Aldehyde dehydrogenase catalyses the further
oxidation of acetaldehyde to acetate:
CH 3 CHO+NADH++H 2 OÆCH 3 COO–
+NADH+2H+
The NADH which is formed in these reactions
must be reoxidized within the mitochondria, but
transfer of the hydrogen atoms into the mito-
chondria might be a limiting process leading to
an alteration in the redox potential of the cell.
This can interfere with the conversion of lactate
to pyruvate, and explains the increased blood
lactate concentration that may be observed after
high alcohol intakes.
Acetaldehyde is metabolized within the liver,
and the acetaldehyde concentration in the
blood remains low, but it is acetaldehyde that
is thought to be responsible for many of the
adverse effects of ethanol. The rate of hepatic
gluconeogenesis is markedly suppressed by the
metabolism of ethanol as a result of the altered
NAD/NADH ratio and the reduced availability
of pyruvate (Krebs et al. 1969). If the liver glyco-
gen stores are low because of a combination of
exercise and a low carbohydrate intake, the liver
will be unable to maintain the circulating glucose
concentration, leading to hypoglycaemia. The
rate at which ethanol is cleared by the liver varies
widely between individuals, and the response
of the individual will depend on the amount of
ethanol consumed in relation to the habitual
intake. It is not altogether clear whether the rate
of metabolism of alcohol is increased by exercise,
and there are conflicting data in the literature
(Januszewski & Klimek 1974). Table 30.1 indi-
cates the amount of alcohol contained in some
standard measures.
Effects of acute alcohol ingestion
on exercise
The variety of effects of alcohol on different body
tissues, and the variability of subject responses
to alcohol, make it difficult to study the direct
effects on sports performance. Generally, the
ergogenic benefits of alcohol intake immediately
before and during exercise are psychologically
driven. Alcohol has been used to decrease sen-
sitivity to pain, improve confidence, and to
remove other psychological barriers to perfor-
mance. However, it may also be used to stimulate
the cardiovascular system, or to lessen the tremor
and stress-induced emotional arousal in fine
motor control sports. Although it is no longer on
the general doping list of the IOC, it is still con-
sidered a banned substance in some sports, such
as shooting and fencing. In some sports, such as
darts and billiards, it is still popularly used as a
(proposed) performance aid, but it remains to be
seen whether this simply reflects the culture of
sports that are widely played in a hotel environ-
ment (for review, see Williams 1991).Exercise metabolism and performance
The American College of Sports Medicine (1982),
and a more recent review by Williams (1991),
have summarized the acute effects of alcohol
ingestion on metabolism and performance of
exercise. Alcohol does not contribute signifi-
cantly to energy stores used for exercise, but in
situations of prolonged exercise it may increase
the risk of hypoglycaemia due to a suppression
of hepatic gluconeogenesis. Increased heat loss
may be associated with this hypoglycaemia as
well as the cutaneous vasodilation caused by
exercise, causing an impairment of temperature
regulation in cold environments. Studies of the
effects of alcohol on cardiovascular, respiratory
and muscular function have provided conflicting
results, but ingestion of small amounts of alcoholalcohol in sport 407
Table 30.1A standard drink contains approximately
10 g of alcohol.Drink Amount (ml)Standard beer (4% alcohol) 250
Low alcohol beer (2% alcohol) 500
Cider, wine coolers, alcoholic soft 250
drinks
Wine 100
Champagne 100
Fortified wines, sherry, port 60
Spirits 30