obese adolescents demonstrated that cardiovascular morbidity was significantly
increased compared with lean adolescents [1–4]. The effect of adolescent obesity
on adult morbidity and mortality seems to be independent of the effects of
adolescent obesity on adult weight status [2]. There are different periods during
which the risk of obesity is increased: early infancy, adiposity rebound in the
period of pre-pubertal growth and adolescent growth phase [5]. Risk factors
and life-style factors associated to development of obesity in childhood are well
identified [6, 7]: family history of obesity, diet, physical activity, mother education,
TV watching. Both dietary and activity patterns result to be responsible
for the increasing prevalence of obesity in childhood [8] and, at least, relationship
between obesity and these factors reflect the principle of energy balance.
Weight maintenance results from equivalent levels of energy intake and
energy expenditure: both these factors are likely targets for obesity prevention
and therapy programs, although physical activity provides the main source of
plasticity in energy expenditure, even among children [9].
Management of the increasing epidemic of obesity in young people must
include prevention strategies concerning nutrition education and physical activity
programs. It is also important to underline that obese children often suffer
discrimination, and it is imperative that treatment does not contribute to this
problem.
Effects of Physical Training in Obese Children
Physical activity is likely to protect from development of obesity, and some
Authors have suggested a role in increasing resting metabolic rate (RMR), that
constitutes 60–75% of daily energy expenditure. It has been demonstrated [10],
that physical exercise appears to influence resting energy expenditure in man; at
contrast, other Authors [11], showed no difference in RMR, overnight metabolic
rate (OMR), and sleeping metabolic rate (SMR), at the beginning and after a
training program. Furthermore, other authors demonstrated: (1) a relationship
between energy expenditure for activity (EEAct), level of activity and adiposity
in a group of 9-year-old boys with different body composition: time spent on
sedentary activities was proportional to fat mass percentage [12]; (2) in freeliving
conditions obese children have a higher total energy expenditure (TEE)
than non-obese children, and the energy expenditure for physical activity is significantly
higher in obese children [13]; (3) energy expenditure assessed by indirect
calorimetry during walking and running at the same speed of exercise is
significantly greater in obese than in control children, in both boys and girls, with
a larger respiratory response to exercise in obese subjects [14], and (4) maximal
aerobic capacity while running and cycling measured by oxygen consumption
(VO2) and carbon dioxide production in obese and non obese prepubertal children,
was significantly higher in obese children for the treadmill test, with this
difference disappearing when VO2max was expressed per kg fat free mass [15].
In a recent study the adjusted VO2 peak values for mass and stature was similar in
obese and normal-weight girls, suggesting that the obese were not impaired in
the pumping capacity of the heart, and in extraction of O2 at the cellular level [16].
The aforementioned data suggest that physical activity is more expensive
for obese than for non obese children, and that the magnitude of workload prescribed
in a physical activity program for obesity therapy, should be designed
to increase caloric output, rather than improve cardiorespiratory fitness.
Many Authors have studied the influence of physical training on RMR,
suggesting an increase of RMR during physical training [17], or indicating an
unaltered RMR [18].
In the study of Broeder et al. [19] RMR, expressed in absolute terms, or
relative to fat-free weight (FFW) remain unchanged after an extended period of
training: in this study physical training was accompanied by a small decline in
dietary intake. In a recent meta-analysis, [20] it has been evaluated how exercise
training influences the composition of diet-induced weight loss: the percentage
of weight lost as fat-free mass for diet-plus-exercise (DPE), subjects
was approximately half of that for dietary-restriction-only (DO) subject of the
same sex. This meta-analysis provides evidence that exercise training reduces
the amount of body weight loss as fat-free mass during diet-induced weight
loss. To better understand the efficacy of training in the management of childhood
obesity, Blaak et al. [21] studied the effect of training on total energy
expenditure and spontaneous activity outside the training hours in obese boys,
demonstrating that an added physical activity leads to an appreciable increase
in the overall energy expenditure of obese children even though there are no
measurable changes in spontaneous physical activity: training stimulated the
energy expenditure during the non-exercise part of the day.
Controlled physical training, without dietary intervention, was studied by
Gutin et al. [22] in a group of black obese 7- to 11-year-old girls: the physical
training group showed a significant improvement in aerobic fitness and a significant
decline of 1.4% body fat, demonstrating that physical training, without
dietary intervention, could improve fitness and body composition of obese girls.
The interindividual variation in the response of body composition on physical
training was studied by Barbeau et al. [23], who were able to demonstrate, in a
group of 71 obese children aged 7–11 years, decreased body fat, increased fatfree
soft tissue, bone mineral content, and bone mineral density mainly in boys
with lower energy intake and more vigorous activity, ethnicity not being correlates
to the changes in body composition. In another study [24], bone density
increased during the period of physical training while no difference was found
for dietary intake of energy, suggesting that regular exercise also without dietary
intervention can enhance the body composition in children with obesity (table 1).
Obese children are likely to have high level of visceral adipose tissue
(VAT). Owens et al. [25] studied the impact of controlled physical training, without
dietary intervention, on VAT in obese children: during physical training
obese children were capable of participating to a high intensity physical training
over a 4-month period, accumulated significantly less VAT as compared with
non-exercising controls, and experienced other beneficial changes in total and
regional body composition (table 2).
Physical training demonstrates his efficacy also on modifying cardiovascular
parameters in obese children. Furthermore, physical training can shift
hearth-period variability (HPV)-derived indexes of cardiac autonomic function
in the direction of less sympathetic activity and greater parasympathetic activity,
supporting the idea that the training program was effective in enhancing cardiovascular
fitness [26]: physical training, in these series, alters cardiac autonomic
function favorably by reducing ratio of sympathetic to parasympathetic activity.
Cardiac parasympathetic activity (PSA) measured by HPV was also studied
[27] in relation to total body and visceral adiposity in obese children demonstrating
that regular exercise that improved fitness and body composition had a
favorable effect on PSA in obese children.
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