*2.1. Participants*

The research on energy expenditure covered 270 students at four police training institutions: two police schools, a police training center, and a police prevention department.

The examination of energy expenditure covered 280 persons trained in 2 Polish police schools and 2 police training centers. The research involved 60 students at the police academy, including 50 men and 10 women; 113 students, all men, trained on specialist courses at the police training center; 47 students at the police school; and 60 policemen trained at the police prevention department.

Due to the small number of women studying in police schools and police training centers, only men took part in the research. Thus, the study covered 50 students of the police academy, 113 students trained in specialist courses at the police training center, 47 students at the police school, and 60 students at the police prevention department. Among the 113 students of the police training center, 74 people were trained on a specialist course for police officers intervening against aggressive and dangerous persons, 18 participated in training for future police dog handlers, and 21 were trained to work in the water police. All students participated in the same theoretical classes and classes on the use of weapons, while the other specialist classes took into account the specificity of the future service in the police.

The research on the students of the police academy and the police school was conducted during typical training activities included in the training plan and covered both theoretical classes in the form of lectures and those related to high physical activity, such as tactics or shooting.

The research was conducted in accordance with the Helsinki Declaration of the World Medical Association and was approved by the Ethics Committee of the Military Institute of Hygiene and Epidemiology (no. 1/XXI 95/2016). Participants received an information sheet about the details of the study, the purpose, and the procedures used as well as potential risks and benefits of their participation.

#### *2.2. Measurement of Height and Weight*

Body height (without shoes) was measured using a portable stadiometer (TANITA HR-001, Tanita Corporation, Tokyo, Japan). Body weight was measured using a bioelectrical impedance analysis (BIA) with the TANITA MC-780 103 device (Tanita Corporation, Tokyo, Japan), with an accuracy of 0.1 kg, according to the procedure specified in the instruction manual (lightly dressed, without shoes). All measurements were performed according to the procedure specified in the instruction manual and without any metal objects.

#### *2.3. Measurement of Energy Expenditure*

The method of analyzing heart rate changes was used to measure energy expenditure. The energy expenditure study included heart rate measurements with a Polar RC3 GPS heart rate monitor (Polar Electro Oy, Kempele, Finland). The values of energy expenditure of the activities performed by the policemen constitute the average value of at least three measurements. The obtained results were the basis for determining the energy demand of policemen in relation to the specificity and nature of training and/or service, as well as for the assessment of the intensity of work, in accordance with the classification given by Lehman (Table 1) [14].

**Table 1.** Classification of work severity on the basis of energy expenditure values for an 8-h working day [6].


#### *2.4. Statistical Analyses*

All statistical analyses were performed using the program R (The R Foundation for Statistical Computing v2.0–1. https://cran.r-project.org, accessed on 20 September 2021). Anthropometric data are shown as mean values ± standard deviation, and differences among experimental groups were analyzed with Student's *t*-test, which were statistically significant when *p* < 0.05. To check the compliance of the variables with the normal distribution, the Shapiro–Wilk test was used, and Levene's test was used for verification of the homogeneity of variance. The differences in the values of energy expenditure of students at individual universities and training centers were calculated using the chi-square test. The data spread is presented in interquartile range (IQR) values.
