title: Carbohydrate feedings and exercise performance: effect of initial muscle glycogen concentration.
abstract: To determine whether the ergogenic benefits of carbohydrate (CHO) feedings are affected by preexercise muscle glycogen levels, eight cyclists performed four self-paced time trials on an isokinetic ergometer over a simulated distance of 70 km. Trials were performed under the following preexercise muscle glycogen and beverage conditions: 1) high glycogen (180.2 +/- 9.7 mmol/kg wet wt) with a CHO beverage (HG-CHO), 2) high glycogen (170.2 +/- 10.4 mmol/kg wet wt) with a non-CHO beverage (HG-NCHO), 3) low glycogen (99.8 +/- 6.0 mmol/kg wet wt) with a CHO beverage (LG-CHO), and 4) low glycogen (109.7 +/- 5.3 mmol/kg wet wt) with a non-CHO beverage (LG-NCHO). The CHO drink (ingested at the onset of exercise and every 10 km thereafter) provided 116 +/- 6 g CHO/trial and prevented the decline in serum glucose observed during both NCHO trials. Performance times ranged from 117.93 +/- 1.44 (HG-CHO) to 122.91 +/- 2.46 min (LG-NCHO). No intertrial differences (P > 0.05) were observed for O2 consumption (75% of maximal O2 consumption), power output (237 W), or self-selected pace (8.44 min/5 km) during the initial 71-79% of exercise. Over the final 14% of the time trial, power output and pace (231 W and 8.62 min/5 km) were similar for the HG-CHO, HG-NCHO, and LG-CHO conditions, but both variables were significantly lower during the LG-NCHO trial (198 W and 9.67 min/5 km, P < 0.05 vs. all other trials).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Human Performance Laboratory, Ball State University, Muncie, Indiana 47306.
authors.forename: J J
authors.initials: JJ
authors.lastname: Widrick
authors.forename: D L
authors.initials: DL
authors.lastname: Costill
authors.forename: W J
authors.initials: WJ
authors.lastname: Fink
authors.forename: M S
authors.initials: MS
authors.lastname: Hickey
authors.forename: G K
authors.initials: GK
authors.lastname: McConell
authors.forename: H
authors.initials: H
authors.lastname: Tanaka
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology; D001786:Blood Glucose / Q000378:metabolism; D004040:Dietary Carbohydrates / Q000008:administration & dosage*; D004734:Energy Metabolism / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D006003:Glycogen / Q000378:metabolism*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D009132:Muscles / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000502:physiology
chemical_list: D001786:Blood Glucose; D004040:Dietary Carbohydrates; D006003:Glycogen