The Effectiveness of PNF Versus Static Stretching
on Increasing Hip-Flexion Range of Motion
Landon Lempke, Rebecca Wilkinson, Caitlin Murray, and Justin Stanek
Clinical Scenario: Stretching is applied for the purposes of injury prevention, increasing joint range of motion (ROM), and
increasing muscle extensibility. Many researchers have investigated various methods and techniques to determine the most
effective way to increase joint ROM and muscle extensibility. Despite the numerous studies conducted, controversy still
remains within clinical practice and the literature regarding the best methods and techniques for stretching. Focused Clinical
Question: Is proprioceptive neuromuscular facilitation (PNF) stretchin g more effective than static stretching for increasing
hamstring muscle extensibility through increased hip ROM or increased knee extension angle (KEA) in a physically active
population? Summary of Key Findings: Five studies met the inclusion criteria and were included. All 5 studies were
randomized control trials examining mobility of the hamstring group. The studies measured hamstring ROM in a variety of
ways. Three studies measured active KEA, 1 study measured passive KEA, and 1 study measured hip ROM via the single-leg
raise test. Of the 5 studies, 1 study found greater improvements using PNF over static stretching for increasing hip flexion, and
the remaining 4 studies found no significant difference between PNF stretching and static stretching in increasing muscle
extensibility, active KEA, or hip ROM. Clinical Bottom Line: PNF stretching was not demonstrated to be more effective at
increasing hamstring extensibility compared to static stretching. The literature reviewed suggests both are effective methods
for increasing hip-flexion ROM. Strength of Recommendation: Using level 2 evidence and higher, the results show both
static and PNF stretching effectively increase ROM; however, one does not appear to be more effective than the other.
Keywords: muscle flexibility, proprioceptive neuromuscular facilitation, hypomobility, tightness
Clinical Scenario
Stretching exercises are commonly prescribed during warm-up and
cool-down protocols, strength and conditioning training programs,
and rehabilitation programs. Stretching is applied for the purposes
of injury prevention, increasing joint range of motion (ROM), and
increasing muscle extensibility.
1
Two common methods of stretch-
ing in clinical practice are static stretching and proprioceptive
neuromuscular facilitation (PNF) stretching. It is generally
believed that PNF stretching will result in increased ROM com-
pared with static stretching due to increased inhibition of the
targeted muscle. Researchers have investigated both static and
PNF stretching techniques to determine the most effective way to
increase joint ROM by altering the extensibility properties of
muscle, but despite the numerous studies conducted, controversy
still remains within clinical practice and the literature regarding the
best methods and techniques for stretching. To add to the contro-
versy, synonymous terms describing ROM measurement are being
implemented but differ in their measurement techniques. In the
articles examined, the terms hip ROM, knee extension angle
(KEA), and hamstring extensibility were used synonymously to
describe the hip-flexion motion that was opposed by the hamstring
group. For the purpose of this article, the term hip-flexion ROM
will be used instead of the previously mentioned terms to merge the
multiple synonymous terms into one.
Focused Clinical Question
Is PNF stretching more effective than static stretchi ng for
increasing hamstring muscle extensibility in a physically active
population?
Summary of Search (Best Evidence
Appraised and Key Findings)
• The literature was searched for level 2 evidence or higher and
a PEDro score of 5/10 or higher for articles that compared
PNF stretching with static s tretching a nd their effects on
hamstring extensibi lity or hip-flexion ROM in a physically
active population.
• The initial literature search returned 11 possible studies related
to static versus PNF hamstring stretching; 5 studies met the
inclusion criteria and were included.
• One study measured hip ROM via the single-leg raise (SLR)
test.
2
• Three studies measured active KEA.
3–5
Two of those studies
used goniometry to measure ROM.
3,5
The remaining study
used an inclinometer to measure ROM.
4
• One study measured passive KEA with goniometry.
6
• One study found greater improvements using PNF over static
stretching for increasing hip flexion.
2
• Four studies found no significant difference between PNF
stretching and static stretching at increasing hip-flexion
ROM.
3–6
Lempke is with the University of Georgia, Athens, GA. Wilkinson is with the Dept
of Sports Medicine, Union Medical Group Bone & Joint Center, Terre Haute, ID.
Murray is with the Dept of Sports Medicine, University of Houston, Houston, TX.
Stanek is with Illinois State University, Normal, IL. Lempke (lblempke@uga.edu)is
corresponding author.
289
Journal of Sport Rehabilitation, 2018, 27, 289-294
https://doi.org/10.1123/jsr.2016-0098
© 2018 Human Kinetics, Inc.
CRITICALLY APPRAISED TOPIC
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Clinical Bottom Line
The reviewed evidence suggests that PNF stretching is equivalent
to static stretching in regard to improving hip-flexion ROM. The
length of treatment varied greatly with only one study utilizing a
stretching protocol for a 4-week period.
2
Of the 5 studies, 4
measured KEA, either actively or passively. Only one study found
self-PNF stretching to be more effective than static stretching for
hamstrings; however, different assessment protocols for hip ROM
were measured. More research must be conducted to make a
definitive and evidence-based decision about the best stretching
technique for increasing hamstring extensibility.
Strength of Recommendation
Using level 2 evidence and higher, the results show that static
stretching and PNF stretching both effectively increase hip-flexion
ROM; however, one does not appear to be more effective than
the other.
Search Strategy
Terms Used to Guide Search Strategy
• Patient/Client group: healthy and active individuals
• Intervention/Assessment: manual or assisted PNF hamstring
stretching
• Comparison: static hamstring stretching
• Outcome(s): increased hamstring extensibility
Sources of Evidence Searched (Databases)
• PubMed
• Ovid
• EBSCO
• Google Scholar
• ScienceDirect
Search Terms
• PNF versus static stretch
• PNF versus static hamstring
• PNF stretch hamstring
• PNF versus static hip
Limits Used
• Level 2 evidence or higher
• PEDro score of 5/10 or higher
• Research published in the past 15 years
Inclusion and Exclusion Criteria
Inclusion Criteria
• Studies were limited to humans
• Limited to English language
• Compared static hamstring stretching with any form of PNF
hamstring stretching
• Subjects were healthy and participated in some form of regular
physical activity
• Studies utilized a randomized control trial design
Exclusion Criteria
• Injured or previously injured population
• Comparison of PNF with static stretching of any other
muscle(s)
• Studies that did not specifically compare PNF stretching with
static stretching
Results of Search
A total of 5 relevant studies were located and categorized as shown
in Table 1 (based on levels of evidence
7
). All 4 examiners searched
the available literature.
Best Evidence
The studies listed in Table 2 were identified as best evidence and
selected for inclusion in this review. These articles were selected
because they were graded with a level of evidence of 2 or higher
and compared the effectiveness of PNF hamstring stretching with
static hamstring stretching by analyzing hamstring extensibility
through either hip ROM or increased KEA.
Summary of Best Evidence
Implications for Practice, Education, and Future
Research
All articles reviewed address the use of PNF stretching versus static
stretching for the purpose of increasing hip-flexion ROM. Overall,
the results from this critically appraised topic are inconclusive in
regard to indicating whether PNF stretching is more effective than
static stretching in increasing hip-flexion ROM. The reviewed
literature demonstrates that hip-flexion ROM will increase regard-
less if PNF or static stretching is utilized.
Stretching techniques are commonly used for the purpose of
increasing muscular extensibility and ROM. Additionally, stretch-
ing techniques can help prevent musculoskeletal injuries, reduce
muscular pain, improve muscular force capabilities, and subse-
quently improve activities of daily living or athletic performance.
5,8
There are many types of stretching techniques, including dynamic,
static, ballistic, and PNF. Of those techniques, 2 commonly used
techniques are static stretching and PNF stretching.
5
Table 1 Summary of Study Designs of Articles
Retrieved
Study design/
methodology of
articles retrieved Level
Number
located Author (year)
Randomized
control trial
25Yıldırımetal
2
(2016)
Lim et al
5
(2014)
Feland et al
6
(2001)
Funk et al
4
(2003)
Puentedura et al
3
(2001)
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Table 2 Characteristics of Included Studies
Study 1
(Yıldırım et al,
2
2016)
Study 2
(Lim et al,
5
2014)
Study 3
(Feland et al,
6
2001)
Study 4
(Funk et al,
4
2003)
Study 5
(Puentedura et al,
3
2011)
Study design Randomized control trial Randomized control trial Randomized control trial Randomized control trial Randomized control trial
Participants Of the 40 students (17 males and 9
females; mean age = 21.5 (1.3) y;
mean body height = 172.8 (8.2)
cm; and mean body mass index =
21.9 (3.0) kg·m
−2
) with bilateral
hamstring tightness, only 26
completed the study (52 lower
extremities). Exclusion criteria:
>70° of hip flexion, history of
hamstring injury, and/or current
musculoskeletal pain.
A total of 48 males (mean age =
22.38 (2.31) y; mean height =
173.63 (3.59) cm; and mean
weight = 68.50 (9.15) kg)
participated in this study.
Inclusion criteria: reduced
hamstring extensibility of 20°
found during the active knee
extension test. Exclusion criteria:
history of injury that could alter
hamstring muscle extensibility
(eg, herniated disk, ligament
damage, muscle damage), history
of neuromuscular surgery within
the last 5 y, or engage in flexibility
training.
A total of 97 subjects (66 males
and 31 females; mean age = 65 y)
volunteered at the Huntsman
World Senior Games. Subjects
were excluded if they had recently
completed an active warm-up,
participated in sporting activities
earlier, were experiencing signs
or symptoms of delayed onset
muscle soreness (DOMS), or had
soreness from previous injury.
A total of 40 division I college
athletes (20 males and 20 females;
mean age = 19.7 (1.4) y and mean
weight = 72.5 (13.4) kg)
participated in this study. Subjects
participated in 3 sports: 20
subjects in baseball, 13 subjects in
field hockey, and 7 subjects in
rowing. No inclusion or exclusion
criteria were annotated.
A total of 30 subjects (17 males and 13
females; mean age = 25.7 (3.0) y) who
were also students and faculty from a
university participated in this study.
Exclusion criteria: possible pregnancy,
hamstring injury within the past year,
exceeding 80° in initial active knee
extension test, and/or participation in
sports that required regular hamstring
stretching. No subjects were excluded.
Intervention
investigated
Subjects were randomly allocated
to one of 4 groups: (1) SS (10
repetitions for 30 s), (2) self-PNF
stretching (contact for 10 s and
relaxed for 10 s), (3) Mulligan
traction straight leg raise
technique (3 repetitions), or (4) no
intervention. SLR tests were used
to assess hip-flexion ROM.
Hamstrings were concluded to be
hypomobile if their SLR was
≤70°. All interventions and tests
were performed bilaterally. The
intervention groups were
supervised during interventions.
All stretching interventions were
performed once a day, 3 d a week
for 4 wk. Subjects were supine
when the researcher passively
flexed the hip joint while the knee
was fully extended to the end
point where firm resistance was
felt in the hamstring muscle
group. Another researcher
measured the hip-flexion angle
with a digital goniometer, and it
was measured and repeated 3
times for each limb with average
value recorded.
Subjects were randomly allocated
to one of 3 groups: (1) static
stretch group (1 repetition for
30 s), (2) PNF hold-relax group (3
repetitions of hamstring isometric
contractions for 6 s followed by
relaxation for 5 s), or (3) control
group. All interventions were
applied to the hamstrings once.
Subjects were positioned supine
on a treatment table with the
nontested thigh and pelvis
attached to the table with velcro.
Active knee extension test was
applied from this position and
uses to assess hamstring
extensibility. Hamstring maximal
voluntary contractions were
assessed in a prone position in 30°
of knee flexion with the ankle
fixed in place before and after
stretching interventions. Postural
balance was assessed via double-
limb balance on a force plate with
the subjects determining their
comfortable stance width and
arms placed by their sides before
and after stretching interventions.
A 360˚ stainless steel goniometer,
surface EMG, and a force
measuring plate were used to
collect measurements.
Subjects were randomly assigned
to one of 3 groups: (1) contract-
relax PNF stretching (2
repetitions of 10 s of stretching
and 6 s of hip extension
contraction; total time of 32 s),
(2) SS (1 repetition of 32 s), or
(3) control group. Subjects
performed 4 toe touch stretches to
decrease the viscoelastic
behavior. All groups were
measured pretest and posttest
using a goniometer (stayed in
place from pretest to posttest
measurements). Knee extension
ROM was measured with the
patient supine on a treatment
table, nontest leg parallel and in
contact with a bar on the table.
Hip was flexed to 90°–100° to
ensure hamstring tightness, and
then, the knee extended until mild
discomfort was felt for both
interventions.
Subjects had baseline hamstring
mobility assessed. Participants
were randomly assigned
following baseline assessment to
either 5 min of PNF or SS. Two
additional variables were assessed
by either 5 min following
stretching without exercise or
5 min following stretching
performed after a 60-min
conditioning program. The
program consisted of 10 min of
cycling exercise performed before
and after an upper-body exercise
program consisting of
weightlifting. Within 7 d, the
procedure was repeated with PNF
and SS crossed over.
Hamstring mobility was assessed
via the active knee extension test.
Subjects were supine on a table,
and the knee and hip were both
placed into 90° of flexion with.
Subjects were asked to actively
extend the knee as far as possible
Subjects were randomly assigned into
one of 2 groups: (1) SS (2 repetitions of
30 s) or (2) HR-PNF stretching (4
repetitions of 10 s maximal isometric
contraction followed by 10 s passive
stretch). Left leg of subjects served as a
control for interventions. Both
interventions resulted in 80 s of
intervention times. Subjected warmed
up for 5 min maintaining a set resistance
similar for all subjects to ensure
consistency between subjects. Subjects
were supine on a treatment table
secured underneath a pulley system that
pulled a nylon rope attached to the
subject’s ankle via a laced ankle brace
that also kept the ankle and foot in a
neutral position. Stretching force was
perpendicular to the lower leg, and
stretching force was applied via free
weights attached to another pulley.
Torque was standardized to 5% of each
subject’s body mass, which resulted in
varying free weight to be applied for
each subject’s intervention. Stretching
instructions were given to the subject
through specified verbal
communication, and durations were
monitored using a stopwatch. Active
knee extension test was measured using
a digital inclinometer (over anterior leg
on tibial tuberosity) 3 times on the
control leg first and then repeated on the
subject’
s test leg.
(continued)
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Table 2 (continued)
Study 1
(Yıldırım et al,
2
2016)
Study 2
(Lim et al,
5
2014)
Study 3
(Feland et al,
6
2001)
Study 4
(Funk et al,
4
2003)
Study 5
(Puentedura et al,
3
2011)
Outcome
measure(s)
Outcome measure was hip-
flexion ROM and was assessed
via passive SLR test.
Outcome measures included
active knee extension angle,
muscle activation during
maximum voluntary isometric
contraction, and static balance.
Outcome measure was passive
knee extension angle.
Outcome measure was hamstring
flexibility via the active knee
extension test.
Outcome measures included the active
knee extension test angles at
premeasurement and postmeasurement.
Main
findings
No differences between groups
were found for age, body mass
index, and initial hip-flexion
ROM. A significant increase in
hip-flexion ROM was found in all
intervention groups after a 4-wk
period (P < .05). Results
demonstrated a significant
increase in hip-flexion ROM in
both the Mulligan TSLR
technique and PNF stretching
groups compared with SS (P = .02
and P = .02). No significant
difference was found between
Mulligan TSLR technique and
PNF stretching groups (P = .92).
A significant difference was
found in active knee extension
ROM after the application of both
stretching interventions (P < .05).
Both intervention groups showed
significant increases in knee
extension ROM compared with
the control group (P < .05). No
significant difference was found
between SS and PNF hold-relax
stretching. The control group
showed no significant difference
in knee extension ROM. Maximal
voluntary isometric contraction
significantly increased only in the
SS group after the stretching
(P < .05). Static balance showed
no significant difference between
stretching techniques in any of the
groups.
Wilcoxon signed-rank tests
showed median difference in
scores between pretest and
posttest were significantly
different in all 3 groups. A
statistical difference from pretest
to posttest was found between the
control group and the CR-PNF
group (P < .001), and the control
group and the static group
(P < .001). No differences were
found between the CR-PNF and
static treatment groups (P = .15).
Results did not change after
accounting for age. Median
differences between both
intervention groups were
significant for men, but not for
women, and for those aged <65 y,
but not for those aged >65 y.
A significant group by time
interaction (P = .05) was found
due to increased hamstring
flexibility achieved with PNF
from the baseline measure to the
60-min post exercise measure.
Post hoc analysis resulted in no
significant differences between
static and PNF at any time points.
Hamstring flexibility showed
significant increases after exercise
for the PNF intervention (P = .05)
compared with no exercise or
baseline. No differences were
found within the SS group across
time. No order effect among
conditions were found, and no
differences between PNF and SS
conditions were observed.
No significant difference was found
among the groups before treatment
(P = .12); however, a significant
difference after the treatment was
present (P < .001). Pairwise
comparisons resulted in a significant
difference between HR-PNF and
control groups (P < .001) and between
SS and control groups (P = .01). No
difference was found between the 2
stretching conditions (P = .78). Both
stretching conditions increased active
knee extension angle significantly over
time (P < .001).
Level of
evidence
22222
Validity
score
PEDro score: 5/10 PEDro score: 5/10 PEDro score: 6/10 PEDro score: 6/10 PEDro score: 7/10
Conclusion A 4-wk stretching intervention is
beneficial for increasing hip-
flexion ROM in bilateral
hamstring tightness; however,
PNF stretching and Mulligan
TSLR technique show no
differences.
Application of either SS or PNF
stretching is effective at
increasing muscle extensibility
without reducing muscle activity
or postural stability. SS and PNF
stretching demonstrated no
significant differences.
No differences in hamstring
flexibility were found between
interventions as a total cohort.
Men may respond differently to
stretching techniques compared
with women, and those
individuals older than 65 y may
find differences between
techniques as well.
Findings suggest that PNF
stretching and exercise may be
more effective in increasing
hamstring flexibility compared
with just PNF without exercise or
SS overall.
Results demonstrate no benefitofSS
over HR-PNF at increasing hamstring
flexibility. Both interventions
demonstrated similar increased changes
in hamstring flexibility.
Abbreviations: CR-PNF, contract-relax PNF; EMG, electromyography; HR-PNF, hold-relax PNF; TSLR, traction straight leg raise; PEDro, Physiotherapy Evidence Database; PNF, proprioceptive neuromuscular facilitation; ROM,
range of motion; SLR, single leg raise; SS, static stretching.
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The static stretching technique is a widely used method that
extends the muscle length by autogenic inhibition exciting the
Golgi tendon organ.
5
This technique involves passively stretching a
given antagonist muscle by placing it in a maximal position of
stretch and holding it there for an extended time period.
5,8
Re-
commendations for the optimal time for holding this stretched
position typically indicate that a 30-second hold time repeated 3 to
4 times will provide the most beneficial results.
8
This type of
stretching technique is considered much safer for sedentary or
untrained individuals.
8
However, the resistance to musculotendinous stretching
involves not only the viscoelastic properties of muscle and con-
nective tissue but also the neurological reflex and voluntary
components of muscular contraction.
5
Therefore, PNF stretching
techniques are used to increase joint ROM by performing voluntary
muscle contraction and promoting muscle relaxation to reduce the
reflexive components that cause muscle contraction.
9
PNF tech-
niques were first used for treating patients who had various
neuromuscular paralyses but are now widely used as a stretching
technique for increasing fl exibility.
9
There are a number of differ-
ent PNF techniques that are used for stretching, including slow-
reversal-hold-relax, contract-relax, and hold-relax techniques.
5,8,9
All involve some combination of alternating contraction and
relaxation of both agonist and antagonist muscles. It is recom-
mended that a 10-second active push phase followed by a 10-
second passive relax phase repeated 3 times be used for optimal
results.
9,10
Theoretically, PNF stretching techniques should be superior
to static stretching techniques because they activate not only the
muscle fibers but also the sensory receptors within the agonist and
antagonist muscle as well.
5
However, our review of the literature
within the last 15 years contests the ideology that PNF is superior
regarding stretching; specifically, of the hamstring group to in-
crease hip-flexion ROM. Out of the 5 studies used in our critically
appraised topic, 4 suggest there are no differences in using static
stretching or PNF stretching to increase muscular flexibility of the
hamstring muscle group.
2–4,6
When comparing the studies used in this critically appraised
topic, 3 studies used hold-relax PNF stretching techniques,
3–5
1 study used contract-relax PNF stretching techniques,
6
and the
last study used a self-PNF hold-relax stretching technique moni-
tored by an investigator.
2
The studies examined participants from
19 to 79 years old,
2–6
and 3 studies used an exercise warm-up.
2–4
Four studies measured extensibility by knee extension
3–6
compared
with 1 study that used hip ROM as its measure.
2
Three studies
included a control group compared with a static stretching group
and a PNF stretching group.
3,5,6
The hamstring muscle group is a multijoint muscle, which is
most frequently damaged in the human body.
3
Stretching techni-
ques are a treatment that is commonly applied to this muscle group
to prevent injury and promote function postinjury. While this
critically appraised topic came to an inconclusive conclusion in
regard to which stretching technique is the most effective in
improving hamstring muscle ROM, it appears that more research
needs to be conducted to come to a defi nitive answer.
Most studies did not include participants with hamstring
pathologies; however, to determine the effectiveness of this treat-
ment technique, perhaps more studies examining individuals with
hamstring hypo mobility should be conducted. An additional factor
to consider is the structural properties that cause a greater resistance
to change in hamstring length in males than females.
11
The studies
examined used a mixture of male and females, but none of the
studies examined differences between males and females in the
control or experimental groups. It is also important to note age can
be a factor as well. In a study conducted by Feland et al,
6
PNF
stretching was superior in regard to ROM in males and those under
the age of 65 years after an initial stretch. Another study also
demonstrated that stretch duration in an older population can allow
for more ROM compared with that of a younger population.
12
Finally, the use of various measurement techniques for hamstrings
(sit and reach, single-leg raise test, KEA, and stand and reach), the
variances in active and passive ROM, the different types of PNF
techniques, the duration of stretches, and the subjective nature of
clinicians’ feelings of tight muscular end feel when putting a
subject into a stretch likely introduces measuring error and vari-
ability even in studies using similar stretching techniques.
Even without consistent evidence to support the use of PNF
stretching over static stretching, there appears to be little to no risks
for clinicians to make their own personal decision in the type of
stretching application. In regard to hamstring stretching, emphasis
should be placed on an initial stretching protocol of 5 days a week
for 6 weeks, then stretching 3 times a week to maintain initial ROM
improvements.
13,14
More research is needed in this area to support
or refute the common belief that PNF stretching is superior
compared to static stretching in regard to ROM benefits. Therefore,
clinicians should base their approach on factors such as patient
preference, stretching frequency, ease of instruction, clinician
expertise and familiarity, and requirements for clinician assistance
rather than on assumptions of relative effectiveness .
References
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