THE INFLUENCE OF STARCH STRUCTURE ON GLYCOGEN RESYNTHESIS AND SUBSEQUENT CYCLING PERFORMANCE 7

Abstract

The present study was designed to evaluate the influence of starch structure on muscle glycogen resynthesis and cycling performance. Eight male cyclists (22 ± 1 yr) completed an exercise protocol (DP) to decrease vastus lateralis glycogen concentration. This exercise consisted of 60 min cycling at 75% VO2max, followed by six 1-min sprints at ≈125%˙VO2max with 1 min rest intervals. In the 12 hr after the exercise each subject consumed ≈3000 kcal (65:20:15% carbohydrate, fat and protein). All of the carbohydrate (CHO) consumed was derived from one of four solutions: 1) glucose (G), 2) maltodextrin (M), 3) waxy starch (W) [100% amylopectin], or 4) resistant starch (R)[100% amylose]. Muscle biopsies were taken from the vastus lateralis muscle after DP and 24 hr later to determine glycogen concentrations. A 30 min cycling time trial (TT) was performed following the 24 hr post-DP muscle biopsy to examine the influence of the feeding regimen on total work output. The post-DP glycogen concentrations were similar among the four trials, ranging from 220.3±29.2 to 264.7 ± 48.3 mmol·kg-1 dry weight (d.w.) muscle. Twenty-four hours after DP, muscle glycogen concentration had increased less (p<0.05) in the R trial(+90.8 ± 12.8 mmol·kg-1 d.w.) than in the G (+197.7± 31.6 mmol·kg-1 d.w.), M (+136.7 ± 24.5 mmol·kg-1 d.w.) and W (+171.8 ± 37.1 mmol·kg-1 d.w.) trials. There were no differences in total work output during the TT, or blood lactate concentration immediately following the TT in any of the CHO trials. In summary, glycogen resynthesis was attenuated following ingestion of starch with a high amylose content, relative to amylopectin or glucose; however, short duration time trial performance was unaffected.