The National Physical Activity Survey was ordered by the Estonian Ministry of Culture. The target population of the survey were permanent residents of Estonia aged 15 to 69 years. According to data of Statistics Estonia, 926,798 people of the required age group lived in Estonia on January 1, 2015 . In the selection of the study group, the proportional model of the population was used, in which all have an equal opportunity of becoming a respondent. Afterwards, the socio-demographic structure of the sample in the breakdown of gender, age, ethnicity and place of residence with the corresponding statistical characteristics of the Estonian population was compared and adjusted if necessary. The initial sample consisted of 1768 respondents, who were visited in their homes by TNS Emor interviewers during September 14 and October 4, 2015. In total, 1004 subjects agreed to participate in the survey. The interviewers were educated to use a tablet, which was pre-programmed with the interview questionnaire. The face-to-face Tablet Assisted Personal Interviewing (TAPI) was conducted for data collection. In TAPI, the interview questions appeared on the tablet screen and the answers of a study respondent were inserted in the computer program by an interviewer immediately during the interview, which permits immediate surveillance of the interviewing process. Interviewers asked no guiding questions during the interview.
The study participants self-reported their age, body height and weight (for calculation of body mass index – BMI kg/m2); educational level (basic or primary, general secondary or vocational, higher); occupation (top manager/manager, professional/specialist/clerk, skilled worker/machine operator/driver; pupil/student; retired; other); monthly income per family member (low – below 300€, average – 301€–550€, over average – over 551€, no income/refused to answer), and place of residence (capital city, town > 35,000 inhabitants, town 3000-35,000 inhabitants, village/rural area).
For the assessment of self-reported LTPA, the LTPA domain of the last seven days interview version of The International Physical Activity Questionnaire (IPAQ-L) was applied . Since the IPAQ-L has not been used in Estonia before the present study, the English version of the questionnaire was translated into Estonian. In the translation process, relevant guidelines and recommendations were taken into account . IPAQ-L was developed and validated at the beginning of the 2000s [13, 14] and is considered a national and international standard for PA surveillance in several countries. The IPAQ-L version provides information about the time spent in and intensity of PA for different domains (occupation, transportation, home, leisure time). Compared to other domains, IPAQ studies have shown the highest validity for LTPA [15–17]. In the present study, the LTPA domain (6 items) of IPAQ-L was used. Respondents were asked to report the frequency and duration of walking, moderate and vigorous intensity LTPA performed for at least 10 min per LTPA session during the last 7 days. Moderate activities were defined as activities with a temperate increase in respiration and heart rate (for example: brisk walking, Nordic walking, bicycling at a regular pace, swimming at a regular pace, doubles tennis). Vigorous activities were defined as activities with a significant increase in respiration, heart rate, and sweating (aerobics, running, fast bicycling, or fast swimming). Energy expenditure was expressed as metabolic equivalents of task (MET) multiplied by the time in minutes per week for walking, moderate and vigorous activity, and for the total LTPA (MET minutes per week). One MET corresponds to 3.5 ml O2 × kg−1 × min−1.
For LTPA items (walking, moderate and vigorous), weekly and average time per day was calculated. 90 subjects were excluded due to confounding or missing data (reporting LTPA in more than 7 days a week, or refused). The final sample for LTPA prevalence analysis was 914 (373 men).
Age was categorized into five groups (15–24 years, 25–34 years, 35–49 years, 50–64 years, and 65–69 years) for both genders.
According to BMI, the study subjects were categorized as ‘underweight’– BMI < 18.5, ‘normal weight’ – BMI 18.5–24.9, ‘overweight’ – BMI 25.0–29.9, and ‘obese’ – BMI >30.0 . Due to the unbalanced men/women ratio 1:17 in ‘underweight’, this group is not presented in the figures. For subjects aged 15–17 years, population-based age-adjusted criteria for BMI categorization were applied .
According to WHO recommendations, at least 150 min of moderate-intensity aerobic PA or 75 min of vigorous-intensity PA throughout the week is recommended for adults aged 18–64 years . For adolescents, the WHO PA recommendation encompasses accumulation of at least 60 min of moderate-vigorous PA in every day of the week . As there are no separate recommendations for LTPA and former research has shown that European adults are mostly physically active during leisure time , the WHO PA recommendations were used as a criterion for achieving a sufficient LTPA level. The latter approach has been implemented in earlier studies concerning LTPA [16, 19]. Regarding achievement of WHO PA recommendations, a dichotomized variable (meeting/not meeting) was created. To meet regularity and accumulation of moderate to vigorous LTPA in adults, the variable had to meet the following criteria: 1) 30 min of moderate LTPA per day on at least 5 days of the week; 2) accumulating 150 min of moderate LTPA per week with LTPA reported on at least 3 days of the week; 3) accumulating 25 min of vigorous LTPA on at least 3 days of the week; 4) a combination of moderate and vigorous LTPA on at least 3 days of the week with a total duration 150 min/week. In adolescents, accumulation of at least 60 min of moderate-vigorous LTPA in every day of the week was regarded as adherence to PA recommendations .
Statistical analyses were carried out with the Statistical Package for the Social Sciences – SPSS, 22 (IBM, Armonk, NY, USA). To characterize the study sample, descriptive data – n, percentage (%), mean, SD, median, 25th and 75th percentile – were calculated. All LTPA distributions were skewed to the right. The unpaired t-test for parametric data and the Mann–Whitney U-test for nonparametric data were used to determine the differences between the groups. The chi-square (χ2-test) test was used to determine significant differences in proportions between the groups. Multinomial logistic regression analysis was conducted to reveal associations between achievement of PA recommendations and age groups, and BMI categories. In age groups the youngest group and in BMI categories the normal BMI category were set as reference groups. For all statistical analyses, the 0.05 level of significance was applied.