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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.