Body composition and weight
are 2 of the many factors that contribute to
optimal exercise performance. Taken together, these 2 factors may
affect an
athlete¹s potential for success within a given sport. Body weight
can
influence an athlete¹s speed, endurance, and power, whereas body
composition
can affect an athlete¹s strength, agility, and appearance. Most
athletes
require a high strength-to-weight ratio to achieve optimal athletic
performance,
and because body fat adds to weight without adding to strength, low
body fat
percentages are often emphasized within many sports (25). However, too
little
body fat results in deterioration of health and performance (22,26).
Athletic
performance cannot be accurately predicted based solely on body weight
and
composition (27).
The primary reason for
determining an athlete¹s body composition is to
obtain information that may be beneficial in improving athletic
performance
(28). Therefore, the determination of an athlete¹s optimal body
weight and
composition for health and competition should be done individually,
because
these factors are strongly influenced by age, sex, genetics, and the
requirements of the sport. Yet, some sports dictate that athletes make
changes
in body weight and composition that may not be optimal for the athlete.
For
example, weight-class sports‹such as wrestling or lightweight
rowing‹may
require athletes to lose or gain weight to qualify for a specific
weight
category. Sports with an aesthetic component‹such as dance, gymnastics,
and
figure skating‹may pressure athletes to lose weight and body fat to
have a
lean physique, although their current weight for health and performance
may be
optimal. With extreme energy restrictions, both muscle and fat mass are
lost,
which may adversely influence an athlete¹s performance. Thus, an
athlete¹s
optimal competitive body weight and relative body fatness should be
determined
when an athlete is healthy and performing at his or her best (29).
Body Composition and Sport
Performance
Percentage of body fat values
for athletes varies depending on the sex of the
athlete and the sport itself. Male athletes with the lowest estimates
of body
fat (less than 6%) include middle-distance and long-distance runners
and
bodybuilders, whereas male basketball players, cyclists, gymnasts,
sprinters,
jumpers, triathletes, and wrestlers average between 6% to 15% body fat
(26,30).
Male athletes involved in power sports such as football, rugby, and ice
and
field hockey have slightly more variable body fat levels (6% to 19%).
Female
athletes with the lowest estimates of body fat (6% to 15%) participate
in
bodybuilding, cycling, triathlons, and running events; higher fat
levels are
found in female athletes participating in racquetball, skiing, soccer,
swimming,
tennis, and volleyball (10% to 20%) (26,30). The estimated minimal
level of body
fat compatible with health is 5% for males and 12% for females (31);
however,
optimal body fat percentages for an individual athlete may be much
higher than
these minimums and should be determined on an individual basis.
Athletes who
strive to maintain body weight or body fat levels that are
inappropriate, or
have body-fat percentages below these minimal levels, may be at risk
for an
eating disorder or other health problems related to poor energy and
nutrient
intakes (8,11,18,22,23,32-34).
Assessment of Body
Composition
Methods for assessment of
body composition are based on either a 2-component
or a multicomponent model and use several different measurement
techniques.
Two-component models divide the body into either fat mass (all lipids
within the
body) or fat-free mass (the remainder after fat is subtracted). The
multicomponent model divides the body into 3 or more components. For
example,
the 3-component model divides the body into fat mass and 2 components
of
fat-free mass (bone mineral and lean tissue). The criterion methods
most
commonly used to assess components of body composition in athletes are
based on
a 2-component or a multicomponent model. Though a multicomponent
criterion model
is preferred for assessing body composition because it provides more
accurate
estimates, measurement techniques required for this model are not
readily
available to most athletes. A 2-component criterion model typically
uses
hydrodensitometry (hydrostatic weighing) or plethysmography (BODPOD)
measurement
techniques, and a 3-component model uses dual-energy x-ray
absorptiometry (DEXA)
measurements. The most common methods used to measure body composition
in field
or clinical settings include anthropometry (skinfolds), bioelectrical
impedance
analysis (BIA), and near-infrared interactance. These field methods are
validated using either 2-component or multicomponent criterion models
(35). When
using these field methods, care should be taken in choosing the
appropriate
validated prediction equation for estimating body composition based on
an
athlete¹s demographics (age, sex, level of adiposity, ethnicity,
and physical
activity) in order to obtain accurate estimates (36).
The relative validity of any
body composition field method depends on its
accuracy compared with the criterion method and its reliability
(reproducibility) (31). DEXA and hydrostatic weighing
(hydrodensitometry) are 2
widely used criterion methods from which field methods of body
composition
assessment for athletes are developed (37-42). Regardless of the method
used,
athletes and coaches should know the errors associated with the body
composition
assessment method being used. With carefully applied skinfold or BIA
methods, it
is possible to estimate relative body fat percentage with an error of
3% to 4%,
and to estimate fat-free mass within 2.5 to 3.5 kg (27,31,35). Thus, if
the
actual body fat percentage is 15%, then predicted values could range
from 12% to
18% (assuming a 3% error). If the actual fat-free mass is 50 kg, then
predicted
values could range from 47.5 to 52.5 kg, assuming an error of 2.5 kg.
If
inappropriate prediction equations for a method are used, poor
measurement
techniques applied or if the measurement equipment is poorly maintained
and
calibrated, the errors associated with the body composition estimate
will be
much larger. Because of the errors associated with body composition
assessment
methods, it is inappropriate to set a specific body-fat percentage goal
for an
individual athlete. Instead, a range of target percentage of body-fat
values
should be recommended.
