Scientific Concept of the National Cohort (status ... - Nationale Kohorte

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A.3 Study design
By using triaxial accelerometers physical activity can be measured and classified with good
accuracy and the amount of activity and the related energy expenditure 532 precisely estimated
according to duration and intensity. With the recently introduced technical and analytical
refinements, these devices are partly able to identify different types of activity. Moreover, the
devices can reliably identify time spent engaging in sedentary behaviors. Despite frequent
claims regarding the harmful health effects of sedentary lifestyle, investigators rarely have
directly measured sedentary behaviors, which have usually been defined as the absence of
higher levels of physcial activity 657, 658 .
Sedentary and light activities are better captured by triaxial accelerometers than by one-axial
sensors or self-report 659 . In addition, several analytical techniques are available to convert
the activity measurements to valid estimates of energy expenditure 660, 661 . Past approaches
to integrate measured acceleration over a fixed period of time into dimensionless activity
counts have shown their inherent limitations, i.e., the effect of the interval lengths on the
classification of intensity or the reduced capability to recognize activity patterns. Currently,
innovative research regarding improved algorithms for estimating energy expenditure and
recognizing activity patterns is in progress 662, 663 .
Procedure of measurement:
Modern accelerometric devices are small and lightweight and can be attached to the body
using elastic belts with minimal inconvenience for the participant. The hip is the preferred
place of attachment, as it constitutes the center of the body mass. Devices will be worn for
7 days to cover variation during the week between work days and weekends. In order to
reduce problems with compliance and nonwearing periods, small size and water resistance
would allow the participants to wear the device for 7 days continuously without the need
to take it off. Although two assessment periods of 1 week (spaced 6 months apart) would
be optimal for quantifying physical activity on an individual level, measurement in the cohort
will be restricted to one 7-day period per participant. The device will be explained and
handed over to the participant during the visit at the study center and will be returned by
mail after 7 days of recording.
For selecting the best-suited device; a feasibility study will be conducted. A combined device
with additional features would be desirable.
Step test
Cardiorespiratory fitness as defined by maximal oxygen uptake (VO2max) is usually assessed
during maximal exercise testing. In the step test, VO2max can be extrapolated
from the heart rate response to the preset work load with good precision 664 . Implementing
a submaximal exercise test increases feasibility, avoids having to exclude participants due
to the extensive exclusion criteria of a maximal exercise test, reduces the burden for the
participants, and also saves costs and time and the need for sophisticated instruments, and
qualified personnel.
Procedure of measurement:
A step test is simple, requires little equipment (a heart rate monitor and a stepper) and can
be conducted at every study center with almost no space requirements. A standardized
step test simultaneously monitors heart rate and the increasing workload is defined by a
recorded time signature.
A.3