Open Access

Background: Physical inactivity is one of the main risk factors for cardiovascular disease, which remains a major cause of death in Germany and around the globe. Thus, investigating prevalences, population trends, high-risk groups, and intervention effects of physical activity (PA) and sedentary time (ST) is highly relevant to public health. To receive reliable data, a key issue in research is to apply an appropriate study design including the carefully considered use of assessments. Otherwise, bias to PA and ST data may be introduced. The present thesis investigates three often overlooked issues related to the impact of measurement on PA and ST research data. The first aim was to examine whether mere measurement alters PA and ST over the course of twelve months (study 1). The second aim was to identify potential socio-demographic and cardiometabolic moderators of the mere-measurement effect (study 2). The third aim was to present design, protocol, and preliminary results of an interim analysis of a randomized controlled trial (RCT) aiming to test whether a video demonstration of PA intensity levels reduces the lack of agreement between self-reported and objectively measured PA (study 3). Methods: Studies 1 and 2 were based on data of a trial to test the feasibility of a brief tailored letter intervention to increase PA and to reduce ST during leisure time. Among a sample of subjects with no history of myocardial infarction, stroke, or vascular interventions, a number of 175 individuals aged 40 to 65 years participated in the study. At baseline, participants received standardized measurement of blood pressure and waist circumference, blood sample taking, and seven-day accelerometry. At baseline and after one, six, and twelve months, participants completed the International Physical Activity Questionnaire (IPAQ). A random subsample received a brief tailored letter intervention at months one, three, and four. A number of 153 participants were included in study 1 using all available data across 12 months. Changes in PA and ST were analyzed using latent growth modeling. For study 2, baseline and one-month follow-up data of 175 participants were used. Dependence of one-month changes in PA and ST on socio-demographic and cardiometabolic variables was analyzed using linear regression models. In study 3, individuals aged between 40 and 75 years were recruited at a shopping mall in Greifswald, Germany. Participants received seven-day accelerometry and were invited to the cardiovascular examination center of the University Medicine Greifswald. After random allocation to experimental and control group, they completed the selfadministered IPAQ – Short Form via tablet-computer. The experimental group additionally received a video demonstration of PA intensity levels before answering the questionnaire. A number of 131 participants were analyzed to receive preliminary results of an interim analysis in order to verify the presumptions made for the a priori power calculation and to decide on early stopping of the study. The difference between the study groups in the agreement between self-reported and accelerometer-based PA was analyzed using a two-sample t-test. Results: In study 1, results revealed no change in leisure-time PA, an increase in transportrelated PA (p = .023), and a tendency towards a reduction of ST (p = .060) between baseline and one-month assessment. Further, ST decreased between six and twelve months (p = .037). Time trends of the intervention group did not differ significantly from those of the assessment-only group. Results of study 2 revealed that men increased transport-related PA more than women (p = .031) and men with higher triglycerides increased transport-related PA less than men with lower triglycerides (p = .043). Men with higher systolic blood pressure reduced ST more than those with lower systolic blood pressure (p = .028). However, this linear association ceased to exist at a level of approximately 145 mmHg. A similar relationship was found for glycated hemoglobin and ST in men. In study 3, preliminary results of the interim analysis revealed a lower formal mean difference in the video group (M = 21.8 min/day, SD = 108.9) compared to the control group (M = 41.0 min/day, SD = 117.4, t(129) = 0.97, p = .166). The p-value lay between the significance (p < .010) and futility (p > .269) boundaries of the test simulations. Conclusions: Results of the present thesis have three implications for considering the impact of PA and ST assessments in cardiovascular research. First, mere-measurement effects within a feasibility trial were found in transport-related PA and ST suggesting to interfere with potential intervention effects. Thus, measurement effects should be considered when planning studies and interventions and when interpreting outcomes. Second, male sex and more favorable triglycerides levels in men were associated with a higher increase of transportrelated PA whereas worse health in men was associated with a higher reduction of ST. Thus, using the mere-measurement effect for prevention purposes may require researchers and practitioners to tailor PA and ST intervention components to individuals’ health condition. Third, the design and protocol of the RCT seems appropriate to test the effect of a novel video on the gap between self-reported and accelerometer-based PA. Preliminary results point to the efficacy of the video.

Background Long periods of uninterrupted sitting, i.e., sedentary bouts, and their relationship with adverse health outcomes have moved into focus of public health recommendations. However, evidence on associations between sedentary bouts and adiposity markers is limited. Our aim was to investigate associations of the daily number of sedentary bouts with waist circumference (WC) and body mass index (BMI) in a sample of middle-aged to older adults. Methods In this cross-sectional study, data were collected from three different studies that took place in the area of Greifswald, Northern Germany, between 2012 and 2018. In total, 460 adults from the general population aged 40 to 75 years and without known cardiovascular disease wore tri-axial accelerometers (ActiGraph Model GT3X+, Pensacola, FL) on the hip for seven consecutive days. A wear time of ≥ 10 h on ≥ 4 days was required for analyses. WC (cm) and BMI (kg m− 2) were measured in a standardized way. Separate multilevel mixed-effects linear regression analyses were used to investigate associations of sedentary bouts (1 to 10 min, >10 to 30 min, and >30 min) with WC and BMI. Models were adjusted for potential confounders including sex, age, school education, employment, current smoking, season of data collection, and composition of accelerometer-based time use. Results Participants (66% females) were on average 57.1 (standard deviation, SD 8.5) years old and 36% had a school education >10 years. The mean number of sedentary bouts per day was 95.1 (SD 25.0) for 1-to-10-minute bouts, 13.3 (SD 3.4) for >10-to-30-minute bouts and 3.5 (SD 1.9) for >30-minute bouts. Mean WC was 91.1 cm (SD 12.3) and mean BMI was 26.9 kg m− 2 (SD 3.8). The daily number of 1-to-10-minute bouts was inversely associated with BMI (b = -0.027; p = 0.047) and the daily number of >30-minute bouts was positively associated with WC (b = 0.330; p = 0.001). All other associations were not statistically significant. Conclusion The findings provide some evidence on favourable associations of short sedentary bouts as well as unfavourable associations of long sedentary bouts with adiposity markers. Our results may contribute to a growing body of literature that can help to define public health recommendations for interrupting prolonged sedentary periods. Trial registration Study 1: German Clinical Trials Register (DRKS00010996); study 2: ClinicalTrials.gov (NCT02990039); study 3: ClinicalTrials.gov (NCT03539237).