Content uploaded by Luci Teixeira-Salmela
Author content
All content in this area was uploaded by Luci Teixeira-Salmela on May 20, 2022
Content may be subject to copyright.
ORIGINAL RESEARCH
Gains in Flexibility Related to Measures of Muscular
Performance: Impact of Flexibility on
Muscular Performance
Gustavo Nunes Tasca Ferreira, MSc, Luci Fuscaldi Teixeira-Salmela, PhD,
and Cristiano Queiroz Guimara
˜es, PT
Objective: Studies that investigated possible correlations between
flexibility and muscular performance are scarce in the literature.
Therefore, the purpose of this study was to investigate the impact of
a program of static stretching on the flexibility of the hamstrings and
on muscular performance of the knee flexors and extensors.
Design: Pre–post experimental design.
Setting: University laboratory.
Participants: Thirty subjects aged 22.8 64.9 years with bilaterally
shortened hamstrings.
Intervention: Using a protocol that has been previously described,
the intervention consisted of 30 sessions of static stretching,
performed bilaterally five times a week for 6 weeks.
Main Outcome Measurements: Measures of knee range of
motion and isokinetic muscular performance (peak torque, angle
of peak torque, and work) of knee flexors and extensors at speeds of
60 and 300 degrees/s.
Results: After intervention, significant gains in measures of flex-
ibility (P,0.0001) were observed, with an average gain of the knee-
extension angle of 12.6°, ranging from 21.2 to 30.7°. In addition, we
found significant increases in the following parameters of muscular
performance: angle of peak torque of hamstrings at 60 and 300
degrees/s (P,0.0001 and 0.018) and for work at 60 and 300
degrees/s for knee flexors (P= 0.012 and 0.005) and for knee
extensors (P,0.0001).
Conclusions: The intervention resulted in gains in measures of
flexibility, and these gains had a positive impact on some parameters
of muscular performance.
Key Words: flexibility, static stretch, muscular performance, knee
joint, hamstrings
(Clin J Sport Med 2007;17:276–281)
INTRODUCTION
Improvements in physical performance have been
a common goal for health professionals.
1,2
Several ways
of maximizing physical performance have been described,
including increases of muscular strength, resistance, and
flexibility.
1–3
Flexibility refers to the ability of a muscle to
stretch, allowing a single joint, or more than one in series, to
move through all ranges of motion.
4,5
Appropriate flexibility
allows the muscular tissue to more easily accommodate
to imposed stresses, promoting more efficient movements,
which, in turn, could help prevent or minimize lesions and
improve performance.
6
Taylor et al
7
found that the muscle-
tendon units had a viscous elastic response to tensile loads:
when stretched and maintained in a constant length, the stress
or force at that length gradually decreases. This decline, or
stress relaxation, demonstrates that the muscle-tendon unit
adapts to the stretch stimulus by increasing its length, and this
adaptation cannot be quickly reversed.
For the most part, publications regarding flexibility
have outlined only aspects related to the magnitude of gains
associated with the time of intervention and/or applied
stretching technique.
4,5
Studies that have investigated possible
correlations between flexibility and muscular performance are
scarce in the literature. Therefore, the purpose of this study
was to investigate the impact of a program of static stretching
on the flexibility of the hamstrings and on muscular per-
formance of the knee flexors and extensors. Our hypothesis
was that the protocol for static stretching would positively
affect the flexibility of the hamstrings, with associated changes
on the performance of the muscles about the knee.
MATERIALS AND METHODS
Subjects
This quasi-experimental clinical trial was carried out with
a sample of 30 voluntary undergraduate students, without gender
restrictions, recruited from the Faculdade de Sau
´de e Ecologia
Humana, Minas Gerais, Brazil. To be included in this study,
subjects had to be between 18 and 39 years of age and
demonstrate shortening of the hamstrings muscles. This was
defined as a knee angle of more than 30 degrees of knee
flexion with the hip held in 90 degrees in flexion.
4,5,8
The
following exclusion criteria were applied: reported pathologies
or physical limitations, such as limited range of motion of the
knee, that could impede the research protocol; complaints
Submitted for publication September 5, 2006; accepted February 23, 2007.
From the Department of Physical Therapy, Universidade Federal de Minas
Gerais, Minas Gerais, Brazil.
Reprints: Luci Fuscaldi Teixeira-Salmela, PhD, Associate Professor,
Department of Physical Therapy, Universidade Federal de Minas Gerais,
Avenida Anto
ˆnio Carlos 6627, Campus Pampulha 31270-010, Belo
Horizonte, Minas Gerais, Brazil (e-mail: lfts@ufmg.br).
Copyright Ó2007 by Lippincott Williams & Wilkins
276 Clin J Sport Med Volume 17, Number 4, July 2007
of lumbar pain; recent surgery; currently in physical therapy
treatment for the lower limbs and/or lumbar spine; or unable to
accomplish the necessary movements for the isokinetic tests
and intervention protocol. The nature of the research protocol
was explained, and the volunteers signed a consent form to
participate in the study, which was approved by the university
ethical review board.
Instruments
Measurements of the flexibility of hamstrings were
obtained with a universal goniometer (Smith & Nephew,
Rolyan INC, Germantown, Wisc), whose validity and reli-
ability were well documented.
9
The amount of applied force to
elevate the volunteer’s leg to obtain the measurements of the
angle of knee extension was controlled by a hand dynamom-
eter and was specifically adjusted for each subject (Microfet2,
Hoggan Health Elaborate, Draper, Utah), whose reliability and
validity have been demonstrated.
10
Measures of muscular per-
formance at the knee were obtained with an isokinetic dyna-
mometer Biodex 3 (Biodex Medical Systems, Inc., Shirley,
NY), which has shown adequate validity and reliability.
11
Procedures
Measurement of Knee-Extension Angle
In accordance with previously established protocols,
4,5
the participants lay in the supine position on an examining
table with both lower limbs extended. The first examiner then
positioned the right hip at 90 degrees of flexion, ensuring that
the lumbar spine remained stabilized by not allowing move-
ment in the other leg. He then passively moved the right
calcaneus toward the final position of knee extension, deter-
mined by the point at which each individual complained of
discomfort or tension of the hamstring muscles, or the point at
which the examiner perceived resistance to the stretching.
In this position, the reference bony landmarks (greater tro-
chanter, lateral femoral condyle, and lateral malleolus)
4,5
were
identified and marked. Later, the markers were aligned so that
measurements could be made. To obtain the goniometric
measures, the first examiner repositioned the right hip and
knee at 90 degrees of flexion, with the volunteer’s calcaneus
now supported by the handheld dynamometer. To guarantee
the maintenance of the angle of 90 degrees of hip joint flexion
during the measurement of the knee-extension angle, a
reference plumb line was positioned perpendicular to the
examining table (Fig. 1). Once the final point of knee exten-
sion was reached, the second examiner recorded the degree of
knee extension with a goniometer, with 0 degrees considered
total knee extension, so that the first examiner remained blind
to all measurements. To increase the reliability of the mea-
sures, the first examiner was blind to the measurement values,
which were registered by the second examiner.
Isokinetic Dyamometer
Initially, standard calibration of the equipment was
carried out according to the manufacturer’s manual. The
volunteers were then submitted to an initial preparatory
activity of a 10-minute warm-up on a stationary bicycle, with
a load of 25 W and a medium speed of 18 km/h. Subsequently,
the individuals were positioned in the dynamometer chair in
the seated position with 85 degrees of hip flexion. The tested
range of motion was 70 degrees, or between 100 and
30 degrees of knee flexion. To familiarize themselves with the
equipment and the test procedures, subjects were allowed to
perform two series of submaximal efforts for three repetitions
of the knee flexion/extension movements for the modalities of
concentric/concentric contractions at previous recommended
speeds of 60 degrees/s
12
and 300 degrees/s.
13
These speeds
also were selected to approximate the demands on the knee
during functional activities, such as gait, sit to stand, and stair
climbing. The individuals were stabilized in the chair with the
equipment belts, and procedures were applied to correct for
gravity. Subsequently, the individuals performed the definitive
tests with maximum effort for five repetitions at each speed,
with a 1-minute rest interval between speeds.
14
The muscles on
the right side were tested first; after a 10-minute rest interval,
the same tests were applied to the left leg. During the tests, the
individuals received verbal encouragement, so that they were
asked to move the dynamometer lever arm with ‘‘the fastest
and strongest force possible.’’ All data were obtained online by
the Biodex software and stored for future analyses. The angle
of peak torque was determined by averaging the torque at each
angle of the range of motion for five repetitions.
Intervention Protocol
The intervention protocol followed the methodology
described by Sullivan et al.
15
To perform hamstring stretching,
each individual was in a standing position with the left foot on
the ground and forward, without any hip rotation. The right leg
was placed on a higher surface, supported on the calcaneus
with the knee fully extended, toes pointing upward without hip
rotation (Fig. 2). The surface was elevated enough to cause
a stretching sensation on the posterior aspect of the thigh.
Seven surfaces with varied heights, ranging from 27 to 89 cm,
were available. Individuals were instructed to lean forward,
maintaining the spinal column erect, the pelvis in ante-
version,
15
and the shoulders retracted, until they perceived
a mild stretching of the posterior aspect of the thigh; this
position was maintained for 30 seconds.
FIGURE 1. Positioning of subjects for measurement of
hamstring flexibility.
q2007 Lippincott Williams & Wilkins 277
Clin J Sport Med Volume 17, Number 4, July 2007 Impact of Flexibility on Muscular Performance
Four stretching cycles were performed, with a rest
interval of 10 seconds. After accomplishing the four cycles
with the right leg, each individual was allowed to rest for
30 seconds; then, the individual repeated the same procedures
with the left leg. Each session was supervised by a third
independent researcher who also monitored the attendance of
the participants but who was not involved in the assessment.
Any missing sessions were made up the following day with
two stretching sessions, one in the morning and the other in the
afternoon, as recommended by Bandy et al.
4,5
Any individual
who missed more than four sessions would be automatically
excluded from the study; this did not occur. Each individual
accomplished five weekly sessions for 6 weeks, totaling
30 sessions. All individuals were tested again after the inter-
vention, using the same previously described procedures. The
time interval between the last stretching session and the second
data collection was 24 hours so that the viscous elastic effects
of the stretching could be dissipated.
16
Statistical Analyses
Descriptive statistics and tests for normality and for
equality of variance were calculated for all outcome variables,
using the statistical package SPSS (version 13.0, 2001, SPSS
Inc.). Because no differences between legs for all investigated
parameters were found, the data for both legs were collapsed
(n = 60). Depending on the data distribution, Student paired
ttests or Wilcoxon tests were calculated to investigate the
impact of the intervention at a significance level of a= 0.05 for
the following outcome variables: knee-extension angle, work
of knee flexors and extensors at 60 and 300 degrees/s, angle at
peak torque of knee flexors at 60 and 300 degrees/s, and peak
torque of knee flexors at 60 degrees/s.
RESULTS
Of the 30 participants, 19 were women (63%) and 11
were men (37%). Their demographic and anthropometric
characteristics are presented in Table 1. The values of peak
force obtained with the handheld dynamometer before the
intervention of 55.18 613.48 Nm did not show significant
differences between those of 55.94 613.22 Nm obtained
after the intervention (P= 0.18), indicating that a similar force
was applied during the measurement of the knee-extension
angles before and after intervention.
Measures of Flexibility
As presented in Table 2, the values of the angle of
extension of the knee of 23.3 69.1 degrees obtained after the
intervention were significantly lower than those of 35.9 65.4
degrees obtained before intervention (P,0.0001), with an
average gain of 12.6 67.8 degrees, ranging from 21.2 to
30.7 degrees.
Isokinetic Measures
The angles of peak torque of the knee flexors obtained
at speeds of 60 and 300 degrees/s after the intervention were
lower than those obtained before the intervention, indicating
a change in the angle of peak torque in the direction of knee
extension for both speeds (Table 2). As presented in Table 2,
the values of peak torque of knee flexors at 60 degrees/s were
127.9 626.0 and 128.1 631.7% before and after the
intervention, respectively, indicating that the intervention did
not result in significant changes of this measure (P= 0.23).
However, the variables related to the work of the knee
flexors showed significant increases in work production after
the interventions at both speeds of 60 degrees/s (P= 0.012) and
300 degrees/s (P= 0.005). The same was observed for the work
produced by the knee extensors, with the obtained values after
training being superior at those obtained before training at both
speeds of 60 and 120 degrees/s (P,0.0001).
DISCUSSION
The results of the present study demonstrate that
a regular program of static stretching resulted in significant
FIGURE 2. Positioning of subjects for stretching the ham-
strings.
TABLE 1. Descriptive Statistics (Mean, SD, and Range) of the
Subjects (n = 30)
Mean 6SD Range
Age, yrs 22.77 64.87 18–38
Height, m 1.67 60.08 1.53–1.84
Body mass, kg 61.80 611.29 44.80–91.20
Body mass index, kg/m
2
22.05 62.92 17.92–31.37
278 q2007 Lippincott Williams & Wilkins
Ferreira et al Clin J Sport Med Volume 17, Number 4, July 2007
improvements in measures of hamstring flexibility associated
with improvements in measures of muscular performance. The
average gains in flexibility of 12.6 degrees corroborate the
results of several studies that have employed similar
interventions.
4,5,17,18
The effects of stretching on flexibility
have been widely investigated, and different approaches have
been employed.
19–21
In the present study, the observed changes
occurred after a 6-week-long intervention, which is believed to
result in long-term effects, and were different from flexibility
changes reported after previous interventions, which were
evaluated immediately after only a single bout of stretching.
19,21
It is well known that gains in flexibility are associated
with higher individual tolerance to pain,
22,23
the viscous elastic
properties of the muscle-tendon units,
7,24
and the increased
number of sarcomers in series.
1,17,25,26
According to Mueller
and Maluf,
27
changes in the levels of physical stress cause
a predictable adaptive response in all biological tissues. When
applying a tensile force on muscular tissue with stretch-
ing, a controlled stress level is actually applied, with the
aim of recuperating its full physiological joint range of
motion.
1,2,4–6,8,15,17,18,28,29
According to Taylor et al
7
and Gajdosik,
1
immediate
gains of flexibility are related to the viscous elastic properties
of the muscle-tendon unit. However, Mueller and Maluf
27
have argued that the regular application of stress forces
induces tissues to adapt positively. Some studies have
confirmed this hypothesis by finding increases in the number
of sarcomers in series in muscles submitted to continuous
stretching programs.
25,26,28,30,31
Although the number of
sarcomers was not a variable investigated in this study, there
is evidence that a muscle submitted to stretching for 4 weeks
results in an increase in the number of sarcomers in series.
25,28
Some factors may affect measures of flexibility and need
to be considered.
32
First is the amount of applied force when
assessing the knee-extension angle: a variable that was
controlled in the present study, where the amount of applied
force obtained with a handheld dynamometer was similar at
both the pre- and postintervention assessments. Thus, the
observed gains of flexibility did not seem to be associated with
changes in an individual’s tolerance to pain and/or stretching.
However, a limitation that needs to be addressed was the
impossibility of controlling the applied torque on the goni-
ometric data. The torque cannot be derived directly from a
dynamometer, because it is the result of the moment arm, as
well as the torque, caused by the weight of the leg, that changes
with the knee angle. However, this distance would be
impossible to predict because the gains in flexibility could
vary between individuals, thus affecting the magnitude of the
moment arm.
Another factor that can affect the consistency of flex-
ibility data relates to the time of day the data collection takes
place.
32
To avoid differences attributable to circadian rhythms,
all measures were obtained at the same time period. In addi-
tion, all assessments were performed 1 day after the end of
the intervention, to dissipate the viscous elastic effects of the
stretching.
16
The volunteers also were monitored regarding
the frequency with which they performed other physical
activities, and changes in this frequency did not occur during
the intervention.
One could argue that the stretching protocol might have
had an impact on the lumbar spine, and it is also possible that
part of the gains in flexibility were related to the effects of
stretching. In the present study, no specific measures of the
lumbar spine were included, but the examiners ensured that it
remained stabilized during both measurement and interven-
tion. However, because the same protocol was applied before
and after the intervention, we believe that the role of the
lumbar spine was minimized. In addition, during the
measurement of range of motion of the knee, the threshold
of force was specifically applied and adjusted for each subject.
TABLE 2. Descriptive Statistics [Means 6SD, and Range (Minimum to Maximum)] of
Selected Outcome Measures Obtained Before and After Intervention (n = 60)
Before After
Knee range of motion, degrees 35.9 65.4 (26–48) 23.3 69.1*(3–43)
Peak torque of knee flexors
60 degrees 127.9 626.0 (91–198) 128.1 631.7 (88–206)
300 degrees 105.77 (56–164) 107.38 (58–158)
Peak torque of knee extensors
60 degrees 261.26 650.76 (166–375) 260.79 651.18 (169–381)
300 degrees 178.52 636.20 (94–244) 182.22 636.15 (97–257)
Angle at peak torque of knee flexors, degrees
60 degrees/s 59.2 68.4 (43–99) 55.3 68.4* (42–82)
300 degrees/s 88.6 612.8 (43–96) 85.2 615.6* (42–96)
Concentric work of knee flexors, %
60 degrees/s 121.3 627.4 (79–186) 125.6 628.5* (80–197)
300 degrees/s 61.2 616.4 (30–105) 64.4 617.1* (34–104)
Concentric work of knee extensors, %
60 degrees/s (%) 240.7 648.0 (160–351) 248.6 653.0* (166–371)
300 degrees/s 116.0 627.7 (72–174) 119.3 628.0* (80–173)
*P,0.05.
q2007 Lippincott Williams & Wilkins 279
Clin J Sport Med Volume 17, Number 4, July 2007 Impact of Flexibility on Muscular Performance
The intervention employed in the present study can be
considered a long-term intervention, and factors that might
possibly influence the results were controlled. Therefore, it
is possible that the stimulus was strong enough to induce
sarcomerogenesis, as has already been demonstrated in studies
with animals.
25,28
The present results also revealed that the
angle of peak torque of the knee flexors changed in the
direction of knee extension at both tested speeds. This change
in angle of peak torque might be explained by an increased
capacity of the knee flexors to vary in length, associated with
a greater number of sarcomers in series, explaining the changes
in angle of peak torque in the direction of knee extension.
The values of the peak torque of the knee flexors at both
speeds were unchanged after the intervention. Changes in peak
torque values that could be detected in the present study could
be associated with the capacity of the muscular tissue to
generate force,
33,34
because the angular speeds, the number
of repetitions, the rest time interval between tests, and the
concentric contraction mode were the same before and after
the intervention. The stimuli necessary to induce hypertrophy
are well documented and involve training sessions with loads
above 70% of maximal voluntary contractions,
35
which did not
occur in the present study. Therefore, the fact that the values of
peak torque of the knee flexor muscles remained unchanged
reinforces previous findings that a program of static stretching
does not necessarily result in gains in isokinetic measures of
muscular strength.
The work of the knee flexors, evaluated at speeds of
60 and 300 degrees/s, showed significant increases after the
intervention. The angular work performed by a given muscle
or muscular group can be described by the following equation:
33
angular work = applied torque 3changes in angular distance.
Considering that the present intervention modified the
flexibility of the knee-flexor muscles and that a possible
explanation for this change would be sarcomerogenesis, it is
possible to speculate that these muscles became more capable
of moving the body segment of the leg through a larger angular
distance in the same time interval.
33,34
Thus, the inclination of
the torque curve becomes steeper, generating a larger area
below the curve, representing greater work generated by the
muscle group.
13
Studies that have compared the parameters of flexibility
with muscular performance are scarce in the literature. Worrell
et al
2
applied two stretching methods, static and proprioceptive
neuromuscular facilitation, in a sample of 19 volunteers, for
a period of 3 weeks, in 15 sessions. Their results indicate mean
gains of flexibility ranging from 8 to 9.5 degrees, depending
on the method, but the differences were not statistically
significant, because of great interindividual variability. They
also found significant increases in the peak of torque of
the hamstrings acting eccentrically at speeds of 60 and 120
degrees/s and concentrically at 120 degrees/s. However, they
did not observe gains in their concentric contractions at
the speed of 60 degrees/s. Their results were explained by
the existing relationship between gains in flexibility and
neuromuscular transmission modifications. Yamashita et al
36
report that stretching can induce increases in the liberation of
free intracellular calcium ions, which, in turn, could poten-
tially facilitate muscular performance.
Handel et al
21
have evaluated the effects of 8 weeks of
unilateral stretching of the hamstrings on muscular perfor-
mance, using contraction/relaxation techniques with 16 vol-
unteers, 3 d/wk, in 24 sessions. They report statistically
significant gains of flexibility for the leg that received the
intervention associated with gains of muscular performance.
They also observed increases of concentric work for the knee
flexor and extensor muscles, which they associate with an
increased number of sarcomers in series. Their results cor-
roborate those obtained in the present study and support
the existing association between flexibility and muscular
performance.
The work for the knee extensors also showed significant
increases after the intervention. Because this muscle group
was not submitted to the stretching protocol, a plausible
justification for such gains could be related to decreases of
resistance imposed by the knee flexors. Considering that the
range of motion tested was 70 degrees (or from 100 to 30
degrees of knee flexion), and considering that inclusion in this
study required the volunteers to have shortened hamstrings, it
is probable that before intervention the passive resistance
imposed by the knee flexors was higher because the
hamstrings developed tension during the final range of knee
extension.
13
After intervention, this passive resistance de-
creased because they became more stretched. Therefore, it is
possible that the smaller resistance imposed by the hamstrings
to extend the knee after intervention could be responsible for
the observed increases in work performed by the knee
extensors.
CONCLUSIONS
The results of the present study demonstrate that
muscular flexibility can be modified, and these modifications
have been shown to be associated with various parameters of
muscular performance, which may have important implica-
tions in the field of sport medicine and might result in benefits
for the treatment and/or prevention of knee injuries.
ACKNOWLEDGMENTS
We acknowledge the support of the Brazilian Govern-
ment Agency (CNPq).
REFERENCES
1. Gajdosik RL. Passive extensibility of skeletal muscle: review of the
literature with clinical implications. Clin Biomech. 2001;16:87–101.
2. Worrell TW, Smith TL, Winegardner J. Effects of hamstring stretching
on hamstring muscle performance. J Orthop Sports Phys Ther. 1994;20:
154–159.
3. Shrier I. Does stretching improve performance? A systematic and critical
review of the literature. Clin J Sport Med. 2004;14:267–273.
4. Bandy WD, Irion JM, Briggler M. The effect of static stretch and dynamic
range of motion training on the flexibility of the hamstrings muscles.
J Orthop Sports Phys Ther. 1998;27:295–300.
5. Bandy WD, Irion JM, Briggler M. The effect of time and frequency of
static stretching on flexibility of the hamstrings muscles. Phys Ther. 1997;
77:1090–1096.
6. Lardner R. Stretching and flexibility: its importance in rehabilitation.
J Bodywork Mov Ther. 2001;10:254–263.
7. Taylor DC, Dalton JD, Seaber AV, et al. Viscoelastic properties of muscle-
tendon units. The biomechanical effects of stretching. Am J Sports Med.
1990;18:300–309.
280 q2007 Lippincott Williams & Wilkins
Ferreira et al Clin J Sport Med Volume 17, Number 4, July 2007
8. Willy RW, Kyle BA, Moore SA, et al. Effect of cessation and resumption
of static hamstring muscle stretching on joint range of motion. J Orthop
Sports Phys Ther. 2001;31:138–144.
9. Rothstein JM, Miller PJ, Roettger RF. Goniometric reliability in a clinical
setting. Elbow and knee measurements. Phys Ther. 1983;63:1611–1615.
10. Bohannon RW. Test-retest reliability of hand-held dynamometry during
a single session of strength assessment. Phys Ther. 1986;66:206–209.
11. Drouin JM, Valovich-McLeod TC, Shultz SJ, et al. Reliability and validity
of the Biodex system 3 pro isokinetic dynamometer velocity, torque and
position measurements. Eur J Appl Physiol. 2004;91:22–29.
12. Worrel TW, Smith TL, Winegardner J. Effect of hamstring stretching
on hamstring muscle performance. J Orthop Sports Phys Ther. 1994;20:
154–159.
13. Osternig LR. Isokinetic dynamometry: implications for muscle testing
and rehabilitation. Exerc Sport Sci Rev. 1986;14:45–80.
14. Parcell AC, Sawyer RD, Tricoli VA, et al. Minimum rest period for
strength recovery during a common isokinetic testing protocol. Med Sci
Sports Exerc. 2002;34:1018–1022.
15. Sullivan MK, DeJulia JJ, Worrell TW. Effect of pelvic position and
stretching method on hamstring muscle flexibility. Med Sci Sports Exerc.
1992;24:1383–1389.
16. Magnusson SP, Aagard P, Simonsen E, et al. A biomechanical evaluation
of cyclic and static stretch in human skeletal muscle. Int J Sports Med.
1998;19:310–316.
17. Chan SP, Hong Y, Robinson PD. Flexibility and passive resistance of the
hamstrings of young adults using two different static stretching protocols.
Scand J Med Sci Sports. 2001;11:81–86.
18. Hartig DE, Henderson JM. Increasing hamstring flexibility decreases
lower extremity overuse injuries in military basic trainees. Am J Sports
Med. 1999;27:173–176.
19. Decoster LC, Cleland J, Altieri C, et al. The effects of hamstring stretching
on range of motion: a systematic literature review. J Orthop Sports Phys
Ther. 2005;35:377–387.
20. Thacker SB, Gilchrist J, Stroup DF, et al. The impact of stretching on
sports injury risk: a systematic review of the literature. Med Sci Sports
Exerc. 2004;36:371–378.
21. Handel M, Horstmann T, Dickhuth HH, et al. Effects of contract-relax
stretching training on muscle performance in athletes. Eur J Appl Physiol
Occup Physiol. 1997;76:400–408.
22. Halbertsma JPK, Mulder I, Go¨eken LNH, et al. Repeated passive
stretching: acute effect on the passive muscle moment and extensibility of
short hamstrings. Arch Phys Med Rehabil. 1999;80:407–414.
23. Halbertsma JPK, Van Bolhuis AI, Go¨eken LNH. Sport stretching: effect
on passive muscle stiffness of short hamstrings. Arch Phys Med Rehabil.
1996;77:688–692.
24. Taylor DC, Brooks DE, Ryan JB. Viscoelastic characteristics of muscle:
passive stretching versus muscular contractions. Med Sci Sports Exerc.
1997;29:1619–1624.
25. Coutinho EL, Gomes AR, Franca CN, et al. Effect of passive stretching on
the immobilized soleus muscle fiber morphology. Braz J Med Biol Res.
2004;37:1853–1861.
26. De-Deyne PG. Application of passive stretch and its implications for
muscle fibers. Phys Ther. 2001;81:819–827.
27. Mueller MJ, Maluf KS. Tissue adaptation to physical stress: a proposed
‘‘Physical Stress Theory’’ to guide physical therapist practice, education,
and research. Phys Ther. 2002;82:383–403.
28. Caiozzo VJ, Utkan A, Chou R, et al. Effects of distraction on muscle
length: mechanisms involved in sarcomerogenesis. Clin Orthop. 2002;
403(Suppl):S133–S145.
29. De Deyne PG. Formation of sarcomeres in developing myotubes: role of
mechanical stretch and contractile activation. Am J Physiol Cell Physiol.
2000;279:C1801–C1811.
30. Goldspink G, Williams P, Simpson H. Gene expression in response to
muscle stretch. Clin Orthop. 2002;403(Suppl):S146–S152.
31. Friden J, Ponten E, Lieber RL. Effect of muscle tension during tendon
transfer on sarcomerogenesis in a rabbit model. J Hand Surg (Am). 2000;
25:138–143.
32. Alter MJ, ed. Cie
ˆncia da Flexibilidade. Porto Alegre, Brazil: Artes
Me
´dicas; 1999.
33. Hamill J, Knutzen KM. Biomechanical Basis of Human Movement.
Philadelphia, Pa: Lippincott Williams & Wilkins; 2003.
34. Lieber RL, Bodine-Fowler SC. Skeletal muscle mechanics: implications
for rehabilitation. Phys Ther. 1993;73:844–856.
35. Cureton KJ, Collins MA, Hill DW, et al. Muscle hypertrophy in men and
women. Med Sci Sports Exerc. 1988;20:338–344.
36. Yamashita T, Ishii S, Oota I. Effect of muscle stretching on the activ-
ity of neuromuscular transmission. Med Sci Sports Exerc. 1992;24:
80–84.
q2007 Lippincott Williams & Wilkins 281
Clin J Sport Med Volume 17, Number 4, July 2007 Impact of Flexibility on Muscular Performance
