mize the rate of CHO ingestion and its subse-
quent oxidation by the working muscles dur-
ing prolonged exercise. In this regard, gastric
volume along with solute energy content and
osmolality are critical determinants of the rate of
gastric emptying during exercise. With regard to
gastric volume, the maximum rate at which CHO
and water can be delivered to the intestine from
an ingested solution is strongly influenced by the
average volume of fluid in the stomach. This, in
turn, is governed by the drinking pattern of the
athlete. The principal findings of studies that
have simultaneously measured rates of gastric
emptying and the oxidation of CHO solutions
that have been ingested in repeated doses during
exercise are, firstly, that the amount of a solution
emptied from the stomach is at least double the
amount that is ultimately oxidized by the active
muscles and, second, provided sufficient is con-
sumed, the peak rates of ingested CHO oxidation
rise to approximately 1 g · min–1after 70–90 min
of exercise (for review, see Hawley et al. 1992).
An interesting observation from those studies
which have fed runners CHO during exercise is
that when there is a performance improvement,
it coincides with a faster running pace over the
latterstages of a race or trial. This effect is similar
to that seen when subjects CHO-load. That is, the
additional CHO does not allow athletes to run
faster, but merely resist fatigue and maintain a
given pace for longer (for review, see Maughan
1994). Unlike submaximal cycling, CHO inges-
tion during steady-state running has been shown
to result in muscle glycogen sparing (Table 42.6).
Although this effect seems limited to the type I
fibres, it could potentially have a profound influ-
ence on performance during long-distance races.
More research specifically related to running
needs to be conducted to confirm the results of
these preliminary studies.distance running 557
Table 42.6The effects of carbohydrate ingestion on distance running performance.
Performance
Dietary treatment Drinking regimen measure Results/comments Reference
A: Placebo 4 h prior, Placebo: 10 ml · kg-^1 30-km treadmill A: 121.7±13.0 min Chryssanthopoulos
CHO solution at BM fluid time-trial et al. (1994)
start and during CHO meal: 2 g CHO ·
B: CHO meal 4 h kg BM B: 121.8±11.4 min
prior, water at At start (8 ml · kg-^1
start and during BM) and every
5 km (2 ml · kg-^1
BM): water or
6.9% CHO
solution
A: Water 250 ml fluid 30-km road race A: 131.2±18.7 min Tsintzas et al. (1993)
B: 5% CHO immediately prior, B: 128.3±19.9 min†
150 ml fluid every
5km
A: Water 250 ml fluid before 30-km treadmill A: 129.3±17.7 min‡ Williams et al. (1990)
B: Glucose solution warm-up, 5 min time-trial B: 124.8±14.9 min‡
(50 g CHO+20 g prior to trial, then:
glucose) 150 ml at 5-km
C: Fructose solution intervals C: 125.9±17.9 min‡
(50 g CHO+20 g
fructose)
Continued