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Stretching and injury prevention - An obscure relationship



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
2004 Adis Data Information BV. All rights reserved.
Stretching and Injury Prevention
An Obscure Relationship
Erik Witvrouw,1 Nele Mahieu,1 Lieven Danneels1 and Peter McNair2
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
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
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muscle damage. Am J Sports Med 1999; 27: 594-9 E-mail:
2004 Adis Data Information BV. All rights reserved. Sports Med 2004; 34 (7)
... 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. ...
... En un sistema con una buena compliance, cuando los elementos contráctiles se encuentran activos a una alta intensidad, una mayor energía puede ser absorbida por el tendón, reduciendo una transmisión del trauma a la fibra muscular. Por contrapartida, cuando existe una pobre compliance, el tendón no es capaz de absorber demasiada energía, lo que se traduce en una transmisión de las fuerzas al músculo 64 . Esto es concordante con algunos estudios que han asociado un incremento del stiffness con una mayor incidencia de daño muscular post ejercicios de tipo excéntrico 66 . ...
... Específicamente, se ha sugerido que tener una flexibilidad insuficiente de los músculos aductores de la cadera (principalmente los biarticulares), generará una mayor tensión a nivel de la zona púbica durante todas aquellas acciones deportivas que son realizadas de manera enérgica con soporte de peso, aumentando la probabilidad de sufrir una lesión crónica en la zona inguinal. Se ha mostrado que una disminución del movimiento de la cadera puede constituir una factor condicionante para la aparición de tensión de la musculatura aductora en jugadores de fútbol profesionales masculinos 90 repentinos y que tienen flexibilidad insuficiente en los músculos aductores de la cadera (músculos biarticulares y mono articulares, están más propensos a sufrir una distención muscular ya que las demandas de absorción de energía pueden rápidamente exceder las capacidades de la musculatura aductora 64,91 . Considerando que la musculatura aductora de cadera presenta componentes biarticulares y mono articulares, la manera más habitual de valorarla es mediante una abducción de cadera (pasiva o activa), con rodilla en extensión o con rodilla en flexión de 90°, para realizar la diferenciación de ambos componentes musculares. ...
... Da Muskeln und Sehnen als Einheit agieren und fließend ineinander übergehen, wird meist von Muskelsehnenverletzungen gesprochen. Von Witvrouw et al. [11] werden Untersuchungen angeführt, die zeigten, dass sich die Viskoelastizität von Sehnen sowohl kurzfristig als auch langfristig durch Dehnen verändern lässt und die Sehnen geschmeidiger werden. ...
... In der Kontrollgruppe gab es zwar signifikant mehr Verletzungen als in der Dehngruppe, aber es wurde nicht zwischen den verschiedenen Verletzungsarten unterschieden. Ob die Reduzierung der Muskelsehnenverletzungen durch kurzfristige Effekte (Vergrößerung der Bewegungsreichweite, Reduzierung der Ruhespannung, Veränderungen der Viskoelastizität [11]) verursacht wurde oder durch eine Kombination mit langfristigen Effekten, lässt sich nicht klären. Hier wären andere Versuchsdesigns nötig [33]. ...
On the effect of stretching as injury prevention - an analysis with special regard to the risk of injury in various sporting activities Abstract Musculotendinous injuries account for a high proportion of all injuries, especially in high-speed strength sports. Both warm-up and regular stretching are expected to reduce musculotendinous injuries. An indication of the extent of reduction is given either as a percentage or as a recommendation of how many years of stretching is needed to avoid musculotendinous injuries. The figures show a wide range (5 - 54%, 5 - 23 years). This article explains how these different figures come about and how they should be interpreted. The different risk of injury in various sports activities and the variation in the volume of training (hours per year) are of particular importance. Twelve primary studies were mainly considered in the corresponding meta-analyses of the last few years. The meta-analyses include different primary studies. Four primary studies in particular are suitable for calculating the relative risk. This calculation shows that about one third of the musculotendinous injuries can be avoided. This result is supported by five other primary studies. It is not clear whether this reduction is caused by short-term warm-up effects or long-term adaptations. As a result, great importance should be given to warm-up stretching in sports practice (dynamic stretching) and regular stretching (all methods: dynamic – static - and contract-relax stretching). In addition to stretching, there are other measures that can reduce the risk of injury, such as eccentric strength training. In future studies, the volume of training and the incidence of injury should be expressed in terms of injuries per 1000 hours. Since these data are missing in many primary studies, the results can hardly be compared. Furthermore, additional variables such as previous injuries should be recorded and included in a multivariate analysis.
... A dynamic warm-up appears to increase both long-term (>5 min) and intermediate performance (>10 s, but <5 min) if athletes are allowed to begin the ensuing procedure in a relatively rested state, due to increased oxygen consumption (Bishop, 2003;Fletcher, 2010). Mechanically, the effects of dynamic stretching (DS) lead to a reduction in the muscle-tendon unit stiffness (Witvrouw et al., 2004). DS and coordination exercises can be incorporated into the warm-up routine. ...
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The aim of this study was to examine the short-term effects of different types of warming up on the range of motion and on motor abilities of rhythmic gymnasts and ballet athletes. Twenty-five athletes participated in this study (11 ballet dancers and 14 rhythmic gymnasts), aged 14,72±1,43. All participants followed an intervention consisting of two warm-up protocols, one with static stretching exercises and the other with dynamic warm up protocol. The two protocols were implemented on two different days for one week. Range of motion (ROM) and hop test measurements were carried out before and after each warm-up session. For the statistical analysis, non-parametric (Wilcoxon) tests and Friedman test were used, and the level of significance was set at p < 0.05. The results showed that both warm-ups had positive effects on ROM and on motor abilities. After applying both protocols, significant differences were observed in all joints. In conclusion, both types of warm-up routines resulted in almost the same level of improvement in ROM and motor abilities; however, it was observed that after the dynamic warm up there was a slightly increased improvement in motor abilities, but it was not statistically significant.
... Stretching is commonly performed to increase flexibility in humans [208,210] to improve performance and to reduce the risk of injury [354]. If the aim is to improve flexibility, Thomas et al. ...
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Stretching is primarily used to improve flexibility, decrease stiffness of the muscle- tendon unit or reduce risk of injury. However, previous animal studies from 1970 to 1990 showed significant hypertrophy effects in skeletal muscle in response to chronic stretching intervention with stretching durations of 30 minutes to 24 hours per day. However, no study in humans was performed using comparatively long stretching durations of more than 30 minutes per day with a daily frequency. The present cumulative dissertation includes six studies aiming to investigate the effects of long-lasting static stretching training on maximum strength capacity, hypertrophy and flexibility in the skeletal muscle. Before starting own experimental studies, a meta-analysis of available animal research was conducted to analyze the potential of long-lasting stretching interventions on muscle mass and maximum strength. To induce long-lasting stretching on the plantar flexors and to improve standardization of the stretch training by quantifying the angle in the ankle joint while stretching, a calf muscle stretching orthosis was developed. In the following experimental studies, the orthosis was used to induce daily long- lasting static stretching stimuli with different stretching durations and intensities in the plantar flexors to assess different morphological and functional parameters. For this, a total of 311 participants were included in the studies and, dependent on the investigation, the effects of daily stretching for 10-120 minutes for six weeks were analyzed. Therefore, effects on maximal isometric and dynamic strength as well as flexibility of the plantar flexors were investigated with extended and flexed knee joint. The investigation of morphological parameters of the calf muscle was performed by determining the muscle thickness and the pennation angle by using sonographic imaging and the muscle cross-sectional area by using a 3 Tesla magnetic resonance imaging measurement. In animals, the included systematic review with meta-analysis revealed increases in muscle mass with large effect size (d = 8.51, p < 0.001), muscle cross-sectional area (d = 7.91, p < 0.001), fiber cross-sectional area (d = 5.81, p < 0.001), fiber length (d = 7.86, p < 0.001) and fiber number (d = 4.62, p < 0.001). The thereafter performed experimental studies from our laboratory showed a range of trivial to large increases in maximum strength of 4.84% to 22.9% with d = 0.2 to 1.17 and ROM of 6.07% to 27.3% with d = 0.16 to 0.87 dependent on stretching time, training level and testing procedure. Furthermore, significant moderate to large magnitude hypertrophy effects of 7.29 to 15.3% with d = 0.53 to 0.84 in muscle thickness and trivial to small increases of 5.68% and 8.82% (d = 0.16 to 0.3) in muscle cross-sectional area were demonstrated. The results are discussed based on physiological parameters from animal studies and in the front of knowledge in resistance training, suggesting mechanical tension to be one important factor to induce muscle hypertrophy and maximal strength increases. Further explanatory approaches such as hypoxia and changes in the muscle tendon unit are debated in the following. Since these studies are the first investigations on long-lasting stretch-mediated hypertrophy in humans, further research is needed to explore the underlying mechanisms and confirm the results in different populations to enhance the practical applicability for example in clinical populations when, e.g. counteracting muscular imbalances or sarcopenia in the elderly.
... This may be attributed to the inability of the muscle to store and release elastic energy required when accelerating, decelerating, and cutting. Therefore, Witvrouw et al., (2004) provides a rationale for injury prevention to increase the compliance of the muscle tendon unit to ensure the demands in energy absorption and release do not exceed capacity of the muscle. This may be achieved via static stretching programmes as presented by Guissard and Duchateau, (2006) although other research contradicts this with Ylinen et al., (2009) (Bezodis et al., 2015). ...
... Devido a capacidade interpretativa do pesquisador, familiarizado com as ideias dos textos e, por meio de um raciocínio formal lógico, consegue-se detectar lacunas, suprir dúvidas, integrar pensamentos, comprovar teorias e\ou levantar indagações para futuros estudos em cima do referencial teórico das obras compiladas (ECHER, 2001;BRIZOLA;FANTIN, 2016 alcançar no basquetebol. A busca booleana manuseou os operadores lógicos "AND" e "OR" para identificação dos artigos com as respectivas palavras-chave: "basquetebol AND\OR flexibilidade", "basketball AND\OR flexibility", "baloncesto AND\OR flexibilidad", "basquetebol AND\OR teste de sentar e alcançar", "basketball AND\OR sit and reach test", "baloncesto AND\OR prueba de sentarse y alcanzar", "basquetebol AND\OR isquiotibiais", "basketball AND\OR hamstring", "baloncesto AND\OR isquiotibiales", "basquetebol AND\OR métodos de flexibilidade", "basketball AND\OR flexibility methods", "baloncesto AND\OR métodos de flexibilidad", "isquiotibiais AND\OR esportes coletivos", "hamstring AND\OR team sports", "isquiotibiales AND\OR deportes colectivos", "flexibilidade AND\OR lesões", "flexibility AND\OR injuries", "flexibilidad AND\OR lesiones", "isquiotibiais AND\OR lesões", "hamstring AND\OR injuries", "isquiotibiales AND\OR lesiones", "teste de sentar e alcançar AND\OR esportes coletivos", "sit and reach test AND\OR team sports", "prueba de sentarse y alcanzar AND\OR deportes colectivos", "isquiotibiais AND\OR anatomia", "hamstring AND\OR anatomy", "isquiotibiales AND\OR anatomía", "flexibilidade AND\OR isquiotibiais", "flexibility Entre os métodos para treinamento da flexibilidade incluem-se estratégias de alongamento que são comumente empregadas nos procedimentos de aquecimento, parte principal da sessão e no volta à calma (WITVROUW et al., 2004;WOOLSTENHULME et al., 2006;NOTARNICOLA et al., 2017;JEEVANATHAN et al., 2018;KURT et al., 2022 (BALTACI et al., 2003;WOOLSTENHULME et al., 2006;AYALA et al., 2011;SPORIS et al., 2011;FONTOURA et al., 2013;CHIK et al., 2019;KOUMANTAKIS et al., 2020;CAMPOS et al., 2021;GAYA et al., 2021;RAMOS et al., 2021). Uma outra modificação aceita neste -GONZÁLEZ et al., 2018;JEEVANATHAN et al., 2018;FORTE et al., 2019;GÜL et al., 2019;O'BRIEN et al., 2020;PARCHURI et al., 2020;RAMOS et al., 2020;RUKADIKAR et al., 2020;USGU et al., 2020;INDRIS et al., 2021;RAMOS et al., 2021;SUSANTO et al., 2021;VILLARREAL et al., 2021;DEMIR;DAĞLIOĞLU, 2022;HASSAN et al., 2022;LOGESWARAN et al., 2022;SAHASRABUDDHE;SADAWARTE, 2022;YUAN et al., 2023). ...
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RESUMO A flexibilidade é uma capacidade biomotora condicionante que contribui para com o desempenho atlético e prevenção das lesões no basquetebol. Então, o objetivo desta pesquisa é avaliar a flexibilidade da musculatura isquiotibial com o teste de sentar e alcançar (SRT) em jogadores de basquetebol. Nesta revisão de literatura, foram consultadas bases de dados eletrônicas (Google Scholar, Scielo, LILACS, MEDLINE and PubMed) onde foram elegidos um total de 24 artigos científicos primários que abordaram o SRT para avaliação da flexibilidade dos isquiotibiais no basquetebol e 63 referências bibliográficas secundárias complementares. O SRT é um teste funcional que mensura a flexibilidade dos isquiotibiais e coluna lombar, possuindo duas versões empregadas no basquetebol: uma tradicional e outra modificada. Constatou-se que jogadoras femininas denotaram maiores níveis de flexibilidade em relação aos atletas masculinos, assim como os basquetebolistas formativos tiveram menores valores numéricos na flexibilidade, quando comparado aos jogadores universitários e profissionais. Em cinco intervenções houveram ganhos médios superiores na flexibilidade, a saber: treinamento pliométrico (39.6±3.9-cm), treinamento vibratório (31.5±0.5-cm), abordagem do tempo training (24.3±17.6-cm), treinamento de força isoinercial (20.9±0.1-cm) e treinamento com bola suíça (20.4±0.2-cm). Verifica-se que quatro destes protocolos de treinamento possuem dominância no regime de contração excêntrico, fator determinante para ganhos elevados na flexibilidade dos isquiotibiais. Entretanto, devido aos desenhos experimentais heterogêneos dos estudos analisados, vigora a impossibilidade de comparações mais aprofundadas entre os mesmos. PALAVRAS-CHAVE: Basquetebol. Testes de Aptidão Física. Músculos Isquiotibiais. Flexibilidade.
... A historically perceived benefit of SS was its purported benefits for decreasing the incidence of injuries [24,39,40]. However, this issue was fractious as well, with reports that enhanced flexibility reduced all-cause injury incidence [41,42] but longitudinal training studies [43] and some reviews [44,45] reported a lack of significant reduction in all-cause injury risk in response to chronic SS. ...
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The use of dynamic stretching as a replacement for static stretching in the warm-up is widespread based on the reports of static stretching-induced performance impairments. While acute and chronic static stretching has been reported to reduce musculotendinous injuries, especially with explosive and change of direction actions, the influence of dynamic stretching on injury incidence lacks a similar volume of literature for acute and chronic responses. It was the objective of this narrative review to examine the acute and training effects of dynamic stretching on injury incidence and possible moderating variables such as dynamic stretching effects on range of motion, strength, balance, proprioception, muscle morphology, and psycho-physiological responses. One study demonstrated no significant difference regarding injury incidence when comparing a dynamic stretching-only group versus a combined dynamic stretching plus static stretching group. The only other study examined functional dynamic stretching training with injured dancers and reported improved ankle joint stability. However, several studies have shown that dynamic activity with some dynamic stretching exercises within a warm-up consistently demonstrates positive effects on injury incidence. Regarding moderating variables, while there is evidence that an acute bout of dynamic stretching can enhance range of motion, the acute and training effects of dynamic stretching on strength, balance, proprioception, and musculotendinous stiffness/compliance are less clear. The acute effects of dynamic stretching on thixotropic effects and psycho-physiological responses could be beneficial for injury reduction. However, the overall conflicting studies and a lack of substantial literature compared with SS effects points to a need for more extensive studies in this area.
... Germe egzersizleri, muhtemelen spor eğitmenleri ve spor hekimliği uzmanları tarafından spor performansını artırma ve yaralanmayı önleme için kullanılan en yaygın rutindir (Witvrouw, et al., 2004). Sportif performans öncesi yapılan germe egzersizlerinin performansı artıracağına ve sakatlık riskini azaltacağına inanılmaktadır (Azeem, & Sharma, 2017;Schilling, & Stone, 2000). ...
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In this study, it was aimed to determine the acute effect of PNF exercises on balance and jump performance. The sample group of the study was Sports Science students 12 male (age: 20.83±1.11 years, Height: 184.41±5.45 cm, Body weight: 72.16±8.03 kg), 12 female (age: 19 years old) .83±0.71years, Height: 168.00±7.95cm, Body weight: 58.66±5.24kg) constituted a total of 24 participants. 5 minutes of jogging and proprioceptive neuromuscular facilitation (PNF) exercise were applied to the participants, and then CMJ (Countermovement Jump) test for vertical jump performance and SJ (Squad Jump) test were applied to determine balance performance, static and dynamic balance test were applied. SPSS 25 statistical package program was used to evaluate the obtained data. According to the results of the evaluation, a significant difference was found at the level of p<0.05 in the intragroup comparisons of the CMJ and SJ values of female volleyball players, and at the level of p<0.05 in the SJ value of male volleyball players. In the static balance in-group comparisons of female volleyball players, a significant difference was found at the p<0.05 level in the mean right-left swing speed, and at the p<0.05 level in the standard right-to-left swing value of the male volleyball players. In the dynamic balance data, in women; A significant difference was found at p<0.05 level in dynamic balance performance, right swing area, right external swing area and right swing reaction time values. As a result, it can be said that PNF exercises contribute positively to the vertical jump and balance performance, and the implementation of these exercises in training and competitions will contribute to the performance of the athletes.
... Germe egzersizleri, muhtemelen spor eğitmenleri ve spor hekimliği uzmanları tarafından spor performansını artırma ve yaralanmayı önleme için kullanılan en yaygın rutindir (Witvrouw, et al., 2004). Sportif performans öncesi yapılan germe egzersizlerinin performansı artıracağına ve sakatlık riskini azaltacağına inanılmaktadır (Azeem, & Sharma, 2017;Schilling, & Stone, 2000). ...
Bu çalışmada PNF egzersizlerinin denge ve sıçrama performansına akut etkisinin belirlenmesi amaçlandı. Araştırmanın örneklem grubunu Spor Bilimleri öğrencileri 12 erkek (yaş: 20.83±1.11 yıl, Boy: 184.41±5.45 cm, Vücut ağırlığı: 72.16±8.03 kg), 12 kadın (yaş: 19.83±0.71yıl, Boy: 168.00±7.95cm, Vücut ağırlığı: 58.66±5.24kg) toplam 24 katılımcı oluşturdu. Katılımcılara 5 dakika hafif tempo koşu ve Proprioseptif Nöromusküler Fasilitasyon (PNF) egzersizi uygulandı ve sonrasında dikey sıçrama performansı için CMJ (Countermovement Jump) testi ve SJ (Squad Jump) testi denge performansını belirlemek için statik ve dinamik denge testi uygulandı. Elde edilen verileri değerlendirmesinde SPSS 25 istatistik paket programı kullanıldı. Değerlendirme sonucuna göre kadın voleybolcuların CMJ ve SJ değerlerinin grup içi karşılaştırmalarında p
... To reach maximal performance output in training and competition, athletes commonly perform different types of warm-up routines to prepare the muscles for the subsequent stress and prevent injuries by increasing range of motion (ROM) (Backman and Danielson, 2011;Behm et al., 2016a;Behm et al., 2021b;Witvrouw et al., 2004). Therefore, stretching exercises have been implemented to the warm-up routines because of their beneficial acute effects in local and global increases in ROM (Behm et al., 2016a;Behm et al., 2016b;Chaouachi et al., 2017;Freitas et al., 2016;Siebert et al., 2022). ...
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Over the last decade, acute increases in range of motion (ROM) in response to foam rolling (FR) have been frequently reported. Compared to stretching, FR-induced ROM increases were not typically accompanied by a performance (e.g., force, power, endurance) deficit. Consequently, the inclusion of FR in warm-up routines was frequently recommended, especially since literature pointed out non-local ROM increases after FR. However, to attribute ROM increases to FR it must be ensured that such adaptations do not occur as a result of simple warm-up effects, as significant increases in ROM can also be assumed as a result of active warm-up routines. To answer this research question, 20 participants were recruited using a cross-over design. They performed 4x45 seconds hamstrings rolling under two conditions; FR, and sham rolling (SR) using a roller board to imitate the foam rolling movement without the pressure of the foam rolling. They were also tested in a control condition. Effects on ROM were tested under passive, active dynamic as well as ballistic conditions. Moreover, to examine non-local effects the knee to wall test (KtW) was used. Results showed that both interventions provided significant, moderate to large magnitude increases in passive hamstrings ROM and KtW respectively, compared to the control condition (p = 0.007 - 0.041, d = 0.62 - 0.77 and p = 0.002 - 0.006, d = 0.79 - 0.88, respectively). However, the ROM increases were not significantly different between the FR and the SR condition (p = 0.801, d = 0.156 and p = 0.933, d = 0.09, respectively). No significant changes could be obtained under the active dynamic (p = 0.65) while there was a significant decrease in the ballistic testing condition with a time effect (p < 0.001). Thus, it can be assumed that potential acute increases in ROM cannot be exclusively attributed to FR. It is therefore speculated that warm up effects could be responsible independent of FR or imitating the rolling movement, which indicates there is no additive effect of FR or SR to the dynamic or ballistic range of motion.
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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.
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 1ms−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 18kmh−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.
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.
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.
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.
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.