Pediatric Exercise Science, 2013, 25, 548-560
© 2013 Human Kinetics, Inc.
Official Journal of NASPEM and the
European Group of PWP
www.PES-Journal.com
Aerobic Fitness
and Physical Activity in Children
Neil Armstrong
University of Exeter
In Volume 1 of Pediatric Exercise Science (PES), a paper by Fenster
et al. (25)
.
investigated the relationship between peak oxygen uptake (peak VO2) and physical activity (PA) in 6- to 8-year-old children. They used both questionnaires and
large-scale
integrated activity monitors (LSIs) to estimate daily PA and determined
.
peak VO2 using an incremental treadmill test to volitional exhaustion. They con.
cluded that peak VO2 correlated well with PA as measured by LSIs but commented
that questionnaire
weakly and nonsignificantly associated with
. data were only
.
LSI and peak VO2 data. Peak VO2 and PA are the most researched and reported
variables in the 25-year history of PES. Yet, the assessment and interpretation of
young people’s aerobic fitness and PA remain problematic and any meaningful
relationship between them during childhood and adolescence is shrouded with
controversy. The present paper uses Fenster et al.’s (25) report as an indicator
of where we were 25 years ago, outlines how far we have advanced since then,
and suggests future directions of research in the study of aerobic fitness and PA.
In the first volume of PES, Fenster et al. (25) investigated. the relationship between
6- to 8-year-old children’s peak oxygen uptake (peak VO2) and physical activity
(PA). Five boys and. 13 girls participated in the study and their data were pooled
for analysis. Peak VO2 was determined during an incremental treadmill test to
voluntary exhaustion and PA was estimated using both questionnaires and largescale integrated activity monitors (LSIs). On the .basis of a significant interclass
correlation coefficient of r = .59 between peak VO2 and the log of LSI average
counts per. hour Fenster et al. (25) concluded that “aerobic capacity, as measured
by peak VO2 correlated well with physical activity as measured by LSI” (p.134).
They also commented that questionnaire
. data were only weakly and nonsignificantly associated with LSI and peak VO2 data.
.
Young people’s peak VO2 and PA are the most researched and reported variables
in. the 25-year history of PES and yet the assessment and interpretation of peak
VO2 and PA and any meaningful relationship between them during growth and
maturation are still shrouded with controversy. The present paper uses Fenster
et. al.’s (25) work as an indicator of our understanding of young people’s peak
VO2 and PA in 1989, briefly reviews what we know in 2013, and suggests future
directions of research.
The author is with the Children’s Health and Exercise Research Centre, University of Exeter, UK.
548
Aerobic Fitness and Physical Activity 549
Peak VO2
.
The term aerobic capacity
is now seldom used to refer to peak VO2, as capacity has
.
no time base. Peak VO2 is usually described
. as a measure of maximal aerobic power
or, more generally, aerobic fitness. Peak VO2, the highest rate at which oxygen can
be consumed during exercise, is widely recognized as the best single measure
of
.
and
a
young people’s
aerobic
fitness.
Aerobic
performance
is
limited
by
peak
V
O
2
.
high peak VO2 is a prerequisite of elite performance in many sports but it does not
describe all aspects of aerobic fitness (10). Other components of aerobic fitness
during youth are less well documented and there are few data on normal values or
time trends so this paper will initially
reflect on the variables measured by Fenster
.
et al. (25) and focus on peak VO2.
.
Peak or Maximal VO2?
Over 60 years ago, Astrand (15) documented that the majority of young people
completed
. an exercise test to volitional exhaustion without demonstrating the plateau in VO2 conventionally associated with the achievement of maximal oxygen
uptake
in adults. Fenster et al. (25) acknowledged this by using the term peak
.
VO2(which was becoming increasingly popular in the pediatric literature at that
.
time) to describe the children’s ‘aerobic capacity’ whether they achieved a VO2
plateau or not. They used an incremental treadmill test and exercised the children
until they could no longer continue despite constant verbal encouragement.
It was
.
concluded that, ‘while reaching maximal oxygen
uptake
(V
O
),
as
evidenced
2max
.
by HR > 200 bpm,
. RER >1, and plateauing in VO2, is difficult in 6- to 8-year-old
children, peak VO2 measurements can be obtained’ (25, p.134). This conclusion
has subsequently been supported by studies which exercised children at treadmill
gradients 2.5–7.5% greater than those achieved
in an initial incremental test to
.
exhaustion. No differences in the peak VO2 attained
across the two protocols
.
was observed, suggesting that a maximal value
of VO2 can be achieved during an
.
incremental test despite the absence of a VO2 plateau (13, 40).
It is challenging to obtain genuine maximal efforts from
young children and
.
of
6- to 8-year-olds.
Fenster et al. (25) were one of the first to report the peak
V
O
2
.
They investigated the test-retest reliability of peak VO2 and noted no significant
difference between the two tests and a reliability.coefficient of 0.67. Support for the
viability of rigorous determination of the peak VO2 of young children. has recently
emerged with a report of the successful determination of the peak VO2 of ~84%
of 792 children aged 6–7 years (21). Within the study, a test-retest analysis
of 20
.
children was undertaken and a typical error of measurement of peak VO2 between
tests
. 5 or 7 days apart of 0.02 L/kg was observed. The authors reported boys’ peak
VO22 to be 11% higher than that of girls confirming the importance of not pooling
boys’ and girls’ values and analyzing data in relation to sex even at a young age (21).
Exercise protocols have been refined over time and with the development of online systems capable of breath-by-breath respiratory gas analysis and sophisticated
electronic cycle ergometers protocols where power output is increased linearly with
time (ramp exercise) have become popular. Ramp protocols are often preferred because
other parameters of aerobic function such as gas exchange thresholds .and respiratory
gas kinetics can be determined in the same test. Young people’s peak VO2 determined
550 Armstrong
using a ramp test has been shown to be as reliable as that determined in tests using
more traditional protocols
. with a typical error across three tests of ~4% (52). With a
ramp test a plateau in VO2 at exhaustion is an infrequent occurrence and commonly
used secondary criteria, such as those used by Fenster et al. (25), cannot unequivocally
validate a maximal effort. However, the use of a follow-up constant workload test at
105% of the maximal power output achieved during the ramp test can confirm whether
a maximal effort has been elicited (16). This methodology is currently becoming widely
adopted with children across a broad range of aerobic fitness (39).
.
Peak VO2 During Growth and Maturation
.
Current knowledge of peak VO2 during growth and maturation is summarized in
the following paragraphs and reviewed and extensively referenced elsewhere
(8).
.
Cross-sectional data show an almost linear increase in boys’ peak VO2 (L/min)
with age and a similar but less consistent
. trend in girls’ values, with some studies
indicating a leveling-off
. in girls’ peak VO2 from ~14 years. Longitudinal data indicate that girls’ peak VO2 increases by ~50% from 11 to 17 years with. boys’ values
almost doubling over the same age range. On average, boys’ peak VO2 values are
~10% higher than those of girls at age 10 years and the sex difference reaches ~35%
by
. age 16 years. Muscle mass is the dominant influence in the increase in peak
VO2 through adolescence and this probably accounts for much of the sex difference
during the late teens, perhaps supplemented
by boys’ greater .blood hemoglobin
.
concentration. Why boys’ peak VO2 is higher than girls’ peak VO2 before puberty
is still not clear. There appear to be no significant sex differences in maximal heart
rate (HR) but evidence from studies using Doppler echocardiography suggests that
maximal stroke index is higher in boys than in girls although whether this is due
to differences
. in cardiac size and/or cardiac function remains to be proven (8).
Peak VO2 is correlated with body
. mass and this is conventionally controlled
for during growth by dividing peak VO2 by body mass and expressing it as the ratio
ml/kg/min as in Fenster et al.’s (25) paper. Tanner (46) pointed out the statistical
limitations of this methodology in 1949 and subsequent papers in the early 1970s
corroborated his concerns (e.g., 31) but. inappropriate use of this ratio in reporting
.
and analyzing young people’s peak VO2 has persisted
(50). When peak VO2 is
.
reported in ratio with body mass, boys’ peak VO.2 is essentially unchanged from
age 8–18 years at ~48 ml/kg/min and girls’ peak VO2 progressively
. declines from
~45–35 ml/kg/min over the same age span. Expressing peak VO2 in ratio with
body mass is of interest in the context of health and well-being and sports where
.
body mass is moved but it has clouded physiological understanding of peak VO2
during growth and maturation.
With body mass appropriately controlled for using
.
allometry boys’ peak VO. 2 increases through childhood and adolescence into young
adulthood. Girls’ peak VO2 increases at least into puberty and possibly into young
adulthood. Longitudinal studies using multilevel modeling have shown that, in
conflict with the conventional (ratio scaling) interpretation, in addition
. to age both
growth and maturation independently and positively influence peak VO2 (e.g., 11).
Are Today’s Young People Fit?
The case for a relationship between aerobic fitness and health and well-being during
youth is well documented (e.g., 19) but how fit should children be? Health-related
Aerobic Fitness and Physical Activity 551
.
threshold levels of peak VO2 have been proposed (e.g., 17). There is, however,
.
little compelling evidence to support the existence of a threshold level of peak VO2
which is associated with either youth health or future adult health.
Few studies have reported data in sufficient detail to estimate the prevalence of
young people who fall below proposed thresholds and there is no compelling evidence
.
to suggest that the current generation of young people have low levels of peak VO2.
A reanalysis of large data sets from my laboratory in relation to the health thresholds
proposed by an expert group from the European Group of Pediatric Work Physiology
[35 ml/kg/min for boys and 30 ml/kg/min for girls] (17) revealed that of 164 untrained
prepubertal children none fell below the threshold (7). Of 220 untrained 11- to 16-yearolds, 3% of the boys and 3% of the girls fell below the threshold (14).
Are Today’s Young People Less Fit Than Previous Generations?
.
An analysis of studies which have assessed young people’s peak VO2 over the last
50 years shows a consistency over time which is quite remarkable considering
that these studies have been performed in different laboratories
. using different
equipment, testing protocols and staff. A review of the peak VO2 data of American boys from the 1930s
. through the 1990s and girls from the 1960s through the
1990s noted that peak VO2 had remained relatively stable among
. boys of all ages
and in young girls. In girls in the 15–19 years age group, peak VO2 was observed
to increase from the 1960s–1970s and then fall back toward 1960s values over the
next two decades (22). Similarly, a systematic review of data of more than 4,000
9- to 17-year-olds from
. five countries over the period 1962–1994 reported a small
mean change in peak VO2 (ml/kg/min) of ~0.1% per decade (10). More recent large
studies of both children (21) and. adolescents (11) support these reviews and show
no apparent reductions in peak VO2. These reports are revealing and consistent but
they are not epidemiological studies and only provide
. a series of local snapshots of
volunteer participants into temporal trends of peak VO2. There are wide variations
within studies of healthy young volunteers, with
. typical coefficients of variation of
~15%, and elite young athletes present peak VO2 values ~50% higher
. than their
untrained peers. Nevertheless, as a population young people’s peak VO2 seems to
have remained stable over
. several decades.
In contrast to peak VO2 data, there are large sets of data on 20m shuttle run
(20mSRT) performance which indicate a temporal decline of ~4% per decade since
1975 in young people’s maximal aerobic performance. 20mSRT performance is
strongly influenced by the body mass the participant carries over the distance run
and it has been shown that increases in body fat over time explain ~50–70% of the
temporal decline in 20mSRT performance (10).
Physical Activity
Fenster et al.’s (25) study used both subjective and objective techniques of estimating
PA and noted only a weak, nonsignificant relationship between the two methods.
They hypothesized that the weak association between LSI and questionnaire data
may be due to the questionnaire data reflecting a whole year whereas LSI data
were collected for only 1 day. For a true picture of PA some account must be taken
of day-to-day variation and most recent studies have monitored PA for at least
552 Armstrong
3 days. It has, however, been recommended that 4–9 days of monitoring, including
2 weekend days might be the minimum period required for a reliable estimate (47).
Fenster et al. (25) did not comment on the (in)activity of the children in relation to health and well-being, probably because evidence-based PA guidelines
were not well-established at the time. Since the publication of Volume 1 of PES
numerous critical reviews comparing and contrasting methods of measuring PA
during youth have been published (e.g., 1). Expert committees have developed
guidelines with which to interpret PA in relation to health and well-being (e.g.,
45) and the PA patterns of young people across the world have been extensively
documented using both subjective (e.g., 28) and objective methodology (e.g., 27).
Current knowledge is briefly summarized in the following sections and reviewed
and extensively referenced elsewhere (24)
Measurement of Young People’s Physical Activity
Even before the publication of Volume 1 of PES more than 30 different methods
of measuring PA had been described (33). Measurement tools and techniques have
been further developed but all current instruments have deficiencies and no single
method can capture all aspects of PA. Some studies have attempted to overcome this
by simultaneously employing more than one method but, as noted by Fenster et al.
(25), correlations between subjective and objective methods are at best low to moderate.
Subjective measures of estimating PA are subject to recall bias and are influenced by the ability of the respondent to accurately recall relevant activities retrospectively. This limitation is particularly pertinent with children who tend to be
less time conscious than adults are and less able to provide details of specific events
from the past. Nevertheless, although there are substantial errors in estimating an
individual’s PA several large, well-designed multinational surveys have provided
insights into young people’s PA at a population level (e.g., 28).
Physiological sensors such as HR monitors have been used to estimate PA
since the early 1970s and were used extensively in the1980s and 1990s (e.g., 3)
until generally replaced by motion sensors as the monitor of choice. Physiological
sensors do not directly measure PA but they can provide clinically relevant data
with which to evaluate relationships between PA and health-related behavior.
Pedometers have been used to monitor PA since the 1920s although Leonardo
da Vinci is reported to have designed a pedometer to measure distance by counting steps somewhat earlier (43). In recent years accelerometers have become the
motion sensor of choice. Data from accelerometers are normally collected over
a specific time period (epoch) and reported as counts per minute (cpm) which
are then converted into estimates of the intensity of PA. The optimum epoch and
appropriate cut-off point with which to describe PA are; however, currently subjects
of intensive research programs. Despite a lack of consensus over interpretation of
data, the ongoing development and application of accelerometers has provided real
advances in understanding young people’s PA (e.g., 27).
Are Today’s Young People Active?
The benefits of regular PA on the health and well-being of youth are well-established
(45) but the precise amount of PA appropriate to optimize beneficial health outcomes
is less clear. The earliest PA guidelines for young people were published by the
Aerobic Fitness and Physical Activity 553
American College of Sports Medicine and based on recommendations for adults
(2). But the first evidence-based PA guidelines, complete with supporting reviews,
were published in a 1994 special issue of PES (41). Subsequently, a number of
public health authorities have endorsed PA guidelines for youth and despite criticism
of the interpretation of the underlying evidence base (48) there is general support
that “school-age youth should participate daily in 60 min or more of moderateto-vigorous physical activity that is developmentally appropriate, enjoyable, and
involves a variety of activities” (45, p.732).
Several large, multinational surveys of young people’s PA have been supported
by the World Health Organization and, although the subjective data collected must
be viewed with caution, the general population trends in relation to PA guidelines are
consistent. More boys participate in moderate-to-vigorous PA (MVPA) than girls do,
with the sex difference being more marked in comparisons of participation in vigorous
PA. The amount of PA experienced by both sexes declines as they move through adolescence. Data from a survey of more than 72,000 13- to 15-year-olds from 34 countries
indicate that self-reported levels of PA from developing countries are lower than levels
from North America and Europe (28). Taken together, recent data on self-reported PA
indicate that between 60% and 70% of youth do not satisfy current PA guidelines (35).
Objective measurement and observation of behavior has established that the
majority of bouts of children’s PA last between 3 and 22 s which makes it difficult
to assess and interpret health-related PA. Using accelerometry the inconsistent use
of cut-off points and epoch lengths confound the quantification of the prevalence of
young people who satisfy PA guidelines. The proportion of young people reported to
meet PA recommendations ranges from 1 to 100% depending on the cut-off points
used to define the intensity of PA. A review of 35 studies of European young people’s
PA illustrates the issue (27). The authors commented that all of the data reviewed
were collected using the same type of accelerometer and that this may enhance
comparability of the findings. They reported 78–100% of participants to meet PA
guidelines with a cut-off point of more than 1,000 cpm applied, 36–87% to meet
recommendations with a cut-off point of more than 2,000 cpm, 3–9% to comply with
a cut-off point of more than 3,000 cpm, and 1% to meet PA guidelines with a cut-off
of more than 4,000 cpm applied. The selection of epoch length also influences the
interpretation of data. A difference of 62% has been reported in the time preschool
children spent in MVPA when a 5-s epoch was compared with a 60-s epoch (49).
Despite the difficulties in interpreting data across studies a consistent trend is
that more boys meet recommendations defined by cut-off points more than 2,000
cpm, more than 3,000 cpm, or more than 4,000 cpm than girls although a decline
in the amount of PA with age is not as readily apparent as with subjective data.
The review underpinning the International Olympic Committee (IOC) consensus
statement on the health and fitness of young people through physical activity and
sport concluded that less than 25% of young people satisfy current PA guidelines
using a cut-off point of 3,000 cpm (equivalent to brisk walking; 35).
Are Today’s Young People Less Active
Than Previous Generations?
Large surveys from the US (34), Australia (37) and Europe (42) have concluded that
there is no clear evidence of young people becoming less active from ~mid-1980s to
554 Armstrong
~mid-2000s. These data are supported by studies using pedometers (38), accelerometers (36), and HR monitors (51), which have reported no change or an increase
in PA over time. Following their critical review of the literature the IOC expert
group concluded that although data on temporal trends in PA should be interpreted
cautiously young people’s PA levels seem to have stabilized at least over the last
two decades (35).
.
Peak VO2 and Physical Activity
Seliger et al. (44) were probably
first to objectively estimate PA and compare it
.
to directly determined peak VO2. They estimated the PA of 11 12-year-old boys
.
using 1 day HR monitoring and found no significant relationships with peak VO2.
More comprehensive studies, including at least 3 days of PA monitoring, have
consistently supported
. this finding and observed weak or no significant relationships between peak VO2 and PA.
HR monitoring studies of 10–16 year olds from the UK (n = 325) reported
no
.
significant correlations between either moderate or vigorous PA and peak VO2 (4, 9).
A similar study of 82 Swedish
. 14–15 year olds observed no significant relationships
between MVPA and peak VO2 in either boys or girls. This study observed weak
. but
significant correlations between ‘activity-related energy expenditure’ and peak VO2 in
both boys and girls but after controlling for
. body fat and maturation none of the PA variables were significantly related to peak VO2 in boys. Highly active boys were compared
.
with the rest of the boys and no significant difference was observed in peak VO2 (23).
A study of 248 Swedish 8- to 11-year-olds used accelerometers to estimate PA
and reported that multiple forward regression analysis
. showed vigorous PA to explain
9% and mean daily PA 1% of the variability in peak VO2 (20). Similarly, a study of 592
Danish. 6- to 7-year-olds noted sustained periods. of PA to explain 9% of the variance in
peak VO2 (21). The relationship between peak VO2 and PA of 424 nonoverweight and
473 overweight, 4- to 19-year-old, Hispanic Americans was explored through generalized estimating equations. The strength of the relationship was observed to be .generally
low to moderate accounting for a small percentage of the variation in peak VO2 (18).
A longitudinal investigation of over 200 children used multilevel modeling to
examine age, sex, and maturation influences
on PA, from 11 to 13 years. With the
.
primary variables controlled for peak VO2 was introduced as an additional variable
and a nonsignificant parameter estimate was recorded (12). Kemper and Koppes
(32) analyzed longitudinal data from participants in the Amsterdam Growth and
Health
. Study. They reported a 30% increase in HPA score and a 2–5% increase
in VO2. max but noted that the functional implications were small and concluded
that, ‘if we take into account that the relationship calculated with autoregression
over the period of 23 years resulted in nonsignificant relationships, we must admit
that
. in this observational study no clear relation can be proved between PA and
VO2 max in free-living males and females’ (32, p. 163).
1989–2013
Since 1989 we have become
. much better informed about the appropriate assessment
and interpretation of peak VO2 and we have a comprehensive, although not complete,
Aerobic Fitness and Physical Activity 555
.
understanding of the development of peak VO2 during growth and maturation. There
is no compelling
. evidence to suggest that as a population. young people have low
levels of peak VO2 or that they have lower levels of peak VO2 than young people of
previous generations did. Nevertheless, as most health-related and sporting activities involve moving
. body mass an increase in body fatness without a corresponding
increase in peak VO2 is a cause for concern in the context of young people’s health
and well-being.
Huge strides have been made in the technology underpinning PA monitoring and evidence-based health-related PA guidelines have been developed and
regularly refined. Consistent trends, regardless of methodology, are that more
boys than girls satisfy PA guidelines and the prevalence of young people satisfying PA guidelines falls with age in both sexes. Inconsistent interpretation of
intensity thresholds confounds data describing the percentage of youth who are
deemed sufficiently active. Self-report data suggest 30–40% of young people
meet current PA guidelines whereas accelerometry data indicate that they are
achieved by less than 25%. Evidence from studies using both self-report and
objective methodology suggests that PA has not declined during the last two
decades.
Future Directions
Aerobic Fitness
When considering children’s PA patterns, spontaneous play, and participation in
most organized games we are concerned with intermittent
. exercise and rapid changes
.
in exercise intensity. Under these conditions peak VO2 and steady-state VO2 are
variables of investigative convenience rather
than
.
. factors underpinning behavior. It
is the transient kinetics of pulmonary VO2 (pVO2) which best describe the relevant
component of aerobic fitness. Furthermore, unique insights into physiological function rest in the transient
or non-steady-state response to a forcing exercise regimen.
.
In addition, the pVO2 kinetics time constant (τ) can be used as a proxy measure of
muscle phosphocreatine (PCr) kinetics and therefore a noninvasive window into the
metabolic activity of the muscle and a means of understanding exercise metabolism
.
during growth and maturation (6). Current knowledge of young people’s pVO2
kinetic responses is briefly outlined in the following paragraphs and reviewed and
comprehensively referenced elsewhere (5).
At the onset of a step transition from rest to moderate exercise (i.e., .intensity
< the lactate threshold, TLAC) there is an almost immediate increase in VO2 measured at the mouth. This phase (Phase I) is associated
. with an immediate increase
in cardiac output and is .independent of muscle VO2. Phase I is followed by. an
exponential increase in pVO2 (Phase II or the primary component) that drives p VO2
to a steady-state (Phase III). Phase II is described by its τ and the shorter the τ the
smaller the anaerobic contribution to the step change in exercise intensity. During
a step change to heavy exercise (i.e., intensity >TLAC but <critical power [CP])
Phases I and II are similar to those observed in the moderate exercise domain
. but
in Phase III the oxygen cost increases over time as a slow
component of pVO2 is
.
superimposed and the achievement of a steady state in pVO2 is significantly delayed.
556 Armstrong
.
During a step change to very
heavy exercise (i.e., intensity >CP but <peak
VO2)
.
.
the slow component of pVO2 rises rapidly with time and reaches
. peak VO2. A step
change
to
an
exercise
intensity
which
requires
a
projected
pV
O2 at or above peak
.
VO2 is classified
as severe exercise.
.
The pVO2kinetic responses of adults
have been researched for over 40 years
.
and the interactions
between
peak
V
O
,
TLAC,
CP, the primary τ, and the slow
2
.
component of pVO2 in describing performance and responding to training have
been well-documented (e.g., 30).. Rigorously determined and appropriately analyzed data on young people’s pVO2 kinetic response to step changes in exercise
intensity in relation to specific exercise domains are sparse. Current data suggest that children are characterized by a faster Phase II τ for moderate, heavy,
and very heavy exercise compared with adolescents and adults. Little is known
about responses to severe exercise. Boys’ primary component τ is faster than
that of girls during step changes to exercise intensities >TLAC but not during
moderate
exercise. During exercise of intensity >TLAC, boys show a truncated
.
pVO2 slow component.compared with girls. During exercise intensities >TLAC,
the magnitude of the pVO2 slow component is reduced and the oxygen cost during
Phase II is higher in young people than in adults but the end-exercise total oxygen
cost is. similar to that of adults. No relationship has been demonstrated between
peak VO2 and the τ of the primary component in either children or adolescents
(5).
.
Future research questions include the following: Is the faster Phase II pVO2
kinetics in children indicative of a faster muscle oxygen delivery and/or a greater
potential for oxidative metabolism in children compared with adults? Why are
there sex differences during the step transition to heavy
intensity exercise but not
.
moderate intensity exercise? Are observations of pVO2 kinetic responses consistent
with an age-related decline in percent of Type I muscle fibers and in accord with
boys having a higher percent of Type
I fibers than similarly aged girls? What are
.
slow
component?
Is the lack of relationship
the mechanisms underlying
the
pV
O
2
.
.
.
between the τ of the pVO2 kinetics and peak VO2 during youth due to. peak VO2
being primarily dependent on oxygen delivery to the muscles whereas pVO2 kinetics
is more dependent on oxygen utilization by the muscles? Is the exercise domain
important. in the relative contribution of oxygen delivery and oxygen. utilization
to peak VO2 kinetics during youth? Does maturation exert an effect on pV
. O2 kinetics
independent of age and body size? How close is the coupling between pVO2 and PCr
kinetic profiles in young
people at the onset and offset of exercise of different intensi.
ties? Is children’s pV
O
kinetics
trainable? If so, what are the relative responses of. the
2
.
Phase II τ and the VO2 slow component in relation to changes (or not) in peak VO2?
What is. the optimum exercise prescription to speed up the t and/or reduce the size
of the VO2 slow component?
These and many other questions require evidence-based answers. The recent
application of technologies such as magnetic resonance spectroscopy, near-infra
red spectroscopy and electromyography to studies of breath-by-breath analyses of respiratory gas kinetics provide appropriate tools. The introduction of
experimental models such as priming exercise, work-to-work transitions, and
manipulation of pedal rates to pediatric exercise studies (6) provide intriguing
avenues for future research into aerobic fitness and developmental exercise
metabolism.
Aerobic Fitness and Physical Activity 557
Physical Activity
PA guidelines for young people have evolved over the last 25 years but are they
optimum? Twisk (48) critically reviewed the literature linking PA with skeletal,
cardiovascular, and psychological health seeking dose-response relationships
or threshold values. He concluded that where there is evidence of a relationship
between PA and health outcomes there is only limited evidence of a particular
pattern of that relationship. More research is required.
There is no consensus on the interpretation of accelerometry data. The percentage of young people reported to meet PA guidelines varies from 1 to 100%
according to the cut-off point used (27). It has been suggested that the use of multiple cut-off points might represent a reasonable compromise until a consensus is
reached (24). But, what is the appropriate cut-off point(s) to represent MVPA? Are
the same cut-off points applicable throughout growth and maturation? Consistent,
rigorous methodology and calibration techniques need to be developed if we are to
understand fully the interpretation of data from accelerometers and their application
to PA during childhood and adolescence.
Recent advances in engineering technology have stimulated the emergence
of highly sophisticated motion sensors with the potential to revolutionize PA data
collection and analysis. It is envisaged that nonintrusive sensors located at multiple
sites on the body and in the environment will be coordinated into a single system
with the data storage and analytical capacity to enable monitoring and interpretation of PA over extended periods of time (29). The most fruitful future direction of
research in PA epidemiology therefore appears to lie in the application of emerging
technology but as Intille et al. (29) point out: “to maximize the effect of physical
activity measurement research being conducted today, investigators must expect
and plan for change so as to fully exploit the potential of the new devices on the
horizon” (29, p.S31). Regardless of the inevitable change in the tools available
to study PA best practices need to be researched and firmly established and it is
interesting to note that one of the coauthors of Fenster et al.’s (25) paper is still at
the forefront of developments (26).
Evidence suggests that
. PA during childhood and adolescence is at best only
weakly related to peak VO2. This is not surprising as young people’s PA seldom
includes exercise
. of the duration and intensity necessary to enhance or even maintain their peak VO2. The emergence of better methods of. assessing and interpreting
PA and components of aerobic fitness other than peak VO2 provides opportunities
for investigating further the elusive relationship between PA and aerobic fitness
during growth and maturation.
Conclusion
Fenster et al.’s (25) exploratory paper in Volume 1 of PES predicted the direction
of much of the research published in the first 25 years of PES. Many of the papers
published in the subsequent 24 volumes of PES have made significant contributions to the advancement of our knowledge of exercise physiology during growth
and maturation. Innovative techniques and technologies have been developed and
their application to the exercising child is opening up numerous opportunities
for further research. Which papers published in PES Volume 25 will provide the
558 Armstrong
inspiration and platform for new discoveries in developmental exercise physiology
over the next 25 years?
References
1. Adamo KB, Prince SA, Tricco AC, Connor-Gorbor S, Tremblay MA. Comparison of
indirect versus direct measures for assessing physical activity in the pediatric population:
A systematic review. Int J Pediatr Obes. 2009; 4:2–27. doi:10.1080/17477160802315010
PubMed
2. American College of Sports Medicine. Physical fitness in children and youth. Med Sci
Sports Exerc. 1988; 20:422–423. doi:10.1249/00005768-198808000-00022
3.Armstrong N. Young people’s physical activity patterns as assessed by heart rate
monitoring. J Sports Sci. 1998; 16(Suppl):S9–S16. doi:10.1080/026404198366632
PubMed
4. Armstrong N, Balding J, Gentle P, Williams JR, Kirby BJ. Peak oxygen uptake and
physical activity in 11 to 16 year olds. Pediatr Exerc Sci. 1990; 2:349–358.
5. Armstrong N, Barker AR. Oxygen uptake kinetics in children and adolescents: A review.
Pediatr Exerc. Sci. 2009; 21(2):130–147. PubMed
6. Armstrong N, Barker AR. New insights in pediatric exercise metabolism. J Sport Health
Sci. 2012; 1:18–26. doi:10.1016/j.jshs.2011.12.001
7. Armstrong N, Kirby BJ, McManus AM, Welsman JR. Aerobic fitness of prepubescent
children. Ann Hum Biol. 1995; 22:427–441. doi:10.1080/03014469500004102 PubMed
8. Armstrong N, McManus AM, Welsman JR. Aerobic fitness. In: Paediatric Exercise
Science and Medicine, 2nd ed., N Armstrong and W Van Mechelen (Eds.). Oxford:
Oxford University Press, 2008, p. 269–282.
9.Armstrong N, McManus AM, Welsman JR, Kirby BJ. Physical activity patterns
and aerobic fitness among pre-pubescents. Eur Phys Educ Rev. 1996; 2:7–18.
doi:10.1177/1356336X9600200103
10. Armstrong N, Tomkinson GR, Ekelund U. Aerobic fitness and its relationship to sport,
exercise training and habitual physical activity during youth. Br J Sports Med. 2011;
45:849–858. doi:10.1136/bjsports-2011-090200 PubMed
11. Armstrong N, Welsman JR. Peak oxygen uptake in relation to growth and maturation
in 11- to 17-year-old humans. Eur J Appl Physiol. 2001; 85:546–551. doi:10.1007/
s004210100485 PubMed
12. Armstrong N, Welsman JR, Kirby BJ. Longitudinal changes in 11-13-year-olds’ physical activity. Acta Paediatr. 2000; 89:775–780. doi:10.1111/j.1651-2227.2000.tb00384.x
PubMed
13. Armstrong N, Welsman JR, Winsley RJ. Is peak VO2 a maximal index of children’s
aerobic fitness? Int J Sports Med. 1996; 17:356–359. doi:10.1055/s-2007-972860
PubMed
14. Armstrong N, Williams J, Balding J, Gentle P, Kirby B. The peak oxygen uptake of
British children with reference to age, sex and sexual maturity. Eur J Appl Physiol.
1991; 62:369–375. doi:10.1007/BF00634975 PubMed
15. Astrand PO. Experimental Studies of Physical Working Capacity in Relation to Sex
and Age. Copenhagen: Munksgaard, 1952.
16.Barker AR, Williams CA, Jones AM, Armstrong N. Establishing maximal oxygen
uptake in young people during a ramp cycle test to exhaustion. Br J Sports Med. 2011;
45:498–503. doi:10.1136/bjsm.2009.063180 PubMed
17. Bell RD, Macek M, Rutenfranz J, Saris WHM. Health indicators and risk factors of
cardiovascular diseases during childhood and adolescence. In: Rutenfranz J, Mocellin
R, Klimt F, editors. Children and Exercise XII. Champaign, Il; Human Kinetics; 1986,
p.19-27.
Aerobic Fitness and Physical Activity 559
18. Butte NF, Puyau MR, Adolph AL, Vohra FA, Zakeri I. Physical activity in nonoverweight and overweight Hispanic children and adolescents. Med Sports Sci Exerc. 2007;
39:1257–1266. doi:10.1249/mss.0b013e3180621fb6 PubMed
19. Cumming S, Riddoch C. Physical activity, physical fitness and health: Current concepts. In: Paediatric Exercise Science and Medicine, 2nd ed., N Armstrong and W Van
Mechelen, Editors. Oxford: Oxford University Press, 2008, pp. 365–374.
20. Dencker M, Thorsson O, Karlsson MK, et al. Daily physical activity and its relation
to aerobic fitness in children aged 8–11 years. Eur J Appl Physiol. 2006; 96:587–592.
doi:10.1007/s00421-005-0117-1 PubMed
21. Eiberg S, Hasselstrom H, Gronfeldt V, Froberg K, Svensson J, Andersen LB. Maximum oxygen uptake and objectively measured physical activity in Danish children 6-7
years of age: the Copenhagen school child intervention study. Br J Sports Med. 2005;
39:725–730. doi:10.1136/bjsm.2004.015230 PubMed
22. Eisenmann JC, Malina RM. Secular trends in peak oxygen consumption among United
States youth in the 20th century. Am J Hum Biol. 2002; 14:699–706. doi:10.1002/
ajhb.10084 PubMed
23.Ekelund U, Poortvleit E, Nilsson A, Yngve A, Holmberg A, Sjostrom M. Physical
activity in relation to aerobic fitness and body fat in 14-to-15 year-old boys and girls.
Eur J Appl Physiol. 2001; 85:195–201. doi:10.1007/s004210100460 PubMed
24. Ekelund U, Tomkinson GR, Armstrong N. What proportion of youth are physically
active? Measurement issues, levels and recent time trends. Br J Sports Med. 2011;
45:859–865. doi:10.1136/bjsports-2011-090190 PubMed
25. Fenster JR, Freedson PS, Washburn RA, Ellison RC. The relationship between peak
oxygen uptake and physical activity in 6- to 8 year-old children. Pediatr Exerc Sci.
1989; 1:127–138.
26. Freedson P, Bowles HR, Troiano R, Haskell W. Assessment of physical activity using
wearable monitors: Recommendations for monitor calibration and use in the field.
Med Sci Sports Exerc. 2012; 44(Suppl):S1–S4. doi:10.1249/MSS.0b013e3182399b7e
PubMed
27. Guinhouya BC, Samouda H, de Beaufort C. Level of physical activity among children
and adolescents in Europe: A review of physical activity assessed objectively by accelerometry. Pub Health. 2013, http://dx.doi.org/10.1016/j.puhe.2013.01.020.
28. Guthold R, Cowan MJ, Autenrieth CS, Kann L, Riley LM. Physical activity and sedentary behaviour among schoolchildren: A 34-country comparison. J Pediatr. 2010;
157:43–49. doi:10.1016/j.jpeds.2010.01.019 PubMed
29. Intille SS, Lester J, Sallis JF, Duncan G. New horizons in sensor development. Med
Sci Sports Exerc. 2012; 44(Suppl 1):S24–S31. doi:10.1249/MSS.0b013e3182399c7d
PubMed
30. Jones AM, Poole DC. Oxygen uptake kinetics in sport, exercise and medicine. London:
Routledge, 2005, pp. 1–405.
31.Katch VL. Use of the oxygen/body weight ratio in correlational analysis: Spurious
correlations and statistical considerations. Med Sci Sports. 1973; 5:252–257.
32. Kemper HCG, Koppes LLJ. Is physical activity important for aerobic power in young
males and females? Med Sport Sci. 2004; 47:153–166. doi:10.1159/000076202
33.LaPorte RE, Montoye HJ, Casperson CJ. Assessment of physical activity in epidemiological research: Problems and prospects. Public Health Rep. 1985; 100:131–146.
PubMed
34. Li S, Treuth MS, Wang Y. How active are American adolescents and have they become
less active? Obes Rev. 2010; 11:847–862. doi:10.1111/j.1467-789X.2009.00685.x
PubMed
35. Mountjoy M, Andersen LB, Armstrong N, et al. International Olympic Committee consensus
statement on the health and fitness of young people through physical activity and sport. Br
J Sports Med. 2011; 45(11):839–848. doi:10.1136/bjsports-2011-090228 PubMed
560 Armstrong
36. Nyberg G, Ekelund U, Marcus C. Physical activity in children measured by accelerometry: Stability over time. Scand J Med Sports Sci. 2009; 19:30–35. doi:10.1111/j.16000838.2007.00756.x PubMed
37. Okely AD, Booth ML, Hardy L, Dobbins T, Denney-Wilson E. Changes in physical
activity participation from 1985-2004 in a statewide survey of Australian adolescents.
Arch Pediatr Adolesc Med. 2008; 162:176–180. doi:10.1001/archpediatrics.2007.26
PubMed
38.Raustorp A, Ekroth Y. Eight-year secular trends of pedometer determined physical
activity in young Swedish adolescents. J Phys Act Health. 2010; 7:369–374. PubMed
39. Robben KE, Poole DC, Harms CA. Maximal oxygen uptake validation in children with
expiratory flow limitation.. Pediatr Exerc
. Sci. 2013; 25:84–100. PubMed
40. Rowland TW. Does peak VO2 reflect VO2max in children? Evidence from supramaximal
testing. Med Sci Sports Exerc. 1993; 25:689–693. doi:10.1249/00005768-19930600000007 PubMed
41. Sallis JF, Patrick K, Long BJ. Overview of the international consensus conference on
physical activity guidelines for adolescents. Pediatr Exerc Sci. 1994; 6:299–302.
42. Samdal O, Tynjala J, Roberts C, et al. Trends in vigorous physical activity and TV
watching of adolescents from 1986 to 2002 in seven European countries. Eur J Public
Health. 2006; 17:242–248. doi:10.1093/eurpub/ckl245 PubMed
43. Saris WH. The assessment and evaluation of daily physical activity in children. A review.
Acta Paediatr Scand. 1985; 318:37–S48. doi:10.1111/j.1651-2227.1985.tb10081.x
PubMed
44. Seliger V, Trefny Z, Bartunkova S, Pauer M. The habitual activity and physical fitness
of 12 year old boys. Acta Paediatr. Belg. 1974; 28:54–59. PubMed
45.Strong WB, Malina RM, Blimkie CJR, et al. Evidence based physical activity for
school-age youth. J Pediatr. 2005; 146:732–737. doi:10.1016/j.jpeds.2005.01.055
PubMed
46. Tanner JM. Fallacy of per-weight and per-surface area standards and their relation to
spurious correlation. J Appl Physiol. 1949; 2:1–15. PubMed
47. Trost SG, McIver KL, Pate RR. Conducting accelerometer-based activity assessments
in field-based research. Med Sci Sports Exerc. 2005; 37:531–543. doi:10.1249/01.
mss.0000185657.86065.98 PubMed
48.Twisk JWR. Physical activity guidelines for children and adolescents. Sports Med.
2001; 31:617–627. doi:10.2165/00007256-200131080-00006 PubMed
49.Vale S, Silva P, Santos R, Soares-Miranda L, Mota J. Compliance with physical activity guidelines in preschool children. J Sport Sci. 2010; 28:175–176.
doi:10.1080/02640411003702694 PubMed
50. Welsman JR, Armstrong N. Interpreting exercise performance data in relation to body
size. In: Paediatric Exercise Science and Medicine, 2nd ed., N Armstrong and W Van
Mechelen (Eds.). Oxford: Oxford University Press, 2008, p. 13–22.
51. Welsman JR, Armstrong N. Physical activity patterns in secondary school children.
Eur J Phys Educ. 2000; 5:147–157. doi:10.1080/1740898000050203
52. Welsman J, Bywater K, Farr C, Welford D, Armstrong N. Reliability of peak VO2 and
maximal cardiac output assessed using thoracic bioimpedance in children. Eur J Appl
Physiol. 2005; 94:228–234. doi:10.1007/s00421-004-1300-5 PubMed