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

The present study was designed to evaluate the influence of starch str ucture on muscle glycogen resynthesis and cycling performance. Eight m ale cyclists (22+/-1 yr) completed an exercise protocol (DP) to decrea se vastus lateralis glycogen concentration. This exercise consisted of 60 min cycling at 75% VO(2)max, followed by six 1-min sprints at simi lar to 125% VO(2)max with 1 min rest intervals. In the 12 hr after the exercise each subject consumed similar to 3000 kcal (65:20:15% carboh ydrate, fat a nd protein). All of the carbohydrate (CHO) consumed was derived from one of four solutions: 1) glucose, 2) maltodextrin (gluco se polymer), 3) waxy starch (100% amylopectin), or 4) resistant starch (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 pos t-DP muscle biopsy to examine the influence of the feeding regimen on total work output. The post-DP glycogen concentrations were similar am ong 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 gl ycogen concentration had increased less (p < 0.05) in the resistant st arch trial (+90.8+/-12.8 mmol . kg(-1) d.w.) than in the glucose (+197 .7+/-31.6 mmol . kg(-1) d.w.), maltodextrin (+136.7+/-24.5 mmol . kg(- 1) d.w.) and waxy starch (+171.8+/-37.1 mmol . kg(-1) d.w.) trials. Th ere were no differences in total work output during the TT, or blood l actate concentration immediately following the TT in any of the CHO tr ials. In summary, glycogen resynthesis was attenuated following ingest ion of starch with a high amylose content, relative to amylopectin or glucose; however, short duration time trial performance was unaffected .