Abstract
This study was undertaken to determine the effects of ingesting 5.0 (CHO-5), 6.0 (CHO-6),
and 7.5 g/100 ml (CHO-7.5) carbohydrate (CHO) solutions on blood glucose and counterregulatory
hormonal responses during prolonged intermittent exercise. Eight well-trained cyclists
performed four trials consisting of seven 12-min cycling bouts at 70% of VO2max with 3 min rest between each ride. A final 12 min ride was an all-out self-paced
performance ride. During the rest interval the subjects ingested either a water placebo
(WP) or one of the CHO solutions at a rate of 8.5 mg/kg/h (approx. 150 ml). Blood
samples were taken at 0, 25, 55, 85, and 115 min of exercise and were assayed for
glucose, glucagon (GG), Cortisol (CT), insulin (IN), epinephrine (EP), and norepinephrine
(NE). Blood glucose levels were significantly lower in the WP trial compared to the
CHO trials at 25 (4.6 ± 0.2 vs 5.7 ± 0.5 mmol/l) and 55 min (4.4 ± 0.3 vs 5.0 ± 0.8
mmol/l). At 85 min blood glucose was significantly lower in the WP compared to the
CHO-6 and CHO-7.5 trials. GG and IN levels were not significantly different between
trials; however, the GG : IN molar ratio was significantly higher in the WP than in
the CHO-7.5 trial. CT was significantly elevated in the WP trial compared to the CHO-7.5
trial. EP and NE levels were not affected by CHO ingestion. These data suggest that
CHO feedings prevent the typical hormonal responses which are responsible for hepatic
glucose release, thus eliciting a possible hepatic glycogen sparing.
Key words
Blood glucose - glucagon - insulin - cortisol - catecholamines -
