Determinants of adolescent exercise behaviour: the psychological response to exercise.

Rationale: Regular leisure-time exercise is a key contributor to health whereas
a sedentary lifestyle is cited as one of the main
causes of the observed rise in BMI and its related disorders. Despite its
well-known benefits, regular leisure-time exercise behavior
drops from childhood to adolescence and reaches unacceptable low proportions in
adulthood, with the majority of people not
engaging in regular exercise at the recommended level. Current intervention
programs still largely adopt a *one-size fits all*
strategy that assumes that the determinants of leisure-time exercise behavior
are the same across all adolescents, and that they
are mostly of social and environmental origin. This ignores the overwhelming
recent evidence that genetic factors also play an
important role in voluntary exercise behavior. We hypothesize that genetic
effects on the acute mood
responses to exercise are key determinants of adolescent exercise behavior.

1.Test the hypothesis that individual differences in the psychological response
to exercise are the major factors underlying heritability of adolescent
exercise behavior.
1a. establish the heritability of the acute psychological responses during and
after a standardized exercise protocol.
1b Test the causality in the association between the acute psychological
response to exercise and exercise behavior, and establish the contribution of
genetic factors to this association.

This study will include assessment of their exercise ability (aerobic fitness
and muscle strength) and the psychological response to various types of
exercise. In the laboratory protocol all subjects will be tested between 10 pm
and 16 pm. Briefly, the twins/siblings will perform 20 minutes of exercise on
an electrically braked bicycle ergometer and 20 minutes of exercise on a
treadmill ergometer at fixed loads that are typical below the intensity of the
ventilatory threshold for most adolescents. To ensure this, heart rate will be
monitored continuously and load will be adjusted when necessary to keep the
intensity at or below 70% of the estimated maximal heart rate. We will assess
psychological state every 5 minutes during exercise and in a 10 minute
post-exercise period of quiet sitting. In between ergometer and treadmill
testing subjects will perform a standardized test of explosive leg muscle
strength. At the end of the session a maximal exercise test will be used to
establish peak VO2max, which will allow us to convert the absolute workloads to
relative percentages of VO2max for each subject. The all-out test will be
conducted on cycle ergometer with direct measurements of oxygen uptake(VO2)
carbon dioxide (VCO2) output and minute ventilation (VE) as through a
face-mask.

There can be risks associated with laboratory exercise testing in adolescents
with suboptimal health. These adolescents will
be excluded through a detailed anamnesis of both the child and the parents
(children without at least one parent or families who
refuse anamnesis will not be included).
There are no benefits for individual participants whose participation is
completely voluntary. Many subjects participate because
they expect to improve scientific understanding of important research questions
the answer to which may benefit society. In this
study such benefits are the identification of the factors that may predispose,
explain, and protect against the development of low
levels of regular exercise behavior and their negative consequences for BMI and
health in general. In addition, the proposed
research may provide guidance in preventing and intervening these problems. The
benefits of the new scientific information that
will be acquired outweigh the small risks involved in this project.