tion and the range for maximum aerobic power
would constitute approximately 30% of maxi-
mum power production (Fig. 1.3).
In Fig. 1.2c, the relationship of respiratory quo-
tient (RQ) as determined from steady-state respi-
ratory exchange ratio (RER) to metabolic power
is presented. RER, which compares oxygen
uptake to carbon dioxide removal in the lungs,
attains steady state at lower levels of power pro-
duction (in this example, less than 1500 W). The
values for RQ vs. power production are modified
from Åstrand and Rodahl (1986). A range is pre-
sented to accommodate different values that
might be obtained during different days as a
result of variations in the athlete’s diet. Utilizing
both the left-side and the right-side ordinates, the
observed RQs indicate a high utilization of car-
bohydrate from approximately 75% of maximum
aerobic power and upwards. The higher
the intensity, the greater is the contribution of
carbohydrate.
An athlete maintaining a diet high in carbohy-
drate will maintain a higher RQ at all levels of
aerobic exercise, whereas the RQ of an athlete
with a low intake of carbohydrate will remain
remarkably lower. During long-lasting events
and training bouts, the RQ will become lower at
any chosen intensity the longer the exercise lasts,
as it is related to increasing free fatty acid avail-
8 nutrition and exercise
ability and falling levels of glycogen in the active
muscles. RQ can also be affected by the ingestion
of a substance such as caffeine which results in an
enhanced utilization of fatty acids for the energy
demands of exercise.Skeletal muscle
A skeletal muscle is made up predominantly of
extrafusal skeletal muscle fibres, long cylindrical
cells which run the length of the muscle, be it
short or long (e.g. 1–300 mm). Intrafusal fibres
are the small skeletal muscle cells found in the
muscle spindles which assist in controlling the
body’s coordinated movement. The muscle also
includes connective tissue which provides some
organization to the muscle’s internal structure
(white connective tissue) and elasticity (yellow
connective tissue). Arteries, veins and capillaries
made up of smooth muscle, connective tissue
and epithelial cells are found throughout each
muscle, serving as the combination delivery/
removal system. Afferent and efferent neurones
connect each muscle to the central nervous
system to provide the muscle with motor control
and send sensory information to the central
nervous system. Fat is found within and between
muscle cells in quantities that become reflected in
the person’s total body composition and percent-Fig. 1.3Marathon pace for a
runner requires approximately
75–80% of maximal aerobic power
and approximately 24% of the
anaerobic power the same
muscles could produce for a
strength exercise. Photo ©
NOPP / Larry Bessel.