The main findings of this paper are that there was no statistical difference between the thoracic kyphosis and the lumbar lordosis in the standing position, while the pelvic forward inclination of the older group is significantly smaller than that of the young group. Thoracic kyphosis, lumbar lordosis, and pelvic forward inclination were significantly different pre and post verbal intervention. In addition, pre and post the intervention in sitting position, the thoracic kyphosis angle and lumbar lordosis angle of the young group were statistically different, and the thoracic kyphosis angle of sitting posture was near zero.
The study of muscle tension in young and older groups found that pre and post the verbal intervention, the left trapezius muscle, left hamstring muscle, left and right soleus muscle, tibialis anterior muscle, and fibula brevius muscle of the two groups showed no significant changes in muscle tension in response to the intervention. In addition, the left and right rhomboid muscles were significantly elongated in young people after the intervention compared with before intervention; the left and right soleus muscles and the left and right quadriceps were significantly shortened. However, only the left rhomboid muscle was significantly elongated in the elderly after the intervention compared with before the intervention.
cervical anterior inclination angle
The increased anterior inclination of the cervical spine indicates the effectiveness of the verbal intervention in both standing and sitting positions. We compared our results with the reference value of cervical anteversion from other studies. The results showed that the cervical anterior inclination 90.67±9.67 degree of the young people in our study was similar to that of Zhu et al. , while the cervical anterior inclination 91.34±9.92 degree of the older people in our study was in contrast with that of Zhou . In addition, the anterior inclination of the cervical spine of the sitting Young is the same as that of Zhou , which is different from what was reported by Hey . This difference may be caused by differences in research methods and within-subjects, because there are obvious differences in the procedures and angle calculation methods of different photogrammetry methods , and even if the data collection methods in the study were similar, the calculation results could be very different .
Previous studies have shown that aging is associated with an increase in cervical anteversion relative to the horizontal direction . Our study shows that the mean value of cervical anteversion is larger in the elderly than in the young, but there is no significant difference between the two groups. This may be caused by differences within the participants. However, Kado et al. found that, like ours, cervical kyphosis decreased significantly in both gender and age groups under 70 years old, and a significant decrease in cervical lordosis curvature was observed in women and young people . In this study, due to the uneven gender distribution of the participants, the gender was not distinguished, but the correlation analysis showed that the cervical anteversion in standing position was significantly and negatively correlated with height, weight, and BMI, but the cervical anteversion in sitting position was not correlated to these anthropometric factors.
Kyphosis angle of thoracic vertebrae
The most obvious and recognizable postural change in the older adult group was an increase in thoracic kyphosis. Our results showed that the 25.42±5.80 degree of thoracic kyphosis in the standing position in the older group was higher than that in the young group (23.28±4.11), but there was no statistical significance. Hu's research results showed that the thoracic curvature of the elderly was 27.5±8.5 degrees and the young group was 23.8±8.5, which were similar to our reference value . In addition, research by Kuo and colleagues also showed that there was no statistically significant difference between the age groups in standing positions . The reason for this phenomenon may be that the older with a significant increase in thoracic kyphosis have other health conditions  and are excluded from the participants. In addition, studies have shown that there is a moderate positive correlation between age and thoracic kyphosis , which is consistent with the results of our correlation analysis.
Thoracic kyphosis is significantly reduced post the intervention in both young and older groups. Although the increase of thoracic kyphosis angle is related to aging, it can be changed through the adjustment of body posture. However, there was no statistical difference in thoracic kyphosis angle between sitting position and standing position. The result of the report in the literature is different from ours. Nishida found that the changes from standing to sitting posture flattened the kyphosis of the thoracic vertebrae , which may be caused by different postural standards or internal differences among the participants. In addition, interestingly, we found that the thoracic kyphosis angle in the sitting position was zero. This may be due to that, under the sitting position, the position of the pelvis on the supporting base was relatively fixed . Without the cooperation of the anteversion of the pelvis, the thoracic vertebrae were straightened for compensation. Long-term fixed posture could lead to an increase in back muscle tension and a series of related disorders such as back pain .
Lumbar lordosis angle
A study has shown that aging is related to the decrease and loss of lumbar curvature . The lumbar lordosis angle of the elderly is significantly smaller than that of the young, and the lumbar lordosis angle of the female is larger than that of the male . The effect of BMI is not significant . However, some researchers found that the reduction of these angles mainly occurred in the middle part of the kyphosis, less in the lumbosacral and thoracolumbar transition, and gender only affected the maximum range of upper body extension . Therefore, the position of the marker point and the definition of the angle will also affect the result. When the same marker point is considered, the reference value of this study result can be used as a reference for body position evaluation in future studies .
Although our research also showed differences between the age groups (7.96±3.14 degrees in the elderly, 9.85±5.73 in the young), the results were not statistically significant. The results of Kuo were the same as ours. They found that the lumbar lordosis angle was 15. 2±9. 3 in the elderly and 16. 0±5. 6 in the young. There was no significant difference between the age groups . In addition, our study was supported by Okpala et al., who found that the lumbar lordosis did not change significantly with age in the normal population . Similarly, our correlation analysis did not show any significant correlation between age, BMI, and lumbar lordosis angle.
In line with the purpose of our study, our results show that the lumbar lordosis angle was significantly increased Post-intervention. The change rate of lumbar flexure in the young and standing was 35.13%, that in older and standing was 41.71%, and that in young sitting was 40.28%, which was higher than the intervention effect of other studies [38, 39]. However, an exception was from Berjano , that they reported the change rate of lumbar lordosis angle of 121.82%.
The results of our study support the hypothesis that increasing the lumbar lordosis curvature by increasing the cervical anterior inclination angle. This practice could be used as an alternative to improving the lumbar curvature by using the pelvic forward inclination angle, especially under sitting conditions. Because the pelvis rotates backward when sitting, the psoas muscle tension decreases , and the lumbar lordosis decreases . Schmidt and colleagues tried to improve lumbar curvature and relieve low back pain by correcting pelvic inclination, but the changes were not statistically significant . In addition, whether in school or at home, school-age children spend more and more time in a sitting posture, and maintaining a sitting posture for a long time will lead to a decrease in lumbar lordosis and thoracic kyphosis . Our study also supports this view, and the results show that the lumbar lordosis angle was significantly reduced in the sitting position compared with the standing position.
Anteversion angle of the pelvis
Our results showed that understanding posture, the pelvic forward inclination were significantly different between the two age groups, and the 22.97±5.01 of young people was significantly higher than that of the older group 9.8±3.22. In addition, the pelvic forward inclination angle was significantly and negatively correlated with age, and BMI, and positively correlated with height. Hu et al. studied asymptomatic Chinese adults and found that the male pelvic inclination was greater than the female in all age groups, and the elder pelvic inclination was greater than the young (young 11.5±7.8, older 14.5±9.5). Another study reported that, in the standing position, the pelvic retroversion angle of the elderly volunteers was larger than that of the young people, and the pelvic retroversion occurred from standing to sitting position . These differences may be linked to age-related spinal degeneration because the thoracic kyphosis angle increases with age and is accompanied by a decrease in pelvic forward inclination to rebalance the spine.
There was a significant difference in pelvic forward inclination pre and post the intervention in standing posture. Some studies have shown that the increase of the anterior inclination of the pelvis is related to the decrease of the cervical angle , which is in line with our results, but because the location of the marker point of the cervical angle in this study is different from that study, when the cervical anterior inclination increases, the anteversion of the pelvis will also increase significantly. In addition, it is reported that the increase in pelvic forward inclination in the standing position may also be related to an increase in lumbar extension . However, some researchers hold the opposite view as they found that the increase of pelvic forward inclination was related to the degree of lumbar lordosis when sitting, but had no relation with the degree of lumbar lordosis when standing . Unfortunately, because of instrument limitations, in our study, we could not measure the pelvic inclination in the sitting position, which may be examined in future research.
Limitations and future research direction
Results of the current study can only apply to healthy people, should not be generalized to populations with back pain and other neuromuscular disorders. In addition, the sample size is relatively small and we could not examine the differences in gender.
Although several studies already explore the relationship between spine angles using external markers, there is still significant variation in the placement of the markers. To optimize the study of different spine angles and to facilitate comparison of the results between different studies, a more standardized method of spine angle analysis is needed.
Despite these limitations, as far as we know, this is still the first study aiming to improve the lumbar lordosis angle by adjusting the position of the head, which can provide a reference for the prevention and treatment of low back pain in the elderly and sedentary groups such as students.