Research indicates that overweight children respond differently both physically and emotionally to
exercise than do children classified as normal weight [13–17]. Excess body fat confounds the
relationship between aerobic fitness, which is measured by maximal oxygen consumption (VO2
max) and age in both male and female children [15]. Thus, excess fat weight serves as a deterrent
to exercise and body movement in general [18–22]. When overweight children are compared with
normal-weight children during submaximal exercise, they exhibit higher cardiopulmonary values
for a given work rate. It is not well understood whether this increase in cardiopulmonary stress per
given work rate is a result of reduced physical activity patterns in obese children, the metabolic
consequences of the excess weight, or the effect of the additional weight on the modality of exercise.
Maffeis and others [14] reported that the cardiopulmonary responses were significantly lower in
17 nonoverweight children than in 23 overweight children during walking and running on a treadmill
at different intensities. This study used the measure of percentage of ideal body weight (%IBW)
to classify subjects as overweight or nonoverweight. The average %IBW was 138.3% in the
overweight children and 95.5% in the nonoverweight children. The study concluded that walking
and running demanded greater energy expenditure in overweight children when compared with
non-overweight children, and more importantly, that overweight children expended more energy
moving their bodies than did nonoverweight subjects. However, this finding differed from the results
in a study by Rowland and others [23]. In this study, heart rate values were not significantly different
between the nonoverweight and overweight subjects while walking at 3.2 mph, 8% grade, and
approximately 97% of VO2 max. Because the intensity of exercise was so close to maximal levels,
these results should be interpreted as such. Interestingly, Loftin and others reported that increased
body mass was associated with lower maximal heart rate in youth [24].
Studies using cycle (non-weight bearing) as opposed to treadmill (weight bearing) ergometry
have yielded conflicting results. Cooper et al. [25] examined the oxygen uptake response in a sample
of 18 overweight children ranging in age from 9 to 17 years during cycle ergometry. The authors
reported normal 02 kinetic responses when moving from rest to exercise. However, the overweight
children had significantly prolonged response kinetics when ventilation (VE) and carbon dioxide
output (VCO2) were observed. The authors concluded that overweight children might have normal
fitness levels for their individual stages of development. Their findings should be interpreted cautiously,
however, because responses may be different during cycle ergometry, as opposed to treadmill,
when the excess body weight of the overweight subject is supported. This is evident when the results
of Maffeis and colleagues are considered [26]. They reported that VO2 max expressed in absolute
values in overweight children was significantly greater than in non-overweight children during
treadmill testing, but not significantly different during cycle ergometry. However, when VO2 max
was expressed relative to fat-free mass, no differences were observed between overweight and
nonoverweight subjects during either walking or cycling protocols [14]. The authors suggested that
overweight children experienced no limitation in maximal aerobic power during weight-bearing or
non-weight-bearing exercise. However, submaximal exercise results were not discussed [21].
Zanconato et al. [27] reported that VO2 max expressed in milliliters per kilogram per minute
was significantly greater in nonoverweight than in overweight children. However, in absolute terms,
VO2 max L/min was not significantly different between the two groups. In the same study, the
performance run time and maximal work rate were also significantly lower in the overweight
compared with the nonoverweight. Loftin and colleagues previously reported that when VO2 max
values are adjusted for total body weight in children a significant bias results [28]. Thus, reporting
VO2 max in absolute values or per kilogram of lean body weight reduces this bias. Allometric
scaling techniques may also be applied to reduce weight bias. As a result of this bias, and because
more research is needed on the obese child’s response to aerobic exercise, pediatric health care
professionals should use caution when interpreting exercise testing results.
ENERGY COST OF LOCOMOTION
The energy cost of locomotion can be described as the metabolic cost or actual energy expenditure
needed to complete a task. As a result of their excess weight, obese children may have a greater
metabolic cost or energy expenditure for executing the same physical activity than does a normalweight
child. This greater cost of locomotion may explain why obese children may not perform as
well as nonobese children during aerobic tasks [8]. In a study by Volpe and Bar-Or [29], the energy
cost of walking was examined in obese and lean adolescent boys who were matched for total body
mass. At the slow and moderate speeds, the obese and lean boys displayed similar energy cost. At
the fastest speed, however, the obese adolescents displayed an energy cost that was 12% higher
than the lean adolescents. Moreover, total body mass rather than adiposity explained a higher
percentage of the variance in energy cost during all the walking speeds.
Wasteful movements, particularly observed in the gait patterns of obese children, also increase
the energy cost of locomotion [8]. Hills and Parker [30] observed the gait patterns of normal weight
and obese prepubertal children while walking at different velocities on a level surface. Even when
the velocity was set at a comfortable pace, the obese children displayed a significantly lower cadence
of steps per minute compared with the normal weight children. During the faster, and especially
slower, speeds, obese children had even more difficulty walking.
McGraw et al. [31] examined differences in gait patterns and postural stability in obese and
nonobese prepubertal boys. Similar to the study by Hills and Parker [30], the obese boys displayed
a significantly lower cadence, slower gait cycle, and reduced time in the swing phase, compared
with the nonobese boys. With regard to postural stability, greater sway areas were observed,
especially in the medial/lateral direction, in the obese boys. The authors concluded that this greater
sway area was a result of the excess weight rather than postural instability [31]. Although these
studies demonstrate that abnormal gait patterns may increase energy cost during exercise in obese
children, it is unknown whether weight loss will reverse this observation.
MUSCLE STRENGTH
Strength training is defined as the use of a series of progressive resistance exercises to improve an
individual’s ability to exert muscular force against a resistance [32]. Investigators suggest that if
properly administered, resistance-training programs may not only be safe but may also help reduce
the risk of injury during other physical activities in children [3,32–35]. In addition, a safe resistancetraining
program will develop and prepare the muscles for sport and competition [32,36]. However,
few studies have examined the obese child’s response to strength training. Sothern and colleagues
have shown that the inclusion of regular resistance training in a program to prevent and treat
pediatric obesity in preadolescent children is not only feasible but also safe and may contribute to
increased retention at 1 year [33,34]. In another report, a meta-analysis examined 30 childhood
obesity treatment studies that included an exercise intervention [37]. Significant improvements in
body composition were associated with programs including high-repetition strength training in
conjunction with moderate intensity aerobic exercise. Thus, the combination of high-repetition
resistance training, moderate aerobic exercise, and behavioral modification may be most efficacious
for reducing body fat variables in overweight children. However, pediatric health care providers
should be careful when recommending strength training to obese children. The American Academy
of Pediatrics separates the terms resistance and strength training from the terms weight lifting,
power lifting, and body building [4,35] and supports properly supervised strength/resistance training
programs as safe methods for strength development in preadolescent children. The developing
musculoskeletal system of the preadolescent child must be considered when designing resistancetraining
programs. The intensity and duration of an individual resistance exercise bout (set) must
be appropriate to the level of maturity of the growing bones and muscles [33]. Pediatric obesity is
associated with advanced bone age and increased bone and muscle density [10]. This may provide
an advantage to obese children when participating in strength training, especially as research
indicates that the enhancement of strength associated with resistance training is not accompanied
by increased muscle size in prepubertal children [38].
Several agencies have published resistive training guidelines for preadolescent children
[3,4,34,35,39,40]. Trained professionals should consult these guidelines before designing a program
specific to their patients’ or students’ needs. Table 6.1 provides general guidelines for resistance
training in children and adolescents [8].
Strength training may provide additional benefits and advantages to obese children. Most
strength exercises are performed while the body weight is supported. In especially severely overweight
youth, this may enhance performance because although the excess fat weight is supported,
the accompanying increased muscle and bone weight will enable more force to be generated. More
research is needed; however, it appears that strength/resistance training may be used safely to
enhance the efforts to prevent and reverse childhood obesity in clinic-based interventions.
MOTOR PERFORMANCE
Fundamental motor skills (FMS) are critical to participation in most physical activities [41]. Okely
and others [41] examined the association between FMS proficiency and body composition among
children and adolescents. The following six FMS measurements were assessed: run, vertical jump,
catch, overhand throw, forehand strike, and kick. Body composition was assessed by waist circumference
and body mass index. An inverse linear association was observed between the overweight
youth’s ability to perform FMS and degree of overweight. Moreover, the overweight youth were
twice as likely as the nonoverweight ones to be in the lowest FMS quintile [41]. Similar results were
also observed when Graf and colleagues [42] examined the correlation between body mass index
and gross motor development in first-grade children (mean age 6.7 years). In the overweight/obese
children, body mass index was inversely correlated with gross motor development and endurance
performance. Thus, excess fat weight may negatively affect the fundamental motor skill performance
of some children. Pediatric health care professionals should provide opportunities for obese children
to participate in activities that both consider and improve impaired fundamental motor skills.
RATING OF PERCEIVED EXERTION
The rating of perceived exertion (RPE) scale designed by Borg [43] is a method of determining
the intensity of subjective effort. Using a number scale from 6 to 20, individuals can rate their
feeling of exertion. For instance, 6 is no exertion at all, whereas 20 is maximal exertion. Marinov
et al. [44] examined ventilatory efficiency and the rate of perceived exertion in obese and nonobese
children during standardized exercise testing. Sixty children, 30 obese and 30 nonobese, ages 6 to
17 years, matched by age, sex, and height, participated in a modified Balke treadmill test. During
standardized work rates, the obese children noted RPEs significantly higher than the nonobese
children. This higher RPE may be attributed to a higher aerobic cost of exercise, which was also
displayed [44]. Bar-Or and colleagues have also observed similar results in work not yet published
[Bar-Or, unpublished].
Ward and Bar-Or examined the use of the Borg scale in exercise prescription for obese children.
The authors [45] found that obese children were able to reproduce exercise intensities when prescribed
to them as numbers on the RPE scale. They did, however, use a narrower range of prescribed
intensities than those available to them. On the cycle, the children overestimated their choice of
low intensities and underestimated their choice of high intensities. During the walking/running
exercises, the children overestimated their choice of all the prescribed intensities [47]. These studies
indicate that obese children may perceive that certain exercises are difficult and perhaps too
challenging. This may, in turn, inhibit their motivation to increase physical activity. However, more
research is needed to support these observations.
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