Analysis of The Global Posture of College Students With Chronic Neck Pain


 Background: Chronic neck pain (CNP) is common, but methods that focus on the cervical spine have not met the patients' medical expectations.Objective: To investigate the global postural difference between students with CNP and healthy people.Design: Cross-sectional study.Methods: Twenty-seven healthy college students without neck pain and 31 students with CNP were recruited and allocated into a control group and a CNP group. Differences in standing postural indicators between the two groups were compared.Results: Compared to the control group, the leg length discrepancy and the right rearfoot angle were larger and the anterior lower limb alignment angle was smaller. In the sagittal plane, the left sagittal lower limb alignment and right cervical alignment angles were larger, while the left and right sagittal body alignment angles in the CNP group were smaller. The odds ratio calculation for the trunk forward lean, right foot valgus, and knee flexion on both sides indicated that these are risk factors for CNP, while knee varus is not a risk factor for CNP. The remaining abnormal postures were shown not to be associated with CNP.Limitation: This study did not conduct in-depth research on the physiological state of the muscles, joints, and other structures, and we did not apply these theories to practice.Conclusions: Abnormal posture in students with CNP is mainly concentrated in the sagittal plane. Trunk forward lean, foot valgus, and knee flexion on both sides are risk factors for CNP.


Introduction
Chronic neck pain (CNP) is a common condition that not only leads to considerable pain and disability, but it also affects the mental state, reduces work e ciency and quality of life, and represents a signi cant medical burden. For this reason, CNP has become a public health and social issue [1,2] . However, to date, the effect of modern medical methods to relieve neck pain and restore neck function in CNP are unsatisfactory. These methods include neck suspenders, analgesic drugs, physical therapy, exercise [3,4] , manipulation [5][6][7][8] , acupuncture [9,10] , massage [11] , and surgery. In other words, these methods, which focus on the cervical spine, have not met the patient's medical expectations. Neck pain may occur as a result of imbalances in the biomechanics of the neck and abnormalities in the entire alignment throughout the body. Recent studies have shown that global posture re-education is an effective treatment for chronic pain, including neck and low back pain [12][13][14] . Meanwhile, some studies have provided evidence that ergonomic assistive devices are useful for correcting poor posture [15] .
Interestingly, these results are in line with the human fascia and muscle chain theory proposed by Myers. According to Myers' "Anatomy Trains -The Myofascial Meridian for Manual and Movement Therapy" [16] , the skeletal muscle system of the human body is a tensile structure. Thus, from a global posture and kinematic chain viewpoint, there must be a connection between the appearance of local symptoms and overall changes in global posture and kinematic chains. Indeed, when a part of the body's tension changes, it will inevitably cause changes in the tension structure of other parts [16] . Similarly, Dr. Janda, a clinical medical scientist from the Czech Republic, proposes three chains responsible for adaptive changes in a certain part of the body from the perspective of clinical assessment and treatment of pain caused by muscle imbalance, namely, the joint, muscle, and neural chains [17] . A kinematic chain reaction, also known as the "wave effect," occurs in the entire movement chain of the human body. The primary movement of a joint can produce up, down, left, or right body adjustments. In other words, when a part of the body is under abnormal pressure, other parts of the body also produce abnormal pressure and tension [18,19] . Deviations within these three chain systems lead to compensatory and adaptive changes in the neuromuscular system. For example, changes in the joint chain affect the function of the muscle and nerve chains, resulting in a corresponding structure and function of the entire kinematic chain. The result of this change is a dysfunctional movement pattern that occurs throughout the body during static standing or exercise, with signi cant compensatory movements or joint pain. Some studies have found that head extension and rounded shoulder posture in patients with CNP is more prominent than in a healthy population, and that the greater the degree of head extension, the more serious the dysfunction [19] . However, another study showed that forward head posture (FHP) did not differ signi cantly between groups nor correlate with muscle performance or CNP clinical characteristics [20] .
Whether the imbalance of the global posture is a risk of CNP remains unclear. We hypothesize that there is a potential mechanical imbalance or "weakened chain" in the global posture of patients with CNP. The Global Postural Systems (GPS) Lab (model GPS400, Chinesport, Italy) was used to measure global postural indicators of a healthy and CNP population to explore the connections between local structural changes in the neck and global posture, and provide new insights for treating CNP.

Methods
This cross-sectional study collected data on college students with and without CNP. The GPS Lab, a professional and reliable assessment tool [21] , was used to measure posture.

Participants
Fifty-eight college students were recruited from ve universities in Guangzhou city. Thirty-one students were enrolled in the CNP group, and 27 students without neck pain during the same period were recruited as the control group. All of the participants provided their informed consent.
The inclusion criteria of the CNP group were as follows: 1) recurrent neck pain (Visual Analogue Scale [VAS] ≥ 3) for more than 3 months; and 2) no history of spinal or trauma surgery. The inclusion criteria of the control group were as follows: 1) no history of neck pain in the past 3 years; 2) no structural  The distance between the medial margin of the scapula and the spine of the third thoracic spine, and the difference of the distance between the two sides

Procedures
Before preparing participants for global postural measurement on the GPS Lab, we determined bilateral leg length differences using the Delta Leg measuring device.
To make global postural indicator measurements using GPS Lab software, we placed marker stickers on speci c bony landmarks on the participants' bodies. All of the participants were asked to undress to underwear, to expose as much skin as possible. The investigator palpated, con rmed, and placed markers on the spinous processes of C7, T3, T6, T9, T12, L3, and S1, PSIS, the midpoint of the shoulder joint, the midpoint of the Achilles tendon, the midpoint of the lower third of the triceps surae, the anterior angle of the acromion, the midpoint of the acromion, the posterior angle of the acromion, the upper and lower angles of the scapula, the ASIS, the midpoint of the tibia, the lateral and medial condyles of the humerus, the larger trochanter of the femur, the midpoint of the lateral side of the knee joint, the lateral malleolus, the external canthus of the eye, and the tragus. The investigator checked the correct position of markers on bony landmarks through the cameras and software of the GPS Lab before photographing. The detailed procedures of the measurement are described in Supplementary 1 and a complete set of global posture photos of the subject are showed in Figure 4.

Statistical analysis
The MS Excel package was used to create a database and enter measurement values. Measurement data are presented as the mean and standard deviation. The comparison between groups was performed using the independent sample t-test. The Mann-Whitney U test was used if the values were not normally distributed. Categorical variables were described by the composition ratio and the chi-square test was used for comparison between groups. The odds ratio (OR) was calculated and the statistical signi cance level was de ned as p < 0.05.

Results
There was no signi cant difference in age (control: 22 (Table 3).   Compared with the control group: * indicates p < 0.05. Compared with the control group: * indicates p < 0.05. PSIS=posterior superior iliac spine. We also investigated whether any abnormal indicators could be attributed to CNP. By calculating the OR, the results showed that the right foot valgus and the sagittal alignment of the body were smaller, the sagittal lower limb alignment and the anterior lower limb alignment were greater than the normal range, and the OR value for neck pain was 6.667, 6.061, 7.125, 0.034, respectively. However, there was no statistical signi cance in other indicators (Table 7). Greater than indicates that the normal range is exceeded, less than indicates lower than the normal range; right high indicates that the right side is high, and left high indicates that the left side is high; ## indicates that the system cannot calculate because the data has a "0" value or is too small. * indicates p < 0.05, and ** indicates p < 0.01. Greater than indicates that the normal range is exceeded, less than indicates lower than the normal range; right high indicates that the right side is high, and left high indicates that the left side is high; ## indicates that the system cannot calculate because the data has a "0" value or is too small. * indicates p < 0.05, and ** indicates p < 0.01.  19 17 Greater than indicates that the normal range is exceeded, less than indicates lower than the normal range; right high indicates that the right side is high, and left high indicates that the left side is high; ## indicates that the system cannot calculate because the data has a "0" value or is too small. * indicates p < 0.05, and ** indicates p < 0.01. Greater than indicates that the normal range is exceeded, less than indicates lower than the normal range; right high indicates that the right side is high, and left high indicates that the left side is high; ## indicates that the system cannot calculate because the data has a "0" value or is too small. * indicates p < 0.05, and ** indicates p < 0.01. Greater than indicates that the normal range is exceeded, less than indicates lower than the normal range; right high indicates that the right side is high, and left high indicates that the left side is high; ## indicates that the system cannot calculate because the data has a "0" value or is too small. * indicates p < 0.05, and ** indicates p < 0.01. Greater than indicates that the normal range is exceeded, less than indicates lower than the normal range; right high indicates that the right side is high, and left high indicates that the left side is high; ## indicates that the system cannot calculate because the data has a "0" value or is too small. * indicates p < 0.05, and ** indicates p < 0.01.

Discussion
The results of the current study showed no statistically signi cant differences in postural indicators other than cervical angle. A prior study by Yip et al. [19] found that patients with CNP hold their head more extended than healthy individuals, and, compared to a healthy population, the sagittal cervical angle is increased, suggesting that the posterior extensor muscles are tense or shortened while the cervical exors are in a passively elongated state. An increase in the cervical angle may therefore be one of the risk factors for the occurrence and development of craniofacial pain, headache, neck and shoulder pain, decreased joint mobility, and muscle stiffness and tenderness [22] . However, the study by Ghamkhar et al. [20] found that forward head posture was not related to neck pain. Another prospective cohort study revealed that a forward head in sitting posture in late adolescence was associated with a reduced risk of persistent neck pain in young adults [23] . This difference may be due to the measurement method. It is worth noting that as the posture of the body changes gradually throughout life, tissue plasticity and adaptability may also contribute to a linear relationship between symptoms and structural changes.
We also showed that the sagittal alignment of the body in students with CNP is signi cantly lower than that in the healthy control group, meaning that the trunk of students with CNP leans more forward than the hips. The forward tilt of the trunk causes the body's center of gravity to move forward, passively elongating the spine's extensor muscles for longer periods. From the perspective of a mechanical lever, the body must increase the corresponding resistance as the torque becomes higher. To balance dynamic torque, the spine extensor muscles, such as the erector spinae and other lumbar muscles posterior to the spine, must generate greater tension, resulting in them becoming overloaded over time. Our results showed that the mean angle of the left sagittal lower limb alignment in patients with CNP was larger than that in the control group and that the left knee joint in students with CNP showed obvious knee exion during quiet, normal standing. This suggests that the patient's knee exor and extensor muscles have a lower ratio or that the hamstring and calf triceps are tense and shortened, and the quadriceps muscle is elongated and weakened in patients with CNP [16,24] . The results of the chi-square test and OR suggests that the decrease of the bilateral sagittal alignment of the body and the increase of the bilateral sagittal lower limb alignment are the risk factors for CNP. Conversely, our results showed that differences in shoulder angle between the two groups were not signi cant, suggesting that the shoulder angle does not contribute to an increased risk of developing CNP.
From the global perspective of anatomical trains or muscle chains, postural balance in the sagittal plane is mainly controlled by a tension-relaxation relationship between the super cial front lines (SFL) and super cial back lines (SBL) [16] . Dysfunction of the SFL can cause the body to lean forward or limit the ability of the body to extend backward. Our study found that patients with CNP leaned their body forward more, increasing the sagittal cervical spine angle, indicating that the SFL is in a shortened and tensed state, while the SBL is elongated. To prevent the trunk from falling forwards, the muscles in the SBL continue to contract and tension increases. Under this "wave effect" in the kinematic chains, abnormal muscle tension and pressure are transmitted caudally and may result in abnormal muscle tension and tightness in the hamstring and gastrocnemius muscles. The cervical vertebrae are the weakest part of the entire spine structure and are more prone to morphological changes in the process of power transmission. The deep front line (DFL) also maintains balance in the trunk and neck. Studies have shown that the muscle strength of the posterior cervical extensor muscles and the deep exor muscles of patients with CNP is lower than those without neck pain [24,25] ; this may explain the knee exion observation in patients with CNP in our study.
We also measured several postural indicators in the frontal plane. The results showed that the rear foot angle and the difference in the length of the lower limbs in the CNP group were larger than those in the control group, while the bilateral anterior lower limb alignments were smaller than the control group. The rear foot angle is an important reference for evaluating ankle valgus. From a global perspective, the cause of this difference may be related to the spiral line (SPL) in the myofascial lines. The SPL functions posturally to wrap the body in a double spiral, which helps to maintain balance across all planes, connects the foot arches with the pelvic angle, and helps to determine e cient knee-tracking in walking.
In a state of imbalance, the SPL participates in creating, compensating for, and maintaining twists, rotations, and lateral shifts in the body [16] . We found that the abnormal link in the posture of students with CNP overlaps with the SPL, including the splenius capitis and cervicis, tibialis anterior, peroneus brevis, and peroneus longus. If we consider the suboccipital muscles that connect to the occipital and the long bones of the tibia that connect the foot bones to be the head and tail of the train, respectively, when the mechanics change in the front of the head, the tail will also change accordingly. This mechanical transmission may explain the occurrence of foot valgus in patients with CNP.
Studies have also shown that knee varus is associated with a decrease in the rearfoot angle and that this can cause adverse effects in the frontal plane of the ipsilateral lower extremity [26] . Our results showed that the knee varus angle of the control subjects was smaller than that of the CNP subjects, which is inconsistent with the results of the aforementioned study. In our study, the sagittal lower limb alignment of students with CNP was smaller than that of the control group, that is, the knee joint was not fully extended. According to the movement characteristics of the knee joint, the force area of the inner side of the knee joint is larger than that of the outer side when fully extended, the tibia is rolled and in torsion relative to the femur, and the knee varus angle is increased at this time [27,28] . We also found that the length difference of the lower limbs in students with CNP was signi cantly higher than that in the control group, which may also have caused the exion angle of the longer leg's knee joint to be larger than the shorter side when the pressure on the two feet is the same. Another possible mechanism is adaptive neuromuscular activity compensation in patients with CNP, but more relevant mechanism studies and larger sample studies are needed to con rm this.
The OR is an indicator of the power of the association between disease and exposure. We demonstrate that the OR values of whether the angle of the sagittal body alignment on both sides was smaller than the normal range, whether the right foot was valgus, whether the angle between the left and right sagittal lower limbs was greater than the normal range, and whether there was neck pain or not, were 6.061, 6.667, and 7.125, respectively, indicating that subjects with trunk exion and rearfoot valgus were more likely to present with CNP. In subjects with normal rearfoot angle, subjects with knee exion were more likely to have neck pain than subjects with normal knee sagittal posture. The OR value of whether the anterior lower limb alignment is greater than the normal range and the neck pain is < 0.034, indicating that knee varus is not a risk factor for neck pain.

Limitations
This study has several limitations that warrant discussion. First. we measured the overall posture but did not conduct in-depth research on the physiological state of the muscles, joints, and other structures (such as muscle strength, hardness, and joint activity), and we did not apply these theories to practice.
Therefore, it is necessary to expand the sample size and include more people in different occupations in future research.

Conclusions
In conclusion, compared to healthy people without neck pain, students with CNP have a larger difference in the length of both lower extremities, a smaller ankle varus angle, a larger knee exion angle, a forward tilt of the pelvis, and an increased extension of the head and neck on the right side. Leaning forward, foot valgus, and knee exion on both sides are risk factors for CNP. Our results indicate that patients with CNP have a more deviant posture in the sagittal plane than healthy people without neck pain, suggesting that restoring the balance of the SBL and SFL will help to treat CNP. From a global postural perspective, strengthening weak muscle groups in the DFL and SPL may improve any dysfunctions in these lines. Meanwhile, tense, shortened muscle groups should be released and lengthened or stretched to improve abnormal posture and restore the mechanical balance to treat patients with CNP and prevent sequelae.

Declarations
Ethics approval and consent to participate The study was approved by the Guangzhou Sport University (IRB approval number: 2018LCLL-12). All methods of this study were performed in accordance with the Declaration of Helsinki. The informed consent document was seen as Supplementary 1.

Consent for publication
We also have obtained the consent from the subject who agreed to publish the images in this paper and signed the informed consent (Supplementary 2).

Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests
All of the authors declare no competing interests.

Funding
This research did not receive any speci c grant from funding agencies in the public, commercial, or notfor-pro t sectors.
Authors' contributions