Standard reference values of the upper body posture in healthy middle-aged female adults in Germany

In order to classify and analyze the parameters of upper body posture, a baseline in form of standard values is demanded. To this date, standard values have only been published for healthy young women. Data for female adults between 51 and 60 years are lacking. 101 symptom-free female volunteers aged 51–60 (55.16 ± 2.89) years. The mean height of the volunteers was 1.66 ± 0.62 m, with a mean body weight of 69.3 ± 11.88 kg and an average BMI of 25.02 ± 4.55 kg/m2. By means of video raster stereography, a 3D-scan of the upper back surface was measured in a habitual standing position. The confidence interval, tolerance range and ICCs were calculated for all parameters. The habitual standing position is almost symmetrical in the frontal plane the most prominent deviation being a slightly more ventral position of the left shoulder blade in comparison to the right. The upper body (spine position) is inclined ventrally with a minor tilt to the left. In the sagittal plane, the kyphosis angle of the thoracic spine is greater than the lordosis angle of the lumbar spine. The pelvis is virtually evenly balanced with deviations from an ideal position falling under the measurement error margin of 1 mm/1°. There were also BMI influenced postural variations in the sagittal plane and shoulder distance. The ICCs are calculated from three repeated measurements and all parameters can be classified as "almost perfect". Deflections from an ideally symmetric spinal alignment in women aged 51–60 years are small-scaled, with a minimal frontal-left inclination and accentuated sigmoidal shape of the spine. Postural parameters presented in this survey allow for comparisons with other studies as well as the evaluation of clinical diagnostics and applications.


Scientific Reports
| (2021) 11:2359 | https://doi.org/10.1038/s41598-021-81879-0 www.nature.com/scientificreports/ All subjects were healthy and free of musculoskeletal complaints and, therefore, they were not being treated for any conditions. Using a questionnaire, disorders in the musculoskeletal or the temporomandibular system were excluded 46 .
Exclusion criteria were: disorders of the musculoskeletal system which required medication, physiotherapy, osteopathic or orthopedic treatment, or were associated with restrictions of movement, e.g. osteoporosis or spinal disc prolapse. In addition, participants who had traumas or operations in the last two years were not included in the study.
A correlation coefficient of ≥ 0.25 (evaluation according to Evans 47 ) and a power of 80% showing at least a significant weak correlation can be assumed, hence a case number of n = 100 can be expected. All volunteers were healthy (none were patients who were undergoing medical treatment) and informed about the study design before giving written informed consent. The study was approved by the local medical ethics committee of the medical faculty (Goethe-University Frankfurt; No. 303/16) in accordance with the relevant guidelines and regulations and its later amendments (Declaration of Helsinki, 1964).
Measurement system. In order to determine the upper body posture a three dimensional back scan was conducted with the videorasterstereography back mapper "ABW-BodyMapper" (ABW GmbH, Frickenhausen, Germany) (Fig. 1). In the process a defined stripe pattern is projected onto the back surface which is then captured by a camera with a defined angle. The projection has a frequency of 50 Hz and a resolution of 1/100 mm. Through a triangulation technique, a 3D model of the back is obtained and parameters defining the spinal posture are calculated. The scan takes 15 recordings in approximately half a second. The system error is specified as < 1 mm (manufacturer information) and the reproducibility is limited by the calculations of the upper body posture defined by markers directly on the skin (< 0.5 mm). Yi et al. 20 have calculated the intra-and interreliabilies of this measurement system and described it as good in both cases. Furthermore, they also proved the correlation between the Cobb angle via X-ray radiography and the bodymapper of the lordosis and kyphosis angles. They concluded that the accuracy of the data increases with the experience of the investigator who places the landmarks on the back of the subject to be measured. Therefore, an experienced or trained examiner was used for this study.
Twenty-three parameters could be evaluated, grouped into three sections: The first group describes the shoulder area, the second outlines the spine while the third group characterizes the pelvis (Fig. 1). A detailed description of the parameters can be found in Ohlendorf et al. 's 25 methods paper.

Experimental setup.
Subjects were asked to undress their upper body down to their underwear, from the neck down to the lower spine; long hair was tied up and necklaces or other reflective jewelry was removed. In order to standardize the position, an orientation line was placed orthogonally to the scanner on the floor to align the big toes. Six reflective markers were then placed on the skin surface, according to the following defined skeletal structures: vertebrae prominens C7, sacrum point at the beginning of the intergluteal cleft, angulus inferior   25 . Light in the room was dimmed to exclude interference with the scan. Participants were asked to stand in their habitual position, with their arms hanging loosely beside their torso and their line of vision directed straight ahead. Three back scans were performed sequentially to minimize intra-individual measuring errors. Three repeat measurements were taken within 2 min and subsequently averaged.
Statistics. All calculations were performed with Bias 11.08 (Epsilon-Verlag, Darmstadt, Germany). The normal distribution of each parameter was tested by using the Kolmogorov-Smirnov-Test with Lilliefors-correction. Mean and median values were calculated accordingly. Upper and lower limits of the tolerance area (TA) show the normal range with 95% of all values within ± 2SD of the average. In order to determine the range of the mean or median values, a 95% confidence interval (CI) was computed; these data were calculated according to the parametric or non-parametric distribution of the parameters.
Since there was a great heterogeneity of the test persons regarding the BMI, a BMI group comparison was carried out using the Kruskal-Wallis test, followed by a multiple Conover-Iman comparison including Bonferroni-Holm correction of the p-values. The same test procedure was used to compare the sporting activity of the subjects. The significance level was 5%.
Ethics approval and consent to participate. This study was approved by the Ethics Committee (303/16) of the Goethe University Frankfurt am Main. All participants signed an informed consent to participate in advance.

Consent to publish.
All individuals have given their consent to publish their images. Table 1 includes the mean or median values, as well as the tolerance area, confidence interval and Intra-classcorrelation of the three measurement receptions of all parameters.

Results
The Contrary to the shoulder inclination in the frontal plane, the pelvic measurements display an almost symmetrical, even position.
According to the classification of Landis and Koch 48 all ICCs are to be classified as "almost perfect", since the lowest ICC is found at the right scapula angle with an ICC of 0.814. All other ICCs have better values.
BMI group comparison. The BMI group comparison according to the WHO classification of the BMI was compared with the following groups: group 1 normal weight, group 2 pre-obese, group 3 obese and group 4 underweight. www.nature.com/scientificreports/ Significant group differences were found in the sagittal trunk decline (p ≤ 0.001), scapula distance (p ≤ 0.01), kyphosis and lordosis angle (p ≤ 0.001 and 0.01, respectively) and lumbar flexion angle (p ≤ 0.001).
The multiple pair comparison refers to the following group differences in the individual parameters: Physical activity. Based on the information they provided in the questionnaire, the women were divided into four groups with regard to physical activity (1: no regular sport, 2: 1x/week, 3: 2x/week, 4: > 2x/week). The group comparison does not show any significance (p ≥ 0.05). The comparison of subjects who regularly exercise (groups 2, 3 and 4) is also not significant, as is the comparison of active subjects who exercise regularly (n = 26) and those who do not exercise regularly (n = 75) (p ≥ 0,05).

Discussion
In this paper, standard values for the upper body posture are presented for healthy female subjects aged 51-60 years. Before discussing the reference values, it is useful to assess the anthropometric data. In comparison to the German Mikrozensus (the most important annual household survey of official statistics in Germany) from 2013 49 and Mensink et al. 50 , the participants in this study were near to the average for the female population 45,49 especially in height ( Table 2). The BMI in the study group was slightly lower than in the German population as there was a higher percentage of underweight and a lower fraction of obese women in the study group. This can be explained by the high percentage (76.26%) of physical activity carried out by the present subjects; 31.68% of the participants reported to exercise three or more times a week which indicates a high awareness of the importance of a healthy lifestyle and a high level of physical activity. Compared to younger women, aged 21-30 years old and also from Germany 26 , the present subjects were smaller (about 3 cm), heavier (about 6 kg) and had a higher BMI (about 3.92 kg/m 2 ).
With regard to the reference values, it should first be noted that the women participating in this study have an almost ideally balanced, or rather symmetrical, upper body posture. Considering the sagittal plane, the posture is kyphotic on a small scale with the kyphosis angle being greater than the lordosis angle by 7.88°. In detail, the participants´ upper body posture has a small rotational component, with the right shoulder having a higher position than the left while also standing more dorsally, but with the pelvic region being balanced; this www.nature.com/scientificreports/ torsion is limited to the thoracic region. In addition, their spines tilted to the left, on average. The deviations from an ideally symmetrical or balanced position indicated tendencies although these fall mostly within the measurement error range. One factor that affects posture is the BMI. It is noticeable that with increasing BMI, especially the comparison between normal and obese subjects, the sagittal trunk inclination becomes more pronounced (greater forward inclination in the cervical and thoracic spine area), and the kyphosis angle, the lordosis angle and the lumbar flexion angle increase. Compared to the BMI, the frequency of physical activity has no influence on the upper body posture. An increasing BMI is often associated with more muscle mass and also more surface fat. Since this measurement method is a representation of the back surface, these changes are obvious. The approx. 20° larger lordosis and kyphosis angle in overweight subjects must, however, be analyzed in further studies in a more detailed way.
The comparison of age-related changes in upper body posture compared to the young group of female subjects aged 21-30 years 26 shows the following differences: In the shoulder region, the position of the shoulder blades is very similar, except for the distance of the anguli inferior scapula which is wider in the older women by 13.5 mm. The scapular rotation also indicates a slightly further dorsally positioned right shoulder, but to a smaller extent (1.66°). Furthermore, the pelvic rotation is also lower by 1.43°, with the younger women having a mirrored pelvic torsion and overall mirrored rotation. With the last two differences falling under the error margin of 1°, the overall difference is small scaled. Opposed to the shoulder width, the pelvic distance is smaller in the present, older participants by 7.33 mm.
Regarding the spinal column, the axis decline is tilted in the opposite direction by 0.75° which falls under the error margin of 1°. In addition, the older women display a smaller overall rotation by 3.42°, whereas the kyphosis (difference 8.83°) and lordosis (difference of 6.32°) angles are greater, indicating a further curved spine.
There may be several reasons for these differences: a higher mean weight and BMI are observed with increasing age 41 , while a declining muscle mass and strength have also been recorded 36 . These changes could be reinforced by hormonal changes 38 during and after menopause but may also be mitigated by physical activity 51 . Athletic activity has no influence on the body posture, although on the muscular constitution.
The distinctive hormonal balance in postmenopausal women 39,40 may lead to an increasing fat mass or rather changes in fat distribution 41 . Hormonal shifts with an increased androgen level, e.g., testosterone in comparison to estradiol may be linked to a lower fat percentage in the legs and an accumulation of abdominal and visceral fat 43 .
Drzał-Grabiec et al. 40 compared two groups of 130 women of different age decades (group 1:60-90 years, group 2: 20-25 years) in terms of upper body posture. There was an increased thoracic kyphosis in the first group in comparison to the second group, an effect which has also been shown by Kado 52,53 . This effect is often caused by age-related changes in components of the spine, such as a loss of height in intervertebral discs and decreasing elasticity of ligaments. Gong et al. 2019 39 in a study of 226 subjects aged from 20 to 89 years, demonstrated an increase of cervical lordosis and thoracic kyphosis. It was also shown that differences between the genders decrease with age, especially after the 6 th decade in the neck region and after the 7th decade in the thoracic region.
Changes in the lumbar lordosis were more heterogeneous, with ranges from no significant differences between younger and older people 54 to a decreasing lumbar lordosis 55 .
The upper body posture is also an important basis of assessment of life quality 7 . Many age related health problems are tightly interwoven with spinal changes as the shifting of the center of gravity 52 . These changes are often interconnected by compensatory mechanisms, thus the change in one parameter involves the adjustment of another 56 . With the participants of this study having, for example, a more pronounced spinal curvature than the younger group while also being healthy and physically active, the physiological changes of postural parameters with age and their respective classification would allow for assessment and risk analysis. As most professions have a sedentary component, the long-term effects of sitting on the parameters of the spine should be investigated.
Limitations of this study are potential causes of measurement errors and should be taken into consideration; for example lightening conditions, such as highlighted spots due to singular light rays or reflective hair accessories www.nature.com/scientificreports/ (which should be removed before the scan) and extensive dark areas, such as large tattoos or shadows caused by excessive skin folds, can also affect the measurement process 23 .
In addition, the position of the BodyMapper in relation to the participant, or the placing of the reflective markers, can also influence the outcome. However, in this study, the placing was performed according to a standardized procedure 57 by trained examiners. Under the premise of an experienced user of the BodyMapper good inter-class correlations can be demonstrated (Table 1). Additionally, Yi et al. 20 show appropriate intra-and inter-rater-reliabilies. Additional limitations of this study are described and discussed in the preliminary method paper 25,26 .
Further investigations should expand these standard values with data regarding the various sex and age constellations to provide a solid baseline for scientific studies, clinical documentation and therapeutical application. Based on this broad database, it could also be investigated as to how the parameters change with age and sex. According to the influence of sedentary time 32,58 , the proportion of working hours should be investigated further in order to evaluate its effects on posture and links to risk assessment associated with spinal parameters 7,52 .

Conclusion
Overall, the women participating in this study have a balanced upper body posture with a slight tilt to the left in the shoulder and spinal column, as measured by the video raster stereography. Further studies could amend this data by using groups of other ages and genders to observe differences and parallels. Furthermore, the diagnostics of misalignments in upper body posture and therapeutic progress in the treatment of spinal conditions could be evaluated.

Data availability
All relevant data are in the manuscript.

Funding
Open Access funding enabled and organized by Projekt DEAL.