70 MalinaActivity protocols in studies on CRF and mus-
cular strength and endurance approximated sys-
tematic training. Allowing for variation among
studies, protocols for CRF involved continuous
PA (approx. 80% of maximal heart rate) for 30–45
min, 3 days per week for 12–16 weeks in youth 8
years of age through adolescence [2]. Protocols
for muscular strength and endurance involved
progressive resistance activities incorporating re-
ciprocal and large muscle groups for 30–45 min,
2–3 days per week, with a rest day between ses-
sions, over 8–12 weeks in youth 6 years of age
through adolescence [3].
Individual differences in growth and matura-
tion are confounding factors in evaluating effects
of PA on health. Indicators of interest change
with normal growth and maturation, and several
(bone mineral accrual, CRF, strength, HDL cho-
lesterol and adiposity) have growth patterns
which are variable during adolescence [4]. Sev-
eral studies highlight an important role for PA
during the interval of maximal adolescent growth
that includes peak height velocity. Longitudinal
d at a sug gest en ha nced ef fec t s of PA on bone m i n-
eral accrual [5] and maximal aerobic power [6]
during the interval of maximal growth in both
sexes.
Data dealing with bone health are largely on
prepubertal children (both sexes) and early pu-
bertal youth (primarily girls). Among older ado-
lescents, the inf luence of PA is more variable but
generally positive.
Indicators of cardiometabolic health are cur-
rently of major interest: low HDL cholesterol,
high triglycerides, elevated blood pressures, im-
paired glucose metabolism, insulin resistance,
obesity and abdominal obesity, among others.
The indicators tend to cluster within individuals
and compose the metabolic syndrome. Higher
levels of PA and CRF are independently associ-
ated with favorable metabolic profiles. Adiposity
is an additional independent risk factor; leaner
youth with low central adiposity (waist circum-
ference) have a more favorable profile [7]. Rela-
tionships are stronger for CRF than for PA [8] ,
but interactions of PA and CRF affect profiles [9].
PA interventions favorably alter risk profiles of
overweight/obese youth, but not all individuals
respond in the same manner [10 –1 2]. Beneficial
effects may be reduced or reversed after program
cessation [13].
The preceding is derived from studies on nor-
mal-weight and overweight/obese youth in devel-
oped countries. Obesity is a consequence of an
imbalance between energy intake and expendi-
ture. Evidence dealing with PA of obese youth is
equivocal, but the obese tend to have deficient
movement skills and physical fitness [4]. The re-
sults highlight a need for critical evaluation of
correlates of food intake, PA and physical inactiv-
ity among obese youth. Physical inactivity is a be-
havior independent of PA [1].
Chronic undernutrition, which is common in
many developing countries, is associated w it h re-
duced PA and physical working capacity in
school-age youth [4]. Conditions in many coun-
tries are changing as they experience the transi-
tion from high chronic undernutrition and asso-
ciated mortality from infectious and diarrheal
diseases to increasing prevalence of overweight/
obesity and of morbidity and mortality from
noncommunicable, degenerative diseases associ-
ated with dietary change and reduced habitual
PA.Conclusions- Regular PA favorably influences bone mineral
accrual, CRF and muscular strength and en-
durance - PA has relatively small effects on lipids, and
on adiposity and blood pressures in normal-
weight and normotensive youth, respectively.
A greater amount of PA may be necessary in
healthy youth - Beneficial effects of PA are more apparent
among ‘unhealthy’ youth – on adiposity in the
Koletzko B, et al. (eds): Pediatric Nutrition in Practice. World Rev Nutr Diet. Basel, Karger, 2015, vol 113, pp 68–71
DOI: 10.1159/000360318