Subjects

At least 200 police officers from a single, federal state police force in Germany are to participate voluntarily in this study. The test persons should be between 18 and 65 years old and work in active service. Since the police service is an extremely diverse profession, with different work demands depending on the department, the planned study focuses on police officers who have a minimum level of physical ability to cope with the given working conditions, for example, wearing up to 20 kg of body protection gear on duty or being routinely exposed to physical confrontations.

Therefore, the subjects will only be included in the study if they are not impaired in terms of performance on the day of the measurement. Prevalent, known musculoskeletal conditions that do not limit the current occupational performance within the units under study do not constitute exclusion criteria. However, excluded from the study would be those police officers who have momentary or permanent occupational performance impairments that do not permit participation in active duty as evidenced, for example, by a certificate of incapacity for work.

An approved ethics application from the Department of Psychology and Sports Science at the Goethe University Frankfurt (No.: 2022-07) has been submitted for the conduct of the study.

Recruitment

The program will be promoted via in-house e-mails from the health department of the respective company and, at the same time, the possibility of registering for the study will be offered. In order to increase the willingness to participate and to clarify any questions in advance, meetings will also be organized with the respective department heads before the start of the studies. An information sheet, which will be posted in the respective departments, will provide additional information about the course of the planned study and the possibility to participate.

Questionnaire survey

The online questionnaire is to be implemented via the SoSci-Survey portal and, thus, made accessible to every participant. The questionnaire is composed of questions from three areas.

Firstly, a modified version of the Nordic Questionnaire (NQ) will be used. This questionnaire was developed by Kuorika et al. [43] in 1987 as part of a project funded by the Nordic Council of Ministers. The questionnaire to be used in this study is based on a reformulated edition of the Federal Institute for Occupational Safety and Health (BAuA) and is currently still being tested. The BAuAquestionnaire differs from the original version by Kuorinka et al. (1987) in that the questionnaire logic has been changed and an additional body region (the lower leg) has been subdivided. However, the questionnaire on which this work is based is oriented towards the original nine body regions designated in the version of the Federal Institute for Occupational Safety and Health (BAuA) and included in the questionnaire translated into German [44]. Corresponding illustrations are also used from the BAuA version. However, some of the questions deleted by Liebers et al. (2021) from the BAuA modified version have been reinstated for the questionnaire used in the present study’s questionnaire. The questionnaire also asks about functional limitations, whether a physician has been consulted within the last 12 months and whether sick leave has been taken due to existing complaints, for example, in addition to the 12-month and 7-day prevalence of MSDs in the relevant body regions [45]. Current studies in the field of occupational medicine and ergonomics use numerical rating scales in the examination of musculoskeletal pain [35, 36]. Therefore, a modified version of the NQ, supplemented by a numerical rating scale, will also be used in the planned examination. The numerical rating scale (NRS) (0–10) rates the severity of the complaints to the individual body regions. A scale of 0 means no pain while a score of 10 means worst pain imaginable.

This makes it additionally possible to differentiate the disorders with regard to the intensity of the complaints. Furthermore, the officers interviewed should be given the opportunity to express an assumption about the cause of the complaints within a free text field, for example, due to the body protection equipment worn on duty. The validity, reliability and sensitivity of the NRS to changes in pain have been rated as high [46,47,48].

Secondly, the questionnaire contains the German version of the Copenhagen Psychosocial Questionnaire (COPSOQ), a self-assessment questionnaire for recording psychosocial factors at the workplace. The COPSOQ was first presented and successfully used in Denmark by Kristensen et al. [49] in 2005; it has also been classified as valid and reliable and is independent of language. The validity and reliability also applies to the German version [50] which has been shortened for the planned survey due to time constraints (questions that were too unspecific for the police service were deleted). Thus, the German version corresponds to the recommendation of Nübling et al. [51] who first examined the translated version of the Danish original in Germany in 2006. The COPSOQ has already been used with various occupational groups such as teachers [37], nurses [38], researchers in mental health [39] and the general Dutch working-age population (n = 55,950) [40].

In this questionnaire, both the work-related stresses/strains and complaints are recorded. Different dimensions are surveyed here, such as the demands of work (quantitative, emotional, work-privacy conflicts), the influence and development opportunities, other work-related factors (work environment, insecurity and conditions), social relations and leadership (feedback, predictability, leadership quality, role clarity, role conflict, sense of community, support at work), as well as the impact of the former dimensions (job satisfaction and engagement, general health, burnout symptoms, presenteeism). The COPSOQ contains response categories ranging from “to a very high extent” to “to a very low extent,“ and the description of the frequency from “always” to “never/almost never”. A high score implies a high degree of the assessed condition.

[49][50][51]The Operational Police Stress Questionnaire (PSQ-Op) is a psychometrically based questionnaire that is used to measure the stress factors of police work [41, 42]. This was developed by McCreary and Thompson in 2006 and is a psychometrically based questionnaire to measure the stress factors involved in police work [41, 42, 52, 53]. The original 20-item questionnaire has been shortened to five relevant questions for this study, with a numerical rating scale (0–7; 0 = no stress at all, 7 = a lot of stress) offered here as response options. Thus, the version to be used in this study is a translation of the Operational Police Stress Questionnaire.

Furthermore, ten questions related to the sample group and four general questions related to the person will be used. In addition, an expert interview consisting of experienced male and female police officers,, as well as newcomers to the profession, will be conducted for the purpose of occupation-specific adaptation. Questions related to the subject collective refer to questions concerning the body protection equipment, the side of the body and the localization (hip/thigh) of the service weapon carried. Moreover, the present sporting activity of the police officers (professional and recreational) are to be recorded. In the same way, the recording of the individual’s state of health is to be taken into account by indicating any previous musculoskeletal disorders and service injuries.

The questionnaire will be created online via the SoSci Survey server. A pretest on students of the police academy will be carried out to check the practicability and quality of the questionnaire. In the pretest, in addition to the regular answering of the questionnaire, comments on the individual pages should be possible in order to note remarks and any difficulties in understanding. Based on the pretest, the questionnaire will be adapted if necessary.

Three-dimensional back scan

The Bodymapper (ABW GmbH, Frickenhausen, Germany) will be used for the three-dimensional measurement of the dorsal upper body posture. Using video raster stereography, the back is optically recorded at a frequency of 50 Hz and a resolution of 1/100 mm at a distance of 90 cm. The system error is specified as < 1 mm (manufacturer’s specification) and the reproducibility is limited (< 0.5 mm) by the calculations of the upper body posture which is defined by markers (retroreflective stickers) directly on the skin. The intra- and inter-reliability of this measurement system is described as good [54]. Furthermore, Yi et al. [54] have also demonstrated a correlation between the Cobb angle (by using radiography) and the lordosis and kyphosis angles (by using the body mapper). However, the accuracy of the data was found to increase with the experience of the examiner who placed the six predefined landmarks (cervical vertebra C7, rima ani, caudal apex of the left and right scapula, and the spina iliaca posterior superior anterior left and right) on the back of the person being measured. Therefore, an experienced examiner will be used for this study.

Finally, twenty-three evaluation parameters to be used in the proposed study have been grouped into three sections: the shoulder, spine and pelvis area (Fig. 1). A detailed description of the parameters can be found in the methods paper of Ohlendorf et al. [32, 55].

Fig. 1

Representation of (A) the image of the camera, (B) the calculated phase image and (C) the matched image from A + B. The three-dimensional back scan is shown in d)

Measurement protocol

Prior to the examination, each participant will generate a four-digit code which is used both at the beginning of the questionnaire survey and for the three-dimensional back measurements in order to record the subject data pseudonymously.

Both series of measurements should take place within one hour on the same day. For the back measurement, three measurement repetitions will be carried out that will be averaged for the statistical evaluation.

All collected data will then be transferred to the statistical program SPSS and saved anonymously as a data set.

Statistical data analysis

Only those questionnaires that have been fully completed will be included in the questionnaire’s evaluation. The data formatting will be carried out via Excel. The questionnaires will be checked for plausibility in the answering behavior. The back measurement data will also be checked for measurement errors and only complete data sets will be included in the evaluation. All data will be evaluated in SPSS Statistics 26 (IBM Deutschland GmbH, Ehningen, Germany).

For the evaluation of the results, the data will be tested for normal distribution while descriptive procedures for sample characterization will be applied and calculated for all variables, taking socio-demographic characteristics into account. The respective response categories are coded into numerical values, based on the assumption that the characteristics are measured metrically, even though the data are ordinally scaled. This is a common procedure in research practice and is much discussed in the literature; it is based on a scale-theoretical assumption that may be accepted if the content hypothesis is empirically confirmed [56]. Depending on the outcome, parametric tests for normal distribution will be used or pseudo normalization will be achieved by a rank transformation of the data. In addition, methods of interference statistics as well as correlation calculations are to be applied. The significance level will be set at 5%. Single items which collect psychosocial workloads factors will be summarized to a new variable in analogy to the dimensions defined above. Responses for each item will be oriented so that higher values implicate a higher psychosocial workload related to the respective dimension. Cronbach’s Alpha will be applied to measure internal consistency of the new index. Based on this, logistic regression will be performed, while the models will be adjusted for important confounders such as age, sex and the extent of physical exercise/sport. A Bonferroni correction will be applied to counteract multi comparison effects.

Hypothesis 1

The overall MSD score and the 15 MSD scores per zone are compared with the MSD scores of the general German population [4]. To counteract differences in the gender distribution, the test will be performed for both sexes individually.

Hypothesis 2

A Pearson correlation will be used to determine the correlation between the 9 dimensions of the three questionnaires and the MSD scores.

Hypothesis 3

A Pearson correlation between the PSQ-Op and dimensions of the NQ and COPSOQ will be performed.

Hypothesis 4

A MANOVA test will be performed between the three questionnaires with respect to gender.

Hypothesis 5

A Pearson correlation between the MSD score for the shoulder and neck and the upper body asymmetry value derived from the video raster stereography is calculated to test the relationship between the MSD score and upper body posture.

Hypothesis 6

A Pearson correlation between age and MSD score will be conducted.