The influence of carbohydrate structure on muscle glycogen resynthesis and performance

The present study was designed to evaluate the influence of carbohydrate structure on muscle glycogen resynthesis. Eight college-aged male cyclists performed a depletion exercise protocol to decrease vastus lateralis glycogen concentration. This protocol consisted of 60 min of cycling at 75% V O2max, followed by 6 - one min sprints at 125 % V O2max, with a 1 min rest between each sprint. Following the depletion exercise, the subjects consumed - 3000 kcal over a 12 hour period, which was calculated to meet each subject's estimated daily energy expenditure. The carbohydrate (CHO), fat and protein content represented 65:20:15% of the calories consumed, respectively, and totaled 450 - 550 g of CHO. All of the CHO was derived from 1 of 4 solutions: 1) glucose, 2) maltodextrin (glucose polymer), 3) waxy starch (100% amylopectin), or 4) resistant starch (100% amylose). Muscle biopsies were taken after the depletion exercise protocol and 24 hours after the depletion protocol to determine glycogen concentrations. The postdepletion exercise glycogen concentration was similar in all 4 trials, and averaged 234.7 mmol/kg dry weight (d.w.) muscle. Twenty-four hours after exercise, the increase in muscle glycogen concentration was less in the resistant starch trial (90.8 f 12.8 mmol/kg d.w.) than in the glucose, maltodextrin and waxy starch trials, in which glycogen concentration increased 168.7 mmol/kg d.w. Following the 24 h post-depletion exercise biopsy, each subject performed a 30 min cycling time trial, so that the relationship between muscle glycogen concentration and performance could be examined. There were no differences in work output during the time trial or blood lactate concentration immediately following the time trial in any of the trials. In summary, glycogen resynthesis is attenuated following ingestion of carbohydrate with a high amylose content, relative to amylopectin or glucose; however, short duration performance at intensities < 75% VO2max is unaffected.School of Physical EducationThesis (M.S.