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Effects of contract-relax vs static stretching on stretch-induced strength loss and length-tension relationship: Stretching and length-tension relationship

Authors:
  • Nicholas Institute of Sports Medicine and Athletic Trauma Lenox Hill Hospital

Abstract

The purpose of this study was to determine the acute effects of contract-relax stretching (CRS) vs static stretching (SS) on strength loss and the length-tension relationship. We hypothesized that there would be a greater muscle length-specific effect of CRS vs SS. Isometric hamstring strength was measured in 20 healthy people at four knee joint angles (90°, 70°, 50°, 30°) before and after stretching. One leg received SS, the contralateral received CRS. Both stretching techniques resulted in significant strength loss, which was most apparent at short muscle lengths [SS: P = 0.025; stretching × angle P < 0.001; 11.7% at 90° P < 0.01; 5.6% at 70° nonsignificant (ns); 1.3% at 50° ns; −3.7% at 30° ns. CRS: P < 0.001; stretching × angle P < 0.001; 17.7% at 90°, 13.4% at 70°, 11.4% at 50°, all P < 0.01, 4.3% at 30° ns]. The overall stretch-induced strength loss was greater (P = 0.015) after CRS (11.7%) vs SS (3.7%). The muscle length effect on strength loss was not different between CRS and SS (stretching × angle × stretching technique P = 0.43). Contrary to the hypothesis, CRS did not result in a greater shift in the length–tension relationship, and in fact, resulted in greater overall strength loss compared with SS. These results support the use of SS for stretching the hamstrings.
Effects of contract-relax vs static stretching on stretch-induced
strength loss and length–tension relationship
S. S. Balle1,2, S. P. Magnusson2, M. P. McHugh1
1Nicholas Institute of Sports Medicine and Athletic Trauma, Lenox Hill Hospital, New York, New York, USA, 2Institute of Sports
Medicine Copenhagen & Musculoskeletal Rehabilitation Research Unit, Bispebjerg Hospital, Faculty of Health Sciences, University
of Copenhagen, Copenhagen, Denmark
Corresponding author: Sidse Schwartz Balle, MD, Nicholas Institute of Sports Medicine and Athletic Trauma, Lenox Hill Hospital,
100 East 77th Street, 2nd floor, New York, NY 10075, USA. Tel: +1 212 434 2700, Fax: +1 212 434 2687, E-mail:
sidse.schwartz@gmail.com
Accepted for publication 5 December 2014
The purpose of this study was to determine the acute
effects of contract-relax stretching (CRS) vs static stretch-
ing (SS) on strength loss and the length-tension relation-
ship. We hypothesized that there would be a greater
muscle length-specific effect of CRS vs SS. Isometric
hamstring strength was measured in 20 healthy people at
four knee joint angles (90°, 70°, 50°, 30°) before and after
stretching. One leg received SS, the contralateral received
CRS. Both stretching techniques resulted in significant
strength loss, which was most apparent at short muscle
lengths [SS: P=0.025; stretching ×angle P<0.001;
11.7% at 90° P<0.01; 5.6% at 70° nonsignificant (ns);
1.3% at 50° ns; 3.7% at 30° ns. CRS: P<0.001; stretch-
ing ×angle P<0.001; 17.7% at 90°, 13.4% at 70°, 11.4%
at 50°, all P<0.01, 4.3% at 30° ns]. The overall stretch-
induced strength loss was greater (P=0.015) after CRS
(11.7%) vs SS (3.7%). The muscle length effect on
strength loss was not different between CRS and SS
(stretching ×angle ×stretching technique P=0.43). Con-
trary to the hypothesis, CRS did not result in a greater
shift in the length–tension relationship, and in fact,
resulted in greater overall strength loss compared with
SS. These results support the use of SS for stretching the
hamstrings.
Stretching is widely performed before athletic events to
enhance performance and perhaps to reduce risk of
injury, as well as within rehabilitation programs. Some
studies suggest that stretching may help reduce the risk
of muscle strain, while other studies question stretching
before athletic events because stretching results in
stretch-induced strength loss (for review, see McHugh &
Cosgrave, 2010; Behm & Chaouachi, 2011).
Stretch-induced strength loss has been shown to be
most apparent at short muscle lengths (Nelson et al.,
2001; Herda et al., 2008; McHugh & Nesse, 2008;
McHugh et al., 2013). This effect is thought to indicate a
rightward shift in the length-tension curve with greater
sarcomere shortening at a given muscle length during
maximum voluntary contractions after stretching
(McHugh et al., 2013). Such an effect implies that
stretching increases the muscle-tendon unit compliance,
thereby allowing greater sarcomere shortening during
isometric contractions.
To date, the length-dependent effect on the stretch-
induced strength loss has only been examined in
response to static stretching (Nelson et al., 2001; Herda
et al., 2008; McHugh & Nesse, 2008; McHugh et al.,
2013). Proprioceptive neuromuscular facilitation is
a popular stretching method within rehabilitation,
especially contract-relax stretching of the stretched
muscle (Sharman et al., 2006; Hindle et al., 2012).
Contract-relax stretching involves a short duration iso-
metric contraction of the target muscle, while in a
stretched position. Upon relaxation, the stretch is either
maintained or increased to a greater range of motion
(ROM) for a certain period of time. Compared with
static stretching, contract-relax stretching should
provide greater tension on the tendon and aponeurosis as
a consequence of the isometric contraction. Significant
tendon and aponeurosis strain has been demonstrated
during isometric contractions (Maganaris & Paul, 2000).
Therefore, the contract-relax stretching technique has
the potential to increase tendon and aponeurosis compli-
ance more than static stretching. Such an effect would
theoretically allow greater sarcomere shortening during
isometric contractions compared with contractions fol-
lowing a static stretching intervention. Thus contract-
relax stretching may result in a greater rightward shift in
the length-tension curve than static stretching. There-
fore, the purpose of this study was to determine the acute
effects of static vs contract-relax stretching of the ham-
string muscle on strength and the length–tension
Scand J Med Sci Sports 2015: ••: ••–••
doi: 10.1111/sms.12399
© 2015 John Wiley & Sons A/S.
Published by John Wiley & Sons Ltd
1
relationship. It was hypothesized that contract-relax
stretching would have a greater effect on the length–
tension relationship.
Methods
Isometric hamstring strength at four different knee flexion angles,
from short to long muscle lengths, was assessed before and after
one of the two stretching interventions, static stretching, and
contract-relax stretching. Five minutes after completing testing of
one leg, the protocol was repeated on the contralateral leg with the
other stretching intervention. Test order for the stretching inter-
vention (static stretching or contract-relax stretching) and leg
(right or left) was randomized using a Latin Square crossover
design giving four possible test sequences. With 20 subjects, each
sequence was repeated four times.
Subjects
Twenty healthy people (14 men, 6 women, age 31.1 ±8.2 years,
height 174.8 ±10.5 cm, weight 70.5 ±13.0 kg) volunteered to
participate in this study. All subjects fulfilled the inclusion and
exclusion criteria. Inclusion criteria: age between 20 and 50 years,
recreationally active, exercising twice a week, being able to run
1 mile in less than 10 min. Exclusion criteria: any current neuro-
muscular disease or musculoskeletal injuries specific to the ankle,
knee, hip joint, or low back within the last year. All subjects gave
written informed consent, and the study was approved by the
institutional review board.
Setup
All strength testing and stretching were performed on an isokinetic
dynamometer (Biodex System 2, Shirley, New York, USA). The
subjects were seated with seat back at 90° to the horizontal and test
thigh flexed 45° above the horizontal while the opposite thigh
rested horizontally on the chair. Restraining straps over the pelvis
and chest secured the position. The lateral condyle of the femur of
test leg was aligned with the input axis of the dynamometer.
During testing, subjects were instructed to keep arms crossed in
front of the chest.
Flexibility
Hamstring flexibility was assessed prior to strength testing and
stretching. While seated in the dynamometer in the test position,
maximum ROM was assessed by passively extending the knee
joint from 100° of knee flexion to the point of significant discom-
fort but not pain. Subjects were asked to grade their stretch dis-
comfort on a visual analog scale (VAS) from 0 to 10, where
0=‘no stretch discomfort at all’ and 10 =‘the maximal imagin-
able stretch discomfort’ (McHugh et al., 2013).
Isometric knee flexion strength
Maximum isometric knee flexion contractions were measured at
four knee joint angles (90°, 70°, 50°, 30° of knee flexion), always
in order from short to long muscle length. All subjects performed
the isometric contractions before (pre) and after (post) stretching.
Subjects were verbally encouraged to give maximal efforts during
two 4-s isometric knee flexion contractions at each joint angle.
Contractions were separated by 15 s, and 30-s rest was given
between each knee joint angle. In order to ensure maximal effort
through the duration of contractions, subjects were provided visual
feedback of the torque-time curve during individual contractions.
However, subjects were not provided feedback on actual torque
values or provided any display of previous contractions during a
subsequent contraction. At each angle, the initial torque prior to
isometric contraction was recorded, and subsequently subtracted
from the torque during maximum contractions. This torque repre-
sented the combination of limb mass and passive resistance to
stretch. The corrected torque value for maximum contractions
represents the contractile force production. The average of the
corrected torque for the two contractions at each angle was
reported. The post-stretching strength tests were performed within
1 min after ended stretching maneuver.
To ensure an adequate evaluation of the descending limb on the
angle–torque relationship, a fifth isometric contraction was added
for flexible subjects. Subjects whose maximum ROM was 20° or
less (more flexible) performed an additional set of isometric con-
tractions at a knee flexion angle 5° shorter than their maximum
ROM.
Stretching procedures
The maximum ROM achieved in the flexibility assessment was
used as the stretch angle for all stretches on that leg. In the static
stretching intervention, the test knee was passively extended from
start position (100°) to subject’s maximum ROM and held at that
angle for 60 s. The stretch was repeated six times, 15 s rest in
between each. In the same manner, the leg was passively brought
to stretching position in the contract-relax stretching intervention.
Subjects were then asked to do a 10-s submaximal isometric knee
flexion contraction (70% of maximal effort), followed by 50 s
with the leg maintained in the stretched position. Submaximal
intensity during contraction in contract-relax stretching was
chosen because previous studies on proprioceptive neuromuscular
facilitation stretching have suggested that higher intensity contrac-
tions could lead to muscle damage, and also, submaximal contrac-
tion intensity (60–65%) during contract-relax stretching has been
shown to be as beneficial as maximal intensity in order to increase
flexibility (Feland & Marin, 2004; Sheard & Paine, 2010; Hindle
et al., 2012). Contract-relax stretching was repeated six times,
each stretch separated by 15-s rest.
Passive resistance to stretch was recorded from the torque
output of the dynamometer during every stretch. The observed
decrease in passive torque at maximum ROM with repeated
stretches was recorded as a measure of the decrease in the passive
resistance to stretch (maximum ROM for each stretch was the
ROM for the first stretch repeated six times). Torque during
the contract-relax isometric contraction was also recorded. The
average torque produced during contract-relax stretching contrac-
tion was expressed relative to the estimated maximum isometric
torque at the angle of maximum ROM. This torque was estimated
by fitting the angle–torque relationship for contractions at 90°,
70°, 50° and 30° to a second-order polynomial and calculating the
torque at the angle of maximal ROM from the derived equation.
This was done because it was not possible to measure contractile
force production at maximum ROM.
Statistical analysis
With 20 subjects in a fully repeated-measures design, it was esti-
mated that there would be 80% power to detect a 10% difference
in the stretch-induced strength loss between contract-relax and
static stretching at an alpha level of 0.05. This estimate was based
on the differences in the stretch-induced strength loss between
limbs previously reported (McHugh et al., 2013).
Differences in stretching intensity (VAS score), maximum
ROM and percent decline in resistance to stretch were compared
between static and contract-relax stretching using paired t-tests.
The muscle length-dependent effect of stretch technique on the
Balle et al.
2
stretch-induced strength loss (absolute torque in N·m) was
assessed using a stretch technique (static vs contract-relax) by time
(pre- vs post-stretching) by angle (90°, 70°, 50°, 30°) repeated-
measures analysis of variance (ANOVA). Relative strength loss
(percent decline in torque from pre- to post-stretching) was com-
pared between stretch techniques using a stretch technique by
angle repeated-measures ANOVA. The relative shift in the angle–
torque relationship (length-tension curve) was assessed by first
expressing knee flexion torque at each joint angle as a percentage
of the torque at the angle of peak torque. Then, a stretch technique
by time by angle repeated-measures ANOVA was performed on
the relative torque values. By expressing torque relative to the
angle of peak torque, any shift in the length-tension curve can be
assessed independently of the stretch-induced strength loss. Effect
of stretch technique on the stretch-induced strength loss was
assessed using a stretch technique by time repeated-measures
ANOVA. Mean ±SD is reported in the text and table, and
mean ±SE is displayed in the figures.
Results
Stretch discomfort (VAS) and decline in passive resis-
tance to stretch at maximum ROM after stretching were
similar for static vs contract-relax stretching (Table 1).
Baseline maximum ROM was slightly greater for the
limb that subsequently performed static stretching (less
flexible) vs the limb that subsequently performed
contract-relax stretching (2.2 ±4,4°, P=0.04). Torque
during the 10 s contraction of the contract-relax stretch-
ing averaged 74.5 ±26.2% of maximal voluntary con-
traction (MVC).
Static stretching resulted in a significant strength loss
(P=0.025), which was more apparent at short vs long
muscle length (time by angle P<0.001; Fig. 1(a)).
Contract-relax stretching also resulted in significant
strength loss (P<0.001), which was also more apparent
at short vs long muscle length (time by angle P<0.001)
(Fig. 1(b)). The average strength loss across all knee
flexion angles was greater after contract-relax stretching
(11.7%) vs static stretching (3.7%) (P=0.015; Fig. 2).
The muscle length effect on strength loss (angle–torque
relationship) was not different between contract-relax
stretching and static stretching (stretch technique by
angle P=0.85). Since pre-stretch maximum ROM was
significantly different between contract-relax and static
stretch legs, this difference was added as a covariate to
ascertain whether the baseline difference affected the
observed stretch-induced strength loss. The stretch
technique by angle interaction remained nonsignificant
when baseline maximum ROM difference was added in
an analysis of covariance (P=0.17). The greater overall
strength loss with contract-relax vs static stretching
remained significant in the analysis of covariance
(P=0.012).
The angle–torque relationship (length–tension rela-
tionship), when expressed as a percentage of the angle of
peak torque, showed a rightward shift after stretching
(time by angle P<0.001, Fig. 3). The rightward shift in
the length-tension curve was due to a decrease in relative
Table 1. Stretching responses
Static stretching Contract-relax stretching P-value
Maximum ROM 19.0 ±7.8° 16.9 ±7.8° 0.04
VAS at maximum ROM 7.3 ±1.2 7.3 ±1.3 0.60
Decrease in passive resistance to stretch 9.7 ±4.7% 10.7 ±7.7% 0.59
Average torque during isometric contraction in contract-relax stretching 74.5 ±26.2% 0.44
Mean ±SD. Torque during contract-relax stretching is expressed as a percentage of estimated maximal torque at maximum ROM. Values were compared
with a target intensity of 70%.
ROM, range of motion; VAS, visual analog scale.
Fig. 1. Isometric knee flexion torque before (pre) and after
(post) static stretching (SS) (a) and contract-relax stretching
(CRS) (b). Torque was measured at four different knee flexion
angles from short (90°) to long (30°) muscle length. There was a
significant stretch-induced strength loss after both static stretch-
ing (P=0.025) and contract-relax stretching (P<0.001), which
for both stretching interventions were most apparent at short vs
long muscle length (time by angle P<0.001). Mean ±SE dis-
played. *P<0.01.
Stretching and length–tension relationship
3
torque at short muscle lengths and an increase in relative
torque at long muscle lengths. For example, in the static
stretching intervention, the torque at 90° (short muscle
length) was 82% of peak torque prior to stretching and
77% after stretching. At 30° (long muscle length) the
torque was 68% of peak prior to stretching and 73% after
stretching. The stretch-induced shift in the length–
tension relationship was not different between stretch
techniques (P=0.88, Fig. 3). The shift in the length–
tension relationship remained not different between
stretch techniques when baseline difference in maximum
ROM was added as a covariate in an analysis of covari-
ance (P=0.31).
For nine subjects whose maximum ROM was 20° or
less (more flexible), an additional isometric strength test
was performed at 5° less than maximum ROM. Isomet-
ric strength measured at this additional knee flexion
angle was unaffected by stretch (static stretching
(pre- and post-stretching) 62.9 ±25.9 N·m vs 67.1 ±
27.0 N·m, contract-relax (pre- and post-stretching)
61.7 ±25.3 N·m vs 58.6 ±32.2 N·m; P=0.84) and there
was no interaction between static stretching vs contract-
relax stretching and stretch (stretch technique by time
P=0.31).
Discussion
The most important finding in this study was that both
static stretching and contract-relax stretching resulted in
stretch-induced strength loss that for both stretching
interventions was most apparent at short muscle length,
with no strength loss evident at longer muscle lengths
(Fig. 1). This muscle length-dependent effect for static
stretching is consistent with previous work (Nelson
et al., 2001; Herda et al., 2008; McHugh & Nesse, 2008;
McHugh et al., 2013), but this is the first study to show
such an effect with contract-relax stretching. However,
contrary to the hypothesis, contract-relax stretching did
not have a greater effect on the length–tension relation-
ship than static stretching (Fig. 3). Furthermore, the
overall stretch-induced strength loss was greater for
contract-relax vs static stretching (12% vs 4%; Fig. 2).
One previous study reported no difference in the stretch-
induced strength loss between contract-relax and static
stretching (Marek et al., 2005). In that study knee exten-
sion strength was assessed isokinetically with concentric
contractions before and after 2 min of quadriceps
stretching. The overall strength loss was marginally sta-
tistically significant with no apparent loss after static
stretching (<1%) and a small strength loss after
contract-relax stretching (6%). The larger values in the
present study are presumably due to the greater stretch-
ing intervention (6 min total stretch time). The magni-
tude of the stretch-induced strength loss in the present
study after static stretching (4%) is very comparable to
the value of 5% reported for static stretching in a previ-
ous study using the same protocol (McHugh et al.,
2013).
The declines in passive resistance to stretch (Table 1)
for static stretching (10%) and contract-relax stretching
(11%) were comparable to values reported previously for
static stretching using the same experimental setup [9%
Fig. 2. The stretch-induced strength loss after static stretching
(SS) and contract-relax stretching (CRS) at four knee flexion
angles. Strength loss (averaged across all angles) was greater
(effect of stretching technique P=0.015) after contract-relax
stretching (11.7%) vs static stretching (3.7%). Strength loss was
progressively less at longer muscle lengths (angle effect
P<0.001) with no difference in angle effect between stretch
techniques (stretching technique by angle P=0.85). Mean ±SE
displayed.
Fig. 3. The angle–torque relationship for maximum isometric
knee flexion contractions expressed relative to torque at the
angle of peak torque before (pre) and after (post) static stretching
(SS) (a) and contract-relax stretching (CRS) (b). Time by angle
(P<0.001) indicates a rightward shift in the angle–torque rela-
tionship. This shift was not different between stretch techniques
(time by angle by stretch technique P=0.88).
Balle et al.
4
(McHugh & Nesse, 2008); 11% (McHugh et al., 2013)].
However, greater declines in passive resistance to
stretch were demonstrated in studies with similar
protocols and experimental setups [20% (Magnusson
et al., 1995); 19% (Magnusson et al., 1996)]. Regardless
of these apparent differences in the magnitude of effect,
it is clear that there was an obvious effect on the vis-
coelastic properties of the stretched muscle group in this
study.
In the current study, there is a possibility that the six
10-s submaximal isometric contractions at maximum
ROM induced fatigue. A limitation in this study was that
electromyography (EMG) was not recorded from the
hamstring muscle group. This may have provided some
insight into possible fatigue effects with contract-relax
stretching. The choice not to record EMG activity here
was based on a previous study using the same experi-
mental setup, demonstrating that increased neural
tension during static stretch exacerbated stretch-induced
strength loss but with no apparent change in surface
EMG activity (McHugh et al., 2013). Thus, it was felt
that EMG activity would not provide any greater insight
into the stretch-induced strength loss here. In retrospect,
EMG activity might have provided insight into potential
fatigue effects with contract-relax stretching. However,
the primary purpose of this study was to examine
whether contract-relax stretching had a greater impact on
the length–tension relationship than static stretching.
Additionally, lack of EMG measurements from the
antagonists meant that it was not possible to determine
whether changes in torque outputs after stretching were
due in part to changes in antagonist activity. An addi-
tional limitation was that the gap between isometric
strength test angles (20°) may have been too wide to
detect changes in the angle of peak torque, since such
changes tend to be in the 5°–10° range. However,
stretch-induced changes in the overall angle–torque rela-
tionship have previously been demonstrated using angle
increments of 20° (Herda et al., 2008; McHugh et al.,
2013) and 15° (McHugh & Nesse, 2008).
The muscle length-dependent effects on the stretch-
induced strength loss have been attributed to increased
compliance in the muscle-tendon unit enabling greater
muscle fiber shortening during isometric contractions at
a given joint angle (McHugh & Nesse, 2008; McHugh &
Cosgrave, 2010; McHugh et al., 2013). The observed
shift in the angle–torque relationship is attributed to
greater sarcomere shortening, such that strength is
decreased at short muscle lengths but increased at long
muscle lengths. It was hypothesized that since the tendon
and aponeurosis are loaded more during contract-relax
stretching, the shift in the angle–torque relationship
would be more apparent with contract-relax stretching.
However, this was not the case. The degree to which
changes in tendon and aponeurosis compliance after
stretching affect the length–tension relationship remains
unclear. Ultrasound imaging of muscle fascicle shorten-
ing may clarify this issue, but studies on hamstring
muscle-tendon units are lacking.
Perspectives
We were expecting to find that contract-relax stretching
resulted in a greater shift in the length–tension relation-
ship than static stretching. This was not the case, with
both stretching techniques resulting in similar rightward
shifts in the length-tension curve.
A leftward shift in the length–tension relationship has
been demonstrated in athletes with recurrent hamstring
strain (Brockett et al., 2004). It remains to be determined
if a stretch-induced rightward shift in the length–tension
relationship has any acute beneficial effects in injury
prevention and rehabilitation.
Strength loss was apparent after contract-relax stretch-
ing but not after static stretching. Therefore, these results
support the use of static stretching for stretching the
hamstrings.
Key words: Stretch-induced strength loss, angle–torque
relationship, hamstring muscle, knee flexion.
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Balle et al.
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... Based on the above arguments, it appears important to consider that stretch-induced performance decrements are likely to be negligible when SS is of short or moderate duration (e.g., < 60 s per muscle), at least when only a few muscles are stretched and/or a complete physical preparation (warm-up) is performed between the SS and exercise or sporting task. It is also notable that, in contrast to the commonly reported performance impairments, five studies that reported strength decrements at short muscle lengths (− 10.2%) observed moderate strength improvements at the longest muscle lengths tested (+ 2.2%) (Balle et al. 2015;Herda et al. 2008;McHugh and Nesse 2008;McHugh et al. 2013;Nelson et al. 2001b). Performance enhancement at longer muscle lengths could be of practical importance, since muscle strain injuries are more likely to occur with the muscle at a longer rather than shorter length (Behm et al. 2016a;Heiderscheit et al. 2010) and many sporting activities require force production at longer muscle lengths. ...
... Therefore, the results of many studies would be vulnerable to a rightward shift that would manifest as a reduced maximal force. In fact, studies in which tests were conducted at several muscle lengths reported post-stretch strength losses at short muscle lengths but moderate improvements at the longest muscle lengths tested (Balle et al. 2015;Herda et al. 2008;McHugh and Nesse 2008;McHugh et al. 2013;Nelson et al. 2001a). Collectively, these data support a rightward shift in the length-tension relation and suggest that at least some of the force loss measured in previous studies might be explained by this mechanism. ...
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Whereas a variety of pre-exercise activities have been incorporated as part of a “warm-up” prior to work, combat, and athletic activities for millennia, the inclusion of static stretching (SS) within a warm-up has lost favor in the last 25 years. Research emphasized the possibility of SS-induced impairments in subsequent performance following prolonged stretching without proper dynamic warm-up activities. Proposed mechanisms underlying stretch-induced deficits include both neural (i.e., decreased voluntary activation, persistent inward current effects on motoneuron excitability) and morphological (i.e., changes in the force–length relationship, decreased Ca²⁺ sensitivity, alterations in parallel elastic component) factors. Psychological influences such as a mental energy deficit and nocebo effects could also adversely affect performance. However, significant practical limitations exist within published studies, e.g., long-stretching durations, stretching exercises with little task specificity, lack of warm-up before/after stretching, testing performed immediately after stretch completion, and risk of investigator and participant bias. Recent research indicates that appropriate durations of static stretching performed within a full warm-up (i.e., aerobic activities before and task-specific dynamic stretching and intense physical activities after SS) have trivial effects on subsequent performance with some evidence of improved force output at longer muscle lengths. For conditions in which muscular force production is compromised by stretching, knowledge of the underlying mechanisms would aid development of mitigation strategies. However, these mechanisms are yet to be perfectly defined. More information is needed to better understand both the warm-up components and mechanisms that contribute to performance enhancements or impairments when SS is incorporated within a pre-activity warm-up.
... 8,9 As a result, the length-tension relationship of the muscles involved in throwing such as internal and external rotators may be manifested through changes in capsular tightness and decreased ROMs. 10 It was confirmed that the altered length-tension relationship of the muscle fibers could limit the maximum force-producing capacity of the muscle. 11 There are several treatment approaches for GIRD in the literature particularly related to stretching intervention with conflicting results. [10][11][12][13][14] One of these approaches is the muscle energy technique (MET), which is time and cost-effective in the clinical settings. ...
... 11 There are several treatment approaches for GIRD in the literature particularly related to stretching intervention with conflicting results. [10][11][12][13][14] One of these approaches is the muscle energy technique (MET), which is time and cost-effective in the clinical settings. ...
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Objective: The purpose of the present study was to investigate acute effects of muscle energy technique (MET) for the posterior shoulder on glenohumeral joint (GHJ) range of motion (ROM) and isokinetic peak torque values of GHJ rotators. Methods: Eighteen male volleyball players volunteered to participate. All participants attended both MET trial for the GHJ horizontal abductors and sham trial. Preintervention and postintervention internal rotation (IR) and external rotation ROM and GHJ rotators isokinetic peak torque values were measured. Repeated measures one-way ANOVA and Bonferroni correction were used for analyzing the differences in the ROM and isokinetic parameters among the trials. Significance was defined as P ≤ .05. Results: The experimental group had a significantly greater increase in GHJ IR ROM postintervention compared to the control group (P = .005). No significant difference between the experimental group and control group was found for external rotation ROM (P > .05). However, a significant increase between the control/experimental and sham trials was found for external rotation ROM postintervention (P = .005). Besides, 60° internal rotator (P = .001) and external rotator (P = .008), and 180° internal rotator (P = .019) and external rotator (P = .049) peak torque values showed significant increase between the experimental and control/sham trials. Conclusion: A single application of an MET for the posterior shoulder provides immediate improvement in GHJ IR ROM and isokinetic peak torque values of both GHJ internal and external rotators in asymptomatic volleyball players. Keywords: Volleyball, muscle strength, shoulder joint
... Furthermore, the trunk extensors strength may have appeared reduced because testing was performed in the prone position, in which the length of trunk muscles was relatively shorter [57]. This has been supported by several studies that have shown a greater strength reduction when muscles were tested at a shorter length (-10.2%), as opposed to the moderate strength gains that were presented when the strength was tested at the longest muscle lengths (+2.2%) [58,59]. Changes in tendon stiffness and the force-length relationship, the stretch-induced contractile "fatigue" or damage, the diminished electromechanical coupling, and/or the reduced central (efferent) drive are among the mechanisms that potentially affect muscle strength production following static stretching exercises [1]. ...
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Although the effectiveness of static self-stretching exercises (SSSEs) and foam roller self-massaging (FRSM) in joint range of motion and muscle strength of the lower limbs has been extensively investigated, little is known about their effectiveness on the posterior trunk muscles. The present study aimed to investigate the acute effects of two 7-min SSSEs and FRSM intervention protocols on the range of trunk movements and the strength of the trunk extensors. Twenty-five healthy active males (n = 14) and females (n = 11) performed each intervention separately, one week apart. The range of motion (ROM) of the trunk-hip flexion (T-HF), the ROM of the trunk side-flexion (TSF) and rotation (TR) bilaterally, as well as the isometric maximum strength (TESmax) and endurance (TESend) of the trunk extensors were measured before and after each intervention. The ROMs of T-HF, TSF, and TR were significantly increased following both SSSEs and FRSM. The TESmax and TESend were also significantly increased after FRSM, but decreased following SSSEs. While both interventions were effective in increasing the range of motion of the trunk, a single 7-min session of FRSM presented more advantages over a similar duration SSSEs protocol due to the increase in the strength of the trunk extensors it induced.
... In addition, when losing balance or falling, an individual may need to reach out with an extended leg beyond the optimum point on their muscle force-length relationship. With stretching, the active length-tension relationship is shifted toward longer muscle lengths (60)(61)(62), with force reductions at short muscle lengths contrasting with moderate improvements at longer muscle lengths (63)(64)(65)(66)(67). Thus, after a stretch training program in which ROM and force capacity at long muscle lengths are increased, an individual who is falling may be able to move a limb further to increase their base of support and react more forcefully while landing in an extended and unbalanced position. ...
Article
Evidence for the effectiveness of acute and chronic stretching for improving range of motion is extensive. Improved flexibility can positively impact performances in activities of daily living and both physical and mental health. However, less is known about the effects of stretching on other aspects of health such as injury incidence and balance. The objective of this review is to examine the existing literature in these areas. The review highlights that both pre-exercise and chronic stretching can reduce musculotendinous injury incidence, particularly in running-based sports, which may be related to the increased force available at longer muscle lengths (altered force-length relationship) or reduced active musculotendinous stiffness, among other factors. Evidence regarding the acute effects of stretching on balance is equivocal. Longer-term stretch training can improve balance, which may contribute to a decreased incidence of falls and associated injuries and may thus be recommended as an important exercise modality in those with balance deficits. Hence, both acute and chronic stretching seem to have positive effects on injury incidence and balance, but optimum training plans are yet to be defined.
... However, the scientific evidence does not promote stretching either for improving performance or for reducing injuries and delayed onset muscle soreness. In fact, it has been established that static stretching leads to an acute loss of strength and power, so-called stretchinduced strength loss [8,[98][99][100], and should therefore probably not be performed before strength training. More specifically, 30-60 min of stretching has been found to cause a 22% (range 14-28%) acute strength loss, while shorter durations of static stretching result in an approximately 8% (range 2-19%) strength loss [98]. ...
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Lack of time is among the more commonly reported barriers for abstention from exercise programs. The aim of this review was to determine how strength training can be most effectively carried out in a time-efficient manner by critically evaluating research on acute training variables, advanced training techniques, and the need for warm-up and stretching. When programming strength training for optimum time-efficiency we recommend prioritizing bilateral, multi-joint exercises that include full dynamic movements (i.e. both eccentric and concentric muscle actions), and to perform a minimum of one leg pressing exercise (e.g. squats), one upper-body pulling exercise (e.g. pull-up) and one upper-body pushing exercise (e.g. bench press). Exercises can be performed with machines and/or free weights based on training goals, availability, and personal preferences. Weekly training volume is more important than training frequency and we recommend performing a minimum of 4 weekly sets per muscle group using a 6–15 RM loading range (15–40 repetitions can be used if training is performed to volitional failure). Advanced training techniques, such as supersets, drop sets and rest-pause training roughly halves training time compared to traditional training, while maintaining training volume. However, these methods are probably better at inducing hypertrophy than muscular strength, and more research is needed on longitudinal training effects. Finally, we advise restricting the warm-up to exercise-specific warm-ups, and only prioritize stretching if the goal of training is to increase flexibility. This review shows how acute training variables can be manipulated, and how specific training techniques can be used to optimize the training response: time ratio in regard to improvements in strength and hypertrophy. Graphic Abstract
... Both HRS and SS were performed using the dynamometer in a sitting position, similar to the previous passive assessments. During HRS, the ankle underwent initially passive DF at a constant velocity of 5°/s, starting from 10° plantar flexion to DF ROM by the dynamometer, after which participants were asked to accomplish submaximal maximal voluntary isometric contraction plantar flexions for 10 s in the same position [28]. After this contraction, the ankle was held at the DF ROM for an additional 20 s. ...
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Various stretching techniques are generally recommended to counteract age-related declines in range of motion (ROM) and/or increased muscle stiffness. However, to date, an effective stretching technique has not yet been established for older adults. Consequently, we compared the acute effects of hold relax stretching (HRS) and static stretching (SS) on dorsiflexion (DF) ROM and muscle stiffness among older adults. Overall, 15 elderly men and nine elderly women (70.2 ± 3.9 years, 160.8 ± 7.8 cm, 59.6 ± 9.7 kg) were enrolled, and both legs were randomized to either HRS or SS stretching. We measured DF ROM and muscle stiffness using a dynamometer and ultrasonography before and after 120 s of HRS or SS interventions. Our multivariate analysis indicated no significant interaction effects, but a main effect for DF ROM. Post-hoc tests revealed that DF ROM was increased after both HRS and SS interventions. Moreover, multivariate analysis showed a significant interaction effect for muscle stiffness. Post-hoc tests revealed that muscle stiffness was decreased significantly after only SS intervention. Taken together, our results indicated that both HRS and SS interventions are recommended to increase ROM, and SS is recommended to decrease muscle stiffness in older adults.
... There is an abundance of literature demonstrating stretchinduced acute increases in joint range of motion (ROM) [1][2][3][4]. Improvements in ROM permit more expansive movements with less resistance [2], enhance longer duration stretch-shortening cycle activity (prolonged amortization or transition phase) performance (i.e., longer distance running, rebound chest press and others) [5,6] and have been reported to enhance muscle force output at longer muscle lengths [7][8][9][10], which is typically the environment where many musculotendinous injuries occur [1]. Moreover, from an injury prevention perspective, increased ROM has been shown to reduce the incidence of musculotendinous injuries specifically with explosive, high speed, and change of direction activities [1]. ...
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Background Stretching a muscle not only increases the extensibility or range of motion (ROM) of the stretched muscle or joint but there is growing evidence of increased ROM of contralateral and other non-local muscles and joints. Objective The objective of this meta-analysis was to quantify crossover or non-local changes in passive ROM following an acute bout of unilateral stretching and to examine potential dose–response relations. Methods Eleven studies involving 14 independent measures met the inclusion criteria. The meta-analysis included moderating variables such as sex, trained state, stretching intensity and duration. Results The analysis revealed that unilateral passive static stretching induced moderate magnitude (standard mean difference within studies: SMD: 0.86) increases in passive ROM with non-local, non-stretched joints. Moderating variables such as sex, trained state, stretching intensity, and duration did not moderate the results. Although stretching duration did not present statistically significant differences, greater than 240-s of stretching (SMD: 1.24) exhibited large magnitude increases in non-local ROM compared to moderate magnitude improvements with shorter (< 120-s: SMD: 0.72) durations of stretching. Conclusion Passive static stretching of one muscle group can induce moderate magnitude, global increases in ROM. Stretching durations greater than 240 s may have larger effects compared with shorter stretching durations.
... The alteration in muscle strength after SS is attributed to an alteration in muscle-tendon unit stiffness [32,33] and neural activity [34][35][36][37]. SS theoretically decreases the force transfer efficiency from the muscle to the skeleton [38] with the decrement in muscle-tendon unit stiffness [32,33] and rightward shift of torque-angle curve [39][40][41]. Trajano et al. [35] reported that central factors were strongly related to the torque reduction immediately after SS and during torque recovery. In the present study, decrement in muscle-tendon stiffness and increment in knee angle at peak torque of isokinetic knee flexion were found regardless of its duration. ...
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Objectives: The purpose of this study was to compare the duration of high-intensity static stretching on flexibility and strength in the hamstrings. Methods: Fourteen healthy males (20.8 ± 0.6 years, 170.7 ± 6.5 cm, 66.4 ± 9.9 kg) underwent high-intensity static stretching for three different durations (10, 15, and 20 seconds). The intensity of static stretching was set at the maximum point of discomfort. To examine the change in flexibility and strength, range of motion, peak passive torque, relative passive torque, muscle-tendon unit stiffness, peak torque of isokinetic knee flexion, and knee angle at peak torque of isokinetic knee flexion were measured. To evaluate a time course of pain, a numerical rating scale was described. Results: Range of motion (P < 0.01), peak passive torque (P < 0.01), and knee angle at peak torque were increased at all interventions. Relative passive torque (P < 0.01) and muscle-tendon unit stiffness (P < 0.01) were decreased at all interventions. Peak torque decreased after 10 seconds of stretching (P < 0.05). Numerical rating scale during stretching was 8-9 levels in all interventions, the pain disappeared immediately after the post-measurements (median = 0). Conclusion: The results suggested that muscle-tendon unit stiffness decreased regardless of duration of high-intensity static stretching. However, peak torque of isokinetic knee flexion decreased after 10 seconds of high-intensity static stretching, though it was no change after for more than 15 seconds of stretching.
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Temporal biomechanical and physiological responses to physical activity vary between individual hamstrings components as well as between exercises, suggesting that hamstring muscles operate differently, and over different lengths, between tasks. Nevertheless, the force-length properties of these muscles have not been thoroughly investigated. The present review examines the factors influencing the hamstrings’ force-length properties and relates them to in vivo function. A search in four databases was performed for studies that examined relations between muscle length and force, torque, activation, or moment arm of hamstring muscles. Evidence was collated in relation to force-length relationships at a sarcomere/fiber level and then moment arm-length, activation-length, and torque-joint angle relations. Five forward simulation models were also used to predict force-length and torque-length relations of hamstring muscles. The results show that, due to architectural differences alone, semitendinosus (ST) produces less peak force and has a flatter active (contractile) fiber force-length relation than both biceps femoris long head (BFlh) and semimembranosus (SM), however BFlh and SM contribute greater forces through much of the hip and knee joint ranges of motion. The hamstrings’ maximum moment arms are greater at the hip than knee, so the muscles tend to act more as force producers at the hip but generate greater joint rotation and angular velocity at the knee for a given muscle shortening length and speed. However, SM moment arm is longer than SM and BFlh, partially alleviating its reduced force capacity but also reducing its otherwise substantial excursion potential. The current evidence, bound by the limitations of electromyography techniques, suggests that joint angle-dependent activation variations have minimal impact on force-length or torque-angle relations. During daily activities such as walking or sitting down, the hamstrings appear to operate on the ascending limbs of their force-length relations while knee flexion exercises performed with hip angles 45–90° promote more optimal force generation. Exercises requiring hip flexion at 45–120° and knee extension 45–0° (e.g. sprint running) may therefore evoke greater muscle forces and, speculatively, provide a more optimum adaptive stimulus. Finally, increases in resistance to stretch during hip flexion beyond 45° result mainly from SM and BFlh muscles.
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Proprioceptive neuromuscular facilitation (PNF) stretching techniques are commonly used in the athletic and clinical environments to enhance both active and passive range of motion (ROM) with a view to optimising motor performance and rehabilitation. PNF stretching is positioned in the literature as the most effective stretching technique when the aim is to increase ROM, particularly in respect to short-term changes in ROM. With due consideration of the heterogeneity across the applied PNF stretching research, a summary of the findings suggests that an ‘active’ PNF stretching technique achieves the greatest gains in ROM, e.g. utilising a shortening contraction of the opposing muscle to place the target muscle on stretch, followed by a static contraction of the target muscle. The inclusion of a shortening contraction of the opposing muscle appears to have the greatest impact on enhancing ROM. When including a static contraction of the target muscle, this needs to be held for approximately 3 seconds at no more than 20% of a maximum voluntary contraction. The greatest changes in ROM generally occur after the first repetition and in order to achieve more lasting changes in ROM, PNF stretching needs to be performed once or twice per week. The superior changes in ROM that PNF stretching often produces compared with other stretching techniques has traditionally been attributed to autogenic and/or reciprocal inhibition, although the literature does not support this hypothesis. Instead, and in the absence of a biomechanical explanation, the contemporary view proposes that PNF stretching influences the point at which stretch is perceived or tolerated. The mechanism(s) underpinning the change in stretch perception or tolerance are not known, although pain modulation has been suggested.
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Proprioceptive Neuromuscular Facilitation (PNF): Its Mechanisms and Effects on Range of Motion and Muscular Function Proprioceptive neuromuscular facilitation (PNF) is common practice for increasing range of motion, though little research has been done to evaluate theories behind it. The purpose of this study was to review possible mechanisms, proposed theories, and physiological changes that occur due to proprioceptive neuromuscular facilitation techniques. Four theoretical mechanisms were identified: autogenic inhibition, reciprocal inhibition, stress relaxation, and the gate control theory. The studies suggest that a combination of these four mechanisms enhance range of motion. When completed prior to exercise, proprioceptive neuromuscular facilitation decreases performance in maximal effort exercises. When this stretching technique is performed consistently and post exercise, it increases athletic performance, along with range of motion. Little investigation has been done regarding the theoretical mechanisms of proprioceptive neuromuscular facilitation, though four mechanisms were identified from the literature. As stated, the main goal of proprioceptive neuromuscular facilitation is to increase range of motion and performance. Studies found both of these to be true when completed under the correct conditions. These mechanisms were found to be plausible; however, further investigation needs to be conducted. All four mechanisms behind the stretching technique explain the reasoning behind the increase in range of motion, as well as in strength and athletic performance. Proprioceptive neuromuscular facilitation shows potential benefits if performed correctly and consistently.
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The purpose of this study was to determine if neural tension during passive stretching affected subsequent strength loss. Eleven healthy subjects (10 men, 1 woman; age 34±12 yr) performed maximal isometric hamstring contractions at 100°, 80°, 60° and 40° knee flexion prior to and after five 1 min hamstring stretches performed in either a spinal neutral position or a neural tension position. One leg was stretched in the neutral position and the other in the neural tension position. Hamstring EMG activity was recorded during all contractions and stretches. Passive resistance to stretch was reduced by 11% after stretching (P<0.01; no difference between neutral or neural tension stretches P=0.41). Stretch-induced strength loss was apparent after neural tension stretches (12%, P<0.01) but not after neutral stretches (5%, P=0.09). There was a rightward shift in the angle-torque curve after neutral stretches (strength loss on ascending limb, strength gain on descending limb, P<0.01). This effect was not apparent after neural tension stretches (P=0.43). Stretching did not affect EMG activity during isometric contractions (<2% decline P=0.58; no difference between neutral and neural tension, P=0.86). Hamstring stretching with the spine in a neutral position did not result in significant strength loss but shifted the length-tension relationship such that strength was decreased at short muscle lengths and increased at long muscle lengths. Hamstring stretching with increased neural tension resulted in strength loss with no associated shift in the length-tension relationship.
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An objective of a warm-up prior to an athletic event is to optimize performance. Warm-ups are typically composed of a submaximal aerobic activity, stretching and a sport-specific activity. The stretching portion traditionally incorporated static stretching. However, there are a myriad of studies demonstrating static stretch-induced performance impairments. More recently, there are a substantial number of articles with no detrimental effects associated with prior static stretching. The lack of impairment may be related to a number of factors. These include static stretching that is of short duration (<90 s total) with a stretch intensity less than the point of discomfort. Other factors include the type of performance test measured and implemented on an elite athletic or trained middle aged population. Static stretching may actually provide benefits in some cases such as slower velocity eccentric contractions, and contractions of a more prolonged duration or stretch-shortening cycle. Dynamic stretching has been shown to either have no effect or may augment subsequent performance, especially if the duration of the dynamic stretching is prolonged. Static stretching used in a separate training session can provide health related range of motion benefits. Generally, a warm-up to minimize impairments and enhance performance should be composed of a submaximal intensity aerobic activity followed by large amplitude dynamic stretching and then completed with sport-specific dynamic activities. Sports that necessitate a high degree of static flexibility should use short duration static stretches with lower intensity stretches in a trained population to minimize the possibilities of impairments.
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An informal review of literature on the use of postisometric relaxation (PIR) type proprioceptive neuromuscular facilitation (PNF) indicates that the force of contraction requested from the athlete ranges from 10 to 100% of maximum voluntary isometric contraction (MVIC). The purpose of this study was therefore to determine if an optimal contraction intensity to elicit maximum positive change in range of motion (DeltaROM) exists. This research question was tested across a convenience sample of 56 (37 male and 19 female) university athletes. Target contractions during PNF interventions were set at 20, 50, and 100% MVIC. Pre- and post-PNF intervention hip flexion range of motion (ROM) was measured on a unilateral straight leg raise. The target MVIC of 20, 50, and 100% elicited mean pre-post intervention DeltaROM of 8.4, 12.9, and 11.6 degrees , respectively (all p < or = 0.0001). Differences in pre-post intervention DeltaROM between target contraction intensities were also significant (p = 0.016 to < or = 0.0001). A peak DeltaROM of 13.3 degrees was found at a PNF contraction intensity of 64.3% MVIC. Where optimizing increased ROM in healthy athletes is the desired outcome of PIR-PNF application, coaches and trainers should elicit contraction intensities of approximately 65% MVIC.
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Stretching is commonly practiced before sports participation; however, effects on subsequent performance and injury prevention are not well understood. There is an abundance of literature demonstrating that a single bout of stretching acutely impairs muscle strength, with a lesser effect on power. The extent to which these effects are apparent when stretching is combined with other aspects of a pre-participation warm-up, such as practice drills and low intensity dynamic exercises, is not known. With respect to the effect of pre-participation stretching on injury prevention a limited number of studies of varying quality have shown mixed results. A general consensus is that stretching in addition to warm-up does not affect the incidence of overuse injuries. There is evidence that pre-participation stretching reduces the incidence of muscle strains but there is clearly a need for further work. Future prospective randomized studies should use stretching interventions that are effective at decreasing passive resistance to stretch and assess effects on subsequent injury incidence in sports with a high prevalence of muscle strains.
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The purpose of this study was (1) to evaluate the reproducibility of a new method of measuring passive resistance to stretch in the human hamstring muscle group, in vivo, using a test re-test protocol and 2) to examine the effect of repeated stretches. Passive resistance offered by the hamstring muscle group during knee extension was measured in 10 subjects as knee flexion moment (Nm) using a KinCom dynamometer. The knee was passively extended at 5 deg/s to the final position where it remained stationary for 90 s (static phase). EMG of the hamstring muscle was also measured. The test re-test protocol included 2 tests (tests 1 and 2) administered 1 h apart. On a separate occasion 5 consecutive static stretches were administered (stretches 1-5) separted by 30 s. Stretch 6 was administered one hour after stretch 5. In the static phase passive resistance did not differ between test 1 and test 2. Resistance declined in both tests 1 and 2, whereas EMG activity remained unchanged. The decline in resistance was significant up to 45 s. For the repeated stretches there was an effect of time (90 s) and stretch (1-5) with a significant interaction i.e., resistance diminished with stretches, and the 90-s decline was less as more stretches were performed. Passive resistance in stretch 6 was lower than in stretch 1. The present study has demonstrated a reliable method for studying resistance to stretch of the human hamstring muscle group. A viscoelastic response of the human hamstring muscle was shown. With 5 repeated stretches, resistance to stretch diminished and each stretch exibited a viscoelastic response, albeit less with each subsequent stretch. The effect of 5 repeated stretches was significant 1 h later.
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The aim of the study was to examine whether increased neural tension during passive hamstring stretching contributes to stretch-induced strength loss. Eleven healthy subjects performed maximal isometric knee flexion contractions (100°, 80°, 60° and 20°) before and after a series of hamstring stretches (six 1-min stretches), performed in either a spinal neutral position or a neural tension position. Effect of stretch technique (neutral or neural tension) on passive resistance to stretch, strength-induced strength loss and electromyography activity during strength tests was assessed with repeated measures analysis of variance. Passive resistance to stretch was reduced by 19% after the series of stretches (p=0.001) with no difference between neutral or neural tension stretches (p=0.41). Stretch-induced strength loss was greater (p=0.043) after the neural tension stretches (13%) vs the neutral stretches (5%). There was an apparent rightward shift in the length tension curve after neutral stretches with a 15% strength loss at muscle lengths shorter than optimum, and a 10% gain in strength at muscle lengths longer than optimum (p<0.001). This effect was not apparent after neural tension stretches where strength loss was 21% at muscle lengths shorter than optimum and 9% at muscle lengths longer than optimum. The addition of neural tension to hamstring stretching increased stretch-induced strength loss but this was not associated with observable neural inhibition. The absence of a rightward shift in the length-tension curve after neural tension stretching indicates that muscle fibre shortening during isometric contractions was unaffected, presumably because tendon-aponeurosis compliance was not increased.
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To examine stiffness, energy, and passive torque in the dynamic and static phases of a stretch maneuver in the human hamstring muscle in vivo we used a test-retest protocol and a repeated stretches protocol. Resistance to stretch was defined as passive torque (in newton-meters) offered by the hamstring muscle group during passive knee extension as measured using an isokinetic dynamometer with a modified thigh pad. In 13 uninjured subjects, the knee was passively extended to a predetermined final position (0.0875 rad/ sec, dynamic phase) where it remained stationary for 90 seconds (static phase). The test-retest protocol included two tests administered 1 hour apart. On a separate occasion, five consecutive static stretches were administered separated by 30 seconds and followed by a sixth stretch 1 hour later. For the test-retest phase, stiffness and energy in the dynamic phase and passive torque in the static phase did not differ and yielded correlations of r = 0.91 to 0.99. During the static phase, passive torque declined in both tests (P < 0.0001). For the repeated stretches, decreases were observed for energy (P < 0.01) and stiffness (P < 0.05) in the dynamic phase and for passive torque (P < 0.0001) in the static phase. However, the decline in the variables returned to baseline within 1 hour. The data show that the method employed is a useful tool for measuring biomechanical variables during a stretch maneuver. This may provide a more detailed method to examine skeletal muscle flexibility.
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In the present study, we examined the hypothesis that stretch of tendinous tissue in the human tibialis anterior (TA) muscle-tendon unit upon isometric dorsiflexion maximum voluntary contraction (MVC) varies along the entire tendinous component length. Ultrasound-based measurements of the excursions of the TA tendon origin and proximal end of the TA central aponeurosis were taken in the transition from rest to MVC in six men. Subtracting the TA tendon origin excursion from the excursion of the aponeurosis proximal end, the aponeurosis excursion was estimated. Estimation of the aponeurosis proximal region excursion was obtained subtracting the excursion of the insertion point of a central region fascicle on the aponeurosis from the whole aponeurosis excursion. Subtracting tendon excursion from the excursion of the central fascicle insertion point, the aponeurosis distal region excursion was estimated. Strain values were calculated dividing the excursions obtained by the original resting lengths. All excursions and lengths were measured in the mid-longitudinal axis of the TA muscle-tendon unit at the neutral anatomical ankle position. Tendon excursion and strain were 0.5+/-0. 08 cm (mean+/-SE) and 3.1+/-0.2%, respectively. Aponeurosis excursion and strain were 1.1+/-0.15 cm and 6.5+/-0.6%, respectively. Aponeurosis distal region excursion and strain were 0.3+/-0.05 cm and 3.5+/-0.3%, respectively. Aponeurosis proximal region excursion and strain were 0.8+/-0.12 cm and 9.2+/-1%, respectively. Aponeurosis excursion and strain were larger by 110-120% (P<0.05) compared with tendon. Aponeurosis proximal region excursion and strain were larger by 165-170% (P<0.05) compared with aponeurosis distal region. These findings are in line with results from in vitro animal material testing and have important implications for theoretical models of muscle function.