Journal of Sport Rehabilitation,1999.8, 195-208
0 1999 Human Kinetics Publishers, Inc.
Effects of Static and Hold-Relax Stretching
on Hamstring Range of Motion Using
the FlexAbillity LEI000
Phillip A. Gribble, Kevin M. Guskiewicz, William E. Prentice,
and Edgar W. Shields
The purposes of this study were to determine the effects of static and holdrelax stretching on hamstring range of motion and to examine the reliability
of the FlexAbility LElOOO compared with the goniometrically measured active knee-extension test. Forty-two participants (18-25 years old) were assigned to either a control, static, or hold-relax training group. Participants
were stretched four times a week over a 6-week period, with four 30-s stretches
per session using a straight-leg-raise method on the FlexAbility LE1000. It
was determined that both static and hold-relax techniques significantly improved hamstring flexibility (ISLR: +33.0S0 f 9.08' and +35.17" 10.39',
respectively). Participants of both techniques reached a plateau in flexibility
improvement between Weeks 4 and 5. Thus, static and hold-relax stretching
are equally effective in improving hamstring ROM. The FlexAbility LEIOOO
and the goniometer were both found to be highly reliable. Therefore, either
measurement technique could be used successfully to measure hip-flexion
ROM.
+
Key Words: straight-leg raise, active knee-extension test, viscoelastic properties
There has been extensive research conducted on muscle flexibility and the
methods that have been employed to try to improve it (1,3,4,6,7,9, 11-13, 1520,25-30,33,35). Ballistic stretching, static stretching, and a number of proprioceptive neuromuscular facilitation (PNF) techniques have been investigated and
compared in the literature (7, 8, 10, 11, 14, 15, 17, 18,20, 30,34, 35). Although
Phillip Gribble, who was a graduate student in the Athletic Training Program at the
University of North Carolina at Chapel Hill during the time of this research, is with the
Department of Health, Leisure, and Exercise Science at Appalachian State University, Boone,
NC 28608. Kevin M. Guskiewicz, William E. Prentice, and Edgar W. Shields are with the
Department of Exercise and Sport Science at the University of North Carolina at Chapel
Hill, Chapel Hill, NC 27599-8700.
196
Gribble, Guskiewicz, Prentice, and Shields
many studies have shown that PNF techniques are superior to static stretching in
improving flexibility, the literature is not conclusive.
Flexibility has been defined as the ability to move a joint through a full,
unrestricted, pain-free range of motion (ROM; 21, 22). The goal of a stretching
routine is to overcome any limitations of the joint that hinder full range of motion.
These can include bony or soft tissue, or neurological limitations. One theorized
mechanism by which increases in flexibility are attained revolves around the viscoelastic properties of the muscle-tendon junction. By placing a load on a muscle,
an attempt is made to overcome its maximum tension levels and create a lengthening of the musculotendinous junction. This can be achieved by exceeding the stress
relaxation level of a muscle (2,8, 11, 17, 18,24,27-29, 36).
Several measurement methods have been used to study flexibility, including
goniometric and instrumental straight-leg-raise measurements (5,9,11,23). However, there has been no substantial research using the HexAbility LElOOO manual
stretching machine and no data to show the reliability or validity of this machine
and its ability to measure and quantify flexibility in the lower extremity.
Goniometric measurement has often been applied to hamstring flexibility
data collection, but various sources of error exist in this measurement technique
(5, 23). The FlexAbility LElOOO is designed to measure flexibility in the lower
extremity using a built-in potentiometer with the capability of implementing both
static and PNF techniques, but no substantialdata exist regarding its reliability and
validity in measuring hamstring ROM.
This study attempted to compare established stretching techniques to determine whether there was a significant difference in flexibility following a 6-week
training program. Accepted parameters for hamstring stretching (1, 27, 31) were
implemented, and static and hold-relax stretching were compared to identify any
superiority that might exist between the two.
The purpose of this study was to determine the effects of static hamstring
stretching and hold-relax hamstring stretching on hip-flexion ROM as measured
by the FlexAbility LE10OO. A second focus of the study was to determine the
reliability and validity of measurements taken with the FlexAbility LElOOO versus
those made with a goniometer.
Methods
Participants
+
Participants were 45 college students (age = 19.67 rt 1.55 years, weight = 64.92
26.47 kg, height = 107.31 rt 8.01 cm) without a history of lower extremity injury
during the previous year who volunteered to participate in this study. They were required to demonstrate a hip-flexion ROM of <80° during a straight-leg-raise test (9).
Prior to participation, participants read and signed the human consent form approved by the University of North CarolinaAcademic Affairs InstitutionalReview
Closed Kinetic Static and Hold-Relax Stretching
197
Board. Participants were randomly assigned to one of three training groups prior
to the initial assessment.
FlexibilityAssessment
All measurements were preceded by a 5-min warm-up period of cycling on a
Schwinn &Dyne ergometer set at 5 kg and 60 rpm. The right leg was chosen as a
standard for measurement on all participants.
Straight-kg-Raise Protocol. The straight-leg-raise (SLR) test was performed
on the FlexAbility LElOOO manual stretching apparatus, and measurements were
taken with the built-in potentiometer. Participants were placed in the supine position on the apparatus with their fingers cupping the end of the table and the movement arm placed beneath the Achilles tendon of the right leg. After piloting the
study, it was determined that excessive hip rotation could best be prevented by
strapping the stabilization belt under the right extremity and across the upper left
femur (Figure 1).
The standard SLR measurement method was chosen from the FlexAbility
menu, and participantswere passively taken into hip flexion as the tester depressed
the up button on the hand-held operating control. During the testing procedure,
participants were instructed to keep their right knee straight. The FlexAbility is
designed to stop movement when it detects force applied against the movement
Figure 1
- Positioning of the participants on the FlexAbility LE1000.
198
Gribble, Guskiewicz, Prentice, and Shields
arm,indicating an initiation of the stretch reflex. The amount of force detected is
preset by the manufacturer. A measurement was taken when the movement arm
stopped its upward motion.
Baseline measurements were taken prior to a 6-week training period, followed by weekly assessments (every third training session) for 6 weeks to determine whether a plateau effect occurred. During the final assessment, a test-retest
was performed for all measurements, with a 30-s rest between stretches, to study
intratester reliability of the SLR protocol using the FlexAbility LE1000.
Active Knee-Extension Test. During the active knee-extension test (AKE),
the participants were placed in a supine position and, again, the right leg was measured. A carpenter's level was strapped to the right femur in line with the greater
trochanter and the shaft of the femur to ensure that the hip was positioned at a 90°
angle to the table during the test. A yardstick was attached to the carpenter's level
to provide a landmark for the goniometer. The participants were asked to extend
their right knee as far as possible. The movement arm of the goniometer was aligned
with the lateral malleolus, and a measurement was taken as the difference from
90' (Figure 2). During the final assessment, a test-retest was performed for all
Figure 2
- Measurement technique for the active knee-extension (AKE) test.
Closed Kinetic Static and Hold-Relax Stretching
199
measurements, with a 30-s rest between stretches, to study intratester reliability of
the AKE protocol using the FlexAbility LE1000.
Training Protocol
Participants were randomly assigned to one of three training groups: control, static,
and hold-relax. All 45 participants performed the pretesting procedures previously
described. Members of the static and hold-relax groups were required to return
three times per week for flexibility training sessions. All training sessions were
preceded by the same warm-up used during measurement sessions. Participants
were asked to abstain from any additional lower extremity flexibility training during the 6-week training period. All sessions were conducted by the same trained
clinician.
The static and hold-relax groups both performed four 30-s stretches during
each training session, with 30-s rests between stretches. The position of the participant was the same during measurement sessions. After being positioned, the
participant's right leg was passively raised into hip flexion with the knee fully
extended. Once the machine achieved the stopping point, the static group participants received a 30-s static stretch and then were lowered back to resting position. During the static stretch, participants were instructed to remain as relaxed as
possible.
The hold-relax group's 30-s stretch was divided into phases. To complete
the initial phase of the PNF stretch, the hold-relax group participants were stretched
to the stopping point and held for 8 s. Next, the agonist muscle group (hamstrings)
contracted isometrically against the movement pad for 7 s. The participants were
then asked to rest at that position for 5 s. Finally, an additional passive stretch was
applied by the tester, via the movement arm, to try to push the joint farther into the
ROM to achieve a new stopping point, which was held for 10 s; then the right leg
was lowered to the resting position. Each hold-relax stretch consisted of four phases,
for a total of 30 s.
Statistical Analysis
A 3 x 2 repeated-measures analysis of variance (ANOVA) and Tukey's HSD post
hoc tests were used to determine whether differences existed in ROM pre- and
posttest for each training group. A 2 x 7 repeated-measures ANOVA was applied
to the results of weekly measurements of both the static and the hold-relax groups.
To determine the significance of weekly ROM assessments in relation to when
maximum ROM was achieved, reliability and validity of the two testing methods
were determined using intraclass correlation coefficients with standard error of
measurement (SEW calculations and a Pearson's product moment correlation,
respectively (see Table 4). Tests were performed using SPSS, version 7.5 (SPSS
Inc., Chicago). The alpha level was set a priori atp < .05. ROM was measured in
degrees.
200
Gribble, Guskiewicz, Prentice, and Shields
Results
Of the 45 participants, there was a mortality rate of 7% (3 participants). Two participants from the static group and one from the hold-relax group dropped out of
the study because of personal conflicts. Attendance rate for all other sessions was
100%. Mean scores for the SLR and AKE tests (Table I), as well as the week-byweek progression of the static and hold-relax groups within the SLR, were calculated (Table 2).
There was a significant group-by-test interaction ( p < .05) for the SLR test
results. Post hoc analysis revealed that both the static group (+33.0X0) and the
hold-relax group (+35.17") improved significantly more than the control group
(+8.9") from pretest to posttest. However, the static group did not significantly
improve when compared with the hold-relax group (Figure 3).
Table 1 Mean Scores (rt SD) for SLR and AKE
Group
n
SLR
control
static
hold-relax
AKE
control
static
hold-relax
Pretest
Posttest
Change
16
12
14
72.28 f 13.09
68.75 f 8.28
63.92 f 13.81
81.19 f 16.99
101.83 f 10.04
99.10 f 10.64
8.90 f 8.54
33.08 f 9.08
35.17 f 10.39
16
12
14
62.03 f 10.22
62.67 f7.43
60.57 f 8.27
65.43 f 13.46
72.00 f 7.59
74.89 f 6.58
3.40 f 8.67
9.33 f 5.49
14.32 f 7.34
Note. SLR = straight-leg raise, AKE = active knee extension.
Table 2 Weekly Mean Scores of SLR (4SD)
Static
Pretest
Week 1
Week 2
Week 3
Week 4
Week 5
Posttest
68.75 18.28
74.33 17.09
84.25 5 10.15
90.75 110.36
95.33 f 9.99
98.83 f 9.60
101.833 f 10.04
Hold-relax
63.93 f 13.81
70.71 f 12.42
83.50 f 10.17
89.93 9.56
94.86 f 8.58
97.93 f 8.62
99.11 f 10.64
+
Closed Kinetic Static and Hold-Relax Stretching
201
There was also a significant
group-by-test interaction (p< .05) for the AKE
test results. Post hoc analysis revealed that both the static group (+9.33') and the
hold-relax group (+14.32") improved signif~cantlymore than the control group
(+3.40°) from pretest to posttest. However, the static group did not improve when
compared with the hold-relax group (Figure 4).
Week-by-week comparison of measurements with the SLR displayed that
between Weeks 4 and 5 a nonsignificant mean difference of 3-27' was observed,
indicating that a plateau effect for improvement in flexibility had occurred (Table
3, Figure 5).
Reliability testing of the FlexAbility LElOOO was assessed using an intraclass
correlation coefficient between Trials 1 and 2 for the posttest on the SLR and
AKE. ICC(2, 1) values and SEMs of .99 (1.70) and .96 (2.37) were calculated for
the SLR and AKE tests, respectively (Table 4). Validity results for comparison of
initial posttest scores (posttest SLR-A vs. posttest AKE-A) yielded a Pearson's
product moment correlation r value of 30, and an r value of .8 1 was produced for
the second set of posttest scores (posttest SLR-B vs. posttest AKE-B).
1-
20
+hold-relax I
posttest
pretest
'Significantly different from pretest
Tukey's HSD = 6.99, p < .05
Figure 3
- Measurement technique for the active knee-extension (AKE) test.
-a
- - + - -control
- - hold-relax
-static
-A
I
pretest
I
posttest
*Significantly different from pretest
Tukey's HSD = 5.57,p < .05
Figure 4
- Mean scores (kSD) for the active knee-extension (AKE) test.
Gribble. Guskiewicz, Prentice, and Shields
202
Table 3 Mean Differences (kSD) for SLR Between Weeks
Difference
+
+
+
Week 1
Week 2
Week 3
Week 4
Week 5
Week 6
6.23 5.74*
11.46 5.93*
6.46 3.95*
4.77+3.37*
3.27 rt 3.61
2.02 f 3.58
*Significant for post hoc value of 4.00.
pretest
Week1
Week2
Week3
Week4
Week5
posttest
"Significant group main effect
Tukev's HSD = 4.00. D < .05
Figure 5
groups.
- Weekly straight-leg-raise mean scores (*SD) for static and hold-relax
Table 4 Posttest Test-Retest CorrelationPearson's Product Moment Values and
ICC Values
r
r?
ICC(2, 1)
SEM
Closed Kinetic Static and Hold-Relax Stretching
203
Discussion
The results indicated that the static and hold-relax groups signif~cantlyimproved
in flexibility when measured using both the SLR test and the AKE test and compared with the control group. Further analysis, however, revealed that neither technique was superior to the other: The two stretching techniques are equally effective in improving ROM.
Women have been found to have greater flexibility than men (7,14,32), but
Etnyre and Lee (7) found no significant difference in mean scores for increases in
flexibility between men and women following a stretching program. Therefore,
we decided that gender was not an issue in assigning participants to the treatment
groups. Based on recommendations by Etnyre and Lee (6), a 6-week study was
performed and participants were measured weekly with the ISLR for the purpose
of discovering when a plateau effect occurred in improvement in ROM. Both the
static and the hold-relax groups reached a plateau during Week 5. This further
demonstratesthat the two methods were equally effective at improving hip-flexion
ROM when using an SLR method of assessment.
The fidings for the SLR test contradictprevious studies that have compared
static techniques with PNF methods (2,7,30). Previous authors have found various PNF techniques to improve hip-flexion ROM more efficiently than static stretching (7, 30), whereas Beaulieu (2) found that static stretching was more effective
than PIW stretching. The results of our study are consistent with previous studies
that illustrated no significant difference between static and PNF techniques (13,
16, 19, 35). In these studies it was demonstrated that both static and PNF groups
had some degree of improvement in flexibility, but there was no significant difference among the groups.
Much of the discrepancy in the literature can be attributed to varying protocols of number of stretches, number of weeks of treatment, measurement techniques, and duration of the stretch. This study used a four-stretch protocol based
on the findings of Taylor et al. (27). In investigatinga 10-repetitioncyclical stretching
routine, no sigmficant improvement in flexibility occurred after the 4th repetition.
Past studies have investigated the duration of a stretch and have incorporated
protocols of up to 15 min for a single stretch (1-3, 11,26, 31). A 30-s and a 60-s
stretch have been found to be equally effective in improving ROM compared with
a 15-s stretch, but a 30-s stretch is recommended for efficiency (1).
Clearly, both the static stretch and the hold-relax stretch are effective in increasing hip-flexion ROM over a period of 6 weeks. However, the SLR is a passive
test, whereas the AKE is an active test. One might think that because the holdrelax group participated in an active stretching protocol, they would have greater
improvement than the static group if quantified with the AKE test. However, both
training groups improved significantly.
A possible explanation for this perceived phenomenon relies on the effects
of autogenic and reciprocal inhibition. Alarge portion (7 s) of the hold-relax stretch
204
Gribble, Guskiewicz, Prenfice, and Shields
is an active contraction, whereas the static stretch was designed to be completely
passive. During an AKE test, the quadriceps group is primarily firing, whereas
during the hold-relax stretch, the active portion is performed by the hip extensor
(hamstrings).
The purpose of a PNF stretchingtechnique is to cause an inhibition in the function of muscle spindles and Golgi tendon organs within the tendon. The hold-relax
technique includes an isometric contraction of the antagonist (hamstrings), which
allows an autogenic inhibition to occur within the hamstring muscle group (22). The
active knee-extensiontest relies on an active contractionof the quadriceps group (agonist) to perform knee extension and complete the stretch. Participants in the holdrelax group experienced a significant change in ROM with the AKE measurements,
as did those in the static group. It is possible that the autogenic inhibition produced
during the hold-relax stretching could simultaneouslyallow reciprocal inhibition.When
the agonist group was active during the AKE test, it might have caused a significant
change in ROM for those who had been trained accordingly.
An autogenic inhibition is also produced, however, during a passive stretch
(SLR). Autogenic inhibition is contingent on the function of the Golgi tendon organs, which not only detect changes in length but also changes in tension. Tension
is produced in the antagonists with both static and PNF hamstring-stretching techniques. Therefore, the presence of autogenic inhibitionwould not be affected if the
measurement technique was an active or passive stretch or if the training method
was a static or hold-relax stretch.
Other PNF techniques used for hamstring flexibility involve contraction of
the quadriceps in an attempt to produce a reciprocal inhibition. The hold-relax and
static techniques incorporate autogenic inhibition of the hamstrings to allow an
increased passive hip-flexion movement. Therefore, an issue for further study would
be to compare PNF techniques with static stretching as tested by both passive and
active methods.
For the SLR test, the control group significantly improved along with the
two treatment groups. Many participants in the training groups reported that because of the warmer weather during the training period, they began to engage in
more activity (i.e., running and basketball) than before the training period started.
However, they had adhered to the stipulation of no additional flexibility training
outside of the current study during the training period. Aquestion arises as to what
extent the increased amount of activity affected improvements in flexibility in this
study.
Additionally, participants were not prohibited from participating in strength
training during the study. Worrell, Smith, and Winegardener (35) found that increased hamstring flexibility had a positive effect on isokinetic hamstring performance. A possibility for future study would be to determine whether strengthtraining
has a significant reciprocal effect on flexibility.
One theorized mechanism by which flexibility improvements occur revolves
around the viscoelastic properties of muscle-tendon junctions. Previous research-
Closed Kinetic Static and Hold-Relax Stretching
205
ers have attempted to explain improvements in flexibility with viscoelastic properties, overcomingthe stretch reflex, or increasing the stretch tolerance (2,8,24,2729,35,36). Muscle demonstrates viscoelastic properties, meaning that the musculotendinousjunction has the ability to lengthen in response to applied loads and
the duration for which they are applied. If a muscle is repeatedly exposed to certain loads for certain durations, a change in length can occur. This decrease in
tension over time is known as stress relaxation (8). Taylor et al. (27) made a case
for the viscoelastic properties of tendons by demonstrating that denervated tendon
would still lengthen in the absence of reflex activity. In order to attain a permanent
change in length, the muscle must be in the plastic deformation phase (36); otherwise, the viscoelastic properties of the muscle-tendon junction allow the tendon to
return to its original, resting length.
Another theory to explain increases in ROM is augmentation of stretch tolerance (11, 12, 18). By repeatedly taking a muscle to the point of pain, the tolerance
associated with a particular length increases and the musculotendinous junction is
allowed to increase in length before pain is perceived. Halbertsma and Goeken (11)
discovered an increase in hamstring flexibility, as well as a participant-reported increase in pain tolerance. They attributed the gains in flexibility to an increase in stretch
tolerance.
The measurements of hip-flexion ROM during the SLR were taken according to one of two protocols: when the FlexAbility LElOOO perceived an increase in
tension against the movement pad (initiation of the stretch reflex) or when the
participant's knee had a flexion moment (a true SLR was no longer occurring).
The actual changes to the musculotendinous junction and the amount of EMG
activity in the tendon were not quantified in this study. However, the participants
were never intentionally stretched to the point that they perceived pain, so their
stretch tolerance was never intentionally stressed. It can therefore be assumed that
the significant improvements in flexibility found in this study were probably the
result of viscoelastic changes in the musculotendinous junctions.
Based on the classification of Yi and Zhenhua (36), it was assumed that the
participants in the two treatment groups at least entered the slow elastic phase and
probably experienced the effects of the plastic deformationphase. This means that
some degree of permanent length change occurred in their musculotendinousjunctions. A question for further study would be how long the length changes experienced over the 6-week period would remain once stretching sessions were discontinued. Additionally, the effects of continued stretching beyond a 6-week period
should be examined.
There was no significantdifferencebetween the static and hold-relax groups,
and both groups plateaued during the same week. Recommendation for the type of
stretching technique to use could not be made based on one technique being more
efficient than the other. Based on the proposals of Moore and Hutton (21) and
Worrell et al. (35), the amount of time and resources available are the factors in
deciding on the most effective stretching technique for improving hip-flexion ROM.
206
Gribble, Guskiewicz, Prentice, and Shields
Measurement Reliability and Validity
One of the purposes of this study was to examine the effectivenessof the FlexAbility
LElOOO manual stretching machine. Intraclass and interclass reliability of previous measurement techniques have been investigated (5,23). Intraclass reliability
was greatly reduced by having the same investigatorperform measurements for all
trials. The current study was intended to examine the benefit of using a computerized machine to reduce the amount of intraclass variability.
Reliability was investigated by using a test-retest method during the posttest
sessions for all three treatment groups. According to the high ICC values and low
SEMs, both techniques are reliable measurements for assessing flexibility.
Validity of the machine was determined by comparing the SLR performed
on the FlexAbility LElOOO with the AKE test performed with a goniometer; the
first trial for the posttest on the SLR was compared with the first trial of the AKE
test for validity, and the same was done for the second trials of both tests.
The high Pearson's product moment correlations suggest that the two techniques for assessinghamstring flexibilityyield similar results. Assuming that the SLR
technique is the commonly accepted standard, our findings suggest that the AKE is a
valid test.
If both the FlexAbility LElOOO and a goniometer can produce measurements
of high reliability and validity, then the question of which tool is more effective might
be answered by determining which is more efficient. Cost, convenience, and time are
all concerns that should be addressed when choosing a measuring implement.Agoniometer is much more cost effective and transportable than the FlexAbility LElOOO,
but the benefit of a manual stretching machine such as the FlexAbility LElOOO is that
exercises can be performed independently of a clinician, thus maximizing time.
Conclusion
The main objective of this study was to compare static stretching with PNF stretching
to determine which is the most effective means of improving hamstring flexibility. It
was demonstrated that when using an SLR technique, both static and hold-relax techniques successfullyimproved hip-flexion ROM over a 6-week period. However, neither technique proved to be more effectivethan the other, and both groups plateaued
during the same week. According to this study, a clinician should choose a stretching
technique based on time constraints, as well as how informed the patient is.
The literature has shown that the AKE test is more efficient at measuring
hamstring flexibility than the SLR. However, the reliability and validity data from
this study have shown how closely the two techniques provide information about
the flexibility of the hamstrings.
The FlexAbility LElOOO proved to be a highly reliable device for measuring
hip-flexion ROM, but a goniometer demonstrated that it was also highly reliable for
taking flexibilitymeasurements. The cost of a device such as the FlexAbility LElOOO
versus the relative inexpensiveness of a goniometer, as well as a greater amount of
Closed Kinetic Static and Hold-Relax Stretching
207
mobility associated with a goniometer, might make it difficult for a clinician to choose
a manual stretching machine over a goniometer for taking ROM measurements.
In this study, the RexAbility LElOOO did not prove to be any more beneficial than a goniometer for providing accurate ROM measurements. However, because it is user-friendly, it could b e incorporated as a very useful training tool for
an athletic team or clinical setting with a high number of athletes o r patients that
require flexibility improvement and maintenance.
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