NUTRITION IN SPORT

suggesting that dietary protein needs are ele-
vated with both endurance and strength exercise.
The data of Gontzea et al. (1974) suggest that
dietary protein needs are elevated with an
aerobic exercise programme (Fig. 10.7) but subse-
quent work by the same group (Gontzea et al.
1975) indicates that this might be true only
transiently during the first few weeks of
an endurance exercise programme (Fig. 10.8).

However, the data in this second investigation

may have been confounded by an exercise train-

ing effect because the exercise stimulus remained

constant over the 3-week period when nitrogen

status was assessed. In other words, the im-

proved endurance capacity (V

.

o2max.) likely expe-

rienced as the study progressed by these

previously untrained subjects would mean that

the same absolute exercise bout represented a

effects of exercise on protein metabolism 139

Pre-exercise

Strength

exercise Recovery

–50 0 50 100 150 200

120

100

80

60

40

20

0

Time (min)

Whole-body leucine oxidation

(μ

mol

.kg

–1

.h

–1

)

Nitrogen balance (g

.day

–1

)

4

2

0

–2

–4 2 4 6 8 10 12 14

Time (days)

Sedentary Exercise Sedentary

Fig. 10.7Effect of an acute endurance exercise bout on nitrogen status (balance) while consuming differing protein
intake in humans. Note that the overall pattern of nitrogen status with exercise is similar with both protein intakes
and that with the lower protein intake (125% of the recommended dietary intake for protein) nitrogen status
becomes negative with the exercise programme, suggesting that this amount of dietary protein, while adequate for
the sedentary individual, is inadequate for exercise. , 1 g protein · kg–1body mass · day–1;
, 1.5 g protein · kg–1
body mass · day–1. Adapted from Gontzea et al. (1974).

Fig. 10.6Effect of a strenuous,
whole-body heavy resistance
exercise bout on oxidation of the
branched-chain amino acid
leucine in humans. Note that
despite the vigorous nature of the
training session, there is little
effect on leucine oxidation either
during the exercise or during 2 h of
recovery. Adapted from
Tarnopolsky et al. (1991).