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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.
Sports Med 2004; 34 (7): 443-449
R
EVIEW
A
RTICLE
0112-1642/04/0007-0443/$31.00/0
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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E-mail: Erik.Witvrouw@UGent.be
2004 Adis Data Information BV. All rights reserved. Sports Med 2004; 34 (7)
... Consiste en la supervisión médica previa a la práctica deportiva, la cual busca detectar lesiones, enfermedades o factores que pongan en riesgo al atleta con el fin de optimizar su rendimiento y promover un ambiente seguro de competición 64 . Los objetivos específicos de la valoración pre-participativa son 65 : ...
... La muerte súbita cardiaca asociada al deporte se define como un evento fatal que acontece de forma natural e inesperada durante la práctica deportiva o en un intervalo de menos de 1 hora de iniciado los síntomas (e.g., dolor torácico, síncope, paro cardiorrespiratorio) en alguien aparentemente sano, aunque algunos investigadores han propuesto un intervalo de hasta 24 horas post ejercicio. Se ha reportado que la etiología cardiaca es la principal causa de muerte súbita en atletas con una incidencia estimada de 1 a 3 por 100.000 64 . Por lo general se describen que las causas de muerte súbita cardiaca en menores de 35 años se relacionan a patología congénita y en mayores de 35 años a coronariopatías secundarias a ateromatosis. ...
... De esta forma, si los sujetos que practican estos deportes tienen una deficiente extensibilidad de la unidad músculo-tendinosa compatible con las demandas de absorción y liberación de energía, estas pueden exceder rápidamente la capacidad de la unidad músculo-tendinosa, conduciendo a un mayor riesgo de lesión de la estructura. En consecuencia, la justificación en la prevención de lesiones en este tipo deportes, consiste en mejorar la compliance de la unidad músculo-tendinosa 64 . De la misma manera, algunos estudios han demostrado que los programas de estiramiento, en búsqueda de mejorar la flexibilidad, pueden influir en la viscosidad del tendón y hacerlo significativamente más extensible de manera que en aquellos deportes que demandan ciclos de estiramiento-acortamiento de alta intensidad, un mayor estiramiento puede ser importante en la prevención de lesiones. ...
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Libro que describe el qué, el cómo y el por qué se hace lo que se hace en relación a las Ciencias Aplicadas al Deporte en el Deporte de Alto Rendimiento en Chile. Estas ciencias apoyan el proceso de preparación y competencia de los atletas chilenos, con el propósito de mejorar el rendimiento deportivo a nivel internacional.
... Traditionally, stretching was purported to increase ROM and consequently decrease injury incidence (3,38). However, there is a lack of consistent evidence for this effect on injuries (1)(2)(3)(4)(5), which may be linked to the type of injuries reported in many studies. ...
... Furthermore, Azuma and Someya (46) incorporated a 12-week stretching program with male high school soccer players, finding an improved ROM and a decrease in muscle tightness, which they indicated may have contributed to the reduction in noncontact lower limb and trunk injuries as well as muscle and tendon injuries after training. Based on this evidence, while stretching may not consistently attenuate all-cause injury risk, a small-moderate positive effect of chronic SS on MTU injury risk in running-and jump-based sports is observed (38,47). ...
Article
Evidence for the effectiveness of acute and chronic stretching for improving range of motion is extensive. Improved flexibility can positively impact performances in activities of daily living and both physical and mental health. However, less is known about the effects of stretching on other aspects of health such as injury incidence and balance. The objective of this review is to examine the existing literature in these areas. The review highlights that both pre-exercise and chronic stretching can reduce musculotendinous injury incidence, particularly in running-based sports, which may be related to the increased force available at longer muscle lengths (altered force-length relationship) or reduced active musculotendinous stiffness, among other factors. Evidence regarding the acute effects of stretching on balance is equivocal. Longer-term stretch training can improve balance, which may contribute to a decreased incidence of falls and associated injuries and may thus be recommended as an important exercise modality in those with balance deficits. Hence, both acute and chronic stretching seem to have positive effects on injury incidence and balance, but optimum training plans are yet to be defined.
... Studies have indicated that preparticipation stretching improves range of motion and muscle compliancy, which may be protective against muscle strain 77 . Although stretching promotes muscle performance in elastic movements such as hops or leaps, it is associated with decreased muscle power in predominantly concentric contractions such as steadystate cycling or jogging 77,78 . For this rea-son, the benefits of stretching alone are unclear. ...
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» Calf strain is a common condition. In high-performance athletes, calf strain contributes to a substantial absence from competition. » Player age and history of a calf strain or other leg injury are the strongest risk factors for calf strain injury and reinjury. » Although the diagnosis is often clinical, magnetic resonance imaging and ultrasound are valuable to confirm the location of the strain and the grade of injury. » Nonoperative treatment is effective for most calf strain injuries. Operative management, although rarely indicated, may be appropriate for severe cases with grade-III rupture or complications. » Further investigation is necessary to elucidate the benefits of blood flow restriction therapy, deep water running, lower-body positive pressure therapy, platelet-rich plasma, and stem cell therapy for calf strain rehabilitation.
... Regular physical activities and exercise provide protection against many cardiovascular and lifestyle associated diseases, improve flexibility, and enhance the overall performance as well. despite the rewards that physical activity and exercise bring, for the aging population, the compliance with this activity is quite low (Witvrouw et al 2004(Witvrouw et al , boulton et. al. 2018(Witvrouw et al , dazau et al 2019. ...
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Active lifestyle is important for all age groups, especially essential among older adults to counter balance the deleterious effects of aging. Scientific literature is scarce about the effect of Proprioceptive Neuromuscular Facilitatio (PNF) stretching on older adults. Therefore, the purpose of this study is to find out the effect of self-administered CRAC stretching on the performance of hamstring curls to fatigue in older adults. We used the same subject repeated measure experimental crossover design, where subjects were randomly allocated into two groups and both the groups were given the Self-Administered CRAC stretching in alternate session to overcome the order effect. The result of this present study demonstrated that there was a significant between-group effect (t =-2.06, p=0.0484) seen. The participants getting CRAC stretching performed 37% and 44% less hamstring curls to fatigue in the respective sessions. In summary, our primary findings indicated enhanced flexibility with an accompanying decrease in the number of hamstring curls performance in response to self-administered CRAC stretching. These findings are unique in that, to our knowledge, no other authors have examined the effects of CRAC stretching on isolated muscle performance with a repeated measures design. Regarding the mechanisms underlying the stretching-induced performance deficit, the decreases in no of hamstring curls we observed in our study tentatively support the hypothesis that stretching may alter the length-tension relationship and the hypothesis that stretching may reduce muscle activation, respectively. CRAC stretching can be made part of a full warm-up routine because of its positive impact on flexibility and musculotendinous injury occurrence in the physically active older population.
... On the other hand, in addition to the contribution of flexibility to sportive performance, it can decrease the frequency of sportive injuries. It has been known that athletes who have higher levels of flexibility levels have less sportive injury risk (Witvrouw et al., 2004). Notwithstanding, bodybuilders were observed to ignore workouts that can enhance range of motion (Barlow et al., 2002). ...
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Bodybuilding is one of the physical activity types which is popular in our country like all over the world. However; the people who are dealing with bodybuilding apply a one-way training program for hypertrophy and it is well known that they disregard cardiovascular exercises that are important in the sense of either increase in performance, or for a healthy life. This study was aimed to assess recreational bodybuilders, from the American College of Sports and Medicine's standpoints. 22 Male athletes (age 19- 42) participated in the study (height 176.9±5.78 cm, weight 80.81±6.44 kg, bodybuilding experience 3 years). The maximal aerobic power levels of participants were measured with Queen College Step Test, flexibilities were measured with trunk flexion test, and back and leg strengths were determined with an isometric dynamometer. Skinfolds were measured with a caliper (Holtain) and Durnin and Womersley Formula was used in measuring body fat percentage, Demographic features and data on the training schedules of participants were obtained from the data collection form which was prepared by researchers. Participants were determined to have, 25.82± 1.7 kg/m2 Body Mass Index of participants (BMI) ) , 51.07 ± 8.02 ml/kg/min maximal aerobic power, 11.48±6.12 cm trunk flexions, 123.59±29.49 kg leg strength, 124.09±26.40 kg back strength, 53,83±7,82 right hand-grip and 13.32±2.80 % body fat percentages 4 Body Mass Index, maximal aerobic power, levels, and body fat percentage of participants were assessed as normal according to ACSM's norms, and their flexibility and strength levels were assessed as low. It was understood that recreational bodybuilders should add flexibility and maximal strength training to their routine training programs. Repeating this study with more samples, measuring strength with 1RM snatch and jerk tests will be more useful for further researches.
... On the other hand, in addition to the contribution of flexibility to sportive performance, it can decrease the frequency of sportive injuries. It has been known that athletes who have higher levels of flexibility levels have less sportive injury risk (Witvrouw et al., 2004). Notwithstanding, bodybuilders were observed to ignore workouts that can enhance range of motion (Barlow et al., 2002). ...
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In this book it was aimed to assess recreational bodybuilders' physical fitness levels by the American College of Sports and Medicine's (ACSM) standpoints.
... For instance, static and ballistic stretching techniques have also been used acutely during pre-exercise routines as a mean to further maximize flexibility 2,9,10 . However, there is no strong evidence to indicate a protective effect of stretching on injury incidence 2,11,12 . Previous observations reported that stretching exercises may induce acute improvement in flexibility and hence might be recommended before athletic events or physical activities that require a large range of motion 14 . ...
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Pre-exercises interventions are frequently implemented in order to maximize athletic performance. In this sense, the aim of this study was to evaluated the effect of three distinct pre-exercise interventions on acute neuromuscular performance in recreational soccer players: 1) parallel squat; 2) static stretching; and 3) ballistic stretching. After all interventions, participants performed a flexibility evaluation (sit-and-reach-test), followed by a squat jump, a counter-movement jump and a 30 meter-sprint test. A one-way analysis of variance revealed: a) a significant decrease in jumping performance was induced by both Stretching conditions when compared to the parallel squat intervention; b) a significant increase in lower limb flexibility after both stretching interventions when compared to parallel squat. In conclusion, it is suggested that a pre-exercise intervention comprised of stretching exercises can acutely increase flexibility, while impairing jump performance in recreational athletes.
... The biological or physiological and psychological characteristics of a person like age, joint mobility, functional stability, biomechanical and anatomical characteristics, previous injuries and inadequate rehabilitation after injury are affected by direct contact are considered as internal factors of injury. In the development of lower limb muscle injuries the most commonly associated risk factor is nonexistence of muscle flexibility (Witvrouw et al. 2001;Witvrouw et al. 2004). ...
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The purpose of the present study was to examine the association between static stretching load and changes in the flexibility of the hamstrings. Twelve healthy men received static stretching for 60 s at two different intensities based on the point of discomfort (100%POD and 120%POD intensity), in random order. To assess the flexibility of the hamstrings, the knee extension range of motion (ROM). Passive torque at end ROM, and muscle–tendon unit stiffness were measured before and after stretching. The static stretching load was calculated from the passive torque throughout static stretching. The knee extension ROM and passive torque at end ROM increased in both intensities (p < 0.01). The muscle–tendon unit stiffness decreased only in the 120%POD (p < 0.01). There were significant correlations between the static stretching load and the relative changes in the knee extension ROM (r = 0.56, p < 0.01) and muscle–tendon unit stiffness (r = − 0.76, p < 0.01). The results suggested that the static stretching load had significant effects on changes in the knee extension ROM and muscle–tendon unit stiffness of the hamstrings, and high-intensity static stretching was useful for improving the flexibility of the hamstrings because of its high static stretching load.
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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.
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An efficient preparation method, which provides wedge‐shaped cross‐section transmission electron microscopy samples, has been developed. It was then used to investigate the structure of as‐deposited cobalt multilayers on silicon substrates by rf plasma sputtering. It was found that an extended reaction takes place between Co and Si probably during the deposition. The cobalt atoms react with the silicon substrate to form an amorphous silicide layer. When the deposited layer is ≪3 nm thick, it entirely reacts with the substrate and can form an amorphous silicide as large as 5 nm. Above 4–5 nm thickness, growth of Co crystallites comes in competition with the formation of the amorphous silicide and limits it to 2 nm. The composition of this amorphous silicide is estimated to be Co 2 Si. In Co/C multilayers, the reactivity between the two materials is negligible, and the coalescence thickness of cobalt is 2–3 nm. At 2 nm, the cobalt layers are noncontinuous and very rough, whereas at 3 nm the critical thickness for crystalline nuclei coalescence has already been reached. The cobalt layers are then polycrystalline and have a reasonable roughness.
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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.
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.
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.
Article
There are 300,000 to 1,215,000 high-school football injuries each year in the United States. These injuries have an important effect on player participation and health care costs. This study investigates what portion of injuries occur during the third quarter of a game, and if completing a warm-up and stretching routine after halftime reduces the incidence of third-quarter injuries. Intervention-group teams participated in a prescribed three-minute warm-up and stretching routine following the halftime break. The control group received no warm-up and stretching intervention. Fifty-five games with 108 total injuries were examined. Overall, ligament sprains and muscle strains were the most common type of injury (38%). In the nonintervention group, injuries occurred most often in the third quarter. Intervention teams sustained significantly fewer third-quarter sprains and strains per game (p less than 0.05), although no significant difference in total third-quarter injuries was noted. These findings suggest an association between post-halftime warm-up and stretching and reduced third-quarter sprain and strain injuries. We suggest a larger-scale, randomized confirmatory study.
Article
We investigated the possibility that tendons that normally experience relatively high stresses and function as springs during locomotion, such as digital flexors, might develop different mechanical properties from those that experience only relatively low stresses, such as digital extensors. At birth the digital flexor and extensor tendons of pigs have identical mechanical properties, exhibiting higher extensibility and mechanical hysteresis and lower elastic modulus, tensile strength, and elastic energy storage capability than adult tendons. With growth and aging these tendons become much stronger, stiffer, less extensible, and more resilient than at birth. Furthermore, these alterations in elastic properties occur to a significantly greater degree in the high-load-bearing flexors than in the low-stress extensors. At maturity the pig digital flexor tendons have twice the tensile strength and elastic modulus but only half the strain energy dissipation of the corresponding extensor tendons. A morphometric analysis of the digital muscles provides an estimate of maximal in vivo tendon stresses and suggests that the muscle-tendon unit of the digital flexor is designed to function as an elastic energy storage element whereas that of the digital extensor is not. Thus the differences in material properties between mature flexor and extensor tendons are correlated with their physiological functions, i.e., the flexor is much better suited to act as an effective biological spring than is the extensor.