Enhancement of swimming endurance in mice by highly branched cyclic dextrin

We investigated the ergogenic effect in mice of administering highly branch ed cyclic dextrin (HBCD), a new type of glucose polymer, on the swimming en durance in an adjustable-current swimming pool. Male Std ddY mice were admi nistered a HBCD, a glucose solution or water via a stomach sonde 10 min bef ore, 10 min after or 30 min after beginning swimming exercise, and were the n obliged to swim in the pool. The total swimming period until exhaustion, an index of the swimming endurance, was measured. An ergogenic effect of HB CD was observed at a dose of 500 mg/kg of body weight, whereas it had no ef fect at a dose of 166 mg/kg of body wt (p<0.05). The mice administered with the HBCD solution 10 min after starting the exercise were able to swim sig nificantly longer (p<0.05) than the mice who had ingested water or the gluc ose solution. The rise in mean blood glucose level in the mice administered with HBCD, which was measured 20 min after starting swimming, was signific antly lower (p<0.05) than that in the mice administered with glucose, altho ugh it was significantly higher (p<0.05) than that in the mice administered with water. The mean blood insulin rise in the mice given HBCD was signifi cantly lower (p<0.05) than that in the mice given glucose. The mice adminis tered with HBCD 30 min after starting the exercise swam significantly longe r (p < 0.05) than the mice who had ingested water, although the enhancement of swimming time was similar to that of the glucose-ingesting mice. The ga stric emptying rate of the HBCD solution was significantly faster (p<0.05) than that of the glucose solution. However, this glucose polymer must have spent more time being absorbed because it has to be hydrolyzed before absor ption, reflecting a lower and possibly longer-lasting blood glucose level. We conclude that the prolongation of swimming endurance in mice administere d with HBCD depended on its rapid and longer-lasting ability for supplying glucose with a lower postprandial blood insulin response, leading to a dela yed onset of fatigue.