Immediate effects of static and proprioceptive neuromuscular facilitation stretching of hamstring muscles on straight leg raise,craniovertebral angle,and cervical spine range of motion in neck pain patients with hamstring tightness: A prospective randomized controlled trial

Abstract

BACKGROUND:

The cranio-cervical flexion exercise and sub-occipital muscle inhibition technique have been used to improve a forward head posture among neck pain patients with straight leg raise (SLR) limitation. However, little is known about the cranio-vertebral angle (CVA) and cervical spine range of motion (CROM) after applying stretching methods to the hamstring muscle.

OBJECTIVE:

To compare the immediate effects of static stretching and proprioceptive neuromuscular facilitation stretching on SLR, CVA, and CROM in neck pain patients with hamstring tightness.

METHODS:

64 subjects were randomly allocated to the static stretching ( $n_{1}=$ 32) or proprioceptive neuromuscular facilitation ( $n_{2}=$ 32) stretching group. The SLR test was performed to measure the hamstring muscle’s flexibility and tightness between the two groups, with CROM and CVA also being measured. The paired t-test was used to compare all the variables within each group before and after the intervention. The independent t-test was used to compare the two groups before and after the stretching exercise.

RESULTS:

There were no between-group effects for any outcome variables ( $P>$ 0.05). However, all SLR, CVA, and CROM outcome variables were significantly improved within-group ( $P<$ 0.05).

CONCLUSIONS:

There were no between-group effects for any outcome variable; however, SLR, CVA, and CROM significantly improved within-group after the one-session intervention in neck pain patients with hamstring tightness.

Keywords

Hamstring flexibility neck pain range of motion straight leg raise limitation stretching methods

1. Background

Neck pain is a predominant problem in the general population and carries a high hazard of ongoing relapses or complaints. The primary peculiarity of neck pain represents a pain in the cervical region, often accompanied by range of motion (ROM) limitations and dysfunction [1]. Forward head posture (FHP) is a common symptom of neck pain with an immoderate anterior head position concerning a perpendicular reference line. A previous study has reported that cervicothoracic junction manual therapy significantly affects the cranio-vertebral angle (CVA) and cervical mobility [2]. Similarly, the cranio-cervical flexion exercise (CCFE) activates deep neck flexor muscles and improves the cervical and thoracic spine’s upright posture when one assumes a prolonged sitting position [3]. It happens because the superficial back line of the myofascial chain connects the neck to the lower limbs, and the soft tissue in the cervical area connects the dura matter and sub-occipital muscle fascia [3].

A limited straight leg raise (SLR) can be a predisposing factor for non-specific lower back pain and alterations in the lumbo-pelvic rhythm [4]. Reduced SLR, as evidenced by the limited ROM in the passive SLR test, could be due to changed neuro-dynamics affecting the sciatic, tibial, and common fibular nerves [5]. A previous study reported that stretching methods had been used to improve the SLR test results used in clinical practice, including static, neuro-dynamic stretching, and proprioceptive neuromuscular facilitation (PNF) stretching [6]. Among the stretching methods, static stretching (SS) and PNF stretching have demonstrated efficacy for increasing SLR [7]. The theoretical basis for these longitudinal neuro-dynamic methods includes mobilizing adhesive tissues around the nerve, which may have resulted from some sort of traumatic incident and may directly influence the nerve [8] and decrease the forces linking structures may have on sensitive neural tissues [9]. Interestingly, the SLR improvement can help recover a normal posture because shortened hamstring muscles influence pelvic and spinal postures [10].

To date, several studies have reported the effects of the sub-occipital muscle inhibition (SMI) technique and CCFE in patients with neck pain or SLR limitation [11, 12] and have found improvements of the SLR and CVA [3]. This study aimed to compare the short-term effects of SS and PNF stretching of hamstring muscles on SLR, CVA, and cervical spine range of motion (CROM) among neck pain patients with SLR limitation.

2. Materials and methods

2.1 Study design

This prospective randomized study was conducted according to the principles of the Declaration of Helsinki. The ethics committee and institutional review board at Korea University Medical Center approved the study (2019AN0109). All study patients provided written informed consent, and their privacy would be protected. Based on previous research for hamstring flexibility in patients with a short hamstring [13], an SLR difference $>$ 3.3 ${}^{\circ}$ between the groups was regarded as a clinical difference. A power analysis was performed to determine the required sample size to achieve an alpha level of 0.05 and a power of 0.8. The results of a pilot study involving five patients in each group indicated that ten patients were required to detect significant SLR differences of $>$ 3.3 ${}^{\circ}$ between the groups. The power for detecting the differences in SLR was 0.801. In total, 64 patients volunteered to participate, and each was allotted using a random-number table to either SS or PNF stretching group for one-session intervention protocol.

Figure 1.

(A) Static hamstring stretching, (B) Proprioceptive neuromuscular facilitation hamstring stretching.

2.2 Sample recruitment

This study was conducted from March to August 2019, and participants were recruited from among hospital patients and visitors. Before the data collection, all patients received an explanation of the experimental protocol, provided by the investigator, and signed an informed consent form before being included. All patients and two outcome assessors were allocated (through a randomized and concealed allocation procedure) to one of the two groups. Only patients with short hamstring who had $\leqslant$ 80 ${}^{\circ}$ of hip flexion angle during the SLR test were included [14]. Patients were identified according to the following criteria: score on the Neck Disability Index (NDI) $\geqslant$ 5 points (mild disability level) [15] and score on the Numerical Rating Scale (NRS) $\geqslant$ 3 at rest or during active cervical movement [16]. Exclusion criteria were an initial SLR $>$ 80 ${}^{\circ}$ , acute lower back and neck pain, history of fractures in any part of the body, history of growth disorders, history of neurological or orthopedic disorders, history of lumbar or cervical herniated intervertebral disc or spinal stenosis, and history of vascular diseases of the head or neck [12].

2.3 Evaluation

Two assessors participated in the study. The intervention and allocation were conducted by a physical therapist (more than 12 years’ experience) who had blinded data analyses and assessments’ features. Analysis and evaluation were performed by an independent physical therapist (more than 15 years’ experience) who was blinded to the intervention protocol.

The SLR test accurately measured the flexibility and tightness of the hamstring muscle. The patient was placed in the supine position on the table with the lower limbs in an extended and relaxed position to measure SLR. The first evaluator held the talus without rotating the hip joint. The subject’s dominant leg was lifted gradually with hip flexion keeping the knee extended until the patient noted discomfort. The opposite limb or pelvis was observed to begin rotating or moving. The second evaluator measured SLR using an AcuAngle ${}^{\@setsize{\scriptsize}{8pt}{\viipt}{\@viipt}\textregistered}$ Angle Level inclinometer positioned on the anterior surface below the tibial tuberosity. In a previous study, the SLR test reported high inter-observer reliability (0.94–0.96) [17].

The CVA was measured from a picture of the patient’s lateral view taken by a digital camera (Sony a55; Sony, Tokyo, Japan), using ImageJ image analysis software (ImageJ 1.8.0, National Institutes of Health, USA). Researchers measured the CVA of each patient in both sitting and standing positions and used a previously described method that reported high reliability of this procedure (intraclass correlation coefficient ICC, 0.88) [18]. The CVA has been projected to lie between a horizontal line running through the spinous process of the seventh cervical vertebra (C7) and a line connecting the ear’s tragus with the spinous process of the seventh cervical vertebra (C7). A smaller CVA is associated with a greater FHP [18].

The CROM was measured by a previously described method using a universal goniometer for which the author found extensive intra- and inter-reliability (ICC $=$ 0.83) [19]. The CROM was used to measure six movements of the cervical spine (i.e., flexion, extension, and right and left components of lateral flexion and rotation) using the universal goniometer. Researchers measured the neck ROM in a neutral sitting position with the hip and knee angles set at 90 ${}^{\circ}$ and both arms crossed over the chest to avoid compensation during the test. The first evaluator measured each ROM in pre- and post-intervention periods.

Figure 2.

Flowchart of the participants throughout the study.

2.4 Procedure in the static hamstring stretching group

Each subject is placed in a supine position to apply the SS technique on the table with all limbs relaxed. Patients in the SS group received hamstrings stretching in the SLR position until resistance from the hamstring muscle was felt by the first evaluator. Each patient’s dominant leg was lifted gradually to 90 ${}^{\circ}$ of hip flexion and maximum knee extension [20]. Five sets of the SS were performed for 30 seconds each, followed by 10 seconds of relaxation. During the 30 seconds, the first evaluator monitored the patients to avoid pelvic and leg movement. A previous study reported that a 30 seconds SS is as efficient as a 60 seconds SS in increasing flexibility [21] (Fig. 1A).

Table 1
Baseline characteristics of the participants ( $N=$ 64)

	SS ( $n_{1}=$ 32)	PNF ( $n_{2}=$ 32)	t/x ${}^{2}$	$P$ value ${}^{\text{b}}$
Sex (male/female)	20/12	14/18	0.27	0.93
Age (years) ${}^{\text{a}}$	35.2 $\pm$ 13.3	30.0 $\pm$ 9.6	0.37	0.94
Height (cm) ${}^{\text{a}}$	168.8 $\pm$ 8.6	174.4 $\pm$ 4.2	0.40	0.93
Weight (kg) ${}^{\text{a}}$	69.3 $\pm$ 14.2	72.3 $\pm$ 11.6	0.57	0.92
Body mass index (kg/Ð¡) ${}^{\text{a}}$	22.8 $\pm$ 3.2	21.76 $\pm$ 5.8	0.54	0.93
NRS (score) ${}^{\text{a}}$	4.1 $\pm$ 1.2	4.0 $\pm$ 1.1	0.26	0.92
NDI (score) ${}^{\text{a}}$	8.6 $\pm$ 5.3	6.9 $\pm$ 3.8	0.24	0.44

${}^{\text{a}}$ Values are expressed as mean $\pm$ SD. ${}^{\text{b}}P$ values were calculated with the independent $t$ -test for the age, height, weight, NRS score, and NDI and the chi-square test for gender. Abbreviations: SS, static hamstring stretching group; PNF, proprioceptive neuromuscular facilitation stretching group.

2.5 Procedure in the PNF stretching group

The PNF stretching used hold-relax (HR) and HR with antagonist contraction (HR-AC) methods to reduce the disturbance of myotatic reflexes, autogenic inhibition, and neural activity in the related muscles [22]. The patient was able to apply PNF stretching in a supine position on the table with all extremities relaxed. The first evaluator lifted the patient’s dominant leg to 90 ${}^{\circ}$ of hip flexion while holding the contralateral leg with the hip and knee in the extension position. The second evaluator used a goniometer to maintain a 90 ${}^{\circ}$ hip flexion. During the HR procedure, each patient was required to produce a 10-second resisted isometric contraction of the knee flexor against the first evaluator’s manual resistance. After the isometric contraction of the knee flexor had occurred, the patient was instructed to immediately perform a concentric antagonist (knee extensor) contraction for 10 seconds and rest for 5 seconds [23] (Fig. 1B).

2.6 Statistical analysis

The statistical analysis was performed using SPSS 22.0 (SPSS Inc., Chicago, IL, USA) at a confidence level of $P=$ 0.05. The values in each group were expressed as mean $\pm$ standard deviation. The normal distribution of the raw data was confirmed using the Shapiro-Wilk test; parametric methods were also used. The chi-square test (gender) and independent $t$ -test (age, height, weight, NRS score, and NDI) were used to compare the patients’ demographic characteristics between SS and PNF stretching groups. The paired $t$ -test was used to compare all the variables within each group before and after the intervention. Through an independent sampled $t$ -test, the SS group was compared with the PNF stretching group to show the differences before and after the stretching exercise. Additionally, consequent to independent $t$ -test analysis, if the pre-test value between the two groups was statistically significant (in this study, angle of cervical extension only), the pre-test value was set as a covariate. Further, analysis of covariance (ANCOVA) was performed on the post-test value between the two groups.

3. Results

3.1 Participants’ general demographics for each group

Excluded patients are shown in Fig. 2. In total, 64 patients were recruited to participate; each was allocated using a random-number table to either the SS or PNF stretching group. This study excluded 7 patients with SLR $>$ 80 ( $n=$ 4), lower back pain ( $n=$ 2), and fibula fracture ( $n=$ 1). Table 1 summarizes the chi-square test’s statistical analysis results and the independent $t$ -test on the general participants’ demographics between the two groups. There were no significant between-group differences in participant characteristics, including age, sex, height, weight, body mass index, NRS, or NDI (Table 1).

3.2 Comparison of the SLR test between the 2 groups

The values of the SLR test in each group are summarized in Table 2. For the intra-subject measurements, significant differences were found between pre-intervention and post-intervention values of the SLR test in the SS and PNF stretching group ( $P<$ 0.05). However, there were no between-group effects for the SLR test ( $P>$ 0.05).

Table 2
Comparison of the SLR test, CROM and CVA measurements for the two intervention groups ( $N=$ 64)

Characteristics	SS ( $n_{1}=$ 32)		PNF ( $n_{2}=$ 32)		t/F	$P$ value ${}^{\text{b}}$
Straight leg raise, Rt ( ${}^{\circ}$ )
Pre-test	71.8	$\pm$ 7.9	72.0	$\pm$ 2.9	$-$ 0.13	0.72
Post-test	84.2	$\pm$ 9.9	80.3	$\pm$ 4.9 ${}^{{\dagger}}$	3.49	0.08
$t$ ( $P$ value ${}^{\text{a}}$ )	5.45 (0.007) ${}^{\ast\ast}$		6.14 (0.005) ${}^{\ast\ast}$
Cervical flexion ( ${}^{\circ}$ )
Pre-test	42.3	$\pm$ 9.9	45.0	$\pm$ 8.2	0.27	0.68
Post-test	47.8	$\pm$ 8.0	52.0	$\pm$ 7.9	1.13	0.31
$t$ ( $P$ value ${}^{\text{a}}$ )	4.74 (0.02) ${}^{\ast}$		5.71 (0.007) ${}^{\ast\ast}$
Cervical extension ( ${}^{\circ}$ )
Pre-test	58.6	$\pm$ 12.1	67.5	$\pm$ 9.1	3.01	0.02 ${}^{\ast}$
Post-test	65.8	$\pm$ 11.3	72.2	$\pm$ 9.9	0.61	0.43
$t$ ( $P$ value ${}^{\text{a}}$ )	4.83 (0.01) ${}^{\ast\ast}$		4.80 (0.02) ${}^{\ast}$
Cervical lateral flexion, Rt ( ${}^{\circ}$ )
Pre-test	34.8	$\pm$ 8.4	36.9	$\pm$ 9.1	0.43	0.69
Post-test	40.2	$\pm$ 7.9	41.7	$\pm$ 7.2	0.01	0.87
$t$ ( $P$ value ${}^{\text{a}}$ )	4.82 (0.01) ${}^{\ast\ast}$		4.81 (0.01) ${}^{\ast\ast}$
Cervical lateral flexion, Lt ( ${}^{\circ}$ )
Pre-test	36.4	$\pm$ 8.5	39.8	$\pm$ 3.4	0.85	0.32
Post-test	42.0	$\pm$ 5.8	44.2	$\pm$ 4.2	0.03	0.69
$t$ ( $P$ value ${}^{\text{a}}$ )	6.02 (0.007) ${}^{\ast\ast}$		6.10 (0.007) ${}^{\ast\ast}$
Cervical rotation, Rt ( ${}^{\circ}$ )
Pre-test	66.4	$\pm$ 7.9	65.8	$\pm$ 7.0	0.55	0.48
Post-test	71.0	$\pm$ 8.1	73.3	$\pm$ 5.9	0.79	0.39
$t$ ( $P$ value ${}^{\text{a}}$ )	4.81 (0.02) ${}^{\ast}$		6.08 (0.007) ${}^{\ast\ast}$
Cervical rotation, Lt ( ${}^{\circ}$ )
Pre-test	67.9	$\pm$ 7.1	68.1	$\pm$ 5.8	0.16	0.82
Post-test	72.6	$\pm$ 6.3	74.6	$\pm$ 5.3	1.23	0.09
$t$ ( $P$ value ${}^{\text{a}}$ )	5.61 (0.007) ${}^{\ast\ast}$		5.97 (0.005) ${}^{\ast\ast}$
CVA on sitting ( ${}^{\circ}$ )
Pre-test	49.0	$\pm$ 4.4	52.6	$\pm$ 5.3	1.74	0.07
Post-test	50.9	$\pm$ 4.4	54.1	$\pm$ 5.9	3.02	0.02 ${}^{\ast}$
t ( $P$ value ${}^{\text{a}}$ )	5.17 (0.008) ${}^{\ast\ast}$		4.50 (0.03) ${}^{\ast}$
CVA on standing ( ${}^{\circ}$ )
Pre-test	50.5	$\pm$ 4.2	53.5	$\pm$ 5.4	1.81	0.06
Post-test	53.1	$\pm$ 3.9	54.9	$\pm$ 4.6	0.23	0.74
$t$ ( $P$ value ${}^{\text{a}}$ )	5.27 (0.008) ${}^{\ast\ast}$		1.82 (0.06)

Note. Values are expressed as mean $\pm$ SD. ${}^{\text{a}}$ Within-group comparison. ${}^{\text{b}}$ Between group comparison. $P$ values were calculated with the analysis of covariance (ANCOVA) for the angle of cervical extension and by the independent $t$ -test for other variables except the angle of cervical extension. Abbreviations: SS, static hamstring stretching; PNF, proprioceptive neuromuscular facilitation; CVA, cranio-vertebral angle; Rt, right; Lt, left. ${}^{\ast}P<$ 0.05, ${}^{\ast\ast}P<$ 0.01.

3.3 Comparison of the CROM measurements between the 2 groups

The values of the CROM measurements in each group are summarized in Table 2. For the intra-subject measures, significant differences were found between pre-intervention and post-intervention values of the CROM measurements for all cervical spine movements in the SS and PNF stretching group ( $P<$ 0.05). However, there were no between-group effects for CROM measurements ( $P>$ 0.05). In particular, since there was a statistically significant difference in the pre-test values between the two groups concerning the cervical extension angle ( $t=$ 3.01, $P<$ 0.05), a further ANCOVA analysis was performed. The ANCOVA analysis also revealed that there was no difference between the two groups ( $F=$ 0.61, $P>$ 0.05).

3.4 Comparison of the CVA measurements between the 2 groups

The CVA measurements on sitting and standing positions in each group are summarized in Table 2. For the intra-subject measures, significant differences were found between pre-intervention and post-intervention values of the CVA on sitting position in the SS and PNF stretching group ( $P<$ 0.05). Moreover, the post-test measurements of the CVA on sitting position in the PNF stretching group were significantly increased compared to those in the SS group ( $P<$ 0.05) (Table 2). However, there were no between-group effects for CVA on standing position ( $P>$ 0.05). For the intra-subject measurements, significant differences were only found between pre-intervention and post-intervention values of the CVA on standing position in the SS group ( $P<$ 0.05) (Table 2).

4. Discussion

The purpose of the present study was to compare the immediate effects of two different types of hamstring stretching methods on SLR, CVA, and CROM in neck pain patients with hamstring tightness. The most important aspect of the present study was that it compared the SS and PNF stretching groups. There were no between-group effects for any outcome variable, however, SLR, CVA, and CROM significantly improved within-group after the intervention.

There were no between-group effects for SLR ( $P>$ 0.05). However, the SLR outcome variables were significantly improved within-group after the intervention ( $P<$ 0.05). Several previous studies have reported that both SS and PNF hamstring stretching increase hamstring flexibility effectively [24, 25]. A systematic review of the literature also reported that the literature on immediate comparative studies between different stretching exercises is limited [25]. However, another study has reported that PNF stretching may increase muscle flexibility and joint ROM more effectively than SS [26]. The results of the present study contradict these findings. Overall, the present study found no significant difference between the SS and PNF stretching groups. This may be attributed to the immediate effects of improved hamstring muscle elasticity and nervous tissue extensibility. Different mechanisms are associated with improved flexibility following the two stretching methods. As to the immediate effects of stretching, it has been suggested that a relaxation in the muscle-tendon unit (MTU) may be related to the improved muscle length [27]. A previous study reported that SS seems to be more effective in reducing muscle tension [28], while PNF stretching reduces both muscle and tendon tension effectively [27]. Interestingly, Bandy and Sanders found that one of SS’s positive effects may be stimulation of the Golgi tendon organ (GTO) [29]. Static tension acting on the MTU has been shown to facilitate the GTO, which may generate autogenic inhibition of the stretched muscle and be very effective at improving hamstring length [29]. Nee and Butler reported that the main aims of hamstring stretching methods are to reestablish normal nerve gliding and neurophysiology to the nerve and surrounding tissues, thus, reducing pain and improving function [30]. Based on this finding, it is probable that both SS and PNF stretching may be very effective in reducing tension and increasing length in the hamstring muscle. Therefore, the SS and PNF stretching’s immediate effect in the present study may have been inadequate to identify SLR differences between the two groups.

The present study found no significant difference in CVA ( $P>$ 0.05) between the SS and PNF stretching groups. However, the CVA outcome variables ( $P<$ .05) significantly improved within-group after both interventions. A previous study reported that the hamstring muscles’ extensibility should affect the anteroposterior orientation in the sagittal curve of the spine and the pelvic posture [31]. Interestingly, the fascia is a connective tissue that encloses every muscle fiber, blood vessel, and nerve in the human body, resulting in the link between muscles, bones, and organs and creating large networks throughout the human body. Based on the tensegrity principle, several studies found a continuity of the facial chain in the upper and lower extremities [32, 33]. Myers suggested that a “schematic map” of the human body’s fascia connections, namely “anatomy trains,” may have harmful effects on globally reduced flexibility [34]. In particular, the anatomy train proposed to be most closely related to the hamstring muscles and lumbar spine is the superficial backline. It contains the plantar fascia and the triceps surae, hamstrings, sacrotuberous ligament, sacrolumbar fascia, erector spinae, epicranial, galea aponeurotica, and frontalis muscles [34]. Based on a reciprocal connection between the cervical and other vertebral column parts, an overall sagittal imbalance results in adaptive changes in the pelvis via a compensatory mechanism [35]. In support of these possibilities, Gajdosik et al. reported that SLR limitation would cause problems at the pelvis and the spine and that stretched hamstring muscles would restore upright posture [10]; thus, restoration of hamstring flexibility is essential for FHP. Based on these studies’ findings, it is also possible that the SS and PNF stretching transfer the force of the hamstring to the pelvis and spine with the result that CVA improves due to the decreased tone of the cervical extensors. Although the present study’s reasons are unclear, it may be attributed to improved upright posture due to altered superficial backline.

The present study found no between-group effects for CROM ( $P>$ 0.05). However, the CROM outcome variables ( $P<$ 0.05) significantly improved within the group after both interventions. Several previous studies reported that FHP is defined as an increased extension of the upper cervical, flexion of the lower cervical and upper thoracic spine, with the shortening of the scalenus anterior and upper trapezius, and sternocleidomastoid muscles, and lengthening of the semispinalis capitis and levator scapulae muscles [36, 37]. Thus, altered cervical muscle length and sagittal cervical spine alignment could potentially result in altered sensorimotor integration via a wrong afferent input from altered soft tissue tone and cervical spine kinematics [38]. A previous study reported that inactivity and shortening of the cervical muscles, structural changes in the soft tissue, and augmentation of connective tissue density caused reductions in the CROM. To resolve these problems, González et al. [39] reported that manual techniques on sub-occipital muscles achieve an immediate improvement in CROM. Conversely, the results of a previous study showed that hamstring stretching exercises significantly improved cervical movement [40]. In the present study, the immediate effects of CROM after SS and PNF stretching were similar to those reported in previous studies. Theoretically, the neural system’s continuity will be in line with the dura mater, which is anatomically linked to the sub-occipital muscles. It is known as the “myodural bridge.” These anatomical relationships can explain the continuity between the cervical spine and the hamstring muscles [41]. Therefore, longitudinal neurodynamic stretching consists of joint movements that cause (mainly) longitudinal excursion through the nerve bed before repeatedly moving one or more joints and also proximal and distal movements of the nerve (or vice versa) [42]. Interestingly, Van et al. [43] reported that increased hamstring stiffness might result from compensation for nonoptimal sacroiliac joint control due to the hamstring muscles’ attachment to the ischial tuberosity. Moreover, hamstring stiffness may affect hip and lumbar functions and cause excessive electromyography activity of the erector spine during dynamic activities. The hamstring muscles can change the force transmission between the lower extremities and the trunk [43]. A hypothesis has been proposed to describe the improvement in ROM following a stretching exercise program. Some researchers relate the enhancement in ROM to structural alterations of the MTU [44]. From a different perspective, an increase in endurance to stretching tension and a reduction in the neural input to the motor neuron pool explain the enhancement in ROM [45]. Accordingly, it is also feasible that mechanoreceptors innervate the fascial system, and the application of passive pressure or traction may create a range of facilitating movement responses [42]. The outcomes of previous studies point to a significant difference in hamstring flexibility between SS and PNF stretching. Furthermore, improved hamstring flexibility can significantly affect cervical movement, based on the minimal clinical variable proposed in a previous study [41]. Based on these studies’ findings, the present study confirmed that the relevant differences were not found in the between-group comparisons performed independently in each study group. However, statistically significant improvement in hamstring flexibility, CVA, and CROM was observed in the within-group comparisons after one session of SS and PNF stretching in neck pain patients with hamstring tightness. These improvements can be attributed to the fact that released hamstring tendons and muscles can improve the pelvic posture in both sitting and standing positions and achieve a better thoracic and upright cervical posture. Furthermore, there are immediate effects on FHP and cervical movement improvements due to the decreased tension of the myodural bridge in the upper cervical region and posterior myofascial chain.

Therefore, the present study’s results indicated that there were no between-group effects for any outcome variable regarding the SS and PNF stretching groups, but SLR, CVA, and CROM significantly improved within-group after the one-session intervention in neck pain patient with hamstring tightness.

4.1 Limitations

Although the between and within-group comparisons demonstrated favorable SS and PNF stretching results, our study’s restrictions can be further addressed in future studies. Researchers did not assess biomechanical or kinematic parameters, such as muscle activation and joint moments. Therefore, future studies that provide direct qualitative parameters evaluating the biomechanical parameters and electromyography recordings from the neck and hamstring muscles are also necessary. Further, the present study focused on patients with SLR $>$ 80 ${}^{\circ}$ , but a previous study has reported that patients with SLR $>$ 70 ${}^{\circ}$ [46]. The patients should be selected considering these aspects in future research. For more effective results in the exercise program, researchers should also consider the effect of static and active exercises. If passive stretching is used, the afferent input from the muscle spindles links to the area of the cortex where it can provoke neuronal cells that elicit muscle contraction. Interestingly, excitation of the supplementary motor area (SMA) and an increase in regional cerebral blood flow (rCBF) were also stimulated during the active and passive movements [47]. However, Stephan et al. reported that the rostral area of the SMA was facilitated by imagining movement. Conversely, the caudal region of the SMA and dorsal anterior cingulate cortex were additionally activated during real movement [48]. Moreover, the rCBF of the active movement was significantly higher than that of the passive movement [47], and activation of the basal ganglia occurred only during active movement [49]. Researchers confirmed the SS and PNF’s immediate effects on the hamstring muscles. However, active exercises may be more effective in long-term follow-up and motor learning, thus, additional statistical analyses, such as regression analyses, should be conducted.

5. Conclusions

The SS and PNF stretching groups had no between-group effects for any outcome variable, but SLR, CVA, CROM significantly improved within-group after the one-session intervention in neck pain patients with hamstring tightness.

Footnotes

Acknowledgments

The authors are grateful to all subjects involved in this study, as well as authors/publishers/editors of all articles, journals, and books reviewed and discussed for this study. This study was supported by a Korea University Grant (K1605431).

Conflict of interest

All authors were fully committed to absolute integrity and remained unbiased throughout the study. None of the authors had any conflicts of interest or carried any commitments that would influence their duties. The roles of the authors in this study are as follows: Eun-Dong Jeong and Chang-Yong Kim are the primary authors and wrote the manuscript, performed the experimental procedures, interpreted the results, managed the study, and provided critical discussion. Nack-Hwan Kim performed the experimental procedures and critical discussion. Hyeong-Dong Kim performed the experimental procedures and critical discussion.

References

Hush

Lin

Michaleff

Verhagen

Refshauge

. Prognosis of acute idiopathic neck pain is poor: a systematic review and meta-analysis. Arch Phys Med Rehabil. 2011; 92(5): 824-829.

Kim

. Comparison of immediate effects of sling-based manual therapy on specific spine levels in subjects with neck pain and forward head posture: a randomized clinical trial. Disabili Rehabil. 2020; 42(19): 2735-2742.

Pontell

Scali

Marshall

Enix

. The obliquus capitis inferior myodural bridge. Clin Anat. 2013; 26(4): 450-454.

Sadler

Spink

De Jonge

Chuter

. Restriction in lateral bending range of motion, lumbar lordosis, and hamstring flexibility predicts the development of low back pain: a systemic review of prospective cohort studies. BMC Musculoskelet Disord. 2017; 18: 179.

Kornberg

Lew

. The effect of stretching neural structures on grade one hamstring injuries. J Orthop Sports Phys Ther. 1989; 10(12): 481-487.

Jull

Sterling

Kenardy

Beller

. Does the presence of sensory hypersensitivity influence outcomes of physical rehabilitation for chronic whiplash? – A preliminary RCT. Pain. 2007; 129(1-2): 28-34.

Borges

Medeiros

Minotto

Lima

. Comparison between static stretching and proprioceptive neuromuscular facilitation on hamstring flexibility: systematic review and meta-analysis. Eur J phys. 2018; 20(1): 12-19.

Falla

Jull

Russell

Vicenzino

Hodges

. Effect of neck exercise on sittingposture in patients with chronic neck pain. Phys Ther. 2007; 87(4): 408-417.

White

Sahrmann

. A movement system balance approach to management of musculoskeletal pain. Physical therapy of the cervical and thoracic spine. 1994; 339-357.

10.

López-Miñarro

Muyor

Belmonte

Alacid

. Acute effects of hamstring stretching on sagittal spinal curvatures and pelvic tilt. J Hum Kinet. 2012; 31: 69-78.

11.

Heredia Rizo

Pascual-Vaca

Cabello

Blanco

Pozo

Carrasco

. Immediate effects of the suboccipital muscle inhibition technique in craniocervical posture and greater occipital nerve mechanosensitivity in subjects with a history of orthodontia use: a randomized trial. J Manipulative Physiol Ther. 2012; 35(6): 446-453.

12.

Aparicio

ÉO

Quirante

Blanco

Sendín

. Immediate effects of the suboccipital muscle inhibition technique in subjects with short hamstring syndrome. J Manipulative Physiol Ther. 2009; 32(4): 262-269.

13.

Castellote-Caballero

Puentedura

Penas

Valenza

Martin

Martos

. Effects of a neurodynamic sliding technique on hamstring flexibility in healthy male soccer players: A pilot study. Phys Ther Sport. 2013; 14(3): 156-162.

14.

Vakhariya

Panchal

Patel

. Effects of various therapeutic techniques in the subjects with short hamstring syndrome. Int J Physiother Res. 2016; 4(4): 1603-10.

15.

Girasol

Dibai-Filho

de Oliveira

de Jesus-Guirro

. Correlation between skin temperature over myofascial trigger points in the upper trapezius muscle and range of motion, electromyographic activity, and pain in chronic neck pain patients. J Manipulative Physiol Ther. 2018; 41(4): 350-357.

16.

Ferreira-Valente

Pais-Ribeiro

Jensen

. Validity of four pain intensity rating scales Pain. 2011; 152: 2399-2404.

17.

Kelln

McKeon

Gontkof

Hertel

. Hand-held dynamometry: reliability of lower extremity muscle testing in healthy, physically active, young adults. Journal of Sport Rehabilitation. 2008; 17(2): 160-17024..

18.

Raine

Twomey

. Head and shoulder posture variations in 160 asymptomatic women and men. Arch Phys Med Rehabil. 1997; 78(11): 1215-1223.

19.

Youdas

Carey

Garrett

. Reliability of measurements of cervical spine range of motion – comparison of three methods. Phys Ther. 1991; 71(2): 98-104.

20.

Aalto

Airaksinen

Härkönen

Arokoski

. Effect of passive stretch on reproducibility range of motion measurements. Arch Phys Med Rehabil. 2005 Mar; 86(3): 549-57.

21.

Bandy

Irion

Briggler

. The effect of time and frequency of static stretching on flexibility of the hamstring muscles. Phys Ther. 1997; 77(10): 1090-6.

22.

Rowlands

Marginson

Lee

. Chronic flexibility gains: effect of isometric contraction duration during proprioceptive neuromuscular facilitation stretching techniques. Res Q Exerc Sport. 2003; 74(1): 47-51.

23.

Kisner

Colby

Borstad

. Therapeutic exercise: foundations and techniques: Fa Davis, 2017.

24.

Chow

. Active, passive and proprioceptive neuromuscular facilitation stretching are comparable in improving the knee flexion range in people with total knee replacement: a randomized controlled trial. Clin Rehabil. 2010; 24: 911-918.

25.

Decoster

Cleland

Altieri

Russell

. The effects of hamstring stretching on range of motion: a systematic literature review. J Orthop Sports Phys Ther. 2005; 35(6): 377-387.

26.

Fasen

O’Connar

Schwartz

Watson

Plastaras

Garvan

, et al. A randomized controlled trial of hamstring stretching: Comparison of four techniques. J Strength Cond Res. 2009; 23: 660-7.

27.

Kay

Husbands-Beasley

Blazevich

. Effects of contract-relax, static stretching, and isometric contractions on muscle-tendon mechanics. Med Sci Sports Exerc. 2015; 47: 2181-2190.

28.

Nakamura

Ikezoe

Tokugawa

, et al. Acute effects of stretching on passive properties of human gastrocnemius muscle-tendon unit: analysis of differences between hold-relax and static stretching. J Sport Rehabil. 2015; 24: 286-292.

29.

Bandy

Sanders

. Therapeutic exercise: techniques for intervention: Lippincot Williams & Wilkins, 2001.

30.

Nee

Butler

. Management of peripheral neuropathic pain: Integrating neurobiology, neurodynamics, and clinical evidence. Physical Therapy in Sport. 2006; 7: 36-49.

31.

Delisle

Gagnon

Sicard

. Effect of pelvic tilt on lumbar spine geometry. IEEE Trans Rehabil Eng. 1997; 5(4): 360-366.

32.

Stecco

Gagey

Belloni

, et al. Anatomy of the deep fascia of the upper limb. Second part: study of innervation. Morphologie. 2007; 91(292): 38-43.

33.

Stecco

Porzionato

Lancerotto

, et al. Histological study of the deep fasciae of the limbs. J Bodyw Mov Ther. 2008; 12(3): 225-230.

34.

Myers

. Anatomy Trains E-Book: Myofascial Meridians for Manual and Movement Therapists: Elsevier Health Sciences, 2013.

35.

Ames

Blondel

Scheer

et al. Cervical radiographical alignment: comprehensive assessment techniques and potential importance in cervical myelopathy. Spine. 2013; 38: 149-160.

36.

Salahzadeh

Maroufi

Ahmadi

Behtash

Razmjoo

Gohari

, et al. Assessment of forward head posture in females: observational and photogrammetry methods. J Back Musculoskelet Rehabil. 2014; 27(2): 131-139.

37.

Finley

Lee

. Effect of sitting posture on 3-dimensional scapular kinematics measured by skin-mounted electromagnetic tracking sensors. Arch Phys Med Rehabil. 2003; 84(4): 563-568.

38.

Goodarzi

Rahnama

Karimi

Baghi

Jaberzadeh

. The effects of forward head posture on neck extensor muscle thickness: an ultrasonographic study. J. Manipulative Physiol Ther. 2018; 41: 34-41.

39.

González-Rueda,

Vanessa

et al. Comparative Study of the Effects of Two Inhibitory Suboccipital Techniques in Non-symptomatic Subjects with Limited Cervical Mobility. J Back Musculoskelet Rehabil. 2018; 31(6): 1193-1200.

40.

Cho

S-H

Kim

S-H

Park

D-J

. The comparison of the immediate effects of application of the suboccipital muscle inhibition and self-myofascial release techniques in the suboccipital region on short hamstring. J Phys Ther Scie. 2015; 27(1): 195-197.

41.

MassoudArab

RezaNourbakhsh

Mohammadifar

. The relationship between hamstring length and gluteal muscle strength in individuals with sacroiliac joint dysfunction. J Man Manip Ther. 2011; 19(1): 5-10.

42.

Dilley

Odeyinde

Greening

Lynn

. Longitudinal sliding of the median nerve in patients with non-specific arm pain. Manl Ther. 2008; 13: 536-543.

43.

Van Wingerden

J-P

Vleeming

Ronchetti

. Differences in standing and forward bending in women with chronic low back or pelvic girdle pain: indications for physical compensation strategies. Spine (Phila Pa 1976). 2008; 33(11): E334-E341.

44.

Morse

Degens

Seynnes

Maganaris

Jones

. The acute effect of stretching on the passive stiffness of the human gastrocnemius muscle tendon unit. J Physiol. 2008; 586(1): 97-106.

45.

Page

. Current concepts in muscle stretching for exercise and rehabilitation. Int J Sports Phys Ther. 2012; 7(1): 109.

46.

Piqueras-Rodríguez

Palazón-Bru

Martínez-St John

, et al. A tool to quickly detect short hamstring syndrome in boys who play soccer. Int J Sports Med. 2016; 37(1): 1-5.

47.

Lolli

Rovaï

Trotta

, et al. MRI-compatible pneumatic stimulator for sensorimotor mapping. J Neurosci Methods. 2019; 313: 29-36.

48.

Stephan

Fink

Passingham

, et al. Functional anatomy of the mental representation of upper extremity movements in healthy subjects. J Neurophysiol. 1995; 73(1): 373-386.

49.

Macerollo

Brown

Kilner

Chen

. Neurophysiological changes measured using somatosensory evoked potentials. Trends Neurosci. 2018; 41(5): 294-310.