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The active knee extension test and Slump test in subjects with perceived hamstring tightness
International Journal of Osteopathic Medicine 8 (2005) 89e97 www.elsevier.com/locate/ijosm
Research report
The active knee extension test and Slump test in subjects with perceived hamstring tightness Kate Elissa Kuilart *, Melanie Woollam, Elizabeth Barling, Nicholas Lucas School of Exercise and Health Sciences, University of Western Sydney, Penrith South, NSW 1797, Australia Received 30 May 2005; received in revised form 15 June 2005; accepted 12 July 2005
Abstract Background: Reduced hamstring extensibility is commonly assumed to be due to stiffness or decreased length of the hamstring muscle group. The first aim of this study was to collect data on the results of the active knee extension test in subjects with perceived reduction in hamstring extensibility. The second aim was to establish the prevalence and location of symptoms induced by the Slump test in those subjects with perceived hamstring tightness. Methods: Forty-two asymptomatic subjects (M Z 21, F Z 21, mean age 23.6, range 18e35) with perceived right hamstring tightness performed the active knee extension test followed by the Slump test. A goniometer and digital photography were used to measure the knee flexion angle of the active knee extension test. A body chart was used to record the location of pain or discomfort produced or relieved during the active performance of the Slump test. Results: Subjects had an average knee flexion angle of 35.2 (SD 14.2; range 15.6e70 ). During the Slump test 66.7% (n Z 28) of the subjects reported symptoms in the posterior knee, 35.7% (n Z 15) reported symptoms in the posterior thigh and 33.3% (n Z 13) reported symptoms in the posterior leg. Combined prevalence of cervical and thoracic symptoms was 14.2%, with only 7.1% experiencing symptoms in the thoracic region. At the last stage of the Slump test 12.0% (n Z 5) of subjects had no change in symptoms, whilst 83.3% (n Z 35) of subjects had either partial relief (n Z 19) or complete relief (n Z 16) of symptoms. Discussion and conclusion: Subjects with perceived hamstring tightness did not appear to have reduced hamstring extensibility when compared to the available normative data. Only 7.1% of subjects reported thoracic symptoms during the Slump test, compared to other reports of thoracic symptoms in approximately 50% of asymptomatic subjects. The high prevalence of posterior lower extremity symptoms induced by the Slump test amongst asymptomatic subjects, which are relieved by cervical extension, suggests that neural structures may contribute to perceived hamstring tightness and the sensation of discomfort produced during hamstring stretches. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Musculoskeletal; Hamstrings; Flexibility; Osteopathic medicine; Slump test; Neurodynamic test
1. Introduction Evaluation of the extensibility of the hamstring muscles is a standard assessment in osteopathic clinical examination.1 Hamstring muscles that demonstrate
* Corresponding author. 50 Lucinda Avenue, Springwood, NSW 2777, Australia. Tel.: C61 2 47 518601; fax: C61 2 47 511570. E-mail address: [email protected] (K.E. Kuilart). 1746-0689/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijosm.2005.07.004
reduced extensibility are often colloquially referred to as being ‘tight’; however, the use of this word is nonspecific and is of limited use in the clinical and research settings. In this article, the use of the term ‘tight’ refers to the subjective perception of reduced extensibility of the hamstring muscle group. Individuals may report the perception of tightness in the posterior thigh and knee, and infer that this sensation arises from the hamstring muscles, because they have knowledge of these muscles and the perception of
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tightness may be increased or reproduced by stretches labelled as ‘hamstring stretches’. Tests for hamstring muscle length or extensibility combine hip flexion and knee extension movements which stretch the structures posterior to the axes of rotation of these joints, including both the hamstring muscles and neural structures (e.g. sciatic nerve, posterior tibial nerve, and common peroneal nerve), inclusive of their connective tissues.2 The perception or sensation of tight hamstrings could therefore be due to sensations arising from the hamstring muscles, or arising from mechanically sensitive neural structures, or a combination of both. Also, the actual range of movement obtained during combined hip flexion and knee extension is influenced by flexibility of these joints, and both the extensibility of the hamstring muscles and functionally related neural structures. There are at least three separate concepts being evaluated during tests for hamstring extensibility, such as the straight leg raise (SLR) and active knee extension (AKE) tests.3 The first concept is that of joint flexibility (the range of motion available at the hip and knee in flexion and extension, respectively), as this is what is being objectively measured (e.g. knee flexion angle). The second concept is that of tissue extensibility (or actual change in length of structures posterior to the axes of rotation of the hip and knee joints), and this is not measured directly, but is inferred from measures of joint flexibility. The third concept is that of sensation (the perception of tightness, discomfort or pain), and this is a subjective measure. The SLR and AKE tests measure joint flexibility, and do not differentiate between (1) the extensibility of muscular and neural tissues; and (2) the origin of the sensations produced by the tests. Therefore, further differentiation is required in order to support the inferences drawn from the outcome of these tests in terms of the extensibility and sensitivity of muscular and neural structures. The Slump test4 can potentially aid differentiation between both muscular and neural extensibility and sensitivity, and therefore forms an important component of clinical examination. 1.1. Hamstring extensibility A lack of hamstring extensibility is thought to induce changes in lumbopelvic rhythm. Kendall et al.3 and Sahrmann5 have reported the association between excessive lumbar spinal flexion and reduced hamstring extensibility when forward bending, sitting, or touching the toes. In support of this observation, McCarthy and Betz6 demonstrated a correlation between tight hamstrings and reduced lumbar lordosis in children with cerebral palsy; especially when sitting. Reduced hamstring extensibility is also thought to predispose athletes to injury. A prospective study of 146 soccer players demonstrated that 21% of players developed hamstring
injuries, and that these players had significantly reduced hamstring flexibility prior to sustaining the injury compared with non-injured players.7 These findings, however, need to be further corroborated in other prospective studies which take into account the extensibility and sensitivity of neural structures. This need is exemplified by Turl and George8 who have shown that 57% of a cohort of Rugby players with a history of grade 1 hamstring strain had positive Slump test responses, defined as typical hamstring pain reproduced during the Slump test and relieved by cervical extension at the completion of the test. Anatomical causes of reduced muscle extensibility have been categorised as ‘muscle shortness’ and ‘muscle stiffness’.5 A short muscle is a musculotendinous unit that has a reduced capacity to be lengthened due to a reduction in the number of sarcomeres in series,9,10 or a reduction in the length or elasticity of the connective tissues (such as occurs with scar tissue formation following injury).5 The stiffness of a muscle does not pertain to the length of the muscle, but is a biomechanical term used to refer to the amount of force necessary to produce elongation of the muscle.11 Muscle extensibility may therefore be affected by changes in length or stiffness, or a combination of these. Physiological causes of reduced muscle extensibility relate to the contractility of the muscle cells. Activity in alpha motor neurons that results in muscle contraction can increase the force necessary to elongate the homologous muscle, and this muscle will have increased stiffness, and decreased flexibility.11 For example, the spasticity of muscles in those with upper motor neuron lesions leads to increased muscle contractility and, therefore, increased stiffness.11 However, physiologically reduced muscle extensibility can also occur in the absence of electromyographic activity, and the mechanisms for this are not well understood.12 Normative data for tests of hamstring extensibility have yielded varying results, and the external validity of prior studies has been corrupted by selection bias and small sample sizes. However, in a recent study of 214 asymptomatic male and female adults (age range 20e 79),13 normative data for the passive knee extension (PKE) test were reported, with the mean knee flexion angle being 38.6 (SD 8.1) for males, and 28 (SD 10.6) for females, with no significant differences between any age group. These findings are consistent with data collected on 1389 Danish school children (age range 13e16), in whom the majority (88%) were found to have a knee flexion angle of less than 40 during a supine active knee extension task with the hip held in 90 of flexion.14 1.2. Neural mechanosensitivity Peripheral nerves are invested and surrounded by connective tissues (e.g. epineurium) that are innervated
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by nervi nervorum that code for mechanical deformation and nociception,15 affording them the function of ‘neural mechanosensitivity’. The mechanosensitivity of peripheral nerves may be normal, decreased or increased. During normal movement, nerves undergo mechanical deformation and move in relation to their surrounding tissues. Compression and tension are the two major forces applied to nerves during movement,16e18 however, sliding movements and friction also occur.19 Whereas some neural compression occurs during most movements, tension is the dominant force applied to the sciatic nerve (including nerve roots, nerve root sleeves and peripheral branches) during straight leg raising and other hamstring type stretches, such as the AKE test.2 Movements that are normally non-painful, but produce mechanical deformation of neural tissues, may elicit a pain response in the presence of peripheral sensitisation, with or without the addition of central sensitisation.20 It is possible that this may reduce the mobility of the neuromeningeal structures and result in a reduced range of movement and the perception of discomfort, or ‘tightness’. Previous studies have shown that blood supply is reduced within a nerve when it is stretched.21,22 The development of tension within a nerve as a result of stretching that nerve also alters nerve conduction,23 and reduces sympathetic outflow to the nerve.24 It is possible that nerve stretching may result in reflex muscle contractility in order to protect the nerve from further stretch; however, this has not yet been demonstrated to occur.25 Physical assessment procedures for the structural differentiation of neural mechanosensitivity and hamstring extensibility have been described by Maitland,4 Shacklock19 and Butler and Gifford.26 The Slump test is advocated for use in clinical examination, and has been shown to be having excellent inter-tester reliability when using reproduction of symptoms during the Slump test followed by a decrease of symptoms with cervical extension as the criterion for a positive test.27 The Slump test is considered to help differentiate between posterior thigh pain due to neural mechanosensitivity and that due to hamstring injury.28e30 The test applies tension to the neural and connective tissue components of the nervous system from the brainstem to the terminations of the sciatic nerve in the foot.31 Neural structures involved in a Slump test form part of a ‘continuous tissue tract’, beginning at the brainstem and consisting of the medulla oblongata, spinal cord, cauda equina, lumbosacral nerve roots and sciatic and tibial nerves.32 The sensation of discomfort or pain during the Slump test in normal, asymptomatic individuals has been inadequately investigated. Butler referred to unpublished data which indicated that approximately 50% of normal asymptomatic subjects experienced pain at the T8eT9 vertebral level, and that the majority also experienced symptoms in the posterior thigh.33 These
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symptoms are reported to be commonly relieved by cervical extension in the final phase of performing the Slump test, and has been corroborated by Johnson and Chiarello.34 Lew and Puentedura35 also found that 81 out of 100 asymptomatic subjects had a positive Slump test, defined as having (1) further knee extension range of motion after cervical extension, or (2) pain felt outside an area that was considered normal. 1.3. Location of symptoms It is reasonable to consider that the symptoms of discomfort, tightness or pain during stretch of the hamstring muscles will be reported by subjects as being felt in the musculotendinous junctions or belly of the hamstring muscles in the mid-posterior thigh, or in the tendons of those muscles as they pass medially and laterally to the knee. Likewise symptoms of discomfort, tightness or pain during stretch of the sciatic nerve/ posterior tibial nerve can be expected to occur along the length of the nerve in the centre of the thigh and in the posterior aspect of the knee and leg.36 Pain that is located predominantly in the posterior aspect of the knee, and not in the substance of the hamstring muscles or their tendons, may indicate a neural source of sensation. However, while these considerations appear logical on anatomical grounds, they remain to be confirmed in clinical studies. There is currently minimal knowledge regarding the involvement that neural tissues have in contributing towards the outcome of hamstring extensibility tests in asymptomatic subjects with perceived hamstring tightness. Active knee extension in the supine position applies tension to both neural and muscular tissues.37,38 To investigate the association between neural mechanosensitivity and perceived hamstring tightness, we utilised a cross sectional study design in order to determine the prevalence of neural mechanosensitivity amongst those with perceived hamstring tightness. We used this group because we wanted to specifically study those people who considered that they had ‘tight hamstrings’ in order to: (1) determine their average AKE values for comparison to normal data; and (2) collect data on the prevalence and location of symptoms produced by the Slump test in this sample. This question is important because the treatment of neural mechanosensitivity is conceptually different from that of reduced muscle extensibility.3,5,36 If neural structures can be identified as being associated with the perception of ‘tight hamstrings’, then a treatment plan that takes this into account should be considered.
2. Materials and methods A cross sectional study was conducted to determine the AKE test values, and the prevalence and location of
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symptoms during a Slump test, in asymptomatic subjects who perceived they had tight hamstrings. Prior to participation, all subjects read an information sheet, signed an informed consent form, and were given the opportunity to have any question answered. The study was approved by the Human Research Ethics Committee of the University of Western Sydney. 2.1. Subjects Forty-three asymptomatic university students who identified themselves as having ‘‘hamstring tightness’’ volunteered for this study. Subjects were limited to those aged between 18 and 35 years, without a history of trauma involving serious injury to the lumbar spine and lower limb; no diagnosis of spinal congenital anomalies, and no history of diagnosed disc herniation, spondyloarthropathy or other spinal pathology. The inclusion criterion for the study was a knee flexion angle of greater than 15 . This angle was used in a similar study39 and was chosen to enable comparisons to be made. One subject had a knee flexion angle less than 15 and was excluded. Forty-two subjects were included in the study and a Slump test was subsequently performed on all subjects. 2.2. Instrumentation A standard, double arm (arm length Z 31.75 cm), clear plastic goniometer with full circle protractor (1 increments) was used to identify knee motion measurements during the active knee extension (AKE) test for initial eligibility for entrance into the study. Digital photography was also used in order to more accurately measure knee range of movement. The images were displayed on a computer screen and a transparent template consisting of a plastic sheet with a horizontal and vertical line marked and a line marked at 75 (15 off 90 ) was placed over the image. The template was used to determine if the subject was eligible to participate in the study (i.e. they had to have a knee flexion angle greater than 15 ). The exact measurements were later taken by placing a grid overlying the computer screen with measurements taken using a goniometer. A wooden box measuring 44.5 cm wide, 42 cm high and 20 cm deep was secured to the table with two Velcro straps; a third strap was used to secure the participant’s right thigh and box, and a fourth strap around the left thigh to minimize left hip flexion during the procedure (Fig. 1). 2.3. Experimental design 2.3.1. Active knee extension test The intra-tester reliability of the AKE test has been previously demonstrated to be excellent.38 The concept
Fig. 1. The active knee extension test: box and patient’s position. Note that the angle q as demonstrated in this example is greater than 15 from the vertical and the subject therefore met the inclusion criterion for the study. Note the various Velcro straps used to secure the box to the table, and to maintain the subject’s alternate leg at 0 hip flexion.
validity of the AKE test is based on anatomical knowledge about the insertions of the hamstring muscle group. Convergent validity of the AKE test has also been demonstrated in a study which compared the AKE with an active SLR and found there to be a high correlation between the results of both tests.37 Subjects were positioned in supine without a pillow underneath their heads, with the left lower extremity in 0 of hip flexion, maintained by a Velcro strap secured to the table. The participant’s right thigh was flexed to 90 , with the right ischial tuberosity placed against the box. The right mid thigh was then strapped to the box (Fig. 1) to maintain this position. Subjects were then instructed to slowly extend their right knee until they felt the first stretch sensation, with the foot relaxed in plantar flexion. The use of the first stretch sensation as the point of completion of the AKE test was used by Turl and George8 and Cameron and Bohannon.37 The subjects were instructed to maintain the posterior aspect of their right thigh in contact with the box. This position was held momentarily in order to measure the AKE angle with a goniometer and to take a digital photograph. This process of knee extension was performed three times and the mean measurement was then used as the basis for inclusion in the study. The measurement of this angle and similar procedures were used as the screening exam for active knee extension in similar studies.8,37 In order to determine the reproducibility of the goniometric measurement of active knee extension, the
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Fig. 2. Panels AeF illustrate the sequential stages of the Slump test used in this study. Instructions to subjects were as follows: panel A: sit up straight with your ankles uncrossed and your knee creases against the edge of the bench; panel B: Slump or ‘‘sag in the middle’’ whilst still looking forward; panel C: flex your neck by drawing your chin to your chest; panel D: extend or straighten your right knee; panel E: dorsiflex your right ankle by pulling your toes towards you; and panel F: extend your neck by looking towards the ceiling.
intra-class correlation coefficient was calculated, and the results suggest excellent intra-tester reliability (ICC 0.99, 95% CI 0.99e1.00). 2.3.2. Slump test Subjects who had been included in the study after completing the AKE test were then instructed to perform a staged Slump test. For the purpose of this present study, a positive response to the Slump test (conceptually indicating neural mechanosensitivity) was said to occur when symptoms produced during the Slump test were partially or completely relieved by cervical extension in the final phase of the test.4,28 The Slump test was performed in a seated position using the sequence outlined by Butler.36 Subjects were asked to perform six stages as read to subjects using standardised phrasing to ensure consistency. The six sequential stages of the Slump test are illustrated in Fig. 2. (1) Sit up straight with your ankles uncrossed and your knee creases against the edge of the bench; (2) Slump or ‘‘sag in the middle’’ whilst still looking forward; (3) flex your neck by drawing your chin to your chest; (4) extend or straighten your right knee; and (5) dorsiflex your right ankle by pulling your toes towards you. After stage 5, each subject was shown a body diagram with regions (i.e. cervical, thoracic, lumbar, buttock, posterior thigh, knee or calf) clearly outlined. Subjects were asked to maintain their position and say in which regions their symptoms were located and these were then recorded on the body diagram. The procedure then continued with stage (6). Extend your neck by looking towards the ceiling. Subjects were then asked whether this final movement reduced their symptoms and to what degree: completely or partially. All subject responses were recorded on a data sheet. A positive test, implicating neural mechanosensitivity as a component of the symptoms, was defined by symptoms that were completely or partially relieved with neck extension during the Slump test. A negative test was defined by symptoms which were unchanged with neck extension, implying that the source of symptoms
originated within the hamstring muscles (inclusive of connective tissue).28 Overpressure is often used in performing the Slump test to increase thoracic flexion, neck flexion, knee extension and ankle dorsiflexion.36 However, overpressure was not used in this study due to difficulties with standardising the pressure applied to different subjects.
3. Results The mean (SD) knee flexion angle of the AKE test was 35.2 (SD 14.2) (range 15.6e70 ). The Slump test was performed on all 42 subjects with reduced AKE. Symptomatic responses to the Slump test by anatomical location are summarised in Table 1. The general responses of subjects to cervical extension (or release of cervical flexion) is summarised in Table 2. The effect of cervical extension, as summarised by anatomical location, is presented in Table 3. When cervical flexion was released at the completion of the Slump test, 83.3% (n Z 35) of the subjects had either partial relief (n Z 19) or complete relief (n Z 16) of their symptoms. There were a total of 57 complaints of pain felt in the posterior aspect of the lower extremity during the Slump test, and of those 57 complaints, 84.2% were relieved, completely or partially, with cervical extension. Of those in the sample with posterior knee pain, which was 66.7% of the total cohort, 89.3% Table 1 Location of symptoms induced by the Slump test (n Z 42) Region
Frequency of symptoms (%)
Cervical Thoracic Lumbar Buttock Posterior thigh Posterior knee Posterior leg
3 3 5 6 15 28 14
(7.1) (7.1) (11.9) (14.3) (35.7) (66.7) (33.3)
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Table 2 Symptomatic response to the Slump test for subjects with perceived hamstring tightness (n Z 42) Symptomatic influence of cervical extension during last phase of Slump test
Subjects (number)
Subjects (%)
Nil change Partial relief Complete relief No symptoms Increased symptoms
5 19 16 1 1
12.0 45.2 38.1 2.2 2.2
had relief with cervical extension. The high prevalence of lower extremity symptoms is in contrast to the relatively low prevalence of symptoms in the cervical (7.1%) and thoracic (7.1%) regions. Only 12% of subjects did not experience any change in symptoms with cervical extension at the completion of the Slump test.
4. Discussion The two aims of this study were to: (1) measure the knee flexion angle of the AKE test in asymptomatic subjects with perceived hamstring tightness, and (2) record the prevalence and location of symptomatic responses to the Slump test. The main findings of this study are that subjects with perceived hamstring tightness were unlikely to have a reduction in hamstring extensibility compared to a normal, healthy population. Therefore, subjects’ perception of tightness in the hamstring area is not explained by reduced hamstring extensibility. The other main finding is that the majority of subjects had a positive Slump test, experiencing partial or complete relief of Slump test induced symptoms with cervical extension at the completion of the test. The data collected on the prevalence of lower extremity symptoms during the Slump test appear similar to other published reports on asymptomatic subjects, however, comparisons need to be carefully considered, because different Table 3 Symptomatic response to the Slump test by anatomic region for subjects with perceived hamstring tightness (n Z 42) Region
Completely Partially relieved relieved (%) (%)
Cervical 1 (33.3) Thoracic 2 (66.7) Lumbar 3 (60.0) Buttock 2 (33.3) Posterior thigh 8 (53.3) Posterior knee 11 (39.3) Posterior leg 5 (35.7) Lower extremity 24 (42.1) (thigh, knee, and leg)
1 1 2 3 4 14 6 24
(33.3) (33.3) (40.0) (50.0) (26.7) (50.0) (42.9) (42.1)
No change (%) 0 0 0 1 3 3 2 8
Increased Total (%)
(0) 1 (33.3) (0) 0 (0) 0 (16.7) 0 (20.0) 0 (10.7) 0 (14.3) 1 (7.1) (14.0) 1 (1.8)
3 3 5 6 15 28 14 57
investigators have used different procedures for performing the Slump test and have used different operational definitions for defining a positive Slump test. Lew and Puentedura35 found that 81% of normal, healthy subjects (n Z 100) had a positive Slump test, defined as having: (1) further knee extension range of motion after cervical extension, or (2) pain felt outside an area that was considered normal. These criteria for defining a positive Slump test are different from that used in the present study. Lew and Puentedura35 used overpressure on the cervical and thoracic spines during the performance of the Slump test, making direct comparisons with the present study difficult, because overpressure is likely to elevate the number of positive responses. In a study of patients with low back pain, with or without referred lower extremity pain, Phillip et al.27 demonstrated a positive Slump test prevalence of 59%. However, like Lew and Puentedura,35 Phillip et al. used overpressure on the cervical and thoracic spines as well as adding passive dorsiflexion to the test. The criteria used by Phillip et al. for a positive Slump test included the reproduction of the subjects’ familiar symptoms that were then relieved by cervical extension or an increase in knee extension range of movement after cervical extension, which makes comparison to the present study difficult. The operational definition for a positive Slump test used by Phillip et al. may also account for the lower incidence of positive responses (59%), relative to the present study (83.3%), which deemed any symptoms (leg, thigh, or back) as a positive response. The present cohort also had a low prevalence of thoracic spine symptoms (7.1%) compared to other reports in asymptomatic subjects of approximately 50%.33 Symptoms induced by the Slump test were unchanged by cervical extension in only 12% of the subjects, and it is likely that their symptoms originated in non-neural structures, such as the hamstring muscles.28 Our interpretation of the results of this study rely on a comparison between AKE test results and normative data based on the passive knee extension (PKE) test.13 Using the PKE test, Youdas et al.13 report a mean knee flexion angle of 38.6 (SD 8.1) for males, and 28 (SD 10.6) for females, with no significant differences between age groups. Data regarding the convergent validity of the AKE and PKE were reported by Gajdosik et al.40 who found that the AKE scores showed significantly greater knee flexion angles when compared with PKE scores (meaning that greater knee extension was observed in the PKE test compared to the AKE test). The average knee flexion angle obtained by the AKE test in our sample was 35.2 , which is within the range of normative PKE data reported by Youdas et al.13 The findings of Gajdosik et al.40 predict that if we had used the PKE test, we would have obtained smaller knee flexion angles (greater knee extension range), and thus gives us confidence that the knee flexion angles
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measured in this sample with the AKE are likely to be representative of normal, and not reduced, hamstring extensibility.13 Differences in the way the AKE test was administered may also have had an impact on the values obtained. For instance, some authors describe the AKE test as having the subject extend their knee to the point of discomfort,8,39,41 while others have the subject extend the knee to the first sensation of stretch.8,37 Obviously, the more effort one uses to extend their knee during an AKE test, the smaller the knee flexion angle will become until complete resistance or myoclonus are initiated. Gajdosik et al.40 conclude that the AKE test may represent a test of ‘initial length’ and that the PKE test may represent a test of ‘maximal length’. Future studies should provide a precise description of the criteria used to determine the endpoint of the test in order to allow meaningful comparisons between studies. Johnson and Chiarello34 have demonstrated that normal healthy males have reduced AKE in the Slump test position, which is relieved by cervical extension. However, these investigators did not measure pain response or pain location during the Slump test, but knee extension range of motion. Our study differs in this regard as we were primarily concerned with measuring sensation during the Slump test, and not knee extension range of movement. In a study by Turl and George,8 subjects with hamstring injuries had no difference in AKE values compared to non-injured matched controls, but those with a history of hamstring strain did have a much higher positive Slump test prevalence, indicating the relevance of neural mechanosensitivity in these subjects.28 Lew and Briggs28 have demonstrated that cervical movements during the Slump test do not change hamstring EMG activity nor tension in the hamstring muscles as measured by a strain gauge attached to the biceps tendon. They conclude that the change in Slump test induced pain during cervical flexion is not due to changes in the hamstring muscle tension or EMG activity. This brings up the question of whether neural mechanosensitivity is of more relevance to the perception of tight hamstrings than is actual hamstring muscle length or extensibility. Ballantyne et al.42 conducted a randomised controlled trial to investigate the immediate effects of a single application of muscle energy technique on the PKE test as a measure of hamstring extensibility. These investigators measured the range of passive knee extension (PKE) test and also the torque force required to produce the onset of discomfort with PKE. Following the application of the intervention greater range of knee extension was achieved before the onset of discomfort; however, the torque force required to produce the onset of discomfort was greater than that required prior to the intervention. When these investigators used the same
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pre-intervention torque force in the post-intervention PKE test, no significant increase in knee extension range of movement was apparent. Therefore, the increased range of knee extension achievable before the onset of discomfort was attributable to an increase in the tolerance of the stretch sensation, rather than any change in the extensibility or length of the hamstring muscle. The authors did not report the location of discomfort, nor investigate whether the discomfort was modifiable with spinal movements (such as cervical flexion or extension). Therefore the origin of discomfort could not be determined from this study. Nevertheless, the findings of Ballantyne et al.42 support the concept that there is a modifiable sensory component to the flexibility of the hip and knee joints in the AKE test that is independent of changes in tissue extensibility. The results of this present study indicate that the perception of hamstring tightness in this cohort is unlikely to be associated with decreases in hamstring length or extensibility. Also, subjects with a perception of hamstring tightness may have a higher prevalence of lower extremity symptoms during the Slump test; however, this possibility needs to be further established against valid normative data on Slump test responses. Neural mechanosensitivity is a possible explanation for the sensation of tightness in the posterior thigh in the absence of reduced hamstring extensibility. However, the higher prevalence of posterior knee symptoms (66.7%) compared to posterior thigh symptoms (35.7%) in the present study suggests that neural mechanosensitivity is a component in the perception of tightness felt by this cohort. Inherent in the design and interpretation of the results of this study are a number of assumptions. Firstly, we assumed that the subjects’ active knee extension movement was similar enough to their knee extension movement during the Slump test in order to make comparisons, despite the former being performed in supine, and the latter in sitting. On the basis of this assumption, subjects’ symptomatic responses to the AKE test were not recorded. Further evidence of a neural component in subjects’ perception of tightness would have been provided if those symptoms provoked during AKE were verified as being those provoked by knee extension during the Slump test, and relieved by cervical extension at the completion of the test. Further research in this area should include this in the study protocol. Also, in order to standardise the methodology, we have treated the group as homogenous by applying the Slump test in the standard sequence of movements. However, it has been demonstrated that the sequence, or order, in which various components of the Slump test are introduced modifies the individual responses to the test.43 Had we modified the sequence of the Slump test (for example by beginning with knee extension and dorsiflexion, and then introducing spinal flexion), we might have obtained different results.
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The results of this study suggest the need to address the mechanical properties of the nervous system when evaluating the perception of reduced hamstring extensibility, as neural tissue appears to be a contributing factor in asymptomatic patients. Regardless of the mechanisms underlying the perception of hamstring tightness, it is recommended that in all patients in whom an assessment of hamstring extensibility is warranted, the Slump test should be evaluated in order to aid differentiation between neural and muscular structures.
5. Conclusion From the results obtained in this study we conclude that subjects, who perceived they had tight hamstring muscles, were unlikely to have reduced hamstring length or extensibility, as suggested by the AKE test. We acknowledge that this conclusion would be further supported if normative data on the AKE were available for comparison. However, in the absence of this data we are only able to make comparisons with normative data on the PKE test. It is postulated that neural mechanosensitivity may play a significant role in explaining ‘perceived hamstring tightness’, supported by the fact that 84.2% of subjects’ posterior lower extremity symptoms induced by the Slump test were relieved by cervical extension. Further, 66.7% of subjects experienced posterior knee pain over the location of the sciatic nerve tract, of which 89% had relief of symptoms with cervical extension. This study adds to the existing knowledge regarding physical testing for neural mechanosensitivity, and the prevalence of positive responses from a Slump test among asymptomatic subjects with perceived hamstring tightness. On the basis of the results obtained in this study, we advocate the routine use of the Slump test in the assessment of patients with perceived hamstring tightness in order to aid differentiation between muscular and neural structures.
References 1. Ward RC, editor. Foundations for osteopathic medicine. 2nd ed. Baltimore: Williams & Wilkins; 2002. 2. Rebain R, Baxter GD, McDonough S. A systematic review of the passive straight leg raising test as a diagnostic aid for low back pain (1989 to 2000). Spine 2002;27:E388–95. 3. Kendall FP, McCreary EK, Provance PG, Rodgers MM, Romani WA. Muscles: testing and function with posture and pain. 5th ed. Baltimore: Lippincott Williams & Wilkins; 2005. 4. Maitland G. The slump test: examination and treatment. Aust J Physiother 1985;31:215–9. 5. Sahrmann SA. Diagnosis and treatment of movement impairment syndromes. St. Louis: Mosby; 2002. 6. McCarthy JJ, Betz RR. The relationship between tight hamstrings and lumbar hypolordosis in children with cerebral palsy. Spine 2000;25:211–3.
7. Witvrouw E, Danneels L, Asselman P, D’Have T, Cambier D. Muscle flexibility as a risk factor for developing muscle injuries in male professional soccer players. A prospective study. Am J Sports Med 2003;31:41–6. 8. Turl SE, George KP. Adverse neural tension: a factor in repetitive hamstring strain? J Orthop Sports Phys Ther 1998;27:16–21. 9. Tabary JC, Tardieu C, Tardieu G, Tabary C. Experimental rapid sarcomere loss with concomitant hypoextensibility. Muscle Nerve 1981;4:198–203. 10. Tabary JC, Tabary C, Tardieu C, Tardieu G, Goldspink G. Physiological and structural changes in the cat’s soleus muscle due to immobilization at different lengths by plaster casts. J Physiol 1972;224:231–44. 11. Mense S, Simons DG. Muscle pain: understanding its nature, diagnosis, and treatment. Philadelphia: Lippincott Williams & Wilkins; 2001. 12. McHugh MP, Kremenic IJ, Fox MB, Gleim GW. The role of mechanical and neural restraints to joint range of motion during passive stretch. Med Sci Sports Exerc 1998;30:928–32. 13. Youdas JW, Krause DA, Hollman JH, Harmsen WS, Laskowski E. The influence of gender and age on hamstring muscle length in healthy adults. J Orthop Sports Phys Ther 2005;35:246–52. 14. Harreby M, Nygaard B, Jessen T, Larsen E, Storr-Paulsen A, Lindahl A, et al. Risk factors for low back pain in a cohort of 1389 Danish school children: an epidemiologic study. Eur Spine J 1999; 8:444–50. 15. Butler D. Mobilisation of the nervous system. Melbourne: Churchill Livingstone; 1991. 16. Yuan Q, Dougherty L, Margulies SS. In vivo human cervical spinal cord deformation and displacement in flexion. Spine 1998;23:1677–83. 17. Werner R, Armstrong TJ, Bir C, Aylard MK. Intracarpal canal pressures: the role of finger, hand, wrist and forearm position. Clin Biomech (Bristol, Avon) 1997;12:44–51. 18. Gelberman RH, Yamaguchi K, Hollstien SB, Winn SS, Heidenreich Jr FP, Bindra RR, et al. Changes in interstitial pressure and cross-sectional area of the cubital tunnel and of the ulnar nerve with flexion of the elbow. An experimental study in human cadavera. J Bone Joint Surg Am 1998;80:492–501. 19. Shacklock M. Clinical neurodynamics. Edinburgh: Elsevier; 2005. 20. Bridges D, Thompson SW, Rice AS. Mechanisms of neuropathic pain. Br J Anaesth 2001;87:12–26. 21. Lundborg G, Rydevik B. Effects of stretching the tibial nerve of the rabbit. A preliminary study of the intraneural circulation and the barrier function of the perineurium. J Bone Joint Surg Br 1973; 55:390–401. 22. Ogata K, Naito M. Blood flow of peripheral nerve effects of dissection, stretching and compression. J Hand Surg [Br] 1986; 11:10–4. 23. Wall EJ, Massie JB, Kwan MK, Rydevik BL, Myers RR, Garfin SR. Experimental stretch neuropathy. Changes in nerve conduction under tension. J Bone Joint Surg Br 1992;74: 126–9. 24. Kornberg C, McCarthy T. The effect of neural stretching technique on sympathetic outflow to the lower limbs. J Orthop Sports Phys Ther 1992;16:269–74. 25. Kerr JM, Vujnovich AL, Bradnam L. Changes in alphamotoneuron excitability with positions that tension neural tissue. Electromyogr Clin Neurophysiol 2002;42:459–71. 26. Butler D, Gifford L. The concept of adverse mechanical tension in the nervous system Part 1: testing for ‘Dural Tension’. Physiotherapy 1989;75:622–8. 27. Phillip K, Lew P, Matyas T. The inter-therapist reliability of the slump test. Aust J Physiother 1989;35:89–94. 28. Lew PC, Briggs CA. Relationship between the cervical component of the slump test and change in hamstring muscle tension. Man Ther 1997;2:98–105.
K.E. Kuilart et al. / International Journal of Osteopathic Medicine 8 (2005) 89e97 29. Kornberg C, Lew P. The effect of stretching neural structures on grade 1 hamstring injuries. J Orthop Sports Phys Ther 1989;13: 481–7. 30. Muckle DS. Associated factors in recurrent groin and hamstring injuries. Br J Sports Med 1982;16:37–9. 31. Massey A. Movement of pain sensitive structures in the neural canal. In: Grieve G editor. Modern manual therapy of the vertebral column. Edinburgh: Churchill Livingstone; 1985. 32. Brieg A. Adverse mechanical tension in the central nervous system. Stockholm: Alonquist and Wiksell; 1978. 33. Butler D. The effect of age and gender on the slump test. South Australian Institute of Technology; 1985. 34. Johnson EK, Chiarello CM. The slump test: the effects of head and lower extremity position on knee extension. J Orthop Sports Phys Ther 1997;26:310–7. 35. Lew PC, Puentedura EJ. The straight-leg-raise test and spinal posture: is the straight-leg-raise a tension test of a hamstring length measure in ‘‘normals’’? Manipulative Therapists Association of Australia. Fourth biennial conference. Brisbane; 1985. 36. Butler D. The sensitive nervous system. Adelaide: Noigroup Publications; 2000.
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37. Cameron DM, Bohannon RW. Relationship between active knee extension and active straight leg raise test measurements. J Orthop Sports Phys Ther 1993;17:257–60. 38. Gajdosik R, Lusin G. Hamstring muscle tightness. Reliability of an active-knee-extension test. Phys Ther 1983;63:1085–90. 39. Webright WG, Randolph BJ, Perrin DH. Comparison of nonballistic active knee extension in neural slump position and static stretch techniques on hamstring flexibility. J Orthop Sports Phys Ther 1997;26:7–13. 40. Gajdosik RL, Rieck MA, Sullivan DK, Wightman SE. Comparison of four clinical tests for assessing hamstring muscle length. J Orthop Sports Phys Ther 1993;18:614–8. 41. Gabbe BJ, Bennell KL, Wajswelner H, Finch CF. Reliability of common lower extremity musculoskeletal screening tests. Phys Ther Sport 2004;5:90–7. 42. Ballantyne F, Fryer G, McLaughlin P. The effect of muscle energy technique on hamstring flexibility: the mechanism of altered flexibility. J Osteopath Med 2003;6:59–63. 43. Lew P, Morrow C, Lee A. The effect of neck and leg flexion and their sequence on the lumbar spinal cord: implications for low back pain and sciatica. Spine 1994;19:2421–4.
Research report
The active knee extension test and Slump test in subjects with perceived hamstring tightness Kate Elissa Kuilart *, Melanie Woollam, Elizabeth Barling, Nicholas Lucas School of Exercise and Health Sciences, University of Western Sydney, Penrith South, NSW 1797, Australia Received 30 May 2005; received in revised form 15 June 2005; accepted 12 July 2005
Abstract Background: Reduced hamstring extensibility is commonly assumed to be due to stiffness or decreased length of the hamstring muscle group. The first aim of this study was to collect data on the results of the active knee extension test in subjects with perceived reduction in hamstring extensibility. The second aim was to establish the prevalence and location of symptoms induced by the Slump test in those subjects with perceived hamstring tightness. Methods: Forty-two asymptomatic subjects (M Z 21, F Z 21, mean age 23.6, range 18e35) with perceived right hamstring tightness performed the active knee extension test followed by the Slump test. A goniometer and digital photography were used to measure the knee flexion angle of the active knee extension test. A body chart was used to record the location of pain or discomfort produced or relieved during the active performance of the Slump test. Results: Subjects had an average knee flexion angle of 35.2 (SD 14.2; range 15.6e70 ). During the Slump test 66.7% (n Z 28) of the subjects reported symptoms in the posterior knee, 35.7% (n Z 15) reported symptoms in the posterior thigh and 33.3% (n Z 13) reported symptoms in the posterior leg. Combined prevalence of cervical and thoracic symptoms was 14.2%, with only 7.1% experiencing symptoms in the thoracic region. At the last stage of the Slump test 12.0% (n Z 5) of subjects had no change in symptoms, whilst 83.3% (n Z 35) of subjects had either partial relief (n Z 19) or complete relief (n Z 16) of symptoms. Discussion and conclusion: Subjects with perceived hamstring tightness did not appear to have reduced hamstring extensibility when compared to the available normative data. Only 7.1% of subjects reported thoracic symptoms during the Slump test, compared to other reports of thoracic symptoms in approximately 50% of asymptomatic subjects. The high prevalence of posterior lower extremity symptoms induced by the Slump test amongst asymptomatic subjects, which are relieved by cervical extension, suggests that neural structures may contribute to perceived hamstring tightness and the sensation of discomfort produced during hamstring stretches. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Musculoskeletal; Hamstrings; Flexibility; Osteopathic medicine; Slump test; Neurodynamic test
1. Introduction Evaluation of the extensibility of the hamstring muscles is a standard assessment in osteopathic clinical examination.1 Hamstring muscles that demonstrate
* Corresponding author. 50 Lucinda Avenue, Springwood, NSW 2777, Australia. Tel.: C61 2 47 518601; fax: C61 2 47 511570. E-mail address: [email protected] (K.E. Kuilart). 1746-0689/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijosm.2005.07.004
reduced extensibility are often colloquially referred to as being ‘tight’; however, the use of this word is nonspecific and is of limited use in the clinical and research settings. In this article, the use of the term ‘tight’ refers to the subjective perception of reduced extensibility of the hamstring muscle group. Individuals may report the perception of tightness in the posterior thigh and knee, and infer that this sensation arises from the hamstring muscles, because they have knowledge of these muscles and the perception of
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tightness may be increased or reproduced by stretches labelled as ‘hamstring stretches’. Tests for hamstring muscle length or extensibility combine hip flexion and knee extension movements which stretch the structures posterior to the axes of rotation of these joints, including both the hamstring muscles and neural structures (e.g. sciatic nerve, posterior tibial nerve, and common peroneal nerve), inclusive of their connective tissues.2 The perception or sensation of tight hamstrings could therefore be due to sensations arising from the hamstring muscles, or arising from mechanically sensitive neural structures, or a combination of both. Also, the actual range of movement obtained during combined hip flexion and knee extension is influenced by flexibility of these joints, and both the extensibility of the hamstring muscles and functionally related neural structures. There are at least three separate concepts being evaluated during tests for hamstring extensibility, such as the straight leg raise (SLR) and active knee extension (AKE) tests.3 The first concept is that of joint flexibility (the range of motion available at the hip and knee in flexion and extension, respectively), as this is what is being objectively measured (e.g. knee flexion angle). The second concept is that of tissue extensibility (or actual change in length of structures posterior to the axes of rotation of the hip and knee joints), and this is not measured directly, but is inferred from measures of joint flexibility. The third concept is that of sensation (the perception of tightness, discomfort or pain), and this is a subjective measure. The SLR and AKE tests measure joint flexibility, and do not differentiate between (1) the extensibility of muscular and neural tissues; and (2) the origin of the sensations produced by the tests. Therefore, further differentiation is required in order to support the inferences drawn from the outcome of these tests in terms of the extensibility and sensitivity of muscular and neural structures. The Slump test4 can potentially aid differentiation between both muscular and neural extensibility and sensitivity, and therefore forms an important component of clinical examination. 1.1. Hamstring extensibility A lack of hamstring extensibility is thought to induce changes in lumbopelvic rhythm. Kendall et al.3 and Sahrmann5 have reported the association between excessive lumbar spinal flexion and reduced hamstring extensibility when forward bending, sitting, or touching the toes. In support of this observation, McCarthy and Betz6 demonstrated a correlation between tight hamstrings and reduced lumbar lordosis in children with cerebral palsy; especially when sitting. Reduced hamstring extensibility is also thought to predispose athletes to injury. A prospective study of 146 soccer players demonstrated that 21% of players developed hamstring
injuries, and that these players had significantly reduced hamstring flexibility prior to sustaining the injury compared with non-injured players.7 These findings, however, need to be further corroborated in other prospective studies which take into account the extensibility and sensitivity of neural structures. This need is exemplified by Turl and George8 who have shown that 57% of a cohort of Rugby players with a history of grade 1 hamstring strain had positive Slump test responses, defined as typical hamstring pain reproduced during the Slump test and relieved by cervical extension at the completion of the test. Anatomical causes of reduced muscle extensibility have been categorised as ‘muscle shortness’ and ‘muscle stiffness’.5 A short muscle is a musculotendinous unit that has a reduced capacity to be lengthened due to a reduction in the number of sarcomeres in series,9,10 or a reduction in the length or elasticity of the connective tissues (such as occurs with scar tissue formation following injury).5 The stiffness of a muscle does not pertain to the length of the muscle, but is a biomechanical term used to refer to the amount of force necessary to produce elongation of the muscle.11 Muscle extensibility may therefore be affected by changes in length or stiffness, or a combination of these. Physiological causes of reduced muscle extensibility relate to the contractility of the muscle cells. Activity in alpha motor neurons that results in muscle contraction can increase the force necessary to elongate the homologous muscle, and this muscle will have increased stiffness, and decreased flexibility.11 For example, the spasticity of muscles in those with upper motor neuron lesions leads to increased muscle contractility and, therefore, increased stiffness.11 However, physiologically reduced muscle extensibility can also occur in the absence of electromyographic activity, and the mechanisms for this are not well understood.12 Normative data for tests of hamstring extensibility have yielded varying results, and the external validity of prior studies has been corrupted by selection bias and small sample sizes. However, in a recent study of 214 asymptomatic male and female adults (age range 20e 79),13 normative data for the passive knee extension (PKE) test were reported, with the mean knee flexion angle being 38.6 (SD 8.1) for males, and 28 (SD 10.6) for females, with no significant differences between any age group. These findings are consistent with data collected on 1389 Danish school children (age range 13e16), in whom the majority (88%) were found to have a knee flexion angle of less than 40 during a supine active knee extension task with the hip held in 90 of flexion.14 1.2. Neural mechanosensitivity Peripheral nerves are invested and surrounded by connective tissues (e.g. epineurium) that are innervated
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by nervi nervorum that code for mechanical deformation and nociception,15 affording them the function of ‘neural mechanosensitivity’. The mechanosensitivity of peripheral nerves may be normal, decreased or increased. During normal movement, nerves undergo mechanical deformation and move in relation to their surrounding tissues. Compression and tension are the two major forces applied to nerves during movement,16e18 however, sliding movements and friction also occur.19 Whereas some neural compression occurs during most movements, tension is the dominant force applied to the sciatic nerve (including nerve roots, nerve root sleeves and peripheral branches) during straight leg raising and other hamstring type stretches, such as the AKE test.2 Movements that are normally non-painful, but produce mechanical deformation of neural tissues, may elicit a pain response in the presence of peripheral sensitisation, with or without the addition of central sensitisation.20 It is possible that this may reduce the mobility of the neuromeningeal structures and result in a reduced range of movement and the perception of discomfort, or ‘tightness’. Previous studies have shown that blood supply is reduced within a nerve when it is stretched.21,22 The development of tension within a nerve as a result of stretching that nerve also alters nerve conduction,23 and reduces sympathetic outflow to the nerve.24 It is possible that nerve stretching may result in reflex muscle contractility in order to protect the nerve from further stretch; however, this has not yet been demonstrated to occur.25 Physical assessment procedures for the structural differentiation of neural mechanosensitivity and hamstring extensibility have been described by Maitland,4 Shacklock19 and Butler and Gifford.26 The Slump test is advocated for use in clinical examination, and has been shown to be having excellent inter-tester reliability when using reproduction of symptoms during the Slump test followed by a decrease of symptoms with cervical extension as the criterion for a positive test.27 The Slump test is considered to help differentiate between posterior thigh pain due to neural mechanosensitivity and that due to hamstring injury.28e30 The test applies tension to the neural and connective tissue components of the nervous system from the brainstem to the terminations of the sciatic nerve in the foot.31 Neural structures involved in a Slump test form part of a ‘continuous tissue tract’, beginning at the brainstem and consisting of the medulla oblongata, spinal cord, cauda equina, lumbosacral nerve roots and sciatic and tibial nerves.32 The sensation of discomfort or pain during the Slump test in normal, asymptomatic individuals has been inadequately investigated. Butler referred to unpublished data which indicated that approximately 50% of normal asymptomatic subjects experienced pain at the T8eT9 vertebral level, and that the majority also experienced symptoms in the posterior thigh.33 These
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symptoms are reported to be commonly relieved by cervical extension in the final phase of performing the Slump test, and has been corroborated by Johnson and Chiarello.34 Lew and Puentedura35 also found that 81 out of 100 asymptomatic subjects had a positive Slump test, defined as having (1) further knee extension range of motion after cervical extension, or (2) pain felt outside an area that was considered normal. 1.3. Location of symptoms It is reasonable to consider that the symptoms of discomfort, tightness or pain during stretch of the hamstring muscles will be reported by subjects as being felt in the musculotendinous junctions or belly of the hamstring muscles in the mid-posterior thigh, or in the tendons of those muscles as they pass medially and laterally to the knee. Likewise symptoms of discomfort, tightness or pain during stretch of the sciatic nerve/ posterior tibial nerve can be expected to occur along the length of the nerve in the centre of the thigh and in the posterior aspect of the knee and leg.36 Pain that is located predominantly in the posterior aspect of the knee, and not in the substance of the hamstring muscles or their tendons, may indicate a neural source of sensation. However, while these considerations appear logical on anatomical grounds, they remain to be confirmed in clinical studies. There is currently minimal knowledge regarding the involvement that neural tissues have in contributing towards the outcome of hamstring extensibility tests in asymptomatic subjects with perceived hamstring tightness. Active knee extension in the supine position applies tension to both neural and muscular tissues.37,38 To investigate the association between neural mechanosensitivity and perceived hamstring tightness, we utilised a cross sectional study design in order to determine the prevalence of neural mechanosensitivity amongst those with perceived hamstring tightness. We used this group because we wanted to specifically study those people who considered that they had ‘tight hamstrings’ in order to: (1) determine their average AKE values for comparison to normal data; and (2) collect data on the prevalence and location of symptoms produced by the Slump test in this sample. This question is important because the treatment of neural mechanosensitivity is conceptually different from that of reduced muscle extensibility.3,5,36 If neural structures can be identified as being associated with the perception of ‘tight hamstrings’, then a treatment plan that takes this into account should be considered.
2. Materials and methods A cross sectional study was conducted to determine the AKE test values, and the prevalence and location of
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symptoms during a Slump test, in asymptomatic subjects who perceived they had tight hamstrings. Prior to participation, all subjects read an information sheet, signed an informed consent form, and were given the opportunity to have any question answered. The study was approved by the Human Research Ethics Committee of the University of Western Sydney. 2.1. Subjects Forty-three asymptomatic university students who identified themselves as having ‘‘hamstring tightness’’ volunteered for this study. Subjects were limited to those aged between 18 and 35 years, without a history of trauma involving serious injury to the lumbar spine and lower limb; no diagnosis of spinal congenital anomalies, and no history of diagnosed disc herniation, spondyloarthropathy or other spinal pathology. The inclusion criterion for the study was a knee flexion angle of greater than 15 . This angle was used in a similar study39 and was chosen to enable comparisons to be made. One subject had a knee flexion angle less than 15 and was excluded. Forty-two subjects were included in the study and a Slump test was subsequently performed on all subjects. 2.2. Instrumentation A standard, double arm (arm length Z 31.75 cm), clear plastic goniometer with full circle protractor (1 increments) was used to identify knee motion measurements during the active knee extension (AKE) test for initial eligibility for entrance into the study. Digital photography was also used in order to more accurately measure knee range of movement. The images were displayed on a computer screen and a transparent template consisting of a plastic sheet with a horizontal and vertical line marked and a line marked at 75 (15 off 90 ) was placed over the image. The template was used to determine if the subject was eligible to participate in the study (i.e. they had to have a knee flexion angle greater than 15 ). The exact measurements were later taken by placing a grid overlying the computer screen with measurements taken using a goniometer. A wooden box measuring 44.5 cm wide, 42 cm high and 20 cm deep was secured to the table with two Velcro straps; a third strap was used to secure the participant’s right thigh and box, and a fourth strap around the left thigh to minimize left hip flexion during the procedure (Fig. 1). 2.3. Experimental design 2.3.1. Active knee extension test The intra-tester reliability of the AKE test has been previously demonstrated to be excellent.38 The concept
Fig. 1. The active knee extension test: box and patient’s position. Note that the angle q as demonstrated in this example is greater than 15 from the vertical and the subject therefore met the inclusion criterion for the study. Note the various Velcro straps used to secure the box to the table, and to maintain the subject’s alternate leg at 0 hip flexion.
validity of the AKE test is based on anatomical knowledge about the insertions of the hamstring muscle group. Convergent validity of the AKE test has also been demonstrated in a study which compared the AKE with an active SLR and found there to be a high correlation between the results of both tests.37 Subjects were positioned in supine without a pillow underneath their heads, with the left lower extremity in 0 of hip flexion, maintained by a Velcro strap secured to the table. The participant’s right thigh was flexed to 90 , with the right ischial tuberosity placed against the box. The right mid thigh was then strapped to the box (Fig. 1) to maintain this position. Subjects were then instructed to slowly extend their right knee until they felt the first stretch sensation, with the foot relaxed in plantar flexion. The use of the first stretch sensation as the point of completion of the AKE test was used by Turl and George8 and Cameron and Bohannon.37 The subjects were instructed to maintain the posterior aspect of their right thigh in contact with the box. This position was held momentarily in order to measure the AKE angle with a goniometer and to take a digital photograph. This process of knee extension was performed three times and the mean measurement was then used as the basis for inclusion in the study. The measurement of this angle and similar procedures were used as the screening exam for active knee extension in similar studies.8,37 In order to determine the reproducibility of the goniometric measurement of active knee extension, the
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Fig. 2. Panels AeF illustrate the sequential stages of the Slump test used in this study. Instructions to subjects were as follows: panel A: sit up straight with your ankles uncrossed and your knee creases against the edge of the bench; panel B: Slump or ‘‘sag in the middle’’ whilst still looking forward; panel C: flex your neck by drawing your chin to your chest; panel D: extend or straighten your right knee; panel E: dorsiflex your right ankle by pulling your toes towards you; and panel F: extend your neck by looking towards the ceiling.
intra-class correlation coefficient was calculated, and the results suggest excellent intra-tester reliability (ICC 0.99, 95% CI 0.99e1.00). 2.3.2. Slump test Subjects who had been included in the study after completing the AKE test were then instructed to perform a staged Slump test. For the purpose of this present study, a positive response to the Slump test (conceptually indicating neural mechanosensitivity) was said to occur when symptoms produced during the Slump test were partially or completely relieved by cervical extension in the final phase of the test.4,28 The Slump test was performed in a seated position using the sequence outlined by Butler.36 Subjects were asked to perform six stages as read to subjects using standardised phrasing to ensure consistency. The six sequential stages of the Slump test are illustrated in Fig. 2. (1) Sit up straight with your ankles uncrossed and your knee creases against the edge of the bench; (2) Slump or ‘‘sag in the middle’’ whilst still looking forward; (3) flex your neck by drawing your chin to your chest; (4) extend or straighten your right knee; and (5) dorsiflex your right ankle by pulling your toes towards you. After stage 5, each subject was shown a body diagram with regions (i.e. cervical, thoracic, lumbar, buttock, posterior thigh, knee or calf) clearly outlined. Subjects were asked to maintain their position and say in which regions their symptoms were located and these were then recorded on the body diagram. The procedure then continued with stage (6). Extend your neck by looking towards the ceiling. Subjects were then asked whether this final movement reduced their symptoms and to what degree: completely or partially. All subject responses were recorded on a data sheet. A positive test, implicating neural mechanosensitivity as a component of the symptoms, was defined by symptoms that were completely or partially relieved with neck extension during the Slump test. A negative test was defined by symptoms which were unchanged with neck extension, implying that the source of symptoms
originated within the hamstring muscles (inclusive of connective tissue).28 Overpressure is often used in performing the Slump test to increase thoracic flexion, neck flexion, knee extension and ankle dorsiflexion.36 However, overpressure was not used in this study due to difficulties with standardising the pressure applied to different subjects.
3. Results The mean (SD) knee flexion angle of the AKE test was 35.2 (SD 14.2) (range 15.6e70 ). The Slump test was performed on all 42 subjects with reduced AKE. Symptomatic responses to the Slump test by anatomical location are summarised in Table 1. The general responses of subjects to cervical extension (or release of cervical flexion) is summarised in Table 2. The effect of cervical extension, as summarised by anatomical location, is presented in Table 3. When cervical flexion was released at the completion of the Slump test, 83.3% (n Z 35) of the subjects had either partial relief (n Z 19) or complete relief (n Z 16) of their symptoms. There were a total of 57 complaints of pain felt in the posterior aspect of the lower extremity during the Slump test, and of those 57 complaints, 84.2% were relieved, completely or partially, with cervical extension. Of those in the sample with posterior knee pain, which was 66.7% of the total cohort, 89.3% Table 1 Location of symptoms induced by the Slump test (n Z 42) Region
Frequency of symptoms (%)
Cervical Thoracic Lumbar Buttock Posterior thigh Posterior knee Posterior leg
3 3 5 6 15 28 14
(7.1) (7.1) (11.9) (14.3) (35.7) (66.7) (33.3)
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Table 2 Symptomatic response to the Slump test for subjects with perceived hamstring tightness (n Z 42) Symptomatic influence of cervical extension during last phase of Slump test
Subjects (number)
Subjects (%)
Nil change Partial relief Complete relief No symptoms Increased symptoms
5 19 16 1 1
12.0 45.2 38.1 2.2 2.2
had relief with cervical extension. The high prevalence of lower extremity symptoms is in contrast to the relatively low prevalence of symptoms in the cervical (7.1%) and thoracic (7.1%) regions. Only 12% of subjects did not experience any change in symptoms with cervical extension at the completion of the Slump test.
4. Discussion The two aims of this study were to: (1) measure the knee flexion angle of the AKE test in asymptomatic subjects with perceived hamstring tightness, and (2) record the prevalence and location of symptomatic responses to the Slump test. The main findings of this study are that subjects with perceived hamstring tightness were unlikely to have a reduction in hamstring extensibility compared to a normal, healthy population. Therefore, subjects’ perception of tightness in the hamstring area is not explained by reduced hamstring extensibility. The other main finding is that the majority of subjects had a positive Slump test, experiencing partial or complete relief of Slump test induced symptoms with cervical extension at the completion of the test. The data collected on the prevalence of lower extremity symptoms during the Slump test appear similar to other published reports on asymptomatic subjects, however, comparisons need to be carefully considered, because different Table 3 Symptomatic response to the Slump test by anatomic region for subjects with perceived hamstring tightness (n Z 42) Region
Completely Partially relieved relieved (%) (%)
Cervical 1 (33.3) Thoracic 2 (66.7) Lumbar 3 (60.0) Buttock 2 (33.3) Posterior thigh 8 (53.3) Posterior knee 11 (39.3) Posterior leg 5 (35.7) Lower extremity 24 (42.1) (thigh, knee, and leg)
1 1 2 3 4 14 6 24
(33.3) (33.3) (40.0) (50.0) (26.7) (50.0) (42.9) (42.1)
No change (%) 0 0 0 1 3 3 2 8
Increased Total (%)
(0) 1 (33.3) (0) 0 (0) 0 (16.7) 0 (20.0) 0 (10.7) 0 (14.3) 1 (7.1) (14.0) 1 (1.8)
3 3 5 6 15 28 14 57
investigators have used different procedures for performing the Slump test and have used different operational definitions for defining a positive Slump test. Lew and Puentedura35 found that 81% of normal, healthy subjects (n Z 100) had a positive Slump test, defined as having: (1) further knee extension range of motion after cervical extension, or (2) pain felt outside an area that was considered normal. These criteria for defining a positive Slump test are different from that used in the present study. Lew and Puentedura35 used overpressure on the cervical and thoracic spines during the performance of the Slump test, making direct comparisons with the present study difficult, because overpressure is likely to elevate the number of positive responses. In a study of patients with low back pain, with or without referred lower extremity pain, Phillip et al.27 demonstrated a positive Slump test prevalence of 59%. However, like Lew and Puentedura,35 Phillip et al. used overpressure on the cervical and thoracic spines as well as adding passive dorsiflexion to the test. The criteria used by Phillip et al. for a positive Slump test included the reproduction of the subjects’ familiar symptoms that were then relieved by cervical extension or an increase in knee extension range of movement after cervical extension, which makes comparison to the present study difficult. The operational definition for a positive Slump test used by Phillip et al. may also account for the lower incidence of positive responses (59%), relative to the present study (83.3%), which deemed any symptoms (leg, thigh, or back) as a positive response. The present cohort also had a low prevalence of thoracic spine symptoms (7.1%) compared to other reports in asymptomatic subjects of approximately 50%.33 Symptoms induced by the Slump test were unchanged by cervical extension in only 12% of the subjects, and it is likely that their symptoms originated in non-neural structures, such as the hamstring muscles.28 Our interpretation of the results of this study rely on a comparison between AKE test results and normative data based on the passive knee extension (PKE) test.13 Using the PKE test, Youdas et al.13 report a mean knee flexion angle of 38.6 (SD 8.1) for males, and 28 (SD 10.6) for females, with no significant differences between age groups. Data regarding the convergent validity of the AKE and PKE were reported by Gajdosik et al.40 who found that the AKE scores showed significantly greater knee flexion angles when compared with PKE scores (meaning that greater knee extension was observed in the PKE test compared to the AKE test). The average knee flexion angle obtained by the AKE test in our sample was 35.2 , which is within the range of normative PKE data reported by Youdas et al.13 The findings of Gajdosik et al.40 predict that if we had used the PKE test, we would have obtained smaller knee flexion angles (greater knee extension range), and thus gives us confidence that the knee flexion angles
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measured in this sample with the AKE are likely to be representative of normal, and not reduced, hamstring extensibility.13 Differences in the way the AKE test was administered may also have had an impact on the values obtained. For instance, some authors describe the AKE test as having the subject extend their knee to the point of discomfort,8,39,41 while others have the subject extend the knee to the first sensation of stretch.8,37 Obviously, the more effort one uses to extend their knee during an AKE test, the smaller the knee flexion angle will become until complete resistance or myoclonus are initiated. Gajdosik et al.40 conclude that the AKE test may represent a test of ‘initial length’ and that the PKE test may represent a test of ‘maximal length’. Future studies should provide a precise description of the criteria used to determine the endpoint of the test in order to allow meaningful comparisons between studies. Johnson and Chiarello34 have demonstrated that normal healthy males have reduced AKE in the Slump test position, which is relieved by cervical extension. However, these investigators did not measure pain response or pain location during the Slump test, but knee extension range of motion. Our study differs in this regard as we were primarily concerned with measuring sensation during the Slump test, and not knee extension range of movement. In a study by Turl and George,8 subjects with hamstring injuries had no difference in AKE values compared to non-injured matched controls, but those with a history of hamstring strain did have a much higher positive Slump test prevalence, indicating the relevance of neural mechanosensitivity in these subjects.28 Lew and Briggs28 have demonstrated that cervical movements during the Slump test do not change hamstring EMG activity nor tension in the hamstring muscles as measured by a strain gauge attached to the biceps tendon. They conclude that the change in Slump test induced pain during cervical flexion is not due to changes in the hamstring muscle tension or EMG activity. This brings up the question of whether neural mechanosensitivity is of more relevance to the perception of tight hamstrings than is actual hamstring muscle length or extensibility. Ballantyne et al.42 conducted a randomised controlled trial to investigate the immediate effects of a single application of muscle energy technique on the PKE test as a measure of hamstring extensibility. These investigators measured the range of passive knee extension (PKE) test and also the torque force required to produce the onset of discomfort with PKE. Following the application of the intervention greater range of knee extension was achieved before the onset of discomfort; however, the torque force required to produce the onset of discomfort was greater than that required prior to the intervention. When these investigators used the same
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pre-intervention torque force in the post-intervention PKE test, no significant increase in knee extension range of movement was apparent. Therefore, the increased range of knee extension achievable before the onset of discomfort was attributable to an increase in the tolerance of the stretch sensation, rather than any change in the extensibility or length of the hamstring muscle. The authors did not report the location of discomfort, nor investigate whether the discomfort was modifiable with spinal movements (such as cervical flexion or extension). Therefore the origin of discomfort could not be determined from this study. Nevertheless, the findings of Ballantyne et al.42 support the concept that there is a modifiable sensory component to the flexibility of the hip and knee joints in the AKE test that is independent of changes in tissue extensibility. The results of this present study indicate that the perception of hamstring tightness in this cohort is unlikely to be associated with decreases in hamstring length or extensibility. Also, subjects with a perception of hamstring tightness may have a higher prevalence of lower extremity symptoms during the Slump test; however, this possibility needs to be further established against valid normative data on Slump test responses. Neural mechanosensitivity is a possible explanation for the sensation of tightness in the posterior thigh in the absence of reduced hamstring extensibility. However, the higher prevalence of posterior knee symptoms (66.7%) compared to posterior thigh symptoms (35.7%) in the present study suggests that neural mechanosensitivity is a component in the perception of tightness felt by this cohort. Inherent in the design and interpretation of the results of this study are a number of assumptions. Firstly, we assumed that the subjects’ active knee extension movement was similar enough to their knee extension movement during the Slump test in order to make comparisons, despite the former being performed in supine, and the latter in sitting. On the basis of this assumption, subjects’ symptomatic responses to the AKE test were not recorded. Further evidence of a neural component in subjects’ perception of tightness would have been provided if those symptoms provoked during AKE were verified as being those provoked by knee extension during the Slump test, and relieved by cervical extension at the completion of the test. Further research in this area should include this in the study protocol. Also, in order to standardise the methodology, we have treated the group as homogenous by applying the Slump test in the standard sequence of movements. However, it has been demonstrated that the sequence, or order, in which various components of the Slump test are introduced modifies the individual responses to the test.43 Had we modified the sequence of the Slump test (for example by beginning with knee extension and dorsiflexion, and then introducing spinal flexion), we might have obtained different results.
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The results of this study suggest the need to address the mechanical properties of the nervous system when evaluating the perception of reduced hamstring extensibility, as neural tissue appears to be a contributing factor in asymptomatic patients. Regardless of the mechanisms underlying the perception of hamstring tightness, it is recommended that in all patients in whom an assessment of hamstring extensibility is warranted, the Slump test should be evaluated in order to aid differentiation between neural and muscular structures.
5. Conclusion From the results obtained in this study we conclude that subjects, who perceived they had tight hamstring muscles, were unlikely to have reduced hamstring length or extensibility, as suggested by the AKE test. We acknowledge that this conclusion would be further supported if normative data on the AKE were available for comparison. However, in the absence of this data we are only able to make comparisons with normative data on the PKE test. It is postulated that neural mechanosensitivity may play a significant role in explaining ‘perceived hamstring tightness’, supported by the fact that 84.2% of subjects’ posterior lower extremity symptoms induced by the Slump test were relieved by cervical extension. Further, 66.7% of subjects experienced posterior knee pain over the location of the sciatic nerve tract, of which 89% had relief of symptoms with cervical extension. This study adds to the existing knowledge regarding physical testing for neural mechanosensitivity, and the prevalence of positive responses from a Slump test among asymptomatic subjects with perceived hamstring tightness. On the basis of the results obtained in this study, we advocate the routine use of the Slump test in the assessment of patients with perceived hamstring tightness in order to aid differentiation between muscular and neural structures.
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