Proximal Hamstring Strains of Stretching
Type in Different Sports
Injury Situations, Clinical and Magnetic Resonance
Imaging Characteristics, and Return to Sport
Carl M. Askling,*†‡ PT, Magnus Tengvar,§ MD, Tönu Saartok,‡ MD, PhD,
†
and Alf Thorstensson, PhD
†
From the Swedish School of Sport and Health Sciences, Stockholm, Sweden, the
‡
Section of Orthopaedics and Sports Medicine, Department of Molecular Medicine and
§
Surgery, Karolinska Institutet, Stockholm, Sweden, and the Department of Radiology,
Sophiahemmet Hospital, Stockholm, Sweden
Background: Hamstring strains can be of at least 2 types, 1 occurring during high-speed running and the other during motions
in which the hamstring muscles reach extreme lengths, as documented for sprinters and dancers.
Hypothesis: Hamstring strains in different sports, with similar injury situations to dancers, also show similarities in symptoms,
injury location, and recovery time.
Study Design: Case series (prognosis); Level of evidence, 4.
Methods: Thirty subjects from 21 different sports were prospectively included. All subjects were examined clinically and with
magnetic resonance imaging (MRI). The follow-up period lasted until the subjects returned to or finished their sport activity.
Results: All injuries occurred during movements reaching a position with combined extensive hip flexion and knee extension.
They were located proximally in the posterior thigh, close to the ischial tuberosity. The injuries were often complex, but 83%
involved the semimembranosus and its proximal free tendon. Fourteen subjects (47%) decided to end their sports activity. For
the remaining 16 subjects, the median time for return to sport was 31 weeks (range, 9-104). There were no significant correlations between specific clinical or MRI parameters and time to return to sport.
Conclusions: In different sports, an injury situation in which the hamstring muscles reach extensive length causes a specific
injury to the proximal posterior thigh, earlier described in dancers. Because of the prolonged recovery time associated with this
type of injury, correct diagnosis, based on history and palpation, and adequate information to the subject are essential.
Keywords: hamstrings; MRI; palpation; recovery time; tendon; various sports
Acute hamstring strains are common injuries in various
sports.4,9,11,16 A few studies have pointed out the possibility
that the demands of different sports and different injury situations are associated with lesions in different regions of the
hamstring muscle group.6,10 Systematic MRI investigations
of acute first-time hamstring strains in 2 specific groups of
athletes have supported this hypothesis.2,3 In sprinters, it was
shown that a high-speed running type of injury consistently
occurred in the long head of the biceps femoris muscle.2 In
dancers, the injuries occurred during stretching exercises
carried out to an extreme joint position and most often
involved the proximal free tendon of the semimembranosus
(SM) muscle. Furthermore, the type of injury seemed to
influence the recovery time. The time back to preinjury level
was demonstrated to be much longer for dancers with a
stretching type of hamstring injury than for sprinters with a
high-speed running type of hamstring injury.1-3 Additionally,
in the group of sprinters, proximity of the injury to the ischial
tuberosity, as estimated both by palpation and MRI, was
associated with longer time to return to preinjury level.2
These findings indicating a relationship between injury situation, muscle-tendon involvement, and recovery time were
so far obtained on rather homogeneous groups of athletes.
*Address correspondence to Carl M. Askling, PT, Box 5626,
Stockholm, Sweden 114 86 (e-mail: carl.askling@ihs.se).
No potential conflict of interest declared.
The American Journal of Sports Medicine, Vol. 36, No. 9
DOI: 10.1177/0363546508315892
© 2008 American Orthopaedic Society for Sports Medicine
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Askling et al
Similar situations (ie, high-speed running and stretching to
extreme joint positions) also occur in other sports as do hamstring injuries. The question arises as to the applicability of
the relationships found in sprinters and dancers to other
sport activities. Anecdotal observations in that direction have
been made in earlier studies, indicating that hamstring
strains occurring during overhead kicking in soccer6 and in
kicking in rugby4 had long recovery times. If these relationships were general, careful documentation of the injury situation, coupled with palpation and/or MRI, would provide a
good basis for making a prognosis for the time required before
return to sport.
The aim of the present study was to investigate the generalizability of our earlier findings of specific injury location and long recovery times for stretching-type hamstring
injuries in dancers.
METHODS
Subjects
Thirty subjects (22 females and 8 males) from 21 different
sports were prospectively included in the study. Mean values
(±1 standard deviation, range) for their age, body mass, and
height were 28 years (±11, 16-53), 63 kg (±10, 48-90), and
1.71 m (±0.08, 1.59-1.92), respectively. Twenty-four subjects
were categorized as elite level (international or national) and
6 as recreational level (Table 1). All subjects were informed
about the background of the study and accepted to participate on a voluntary basis. Approval of the study was obtained
from the Regional Ethics Committee.
The American Journal of Sports Medicine
clinical examination and MRI investigation varied but was
not allowed to exceed 12 months. The clinical examination
had to reveal pain on palpation of the area of origin of the
hamstring muscles at the ischial tuberosity or slightly
(0-5 cm) below, pain in a passive straight-leg raise test, and
increased pain with addition of an isometric hamstring
contraction during that test. The pain had to be localized
close to the ischial tuberosity also in these latter 2 tests. In
all subjects included in the study, the subsequent MRI
investigation had to confirm the suspected injury.
Exclusion Criteria. Exclusion criteria comprised an
unclear injury situation; earlier hamstring strain at the
same side during the last 12 months before the present
injury; total rupture or avulsion of 1, 2, or all 3 hamstring
muscles (determined by MRI); extrinsic trauma to the posterior thigh; ongoing or chronic low back problems; and/or
pregnancy. Three subjects were excluded based on the MRI
investigation, 1 had a total rupture of the SM, and the
other 2 had no injury that could be detected with MRI.
Clinical Examination. At the clinical examination, the
subjects were interviewed about the injury situation—the
movements or exercises during which the injury had
occurred as well as what kind of rehabilitation they had
undergone. Palpation of the posterior thigh was performed
with the subjects prone and the knee extended. The point
where the subject noted the highest pain on palpation was
marked, and the distance between this point and the palpated ischial tuberosity was measured. Clinical examinations and interviews were in all cases performed by the
first author.
Magnetic Resonance Imaging Investigations
Subject Enrollment, Inclusion/Exclusion Criteria,
and Clinical Examination
During the recruitment of athletes for our previous studies of
acute first-time hamstring strains in sprinters and dancers,1
the first author (C.M.A.) was contacted via telephone or email by many athletes (coaches, medical staff, parents) in
other sports describing different types of hamstring strain.
In some cases, they described an injury pattern similar to
that of the dancers, namely that the injury occurred in a situation in which the hamstrings reached extensive length by
a combination of hip flexion and knee extension. Some contacted the first author soon after their injury and others after
longer time periods due to persistent symptoms and ineffective treatments. When we realized that this injury type
appeared to exist in other sports as well, we decided to collect
this type of hamstring strain from different sports in parallel with our ongoing study on well-defined sprinters and
dancers. Inclusion criteria are given below. The recruitment
period for the present study extended over 2 years
(November 2004 through November 2006).
Inclusion Criteria. To be included, the subject had to
have a distinct history of acute sudden pain from the posterior thigh occurring in a position with combined extensive hip flexion and knee extension during competition,
training, or performance. The time from the injury to the
The MRI investigations were performed on a 1.0-T superconductive MRI unit (Magnetom Expert, Siemens, Erlangen,
Germany). Briefly, longitudinal, sagittal, and frontal short TI
inversion recovery (STIR) images as well as transversal T1weighted, T2-weighted, and STIR images (5-mm slice thickness and 0.5-mm gap) were obtained from both legs.2
A muscle was considered injured when it contained high
signal intensity (edema) on the STIR images, as compared
with the uninjured side. A tendon was deemed as injured if
it was thickened and/or had a collar of high signal intensity around it and/or had high intratendinous signal intensity, as compared with the uninjured side. An injury in the
SM muscle was allocated to 1 or more of 6 different regions
within its muscle-tendon complex.3 The edema was analyzed, and the maximal craniocaudal length and the most
cranial pole of the injury were identified, and the perpendicular distance between the level of this pole and the
level of the most caudal part of the ischial tuberosity
was measured.3 Presence of bone edema, defined as
high signal intensity intraosseously in the ischial tuberosity on 2 consecutive STIR sequences or on 2 STIR
sequences in 2 planes on the injured side, was registered.
A plain radiograph of the pelvis was obtained from all the
subjects to identify possible skeletal injuries (eg, avulsion
fractures).
Vol. 36, No. 9, 2008
Proximal Hamstring Stretching-Type Strains
1801
TABLE 1
Age, Sex, Sport, Level of Performance, Injury Situation, Muscles Involved, and Time to Return to Sporta
Subject
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Age/Sex
Sport
Level
Situation
Muscles Involved
Time to Return
to Sport (weeks)
20/M
35/F
48/F
48/F
22/F
36/M
21/F
33/F
24/F
52/F
18/F
19/F
24/F
18/F
21/F
27/M
16/F
18/M
27/M
24/F
31/M
29/M
20/F
21/F
22/M
27/F
18/F
19/F
53/F
49/F
Acrobatics
Aerobics
Aerobics
Aerobics
Ballet
Ballet
Bodybuilding
Cheerleading
Climbing
Cross-country skiing
Dance education
Dance education
Dance teaching
Decathlon
Floor ball
Floor ball
Gymnastics
Ice hockey
Judo
Pentathlon—modern
Pole vault
Running—long distance
Sprint
Soccer
Soccer
Taekwondo
Tennis
Tennis
Tennis
Yoga
I
R
R
R
I
I
N
I
I
R
N
N
N
I
I
R
I
N
I
I
I
I
I
N
I
I
I
I
I
R
Sagittal split
Sagittal split
Stretching
High kick
High kick
High kick
Stretching
Sagittal split
Sagittal split
Sagittal split
Stretching
Stretching
Stretching
Stretching
Side split
Sagittal split
Stretching
Side split
Side split
Side split
Stretching
Stretching
Stretching
Sagittal split
High kick
High kick
Sagittal split
Sagittal split
Sagittal split
Stretching
ST, BFlh
SM
SM
SM, QF
QF, AM
SM, QF
SM, QF
SM
SM
SM
SM
SM
SM, ST, QF
SM
SM
SM
SM, ST
SM
SM, ST, QF
SM
ST, BFlh
SM, BFlh
SM
SM
ST, BFlh
AM
SM, QF, AM
SM, QF, AM
SM
SM
40
–
40
–
12
12
80
–
–
104
–
25
26
–
–
80
–
–
–
–
36
71
–
–
13
24
13
9
–
44
a
I, international level; N, national level; R, recreational level; AM, adductor magnus; BFlh, biceps femoris, long head; QF, quadratus
femoris; SM, semimembranosus; ST, semitendinosus; –, retired from their sport.
Follow-up
The follow-up period lasted until the subject returned to
sport or decided to give up his or her sports activity. The
subjects were asked to register the first full week when
they could train and/or perform in their sport again, note
if they still had any symptoms at that time, and give that
information by telephone to the first author. If the subjects
decided to stop with their sport, they were to inform the
first author directly, and a clinical examination was then
made. The subjects’ rehabilitation was administrated by
their respective physician and/or physiotherapist and was
not controlled as a part of this study.
Statistics
The Shapiro-Wilk W test was applied to examine normality in the distribution of data. Spearman rank order correlation was calculated between subjects’ MRI parameters,
palpation data, and time to return to sport. The MannWhitney U test was used to detect statistical differences in
age, sex, and level of performance between the group of
subjects returning to sport and the group who did not, and
in time before return to sport for elite versus recreational
level, and team versus individual sports, respectively. The
significance level was set at P < .05.
RESULTS
Clinical Examination
The median time for the first clinical examination was 12
weeks (range, 1-51) after the injury. The individually
reported rehabilitation preceding the first clinical examination was too divergent to allow any systematic analysis.
All 30 subjects reported that they had sustained their
injuries during athletic movements, where the hip was in
extensive flexion and the knee extended (Table 1). Four
injuries occurred while warming up, 2 while cooling down,
3 during supported stretching (help with the stretching
procedure from another person), and the remaining 21
during matches, performance, or training sessions. Four of
the subjects (13%) had to acutely interrupt their activity,
but all the others were able to continue despite pain and
stiffness. Twenty-six subjects (87%) experienced a “pop”
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Askling et al
The American Journal of Sports Medicine
when the injury occurred, and in 8 cases, that sound was
even heard by people in the vicinity. At the injury occurrence, 20 subjects (67%) stated that they felt acute pain at
the injury site close to the ischial tuberosity. All subjects
had sought medical advice and rehabilitation support at a
median time of 9 weeks (range, 1-24) after the injury.
The mean distance (± 1 standard deviation, range) from
the point with the most pain to palpation to the ischial
tuberosity was 2 cm (± 1, 0-5). There was no significant correlation between the location of the point of most pain to
palpation and time to return to sport (r = .262, n = 16) (see
Follow-up, below).
MRI Investigation
The median time for the MRI investigation was 13 weeks
(range, 1-52) after injury. In 4 cases, bone edema was
detected on the injured side. The plain pelvic radiograph
did not show any abnormalities.
The SM muscle was the most commonly injured part of
the hamstrings, as evidenced in 25 of the 30 subjects
(83%), followed by quadratus femoris (27%), semitendinosus (20%), biceps femoris long head (10%), and adductor
magnus (10%). As shown in Table 1, the injuries occurred
at 1 muscle-tendon site in 17 subjects (57%), 2 sites in 9
cases (30%), and 3 sites in 4 cases (13%). All of the 25
injuries that were located in the SM involved its proximal
free tendon, and 1 of them also involved the adjacent proximal muscle-tendon junction. Typical MRI findings early (1
day after injury) and late (11 months after injury) are
shown in Figures 1 and 2, respectively.
The most cranial pole of the injury was, on average, 30 mm
(standard deviation ± 16; range, 0-66) cranial to the caudal
border of the ischial tuberosity. The mean craniocaudal
length of the injury was 71 mm (standard deviation ±58;
range, 10-214). None of the calculated correlations were significant between the length of the injury or the distance to
the ischial tuberosity and the time to return to sport (r = .031
and –.198, respectively; n = 16) (see Follow-up, below).
Follow-up
Fourteen subjects (47%) decided to finish their sports
careers due to chronic symptoms from their hamstring
injuries. The decision to quit in this group was made after a
median time of 63 weeks (range, 26-104). Three of these subjects gave multiple reasons but stated that the hamstring
injury was a major factor that influenced their decision to
end their sports activities. All the subjects who decided to
discontinue their sports participation showed signs of injury
at the clinical examination after the decision (ie, palpation
pain close to the ischial tuberosity, pain in a passive
straight-leg raise test, and increased pain with addition of
an isometric hamstring contraction during that test).
The median time before return to sports for the remaining 16 subjects was 31 weeks (range, 9-104). At the time
the 16 subjects decided to go back to their sport, 2 reported
no symptoms, whereas 14 reported a variety of persisting
problems, such as feelings of insecurity (n = 14), pain when
sitting (n = 10), pain when putting force demands on the
hamstrings during lengthening (stretching) (n = 8), and a
Figure 1. Frontal (A) and transverse (B and C) magnetic resonance short TI inversion recovery images of a typical acute
(1 day old) stretching-type injury to the posterior thigh involving the proximal free tendon of the semimembranosus (SM)
close to the ischial tuberosity (marked with an asterisk in A
and B) and with a “collar” of edema (arrow) around the tendon. B, the involvement of the adductor magnus (arrowhead)
and quadratus femoris (curved arrow) in the same injury is
shown. C, the image shows the injury 5 cm caudal to the
ischial tuberosity, and the arrow marks the edema surrounding the proximal tendon of the SM.
Vol. 36, No. 9, 2008
Proximal Hamstring Stretching-Type Strains
1803
in the time for return to sport between subjects in individual sports versus team sports.
DISCUSSION
Figure 2. Transverse T1-weighted magnetic resonance
images of an 11-month-old injury. Both images show the
thickened proximal free tendon (arrows) of the semimembranosus 0.5 cm (A) and 5 cm (B) caudal to the ischial tuberosity (see Figure 1C).
need for extra attention to warming up before performance
(n = 8). There were no statistically significant differences
between the group that returned to sports (n = 16) compared with the group that did not (n = 14), with respect to
age, sex, or level of performance. The time to return to
sports was significantly longer (P = .021) for the subjects at
a recreational level (median, 62 weeks; range, 40-104; n = 4)
compared with the subjects at an elite level (25 weeks;
range, 9-80; n = 12). There were no significant differences
This study shows that for a variety of sport activities, an
injury situation with a combination of extensive hip flexion
and knee extension can lead to a specific injury to the proximal part of the posterior thigh similar to that earlier
described for a well-defined group of dancers.1,3 This work
further expands previous data on dancers by demonstrating
that this particular type of injury not only occurs in slow
stretching movements (eg, splits) but also during relatively
fast movements in performance or match situations. This
study also shows that both the clinical examination and MRI
investigation could demonstrate clear findings as late as 51
and 52 weeks after the injury, respectively. The specific characteristics of the injury included a combination of the following: a “pop” when the injury occurred, relatively minor pain
acutely, closeness to the ischial tuberosity, and involvement
of the proximal free tendon of the SM.
The severity of the injury was indicated by the fact that
a remarkably large number of subjects (47%) actually
chose to give up their sport after an extended time of rehabilitation (median, 63 weeks). The recovery time for the
remaining 16 subjects was prolonged (median, 31 weeks)
but not as long as that earlier reported for dancers
(median, 50 weeks).3 One explanation for this discrepancy
could be that the criteria for return were different. In the
dancers, the criterion was that they should be able to perform at their preinjury level in professional dancing. The
criterion for the subjects from various sport activities in
the current study was that they considered themselves
capable of returning to sport activities at all. It is noteworthy that a majority (88%) of the subjects, upon returning to
sports, still reported symptoms from the injury.
The muscle-tendon complex most often involved in the
current type of injury was the SM (83%). This is in accordance with the results from the study on dancers, where
87% of the injuries involved the SM. Furthermore, all
injuries in the present study located in the SM involved its
proximal free tendon. Free tendon involvement may be
related to prolonged time to return to preinjury level as we
have shown in sprinters and dancers.2,3
The complexity of the injury might be a contributing factor to the extended recovery time. Even though the current
injury is referred to as a “hamstring strain,” it clearly
involved more than just hamstring muscles. In as many as
13 subjects (43%), 2 or 3 muscles were involved. In 8 of the
30 subjects, an injury to the quadratus femoris was demonstrated. Involvement of the quadratus femoris in posterior
thigh injuries has been reported before, however, not distinguishing the injury situation.8,12,13,15 An exception is our
study on dancers,3 where involvement of the quadratus
femoris was detected in 87% of the injuries occurring during slow-speed stretching exercises (splits). The reasons for
the complexity of the injury, as opposed to the more distinct high speed–type of injury in the sprinters as noted
above, are presently difficult to explain.
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Askling et al
The delay from the injury occurrence to the clinical examination and MRI investigation varied and was rather long
for some subjects. Thus, the collected data were subject to
various degrees of recall bias. Nonetheless, all subjects
included could describe the injury situation in a very distinct way. This is in line with earlier observations that recall
is facilitated if the self-report concerns only 1 specific
injury.5 A likely contributing factor was that the injury influenced the subjects’ lives in a dramatic way by preventing
them from participating in sports. In addition, we realize
that a consistent time from injury to the MRI investigation
might have given additional information. However, it is
notable that the current approach, despite the variation
within the material, was able to show a consistent picture of
injury characteristics. Finally, it would have been valuable if
the rehabilitation protocol had been controlled during the
follow-up period. Actually, there is only 1 study available
investigating the effect of different rehabilitation programs
after acute hamstring strains from a short-term (time to
return to sport) and long-term (reinjuries) perspective.14
Because it is likely that different types of hamstring injuries
require different, specific types of rehabilitation regimens,
more prospective randomized studies are needed comparing
and evaluating rehabilitation programs after different types
of well-defined hamstring strains.7
Clinical Implications
On the basis of the present results, in cases of injuries to the
proximal posterior thigh, the clinician should request a
detailed description from the patient about the cause of the
strain and also perform a careful palpation. Magnetic resonance imaging studies can confirm the injury during a long
period after injury (in this study, as long as 12 months) and
should always be conducted when a total rupture is suspected. It is essential that the athlete get relevant information from the medical staff about the risk of prolonged
recovery time. Most athletes do not realize that this type of
strain may in fact be a serious injury, in many cases even
career-ending, and therefore neglect to seek early medical
advice. A typical scenario may be that the injured person
comes to the clinic several months after the injury occurrence, complaining about pain when executing movements
reaching extreme joint positions and/or when sitting for long
periods of time.
CONCLUSION
This study shows that in different sports, an injury situation with a combination of extensive hip flexion and knee
extension gives rise to a specific injury to the proximal part
of the posterior thigh, earlier systematically described for
dancers. Information about the injury situation and the
location of pain on palpation provides enough reason to
The American Journal of Sports Medicine
suspect this type of injury. An MRI investigation can confirm the exact location and extension of the injury. It is
important to inform the subject that this type of injury,
despite its relatively mild initial symptoms, generally
implies a prolonged rehabilitation period before returning
to sport.
ACKNOWLEDGMENT
The authors thank Dr Klas Östberg, Solnakliniken, and
the radiography staff at Sophiahemmet for their skillful
contributions to this research. The authors also thank the
Swedish Center for Sport Research for financial support.
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