fatigue during the latter part of training sessions
and prescribe a carbohydrate supplement only to
those who consistently seem to have difficulty
maintaining their work output.
There is a more fundamental question than
whether or not carbohydrate supplementation is
effective in improving training performance. By
preventing the decline in blood glucose concen-
tration during training, we effectively eliminate
one of the physiological/metabolic stresses
imposed by the training. Since training is a
careful dosage of physical stress to create long-
term adaptations that will ultimately improve
competitive performance potential, elimination
of these stresses may lessen the degree of adapta-
tion experienced by the athlete. Whether or not
one adapts in a performance-enhancing way to
low carbohydrate availability is not currently
known, but this may be part of the stimulus that
improves glycogen storage in endurance athletes
(Gollnicket al. 1973; Piehl et al. 1974; Costill et al.
1985a).
Carbohydrate ingestion after training
Studies have shown that muscle glycogen resyn-
thesis is accelerated when carbohydrate is
ingested within 1–2 h after the exercise is stopped
(Ivyet al. 1988). In this immediate postexercise
period, evidence suggests that high glycaemic
index sugars may be the preferred carbohydrate
source since insulin is known to be a potent
activator of muscle glycogen synthase. A recent
study also suggests including some protein in
the postexercise meal because the protein will
augment the insulin response to the carbohy-
drate and thereby stimulate an even greater rate
of muscle glycogen storage (Zawadzki et al.
1992). Since competitive swimmers likely experi-
ence large decrements in muscle glycogen
concentration during single training sessions, it
seems wise to provide a carbohydrate source
soon after the training session ends. This strategy
may be helpful in preventing the chronic muscle
glycogen depletion that undoubtedly occurs in
many swimmers, especially those training twice
per day.
Chronic muscle glycogen depletion
and overtraining
With all the training competitive swimmers do, it
is not surprising that overtraining has become
almost an epidemic in swimming. The frequent,
high-volume, and high-intensity training these
athletes perform often results in a chronic muscle
fatigue that, if unchecked, may lead to the devel-
opment of an overtraining state. Chronic muscle
fatigue has been linked to failure to adequately
replace the muscle glycogen stores between
training sessions due to the combination of
heavy training and inadequate dietary carbohy-
drate intake. Since a competitive swimming
season may last as long as 25 weeks before a
break from training is taken, swimmers can
suffer from chronic depletion for up to 6 months.
At the end of most swimming seasons, swim-
mers gradually reduce both the volume and
intensity of training in preparation for their
season-ending competition. This ‘taper period’
has not been studied extensively, but the few
studies that have been done indicate that
improved strength or power and increased
muscle glycogen stores may be partly responsi-
ble for the enhanced performance that typically
occurs with the taper.Protein requirements during
swimming training
The prior discussion concerning carbohydrate
needs of competitive swimmers suggests that
many swimmers may experience chronic muscle
glycogen depletion during their daily training.
Lemon and Mullin (1980) have shown that
protein catabolism is accelerated when exercis-
ing while glycogen depleted. Therefore, com-
petitive swimming training may often result in
increased protein catabolism that needs to be
compensated for with extra dietary protein
intake. Furthermore, the relatively low energy
intake that has been reported for some swimmers
may also trigger an increase in protein
catabolism.
Lean body mass has been shown to signifi-