athlete can generate. The final burst of power (or
‘kick’) results from a combination of high utiliza-
tion of both anaerobic glycolysis and aerobic
power. In the range of events that last between
30 s and 12 min, a combination of anaerobic gly-
colysis and oxidative metabolism provides most
of the energy necessary to resynthesize ATP and
permit the athlete to continue. The lower the
demand for power, the better the oxidative
metabolism can provide the energy for ATP
resynthesis. Anaerobic glycolysis involves only
carbohydrate and, at these high intensities, even
aerobic metabolism draws upon carbohydrate in
preference to fat.
An athlete who performs to exhaustion
in approximately 3–12 min challenges the car-
diorespiratory and metabolic mechanisms so
that aerobic metabolism eventually attains its
highest level. When this occurs, the oxygen
uptake is identified as either ‘maximum oxygen
uptake’ (V
.
o2max.) or ‘maximum aerobic power’.
It is not uncommon to read and hear the term
‘maximum exercise’ used to refer to intensities
that result in maximum oxygen uptake. The term
is completely misleading, given the fact that the
athlete can produce power anaerobically for
short periods of time that is four to five times as
great as that which can be developed utilizing
maximum aerobic power.
Fat is stored to a limited extent inside the
6 nutrition and exercise
muscle cells but can be mobilized during exercise
from depots around the body for transport by the
circulatory system to active muscle cells. Carbo-
hydrate is stored inside the muscle cells as glyco-
gen but can also be mobilized as glucose from
glycogen stored in the liver.Power, energy and endurance
The information presented in the three panels of
Fig. 1.2 provides vivid examples of the relation-
ships among human metabolic power produc-
tion, the sources of energy and the ability to
endure at specific exercise intensities. In panel A,
the relationship between endurance (or time to
exhaustion) is plotted vs. metabolic power. For
the sample athlete, power production of about
5000 W can be assumed to come solely from
energy stored in skeletal muscle ATP and PCr.
In the range of 2000–4000 W, anaerobic glyco-
lysis assumes major responsibility for the provi-
sion of energy. This results in the production of
large amounts of lactic acid and lowered pH in
the sarcoplasm, which are believed to eventually
hinder force and power development by the
muscle fibres. Lactic acid values in the blood rise
commensurate with muscle concentrations.
For the athlete in the example, oxidative
metabolism begins to make a major contribution
of energy for ATP and PCr resynthesis once theFig. 1.1Olympic weightlifting is
an example of a sport in which the
competitive performance is so
short that all of the energy for the
lift is provided by the high-energy
phosphates, ATP and PCr. Photo
© Allsport.