| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Guest Access | Sign In via User Name/Password
|
|
|
|||||||
Guest Access | Sign In via User Name/Password |
|||||||||
Dr. Washington is Chairman, Department of Pediatrics, Hospital for Infants and Children, Presbyterian St. Lukes Medical Center, Denver, CO.
Correspondence to: Reginald L. Washington, MD, Rocky Mountain Pediatric Cardiology, P.C., P/SL Professional Plaza West, 1601 E. 19th Ave, Suite 5600, Denver, CO 80218
All aerobic energy-producing reactions in the body depend
on oxygen; therefore, an indirect estimation of energy production can
be obtained by using an individual’s oxygen consumption
(
O2). In 1923, Hill and
Lupton1
reported that each person has a maximal level of
oxygen consumption (O2max) that equals
maximum aerobic power. The measurement of
O2max uses a progressive incremental
exercise test, usually performed on a treadmill or cycle ergometer to a
point where further increments of work are theoretically accompanied by
a plateau of O2. High
O2max values are important because they
reflect good function of the cardiovascular system. At the work rate
corresponding to O2max, additional work
is limited, and the muscle and blood lactate acid concentrations
accelerate. This acceleration signals a rapid increase in the anaerobic
metabolism during exercise and has been termed the anaerobic threshold.
The O2 at the anaerobic threshold
correlates well with O2max in children
and may serve as an effective submaximal marker of aerobic
fitness.2
The O2max for an individual, however, is
subject to multiple variables that must be considered when comparing
population studies. For example, O2max
obtained with a treadmill is higher than the
O2max obtained using a cycle ergometer.
Individuals who are well motivated, coordinated, or physically trained
perform better and will have a higher value for
O2max. Performance is not exclusively
related to O2max. If two athletes have
the same value for O2max, the one with
the lowest oxygen requirement during exercise will be a better
performer.3
Two athletes may have the same performance,
although their O2max values are
different. This means that the one with the lower
O2 is compensating with a higher
efficiency. Economy of movement is thus a critical component of aerobic
fitness.
Boys have a high O2max when exercising
if they are compared to girls. This difference is most noticeable if
O2max is expressed in L/min. The
difference is less noticeable when O2max
is scaled to body weight and expressed as mL/kg/min. These gender
differences are noticed even before puberty, but the magnitude of these
differences nearly doubles after puberty.4
The reason for
these gender differences has been widely studied.
O2max has been scaled in a variety of
ways including body weight, lean body mass, surface area, skeletal age,
exponents of height, hemoglobin concentration, and prior physical
activity.5
In this issue of CHEST (see page
629), Rowland and colleagues demonstrated that differences in stroke
volume as well as body composition contribute to the gender-related
variations in O2max during childhood.
This observation adds yet another variable in the explanation of gender
differences and O2 in children. This
study suggests that the delivery of oxygen to exercising muscle by the
circulatory system may be a limitation to peak exercise performance and
that this difference may be gender specific in prepubertal boys and
girls.
The implications of this observation are intriguing. Will we in
the future be measuring heart size or function as part of a fitness
evaluation? Should children with congenital heart disease, pulmonary
disease, or circulatory difficulties be viewed differently or perhaps
tested differently than "normal children?" Is one’s ability to
deliver oxygen to the exercising muscle trainable? Do two individuals
with identical oxygen delivery systems, lean body mass, hemoglobin,
daily physical activity, efficiency during exercise, and motivation
have identical O2max values regardless
of gender. If so, then are we simply scaling
O2 in such a manner that it is biased
against girls, or is there a true difference in
O2 that is gender specific?
Despite our incomplete understanding of
O2max, it is still an important clinical
tool. It may become more important when we have a clear understanding
of how it should be measured. In the future, we might measure every
individual’s O2max and use that value
to assess individual physical fitness throughout childhood. We might
expect improvement of an individual’s
O2max with growth during development,
much as we expect an increase in height or weight. We might use this
change (or lack thereof) in O2max to
determine when to intervene and to evaluate the success of an
intervention (timing of heart surgery, for example). Our understanding
of all components of O2max is still
incomplete. Rowland and colleagues have added an additional piece to a
complex physiologic parameter.
References
This article has been cited by other articles:
|
|
 |
|
  C. Karila, J. de Blic, S. Waernessyckle, M.-R. Benoist, and P. Scheinmann Cardiopulmonary Exercise Testing in Children : An Individualized Protocol for Workload Increase Chest, July 1, 2001; 120(1): 81 - 87. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
