NUTRITION IN SPORT - Index of

quantifying exercise is with SI units. The bout of
exercise can be described as follows:
Power developed on the ergometer: 300W
Duration of exercise: 600 s (10 min)
Metabolic power (derived from oxygen uptake):
1500W
Total metabolic energy utilized
=1500 W¥600s=900000 J=900 kJ
Mechanical efficiency
=300 W/1500 W¥100=20%
If work is calculated by using a ‘kilogram of
force’ (an improper unit of measurement!), a
kilogram-metre can be utilized as an unsanctioned
unit to quantify work. Conversion factors
would be utilized to convert kilogram-metres
per unit of time into the correct unit for power,
the watt. If the calorie is used to quantify metabolic
energy, conversion factors must be utilized
to obtain a measurement of metabolic power that
can be compared to the power transferred to the
cycle ergometer. It is far easier to utilize SI units
throughout all research activity and scientific
writing: the newton, the metre, the second, the
joule and the watt. (It is important to call attention
to the fact that a kilogram-metre [kg-m] in
the SI is actually the correct unit of measurement
for torque.)
There are an infinite number of configurations
of force and velocity (determined by cadence on
the ergometer) that can produce the desired
external power produced and therefore metabolic
power desired.
In this volume, the editorial decision was
made to acknowledge the continued and extensive
use of the kilocalorie (kcal) in much of the
scientific literature for the quantification of the
energy content of foods and therefore to permit
the use of this unit of measurement in the various
chapters where considered expedient.
Energy for muscle activity
The mechanical and biochemical events associated
with muscle cell force development are
basic exercise physiology 5
described in detail in Chapter 2. However, it is
worth making the following general comments
and observations as related to nutrition for sport.
The immediate source of energy for muscle
force and power production is adenosine
triphosphate (ATP). ATP is the final biochemical
carrier of energy to the myofilaments for the generation
of force. The breakdown of phosphocreatine
(PCr) serves to reconstitute ATP when other
sources contribute little or no energy. Each
muscle cell then becomes dependent on fat (fatty
acids), carbohydrate (glucose and glycogen) and,
to a very limited extent, protein (amino acids) as
the sources of energy to resynthesize ATP and
PCr during exercise. All persons concerned with
the nutrition of the athlete must consider the
nutritional demands of the long-term conditioning
programme, the preparation for competition
and the competitive event itself, when planning
individual meals as well as the weekly and
monthly dietary programmes.
It is generally accepted that the muscle cells
obtain all the energy needed for short-term sport
performance of a few seconds (as in the throwing
and jumping events of track and field, weightlifting
and springboard and platform diving)
from ATP and PCr (Fig. 1.1). These compounds
are then resynthesized during recovery. When a
sport performance lasts approximately 10 s (e.g.
the 100-m run), other energy sources, including
especially anaerobic glycolysis (resulting in lactic
acid formation in the muscle), must also contribute
to the resynthesis of ATP. The lower the
intensity and the longer the event, the better able
is aerobic glycolysis to contribute energy. It is
also assumed that, during events that are still
considered ‘sprints’ but that last longer than a
few seconds, aerobic metabolism begins to make
a contribution to ATP resynthesis.
As the duration of the exercise period
increases still further, the energy from the oxidation
of a combination of fat and carbohydrate
becomes a significant source of energy. If exercise
lasts 15min or longer, such intensities demand a
steady-state of aerobic metabolism (i.e. lower
than maximum aerobic metabolism) except for
any final effort that calls forth all the power the