should be included as an important warm-up component before the uptake of recreational sports activities due to its potential positive effect on flexibility and musculotendinous injury prevention. However, in high-performance athletes, short-duration StS has to be applied with caution due to its negligible but still prevalent negative effects on subsequent strength and power performances, which could have an impact on performance during competition.
  • ... Programas de treino que envolvem exercícios de alongamentos são amplamente utilizados pela população. A exemplo disso, praticantes de treinamento resistido e de outras modalidades esportivas adotam a prática de alongamentos visando uma preparação corporal para a prática do exercício, assim como um componente auxiliar na prevenção de lesões osteomusculares e também na melhora de aspectos relacionados a postura (ALMEIDA; JABUR, 2007;SHRIER, 1999;WITYROUW et al., 2004;YOUNG, 2007). ...
    Article
    Full-text available
    RESUMO O alongamento muscular é fundamental para manutenção ou melhora dos níveis de flexibilidade. Ao longo dos anos, com o efeito do envelhecimento, essa capacidade tende a ser prejudicada. A prática regular de exercícios físicos pode proporcionar uma redução desses prejuízos, assim como também beneficiar outras capacidades físicas, como a força muscular. Contudo, a união dessas duas capacidades, principalmente em uma mesma sessão de treino, é questionada na literatura, tendo em vista que o alongamento precedendo o treinamento de força pode oferecer prejuízos no rendimento. O objetivo desse estudo foi analisar a influência aguda dos alongamentos estáticos e dinâmicos sobre a produção de força muscular máxima de homens treinados. Participaram da pesquisa 12 indivíduos do sexo masculino, maiores de 18 anos e com experiência mínima de 6 meses em treinamento resistido. Todos os indivíduos foram submetidos a três condições: sem alongamento (AS), alongamento estático (AE) e alongamento dinâmico (AD). Posteriormente ao protocolo de alongamento, os indivíduos foram submetidos aos exercícios supino reto e leg press 45º para avaliar a força muscular máxima a partir do teste de 1 RM. O intervalo entre cada um dos protocolos de teste foi de 48 horas. Utilizou-se o teste ANOVA de medidas repetidas para comparar os protocolos. Não foi encontrada diferença estatística na carga média nas três situações, assim como na comparação de pares, baseada em médias estimadas de 1RM. Conclui-se que a prática prévia de alongamento estático, dinâmico, ou sem alongamento, não influem na produção de força máxima em adultos praticantes recreacionais de treinamento resistido. Palavras-chave: Alongamento estático. Alongamento dinâmico. Força máxima. ABSTRACT The muscle stretching is essential to maintaining or improving levels of flexibility. Over the years, with the effect of aging, that capacity, tends to be impaired. The regular practice of physical exercises can provide a reduction of these losses, as well as benefit from other physical capacities, as muscular strength. However, the Union of these two capacities, mostly in the same workout, is questioned in the literature, since the stretching preceding strength training can offer income losses. The aim of this study was to analyze the acute influence of dynamic and static stretching on the production of maximum muscle strength in trained men. Participated in the research, 12 male individuals, older than 18 years old, and with 6 months of minimum experience in resistance training. All individuals were exposed to three conditions: no stretching (NO), static stretching (SS) and dynamic stretching (DS). After the stretching protocol, individuals were subjected to exercises bench press and leg press 45° to evaluate maximum muscle strength from a 1 MR. The interval between each protocol test was 48 hours. We used the repeated measures ANOVA test to compare the protocols. No statistical difference was found in load average in three situations, as well as in the comparison of pairs, based on estimated average 1MR. It appears that the prior practice of dynamics, static, or the lack of stretching, do not influence the maximum force production in adult recreational practitioners of resistance training.
  • ... It is generally agreed, however, that sports with highintensity stretch-shortening cycles require a high storage capacity for potential energy and therefore need more compliant muscle-tendon units. 10 More compliant muscle-tendon units are better equipped for the rapid transfer of maximal energy during physical activity and are less likely to injure from forces applied. As CrossFit is considered a high-intensity and fast-paced workout, the need for optimally compliant muscletendon units cannot be overstated. ...
    Article
    Full-text available
    Background CrossFit is an increasingly popular, rapidly growing exercise regimen. Few studies have evaluated CrossFit-associated musculoskeletal injuries on a large scale. This study explores such injuries and associated risk factors in detail. Objective To identify the most common musculoskeletal injuries endured during CrossFit training among athletes at different levels of expertise. Design Survey-based retrospective cross-sectional study. Setting Distribution at CrossFit gyms in the United States and internationally. Also published on active online forums. Participants A total of 885 former and current CrossFit athletes. Methods Institutional review board-approved 33-question Web-based survey focused on CrossFit injuries and associated risk factors. Survey submissions were accepted for a period of 6 months. Main outcome measurements Specific injuries with associated workouts, risk factors that affected injury including (1) basic demographics, (2) regional differences in reported injuries, (3) training intensity, and (4) expertise level at time of injury. Results Of the 885 respondents, 295 (33.3%) were injured. The most common injuries involved the back (95/295, 32.2%) and shoulder (61/295, 20.7%). The most common exercises that caused injury were squats (65/295, 22.0%) and deadlifts (53/295, 18.0%). Advanced-level (64/295, 21.7%) athletes were more significantly injured than beginner-level (40/295, 13.6%) athletes. International participants were 2.2 times more likely than domestic US participants to suffer injury. Individuals with 3+ years of CrossFit experience were 3.3 times more likely to be injured than those with 2 or less years of experience. Participants who trained for 11+ h/week were significantly more likely to be injured than those who trained less than or equal to 10 h/week. Conclusions As CrossFit becomes more popular, it is important to monitor the safety of its practitioners. Further studies are needed to explore how to lower this injury prevalence of 33.3%. Areas to focus on include factors that have caused the regional (international vs US states) differences, level of expertise/experience differences (advanced level vs intermediate and beginner levels), and stretching routine modifications.
  • ... Witvrouw et al. [36] stated that pain tends to be increased by direct stretching application, and the results of this study suggest that the PNF irradiation method can be used to safely stretch the hamstring muscle instead of the direct stretching method. ...
  • ... Joint flexibility is also an important component to consider. Joint range of motion (ROM), as well as the resistance to stretching (i.e., muscle and tendon stiffness) are important physical characteristics that influence the capacity to perform athletic tasks and can be associated with muscle strain injury risk, especially in high-intensity activities that involve many stretch-shortening cycles ( Witvrouw et al., 2004;Watsford et al., 2010). ...
    Article
    Full-text available
    Background Foam roller and vibration techniques are currently used to assist in recovery after fatigue. The main purpose of this study was to determine the effects of the use of a foam roller with and without vibration on dynamic balance, ankle dorsiflexion, hamstring and lumbar spine flexibility and perceived knee and ankle stability after an induced fatigue protocol. Methods A total of 24 healthy recreationally active participants (17 males and seven females) were recruited to a randomized cross over trial consisting of; no treatment (NT), foam roller treatment (FR) and vibration foam roller treatment (VFR). The assessments included; the Sit & Reach test, Y balance test and post-treatment perceived knee and ankle stability. Measurements were taken after a standardized warm up (baseline) and repeated following an exercise-induced muscle fatigue protocol consisting of repeated lunges until volitional fatigue. The three treatment conditions were assessed on three separate days in a randomized order. A 3 × 3 repeated measures ANOVA was used to investigate differences between the three treatments over the three time points and a one factor repeated measures ANOVA was used to determine any differences between treatments using the Global Rate of Change scale when considering perceived stability. Results FR and VFR conditions both showed a greater ankle dorsiflexion range of motion (ROM) ( p < 0.001), greater posteromedial and posterolateral reach distances ( p < 0.001) and a better knee and ankle perceived stability ( p < 0.001) when compared to the NT condition. A trend toward significance was observed in the hamstring and lumbar spine flexibility ( p = 0.074) in both treatment conditions when compared to the NT condition. However, no differences were seen between the FR and VFR conditions. Conclusions Both FR conditions seem to assist in exercise-induced muscle fatigue recovery with improvements in ROM, balance and perceived stability.
  • ... D'autre part, il est depuis longtemps accepté dans l'inconscient collectif que les étirements peuvent diminuer le risque de blessures liées à l'activité physique (Witvrouw et al. 2004). Bien que quelques études aient mis en doute l'utilité des étirements pour la prévention des blessures (Thacker et al. 2004;Lauersen et al. 2014), certains auteurs ont montré une relation entre un manque de flexibilité et un nombre de blessures plus important (Jones et Knapik 1999 Ces neurones sont répartis au niveau de l'aire M1 selon une cartographie de la musculature striée squelettique, mise en évidence par Penfield (Penfield et Jasper 1954). ...
    Thesis
    Dans un contexte de performance sportive, de réhabilitation ou de santé, les étirements sont couramment utilisés dans le but de préparer le système neuromusculaire à l’exercice subséquent. Si la littérature montre majoritairement que les étirements altèrent de façon aigue la performance musculaire et/ou fonctionnelle, il existe toutefois des études dont les résultats diffèrent, suggérant l’influence d’un certain nombre de facteurs sur la variabilité des réponses du système neuromusculaire. Pour une meilleure compréhension de cette variabilité et des mécanismes impliqués, cette thèse avait pour objectif d’examiner l’influence de différents paramètres sur le système neuromusculaire : la durée d’étirement, le groupe musculaire et la modalité d’étirement. Au travers de quatre études, il a été montré que les étirements statiques pouvaient altérer la production de force maximale et les propriétés neuromusculaires indépendamment de la durée d’étirement. Cependant, il est apparu que ces modulations étaient spécifiques au muscle, et plus précisément à la raideur relative du système musculo-tendineux. Indépendamment de la durée d’étirement, les étirements statiques ne seraient pas efficaces pour préparer le système neuromusculaire à une activité musculaire subséquente, et notamment pour des muscles raides. Plus particulièrement, les étirements dynamiques ne paraissent pas plus efficaces. Même si les effets néfastes ont été diminués comparativement aux étirements statiques, ils ne favoriseraient pas davantage la production de force ni la commande nerveuse. Toutefois, il est intéressant de noter qu’une durée courte d’étirements dynamiques peut réduire la résistance passive à l’étirement, et donc augmenter potentiellement l’amplitude articulaire maximale, sans affecter les capacités de production de force. Finalement, les étirements dynamiques pourraient être envisagés comme une activité musculaire dynamique, qui compense partiellement les effets néfastes de l’étirement sur la performance musculaire. D’un point de vue pratique, ceci suggère que ce type d’étirements peut être réalisé avant une performance, mais néanmoins accompagnés d’une activité musculaire de plus haute intensité, afin d’optimiser les effets de l’échauffement musculaire sur le système neuromusculaire. En définitive, la variabilité des réponses du système neuromusculaire serait dépendante de facteurs spécifiques, tels que la modalité d’étirement et la raideur relative du système musculo-tendineux, soulignant l’importance de les prendre en considération dans la pratique.
  • ... Respecto a esta última idea, a pesar de que los deportistas tienen la creencia de que estirar es una mecanismo de prevención, no ha sido posible establecer una vinculación consistente entre ambas variables (Weldon & Hill, 2003). Existen estudios que no han observado efectos sobre la prevención de lesiones a partir de la inclusión de ejercicios de estiramientos (Pope, Herbert, Kirwan, & Graham, 2000), mientras que otros han indicado un posible efecto positivo entre ambas variables (Witvrouw, Mahieu, Danneels, & Mcnair, 2004). ...
    Article
    La capacidad de rendimiento en deportes de equipo se ha incrementado en los últimos años. Para afrontar esta realidad el participante de estas disciplinas no sólo debe ser entrenado con éxito, sino también preparado para expresar su potencial rendimiento en competición. El calentamiento previo al partido es la práctica que permite la transición óptima del estado de reposo al de máxima actividad de forma segura y eficaz. Esta estrategia tiene beneficios para el rendimiento y la prevención de lesiones debido a una serie de respuestas fisiológicas. Entre estos cambios destacan el incremento de la temperatura y modificaciones neuromusculares. Para conseguirlo es necesario ajustar los contenidos y la carga dentro de una estructura que responda de manera específica a las demandas de estos deportes. En la actualidad se piensa que en esta estructura es necesario dejar lugar para la inclusión de estrategias de post-activación potenciación. Los entrenadores y preparadores físicos deben hacer el esfuerzo por regularizar estos estímulos dentro del calentamiento, sin perder el sentido técnico-táctico que debe estar presente para conseguir una activación completa y significativa del rendimiento.
  • Article
    Limited information is available on whether stiffness is different within and between the constituents of the hamstring, i.e., the biceps femoris long head (BFlh), semitendinosus (ST), and semimembranosus (SM). Therefore, understanding of hamstring injuries and stretching effect on hamstring stiffness is difficult. The present study primarily aimed to identify whether passive muscle stiffness differs between the BFlh, ST, and SM, and between the proximal, middle, and distal sites within each muscle. Secondly, the effect of stretching exercise on the heterogeneity in passive muscle stiffness was examined. In the lengthened hamstring positions by extending the knee joint or flexing the hip joint, passive muscle shear modulus (a measure of stiffness) at the proximal, middle, and distal sites of the BFlh, ST, and SM was measured by using ultrasound shear wave elastography. Furthermore, before and after five repetitions of 90‐s static stretching for the hamstring, passive muscle shear modulus at the proximal and distal sites of the SM was measured. The shear modulus was significantly higher in the SM than in the BFlh and ST and higher at the distal site than the proximal site in all muscles. After the stretching, the higher shear modulus at the distal site of the SM compared to the proximal site was still observed (pre‐stretching: +80%, post‐stretching: +81%). These findings indicate that passive muscle stiffness varies within the hamstring regardless of performing stretching exercise and that passive muscle stiffness is not highest at the proximal site of the SM where a stretching‐type hamstring strain typically occurs.
  • Article
    Full-text available
    En las últimas décadas ha aumentado el número de participantes en carreras populares de resistencia, sobre todo, de atletas veteranos. El objetivo de este estudio es determinar las características sociodemográficas del atleta veterano en relación a variables personales, de entrenamiento y lesión. Se elaboró un cuestionario ad hoc con estas variables. El perfil del corredor veterano es un varón en torno a los 40 años, con estudios universitarios, que trabaja y vive en pareja, que entrena 4 días a la semana y recorre sobre 50 kilómetros semanales. Se destaca la alta prevalencia de lesiones en esta población y el único factor que predispone a la lesión es el número de sesiones semanales de entrenamiento.
Literature Review
  • Article
    Summary Muscle force, electromyogram and length were monitored in the medial head of the gastrocnemius (MG) muscle in freely hopping wallabies (Thylogale billardierii Desmarest). During take-off hops from rest, MG muscle developed force with an isometric contraction. For constant-speed hops, force was produced in MG muscle during rapid stretch. The muscle resisted this stretch with a constant impedance that was independent of hopping speed. The rate of stretch of the muscle during high-speed hopping was as high as lms" 1 (5-6 muscle lengths per second) at the onset of stretch and slowed to no stretch at the peak of force. Since the mechanical impedance was constant while the stretch velocity changed, there was no significant viscosity present in the muscle. The tendon stretched by 3-2% at 7kmh -1 hopping and by 4-4% at lSkmh"1 hopping. Elastic energy storage in the tendons increased with hopping speed but the percentage of total work done by elastic recoil of the whole muscle did not increase at higher hopping speeds. The significance of the muscle stretch is in producing high forces rapidly and, in addition, there is considerable energy storage in the tendons.
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    Summary Force recordings of the pectoralis muscle of European starlings have been made in vivo during level flight in a wind tunnel, based on bone strain recordings at the muscle's attachment site on the humerus (deltopectoral crest). This represents the first direct measurement of muscle force during activity in a live animal based on calibrated bone strain recordings. Our force measurements confirm earlier electromyographic data and show that the pectoralis begins to develop force during the final one-third of the upstroke, reaches a maximal level halfway through the downstroke, and sustains force throughout the downstroke. Peak forces generated by the pectoralis during level flight at a speed estimated to be L3.7ms~' averaged 6.4N (28% of maximal isometric force), generating a mean mass-specific muscle power output of 104 W kg"1. Combining our data for the power output of the pectoralis muscle with data for the metabolic power of starlings flying at a similar speed yields an overall flight efficiency of 13 %. The force recordings and length changes of the muscle, based on angular displace- ments of the humerus, indicate that the pectoralis muscle undergoes a lengthening-shortening contraction sequence during its activation and that, in addition to lift and thrust generation, overcoming wing inertia is probably an important function of this muscle in flapping flight.
  • Article
    This target article addresses the role of storage and reutilization of elastic energy in stretch-shortening cycles. It is argued that for discrete movements such as the vertical jump, elastic energy does not explain the work enhancement due to the prestretch. This enhancement seems to occur because the prestretch allows muscles to develop a high level of active state and force before starting to shorten. For cyclic movements in which stretch- shortening cycles occur repetitively, some authors have claimed that elastic energy enhances mechanical efficiency. In the current article it is demonstrated that this claim is often based on disputable concepts such as the efficiency of positive work or absolute work, and it is argued that elastic energy cannot affect mechanical efficiency simply because this energy is not related to the conversion of metabolic energy into mechanical energy. A comparison of work and efficiency measures obtained at different levels of organization reveals that there is in fact no decisive evidence to either support or reject the claim that the stretch- shortening cycle enhances muscle efficiency. These explorations lead to the conclusion that the body of knowledge about the mechanisms and energetics of the stretch-shortening cycle is in fact quite lean. A major challenge is to bridge the gap between knowledge obtained at different levels of organization, with the ultimate purpose of understanding how the intrinsic properties of muscles manifest themselves under in-vivo-like conditions and how they are exploited in whole-body activities such as running. To achieve this purpose, a close cooperation is required between muscle physiologists and human movement scientists performing inverse and forward dynamic simulation studies of whole-body exercises.
  • Article
    The effects of movement amplitude and contraction intensity on triceps surae and quadriceps femoris muscle function were studied during repetitive hopping. In vivo forces from Achilles and patellar tendons were recorded with the optic fibre technique from eight volunteers. The performances were filmed (200Hz) to determine changes in muscle-tendon unit length and velocity. When hopping with a small amplitude (23° knee flexion during the ground contact phase), the Achilles tendon was primarily loaded whereas patellar tendon forces were greater in large-amplitude hopping (56° knee flexion). In spite of the different magnitudes of stretch in the quadriceps femoris muscle, the stretching velocity and activity patterns of the quadriceps muscle were similar in both conditions. Simultaneously performed electromyographic (EMG) recordings revealed that preferential preactivation of the gastrocnemius muscle was evident in both jumping conditions. The triceps surae muscle was strongly active in the eccentric phase of small-amplitude hopping. Results from hopping with small knee-joint displacement suggest that there may be a particular frequency and jumping height at which the elastic bouncing is best utilized and at the same time the concentric phase is most economical. Results also support earlier observations that the economy of the shortening phase must be compromised at some point in order to produce more power and improve the jumping height.
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    Sixteen experienced male powerlifters served as subjects in a training study designed to examine the effect of flexibility training on: (i) the stiffness of the series elastic components (SEC) of the upper body musculature and (ii) rebound and purely concentric bench press performance. Nine of the subjects participated in two sessions of flexibility training twice per week for 8 wk. Prior to and after the training period the subjects' static flexibility, SEC stiffness, rebound bench press (RBP), and purely concentric bench press (PCBP) performance were recorded. The flexibility training induced a significant reduction in the maximal stiffness of the SEC. Furthermore, the experimental subjects produced significantly more work during the initial concentric portion of the RBP lift, enabling a significantly greater load to be lifted in the post-training testing occasion. The benefits to performance achieved by the experimental group consequent to flexibility training were greater during the RBP lift as compared with the PCBP lift. The control subjects exhibited no change in any variable over the training period. These results implied that the RBP performance enhancement observed consequent to flexibility training was directly caused by a reduction in SEC stiffness, increasing the utilization of elastic strain energy during the RBP lift.
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    Twelve experienced male weight lifters performed a rebound bench press and a purely concentric bench press lift. Data were obtained pertaining to 1) the benefits to concentric motion derived from a prior stretch and 2) the movement frequency adopted during performance of the stretch-shorten cycle (SSC) portion of the rebound bench press lift. The subjects also performed a series of quasi-static muscular actions in a position specific to the bench press movement. A brief perturbation was applied to the bar while these isometric efforts were maintained, and the resulting damped oscillations provided data pertaining to each subject's series elastic component (SEC) stiffness and natural frequency of oscillation. A significant correlation (r = -0.718, P less than 0.01) between maximal SEC stiffness and augmentation to concentric motion derived from prior stretch was observed. Subjects were also observed to perform the SSC portion of the rebound bench press movement to coincide with the natural frequency of oscillation of their SEC. These results are interpreted as demonstrating that the optimal stiffness in a rebound bench press lift was a resonant-compliant SEC.
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