The effect of one or three repetitions of target-muscle PNF stretching on acute hamstring extensibility Randomised Clinical Trial Bonarrigo T, Cristovão S, Lau R, Kaljusto K, Read A. European School of Physiotherapy, Amsterdam University of Applied Sciences, Tafelbergweg 51, Amsterdam, The Netherlands 27 March 2017
Abstract Introduction: Existing literature is lacking on the effect of the number of repetitions of target muscle proprioceptive neuromuscular facilitation (TM-PNF) stretching on the extensibility of hamstring muscles, after a single session. Further knowledge about this would be beneficial in the clinical setting, by assisting therapists in finding a balance between time-efficiency and maximising benefits from the PNF session. Aim: To assess if three repetitions of TM-PNF (Intervention 0) are more effective than a single repetition of TMPNF (Intervention 1) for improving acute extensibility of the hamstring muscles Methods: Thirty-seven (17 males, 20 females) young adults (mean 23.1 SD 2.9 years) were assessed on hamstring extensibility as measured by the sit-and-reach test (SRT), before (SRTpre) and after (SRTpost) one or three repetitions of TM-PNF stretch intervention. Results: Results showed a significant difference between the outcomes SRTpre and SRTpost for both Intervention 0 (p = 0.00) and Intervention 1 (p = 0.00). However, there was no significant difference between groups. Conclusion: TM-PNF stretching for one or three repetitions was as effective for improving acute hamstring extensibility in young healthy adults. The clinical implication for therapists is that for time efficiency and maximum benefits, one repetition of TM-PNF is as effective as three. Amsterdam University of Applied Sciences, All rights reserved. Keywords: target muscle proprioceptive neuromuscular facilitation, hamstrings, flexibility, extensibility, repetitions, stretching
Cristovão et al. (2017) | European School of Physiotherapy
single bout of static stretching in increasing
Introduction Maintenance of adequate muscle flexibility is important in rehabilitation from illness or injury, since immobility often leads to a reduction in flexibility. It is also considered to be important in injury prevention - a short, tight muscle can inhibit normal joint range of motion, and is also more easily over-extended and strained (Wan et al. 2016). As hamstring injury is a common sport injury, and stretching has been recommended to prevent this type of injury (Franklin et al. 2000, Thacker et al. 2004, Orchard et al. 2005), it is important to consider how to best optimise flexibility of the hamstring muscles in Various techniques to increase hamstring muscle have
proprioceptive
To our knowledge, previous research has not focused on the effect of the number of repetitions of TM-PNF stretching on the extensibility of hamstring muscles, after a single session. If we can better understand how to attain optimal benefits of TMPNF
stretching
of
the
hamstrings,
we
can
recommend to therapists a tool to use that is timeefficient and therefore may be incorporated easily into a rehabilitation session. This randomised clinical trial addresses the question: In young adults, are three repetitions of TM-PNF more effective than a single repetition of TM-PNF for improving acute
healthy individuals. flexibility
hamstring flexibility.
been
described,
neuromuscular
including
facilitation
extensibility of the hamstring muscles, as measured by the sit-and-reach test (SRT)?
(PNF),
ballistic stretching and static stretching (Etnyre et al.
Methods
1988, Franklin et al. 2000, Decoster et al. 2005). “Contract-Relax”
PNF,
or
target
muscle
Participants
proprioceptive neuromuscular facilitation (TM-PNF),
Target participants
involves passive stretch of the target muscle, then
Young adults were recruited on a voluntary basis
an isometric contraction of the same muscle,
from the international student population of the
followed by relaxation and passive movement into
European School of Physiotherapy at Amsterdam
further stretch (Feland et al. 2004). In terms of
University of Applied Sciences.
hamstrings PNF, there is evidence of an acute temporary increase in flexibility (Etnyre et al. 1988,
Inclusion & exclusion criteria
Decoster et al. 2005, O’Hora et al. 2011), but the
To be eligible participants must also be:
varying stretching protocols make it difficult to
1. Between 18 to 40 years of age, regardless of
determine the most effective and efficient methods
gender and nationality.
for improving hamstring extensibility in a single
2. Able to understand written and spoken English.
stretching session.
The following are exclusion criteria:
Spernoga et al. (2001) suggest that frequency and
1. Injury to the lumbar spine or lower extremity in
duration of stretching can influence flexibility gains.
the past three months (including dislocations,
In clinical practice there are time constraints, so
fractures, muscle tissue damage (whether grade 1,
determining the optimal frequency and duration for a
2 or 3), structural damage to the joints and wounds
single stretching session is important. Bonnar et al.
on the hamstrings.
(2004) found there to be no significant difference in
2. Having participated in an exercise activity 12
hamstring flexibility gains, whether the isometric
hours prior to the trial.
contraction of the target muscle is held for three, six
3. Inability to reach the slider on the SRT box for the
or 10 seconds. Therefore, isometric contractions as
baseline measurement.
short as three seconds can be effective and efficient
4. Reaching the maximum on the slider on the SRT
during a single stretch session in the clinical setting.
box for the baseline measurement.
Meanwhile, O’Hora et al. (2011) demonstrated that
5. Informed consent not obtained.
a single bout of TM-PNF is more effective than a
Cristovão et al. (2017) | European School of Physiotherapy
Procedure(s)
Standardised operating procedure
Subject recruitment
The
The recruitment drive was conducted via Facebook,
performed
emails,
short
procedure to ensure uniformity and minimise
first
variability. This can be found in the supplementary
and
presentations
through at
appearances
school
lectures
and in
the
academic week of the semester (February 6th to
interventions
and
following
a
measurement standardised
were
operating
document to this paper.
10th). An online sign-up form was used for registration.
Equipment The SRT is a field test commonly used to measure
Randomisation and concealed allocation
flexibility of (both) the hamstrings and low back
Allocation of participants to the two intervention
(Baltaci et al. 2003). Meta-analysis by Mayorga-
groups was randomised. Identity codes were
Vega and colleagues (2014) showed the SRT has a
created in a numerical order, and assigned to each
moderate mean correlation coefficient of criterion-
participant when they arrived to the trial. The
related validity (gender, age and level of extensibility
assigned
of
identity
codes
were
randomised
by
hamstrings
of
participants)
for
estimating
inscription to an intervention group by the principle
hamstring extensibility (rp range= 0.46-0.67). 4 cm
investigator using the “randBETWEEN” function on
is the minimal clinically important difference (MCID)
Microsoft® Excel. The interventions were named
for the SRT (Lopez-Miñarro et al. 2010). The
Intervention 0 or 1 for three or one repetitions of
reliability coefficient of the SRT is 95% (Mayorga-
TM-PNF respectively. After receiving informed
Vega et al. 2014).
consent to participate in the study via a signed form,
The test was administered using a standard SRT
the principal investigator referenced the individual’s
box, measuring length of base 35 cm, width 45 cm,
identity code against the corresponding group it was
height 32 cm and length 55 cm. The top of the box
randomly allocated to, to decide allocation. This
has a standard meter ruler attached measuring up
ensured allocation was concealed from the principal
to 50 cm. A metal slider is placed at a tangent to the
investigator and all other investigators until the
ruler, to assist with accuracy of measurement.
moment of assignment. Variables Blinding
Participants from both groups had their pre- and
Triple-blinding was achieved with participants, data
post-test
collectors and assessors by naming the two
anthropometric data (gender, height, BMI, practicing
intervention groups Intervention 0 and 1 for three or
yoga) was collected before testing.
one repetitions of TM-PNF respectively. These
The independent variable was the number of
labels were used consistently for participants, data
repetitions of TM-PNF stretching intervention (three
collection and data analysis. The two interventions
versus
were performed in the same room, one at a time,
dependent variable was hamstring extensibility as
each intervention by a different physiotherapist; the
measured by the SRT in centimetres (cm) to the
SRT measurement was conducted in an adjacent
closest 0.5 cm.
room. The data collector was not present when
The primary outcome was hence the difference in
interventions were carried out. The participant was
scores of the SRT in cm before and after the
blinded
intervention.
to
the
intervention
alternative intervention group.
received
by
the
measurements
one
repetitions
taken,
of
and
TM-PNF)
additional
and
the
Secondary outcomes were the anthropometric data mentioned
above
which
were
recorded
from
participants to analyse any additional effect on the primary outcome.
Cristovão et al. (2017) | European School of Physiotherapy
Data collection
SPSS® data analysis consisted of two main steps:
Data collection took place in February 2017. The
initial data analysis and comparison of interventions
principal investigator was the only person managing
outcomes.
the Microsoft® Excel spreadsheet where the data
descriptive statistics, analysis of outliers, a check for
was recorded in order to ensure blinding. The data
normality, and comparison of means between the
collector recorded the pre-intervention and post-
two intervention groups. The normality analysis
intervention measurements (SRTpre and SRTpost
included a check of mean and median, visual
respectively) on a paper recording form and entered
interpretation of the histograms, and results of the
the data into a raw data sheet for analysis. The
Shapiro-Wilk statistic. Comparison of means was
assessor performed the data analysis with the IBM®
carried out with either the independent sample T-
SPSS® version 22.0 statistical package (the latter
test for normally distributed variables, or the Mann-
results were downloaded into a Microsoft® Excel
Whitney
format).
variables. For gender, being a categorical variable, the
The
U
test
Chi-square
for for
data
analysis
non-normally independence
test
was
employed.
outcomes comprised of the paired sample T-test to
identify missing data, data that met exclusion
estimate if there was a significant difference
criteria, non-logical values (e.g. height expressed in
between SRTpre and SRTpost within groups, and
meters
calculate
the independent samples T-test to determine if there
descriptive statistics and create scatter plot graphs.
was a significant difference in SRTpost between
The assessor created the following new continuous
groups. A p-value of <0.05 was used to reject the
variables:
null hypotheses.
BMI
in
centimeters),
(calculated
as
weight
of
distributed
The assessor performed a preliminary analysis to
than
comparison
included
Data analysis
rather
The
initial
intervention
(kg)/height(m)^2), SRTpre (calculated as average of
The intervention labels were then changed from
the three pre-intervention measurements), SRTpost
Intervention 0 and 1 to 3 TM-PNF and 1 TM-PNF
(calculated as an average of the three post-
respectively after the intervention groups were
intervention
revealed for a clear representation of data and
measurements),
and
SRTchange
(calculated as the difference between SRTpost and
results tables in this paper.
SRTpre). Next to that, categorical variables were created: gender (assigning a 1 if female, and a 2 if
Results
male); yoga (assigning a 0 if the person was not a practitioner, and a 1 if (s)he was); height (assigning a 1 if below average, and a 2 if above average, where
the
average
was
that
of
the
whole
population); and BMI group (assigning a 1 if the person had BMI lower than 22.99, and a 2 if the BMI was higher than that). The BMI categorisation was chosen based on the comparison between the BMI international classification (WHO, 2004) identifying four categories (underweight < 18.50; normal further
Initial data analysis In total, 42 participants were recruited for the study. Following review, five participants were excluded in total; four because their SRTpre performance reached the SRT box maximum, thus their data was not recordable, and one because the age of the participant was not compliant with the inclusion criteria. Data analysis was thus performed on 37 participants.
split in two classes being 18.5 – 23 and 23 – 25; overweight 25 – 30; obese > 30) and the average and median BMI of the whole population (22.4 and 22.2 respectively). The assessor then converted the data from Microsoft® Excel format into an SPSS® data sheet.
Baseline characteristics and normality of data Baseline characteristics are presented in Table 1, while the outcome of the check for normality can be found in Table 4 (see appendix).
Cristovão et al. (2017) | European School of Physiotherapy
and SRTpost for both 3 TM-PNF (t(17) = -6.82; p = Having assessed normality, next step was to
0.00) and 1 TM-PNF (t(18) = 8.87; p = 0.00).
compare the means for each variable between the 3
The p values are reported and can be found in
TM-PNF
Table 3.
and
Depending
if
1
TM-PNF
the
intervention
variables
were
groups. normally
distributed, either the independent samples t- tests
Comparison between groups
or the Mann-Whitney U test. The p values are
The
reported and can be found in Table 4 (see
between 3 TM-PNF and 1 TM-PNF intervention
appendix). No significant difference was found in the
groups. Results show that there was no significant
baseline characteristics of our two groups.
difference in the outcome SRTpost (t(35) = 0.39; p = 0.70).
Comparison within groups The assessor compared the means within each intervention group. Results show that there was a significant difference between the outcomes SRTpre
assessor
compared
the
mean
SRTpost
Cristovão et al. (2017) | European School of Physiotherapy
practitioners. Only for BMI groups a significant Effect size
difference was found (p = 0.05).
After the trial, the effect size was calculated employing the Cohen’s d coefficient, which resulted in a small effect size (0.13).
Discussion This study sought to answer the research question: In young adults, are three repetitions of TM-PNF
Secondary outcome measures analysis
more effective than a single repetition of TM-PNF
After answering the research question, an additional analysis (including correlation analysis, Table 5 in appendix)
was
carried
out
on
the
impact on the interventions outcome independently of what the intervention was. The assessor looked at means and standard deviations and calculated correlation
between
the
available
anthropometric measures (gender, height, BMI) and SRTpre,
SRTpost,
categorical
variable
and
SRTchange.
‘Yoga’
was
A
new
created,
with
participants divided depending whether (s)he was a practitioner or not (1 – 0). For this variable, mean, standard deviation and correlation with SRTpre, SRTpost, and SRTchange were also determined (Table 5 in appendix). Within each intervention group, participants were divided by gender to assess if any significant difference could be found for the variable SRTchange. A normality check was first carried out, followed by the comparison of the means with the independent t-test, for which no significant difference could be found (results are in Table 6 and Table 7 in appendix). New datasets were
created
based
on
the
muscles, as measured by the SRT?
collected
anthropometric measures to assess if they had any
the
for improving acute extensibility of the hamstring
following
categorisations: gender (Female – Male); height
Primary outcome measure It was found that both one and three repetitions of TM-PNF stretching were sufficient to produce a significant change in acute hamstring extensibility, with the change in SRT scores between pre- and post-intervention as the main outcome measure. This was in line with what we expected, even though there was no direct evidence for it, but it was alluded to by existing literature indicating that even three-second-long
isometric
contractions
are
effective in a single session of stretching (Bonnar et al. 2004). However, there was no significant difference found between interventions, where we expected the outcome of three repetitions of TMPNF stretching to be significantly better than one repetition of TM-PNF stretching, by virtue of the fact that in the former intervention, participants have the opportunity to move into a further range. This indicates that one repetition of TM-PNF stretching is as
effective
as
three
repetitions
of TM-PNF
stretching, which has time-saving implications in practice.
(below average – above average, where the average was that of the whole population); BMI (below average – above average, being the cut-off point being the same as explained in the data analysis section); and yoga (Y – N, depending if the participant was a practitioner or not). As done before, a normality check was performed for the variable SRTchange, followed by comparison of the means was carried out with the independent t-test (results shown in Tables 6 and 7 in appendix). No significant
differences
were
found
in
the
improvements of female versus male, by height group, and non-yoga practitioners versus yoga
Validity of the SRT For the standard SRT box used in this study, it has been
suggested
that
limb
length
differences
between people would influence reaching distance, where people with a larger arm-to-leg length ratio relative to others in the study would get a better result, while those others are at a disadvantage (Hoeger et al. 1990). The modified Sit and Reach Test (MSRT) was thus proposed by Hoeger and colleagues (1990) to control for these proportional differences as the zero point is adjusted for each individual, based on their sitting reach position.
Cristovão et al. (2017) | European School of Physiotherapy
However, Mayorga-Vega and colleagues (2014)
the
found that there was still lower criterion validity of
contraction at intensities closer to their personal
the MSRT as compared to a classic SRT.
maximal effort. Therefore if participants did not give
Furthermore, as the primary outcome is the
20% of their maximal effort in this trial, this could
difference
post-
potentially affect the validity of the results. A trial run
intervention, body proportions would be negated in
could have improved the participants’ ability to
obtaining the measure and are hence not relevant. If
follow the instruction accurately. However, this was
the outcome was simply a result based on a one-
not possible given that the experiment was a test of
time
effectiveness of a single repetition of TM-PNF.
between
measurement,
scores
then
pre-
and
differences
between
participants
performed
Participants
influence the outcome and would have to be taken
measurement area after the intervention, which may
into account.
have influenced the acute effects of the TM-PNF.
A potential confounding factor which could influence
However, significant differences were still found for
the primary outcome measure was the effect of
both intervention groups, illustrating the lasting
movement in the lumbar spine while performing the
effectiveness of the interventions. This is also
SRT. However, research yielded that the SRT has
translates
low
usefulness of the interventions on acute hamstring
validity
for
estimating
lumbar
into
required
functional
to
target-muscle
participants in terms of leg or arm length would
criterion
were
the
walk
application
to
of
the
the
extensibility, as compared to a stronger moderate
extensibility.
criterion
In this trial there was no control group, since the aim
validity
for
estimating
hamstrings
extensibility (Mayorga-Vega et al. 2014).
of the trial was to investigate any differences in the effectiveness of one- versus three- repetitions of
Internal validity The
SOPs
TM-PNF; rather than to investigate the effectiveness ensured
of TM-PNF compared to no intervention. However,
standardisation of the procedure employed in the
since there was an improvement between SRTpre
SRT box measurements, and standardisation of the
and SRTpost for both the interventions groups, a
interventions. Standardisation of each intervention
control group would be useful to show whether any
was
one
of this change was simply due to repetition of the
physiotherapist perform each intervention on all
SRT. This would increase validity of our conclusions
participants.
about the effectiveness of TM-PNF.
further
used
in
ensured
this
by
RCT
having
just
The number of repetitions of TM-PNF was to be the only difference between the two interventions. To
External validity
ensure this, detailed procedures were defined in the
Participants showed large heterogeneity in terms of
SOP for each intervention, and the physiotherapists
country of origin and sports practiced. They did not
were present to observe each other’s interventions,
show
thereby minimising any discrepancies in the way the
generalisations to a wider population can be made
TM-PNF was performed.
about the relationship between BMI on the test
A limitation was the inability to confirm that
outcome, the sample population would need to
participants followed the instruction to give 20% of
display a wider range of BMI.
their maximum effort in the active hamstring
Since participant registration for the trial was on a
contraction phase of TM-PNF. There were large
voluntary basis, there was potentially a sample bias,
differences in the force output across participants,
in favour of terms of individuals who are more
but this is to be expected given that the effort
interested in stretching and flexibility training.
required was a percentage of the individual
However, since no correlation was found between
participant's maximum. A previous trial by Kwak et
the effectiveness of TM-PNF stretching and yoga
al. (2015) found TM-PNF to be more effective when
participation versus non-yoga participation, the
a
huge
variation
in
BMI.
Before
any
Cristovão et al. (2017) | European School of Physiotherapy
effect of this potential sample bias on the external
Existing literature on the relationship between BMI
validity of the trial can be assumed negligible.
and hamstring extensibility is inconclusive, only having been explored in very specific subject groups
Secondary outcome measures
such as adolescents and osteoarthritic subjects
Existing literature has consistently found that
(Arora et al. 2013, Onigbinde et al. 2013, Al-Asiri et
women have higher hamstring extensibility than
al. 2015). Therefore, this study looked at any
men (Etnyre et al. 1988, Krivickas et al. 1996).
possible relationship between BMI and the primary
Furthermore, Marshall and colleagues (2014) went
outcome measure, because gaining insight into this
on to ascribe this disparity to differences in stretch
would be potentially useful for recommendations
tolerance.
to
around weight management. There was a significant
examine whether the study revealed any between-
difference found between the two BMI groups,
sex
TM-PNF
where the under average group performed better
intervention. Whilst females consistently performed
than the above average group. However, the
better on average than males, both pre-intervention
unequal distribution of participants between two of
and post-intervention, no significant differences
those groups (with an increased tendency towards
were found in the primary outcome measure
below average weight), as well as a relative
between genders, suggesting that the intervention is
homogeneity across the sample (rather than having
not selective and is effective regardless of gender.
participants
Ben and colleagues (2010) postulated that the
international weight classes) indicate that more
extensibility of yogis and yoginis was due to the
research should be done before drawing any
specific stretching regimes practiced, or at least the
correlations between BMI and SRT results.
Hence,
differences
the
in
researchers
response
to
wanted
the
ranging
across
the
true
BMI
self-selecting biases of those predisposed to good extensibility. Furthermore, it was found that yoga
Further recommendations
has an effect on hamstring flexibility (Amin et al.
This trial has shown that one repetition of TM-PNF
2014). This study sought to find out if there were
is as effective as three repetitions of TM-PNF in
any differences between practitioners and non-
healthy young adults. This evidence can be used to
practitioners of yoga. Hence, another secondary
support the development of a protocol for TM-PNF
outcome highlighted for analysis was whether there
stretching in this population.
was a relationship between the primary outcome
Further research is recommended to show that the
measure and participants who are or are not
significant differences seen in the primary outcome
practitioners of yoga. However, no significant
measure for both intervention groups was not just
differences
due to repetition of the SRT. This can be done by
between
in those
the
primary
two
outcome
categories
measure
were
found,
introducing a control group in the study design.
potentially because possessing good extensibility
The protocol developed will be applicable to healthy
does
young
not
necessarily
relate
to
increased
adults,
and
may
be
used
during
a
effectiveness of TM-PNF, or the inverse for those
physiotherapy assessment or treatment session, if
who do not have good extensibility.
hamstring extensibility is thought to pose a problem
As limb lengths may have been a potential
to a client. The protocol may also be used to
influencing factor in differences between groups
increase the extensibility of the hamstrings pre- or
(Hoeger et al. 1990), height of participants was a
post-sport to prevent injury and / or improve
secondary outcome measure taken into account for
performance. To apply the protocol to the wider
the analysis. However, no significant differences in
population, further research would be recommended
the primary outcome measure between those of
into:
above and below average heights were found.
repetitions of TM-PNF for other age categories; and
the
effectiveness
of
one
versus
three
the effectiveness of one versus three repetitions of
Cristovão et al. (2017) | European School of Physiotherapy
TM-PNF in subjects with hamstring injury, where the integrity of the muscle tissue is disturbed.
● Bonnar B, Deivert R, Gould T. The relationship between isometric contraction durations during hold-relax
stretching
and
improvements
of
hamstring flexibility. J Sports Med Phys Fitness.
Conclusion
2004;44(3):258-61.
This study has demonstrated that one repetition of TM-PNF stretching is effective for improving acute hamstring extensibility in young healthy adults. This is relevant for therapists who want to attain maximum benefits while being time efficient in the rehabilitation of their patients. TM-PNF may be useful as a warm up or ‘pre-intervention’, prior to the main therapy, For example, prior to performing a straight-legged deadlift, a single repetition of TMPNF may be considered as a quick intervention preexercise to reduce risk of injury.
● Decoster L, Cleland J, Altieri C, Russell P. The effects of hamstring stretching on range of motion: a systematic literature review. J Orthop Sports Phys Ther. 2005;35:377-87. ● Etnyre BR, Lee EJ. Chronic and acute flexibility of men and women using three different stretching techniques. Res Q Exerc Sport. 1988;59(3):222–228. ● Feland J, Marin H. Effect of submaximal contraction
intensity
proprioceptive
in
contract-relax
neuromuscular
facilitation
stretching. Br J Sports Med. 2004;38(18):1-2. ● Franklin B, Whaley M, Howley E, Balady G,
Acknowledgements The authors thank Mr. Jesse Arden for his assistance in the planning of this study and
American College of Sports Medicine. ACSM’s guidelines for exercise testing and prescription. 6th ed. Philadelphia, PA: Lippincott Williams &
research article.
Wilkins, 2000. ● Hoeger WWK, Hopkins DR, Button S, Palmer
References
TA. Comparing the sit and reach with the
● Al-Asiri ZA, Shaheen AAM. Body mass index and health related physical fitness in saudi girls and adolescents aged 8 - 15 years. Open Journal
of
Therapy
and
Rehabilitation.
2015;3(4):116-25. ● Amin DJ, Goodman M. The effects of selected asanas in iyengar yoga on flexibility: pilot study. J Bodyw Mov Ther. 2014;18(3):399-404. ● Arora A, Souza SD, Yardi S. Association between body mass index and hamstring/back flexibility in adolescent subjects. International Journal of Science and Research. 2013;5(7):1-4. ● Baltaci G, Un N, Tunay V, Besler A, Gerceker S. Comparison of three different sit and reach tests for measurements of hamstring flexibility in female university students. Br J Sports Med. 2003;37:59-61. ● Ben M, Harvey LA. Regular stretch does not increase muscle extensibility: a randomized controlled trial. Scand J Med Sci Sports. 2010;20(1):136-44.
modified sit and reach in measuring flexibility in adolescents. Pediatr Exerc Sci. 1990;2(2):15662. ● Krivickas LS, Feinberg JH. Lower extremity injuries in college athletes: relation between ligamentous laxity and lower extremity muscle tightness.
Arch
Phys
Med
Rehabil.
1996;77(11):1139-43. ● Kwak DH, Ryu YU. Applying proprioceptive neuromuscular facilitation stretching: optimal contraction intensity to attain the maximum increase in range of motion in young males. J Phys Ther Sci. 2015;27(7):2129-32. ● Lopez-Minarro PA, Vaquero-Cristobal R, Muyor JM, Espejo-Antunez L. Criterion-related validity of sit-and-reach test as a measure of hamstring extensibility
in
older
women.
Nutr
Hosp.
2015;32(1):312-31. ● Marshall PWM, Siegler JC. Lower hamstring extensibility in men compared to women is
Cristovão et al. (2017) | European School of Physiotherapy
explained by differences in stretch tolerance. BMC Musculoskelet Disord. 2014;15(223):1-7. ● Mayorga-Vega D, Merino-Marban R, Viciana J. Criterion-related validity of sit-and-reach tests for estimating hamstring and lumbar extensibility: a meta-analysis. J Sports Sci Med. 2014;13(1):114. ● O’Hora J, Cartwright A, Wade C, Hough A, Shum G. Efficacy of static stretching and proprioceptive neuromuscular facilitation stretch on hamstrings length after a single session. J Strength Cond Res. 2011;25(6):1586-91. ● Onigbinde AT, Akindoyi O, Faremi FA, Okonji A, Shuaib O, Lanre OO. An assessment of hamstring
flexibility
of
subjects
with
knee
osteoarthritis and their age matched control. Clinical Medicine Research. 2013;2(6):121-5. ● Orchard J, Best T, Verrall G. Return to play following muscle strains. Clin J Sport Med. 2005;15(6):436–41. ● Spernoga S, Uhl T, Arnold B, Gansneder B. Duration of maintained hamstring flexibility after a
one-time,
modified
hold-relax
stretching
protocol. J Ath Train. 2001;36(1):44-8. ● Thacker S, Gilchrist J, Stroup D, Kimsey C. The impact of stretching on sports injury risk: A systematic review of the literature. Med Sci Sports Exerc. 2004;36(3):371-8. ● Wan X, Qu F, Garrett W, Liu H, Yu B. Relationships among hamstring muscle optimal length and hamstring flexibility and strength. J Sport Health Sci. 2016.;4(9):1-8. ● World Health Organisation – BMI classification [online]. Perth: World Health Organisation; c 2005 [last update Feb. 2017; cited 2017 Feb 26]. URL: http://apps.who.int/bmi/index.jsp?introPage=intro _3.html
Cristovão et al. (2017) | European School of Physiotherapy
Appendix
