NUTRITION IN SPORT

power output falls to approximately 2000 W.
It is at power productions of 1500–1800 W that
the maximum oxygen uptake (V

.
o2max.of 2.7
mmol · s–1) is elicited for this athlete during the
final stage of an exercise bout. At 1500 W, the
athlete could sustain exercise for approximately
8 min but at 1800 W, for less than 5 min.
Below 1500 W (Fig. 1.2b), the athlete is able to
sustain exercise for extended periods with com-
pletely or nearly completely aerobic metabolism,
utilizing fat and carbohydrate to resynthesize
ATP and PCr. The letter ‘M’ is placed on the

abscissa to indicate the power production corre-

sponding to about 75–80% V

.

o2max.that the

athlete could sustain for a marathon (42.2 km). At

any higher level, the athlete would enlist anaero-

bic glycolysis, accumulate lactate and lower pH

values in the skeletal muscle cells, and be forced,

eventually, to reduce power or stop.

Note the relatively narrow range of power pro-

duction that can be produced completely aerobi-

cally by comparing Fig. 1.2b with Fig. 1.2a.

Marathon pace in this example would constitute

approximately 24% of maximum power produc-

basic exercise physiology 7

*

*

*

*

40

30

20

10

0

Endurance time to exhaustion (min)

0 2000 4000 6000

Metabolic power (W)

3

2

1

1.0

0.9

0.8

0.7

100

75

50

25

0

0

25

50

75

100

Rest 500 1000 1500 2000 6000 Rest 500 1000 1500 2000 6000

Metabolic power (W) Metabolic power (W)

M

V

O^2

(mmol

–1.s

)

.

RQ

%

CHO

%

Fat

(a)

(b) (c)

Fig. 1.2The relationships of (a) endurance time, (b) oxygen uptake in steady state, and (c) respiratory quotient
(RQ) and percentage substrate utilization to human metabolic power production. Values presented for power are
representative for an 80-kg athlete.